Geological control of physiography in southeast

Queensland: a multi-scale analysis using GIS

Jane Helen Hodgkinson

Bachelor of Science (Hons), Geology

(Birkbeck University of London, UK)

School of Natural Resource Sciences

A thesis submitted for the degree of Doctor of Philosophy

Queensland University of Technology

2009

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STATEMENT OF ORIGINAL AUTHORSHIP

The work contained in this thesis has not been previously submitted for a degree or diploma at any other higher education institution. To the best of my knowledge and belief, the thesis contains no material previously published or written by another person except where due reference is made. Signed………………………………… Jane Helen Hodgkinson Date……………………………

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ABSTRACT

The study reported here, constitutes a full review of the major geological events that

have influenced the morphological development of the southeast Queensland region.

Most importantly, it provides evidence that the region’s physiography continues to

be geologically ‘active’ and although earthquakes are presently few and of low

magnitude, many past events and tectonic regimes continue to be strongly influential

over drainage, morphology and topography. Southeast Queensland is typified by

highland terrain of metasedimentary and igneous rocks that are parallel and close to

younger, lowland coastal terrain. The region is currently situated in a passive margin

tectonic setting that is now under compressive stress, although in the past, the region

was subject to alternating extensional and compressive regimes. As part of the

investigation, the effects of many past geological events upon landscape morphology

have been assessed at multiple scales using features such as the location and

orientation of drainage channels, topography, faults, fractures, scarps, cleavage,

volcanic centres and deposits, and recent earthquake activity. A number of

hypotheses for local geological evolution are proposed and discussed. This study has

also utilised a geographic information system (GIS) approach that successfully

amalgamates the various types and scales of datasets used.

A new method of stream ordination has been developed and is used to

compare the orientation of channels of similar orders with rock fabric, in a

topologically controlled approach that other ordering systems are unable to achieve.

Stream pattern analysis has been performed and the results provide evidence that

many drainage systems in southeast Queensland are controlled by known geological

structures and by past geological events. The results conclude that drainage at a fine

scale is controlled by cleavage, joints and faults, and at a broader scale, large river

valleys, such as those of the Brisbane River and North Pine River, closely follow the

location of faults. These rivers appear to have become entrenched by differential

weathering along these planes of weakness. Significantly, stream pattern analysis has

also identified some ‘anomalous’ drainage that suggests the orientations of these

watercourses are geologically controlled, but by unknown causes. To the north of

Brisbane, a ‘coastal drainage divide’ has been recognized and is described here. The

divide crosses several lithological units of different age, continues parallel to the

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coast and prevents drainage from the highlands flowing directly to the coast for its

entire length. Diversion of low order streams away from the divide may be evidence

that a more recent process may be the driving force. Although there is no conclusive

evidence for this at present, it is postulated that the divide may have been generated

by uplift or doming associated with mid-Cenozoic volcanism or a blind thrust at

depth. Also north of Brisbane, on the D’Aguilar Range, an elevated valley (the

‘Kilcoy Gap’) has been identified that may have once drained towards the coast and

now displays reversed drainage that may have resulted from uplift along the coastal

drainage divide and of the D’Aguilar blocks.

An assessment of the distribution and intensity of recent earthquakes in the

region indicates that activity may be associated with ancient faults. However, recent

movement on these faults during these events would have been unlikely, given that

earthquakes in the region are characteristically of low magnitude. There is, however,

evidence that compressive stress is building and being released periodically and

ancient faults may be a likely place for this stress to be released. The relationship

between ancient fault systems and the Tweed Shield Volcano has also been discussed

and it is suggested here that the volcanic activity was associated with renewed

faulting on the Great Moreton Fault System during the Cenozoic. The

geomorphology and drainage patterns of southeast Queensland have been compared

with expected morphological characteristics found at passive and other tectonic

settings, both in Australia and globally. Of note are the comparisons with the East

Brazilian Highlands, the Gulf of Mexico and the Blue Ridge Escarpment, for

example. In conclusion, the results of the study clearly show that, although the region

is described as a passive margin, its complex, past geological history and present

compressive stress regime provide a more intricate and varied landscape than would

be expected along typical passive continental margins.

The literature review provides background to the subject and discusses

previous work and methods, whilst the findings are presented in three peer-reviewed,

published papers. The methods, hypotheses, suggestions and evidence are discussed

at length in the final chapter.

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Keywords

Geomorphology, GIS, Drainage patterns, Stream-ordering, southeast Queensland,

Passive margin, Earthquake distribution

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LIST OF PUBLICATIONS

REFEREED INTERNATIONAL JOURNAL PAPERS PAPER 1

Title: The influence of geological fabric and scale on drainage pattern analysis in a

catchment of metamorphic terrain: Laceys Creek, southeast Queensland, Australia

Authors: Jane Helen Hodgkinson, Stephen McLoughlin, Malcolm Cox

Status: Published November 2006 (available on-line from July 2006)

Journal: Geomorphology, 81 394-407

PAPER 3

Title: Drainage patterns in southeast Queensland: the key to concealed geological

structures?

Authors: Jane Helen Hodgkinson, Stephen McLoughlin, Malcolm Cox

Status: Published December 2007

Journal: Australian Journal of Earth Sciences, 54 1137-1150

REFEREED CONFERENCE PAPER

PAPER 2

Title: The correlation between physiography and neotectonism in southeast

Queensland

Authors: Jane Helen Hodgkinson. Stephen McLoughlin, Malcolm Cox

Status: Reviewed for DEST purposes, published in conference proceedings,

presented with poster (Appendix 1)

Conference: Australian Earthquake Engineering Society Conference, Canberra, ACT November 2006

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ACKNOWLEDGEMENTS

I wish to acknowledge the support and encouragement provided by my principle

supervisor, Dr Stephen McLoughlin who gave invaluable advice and comments, who

gave his time generously and whose ability and standards I will always strive to

emulate. My associate supervisor, Associate Professor Malcolm Cox also provided

constructive support, held many useful discussions, and contributed his valuable time

for the review of manuscripts, for which I am very grateful.

I am indebted to Dr Andrew Hammond for his help, support and valuable advice, and

for our countless beneficial talks and debates. I am grateful to Dr Micaela Preda for

sharing her wealth of GIS knowledge with me and for our constructive discussions

with regard to local geology and geomorphological analysis. I also acknowledge the

helpful and educational discussions and field trips with Mr Bill Ward whose interest

in the subject of geomorphology is valuable and encouraging. Further, I wish to

express my gratitude to Mr Nate Peterson who provided valuable assistance with GIS

methodology.

This research project would not have been possible without the datasets provided by

various sources. Special thanks go to Dr Dion Weatherly and Mr Col Lynam at the

Earth Systems Science Computational Centre (ESSCC), University of Queensland,

for their enormous encouragement with my project, for their collaborative

discussions and for providing their valuable earthquake database. Thanks also goes

to Geoscience Australia for further earthquake data, and to Pine Rivers Shire Council

and the Geological Survey of Queensland at the Department of Mines and Energy

(Queensland Government) for providing geological, topographical and drainage data,

which were required for GIS analysis. Datasets were also obtained from

USGS/NASA via their on-line service, without which, the first paper could not have

been written.

I would like to thank all the staff and students in the School of Natural Resource

Sciences at QUT, whose help and encouragement have been a great benefit to me in

the course of this study. I also thank the staff at the School of Earth Sciences,

Birkbeck University of London, among other things, for inspiring me in the

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wonderful subject of geology. I also thank all my friends and family both in Australia

and the UK, who believed I could do this. I especially thank Jean and David

Hodgkinson, Madonna O’Brien, Ben Henderson, Jennifer Baker, Caroline Cole,

Jeanette Fleming, John Hodge and everyone from the ‘Whitton School Class of

1982’, whose humour and friendship has been invaluable. A particularly special

thank you goes to Jonathan Hodgkinson, my husband, friend, field assistant, fellow

student and room-mate at QUT, whose help and encouragement is beyond measure. I

also express my gratitude to my late parents to whom I dedicate this work. One of the

most important things they taught me was the value of enquiry, without which,

science would go nowhere.

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TABLE OF CONTENTS STATEMENT OF ORIGINAL AUTHORSHIP iii ABSTRACT v Keywords vii LIST OF PUBLICATIONS viii Refereed International Journal Papers viii Refereed Conference Paper viii ACKNOWLEDGEMENTS ix INTRODUCTION 1 Setting 4 Scope of study 5 Methods and summary of results 6 LITERATURE REVIEW 10 INTRODUCTION 12 INTRODUCTION TO GEOMORPHOLOGY 14 Surface processes: Weathering and erosion 14 Climate 20 Palaeoclimate and present-day climate in southeast Queensland 22 Regolith and ground cover 23 Effects of sea-level change 24 Anthropogenic influence 26 The role of lithology and rock fabric in geomorphology 30 The role of tectonics and major geological events in geomorphology 38 Neotectonism in Australia 48 Post-Mesozoic tectonism in southeast Queensland 54 GEOMORPHOLOGICAL ANALYSIS 59 Drainage patterns 59 Palaeosurfaces, palaeodrainage and current drainage patterns in southeast Queensland 62 Stream ordering 63 Data analysis 65 Erosion analysis 66 SOUTHEAST QUEENSLAND 70 Introduction to the study area 70 Reasons for selecting the study region 70 Geological history 74 Faulting 85 Sea level influences 86 Terraces 86 Incision 87 Geology of Pine Rivers and Laceys Creek: a fine-scale case study 93 Previous geomorphological studies of southeast Queensland 95 ANALYSIS METHODS USED IN THIS STUDY 102 Digital elevation models (DEMs) 102 Geological data 103 Earthquake data 103 Geographic Information Systems (GIS) and choice of GIS products 103 Remote sensing 106 Spatial analysis 106 Methods of channel analysis 107 Stream ordering 108 SUMMARY 111 References 114 PAPER 1 135

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Introduction to Paper 2 163 PAPER 2 165 PAPER 3 183 CONCLUSIONS 215 Summary of results and major findings 216 Hypothesis 1 216 Hypothesis 2 217 Hypothesis 3 218 Additional findings 219 Implications for future research 222 Other observations and general discussion 223 Implications for evaluating the evolution of the landscape 230 Evidence of past geological events in the present landscape 230 National and international significance 234 Evolutionary model 238 Précis of main findings 238 Future work 239 References 240 APPENDICES 243 Appendix 1 - AEES2006 Poster 245 Appendix 2 - A GIS and map-analysis deficiency 247 Appendix 3 - Other software products used 249 Appendix 4 - Statistical analysis of planar features in Laceys Creek 251

INTRODUCTION

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INTRODUCTION

Geological processes are a primary control upon landscape physiography, as internal

modifications of the Earth often lead to distortion and contortion of the surface.

These internal modifications of Earth’s crust are also responsible for the location of

hydrocarbon reservoirs, aquifers, mineral accumulations and geological hazards such

as active faults. Geological controls on physiography range from large scale

processes such as plate movements, folding, faulting and jointing to the finer scale,

where variations in the mineralogy of rocks, micro-fractures and porosity can lead to

differing susceptibility to weathering. The derived physiography is, therefore, a result

of both endogenic processes and exogenic modification by agents of weathering and

erosion. These interactive processes may also generate geological hazards, such as

unstable slopes or the superposition of valleys on faults (of importance for dam

location). Various methods of physiographic analysis can be used to interpret the

evolution of the landscape, from which we may deduce the underpinning lithological

and structural influences. This type of analysis can greatly enhance understanding of

sub-surficial geology and is an effective tool for geohazard identification and

resource exploration.

The main objective of this study is to improve understanding of the controls on

landscape evolution in southeast Queensland, as this may be an important

consideration for future land use. An improved understanding of the influences on

local physiographic evolution can then be used to interpret landscape development in

similar tectonic settings globally. Key to this study was identification of the extent to

which geological processes influence the existing landscape morphology of southeast

Queensland. This was undertaken by analysis and interpretation of the genesis of

various physiographic features including fine-scale streams, major drainage systems,

scarps, valleys and plains at varying scales. Geomorphological analysis was

undertaken at both regional and catchment scales to assess the influences of

different-magnitude geological features on southeast Queensland’s physiography.

Although landscapes develop from the interaction of both internal and external

processes, one of these processes typically dominates the evolution of the system. In

particular, this research seeks to determine whether geological features (structure and

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lithology) sufficiently correlate with physiographic features to be deemed the

dominant influence on the evolution of the landscape in southeast Queensland. An

individual index is not sufficient to determine the main control of the landscape, so

this study evaluates multiple criteria at various scales, to identify whether geological

processes are (or were) dominant in the development of southeast Queensland’s

landscape. To establish whether more than one major influence exists, the research

uses a sequential approach and the results are presented in three peer-reviewed,

published papers.

Setting Around 370-220 Ma, the easternmost part of Australia was accreted onto the older

cratonic part to the west. Subsequently, the easternmost part has been modified by

epicratonic basin development, rifting and putative hotspot volcanism, which has

contributed to a vast array of natural resource deposits in the region and has

presumably imposed strong influences on the land’s topography. The area for this

study is situated on the eastern margin of the Australian continent (approximately

151° 53', 26° 11'S to 153° 31', 28° 30'S), and covers approximately 41,000 km2.

Although the topography of the region is generally subdued by world standards,

some steep and mountainous areas also exist. Outcrop availability and accessibility is

generally moderate to poor and commonly limited to road cuttings, due to deep soil

and extensive vegetation cover. Furthermore, the region is currently undergoing

extensive land-use change particularly due to rapid urbanisation and development;

the area represents one of the fastest population growth centres in Australia

(Australian Bureau of Statistics, 2006).

The region’s geomorphology has been generally well studied, albeit on piecemeal

basis (e.g. Marks, 1933; Watkins, 1967; Arnett, 1969; 1971; Donchak, 1976;

Beckmann and Stevens, 1978; Lucas, 1987; Cuthbertson, 1990; Childs, 1991). In

summary, the western, southern and northern margins of the study area are fringed

by highlands (mainly plateaux over 300 m. a.s.l.), and a dissected highland area (the

D’Aguilar Ranges) occurs central to the region. Foot hills and coastal plains occur

across the remainder of the area, principally in the east, and escarpments are also

fairly common across the region. Eastern Australian rivers may be considered to be

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shorter than others by global standards, although runoff is generally higher and more

variable. This is due to the climate variations dictated by the region’s mid-latitude

position and the competing influences of the western Pacific tropical monsoon and

temperate frontal systems that impose a Mediterranean climate on the southern half

of the continent (Finlayson and McMahon, 1988). By Australian standards, rivers in

southeast Queensland are moderate in size with moderate to high discharge that

varies seasonally. Many streams are ephemeral and flow mainly in response to heavy

summer rainfall events. The main drainage systems of the region display strong

northwest-southeast and northeast-southwest trends similar to those of some large

faults in the region. Similarly, a strong northwest-southeast trend is evident in the

distribution and foliation of rock units located in southeast Queensland, this being

related to late Palaeozoic – early Mesozoic convergent margin deformation.

Earthquake data over the past 130 years records only two earthquakes of >5

magnitude (Richter scale) in the region and more than 50 that were >2 magnitude

(ESSCC, 2006). Although the database provides discontinuous evidence of

earthquake activity spatially and temporally, the foci of many earthquakes are clearly

positioned in shallow clusters and even a casual examination reveals alignment of

many epicentres within discrete corridors.

Scope of study Southeast Queensland has been selected as the study area primarily due to its

complex geological history and varied physiography. Despite many investigations of

the region, detailed information on the genesis of landscape features at a regional and

local scale is deficient. As the human population in the region is rapidly increasing

concomitant with residential, commercial and industrial development, a better

understanding of the driving forces behind geomorphological change is critical for

future landscape management. Understanding the evolution of other regions with a

similar climatic setting and complex mix of both convergent- and passive-margin

geological histories may also benefit from the methods and results presented in this

study.

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Methods and summary of results Remote sensing is a valuable tool for studying landscapes that may be inaccessible

and/or very large, such as the southeast Queensland region. Remote sensing has been

used here to analyse the alignment, position and form of physiographic features

including mountains and highlands, valleys, drainage channels, scarps and lowlands.

Other datasets were also integrated into the analysis including rock types and fabric,

earthquake locations and geological structures. The method further lent itself to

analysis at multiple scales from regional to sub-catchment settings.

In the following section a review of the literature provides an introduction to some of

the principles of geomorphology. This is followed by a review of the methodologies

employed for geomorphological analysis, their advantages, problems and

applicability to the southeast Queensland region. The geology of southeast

Queensland is then summarized and previous studies of the region’s geomorphology

are examined. The literature survey concludes with a review of the specific analytical

methods employed in this study, the limitations of the data and an outline of the need

for a new methodology for stream ordering in drainage network analysis.

The first part of the results (presented as paper one) analysed whether drainage

orientation is affected by its underlying rock fabric, including cleavage, joints,

fractures and faults. The hypothesis tested in paper one was:

“Complex geological fabric of metamorphic rocks of southeast Queensland

has control over orientation of streams at the sub-catchment scale”

This was tested in a sub-catchment where the meta-sedimentary rock types retain

some bedding features but are complicated by multiple orientations of cleavage,

joints and faults. The aim was to assess the orientation of streams within a catchment

developed on two juxtaposed metamorphic rock types and identify the extent to

which streams show alignment with the underlying rock-fabric. Having introduced a

new stream-ordering method for this study, as other methods were not suitable, a

positive result for some stream-orders suggested that there is some geological control

on drainage architecture at this scale. The results showed that higher order streams in

the sub-catchment had a similar orientation and close spatial relationship with

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fractures and faults. Analysis of other faults and drainage channels outside of the

sub-catchment also revealed a similar correlation which required further exploration.

A second investigation of geological control on the landscape incorporated a spatial

investigation of recent shallow earthquakes across the whole of southeast

Queensland, to assess whether the streams and valleys that showed a correlation with

ancient faults might be influenced by continuing earth movements along these

structures. The hypothesis tested in paper two was:

“The location of recent earthquakes in southeast Queensland aligns with

geomorphological features such as scarps, mountain ranges and valleys”

The aim of paper two was to identify, firstly, whether earthquake epicentres show

spatial alignment and, secondly, whether any ancient geological and

geomorphological features (including faults, scarps, river valleys, highland

lineaments) align with trends of earthquake epicentres. From this information the

study discusses whether neotectonics plays an ongoing role in the evolution of the

landscape. The results showed an alignment of low magnitude, shallow earthquakes

with some strong geomorphological trends such as large river systems and areas of

highlands. This suggests that tectonics may be playing an active albeit minor role in

present-day landscape modification. Although the results were positive, the

earthquake database and earthquake monitoring is fairly sparse and may not

represent a thorough picture of neotectonism in the region. Therefore, the results are

not sufficiently comprehensive to reflect the full scale of neotectonic influence on the

landscape. Further data is clearly needed to clarify the role of this process.

Strong relationships have been proven to exist between ‘non-random’ drainage

patterns and structures underpinning the landscape, especially where tectonic

features such as uplifted or down-thrown blocks, and faults and folds are of strong

amplitude. Combining the geology-drainage relationships similar to those found in

paper one, with the scale and relationships in paper two, a third measure of

geological control on the landscape was introduced into the research (paper three).

This involved drainage pattern analysis at the regional scale. Drainage orientation

and patterns and physiography were compared to the distribution of geological

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structures, lithostratigraphic packages of various ages, igneous intrusions and

earthquake corridors, to assess the degree to which geological features of various

ages and origins influence the modern physiography. The hypothesis tested in paper

three was:

“Drainage networks across southeast Queensland show repeating, aligned

and anomalous patterns that are controlled by a range of geological structures of

varying age”

The history of southeast Queensland is tectonically complex and although the affects

of some ancient tectonic events on the landscape might still be evident, it is equally

possible that over the intervening time, other processes may have obscured some of

the original influences on the physiography. However, the results of paper one show

a strong relationship exists between fine-scale streams and underlying rock structure

and fabric that date back to at least the Late Carboniferous, even though these rocks

have been influenced by a range of subsequent geological processes (nearby

convergent margin pluton intrusion, regional uplift, passive margin development, and

local emplacement of volcanic plugs). The results of paper two revealed common

alignment between recent shallow earthquakes and large ancient valleys that also

correspond to a Permian-Triassic trend of strike-slip faulting and the orientation of

major tectono-stratigraphic unit boundaries. The results of paper three show a

variety of associations between geological features and physiography that include

volcanoes, rock types, faults, block emplacements and tectonic tilting that occurred

over various stages of southeast Queensland’s geological history.

Integration of the datasets within a Geographic Information System (GIS)

provided a suitable platform for this analysis and led to new insights into the extent

to which the physiography of the region is controlled by geological structures such as

faulting and rock fabric. Additionally, the results suggest that previously unknown

geological structures may control some important physiographic features and that

some parts of the region may have been subject to neotectonic modifications. The

results ultimately lead to the conclusion that there is a strong geological control over

existing morphology providing sufficient evidence that surface or exogenic controls

are not the dominant factor influencing the present landscape.

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“The greatest obstacle to discovering the shape of the earth, the

continents, and the oceans was not ignorance but the illusion of

knowledge.”

Daniel J. Boorstin 1914 - 2004

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LITERATURE REVIEW

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INTRODUCTION Tectonism must be acknowledged as a primary control on the structure and

physiography of land masses. It is responsible for the position of landmasses, and

within them, the location of geological units, faults, joints and other planes of

weakness. It also involves uplift of broad regions and basin subsidence. Weathering

and erosion further modify the landscape and, as they are acting upon a terrain that

has been ‘processed’ by a primary force, are described as secondary processes. The

use of the terms ‘primary’ and ‘secondary’ describes the order in which the processes

occur and not the relative importance of the process. Although these processes may,

and often do, occur concurrently, weathering and erosion are exogenic, acting upon

the endogenically processed landscape, hence the term ‘secondary process’ is

applied. Primary processes can directly generate landscape features, such as hills or

mountains and scarps, resulting from folds, uplift and faults. However, the additional

action of secondary processes upon planes of weakness, such as faults, joints and

folds, or the differential weathering of juxtaposed lithologies of different durability,

can also lead to further landscape alteration.

Geological structure and tectonics are intrinsically linked to a range of

geomorphological features so, in reverse, it is possible to analyse the landscape to

establish how it has been influenced by geological features and tectonic events (e.g.

Ellis et al., 1999; Burrato et al., 2003; Vannoli et al., 2004; Delcaillau et al., 2006).

Primary controls can have an influence at multiple scales: on entire landmasses,

terrane emplacement, fault systems, folding and even microstructures. Tectonics may

down-throw rocks, positioning them for deep burial and metamorphism; uplift them,

exposing them to weathering and erosion; fracture and weaken them for further

preferential weathering; move and deform them one or many times causing complex,

multiple-scale changes to a rock’s strength, form and character. These changes may

produce landscape features of varying magnitudes either as a direct result of the

primary process, or a result of secondary processes acting upon the primary

landforms.

The product of primary controls at multiple-scales across a complex

landscape is the primary focus of this research. The aim is to determine the extent to

which geological control over the landscape is reflected in its morphology, by

performing analyses of integrated multiple-scale geomorphological, geophysical and

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geological datasets using a Geographic Information System (GIS). In particular the

work will establish whether underpinning structure or lithology correlate with the

positions and orientations of drainage channels as opposed to stream placement being

dominantly influenced by secondary processes. Scales analysed vary according to the

types of features being investigated. At the finer scale, analysis has been performed

on terrains developed on low-grade metamorphic rock that was originally turbiditic

sediments, but which was later buried, deformed, uplifted and deformed further. On a

broader scale, analysis was performed on the regional structure of an area that has

been affected by both convergent and passive margin tectonism and which has been

fractured, uplifted, in places down-thrown, and is composed of sedimentary,

metamorphic and igneous rocks. The study also focuses on a variety of spatial scales

from sub-catchment to multi-catchment regions. The drainage pattern analysis seeks

to reveal drainage patterns that cannot be explained by presently defined geological

structures but which, by the nature of their patterns, suggest a geological control. The

research, therefore, may reveal the locations of previously unknown, unmapped or

deep-seated geological structures that may have implications for planning

infrastructural developments in the region.

The literature review explains how primary and secondary processes lead to

geomorphological change, and considers the relevance of geological control over

geomorphology. The regional features of southeast Queensland and the finer-scale

case study area of Laceys Creek are presented, together with a review of previous

work in this branch of the geosciences both within this study area and globally. The

review also discusses the methods involved in the current study in the context of

methodologies applied elsewhere and of limitations of the available data. The review

then considers the importance of identifying geological control where landscape

alteration is being evaluated in relation to anthropogenic activity.

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INTRODUCTION TO GEOMORPHOLOGY

Geomorphology, from the Greek ge, meaning earth and morfé meaning form, is the

study of landforms including their evolution and origin. Geomorphological analysis

provides an understanding of past surface-shaping processes and events and helps

predict future landscape changes. Additionally, geomorphological studies are

increasingly becoming a valuable supplementary method for identifying recent and

current tectonic processes. It has become a useful tool for a wide variety of

applications including land management (e.g. Gupta and Ahmad, 1999; Andreas and

Allan, 2007), engineering of roads and dams (e.g. Seppala, 1999; Graf, 2005),

location and management of water resources (e.g Thoms and Sheldon, 2002;

Ghayoumian et al., 2007), geohazard analysis including evaluation of slope stability

(e.g. Dominguez-Cuesta et al., 2007; Schulz, 2007; Kirby et al., 2008), and it has

even been used as an indicator of global warming (Goudie, 2006).

Geomorphological features such as mountains, hills, slopes, valleys, gullies, plateaux

and drainage channels of all scales, typically form from the interaction of both

endogenic and exogenic processes. The following section discusses these processes

and their inter-relationships.

Surface processes: Weathering and erosion From an exogenic perspective, weathering and erosion (‘surface processes’) act upon

uplifted, extruded, exposed or emplaced rock units. Alabyan and Chalov (1998)

stated that channel development strongly relies upon water discharge and river slope

and emphasised that the greater the stream power, the stronger the branching

tendency of a river system. Nevertheless, there are other controls that may be equally

important whether from an exogenic or endogenic perspective. Endogenically, for

example, lithology and induration controls a unit’s erodibility.

Weaknesses and differences in rock strength within a rock unit or between

abutting or juxtaposed units, may lead to differential weathering causing physical

surficial features to form at varying scales, such as gullies, channels and basins. A

plane or line of weakness in a rock may be exploited by surface processes such as

fluid flow. Then, as a preferential course of drainage, it may eventually erode to form

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a channel. Such channels may become widened or incised, retaining the original

orientation, even though it may no longer rely on the original plane of weakness to

be the preferred location of flow. Furthermore, the physical feature that originally

caused preferential flow may no longer exist although the orientation and drainage

pattern that it initiated may persist. Channels, directly following geological

weaknesses or following ‘ghost’ features (structures now completely eroded), both

represent manifestations of geological control of the landscape.

The form and pattern of river channels is affected by a multitude of processes

such as: changes in climate that may, for example, lead to increase or decrease in

precipitation and vegetation cover; anthropogenically forced changes to ground

cover; sea-level changes; and uplift and down-warp of the landscape. These factors

are discussed below and although they are typically described as discrete processes,

they frequently occur simultaneously. Early workers such as Gilbert (1917)

recognized that a river channel may adjust its character following many types of

disturbance to the land such as uplift, down-throw, tilting or warping, hence these

factors have been the focus of fluvial geomorphological studies for many years.

Alteration of these parameters may lead to adjustment of the stream’s longitudinal

profile but may equally induce stream widening and downstream aggradation (Doyle

and Harbor, 2003). Further incision of the landscape and backfilling of the upper

reaches of channels may also ensue (Woolfe et al., 2000).

Although erosion may occur over long periods of time, it may also occur

suddenly and the causes of abrupt erosion events have been explored widely. For

example, Thornes and Alcantara-Ayala (1998) investigated the main cause of mass

hill-slope failure that occurs on metamorphic rocks in the mountains of southeast

Spain. Anthropogenic activities had been suggested as the cause, although this was

later discounted as the events were ‘unpredictable’. They concluded that mass

failures depended on the slope material properties, topography, climate and

hydrological interactions: where there appeared to be relatively poor resistance and

impermeability in the metamorphic rocks (such as phyllites), mass movement was

enhanced, both at shallow depths, within the regolith and deep-seated within the

bedrock. However, in northern Spain, Calcaterra et al. (1998) noted that natural

slopes failed less frequently than man-made slopes of similar angle in low-grade,

weathered, metamorphic rocks, suggesting that the natural slopes were more likely to

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be closer to equilibrium and better able to withstand variations in weather patterns. In

the French Riviera, where high-relief steep slopes with a large variety of rock types

occur, shallow, first time landslips (i.e. those that are not repeated) were linked to

long periods of heavy rain, and deeper-seated landslips were the result of longer-

period gravitational and tectonic effects coupled with weathering (Julian and

Anthony, 1996). Two rain thresholds were identified as being necessary to

destabilise slopes in the Himalayas during monsoonal rain – the rain thresholds being

values of the seasonal accumulation plus the daily total (Gabet et al., 2004).

Additionally, it was found that the slope angle controls the amount of daily total

rainfall required to destabilise the slope; water storage determines the amount of

seasonal rainfall required to destabilise and trigger slope failure. They concluded that

thinner regolith on steeper slopes will fail faster than thicker regolith on gentler

slopes.

In southeast Queensland, Granger and Hayne (2000) reported that the most

common trigger for slope failure in the region is an episode of intense rainfall and

that antecedent rainfall may be of critical importance. Hoffmann et al. (1976) stated

that this is particularly the cause for landslides on the steepest slopes. Granger and

Hayne (2000) further stated that long, antecedent rainfall events are most relevant to

deep-seated, slow moving landslides and that short, antecedent rainfall periods are

relevant to shallow slips and shallow debris flows. Where natural forest cover has

been removed, groundwater levels may rise significantly due to a reduction in

transpiration. With the increase in groundwater levels, the pore pressure is also

amplified leading to a reduction in shear strength of surface materials. In these

circumstances, even minor rainfall events may be sufficient to cause failure of rock

and/or the overlying soil horizon by raising pore pressure above critical levels. This

has been found to occur on the cleared slopes of the Tertiary basalt plateaux and

ranges of southeast Queensland where landslides are particularly common (Willmott,

1987). On the Maleny-Mapleton plateau for example, Willmott identified several

types of slides including debris slides or flows on scarps and very steep slopes; small

rotational slides or slumps on the moderate slopes; and also complex multiple

rotational slides that affect broad areas up to 1 km in width. Although the latter type

is slow moving, they are typically reactivated in extreme wet seasons. Willmott

(1987) also described the basalt terrain as geologically sensitive, resulting from

16

accumulations of unconsolidated debris that may be easily mobilised; alternating

horizons of porous and massive basalts that direct groundwater flow outwards to the

slopes; swelling clays within the soil and colluvium that lose strength on saturation;

and the presence of soft sediments underlying the basalt, which themselves may fail.

From his work, it is clear that surface or endogenic processes are responsible for

shaping the landscape, and although the slopes are less stable due to previous

deforestation or major rainfall events, the ultimate control of the landslides is

typically geological.

Rotational slides, both semi-circular and back-tilted, are evident in the Mount

Mee area and sites underlain by the Neranleigh-Fernvale Beds through the Brisbane

region. Some rotational slides in the area were found to have occurred on slopes as

low as 11° (Granger and Hayne, 2000). Soil slumps were also observed on grassed

slopes of 11 to 17° in areas underlain by greenschist. They concluded that there may

be an increased susceptibility to landslips in the greenschist-derived soils and also

colluvial soils derived from banded chert. Willmott and Surwitadiredja (2003) also

confirmed that landslides in the Mount Mee area were primarily caused by

groundwater seepage and the removal of forest cover on the deep soils that

developed on the basalts and greenschists. A debris flow is evident in the western

part of Pine Rivers where loose material has been mobilised by torrential rainfall on

a steep mountain side (Granger and Hayne, 2000). Such events are fairly common on

slopes of greater than 25° and particularly common on slopes that formerly supported

rainforests on the Neranleigh-Fernvale Beds. Small landslips have also occurred on

the bank of the South Pine River in Cenozoic sediments of the Petrie Formation. On

the Bunya Phyllite, rockslides have been observed on the steep banks of the Brisbane

River (Granger and Hayne, 2000). A large debris flow occurred in the Laceys Creek

catchment, southeast Queensland, after heavy rains in January, 1974, a rainfall event

that caused widespread flooding, ground saturation and many other events of mass-

wasting in southeast Queensland. The debris flow in Laceys Creek consisted of

completely weathered Bunya Phyllite and highly weathered Neranleigh-Fernvale

Beds; although it was triggered by saturation, it was aided by ‘an intersecting system

of a vertical faults and joints’ leaving a head scarp of 10 m height corresponding to

the orientation of the fault and joints (Hofmann et al., 1976). Other landslides that

were observed at this time, for example at Mt Nebo, Mt Mee and near Woodford

17

were on varying slopes, but all were caused by ground saturation. However, the

example at Laceys Creek demonstrates that lithological fabric and structure of the

underlying rocks may strongly control mass-wasting episodes. Examples of some

erosional features that have been identified in the Pine Rivers area of southeast

Queensland are highlighted in Table 1.

Angle

of slope

Description of erosion Example in SEQ

>25° Small debris slides, rotational slumps,

debris flows

Neranleigh Fernvale

Beds, Brisbane River

region,

17-25° Rotational slumps in soil and colluvium on

concave slopes around gully heads (slumps

can also occur from 11° on greenschist

derived or red colluvial soil)

Neranleigh Fernvale

Beds; Bunya Phyllite

20-25°g Small debris slides, rotational slumps or

debris flows in deep pockets of soil or

colluvium

Rocksberg Greenstone,

high country such as

western Pine Rivers

11-25° Small rotational slides in colluvium (sand,

soil, clay and rock debris)

Undulating plateaux and

middle country

<11° slumps Plateaux, river banks,

river terraces and

channels

Table 1. Examples of erosional features in southeast Queensland (after Hofmann et al., 1976; Granger and Hayne, 2000)

Although rainfall and slope are commonly identified as the combined causes of

landslip, Scheidegger (1998) also identified that local, modern tectonic stress was the

cause of landslides in the Chinese Himalayas. He stated that, although it is

commonly assumed that progressive erosion over-steepens slopes leading to

destabilisation and that landslips are commonly triggered by extreme weather or

prolonged rainfall, endogenic processes are also of major importance to mass

movements and are commonly overlooked. Scheidegger and Ajakaiye (1994)

identified that, in Nigeria, apparent ‘erosional features’ such as gullies, have a

definite orientation pattern due to endogenic control; where cracks occurred due to

18

tectonic stress, unstable features were formed that later led to a landslide. They

concluded that tectonics was the primary contributor to the landslide, even though it

did not trigger the ultimate event.

Although mass-wasting occurs episodically, the principle land-forming

surface process in southeast Queensland at present is fluvial erosion. Average runoff

and peak discharges have been calculated for the Moreton Region (for example

Hofmann et al., 1976): peak discharge occurs January to March during which period,

flooding incidents and erosion rates are highest. All main streams in the Moreton

Region eventually drain to the coast and have relatively steep upper catchments and

meandering middle to lower reaches. This is typical of southeast Queensland. In

these catchments, erosive forces are influenced by the gradient and length of slope

and finer, less cohesive grains will generally erode more readily than coarse-grained

and more cohesive soils and rocks (Hofmann et al., 1976) except in cases where

ionic bonds generate special cohesive forces in very fine-grained (clay-rich)

sediments. Down-cutting is evident in the headwaters of many southeast Queensland

drainage systems, particularly in the D’Aguilar Range where gully transverse profiles

are commonly V-shaped and bedrock channels form low-order streams (Hofmann et

al., 1976); higher order channels typically deepen and widen into alluvial channels

on valley floors. North of Brisbane on the Pine River, the ‘Strathpine Terrace’

(Beckmann, 1959), a stream channel and flood plain deposit of Pleistocene age,

(deposited when sea levels were interpreted to have been approximately 4.5 – 6 m

higher than today) has been incised despite receiving sediment from local streams.

Where headwater swales have not kept pace with erosional lowering of the main

valley, small hanging valleys also occur in the Strathpine Terrace, near Harrisons

Pocket (Hofmann et al., 1976). Gully erosion is evident in the Samford Valley, which

is floored by strongly weathered granitic rock. The main modification that occurs in

the middle and lower reaches of streams in the Pine Rivers catchments is meander

migration and during major floods (such as January 1974) bank erosion has caused

channel straightening. Using the modelling software, SedNet, Olley et al. (2006)

identified high and medium gulley erosion rates in the upper Lockyer, middle

Laidley and western Bremer catchments. However, Caitcheon et al. (2005) identified

that down-cutting and gulley erosion are not the only surface processes presently

19

contributing to stream sediment load, and they reported that hillslope erosion is

significant in the middle Lockyer and upper Brisbane catchment regions.

Climate Variations in stream morphology can reflect changes in climate (Kershaw and

Nanson, 1993; Nanson et al., 2003; Thomas et al., 2007). The sedimentary sequences

caused by varying conditions become stacked, from which, climate change can be

ascertained (Read et al., 1991; Steckler et al., 1993). Variations between greenhouse

and icehouse conditions have profound affects on the landscape. Sedimentary

evidence suggests that low-amplitude and high-frequency sea-level changes during a

greenhouse period will lead to moderate to low variations in the location of the

shoreline, modest to low continental erosion, and aggrading carbonate ramps that are

infrequently sub-aerially exposed and eroded (Séranne, 1999). Conversely, during

icehouse conditions, when cooler and warmer, and drier and wetter periods rapidly

oscillate, along with high-amplitude sea-level changes, the shoreline location will

fluctuate more broadly over time. Furthermore, continental weathering becomes

enhanced, providing more terrigenous sediments for transport by streams to the

shoreline, producing a prograding terrigenous wedge (Séranne, 1999). In addition to

flow regime, channel form and initiation, climate may also directly impact on

bedrock form as flow regime also affects the amount and type of sediment supplied

to the system. For example, in The Sprongdøla, southern Norway, climate is

responsible for frost-shattered bedrock, which itself directly influences the

geomorphology, but in turn also provides the sediment source (McEwen and

Matthews, 1998). In wet tropical climates, a greater degree of chemical weathering

can impose quite a different signature on the sediments derived from the same parent

rocks.

As climate affects landforms and weathering profiles, the study of the

position of landforms and their potential age, can give an indication of palaeoclimate.

The amount of rainfall, angle of slope, the surface texture and resulting runoff will

affect the amount of erosion and the position and stability of the watertable will

control the weathering profile (Gasparini et al., 2004). How ‘heavy’ a rainfall event

is, the length of a rainfall event, and even the size of raindrops will have an effect

upon the erosion, ensuing slope and channel shape and overall resulting landforms

20

(Bill Ward, 2006, Pers Comm). Temperature, rainfall distribution and type of events

affect the quantity and variety of overland cover. For example, warm regions that

receive frequent rainfall may be rich in vegetation that may control the influence of

overland flow, infiltration and erosion. Burch et al. (1987) noted that runoff in a

catchment that had been completely cleared of forest behaved as if the ground was

constantly in an advanced stage of saturation, whereas a similar-sized neighbouring

catchment still vegetated by natural remnant eucalypt forest, remained more

permeable allowing runoff to be delayed until the soils became wet. High

temperatures frequently ‘bake’ and dry exposed soils and this will lead to greater

erosion during rainfall events. Infiltration is decreased when heavy precipitation

occurs on a hardened soil and overland flow occurs more readily. Such events are

typical in many tropical and subtropical zones including southeast Queensland. The

predictable outcomes that might be expected from these surface processes have been

used by workers in this field to compare weathering, erosion and climatic factors

with patterns in the resulting features (Woolnough, 1927 cited by Watkins 1967;

Bryan, 1939; Whitehouse, 1940). Climate change may also lead to changes in

vegetation type and cover. Rich vegetation covering the landscape can provide

stability for slopes via soil-binding roots and reduce the power of rain upon the soil.

Furthermore, evaporative losses occur when precipitation is first intercepted by

foliage and the magnitude of run-off is much lower resulting in reduced overland

flow (Bonnet et al., 2001). This can lead to more gradual and more thorough

infiltration than a similar style of rainfall falling on sparsely vegetated land, although

is it also argued that leaf debris can prevent infiltration. Nevertheless, runoff from

leaf matter still prevents some erosion that otherwise would have occurred if rainfall

was directly onto the soil or rocks. The main contributing factors of channel

initiation brought on by overland flow (Bonnet et al., 2001) are climate, vegetation

coverage, precipitation patterns and ‘weatherability’ of underlying rocks. Channel

initiation requires the upper tips of the first-order channels to correspond with a point

where erosion can be generated due to sufficient shear-stress induced by overland

flow.

21

Palaeoclimate and present-day climate in southeast Queensland During the late Cenozoic, climate in southeast Queensland varied between long, dry

periods and shorter, humid periods. Sheet-wash and scarp-retreat during dry periods

resulted in pediments and pediplain, and upper erosion surfaces such as at

Stanthorpe, the crest of the D’Aguilar Range and the Mount Mee Plateau (Watkins,

1967). During humid periods thalwegs were accentuated by more linear erosion,

pediplains were rejuvenated and topographic relief became more dissected, such as

in the Lockyer Valley and upper Logan and Mary river areas (Watkins, 1967). The

upper erosion surface is a well-preserved pediplain that has been lateritised, although

the laterite was stripped, leaving a surface of silcrete in places, such as Miocene-aged

surfaces west of the Great Divide. Closer to the coast, the upper erosion surface of

Eocene-Oligocene age is warped with an approximate north-south axis of uplift with

the axis rising towards the south. A lateritised pediplain surface at approximately 15-

60 m above sea level, of Pliocene age, shows pediplain and lateritisation conditions

continued until the onset of the Pleistocene. Dissection of this surface took place

when conditions became more humid, although the pediplain was not completely

obliterated. Uplift and warping of the erosion surfaces was brought about by

Cenozoic volcanic activity. During this time, the Middle Erosion Surface developed

(Watkins 1967) and this surface (at 120-210 m) is present, as discontinuous

pediment-like surfaces flanking the D’Aguilar Range (Hofmann et al., 1976).

Cenozoic deep-weathering profiles and duricrusts in southeast Queensland suggest

that climates were generally more humid and warmer than at present (Grimes, 1988).

The Lower Erosion Surface (at 15-80 m) of predominantly Pliocene age is

interpreted to have extended into the Pleistocene, during which time the three erosion

surfaces became dissected (Watkins, 1967). This may have been due to lower sea-

level (Hofmann et al., 1976) or uplift, greater humidity and increased runoff

(Watkins, 1967). The strongly fluctuating sea levels of the Pleistocene suggest that

base level falls may have been the key driving force for fluvial incision of the

Pliocene surfaces. The Lower Erosion Surface is preserved in the upper reaches of

the North Pine River approximately 60-80 m a.m.s.l. (Hofmann et al., 1976). More

recently, a coastal depositional plain of approximately 3 m a.m.s.l emerged exposing

a narrow lower coastal plain (Watkins, 1967).

22

The present climate in southeast Queensland is subtropical, typically with wet

summers and dry winters. It is generally considered to be a humid climate with

humidity increasing in the summer. Although Watkins (1967) stated that the

Kingaroy-Darling Downs area ‘represents an island of arid climate’, this description

is incorrect as mean annual rainfall in the area is approximately 800 mm and summer

months are typically humid (Bureau of Meteorology, 2008). The current climate of

southeast Queensland causes aeolian, pediplain and fluvial erosional processes to

occur, and also processes that lead to the formation of calcrete, silcrete or laterite

(duricrust) (Watkins 1967).

Regolith and ground cover Surface processes include both mechanical and chemical weathering: the former

where colluvial and fluvial processes physically break down material at the surface;

the latter where grains are dislodged from the parent rock by mobilisation of

chemical species principally via the action of groundwater movement in southeast

Queensland. The depth and type of weathering profile and regolith that forms on

bedrock is strongly controlled by climate. For example, a deep profile and duricrust

will form where the climate is warm and humid. However, lithology also plays a role

in the formation of the weathering profile as the composition, permeability and

structure of the rock (such as jointing) will dictate the rock strength and

weatherability. The weathering profile may also be controlled by topography:

shallow valleys where water preferentially flows will form deeper weathering

profiles than steep slopes. However, the intensity of erosion is equally important. If

erosion is too fast, weathered material will be quickly removed and a profile will not

form. If deposition is too rapid, fresh sediment will cover the surface (Grimes, 1988)

potentially accumulating a sediment pile incorporating multiple palaeosols.

Deeply weathered land surfaces are a common feature in low latitude regions

that have not been affected by Pleistocene glaciation or aeolian erosion and occur in

regions such as Asia, central Africa, northern South America and Australia (Taylor

and Howard, 1999). Taylor and Howard showed that alternating cycles of chemical

and mechanical weathering are closely related to tectonic processes. Mechanical

weathering typically occurs in times of tectonic activity and in particular during

23

crustal uplift; chemical weathering (or deep weathering) typically occurs in times of

tectonic quiescence. Taylor and Howard further noted that where the rate of

accumulation of weathered products exceeds the rate of removal (recharge-dominant

hydrological regime), these areas experience tectonic quiescence (no or low tectonic

activity) and persistent deep-weathering. They argued that conversely, where the rate

of accumulation of weathered products is less than the rate of removal (run-off

dominant regime) tectonics is typically influencing the landscape. To summarise,

where there is bare rock or low surface cover that has not been influenced by aeolian

or glacial processes, tectonic uplift is dominant. Similarly, Montgomery (2003)

identified three different landscape types: chemical weathering dominant landscapes,

such as ancient cratons, where chemical weathering exceeds mechanical denudation;

low-relief and post-orogenic landscapes, where hill-slope processes and erosion rates

are reflected by the mean slope and local relief; and steep terrain and tectonically

active landscapes. Broadly speaking, these landscapes relate to ancient cratons, post-

orogenic landscapes and active orogens respectively. The models of both

Montgomery and Taylor and Howard identify that surface processes are typically

controlled by the underlying geological regime. In summary, their work suggests that

landscapes are characterised by deep weathering profiles where there is low tectonic

activity and conversely, where there is low regolith development, greater tectonic

activity is most likely occurring although these represent end-members of the soil-

forming spectrum and most landscapes fall between the two.

Effects of sea-level change Sea-level change may be eustatic or it may be local (with reference to areas

undergoing active uplift or subsidence). It can be related to ice-sheets loading the

crust, or isostatic rebound (where the crust rebounds after an ice-sheet melts);

tectonics, where uplifted or downthrown land masses may experience a relative

change in sea-level; or climate change which might physically alter the volume of

water in the oceans. Slope and stream power are important factors in channel

formation. Increased rainfall will provide a greater water supply and increase stream

power, which, depending on slope, may lead to deepening or widening of rivers.

Numerical modelling has shown that, during eustatic sea-level fall, a strong drainage

connection can exist on passive continental margins that links the drainage basin

24

with the depocentre on the shelf, but bypasses the exposed shelf. This connection

between the terrestrial (on-shore) and marine drainage system environments exists as

a single, cross-shelf river, causing there to be just one depocentre and preventing

inland, catchment-derived sediment from being deposited on the upper continental

slope (Meijer, 2002).

Although adjustment to a river’s longitudinal profile has been linked with

tectonic influence (for example Demoulin, 1998) it can also be a general

characteristic of changes in base-level, including anthropogenic and climatic driven

changes. It is widely accepted that, as a consequence of sea-level (or any base-level)

fall, incision of streams and rivers will occur, due to an enforced new base-level;

conversely, with sea-level rise, it is expected that streams will aggrade, or

accumulate sediment particularly in the lower part of their course (Miall, 1991).

Many sequence stratigraphic models employ this interpretation (for example Vail,

1987; Posamentier et al., 1988; Posamentier and Vail, 1988). Similarly, it is expected

that the longitudinal profile of a river system will adjust accordingly, causing a

shortening of the curve with a relative rise in sea-level, and falling sea-level causing

incision and lengthening of the curve. However, some workers suggest that sea level

change may cause only minor alterations to a drainage system and this is discussed

further, later. Additionally, other workers have proposed that incision during a low-

stand is not necessarily the ‘norm’ (Wood et al., 1993; Woolfe et al., 1998; Woolfe et

al., 2000). Woolfe et al. (2000), for example, suggested that drainage of the Herbert

River, Queensland, would become further incised should sea-level rise and would

aggrade onto the Great Barrier Reef should sea-level fall. These assertions were

made on the basis that bed erodibility, stream gradient and flow velocity, all of which

may induce incision should they increase, are unlikely to change should there be sea-

level fall by less than 100 m. They ascertained that channel incision would be driven

sea-ward with alluvial filling of previously incised channels. They also identified

that, should sea-level rise, present day incision would migrate landward and fill

downstream with increased sediment supply from the newly incised channels

upstream. This alternative model is important as the present-day prediction is for sea-

level to rise. Should this occur at a sufficient rate to drown the coastline, channel

incision may move landward and channel filling will occur at the seaward end of a

drainage system. The geomorphology and evolution of the Herbert River has been

25

well documented. A similarly good understanding of other drainage systems would

be useful for assessing the impacts of sea-level changes upon the system in other

locations. The time-scale over which changes occur is also important. For example,

Thomas et al. (2007) reported that apparent changes in the climate may be

accentuated at the catchment scale, if the catchment is highly sensitive to change.

Conversely, they found that in their study area in northeast Queensland, although

changes at the decade or century scale were not apparent, there was landscape-based

evidence for longer-term changes in climate. Rivers may avulse due to changes in

sea level although this may also occur due to variations in climate (for example

Allen, 1978; Shanley and McCabe, 1991) although previous down-cutting and

incision may prevent a river from avulsing (Meijer, 2002). The processes controlling

river patterns can be difficult to identify without the integration of a very broad range

of climate, eustatic, tectonic, lithological and structural variables. The presence of

one indicator is not sufficient evidence to substantiate a claim that there is geological

control over a drainage pattern. Therefore, where geological control is hypothesised,

multiple indices should be sought (Demoulin, 1998; Holbrook and Schumm, 1999).

Anthropogenic influence Since the quantity and type of vegetation cover will promote or prevent surface

erosion, it is important to recognise that anthropogenic influence upon ground-cover

may have equally broad effects on the landscape (Bronstert et al., 2002). Changes in

land-use may alter vegetation type and quantity, leading to changes in runoff,

weathering, erosion and landscape alteration. Increasingly, studies such as the

Biospheric Aspects of the Hydrological Cycle (Hutjes et al., 1998), are focussing on

the impact of human-induced changes to vegetation cover and how the changes

influence the lateral redistribution of water and its transported constituents. Many of

these studies reveal subtle impacts on the surface and subsurface environment that

might not be predicted from the nature of the anthropogenic processes.

The Copper Basin, Tennessee, USA, was subjected to 100 years of logging,

mining, grazing, fire, and water acidification and was reforested approximately 50

years ago. A study in the region to measure the impact of land-use change identified

that although soil erosion decreased within 10 years of replanting, runoff rates

remained high and organic matter in the soil remained low, suggesting that landscape

26

recovery even in humid areas of high biotic productivity may be slow and changes

may have prolonged effects (Allan and Peterson, 2002). A landslip study in the

Ocean View plateau of Mount Mee, southeast Queensland, identified that the plateau

consisted of ‘bulging’ slopes which indicate slow downhill movement of soil beneath

the grass mat, which may lead to land-sliding (Hofmann et al., 1976). The Ocean

View area was cleared of native vegetation in the early 1900s and small slumps and

landslips are visible despite revegetation of the area having commenced. In the upper

Murrumbidgee catchment, southeastern Australia, Olley and Wasson (2003)

identified a major adjustment to catchment dynamics since the settlement of

Europeans. Results demonstrated that sediment flux altered and gully erosion

increased significantly due to the introduction of grazing, damming of rivers and

changes in vegetation. Large tracts of land in southeast Queensland have been

cleared of trees for up to 100 years, mainly for cultivation and grazing, but also for

urban development. This has generated changes in drainage volume and rates and

potentially influenced other surface processes. A study of a substantially cleared

catchment, Mount Samson Creek, north of Brisbane in southeast Queensland,

identified that the creek carried approximately three times the suspended solids than

that of neighbouring creeks (Laceys and Baxters creeks) where the catchments of the

latter had only partially been cleared (Hofmann et al., 1976). It is evident from the

literature that land use changes affect runoff, and many studies have focused on

measuring increase in runoff due to deforestation. However, the impact of re-

afforestation is also important for considering the impact of land-use change. For

example, a study in the Ebro catchment, Spain, identified that annual stream

discharge has decreased considerably over the last few decades during which time

there has been a substantial increase in forest cover due to re-afforestation and farm-

land abandonment (Gallart and Llorens, 2004). Similarly, modelling has also

predicted that a reduction in flow would occur in response to large-scale re-

afforestation in the Macquarie River, New South Wales, Australia (Herron et al.,

2002). This modelling also accounted for climate change variation.

Individually, climate variation and anthropogenic influence can both lead to

changes in runoff and stream flow. However, anthropogenic changes to the landscape

can be compounded by climate change (and vice versa). Some studies have been

undertaken to identify the combined influence of climate change, runoff and

27

evapotranspiration in agricultural regions. For example, modelling has predicted that

an ephemeral catchment of cleared farm land, like many of those in southeast

Queensland, would experience four times the percentage change in runoff to the

percentage change in rainfall, and in a wet or temperate catchment, the percentage

change in runoff may be about twice the percentage change in rainfall (Chiew and

McMahon, 2002).

A common anthropogenic change on landscapes is the formation of man-

made lakes. These create an artificial base level to which the catchment above and

below the new dam will adjust. Adjustment is complex and may vary depending on

the maturity of the catchment prior to damming. A forced base-level rise can have

devastating effects upon the catchment upstream. Where sediment may previously

have been transported downstream to lower gradient, alluvial and coastal plains,

sediment is instead deposited where the stream gradient may have once been

relatively steep. Sedimentation will occur at the mouths of the streams that feed into

the lake as energy levels decrease rapidly where previously, energy levels would

have been higher. Downstream from the dam, braided channels would be expected to

narrow and a reduction in channel migration rate of meandering channels would

occur (Friedman et al., 1998). Although this was the case for streams downstream of

the Flaming Gorge Dam in Utah and Colorado, USA, the magnitude of narrowing

was not found to correlate linearly with the distance downstream from the dam.

However, it related to the degree to which peak flows had been reduced by the dam

(Grams and Schmidt, 2005). Other changes may also occur when the lake level

changes intermittently, due to rainfall and water-use variation. Lake Samsonvale in

southeast Queensland for example, built and filled in the mid-1970s has caused

deposition at the interface between the lake and the feeder-streams. When lake levels

fell in 2007, the deposits were exposed and the ‘deltas’ prograded further into the

lake. These surfaces have since been drowned due to recent increased rainfall.

Similar continuing adjustment would occur at other lakes in southeast Queensland,

including Lake Somerset, Lake Wivenhoe and smaller dams situated on agricultural

properties in the region. The net effect will equate to a decrease in sediment delivery

to the coastal regions, as sediment that would have been transported to the coast is

instead trapped behind dams. A report in 2001 identified that the natural flow rates of

the rivers hosting lakes Kurwongbah and Samsonvale have been reduced by the

28

formation of the dams (Abal et al., 2001). Upstream of the dams, flow rates have

altered where longitudinal profiles have adjusted to the new base-level and

downstream of the dams, flow rates are controlled by the dams. The report also

identified that the proliferation of small farm dams in rural areas upstream of the

major dams trap and store minor flows individually but, cumulatively, have a large

impact upon base flow conditions. Douglas et al. (2003) reported that sediment from

the Neara Volcanics which, in the Brisbane River catchment region, all lie upstream

of the Lake Wivenhoe dam, are not recognizable in sediment contributions in

Moreton Bay.

During the January 1974 cyclone and ensuing flood events of southeast

Queensland, bank erosion was observed in the lower reaches of Laceys Creek: the

stream removed the entire flood plain in some areas that consisted of several hundred

lateral metres of a previously cleared bank (Hofmann et al., 1976). Hofmann et al.

(1976) also attributed forest clearing to increased gully erosion in the north of

Kobble Creek catchment, and additionally identified that indiscriminate gravel

excavation on the South Pine River was linked to changes in river flow and increased

major bank erosion during floods.

Although it may appear that anthropological changes to the landscape cause

far-reaching affects, some parts of southeast Queensland are clearly little-affected by

land-use change. For example, a study of Coombabah Lake, on the Gold Coast,

identified that although natural processes have fluctuated over its >6000 year history,

its current state suggests human activities surrounding the catchment have caused no

adverse affects (Frank and Fielding, 2004).

A review of major catchments of southeast Queensland, including the

Bremer, Lockyer and Wivenhoe subcatchments (Caitcheon et al., 2005), identified

the major sources of sediment to Moreton Bay and the lower Brisbane River. Using

the SedNet modelling package, coupled with erosion process tracing, the results

identified gully and stream bank erosion, and also hillslope erosion from both

grazing or cultivated lands. From their previous analysis, they identified that soil

from forests was deemed to be similar to grazing soil. The majority of sediment that

reached Moreton Bay, originated from the Lockyer catchment and a smaller but

substantial amount of sediment came from the Bremer catchment. Little sediment

that originated north of Wivenhoe and Somerset dams reached the mid-Brisbane

29

River, probably due to the sediment being captured by the lakes. In the Wivenhoe

catchment, sediment was mostly sourced from the lower to middle reaches of Kilcoy

Creek primarily as a result of stream bank and gully erosion, although hillslope

erosion was predicted as the dominant sediment source in western tributaries of

Kilcoy Creek. In the upper Brisbane River, sediment was mainly sourced from

grazed hillslopes, whereas downstream of the Lockyer, in the lower Brisbane River,

sediment was primarily derived from channel erosion. The results in the Lockyer

catchment were less conclusive although they suggested that upper Lockyer sources

were mainly eroded grazing land, and the lower Lockyer was a combination of

channel erosion and cultivated land erosion. Results from the lower Bremer

suggested the dominant sediment source is channel erosion with smaller amounts of

sediment derived from cultivated soils. Gully formation, [defined by Caitcheon et al.

(2005) as ‘incision of valley floor alluvium since European settlement’ p8] and gully

alteration over the past 150 years, were also analysed. Caitcheon et al. concluded that

most gully erosion occurs at a slower rate now than when the gully networks

originally developed, having potentially reached an approximate state of equilibrium.

Gully erosion, as with riverbank erosion, continue to add to bed-load and suspended

sediment supply, whereas hillslope sources only supply sediment to the suspended

load budget although some new gullies develop in these areas, particularly during

times of flood and increased overland flow rates.

The role of lithology and rock fabric in geomorphology Crustal deformation may be instantaneous or may take place over millions of years.

Where the crust is weakest, deformation may occur due to compressional or

extensional stress often caused by the movement of tectonic plates (Figs. 1,2 and 3).

Nevertheless, whether movement is gradual or sudden, each motion can contribute to

the generation of various surface features such as gently undulating hills or sheer

scarps, although not all tectonic movements produce surficial expressions. The

theory of plate tectonics has been dominant since the 1960’s and its processes can

explain diverse styles of deformation and movement of Earth’s crust (e.g. Dietz,

1961; Hess, 1962). Through plate motion and the associated crustal stress, landscape

features such as fault systems, orogenic belts, hills and valleys may form, which are

30

altered further by surficial processes including weathering and erosion, concurrently

acting upon them.

The mineralogical composition and organization of rocks dictates their

susceptibility to weathering and erosion; marl or clay-rich beds may erode faster than

indurated quartzose sandstone, for example, and if juxtaposed, this will be reflected

in physiographic differences in the landscape (Fig. 4). Most major mountain ranges

such as the Pyrenees in Spain (Fig. 4), show examples of slope variations that have

been caused by the differential weathering of distinct sediment types. Sedimentary

rocks typically contain many beds of different lithology caused by the sorting of

sediment type and size during deposition. This can lead to dissimilarity in rock

strength and chemical stability between beds. When exposed or close to the surface,

the variable competence layers will be subjected to differential weathering. Regions

with breached folds in sedimentary rock typically show strongly surficial expression

of differential weathering of lithologies from whole landscape to outcrop scale

(Figure 5). Igneous rocks may also vary in strength depending on their mineralogy.

Often intruded into rocks of a different strength, they may weather more slowly than

the surrounding rock. Excellent examples of this are expressed in southeast

Queensland where the outer flanks of mid-Cenozoic felsic volcanoes have eroded,

and the more resistant volcanic necks now remain as the Glass House Mountains

(Figure 6) and plugs of the Mt Alford region. Alternatively, the intruded igneous

body may erode more quickly than the surrounding rock, forming a basin in the

landscape. An example of this type is the bowl-shaped Samford Valley in southeast

Queensland, which is formed on the strongly weathered material of the Samford

Granodiorite surrounded by hills developed on a more resistant thermally

metamorphosed aureole in the Neranleigh-Fernvale Beds (Figure 7). Minerals within

a rock may alter over time if heat, temperature and pressure are changed after its

initial crystallisation or deposition. Where temperature and/or pressure are increased,

mineral alteration may lead to a preferred orientation of minerals, such as mica, and

the development of foliation. Foliation is best developed in regionally

metamorphosed rocks; this is a planar fabric caused by the parallel alignment of

crystals leading to a slatey, phyllitic, schistose or gneissose texture or cleavage.

Stress and associated strain may also lead to physical alteration in the structure of the

rock causing folds and discontinuities such as faults, shear zones and joints, which

31

may occur in association with one another even at the microscale. In folded rocks,

for example, weaknesses may occur due to tension within the rock-fabric, allowing

weathering to exploit these zones. This will present natural planes of weakness that,

if eroded, will expose other rocks that may weather differentially.

The fractures, cleavage, joints, preferred mineral alignment or fault gouge

displayed by a rock are caused by a specific orientation of stress or folding. This may

cause repeated and parallel planes of weakness in rocks. Bedding and other

sedimentary features may also result in repeated and aligned fabrics. Such bedding

and structural features are commonly exploited by differential erosion to produce

step- and ridge-like patterns in the landscape (Figure 8). These rock patterns can

occur in areas ranging from outcrop to continental scale. Where streams incise to

bedrock, they commonly follow bedding and fracture patterns and become deflected

along these discontinuities to generate ‘anomalous’ drainage patterns (for example

Holbrook and Schumm, 1999). Such patterns are typically expressed by parallel,

conjugate, radial concentric or other geometric arrangements of streams, gullies, hill

slopes and scarps. Recognition of anomalous drainage patterns is typically a strong

index of geological control rather than exogenic or regolith control of stream flow.

Surface processes take advantage of the geology to form the landscape’s

morphology, but the geology itself is potentially a product of numerous events and

tectonic settings. The morphology of some regions may display patterns that were

controlled by a previous terrain or rock unit that has since been eroded or altered. In

such a case, the remnant morphology still shows there was an original geological

control, but to ascertain whether control is recent or ancient, further examination of

the geomorphology is required. This involves study of the morphology at varying

scales, such as that being undertaken in this research, in order to identify the long-

term geological history of a region and the degree and extent to which drainage is

being geologically controlled.

Stream orientation and control can be used to identify the timing of events.

For example, large, aligned streams that both meander and cut across lineaments may

provide evidence that the stream orientation was caused by an ancient control no

longer present, and that surface processes have since taken over its morphological

development. Alternatively, where many low-order streams are found to change

direction, this might suggest fairly recent uplift. Drainage patterns will respond to

32

changes both in topography and base level imposed by uplift and subsidence

(Burbank et al., 1996). Changes may include adjustments to channel gradient and

width, sinuosity, bed load grainsize and extent of alluvial cover, and bed morphology

and roughness (Whipple, 2004). A stream’s orientation may be an indicator that

changes have been constrained by an endogenic factor as outlined above. Where 1st

order or other low order streams are aligned with others of similar and higher orders,

or aligned with visible and underlying rock fabric, it generally indicates an existing

or ongoing geological control. Therefore, study of these features at multiple scales is

important to understand whether the control is recent or ancient.

Depending on the exposed surface and angle of dip of the planes of

weakness, the resulting eroded surface may have broad scale implications: for

example, the River Torrens in the Mt Lofty Ranges, east of Adelaide is strongly

controlled by phyllitic and gneissic cleavage (Twidale, 2004). Planes of weakness

resulting from faulting and jointing can be exploited by precipitation seepage. Fluid

flow within and over this type of weakened rock may lead to erosion and widening of

such planes, providing preferential conduits for further fluid flow. The courses of the

Rhône and Rhine rivers in the Alps for example, are trapped by faults, the planes of

which display lower erosional resistance than adjacent lithologies. This, combined

with enhanced discharge of the rivers and low erosional resistance of their bedrocks

probably increased surface erosion relative to neighbouring areas (Schlunegger and

Hinderer, 2001).

Geological features such as faults, fractures and lithological differences are

rarely visible in a continuous manner across large regions due to regolith cover and

in cases where groundcover is dense, such as in southeast Queensland, inference of

underlying control must be made based on what can be seen and measured. If

geological fabric is known in only part of a region, and alignment of that fabric with

morphological features is evident, the implication may be that the same geological

control exists across the broader region containing that pattern of morphological

alignment or repetition.

33

Figure 1 Simple schematic cartoon to illustrate some structural geology features that may control landforms in a compressional regime

Figure 2 Faulting that may occur in an extensional regime

34

Figure 3 Folded sandstones in a sheer cliff face, Sandgate, Queensland

Figure 4 Differential weathering causing slope variations, Pyrenees, Spain

35

Figure 5 Faulted and folded sedimentary rocks displaying differential weathering, Shorncliffe, southeast Queensland

Figure 6 The Glasshouse Mountains, southeast Queensland. The outer part of the volcanoes and the surrounding rocks have been eroded leaving the volcanic plugs protruding from the landscape. (Photograph courtesy of David Hodgkinson)

36

Figure 7 Aerial view of Samford Valley, southeast Queensland. Samford is situated on an eroded granitic batholith that intruded the regionally metamorphosed Neranleigh-Fernvale Beds. The Samford Granodiorite has eroded preferentially, and has formed a basin surrounded by a thermally metamorphosed aureole developed within the Neranleigh-Fernvale Beds. (Photograph – Google Earth)

Figure 7 Aerial view of Samford Valley, southeast Queensland. Samford is situated on an eroded granitic batholith that intruded the regionally metamorphosed Neranleigh-Fernvale Beds. The Samford Granodiorite has eroded preferentially, and has formed a basin surrounded by a thermally metamorphosed aureole developed within the Neranleigh-Fernvale Beds. (Photograph – Google Earth)

Figure 8 Folded strata under compressive stress may form microstructures within the fabric. Extension within the crests of antiformal folds may cause joints and fractures to form which could increase weathering in these zones

Bedrock lithology may influence stream behaviour such as the orientation of

flow, degree of meandering and anastamosing, and the magnitude of down cutting.

Fine-scale structures such as phyllitic cleavage have been identified as controlling

large streams (for example Holbrook and Schumm, 1999; Twidale, 2004) where the

rock type is ‘soft’ or weakened and more susceptible to erosion allowing incision, or

37

where the rock types are more resistant and force the direction of flow. One aim of

this research is to identify whether such a control is exerted over streams at multiple-

scales, from first order through to major channels.

The role of tectonics and major geological events in geomorphology The influence of structural control over surface features including stream patterns has

been recognised as an important asset for better understanding of the geology and

structure of large areas (Hills, 1960). Tectonics is a widely accepted cause of

geomorphological change, and acts as a primary control upon the shape of the

landscape (e.g. Ollier, 1995; Burrato et al., 2003; Vannoli et al., 2004; Delcaillau et

al., 2006). The geomorphological approach has been used to analyse and better

understand the effects of recent tectonism in several areas (for example Oguchi et al.,

2003; Palyvos et al., 2006). In Greece, for example, geomorphology and drainage

patterns have been used to identify active normal fault evolution (Goldsworthy and

Jackson, 2000). Schlunegger and Hinderer (2001) examined the potential geological

controls upon the anomalous drainage patterns in the Alps and concluded that

enhanced rates of crustal uplift, associated with frequent small earthquake events

were responsible. Drainage pattern anomalies have been used in the Turkana Rift,

north Kenya, as ‘key-markers’ to establish the location of large-scale transverse fault

zones (Vétel et al., 2004). Barbed drainage such as that seen in the Cowan River,

Western Australia (Clarke, 1994) and the Clarence River, New South Wales

(Haworth and Ollier, 1992) are distinctive evidence of warping or uplift of the

landscape.

Drainage is known to commonly follow the orientation and plane of faults

that provide a natural channel as outlined above. Faults caused by high magnitude

earthquake events may cause large-scale surface ruptures providing a natural location

for preferred fluid flow. However, small faults and fractures can also be the site of

preferred overland flow. Joints and faults resulting from even minor (low magnitude)

earthquake events, may occur in repeating alignment, as stress orientation is typically

relatively stable for long periods of time. Small, aligned faults and fractures may

eventually merge where fault tips slowly migrate, lengthening the faults and

changing the stress dynamics (as discussed in more detail below). Coalescence of

faults in this way may lead to the appearance of large faults which may simply

38

represent a composite system of smaller faults. Therefore, even very small fractures

caused by low magnitude earthquake events can, over time, provide a preferred

position for overland flow. Attraction of further stream flow along the plane will

eventually lead to deepening and widening of a channel.

Cowie and Roberts (2001) presented a conceptual model showing multiple

stages in fault-growth. Initially, an array of small faults forms across a region and

slowly extends in length and throw. As this continues, the faults interact and the

overall fault-array profile changes. The displacement-to-length ratios increase over

time and when multiple faults have joined with others, central portions of the fault

will eventually have greater throw than the distal portions. The temporal and spatial

variations of movement along faults and fault arrays may be explained using the non-

characteristic earthquake model, first proposed by Roberts (1996b), which provides a

model that not only accounts for spatial variations in cumulative throw but also for

ruptures that are shorter than the host fault segment. The model also implies that

recurrence intervals vary temporally for an individual locality. Roberts concluded

that palaeoseismological evidence from one site along a fault segment should not be

used to imply earthquake recurrence at another on the same fault. Roberts and

Minchetti (2004) and Roberts et al. (2004), working in the Lazio-Abruzzo

Appennines, central Italy, further showed that interactions of multiple fractures along

a fault segment are complex, but knowledge of scaling relationships between the

fault throws and lengths may assist prediction of throw-rates and with it seismic

hazard. The ratio of maximum displacement to length on a fault is an important

characteristic for assessing slip rates and for future earthquake prediction (Cowie and

Roberts, 2001). The fact that many faults grow by the connection of smaller fault

segments (Peacock and Sanderson, 1991; Roberts, 1996a) is an important

consideration in a region where low magnitude earthquakes are most typical;

numerous small scale earthquakes over time may not directly be a geohazard, but

could play a large part in the evolution of landscape morphology. Some earth

movements may be slow and steady, leading to potentially large displacements over

time. Slow earthquakes have occurred in many regions. They are defined in the

literature as discontinuous events that release energy over long periods of up to

several months, unlike typical earthquakes that may release energy in just seconds or

minutes (e.g. Kanamori and Stewart, 1979; Linde et al., 1996). These events may be

39

accompanied by earth tremor and may be detected at some very low frequencies.

They may provide a link between shallow and deep crustal events. Aseismic creep

and slow earthquakes may lead to earth movements equivalent to moderate or large

earthquake magnitudes and on such faults, seismicity may account for as little as 2%

of total moment release (Amelung and King, 1997; Scholz, 2002). However, in order

to resolve aseismic creep, an accurate background deformation rate must be

measured to identify regions of anomalously high deformation rates (e.g. Linde et al.,

1996; Kitagawa et al., 2006) and background deformation rates have not yet been

calculated for southeast Queensland.

Earthquakes of > M 5 (M 5.6 for example) are known to cause ground surface

displacement by nearly 10 m (for example, Fort Sage Mountains, CA., USA, 1950

cited in Wells and Coppersmith 1994, p.976) and earthquakes of M 7 or greater have

caused surface displacements of 10’s or hundreds of kilometres in length (for

example Luzon, Phillipines, M 7.8, 1990, surface rupture length 120 km, Wells and

Coppersmith, 1994, p.981). It is generally considered that low magnitude events

(M<4) do not cause surface displacement. A widely cited reference in support of this

hypothesis is the work carried out by Wells and Coppersmith (1994). Wells and

Coppersmith used a ‘global’ earthquake database and from the results they inferred

that surface displacement is unlikely below M 6. However, they also stated that this

inference is based on regression analysis for which standard deviations were large.

This qualification is commonly overlooked and, therefore, the likelihood of no

surface expression resulting from earthquakes M<4 is typically assumed to be ‘fact’.

However, other workers have subsequently provided evidence that significant

surface displacement can be produced by earthquakes of much smaller magnitudes.

For example, in the Appenines and in Sicily, earthquakes of M 2.7 to M 4 have

commonly caused surface ruptures from 100 m to more than 2 km long

(Mohammadioun and Serva, 2001; Serva et al., 2002; Michetti et al., 2005). These

earthquakes were of shallow depth as are modern earthquakes occurring in southeast

Queensland. Michetti et al. (2005) stated that different scaling laws exist between

earthquake magnitude and surface faulting parameters as a function of, for example,

style of faulting, focal depths, heat flow and other geodynamic settings. It is evident

that the dataset used in the study by Wells and Coppersmith may have been lacking

40

data from a full suite of potential seismic landscapes and, therefore, their results

should not be treated as being definitive.

Although rivers that incise to bedrock may follow fracture patterns at

multiple scales (Howard, 1967; Droste and Keller, 1989; Holbrook and Schumm,

1999), rivers floored by unconsolidated alluvial material may also be affected by

geological controls. Such rivers are sensitive to even subtle changes in the gradient

of the topographic surface and may respond to tectonic tilting in several ways. In

particular, they are deflected by surficial warping (for example Goodrich, 1898;

Zernitz, 1932; Howard, 1967; Holbrook and Schumm, 1999). The affects of surficial

tilting or warping on drainage include: degradation in foretilted and aggradation in

back tilted reaches; channel deflection around zones of uplift; shifts in channel

pattern to compensate for tilting changes in bed-load grainsize; changes in frequency

of overbank flooding (Holbrook and Schumm, 1999) and anomalous steepening of

channel gradients (Kirby et al., 2008). The affects of uplift are most prominent for

low-gradient streams. Longitudinal profiles of streams that encounter zones of active

subsidence or uplift will traverse or be deflected by the deformed zone (Holbrook

and Schumm, 1999). A stream can cross a zone of uplift if the rate of incision

outpaces the rate of uplift, and if the river course is already well established at the

site of deformation prior to uplift (Holbrook and Schumm, 1999). Warping of the

surface may cause terraces and valley floors or longitudinal profiles to become

convex causing degradation, or they may become concave, where aggradation will

occur (Burnett, 1982; Burnett and Schumm, 1983; Ouchi, 1985; Schumm et al.,

1994). The Rio Grande River in Mexico, for example, traverses the dome of the

Socorro magma body in New Mexico; the river is aggrading in the down-warped

reaches downstream and upstream of the domal axis, and incising where steepened

gradients are occurring across the dome (Ouchi, 1985). In the eastern Himalayas, the

longitudinal profiles of many rivers vary, although the variability of structure and

profiles of the rivers could not be attributed to climatic variation (Baillie and Norbu,

2004). Tectonic factors were concluded to be the main controlling process in their

development. Terraces of the River Ganga, India, which is in an active foreland

basin, were analysed by Srivastava et al. (2003). Although climate-related sea-level

change had previously been suggested as the cause of incision and terrace formation,

their results suggested that regional up-warping caused by a significant tectonic event

41

approximately 6 ka led to the incision of the river by several metres, causing the

formation of terraces in many parts of the system. Westaway (2002b; 2002a)

concluded that river terrace sequences produced globally during the late Pliocene and

early middle Pleistocene were caused by uplift of a thickening continental crust. He

suggested that the thickening was caused by flow in the lower crust that was induced

by cyclic surface loading caused by both ice-sheet formation and retreat and by sea-

level fluctuations. Uplift by up to hundreds of metres has led to the formation of

multiple river terraces along some rivers, such as at the Vlatva near Prague and the

Thames in southern England. Stepped river terraces in Canterbury, New Zealand,

were caused by uplift of approximately 30 m, that preceded a faulting event and led

to accelerated river incision and terrace formation (Campbell et al., 2003). Koss et

al. (1994) showed from experimental studies that simple rise and fall of base-level

can have little effect upon a drainage basin. Most importantly they identified that a

change in base-level had a more significant effect on the shelf area, and a

considerable lag time occurred before any secondary effects were seen in the

drainage basin. Tebbens et al. (2000) studied the River Meuse in northwest Europe,

in relation to sea-level rise and concluded that long-term fluvial dynamics were not

effected by sea-level rise, although downstream, high-stands were marked by river

terraces. Having assessed the formation of river terraces in northwest Europe,

Bridgland (2000) identified that, although climatic fluctuations were the driving

force behind terrace formation, the link was indirect, as the terraces were only found

to have formed where uplift was also experienced. Bridgland concluded that uplift

may have been due to isostatic adjustment following unloading and redistribution of

sediments off-shore. Berryman et al. (2000) recognised that terraces in the lower

Waipaoa River, North Island, New Zealand, were strongly controlled by uplift, but as

the down-cutting rate exceeded uplift, climate fluctuations were likely to be the

primary control on the terrace formation in the region.

Depending on the amount of deformation and direction of tilting of the

landscape, channel patterns may be altered either directly or indirectly. Sufficient

decreases in slope may cause a channel to transform from braided or meandering to

straight or anastamosing, or vice versa. Meandering streams may be altered to

braided (Twidale, 1966; Burnett, 1982) or may become anastamosing (Burnett, 1982;

Ouchi, 1985). However, it is less likely that complete shifts in pattern will occur and

42

more likely that subtle changes will develop (Holbrook and Schumm, 1999). For

example, an increase in slope might cause a meandering channel to increase

sinuosity, or conversely reduce sinuosity in response to a decrease in slope (for

example Welch, 1973; Burnett, 1982; Ouchi, 1985; Jorgensen, 1990; Boyd and

Schumm, 1995; Holbrook and Schumm, 1999). The low-gradient Mississippi River

reduces its sinuosity where it crosses the Lake County uplift. A 10 m high

topographic bulge is caused by active deformation and where gradients increase on

the down-dip flank, sinuosity increases (Russ, 1982; Schumm et al., 1994; Holbrook

and Schumm, 1999). Less intense deformation can also cause a multitude of changes

to drainage. A good example of this is in the Sorbas Basin of southeast Spain, where,

during the later stages of basin inversion, sheetflood conditions evolved to braided

drainage that later changed further to small meandering channels (Mather, 1993).

Later still, river capture occurred, cutting off the original sediment source from the

rest of the system, and although this caused a decrease in water supply, it also led to

an increase in the water-to-sediment ratio. Although sedimentation was reduced

initially, the increase in water-to-sediment ratio initiated minor incision that provided

a new sediment supply downstream where channels were easily choked and the

system was eventually abandoned. The system has since become rejuvenated due to

modern conditions (Mather, 1993).

Although there are multiple responses to surface tilting and deformation,

other controlling factors may have similar results. For example, although sharp

deflections in a river pattern may reflect tectonic deformation, they may also be

caused by streams coming into contact with particularly resistant material (Holbrook

and Schumm, 1999). Nevertheless, in the absence of tectonic forcing, changes in

river pattern, stream avulsion and alterations to channel transverse and longitudinal

profiles are all potential signs of other endogenic controls and reflect an alternative

geological control of the landscape. As discussed above, changes in base-level (or

relative sea-level changes) may cause modifications to a drainage system although

there may be a considerable lag time between any affects observed at the coast line

and influences on the catchment inland. Uplift of bedrock streams that are exposed to

base-level fluctuations can be affected in several ways depending on, for example,

near-shore bathymetry and the relationship between the rate of base-level change and

wave-base erosion (Snyder et al., 2002). It was also reported that channels will

43

lengthen over time if rock-uplift rates exceed wave-base erosion; stream-profile

concavity and steepness may also be affected. However, as previously discussed, on-

shore influences of base-level change may be minor and are unlikely to affect the

whole of a catchment.

Some drainage and morphological features are common to the various

tectonic settings. The Corinth Graben, Greece, is an area of rapid subsidence and the

region is bounded by asymmetric listric faults and characterised by antecedent

drainage, reverse drainage and drainage flowing parallel to faults with strong control

by transfer faults (Zelilidis, 2000). In the northwestern Himalayas, India, a collisional

tectonic zone, a drainage system typical of such settings has developed many

drainage channels parallel to the range confined by antiforms. Antecendent drainage

is also typical of settings where ancient rivers have maintained their original course

throughout folding and uplift events and the Sutlej River is such an example,

although it has been partially diverted and is now trapped within and parallel to the

folded ranges (Malik and Mohanty, 2006). A rifted continental margin or passive

margin, typically displays a low-relief, highly weathered upland area or range usually

with simple landward drainage, and a deeply incised, high relief coastal area

demarcated by a seaward-facing escarpment where simple drainage typically flows

directly to the coast. Between the range and the escarpment, drainage is typically

complex and may be influenced by the location of normally faulted blocks parallel to

the escarpment and coast (for example Ollier, 1985; Seidl et al., 1996). High

sediment loadings along passive margins may also generate extensive listric growth

faulting that may further influence stream position, stream character and sediment

accumulation. Passive margins with these characteristic morphological features

include the coastal zone flanking the East Brazilian Highlands, the area to the east of

the Drakensburg Mountains of South Africa (Ollier, 1985) and the Atlantic Coastal

Plain flanking the Blue Ridge escarpment of the Appalachian Mountains, eastern

North America (Spotila et al., 2004). In northeast Brazil, recent work (Bezerra et al.,

2008) has revealed that geomorphological evolution of the passive margin does not

comply with the pediplanation model (for example King, 1956) that assumes uniform

regional uplift and concomitant development of erosion surfaces, whilst the uplifted

margins remained uplifted following rifting. After rifting, some subsidence

commonly occurs driven by conductive heat loss and thermal contraction of the

44

lithosphere (McKenzie, 1978). This is also generally assumed to be uniform across

the rifted margin. Bezzera et al. (2008) recognised that in contrast to the model, the

passive margin of northeast Brazil has subsided locally rather than uniformly, and

that the sedimentary basins along the passive margins are no longer tectonically

inactive. They concluded that the present day compressive regime in northeast Brazil

has reactivated faults that have induced the subsidence. As would be expected, other

passive margins also show extensive evidence of subsidence following rifting such as

in West Greenland, the Antarctica Margin, north of Victoria Land (Bezerra et al.,

2008) and the Gulf of Mexico that has continued to subside since rifting occurred in

the Triassic and where basin fill has provided one of the most valuable sources of oil

in the world (e.g. Sharp and Hill, 1995; Galloway et al., 2000). The Queensland and

Marion plateaux off-shore at the northeast Australian passive margin display signs of

subsidence far in excess of the expected thermal subsidence (Müller et al., 2000).

This has been attributed to accelerated tectonic activity for at least the last 9 Ma and

continues at present due to the margin putatively overriding a slab burial ground. The

passive margin of the northern South China Sea has a complex geological history

similar in some ways to that of Queensland having experienced both accretion and

rifting processes. Thermal subsidence followed rifting and as a consequence, large

carbonate platforms and reefs that had formed on the new continental edge were

drowned (Lüdmann and Wong, 1999) although active tectonics have not been

identified in this region as a cause for increasing subsidence. Holdgate et al. (2008)

analysed the east Victoria Highlands, southeast Australia, and identified that uplift

and divide migration has occurred through the Cenozoic (following the Tasman

rifting event in the Late Cretaceous) and continues to the present day. However, this

area has a complex history having experienced interactions with several tectonic

plates and uplift has been attributed to block faulting and reactivation of basement

faults due to the present compressive stress regime. In contrast to subsidence, plate

boundaries may be ‘underplated’ through intrusion of large, sill-like magma bodies,

such as those in the Karoo province of southern Africa (Cox, 1980).

In the Dead Sea transform and rift zone, sediment loading has lead to arching

of the Galilee region, northern Israel, which has created a north-south water divide.

The widespread and complex uplift and tilting of the landscape has resulted in

abandoned and incised channels, reversed drainage and incised meanders (Campbell

45

et al., 2003). The Maraetotara Plateau, New Zealand, is an extensional setting, where

drainage is disrupted by normal and listric faulting, horst ridges, blocks, graben and

depressions that cause drainage to be reversed on back-tilted blocks and captured in

fault and depression zones, although some antecedent drainage may remain where

the orientation has been able to prevail despite tectonic changes in the landscape

(Pettinga, 2004). The thrust-faulted terrain of Hawkes Bay, New Zealand, is

characterised by surface expressions of reverse and thrust faults, isoclinal and

recumbent folds and hills that are complexly deformed. The regional uplift has

resulted in drainage patterns aligned parallel to structural grain as well as

rejuvenated, incised streams and uplifted and tilted marine terraces. Back tilting near

the coast is considerable at up to 30° and gravitational collapse is widespread in the

region (Pettinga, 2004). As illustrated, different tectonic settings tend to display a

variety of drainage characteristics. However, some characteristics such as terraces

and parallel or reversed drainage may occur in more than one setting. Frankel and

Pazzaglia (2005) used the model of the passive margin escarpments to assess

escarpments developed in active mountain fronts and their work successfully showed

that models are not always specific to a given setting. Similarly, some localities

clearly display characteristics of more than one setting as a result of complex and

varied geological histories involving compression, extension and transcurrent

movements.

Eastern Australia is a passive margin tectonic setting and the principal

geomorphological features include the Great Divide, and approximately parallel to

this, the Great Escarpment. In the south of eastern Australia, these two features lie

close to one another, but north of Brisbane they run in a north-northwest orientation

away from the coast, with the divide moving farther inland and the two become

spatially distant from one another. Although the Great Divide is not a significant

mountain range by relative height, its position is critical to characterising the coastal

drainage of eastern Australia. In southeast Queensland, where the divide is relatively

close to the coast line, the position of the Great Divide causes coastal catchments to

be small with limited sediment budgets (Jones, 2006a). The Great Divide acts as a

drainage divide, separating drainage that flows westward from that which flows to

the Pacific (Ollier and Stevens, 1989). Generally, a great escarpment would migrate

away from the coast due to erosion. However, escarpment migration may depend on

46

several factors such as the presence of incising bedrock channels on the escarpment

and high elevation relative to the continental hinterland (Spotila et al., 2004).

Alternatively, escarpments may degrade under circumstances where streams adjust to

base-level changes or where erosion in valleys exceeds that on escarpment-face

interfluves (Spotila et al., 2004). The inability of escarpment streams to incise due to

small drainage areas would also lead to escarpment degradation rather than

migration. The Blue Ridge Escarpment flanking the passive margin of eastern North

America is interpreted to have survived for an exceptionally long time, despite

climate changes, as it has undergone long-term, slow but steady erosion (Spotila et

al., 2004). The morphology of the central Namibian margin is generally

characteristic of passive margins, with a well-defined escarpment, inland drainage

divide and inland plateau. However, Cockburn et al. (2000) identified that the

escarpment has retreated anomalously slowly. They conclude that this is unlikely to

be simply due to highly resistant lithologies or climatic changes. They state that there

is an important link between the location of the drainage divide and the location of

major escarpments and, therefore, proposed that there has been flexural isostatic

rebound that has ‘pinned’ the inland drainage divide in place and controlled the

location and evolution of the escarpment. Although the great escarpment of

southeastern Australia is also well preserved, in the Queensland region it is less well

preserved and in some places is cryptic (Ollier, 1982).

The rivers of eastern Australia display an unusual pattern, probably due to

migration of the Great Divide where westward-flowing headwaters have been

captured and reversed (Taylor, 1911). The divide and escarpment are thought to have

migrated due to both erosion from the coastal streams and also migration of the axis

of uplift away from the coast (Watkins, 1967). The former is probably true: streams

may now be incising into the scarp causing westward migration. Migration of the

axis of uplift is also possible and this would suggest its position is now to the west of

the main scarp, which would cause the streams to its east to more freely flow towards

the ocean, perhaps over the edge of the retreating scarp and to the coast. Further

examination of this model is undertaken later in this study: topographic and drainage

maps show that streams rarely flow directly eastwards to reach the coast in the

southeast. If the axis of uplift has now migrated to the west, flow should now be

towards the ocean, rather than away from it. Should this be the case, small, low

47

order, ‘youthful’ streams, would display modern drainage conditions and flow

towards the coast. However, as described in paper 3, some streams change direction

and flow away from the scarp, which suggests perhaps renewed uplift in this area.

Stream networks do not wholly flow to the east in this region unless they are on the

low-lying coastal plain. Those on higher ground flow in diverse orientations before

finally joining other rivers then flowing to the coast. This suggests that uplift is

actively continuing in this region. The fact that small, relatively poorly developed

and, therefore, young streams are turning away form the scarp suggests tilting to the

east may have occurred in the recent past when the small streams as headwaters

started to flow, but have since changed direction due to reverse tilting towards the

west. This is further investigated later in this thesis.

Neotectonism in Australia In the past, the general view has been that Australia is relatively ‘tectonically inert’

(Sandiford, 2003). However, work in this area has increased and results show

tectonic influence is somewhat greater than previously acknowledged; earthquake

hazards in Queensland for example, are much greater than previously thought (Mora,

1996). Twidale and Bourne (2004) more recently confirmed that tectonic forces not

only modified the Australian landscape in the past, but continue to do so. The

Australian continent is situated within the Indo-Australia Plate, which is presently

under compressional stress. Modification of the land will occur in order to

accommodate shortening of the continental mass where the crust is weakest. Folds,

faults and joints resulting from such tectonic movement, have long been known to

produce a variety of distinctive land surface features such as scarps and diverted river

channels (e.g. Hobbs, 1904; 1911; Zernitz, 1932; Strahler, 1960; 1966; Twidale,

1980; Scheidegger, 1998; Scheidegger, 2002; Ericson et al., 2005).

The orientation of the compressional stress field across the continent varies

due to the multiple plate boundaries surrounding Australia (Hillis, 1998; Hillis et al.,

1999; Hillis and Reynolds, 2000; Hillis and Reynolds, 2003; Nelson and Hillis,

2005). Intraplate earthquakes typically occur less frequently and at shallower depths

than those at plate boundaries, although, relative to other intraplate regions,

Australian earthquake activity is moderate to high (Global Seismic Hazard

48

Assessment Program, 1992-1997: Fig 9; Cuthbertson and Jaumé, 1996; Clark and

McCue, 2003).

Figure 9 Stress Map of Australia showing variation of stress orientation across the continent: note stress orientation in the southeast Queensland Region ('Brisbane') is northeast (after Hillis and Reynolds, 2000). Explanation to the key: regime: 'NF' – normal faulting; ‘SS’ – strike-slip faulting; ‘TF’- thrust faulting; ‘U’- unknown faulting regime. Quality ranked as A, highest quality to D, lowest quality (Clark and McCue, 2003)

Geohazard maps may be well-constrained where recent earthquakes can be

related to known geological structures and where earthquake monitoring stations are

closely spaced. However, evidence is lacking to confidently correlate the geology of

Australia with many Australian earthquakes. Consequently, the extent of current

tectonic activity along most structures in the region is poorly known (after Zoback

and Zoback, 1991; Zoback, 1992). Accurate location of an earthquake requires the

event to be recorded by several stations and this is particularly important for small

events, such as those typical in Queensland, where accurately locating earthquakes,

is a difficult task (e.g. Levshin and Ritzwoller, 2002). An estimated earthquake

location may be inaccurate, especially when derived from early records. Therefore,

care must be taken when relating them to physiography such as scarps, slopes, hills

49

or valleys. An earthquake focus (location within the Earth) rarely aligns precisely

with surface-features such as mapped faults, scarps and joint systems due to the dip

on a fault. Surface expressions of small magnitude earthquakes in southeast

Queensland are rare. Nevertheless, as the distance from epicentre to surface-feature

will increase as the focal-depth increases, the epicentre and hypocentre of shallow

earthquakes are often closely related. The accurate calculation of focal-depth

however, is often a challenge (e.g. Kondorskaya et al., 1989; Ogata et al., 1998;

Husen et al., 1999; Bondár et al., 2004) and as this parameter may be largely

inaccurate, it should be treated with caution. The error margin for epicentre location

increases, as the focus depth increases. Therefore, epicentres for the more shallow

foci should be more accurately placed. A procedure for more accurately calculating

epicentres has been tested and results showed that, for local networks (0° to 2.5°),

where at least 10 stations occur within a 250 km range, a minimum of one should be

within 30 km in order to provide an epicentre location within 5 km accuracy, with a

95% confidence level (Bondár et al., 2004). Earthquakes in southeast Queensland are

typically low magnitude and of shallow origin. The monitoring system is closely

spaced to identify the location of very small earthquakes mainly around dams.

Therefore, it is reasonable to assume that because the epicentre and focus are

spatially relatively close, the error margin for the accurate location of the epicentre is

reasonably small. To allow for earthquake location errors, it would be practical to

assign earthquakes to a corridor of approximately 30 km width, to describe a zone

approximately within which the earthquake epicentres are situated.

In southeast Queensland, few well-located events have been identified

although it is generally accepted that earthquake activity in the region occurs mainly

onshore. Focal mechanism analysis has identified reverse faulting and northeast-

southwest compression in the region (Cuthbertson, 1990; Cuthbertson and Murray,

1990; ESSCC, 2006). Large earthquakes in Australia usually occur where little or no

recent activity has been recorded previously (Brown and Gibson, 2004),

nevertheless, work continues to target regions that experience relatively high

recorded seismicity, such as the Flinders Ranges in southern Australia (e.g. Celerier

et al., 2005). A multiple tiered approach to modelling Australian-style earthquakes

was recommended by Brown and Gibson (2004). They proposed an approach that

must include identification and mapping of active faulting on a local scale and

50

gravity, topography and seismicity surveys on a regional scale. In the USA and in

New Zealand, active-fault source-data is included in earthquake hazard assessment

and has already proven to be valuable; this may be equally beneficial to Australian

hazard assessment (Clark and McCue, 2003). Holdgate et al. (2008) reported that

earthquake epicentres in part of the East Victoria Highlands, southeast Australia,

show good correspondence to local faults such as the Mt. Beauty and Buffalo faults,

which may correspond to the current axis of maximum uplift in the region. Their

analysis of the region charted the uplift history of the area and concluded that

Cenozoic uplift and tilting by several hundred metres is evident and uplift continues

to the present day.

Earthquake monitoring in Queensland, by international standards is generally

sparse and has only operated over recent decades (Cuthbertson and Jaumé, 1996).

However, Queensland earthquakes have been recorded since the late 1800’s (Rynn,

1987). In 1937 the first international monitoring station for Queensland was opened

in Brisbane. This was followed by the Charters Towers station in 1957 (Cuthbertson

and Jaumé, 1996) and subsequently, a seismic monitoring network developed. After

1977, this expanded considerably, as detailed monitoring was implemented around

the large dams, Lake Somerset and Lake Wivenhoe, which were integrated with

other seismographs into a state-wide network, monitored by the University of

Queensland (UQ) from 1993 (the QUAKES Centre). Funding was withdrawn in

1998 and the operational instrumentation at UQ has been gradually decommissioned.

There are 22 Queensland Government seismograph stations that have continued to

collect data since 2000 and these are under commercial contract to ES&S (Victoria).

Although the monitoring network and historical earthquake database contracts are

currently under review by the Queensland State Government, the QUAKES Centre,

which evolved into the Earth Systems Science Computational Centre (ESSCC)

continues to be involved in the study of earthquake modelling and prediction (Col

Lynam at ESSCC, pers. comm. 2006). As discussed, earthquake locations are

commonly inaccurate due to the temporal and spatial variations in the earthquake

datasets and this is a problem particularly where small magnitude earthquakes are

detected by only a few stations. However, the ‘localised’ recording stations proximal

to southeast Queensland dam-sites form a concentrated network that allows the

51

location of epicentres and foci for small magnitude earthquakes to be recorded and

reasonably well constrained for the study region.

A relatively high incidence of earthquakes in southeast Queensland have been

recorded close to the dams. This may be due to the concentration of the monitoring

network within the dam vicinity, or they may be reservoir-induced earthquakes that

typically can occur due to crustal loading or a change in pore-pressure leading to the

premature release of stress (e.g. Gibson, 1997; Scholz, 2002). However, ‘no

abnormal activity’ was reported following preliminary analysis and only limited

induced seismicity was identified in the vicinity of the monitored reservoirs in

southeast Queensland (Cuthbertson, 1995; Cuthbertson et al., 1998). Some slightly

higher magnitude earthquakes were located in distal areas (Fig. 10) in alignment with

the large fault system that underlies the largest reservoirs in the region. This suggests

that the fault system may be releasing stress in locations other than near the

reservoirs.

The Queensland earthquake database represents only a very short period of

time geologically (less than 140 years) and it is possible that the recorded

earthquakes may not be a representative sample of all seismic activity in the region.

As most of the earthquakes recorded are the result of the more detailed monitoring

system now in place, the database may represent a bias towards smaller earthquakes

only occurring more recently. Prior to the installation of the new network, fewer

small earthquakes may have been recorded as only seismographs situated close to the

epicentre would have detected such small magnitude events. Following the

installation of the more condensed network, although more very small events have

been recorded, the network has not been consistent for very long periods of time.

Therefore, it is important to recognise that the database is not a fair representation of

earthquakes in Queensland, even over the short term. For evidence of the frequency

of all orders of earthquakes and resulting deformation, we must look beyond our

monitoring equipment for other evidence of tectonic activity.

Considering the size of local fault systems in southeast Queensland, it is

possible that the maximum magnitude earthquake that may occur in the region could

be 6.5 to 7 magnitude (D. Weatherley, ESSCC, University of Queensland, pers.

comm. 2007). However, as previously discussed, it is also possible that a large fault

could result from many smaller events where small faults have conjoined over time.

52

Figure 10 Earthquake epicentres, main drainage, major faults and joint systems in southeastQueensland. Blue circles indicate earthquakes clustered at reservoir locations. Red ovals indicate earthquake clusters on same fault system distally located from reservoirs

Although the southeast Queensland earthquake database contains evidence of

earthquake events in the region in the very recent past, physical evidence of these

particular events on the landscape surface may be obscure. With respect to aseismic

creep, an accurate background deformation rate has not yet been calculated for

southeast Queensland and, therefore, it is not possible to identify regions of

anomalously high deformation rates (e.g. Linde et al., 1996; Kitagawa et al., 2006).

If there has been deformation in the lower crust, it has not been measured.

53

Post-Mesozoic tectonism in southeast Queensland There is good evidence of surface displacement in southeast Queensland that

occurred during the Cenozoic. Substantial subsidence during the Cenozoic led to the

formation of some spatially small but significantly deep sedimentary basins flanking

Palaeozoic blocks of southeast Queensland. In the Petrie and Oxley basins for

example (Fig 11), accumulation of continental sediments has been estimated to

exceed 300 m in thickness (Houston, 1967; Cranfield et al., 1976). The subsidence

and vertical displacements required to provide accommodation space for these thick

sedimentary piles is substantial and faulting may be at least partly responsible for the

formation of these basins (Houston, 1967; Cranfield et al., 1976).

Mid-Cenozoic volcanic eruptions that constitute the Main Range Volcanics,

(e.g. Stevens, 1965; Murphy et al., 1976; Cranfield and Scott, 1993) emplaced

extensive basalt sheets that rest upon several raised land surfaces in southeast

Queensland (Fig. 12). The occurrence of these highland terrains, for example along

the Blackall Range implies peneplanation in the late Mesozoic-Paleogene and later

uplift. In the northeast of the region, the emplacement of clusters of Eocene and

Oligo-Miocene basaltic and felsic volcanics are most likely to have been associated

with tectonism, thermal doming, and crustal loading. Several of the volcanic vents

are aligned (see Fig. 12), suggesting structural controls on their emplacement.

Sussmilch (1933) identified that the Tertiary age basalts cap both the peneplains at

high altitudes and some low lying strata at the level of the coastal plain; from this he

concluded that the peneplains have been uplifted relative to what is now the coastal

plain and also that the scarp that divides the coastal plain and the highlands is a fault

scarp. Further, Sussmilch stated that Dr W. H Bryan pointed out to him that the

‘Neranleigh beds occur both in the Coastal Plain and in the adjoining Mt.

Tambourine Horst…’. He concluded that this is evidence that the morphology is not

due to differential erosion.

54

Figure 11 Map of the southeast Queensland region identifying locations of: Cenozoic basins; Wellington Point, North Pine Fault and West Ipswich Fault where Cenozoic faulting was identified (2001); location of South D’Aguilar block in relation to paleocurrent flow direction (red arrows) in the Clarence-Moreton Basin (Jurasssic) sediments (Cranfield et al., 1976); spot heights shown to clarify uplift of South D’Aguilar Block relative to surrounding area

55

Figure 12 Distribution of the Cenozoic Main Range (and associated) Volcanics (shown in red)

Renewed movement along ancient fault zones has disturbed Cenozoic

sediments, such as at Wellington Point, Ipswich (West Ipswich Fault) and Strathpine

on the North Pine Fault (Cranfield et al., 1976 p 115);Fig. 11). A small fold and

severe disturbance of the Petrie Formation was reported at Strathpine where a series

56

of north-northwest trending faults were observed with dips up to 60° (Jones, 1927;

Houston, 1967). Minor faulting has also been identified in the Oxley Group deposits

(Houston, 1967).

Palaeodrainage patterns in the Bundamba Group Jurassic sediments of the

northeast Clarence-Moreton Basin, flow consistently towards the D'Aguilar Block

(O’Brien and Wells 1994; Fig. 11). Parts of the present-day surface of the South

D’Aguilar block are approximately 300-600 m above sea level. This implies that the

D’Aguilar Block has been uplifted by at least this amount, relative to the surrounding

blocks since cessation of Jurassic-Cretaceous sedimentation in the Clarence-Moreton

Basin. The geological history of southeast Queensland has been dynamic, substantial

changes have occurred since the Jurassic and certainly through Cenozoic time;

therefore, the region should not be considered as geologically dormant.

Orientation of the Great Moreton Fault system (Fig. 11) through southeast

Queensland is aligned with the location of recent, small magnitude earthquakes (see

paper 2) and orientation is approximately northwest-southeast. It is obvious both

from the length and extent of displacement that the fault is not a result of recent,

small magnitude events. As previously discussed, the probability that such events

will cause any surface displacement is low. It might be concluded that very large

earthquake events in the ancient past caused the large fault system to occur.

However, having considered the discussion above, it should not be discounted that

many small magnitude and frequently occurring events over a long time frame, could

have collectively produced the significant discontinuity and surface expression

evident in this region. Although it is possible that a large event did occur in the past,

the system may be the result of multiple, small magnitude earthquakes that could

individually produce small movements or simply cause rock strength to decrease.

Either way, this may encourage preferential weathering along the orientation of the

fault, or along associated small joint systems that occur in specific orientations

related to the stress in the area. Such planes of weakness would lead to weathering

and erosion and encourage aligned drainage along this fault system. Presently active

or recent faulting is not necessary for the entrapment of the drainage segments along

the faults. The Brisbane River is a large, well developed watercourse and is situated

close to, and well aligned with the northern sector of the Great Moreton Fault for

most of its upper reaches. This is a typical example of a bedrock-based river

57

58

following faults and joints (Howard, 1967; Droste and Keller, 1989; Holbrook and

Schumm, 1999), but the location of the Brisbane River along the line of the faults

makes no assumption about the size of the earthquake event(s) that caused the main

fault or adjoining fault sections. If a large earthquake event was the cause of the

Great Moreton Fault, entrapment caused by surface rupture may have been the origin

for the river, although today we have no evidence of this. In southeast Queensland,

where earthquake activity is low in number and magnitude and where drainage has

already developed throughout the area in line with many existing faults, further

earthquake activity of low or moderate magnitude is most likely to just enhance

existing zones of weakness already exploited by drainage. The location and

magnitude of small earthquakes in the region suggests that if similar future events

occur, they will not cause surface displacements and, therefore, will not actively

entrap new watercourses. The events may provide a basis for the location of the

drainage to remain where it already is by increasing the size of joints, faults or rock

weakness via which fluid flow can continue to take advantage. Over time, the

ongoing occurrence of localised, shallow earthquakes that may align with the

presently existing fault and drainage system may result in extending the course of the

rivers upstream.

Large earthquakes have not been recorded in the recent geological past in this

region and are not considered to be ‘characteristic’ at present day, although this

should not be taken to mean that large events will not happen in the future.

GEOMORPHOLOGICAL ANALYSIS

Drainage patterns As rock characteristics can effect drainage patterns, it is of no surprise that the

interpretation of drainage patterns has proven to be a powerful tool for analysing and

better understanding structural geology (for example, Hills, 1960; 1963; Twidale,

2004). Drainage patterns have been studied and used as an instrument for a wide

range of theoretical and applied geological investigations (e.g. Strahler, 1966;

Schumm and Khan, 1972; Twidale, 2004; Vétel et al., 2004; Delcaillau et al., 2006)

and the significance of channel patterns has been reviewed at length (Hobbs, 1911;

Zernitz, 1932; Twidale, 2004).

Following an extensive review of river patterns, Twidale (2004) concluded

that most river patterns are determined by structure and slope, and diversions from

and anomalies within these patterns are commonly caused by active faults and folds.

This theory has been tested successfully in several projects (for example: Ellis et al.,

1999; Schlunegger and Hinderer, 2001; Vétel et al., 2004). Non-random channel

orientations may be controlled by endogenic influences such as geological structure

or ancient stress regimes (Scheidegger, 1979a; Ellis et al., 1999). Random or

dendritic patterns are less likely to be geologically influenced (Zernitz, 1932) and

more likely to be influenced by exogenic controls such as climate. Some rivers show

correlation and repeating alignment with straight or gently arcuate structural features

such as faults, bedding and fold axes to produce drainage systems with a distinctive

pattern (Zernitz, 1932; Twidale, 2004). Regular channel patterns (e.g. trellis,

rectangular and parallel drainage networks Twidale, 1980) can be a particularly

valuable guide to underlying geological structures in areas of poor outcrop. Initially

following slope, rivers will later adjust to structure as they incise into bedrock,

although, as slope may be controlled by active tectonism, even low order channels,

prior to incision, may be geologically controlled.

Kirby et al. (2008). have shown that analysis of stream gradients can also

reveal underlying structure and seismic hazards. Earlier geomorphological analysis

of the Longmen Shan Mountain Range, Sichuan Proince, China, had revealed abrupt

59

changes in river segment gradients through the region but few other signs of active

faulting. The region experienced a 7.9 magnitude earthquake in May 2008. The

change in river profile gradients strongly coincided with the fault trace indicating

that long-term uplift had preceded the May 2008 event. Kirby et al. (2008) concluded

that this is the most compelling evidence to-date that the landscape ‘encodes

information about the rates and patterns of tectonic activity’. Such studies may be

particularly relevant for detecting hidden or blind faults in areas of extensive soil or

vegetation cover.

As discussed in a previous section, rock fabric can influence drainage

patterns but this is not restricted to regional scales (e.g. Twidale, 1972; Scheidegger,

1979a; Scheidegger, 1979b; Ackermann et al., 1997; Eyles et al., 1997; Eyles and

Scheidegger, 1999; Beneduce et al., 2004). Although it has long been assumed that

the relationship occurs as a result of zones of weakness in the bedrock becoming

enhanced by weathering and erosion processes, most data have been inadequate to

confirm this (Ericson et al., 2005). Large numbers of fracture traces may be

accurately mapped and measured where exposures are abundant and regolith cover

does not obscure structural details (e.g. Scheidegger, 1979b), although this method is

less suitable for assessing the structure-drainage relationship in catchments where

natural surface features are concealed by regolith, vegetation and human

infrastructure.

Some studies have analysed the diverse structural influences on drainage

patterns. The relationship between joints and channels in parts of a granite-

dominated catchment in the Sierra Nevada, USA, was demonstrated using high-

quality aerial photographs and correlation was assisted by the high degree of bedrock

exposure. Results showed that, in places, this relationship was evident irrespective

of regional slope (Ericson et al., 2005). In New South Wales, Australia, a finer scale

study has shown a correlation between gully orientation and bedrock joints, and

despite the presence of regolith and vegetation cover, results showed the strength of

this correlation is strongly dependent on the bedrock lithology (Beavis, 2000). A

study in the Macaronesian Islands, revealed a good correlation between stream

orientations and ridge trends, which suggests a common tectonic control on the

landforms (Scheidegger, 2002). On a coarser scale, in the Chinese Himalayas,

tectonic fabric has been shown to exert a first-order control on landscape patterns

60

(Scheidegger, 1998). In central Italy, slopes and valley trends were found to strongly

correspond with Appenine and anti-Appenine lineaments (Alexander and Formichi,

1993). Tectonic controls are also the main influence on valleys, gorges and many

other large-scale landforms (Scheidegger, 2001). A relationship between trellis-style

channel networks and geological controls was suspected for many decades, and

although some workers found this to be weak (1971; Mock, 1976), more recently it

has been quantitatively demonstrated (Abrahams and Flint, 1983). It has been

suggested that bedrock fractures and metamorphic cleavage are, respectively, the

likely controls on the incised meanders of the Shenandoah River, USA, and the

channel-and-gorge systems of the meandering River Torrens, Mt Lofty Ranges,

Australia (Twidale, 2004).

As first described by Powell (1875), the base level is the lowest limit to

which rivers can erode – the ultimate base level being sea-level. Channel slope and

longitudinal profile, first discussed by Gilbert (1877), might theoretically reach a

state of equilibrium where the channel bed was neither aggrading nor degrading.

Longitudinal profiles and hill slopes on which overland flow occurs typically erode

to form a concave-upward shape (Watkins 1967). However, the idealistic

longitudinal profile is rarely reached: hillslopes commonly vary in shape due to

ongoing changes in tectonics, fluctuations in sea-level and climate. For example,

where sudden, heavy and prolonged rainfall occurs in regions of desiccating heat and

heavy rain events, such as in regions of New Zealand and southeast Queensland,

hillslopes are more likely to form in a convex upwards shape (B. Ward. 2006, Pers.

Comm.). Some geomorphological features such as peneplanation surfaces are typical

results of certain palaeoclimatic regimes. Demoulin (1998) concluded that although

tectonics can influence a longitudinal profile, it is not possible to assign a specific

profile to a specific tectonic regime because so many additional factors also

influence the profile, including lithology, climate and history of an area. Meijer

(2002) stated that where a longitudinal profile may have adjusted to a base-level

previously, if that base-level is reached again, drainage channel alteration will not be

equal to the first time that particular base-level was reached, as some of the ‘work’

was already done in the past. This may be similar for any other changes forced on the

landscape such as those caused by tectonic processes. Therefore, care should be

taken if assigning a longitudinal profile to a particular setting, or if using the affects

61

of past changes as a forecast for future changes. Fuzzy-logic may be suitable for use

in such predictive modelling. Asymmetry of longitudinal profiles and stream cross-

sections should also be used with caution as an indicator of setting. Asymmetry of

both cross-stream and downstream planes of a river is independent; asymmetry in

one plane does not automatically imply asymmetry in the other which indicates that

the drivers of each are unique (Rayburg and Neave, 2008). This suggests that, where

streams may appear to be symmetrical, some asymmetry may also exist as it can vary

greatly with changes in flow stage. An index of cross-sectional asymmetry was

formulated by Knighton (1981). However, the index did not prescribe individual

cross-sectional types to specific flow and drainage pattern regimes, hence it is

difficult to apply. Tectonic adjustment may alter river height; for example if uplift is

not met with sufficient down-cutting, a river may broaden and become shallower, or

if down-cutting occurs rapidly, incision may narrow and deepen a river. However, a

river’s asymmetry may adjust seasonally or with longer term climate change and

alone, may not be indicative of tectonic setting.

It has been suggested that all of southeast Queensland’s current drainage

resulted from headward capture of drainage previously flowing westward and also

the migration of the axis of uplift away from the coast (for example, Gasparini et al.,

2004). Under modern landscape controls, old streams may continue to take

precedence and maintain their original course, and smaller or younger streams may

be initially diverted away from an older stream before eventually joining it.

Palaeosurfaces, palaeodrainage and current drainage patterns in southeast Queensland Drainage patterns in southeast Queensland are typically non-dendritic. Many rivers

and small streams of all orders display combinations of angular, radial, dendritic,

parallel and trellis style drainage patterns and this is explored further in paper 3.

Non-dendritic drainage usually indicates that a geological control exists. A study of

the Rocksberg catchment, north of the North Pine River, southeast Queensland,

revealed that larger channels commonly followed the orientation of both faults and

foliar weaknesses in the phyllitic rocks (Arnett, 1971). The study concluded that

lithology, vegetation and aspect did not have any significant influence on drainage

and slope structure. In the Caboolture region, northeast of Rocksberg (Roy et al.,

62

1980), strong tributary alignment was identified as being controlled by the location

of geological units as well as a zone of relative weakness where greenstones and

phyllite are interbedded along the line of a postulated fault zone. Roy et al. (1980)

concluded that these geological influences were not apparent at the individual site

level of soil-slope associations. It was also evident that soil and slope, and profile

aspects, appeared to have no control over drainage orientations (Arnett, 1969; Arnett,

1971; Roy et al., 1980). These examples in the study area indicate that stream

orientation and drainage pattern analysis are an important part of assessing

geomorphological control.

Stream ordering Before drainage patterns can be validly characterized, stream segments are typically

ordered within a network. Each stream ‘order’ is designed to represent a category

within a hierarchical relationship of segments constituting a stream network. The

ordering system usually designates a number that should be relative to other

segments within the hierarchy. The three most commonly used ordering systems

were proposed by Horton (1945), Strahler (1957) and Shreve (1967), in which, the

uppermost ‘fingertip’ streams are typically designated as first order. Order numbers

increase downstream as further tributaries join each segment, although each

ordination system ranks downstream segments differently. In some cases the stream

order does not reflect the true position of the stream in the network; in other cases,

the stream order does not reflect its relationship with other streams of similar

position in the network. This can be problematical for some applications but is often

overlooked. Ordering systems are discussed in greater detail in a later section.

A study undertaken in New Jersey (Ackermann et al., 1997) identified that

‘low Strahler order channels’ followed underlying bedrock structures more

frequently than higher order streams. It was concluded that the higher order streams

had greater power and, therefore, were able to cut across structures and did not

follow the structures as frequently as lower order streams. Although streams of

greater power may have the ability to cut across underlying structure, the conclusions

made in that study assumed that all higher order streams in the catchment had greater

power than all lower order streams. However, the streams designated in that study as

‘higher order’ may not have been topologically equivalent and may not represent

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sufficient similarity for such comparison. Furthermore, the Strahler ordering system

does not account for the stream power when orders are assigned. The order numbers

are relatively meaningless in relation to ‘size’ or ‘power’ of a stream. For example,

in a Strahler system, a 4th order stream may have many times greater or lesser power

than others of similar rank in the network. Although it would be a reasonable

conclusion that a high powered stream may cross-cut a structure whereas a low

powered stream cannot, these results should not be discussed in terms of stream

orders, simply because no ordering system incorporates stream power within its

definitions; at best a stream ordering system can compare relative position of stream

segments across a single network. However, even this cannot fully be achieved with

the present ordering systems and highlights the need for a new ordering system.

Another example of a study in which the misuse of stream orders may have

lead to false conclusions is a study by Demoulin (1998) who tested for tectonic

control upon longitudinal profiles of rivers in the Ardenne, Belgium. Demoulin

measured the profiles of 24 rivers of 3rd to 5th order having used the Strahler ordering

system. However, there was no discussion as to why these orders were selected

suggesting the only thing these streams had in common was their order number.

However, using the Strahler system, 3rd, 4th and 5th order streams can be

topologically dissimilar and very different in character. For example, within the 24

streams used by Demoulin, the stream lengths varied from approximately 21 km to

65 km and the stream gradients ranged from 1.61° to 18.44°. As the Strahler stream

orders do not identify a particular style, similar type or topological position of each

stream in the area, characteristics of the streams such as longitudinal profile may be

influenced by different controls to different extents and, therefore, this stream set

may not have been a suitable sample for this study. Ideally, streams with similar

topological placement in the catchment, would be a better measure if comparing the

characteristics of a group of streams to identify a particular control over their

longitudinal profiles. A range of characteristics for each stream was measured and

used within Demoulin’s (1998) analysis. Although the conclusion correctly identified

that it is essential to consider a number of parameters as well as each parameters’

significance, the use of these streams as a relevant set for this analysis is debatable.

The value of commonly used ordering systems is discussed further in the ‘Methods’

chapter.

64

Data analysis Statistical analysis of data requires a suitable methodology. Traditional statistical

methods are not applicable to all datasets and other, qualitative, methods are often

utilised. Analysis of the landscape by comparing the orientation of drainage with the

orientation of geological structure requires comparison of multiple sets of linear

features. This may be undertaken on a case-by-case basis by comparing the

orientation of streams with the orientation of separate planar rock fabric features

such as faults, scarps, hillslopes, cleavage and joints. The orientation of these

features may be described as axial data (or double or zero-headed vectors), whereas

streams may be described as vectorial data (or uni-directional vectors). Due to the

nature of circularly derived measurements, where 0° = 360°, standard statistical

procedures cannot confidently be applied to directional data (e.g. Jones, 1968). This

causes a problem as, for example, a stream with orientation towards 358° may be

close in orientation towards a fault of 2° although statistical analysis would suggest

otherwise. The same problem also arises using the orientations as axial data. The

problem is then compounded where clusters of faults of multiple orientations are

being compared with several hundred channel reaches, also of multiple orientations.

Recognition of clear patterns in these datasets has proven unsuccessful in trial

analysis for this research. Although statistical analysis of directional data has been

explored to some extent in a variety of scientific disciplines where orientation data

naturally occur, such as determination of circular averages for palaeocurrent trends

derived from measurement of cross-stratification (for example Krumbein, 1939;

Krieger Lassen et al., 1994), difficulties remain in identification of multiple trends,

groups and clusters that may exist in directional datasets, specifically where multiple

clusters are known to exist and where both axial and vectorial data are being used.

Although some progress has been made on this subject (e.g. Fisher, 1996; Jones,

2006b), the methods do not lend themselves to the comparison of channel orders

across a drainage network where lineations in underlying rock fabric cause multiple

clusters controlled by multiple processes. Parametric orientation statistics in relation

to earth sciences have been discussed by Kohlbeck and Scheidegger (1985) who

noted that statistical methods typically seek to describe a mean value, a deviation

from that mean, or a closeness of fit between data sets. For datasets such as those

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used in this study, however, it is more important to seek correlations between the

datasets, than to find averages and standard deviations within it, in order to analyse

the multi-modal (multiple cluster) nature of the data.

For the purposes of this study, it would be necessary to compare vectorial

stream orientation, which is probably also multi-modal, with axial, planar rock fabric

that are known to be multi-modal. A MATLAB® (a registered trademark of the

Mathworks, Inc.) script has recently been prepared specifically to deal with the

vectorial data, and axial data may be dealt with using the process described by

Krumbein (1939). However, comparison of the two types of data is problematical as

they both require different treatment. The analysis is further complicated by the

known (and unknown) multi-modal aspect of the datasets and ‘general inclusive

computer programs’ do not currently exist to analyse such datasets using all potential

scripts and processes (Jones, 2006b). For this study, simple graphical analysis, in the

form of rose diagrams, is the most utilitarian procedure and provides the most readily

understandable comparison of parameters to the reader.

Erosion analysis As previously discussed, surface processes play a large part in the evolution of

landscape morphology. Erosion and deposition throughout the landscape leads to

commonly slow, but obvious changes. To identify the degree of erosion and erosion

susceptibility typical in different parts of catchments or regions, it is common to

calculate an index based on several measurable characteristics. Erosion index maps

have been developed using various methods worldwide, each with varying degrees of

success, although well-tested and reliable input data is the main requirement.

One such method of index mapping is the SEIMS network (Soil and

Environment Interaction based Mapping System; (Selvaradjou et al., 2007) Using

‘predictors’ including soil organic carbon content, slope, altitude, soil-water storage-

capacity, soil erodibility, soil crusting, land cover percentage, rainfall, temperature,

and mean annual potential evapotranspiration, a cumulative index or EIS

(Equilibrium Index of System) is calculated and used as the Erosion Index. This

method was used for Europe as all parameters had previously been calculated and

obtained from other sources such as the European Soil Data Centre (ESDAC).

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Although the method proved to be suitable for Europe, a full set of similar datasets is

not available for southeast Queensland and presently cannot be applied to this region.

Soil erosion estimation may be calculated using several erosion models such

as the Revised Universal Soil Loss Equation (RUSLE) (Renard et al., 1997), Water

Erosion Prediction Project (WEPP; (Flanagan and Nearing, 1995), and the Soil and

Water Assessment Tool (SWAT; (Arnold and Allen, 1992; Arnold et al., 1998). The

models were designed to quantify the amount of soil erosion from various areas and

identify areas that are vulnerable to soil erosion. However, they typically did not

address the sediment delivery ratio and, therefore, could not estimate the sediment

delivered to a given downstream part of a catchment, hence a further model was

developed specifically for this purpose: Sediment Assessment Tool for Effective

Erosion Control (SATEEC; (Lim et al., 2005). Additionally, although still a favoured

method, RUSLE only calculates sheet and rill erosion, does not predict the effects of

concentrated runoff and assumes that rain energy is directly related to erosion yield.

The latter may be problematic as soil characteristics, such as texture and permeability

that both affect susceptibility to erosion can change temporally, especially where

climate and land-use fluctuate. Nevertheless, RUSLE is used widely and calculates:

A=R*K*LS*C*P

where: A is the computed spatial average soil loss and temporal average soil loss per

unit area (for example tonnes/acre/year);

R is the rainfall-runoff erosivity factor;

K is the soil erodibility factor (the soil loss rate per erosion index unit is

measured on an area defined as 22.1 m long of uniform 9% slope on a

continuous clean-tilled fallow);

L is the slope length factor (ratio of soil loss from the field slope length to

soil loss from a 22.1 m length under identical conditions);

S is the slope steepness factor (ratio of soil loss from the field slope gradient

to soil loss from a 9% slope under identical conditions);

C is the cover management factor (ratio of soil loss from an area with

specified cover and management to soil loss from an identical area under

identical conditions); and

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P is the support practice factor (ratio of soil loss with a support practice such

as contouring, strip cropping or terracing to soil loss with straight-row

farming up and down slope).

Slope and slope-length (S and L) are typically considered together, reflecting

the terrain at a given site.

Ouyang and Bartholic (2001) developed an on-line GIS based soil erosion

prediction method for regions in the USA where digital soil data is available and can

be added to the K value of a chosen soil survey. Although some of these values may

be calculated for southeast Queensland, C and P values may be somewhat vague as

to date, they have not been calculated for the entire region. All erosion indices rely

upon accurate and specific data for input and where it is not available, generalised

values may not be suitable. Probably the most complete study of the erosion source

and processes for southeast Queensland, was a project undertaken by Caitcheon et al.

(2005) and presented as a commercial-in-confidence report for Moreton Bay

Waterways and Catchments Partnership. The region studied was described as the

western catchments and comprised the Bremer, Lockyer and Wivenhoe catchments.

The study’s aim was to identify the main causes of erosion and main sediment and

nutrient (phosphorous and nitrogen) sources to Moreton Bay, using the SedNet

model and further testing using spatial source and erosion process tracing. Hillslope

erosion estimation was calculated using RUSLE, although it was stated that most

hillslope-eroded soil remains trapped on the hillslope, with little delivered to the

stream. Although detailed gully mapping for the region was unavailable, they used

calculations for gully density, previously calculated by Prosser et al. (2003) who

used a statistical data-mining tool called Cubist. The authors concluded that in areas

such as southeast Queensland, where limited data is available, complementary

methods should be combined for best results. In addition to the erosion delivery

processes being analysed, Caitcheon et al. (2005) analysed nutrient load

(phosphorous and nitrogen) sources. Due to the scope of the report, it did not provide

an interpretation with respect to the causes of the dominant processes. As discussed

earlier, Taylor and Howard (1999) and Montgomery (2003) provided evidence that

landscape types may be dominated by specific erosion processes: where chemical

weathering dominates, the landscape is most likely to be tectonically quiescent and

where mechanical weathering dominates, the landscape may be presently or recently

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tectonically active. In their report, Caitcheon et al. (2005) reported that the sediment

sources are hillslope, gully and river bank erosion and nutrient sources are dissolved

loads in runoff water and point sources such as sewage treatment plants. Where

nutrient loads are being mobilised and transported they may be related to, or may

include the process of chemical weathering. However, whether the nutrient loads

may be caused primarily by chemical weathering is not conclusive. Mechanical

weathering is clearly evident in the region and although this may suggest the region

is not tectonically quiescent, the results may have been accentuated by anthropogenic

influence. Although it is intuitive that chemical weathering would dominate the

seasonally moist subtropical landscape of southeast Queensland, to cleary

demonstrate whether mechanical or chemical weathering/erosion processes are

dominant, the results of Caitcheon et al. (2005) would require further information

and analysis to separate the anthropogenic influences on the levels of erosion and the

source of nutrient loads. It is necessary, therefore, to use other means to determine

whether southeast Queensland has a tectonically active or quiescent landscape, such

as the methods used in this thesis. This will provide further information in order to

allow future landscape erosion studies to establish the level of anthropogenic

influence on the landscape.

Soil erosivity indices are valuable for land-use management, planning,

conservation and environmental education, and may provide a snap-shot of present

susceptibility to erosivity in the region. Where this study ultimately aims to identify

the overall geological control of the landscape, an erosivity index is more suitable for

measuring the effects of surface processes upon the landscape. An erosion index

map, whilst valuable for many purposes, will better describe the effect that surface

processes might have on today’s land-surface. Whilst it could be argued that an

erosivity index will measure the susceptibility of a geologically controlled landscape

to erosion, an index ultimately describes exogenic control and erosion potential at a

given point in time. The research completed by Caitcheon et al. (2005), may be a

suitable alternative to an erosivity index given the paucity of data in the region. In

particular, a full soil mapping database is not currently available for the region and

broadly generalised values for some other factors would also be required. Although

factors such as slope and slope length can be calculated in GIS, values for C and P in

the region are not available for a RUSLE calculation across the entire region; a

69

calculation using the SEIMS method for example, would be lacking many other

factors such as soil organic carbon content, soil water storage capacity and soil

crusting. The author is presently engaged in using the Self-Orgainising Map (SOM)

method (Kohonen, 2001) within the software SiroSOM (for example Fraser and

Hodgkinson, 2008) to assist soil-mapping in forestry areas of southeast Queensland,

as detailed soil information is not widely available. This may provide a new method

for broad-scale soil suitability mapping across the region and provide useful

information for an erosion index map in the future. Presently, however, insufficient

data is available to produce a reliable erosion index map for southeast Queensland,

based on present methods. Should this data become available, an erosivity index will

only describe erosivity potential and is unlikely to describe the degree of geological

influence on present landscape morphology: therefore, this method is beyond the

scope of this thesis.

SOUTHEAST QUEENSLAND

Introduction to the study area The study area (Fig 13a,b) corresponds broadly to the region covered by the Moreton

1:500 000 Geology Map (Whitaker and Green, 1980). The climate is subtropical,

typically with warm, dry winters (March – October) and hot, wet summers

(November to February). Rainfall is strongly seasonal and highly variable causing

water resources to be limited. Artificial reservoirs are required to provide the

majority of the region’s water supply. The largest artificial reservoirs are built in the

biggest river valleys in the region and these are typically situated in faulted zones.

Seismicity over the past 130 years has been relatively high compared to other

intraplate regions although most earthquakes are of low magnitude. Over this period,

56 earthquakes of >2 magnitude were recorded in the region. Seventeen of these

were >3 magnitude and two were >5 magnitude (ESSCC, 2006).

Reasons for selecting the study region The primary reason the area was selected for this study is that it has varied

morphology, complex geology and a complex geological history lending itself to a

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broad scope of geomorphological analyses at varying scales. The region currently

constitutes a passive margin tectonic setting although for much of its Palaeozoic and

early Mesozoic history it was under compressive stress within a convergent plate

margin setting. Although most geological knowledge of the region was gained when

it was of greater interest as an ‘unexplored’ area, the region is reasonably well

understood geologically and is known to be extremely complex but requires further

examination. However, recent and more detailed study has been lacking at a regional

and local scale and therefore, is open to further exploration and interpretation.

Morphologically, the region consists of plateaux, scarps, rugged and even terrains,

lowland, coastal flats and gently sloping hills.

This region provides a challenge to the question whether the landscape

morphology is strongly or weakly geologically controlled. A less complex region

with less morphological variation and more simple geological composition may have

more clearly revealed the answer to this question. The current study provides a new

and more in-depth assessment of the landscape that developed on rocks that formed

in a mixture of accretionary, volcanic and passive margin settings. As this particular

study aims to identify whether geological factors control the form of the landscape,

the results would be of use to workers studying other areas of comparable geological

terrain such as mixed accretionary and passive margins. Brazil and China for

example, have complex geological histories and their coastal regions now represent

passive margins but they do not conform to the simpler geology of more ‘classical’

passive margins such as the Atlantic Coastal Plain of the United States. This work

may provide a basis for future prediction of landscape and coastline alteration that

may occur due to both land use and climate change. The southeast Queensland

region is generally well understood with respect to its geological history and the

region is reasonably well studied with respect to surface processes. However, the

interrelationships of these parameters are less well understood and require further

analysis. The region provides a basis for multiple scale studies as the variety of rock

types, ages, processes and stresses is broad. The study area has also been selected as

it is quoted as being one of the fastest growing population centres in Australia

(Australian Bureau of Statistics, 2008). Approximately 4.2 million people live in

Queensland (estimated 31 Dec 2007), 66% of whom live in the southeast of the state.

The region is currently undergoing extensive urbanisation and development. There is

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increasing demand on water and other resources, and locating suitable settlement

areas for the expanding population is essential. Knowing what drives the shape of

this landscape in addition to surface processes, is important for development and

future planning. This study will provide a better understanding of how geology

controls the landscape of southeast Queensland and in so doing, may provide new

insights into the geological processes of the region.

Although previous studies show relationships between faults, fracture

patterns and stream orientation, this does not imply that all channels or valleys are

endogenically controlled. To identify those channels and landscape elements that are

geologically controlled, analyses are required both at a local and regional scale. As

discussed previously, tectonic processes are responsible for many landscape features,

but it would also be valuable to asses the current state of seismicity in the region, as

the location of recent earthquakes may identify areas that are perhaps under the

influence of recent stress changes. Earthquake risk in southeast Queensland has been

assessed based on past events (Granger and Hayne, 2000). For a better understanding

of the current tectonic regime, studies to correlate mapped geological structures with

the delineation of seismically active zones has been attempted (Cuthbertson, 1990;

Cuthbertson and Murray, 1990). As earthquake monitoring is ongoing, assessment of

the alignment of earthquake epicentres in relation to known faults will improve, and

with continued monitoring and more data, lineaments will be modified and refined

(Cuthbertson, 1990); a more up to date review using modern techniques and a larger

dataset would be of value.

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73

73

Figure 13 Location map a) Australia, b) southeast Queensland, c) North Pine River and Laceys Creek catchments and drainage

Geological history The geology of southeast Queensland (Fig. 14) is the result of a complex series of

compressional and extensional events from the late Palaeozoic to Mesozoic followed

by Cenozoic block-faulting, intrusions and volcanism. During the Late

Carboniferous, the Australian continent was part of Gondwana. At this time, in

association with a west-dipping subduction zone, the Connors-Auburn Volcanic Arc,

an Andean-type volcanic chain, together with a central forearc basin (the Yarrol

Basin) and an accretionary prism in the east (Wandilla Slope and Basin) developed

(Day et al., 1978; Plumb, 1979; Murray and Whitaker, 1982; Day et al., 1983;

Fergusson and Leicht, 1993). The postulated locations of these events in relation to

the present shoreline are shown in figure 15. This province formed the northern

sector of the New England Fold Belt. Shortening of the accretionary prism and

deformation and local obduction of oceanic crust (Day et al., 1978; Plumb, 1979) led

to low grade metamorphism and uplift in the southeast Queensland sector of the New

England Fold Belt (e.g. Fleming et al., 1974; Cranfield et al., 1976; Holcombe, 1978;

Murphy et al., 1979; Murray et al., 1979). The location of rocks that relate to this

episode are presently situated as shown in figure 16

During the Early Permian, andesitic volcanism resumed (Day et al., 1978;

Day et al., 1983) and the convergent tectonic regime persisted throughout the

remainder of the Permian and most of the Triassic, forming the Hunter-Bowen

Orogeny. Associated forearc and backarc subsidence allowed the formation of

widespread shallow seas and new sediments were deposited on the older,

Carboniferous, metamorphosed terranes. Small plutons intruded into the old

accretionary wedge and offshore a new subduction zone developed (Willmott, 2004).

During the Middle Triassic an extensional event commenced, causing further

volcanics and granitic intrusions (e.g. Evernden and Richards, 1962; Webb and

McDougall, 1967; Cranfield et al., 1976). Tight folding, metamorphism, uplift and

the development of mountainous terrain followed (Cranfield et al., 1976; Plumb,

1979; Willmott, 2004). The present location of rocks emplaced from 286 – 265 Ma is

shown in figure 17.

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Figure 14a Geological map of Moreton District, southeast Queensland. 1:500 000. Extract of map sheet compiled by W. G. Whitaker and P. M Green, from data available at June 1978, printed 1980. Regional Mapping Section, Geological Survey of Queensland. Key to rock units see next page.

75

76

Figure 14b Key to rock units - geological map of Moreton Scanned map also available online at Geoscience Australia : http://www.geoscience.gov.au/geol250k/250dpi/moreton.jpg

During Middle to Late Triassic dextral movement on the Demon Fault, a large

meridional transcurrent fault, thought to extend over 550 km, displaced basement

rocks by up to 23 km (Wellman et al., 1994). The fault extends from northern New

South Wales under the Clarence Moreton Basin and extends to north of Brisbane.

From the Late Triassic to Early Cretaceous, extensional epicratonic basins, such as the

Nambour, Clarence-Moreton, and Maryborough basins formed and accumulated

paludal, braided river and deltaic sediments (Day et al., 1983). During the Early

Cretaceous, subduction lead to the emplacement of calc-alkaline volcanics in the

Maryborough Basin (Stevens, 1969; Plumb, 1979). This was followed by extension,

possibly coupled with a eustatic rise in sea level (Vail et al., 1977; Day et al., 1983)

causing large areas, such as the Maryborough Basin, to be filled with thick paludal

and deltaic sediments. The locations of rocks that relate to the interval from 265 – to

140 Ma are shown in figure 18. Although it is generally assumed that Gondwana

moved northwards during Permian, Triassic and Jurassic times, it has alternatively

been suggested that the continent moved southwards during this period, which would

have had major climatic and tectonic effects upon the landscape (McKellar, In press).

The eastern fringe of Gondwana began to break up approximately 120 million

years ago (Veevers and Evans, 1975; Powell et al., 1976; Branson, 1978; Veevers,

2001; Willmott, 2004). Of particular significance to the region, between 70 and 45

million years ago, crustal doming initiated fracturing of the crust along the eastern

margin of Australia that lead to the opening of the Tasman and Coral seas. Passive

continental margins such as the east coast of Australia are typically characterised by

broad, low-relief, high elevation plateaux coupled with a dissected coastal zone. The

process of rifting causes uplift, which in turn initiates coastal erosion and this

typically creates seaward facing escarpments and coastal plains (e.g. Ollier, 1982;

Seidl et al., 1996; Ollier and Pain, 1997). The Great Dividing Range, now referred to

as the Great Divide, is considered to be the product of crustal up-warping during

rifting. The older term ‘Great Dividing Range’ is rarely used because in many places

the drainage divide between easterly and westerly flowing streams it is situated in

relatively flat terrain (Ollier and Stevens, 1989). To the east of the Great Divide, or in

some places, superimposed on it, lies the Great Escarpment of eastern Australia

(Ollier, 1982). Ollier argued that the Great Escarpment can be traced almost

continuously along the east coast of Australia. However, in some places the

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escarpment is absent or indistinct. Significant uplift probably occurred along the

flanks of the Tasman rift system resulting in inversion of the local Mesozoic basins.

The Clarence-Moreton Basin consists of infill that was emplaced during the

Mesozoic, a time when the present eastern coast of Australia did not yet exist and the

continental rocks extended well to the east. At this time drainage in southeast

Queensland was mainly towards the northwest. When the basin was inverted after the

mid-Cretaceous, the Great Divide was formed across the basin and drainage

modifications occurred, such as the capture and reversal of part of the Condamine

River by Clarence River (Haworth and Ollier, 1992). Steep escarpments that were

established during this uplift event retreated and were later modified by erosion and

tectonic activity. In eastern Australia as a whole, it is generally accepted that the Great

Divide separates the western area characterised by simple dendritic drainage, from the

east where a substantial number of drainage patterns reflect endogenic controls (Ollier

and Haworth, 1994; Ollier and Pain, 1997).

Figure 15 Postulated position of subduction zone features in relation to the present southeast Queensland coastline

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Figure 16 Present position of rocks 370 - 300 Ma

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Figure 17 Present position of rocks from 286 - 265 Ma

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Figure 18 Present position of rocks from 265 - 140 Ma

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Figure 19 Present position of rocks and sediments from 70 - 22 Ma

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Figure 20 Present position of rocks and sediments from 6 - 0 Ma

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Rocks emplaced 70–22 Ma are distributed widely but discontinuously across

the studied region (Figure 19). Localised subsidence during the Paleogene was

responsible for the formation of the small Oxley, Petrie and Booval basins in which

clay, limestone, silt, oil shale and basalt accumulated in lacustrine and paludal

environments. Erosion during the Neogene shaped the modern, subdued topography

of the region (Willmott, 2004). From 30 to 2 million years ago, Australia migrated

northwards, and is thought to have moved over one or more hotspots; this caused

eruption of localised volcanoes such as the Glasshouse Mountains (Jensen, 1903;

Jensen, 1906; Stevens, 1971; Willmott, 2004). Other mid-Cenozoic volcanics were

emplaced across the region in places such as the Main Range and the Lamington-

Moogerah areas(Stevens, 1965; Stevens, 1966). Mount Warning (also commonly

called the Tweed Shield Volcano), which is situated on the Queensland, New South

Wales boarder, was originally up to 100 km in diameter. K/Ar dates indicate the

eruption occurred between approximately 20.5 and 22.3 (Ewart et al., 1980). The

eruptive centres of the Main Range Volcanics are not defined and it has been

suggested that lava erupted from multiple vents and fissures (Ewart et al., 1980). K/Ar

ages indicate eruption dates of approximately 22.5-24.5 M.y. (Webb et al., 1967). The

Maleny Basalts at the Blackall Range have a broader eruptive date range of 21-34

M.y. although an approximate age of 25.2 M.y. has been obtained from a megacrystal

andesine and anorthoclase from one of the youngest flows (Ewart et al., 1980). The

Blackall Range is isolated from the Main Range volcanics and Mount Warning but is

in close proximity to the Glass House Mountains for which, a date of 25.4 M.y has

been obtained from K-Ar dating (Webb et al., 1967). Ewart et al. (1980) proposed a

genetic link between the Glass House Mountains and the Maleny Basalts.

Neogene deposits are distributed throughout the coastal area (Figure 20).

Between approximately 6 million and 400,000 years ago, small basaltic volcanoes

erupted in the Bundaberg and Gayndah areas, although their origins are not well

understood (Willmott, 2004): their age-trend does not conform to the southward

younging of other hotspot-related volcanism of eastern Australia (Robertson, 1985;

Sutherland, 1985; 2003). Since that time, both erosion and deposition continued and

alluvial deposits and shallow marine have accumulated on flood plains, deltas,

estuaries, spits, sandbars, coastal dune systems and back-barrier lagoons. The coastal

plain is largely underlain by Devonian-Carboniferous Neranleigh-Fernvale Beds to

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the south of Brisbane, and Triassic to Jurassic mudstones and sandstones of, for

example, the Kin-Kin Beds in the north and Landsborough Sandstone in the central

coastal region.

Faulting Little has been published regarding age constraints on fault activity in southeast

Queensland (Humphries, 2003). Recent geotechnical core logging for civil

engineering works in southeast Queensland has identified some discrepancies in the

published geological maps (Brisbane City Council, City Design, Ground Engineering,

pers. comm. 2006). Of particular importance is the Buranda Fault (Bryan and Jones,

1954) that may have caused up to 11 km of sinistral terrain displacement through the

Brisbane Gap following a line close to the present course of the lower Brisbane River.

The position and even the very existence of this fault has long been a source of

contention. Nevertheless, the proposed location of the Buranda Fault marks an

important discontinuity between metamorphic rocks in the southeast and northwest of

the Brisbane region. Evidence of slickensides, fault breccias, and ‘abnormal strikes’

were given for the location of the fault (Bryan and Jones, 1954; Hill and Denmead,

1960 p.134) although its existence appears to have since been questioned as the fault

is no longer included on modern geology maps, such as the 1:500,000 Geology of

Queensland Map (Geological Survey of Queensland (2003). The ages of most major

faults in the region are only loosely constrained by the minimum ages of their

bounding strata.

Murray (1988) suggested that the Gympie Province (Fig. 13), together with

New Caledonia and part of New Zealand once belonged to a single Permian volcanic

arc complex, which was later broken apart by large-scale strike-slip faulting. This

process emplaced the Gympie Province tectonically to its present position in about the

Middle Triassic. Murray et al. (1987) reviewed the Geology of the Gympie district

and proposed that the North Pine Fault is potentially a terrane boundary. They further

suggest that the northern section of the fault is veiled by the Esk Trough (Fig. 13),

although there is little evidence for this and they also recommended more work on

this subject may better constrain the geological history of this area.

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Sea level influences Approximately 2 million years ago, when sea level was up to 120 m below the present

level during ice-house conditions, the eastern Australian shelf was exposed,

weathered and incised and as ice melted, sea levels rose and drowned the lowlands.

Williams et al. (1998) suggested that 6500 years ago sea-level was 1 m higher than at

present and Flood (1981) suggested that present sea-level was reached about 3000

years ago. However, Ward and Hacker (2006), working on the Brisbane coastal

region, proposed that the sea reached its present level between 6500 and 6000 years

ago. They described the sediments of the area as ‘an alluvial landscape veiled by

marine sediments’ and discussed the evolution of area in great detail. Their work also

identified oscillating levels of the shore-line in the past 6000 years around the

Brisbane Airport region and they assign these adjustments to relative changes in sea-

level due to settlement and drainage of soft ground.

Terraces Some rivers in southeast Queensland display terraces and incision that represent

responses to changes in relative base-level, which may have been caused by eustatic

sea-level change or local crustal uplift. In the Gold Coast region, for example, an

extensive study identified over 15,000 ha of lower and upper river terraces, the latter

of which included 627 ha of older age terraces greater than 10,000 years old

(Whitlow, 2000). The older terraces are found in the lower Logan and Albert rivers

and parts of the Nerang valley, for example. The younger Pleistocene upper terraces,

consisting of gravel, sand, silt and clay, account for 36% of alluvial deposits in the

Gold Coast region and are found in places such as the Coomera and Nerang valleys

and the Pimpama cane-lands. Some 7,700 ha of Pleistocene, low level alluvial

terraces, consisting of gravel, sand, silt and clay grading into floodplain alluvium

were reported as accounting for 40% of Gold Coast alluvial deposits and are found for

example in the lower Logan and Albert rivers, Hotham Creek and the Currumbin

Valley. The terraces provide economic opportunities for gravel extraction and

commercial extraction presently occurs in the region, for example in the Upper

Coomera and Pimpama terraces. A similarly broad study for the rest of southeast

Queensland is not yet available although other gravel terraces are evident in similar

settings to those described in the Gold Coast region. Terraces north of Brisbane such

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as on the Pine River at Dohles Rocks, North Pine River at Four Mile Creek and

Lawnton and also west of Petrie, and the South Pine River at the Strathpine Flats and

southwest of Bald Hills, have all been described in some detail by Hoffmann (1980).

Ages of the terraces in the region are vague but Hoffmann proposed an age of

approximately 120,000 to 130,000 years for the Strathpine Terrace when sea-level

was approximately 5 m higher than at present. The 25 m DEM used in the present

study is too coarse to derive cross-sections of small streams resolving the details of

the terraces identified by Hoffman. However, Hoffman presented detailed cross-

sections of several reaches of the North and South Pine rivers showing the extent and

variation of deposits in the lower Pine River valleys and terraces identified in the area.

The Strathpine Terrace is at an elevation of 5 m near the North Pine River mouth and

the terrace extends along most of the North Pine River. The terrace has been incised

by up to 18 m and Hoffman suggested a general northward migration of the ancient

Pine River during deposition of the Strathpine deposits. The Lawnton Terrace is

approximately 6 km from the present shoreline and lies between Four Mile Creek and

the North Pine River. The terrace is approximately 2 to 6 m in elevation. Some terrace

remnants occur along the South Pine River. Hoffman’s review concluded that the

Strathpine deposits are the result of larger streams during the late Pleistocene that

were later benched and incised by subsequent fluvial erosion. Terraces across

southeast Queensland represent the locations of previous flood plains and their

abandonment and incision indicates a change in fluvial regime and relative sea-level

fall although as discussed previously, uplift and eustatic sea-level change may both

have been involved.

Incision Another indication of stream habit and morphology changing as a response to relative

sea-level fall is the down-cutting and incision of meandering streams, whilst the

meanders are retained. Incised meanders are present in many catchments and typical

examples include low order streams such as Terrors Creek at Ocean View on Mount

Mee, and high order rivers such as portions of the lower Brisbane River. Figure 21a,b

shows a cross-sectional view across a tight meander in the lower Brisbane River and

reveals the incised nature of this part of the river; the typical level of the coastal plain

being 8-10 m above normal river level in this area. The banks are relatively steep and

87

only slightly asymmetrical – features typical of relatively rapid incision. Hoffman

(1980) made a similar observation of incised meanders into bedrock in the Pine

Rivers area and concluded it was superimposed from a Cenozoic or Mesozoic erosion

surface. Incised meanders indicate rapid relative fall in base-level (B. Ward pers.

comm.) and although this may have been eustatic sea-level fall, it may also have been

due to tectonic uplift (for example Gardner, 1975; Campbell et al., 2003). Although

Hoffmann suggested an age of 120,000 to 130,000 years for the Strathpine Terrace, he

argued this on the basis of the known age of a sea-level highstand at this elevation.

His argument was counter to Beckmann’s (1959) provisional suggestion that the

terrace was only 50,000 to 30,000 years BP at which time sea-levels are now known

to have not been high enough. However, a more definitive age of sediments would be

required to fully rule out the possibility that the terrace formed as a result of uplift and

confirm that it was a result of eustatic sea-level change.

Although the 25 m DEM used in this study was too coarse to derive fine-scale

detail of, for example, minor terraces, the DEM is able to display coarser detail and

has been used here to generate the longitudinal profiles of the Brisbane and North

Pine rivers as examples of both long and short catchments in the region (Figs 22 a-c).

Hoffman (1980) suggested that the hypsometric curve of the Pine River drainage

basin indicates that the basin has almost reached the final stage of landscape

evolution. However, this hypothesis is somewhat over-simplified, as the hypsometric

curve (Fig. 22c) does not show a smooth sigmoidal curve but in contrast, shows a

series of short drops and shelves. These are likely to have been caused by the

variation in bedrock types and local faulting, and in the lower reaches may also be

eustatically influenced. Similar analyses of the stages of landscape evolution for all

other river systems in southeast Queensland have not been undertaken. As the

conclusion regarding the Pine River system, reached by Hoffman (1980), was

oversimplified, further study on other rivers in the region is required to identify local,

regional and global influences.

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Figure 21a Location of A-A' meander cross-section superimposed on 25 m DEM of region

89

Cross section across A-A' meander - Lower Brisbane River

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Figure 21b Cross section A-A' across meander showing incision status of meander in the Brisbane River

Longitudinal profile of Upper Brisbane River to lake

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longitudinal profile of Brisbane River from lake to shore

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Figure 22b Schematic longitudinal profile of the lower Brisbane River from Lake Wivenhoe to the shoreline

longitudinal profile of North Pine River source to sea

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Figure 22c Schematic longitudinal profile of North Pine River, Southeast Queensland

Catchments in southeast Queensland are typically 30-60 km in length,

although the Logan, Bremer and Brisbane River catchments are more than twice this

length. The average catchment length in southeast Queensland is approximately 68

km and the shortest are the North Pine, South Pine and Caboolture rivers each of

which, is approximately 30 km in length. The Brisbane River catchment is over 160

km long: above Lake Wivenhoe the river has an average grade of 0.57116% but

below the lake its gradient drops to an average of 0.059771% grade. The average

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gradient of North Pine River is 0.336838%. The upper 7000 m average gradient is

0.76861%; the middle 18000 m average gradient is 0.20174% and the average grade

of the lower 11000 m of the river is 0.15899%. The steep upper catchment of the

Brisbane River in comparison with the less-steep lower portion reflects the high

topography of the D’Aguilar range that the upper catchment drains. The steep but

very short North Pine River is also a product of the uplifted South D’Aguilar block,

over which the upper and middle river flows. The middle section has a less-steep

gradient reflecting the less resistant and more eroded rock types such as the Bunya

Phyllite, juxtaposed to the more resistant rocks of Mount Mee (e.g., the Rocksberg

Greenstone). Typically, the lowest order streams in southeast Queensland flow over

regolith but middle order streams in the steeper parts of the catchments have incised

to bedrock. Some less-steep middle order streams such as the Laceys Creek main

trunk, are ‘armoured’ with very coarse gravel to boulder sized clasts and higher order

streams have beds of finer sediment. Streams that have incised into bedrock contain

relatively young, mobile sediments (Hofmann, 1980). Controls on the orientation of

streams in the Laceys Creek catchment is explored in detail in paper 1. Where

southeast Queensland streams are not confined by incision and are able to meander,

they are typically asymmetrical due to the nature of meandering streams, although

even along some straight sections such as on the North Pine River near Dayboro, the

river valley is also asymmetrical (Fig 23). In this case, the asymmetry is most likely

caused by the juxtaposition of rocks of differing erosional resistance and in particular,

the river valley has preferentially eroded away from the North Pine Fault at this

location into softer rock.

Section NE to SW across Upper North Pine River near Dayboro

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Figure 23 Section across North Pine River near Dayboro showing asymmetry – the North Pine Fault is situated approximately on the northeast bank of this section although surface expression of the fault has not been seen at this location. Asymmetry is most likely caused by the location of the fault and differential weathering of juxtaposed units controlled by the fault.

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Geology of Pine Rivers and Laceys Creek: a fine-scale case study The North Pine River (Fig 13c) drains the northern two-thirds of the Pine River

Drainage Basin: the southern one-third is drained by the South Pine River. As stated

above, Hofmann (1980) described the hypsometric curve of the Pine River Drainage

Basin and defined it as having almost reached the final stage of landscape evolution

(the monadnock stage, after Strahler 1957). Major streams in the Pine Rivers

catchments commonly meander, although the majority of the meanders are incised

into bedrock, suggesting that the stream pattern is superimposed from an older erosion

surface that has since been uplifted causing down-cutting faster than the stream can

adjust its drainage pattern. Hofmann (1980) suggested this may have continued from a

Paleogene or Mesozoic erosion surface. Nevertheless, he also stated that the drainage

pattern is fault-controlled and identified that the North Pine River strongly follows the

course of the North Pine Fault. Part of the North Pine River was dammed in 1976,

forming a reservoir, Lake Samsonvale. The Pine Rivers catchment drains an area

exposing diverse rock units that include the: Rocksberg Greenstone (11% of area);

Kurwongbah Beds (5% of area); Bunya Phyllite (34% of area); Neranleigh-Fernvale

Beds (21% of area); hornfels (1% of area); Permo-Triassic volcanics and Triassic

granitoids (13%); Landsborough Sandstone (5%); Petrie Formation (10%) and

Cenozoic basalt (<1%) (Hofmann, 1980).

Laceys Creek is the largest subcatchment of the North Pine River system. It is

situated approximately 50 km north of Brisbane, southeast Queensland (Figs 13 b,c)

and is located upstream of the artificial Lake Samsonvale. Lake Samsonvale is an

important part of southeast Queensland’s reticulated water supply. Laceys Creek

catchment is located within the South D’Aguilar Block of the New England Fold Belt.

The block is characterised by north-northwesterly trending geological assemblages

representing a volcanic arc, backarc/forearc basins and subduction complexes

(Murray et al., 1987; Coney, 1992; Little et al., 1992; Holcombe et al., 1997b,b; Betts

et al., 2002) and consists of steeply dipping, north-northwesterly to south-

southeasterly striking, pre-Permian meta-sediments and meta-volcanics (Denmead,

1928; Belford, 1950; Bryan and Jones, 1962; Tucker, 1967; Wilson, 1973; Cranfield

et al., 1976). The two dominant geological units in the Laceys Creek catchment are

the Bunya Phyllite and the Neranleigh-Fernvale Beds, which are of similar

sedimentary origin, but have different fabrics and metamorphic grades. The

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Rocksberg Greenstone is overlain by the Bunya Phyllite, which crops out in a north-

northwest-trending belt, situated on the southwest flank of the Rocksberg Greenstone

in the Pine Rivers catchment: the transition between the Rocksberg Greenstone and

Bunya Phyllite is represented by the intercalation of meta-volcanics and meta-

sediments. The Bunya Phyllite is strongly foliated, consists of arenites and lutites

metamorphosed to greenschist facies, and is a dominantly pelitic suite of

metasediments with some intercalated meta-basic volcanic rocks. Bands of alternating

quartzose and micaceous rock are crossed by veins of quartz with accessory graphite

and calcite. Grain size is typically less than 0.01 mm. The original sediments of the

Bunya Phyllite have been interpreted as marine deposits of a relatively deep-water

environment. They may represent the oceanward facies equivalent of the Neranleigh-

Fernvale Beds and may be older than Carboniferous in age (Cranfield et al., 1976).

The Bunya Phyllite forms rugged slopes within the Laceys Creek catchment, with

elevations of 80 to 420 m a.s.l. and covers an area of 12.9 km2.

The Neranleigh-Fernvale Beds cover an area of 68.9 km2 in the Laceys Creek

catchment (Fig. 13c). They are exposed against the southwestern margin of the

Bunya Phyllite and they form rugged hills up to 100 to 660 m a.s.l. Although an

accurate age for the Neranleigh-Fernvale Beds has not been determined, it is placed

between the mid-Devonian (Fleming et al., 1974) and mid-Carboniferous (Green,

1973). The unit was subjected to low-grade metamorphism towards the end of the

Carboniferous (Cranfield et al., 1976). The Neranleigh-Fernvale Beds consist of

conglomerates, radiolarian cherts, argillaceous rocks, arenites, basic volcanics and

minor limestone (Cranfield et al., 1976). Within the Pine Rivers area, thinly bedded

siltstone and shale are widespread, In some places, these are sheared and phyllitic.

Arenites are also well developed in the area. Some original bedding is well preserved

and cross-bedding is also common. The lithologies and bedforms suggest that

deposition occurred in a relatively deep-water, marine environment that experienced

periodic turbidity flows. The Neranleigh-Fernvale Beds have been regionally

metamorphosed to greenschist subfacies, but to a lower grade than that of the Bunya

Phyllite (Winkler, 1967). Triassic intrusions such as the Mount Samson and Samford

granodiorites thermally metamorphosed the surrounding Neranleigh-Fernvale Beds.

The exact stratigraphic relationship between the Neranleigh-Fernvale beds and the

Bunya Phyllite has not been clearly established. The Neranleigh-Fernvale Beds are

94

considered to have been thrust over the Bunya Phyllite and a major shear zone has

been located along their contact (Cranfield et al., 1976). Although several north-

northwest trending fold axes are mapped (Denmead, 1928; Belford, 1950; Cranfield et

al., 1976), precise structural relationships are not clear (Cranfield et al., 1976). The

pre-Permian rocks were folded along north-northwesterly trending axes during the

New England orogenic event in the Late Carboniferous and further deformation

occurred during the Late Permian and Early Triassic. This was followed by block

faulting and the emplacement of granitic intrusions, several of which are located in

the North Pine River catchment. Further folding took place along north and northwest

trending axes during the late Middle Triassic (Cranfield et al., 1976; Holcombe et al.,

1993, 1997a). Due to the multiple episodes of deformation that affected the area,

diverse bedding, cleavage, joint and fault orientations have developed within the

units. During the Paleogene, small intermontane sedimentary basins, formed through

eastern Australia, such as the Petrie Basin in the North Pine catchment, within which,

approximately 300 m of sediment accumulated; the Petrie Basin may be partly

erosional and partly tectonically controlled (Cranfield et al., 1976). Sediments of

Paleogene age are largely undisturbed although rejuvenated faults such as the North

Pine Fault (Cranfield et al., 1976) have locally tilted bedding.

The close proximity of the highlands to the coast provides short and typically

steep catchments. On steeper parts of the catchment, a thinner weathering profile has

formed. Erosion may occur on steeper or more exposed areas, causing a thinner or

complete lack of a weathering profile, regolith or soil. Streams developing in these

areas will form on or in close proximity to bedrock and orientation will be more likely

influenced by the lithology. Behind the relatively steep coastal rise, the hinterland is

moderately dissected by faults and block boundaries, lending themselves to locations

of preferential drainage. Streams in that area are, however, generally less steep than

the coastal drainage catchments and may accumulate more sediment and be prone to

more ground cover. However, the rock fabric may still bear an influence over the

drainage pattern due to the variation in ground cover and age of drainage channels.

Previous geomorphological studies of southeast Queensland A range of geomorphological studies of southeast Queensland have been undertaken

although these have been conducted mainly on a piecemeal basis (e.g. Taylor, 1911;

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Marks, 1933; Watkins, 1967; Arnett, 1969; 1971; Donchak, 1976; Beckmann and

Stevens, 1978; Lucas, 1987; Cuthbertson, 1990; Childs, 1991; Ollier and Haworth,

1994). In summary, previous work has described southeast Queensland as consisting

of foot hills and coastal plains to the east and plateaux and highlands (over 300 m

a.s.l.) in the west, south and north and escarpments common across the whole region;

the DEM shows the distribution of the high and lowlands quite clearly (Fig. 24). The

main drainage systems have been described as displaying strong trends of northwest-

southeasterly and northeast-southwesterly that are similar to the orientation of many

faults (Fig. 25).

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Figure 24. 25 m DEM of the study region showing the main drainage and key locations

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Figure 25. Faults (brown lines) and main drainage (blue lines) in southeast Queensland

98

Using Landsat images of the northern part of the region, Childs (1991) showed

that the faults correspond with channel orientation and the main ranges and drainage

systems are strongly concordant with the bedrock geology. However, some major

faults indicated on geological maps could not be identified on the Landsat images and,

therefore, may lack surface expression (Humphries, 2003): they may have

unfavourable illumination for Landsat (Childs, 1991) or it may be due to the scale at

which the images were processed. Taylor (1911) observed a clear association between

regional river patterns and structural geology. He identified that headwaters of

westward-flowing streams were captured and reversed, due to westward migration of

the Great Divide in eastern Australia. To the east of the Great Divide in Queensland,

rivers typically flow parallel to the coast along major structural lines (Beckmann and

Stevens, 1978). Endogenic control is further observed where Cenozoic volcanism has

disturbed part of the drainage pattern. For example, in the Clarence River system

drainage pattern, eastern Australia, stream reversal is postulated, on the basis of the

orientation of barbed tributaries suggesting that the Clarence River possibly once

flowed north joining what is now the Condamine River (Haworth and Ollier, 1992).

South of Brisbane, in New South Wales, the Coastal Range acts as a barrier and

prevents drainage from crossing the range from west to east (Ollier and Haworth,

1994). South of Brisbane, the Great Divide, the Great Escarpment, the coastline and

the continental shelf trend south-southwest, whereas these trends change in

orientation at the Clarence-Moreton Basin and north of Brisbane are aligned north-

northwest (Ollier, 1985; Ollier and Haworth, 1994). Ollier (1982; 1985) and Ollier

and Stevens (1989), described the Great Escarpment in detail and they identified that

the escarpment controls drainage in eastern Australia. Ollier (1982) also identified

that despite the Great Escarpment being mainly continuous throughout the length of

the east coast of Australia, it appears to be ‘absent or obscured’ in some parts,

particularly in southeast Queensland. Smaller shore-parallel escarpments have also

been identified in the Gympie region. Late Miocene to early Pliocene uplift in the

region initiated the development of an erosion surface that was tilted in the late

Pliocene, forming northwest dipping cuestas (Murphy et al., 1976). On the eastern

edge of the cuestas and continuing close to either end of the Maleny – Mapleton reach

of the Great Escarpment, two low, coastal scarps formally named the Glass House

Scarp and the Como Scarp (Coaldrake, 1960; 1961) have been described as old

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coastline features; each are described as forming local drainage divides (Murphy et

al., 1976; Cranfield, 1994). Coaldrake (1960) described the scarps as being a clear

break in the pattern of soil and drainage and stated that although both incise into

Mesozoic sandstones, the two scarps are of different ages: he suggested that the Como

Scarp is a stranded Pleistocene shore line, and that the Glasshouse Scarp is older,

suggesting that neither are part of the Great Escarpment. Tilting of the erosion surface

may have been responsible for the reversal of some small creeks in the Mary River

catchment (Murphy et al., 1976). However, no mechanisms for the late Miocene to

early Pliocene uplift and late Pliocene tilting were proposed by Murphy et al. (1976).

Further geological control on drainage is evident in other parts of eastern

Australia, such as the Victorian Central Highlands where Cenozoic basaltic eruptions

covered and preserved a paleodrainage network where streams clearly altered

direction where they encountered a system of parallel and intersecting normal faults

(Holdgate et al., 2006). The interpretation of remnant landforms has led to a better

understanding of landscape evolution through deep time in some regions. For

example, the catchments of the Fitzroy and Burdekin Rivers are now known to have

enlarged towards the west during the Cenozoic, capturing other streams, which caused

an increase in sediment transport to the coast (Jones, 2006a). The movement of

catchment boundaries over time may have enormous implications for hydrogeology,

groundwater chemistry, and soil and regolith properties (Ollier, 2001).

An interpretation of Brisbane River’s physiography and its surrounding

catchments suggested that the escarpments were shaped by erosion and that structural

lines of faulting, jointing and zones of preferential weathering in the area, coincide

with drainage patterns to some degree (Marks, 1933; Beckmann and Stevens, 1978).

In an extensive geomorphological review of the Moreton District, southeast

Queensland, Sussmilch (1933) discussed river channel positions, although not

drainage patterns per se. Sussmilch described the general geomorphology and also

discussed the relationship between the complex series of horsts that separate the

eastern coastal plain from the continuous high western plateau. Sussmilch also first

described the Brisbane Gap, which is a low-lying division between the Beenleigh

(then ‘Tambourine’) and D’Aguilar Blocks. Sussmilch observed that the main

drainage systems that flow through the Brisbane Gap, specifically the Brisbane and

Logan rivers, do not flow along the lowest part as might occur if the division between

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the two blocks was simply the result of erosion; the two rivers respectively flow along

the northern and southern edges of the gap and both are incised into the bedrock.

Between these is Tingalpa Creek, which is a relatively short coastal stream The

southern margin of the Brisbane Gap may be an east-west fault, previously suggested

by Denmead (1928) and its northern boundary is a fault-scarp along the southern

margin of the D’Aguilar Block. Sussmilch (1933) further stated that although the

Stanley River starts close to the coast, it flows in a general southwest direction to join

the Upper Brisbane River near Esk. However, he did not suggest any explanation for

this anomalous drainage pattern.

For the upper Brisbane River catchment, it has been proposed that, due to

back-cutting of the Stanley River during Late Miocene-Early Pliocene times, drainage

was reversed, potentially having been assisted by minor tilting to the west, although

no evidence to support this hypothesis was given (Beckmann and Stevens, 1978).

Beckmann and Stevens also suggested that several coastal rivers that now discharge

directly into Moreton Bay, including the Caboolture and Pine Rivers, may have

previously flowed into the Brisbane River when sea-level was much lower than at

present. Landsat images of the Sunshine Coast area reveal many straight, arcuate and

sub-arcuate patterns in landform lineaments (such as scarps, highlands and valleys),

that do not coincide directly with the location of lithological units when compared

with geological maps (Lucas, 1987). Although differential erosion is an important

factor of landform development in the Brisbane region, Marks (1933) undertook a

review to ascertain whether other explanations for the location of hills and valleys,

and river patterns in particular were viable. The results showed that some drainage

divides exhibited ‘a complete disregard’ for the underlying geology and that some

rivers clearly follow the site of fault zones.

From the above précis of some of the work already conducted on

geomorphology in southeast Queensland, it is clear that although there is patchwork

evidence of strong geological controls on drainage and topography in the region, a

thorough and integrated understanding of the extent to which the landscape is

endogenically controlled does not yet exist. This thesis aims to enhance understanding

of the physical controls on the evolution of the landscape in this region.

101

ANALYSIS METHODS USED IN THIS STUDY

The main methods used in this study include spatial analysis of datasets on a

geographic information system (GIS), stream pattern analysis and stream ordering;

basic field work was also undertaken to map geological structures and to ground-truth

previously mapped geological and topographic features.

Digital elevation models (DEMs) Datasets were obtained from public sources including Queensland Government (2003;

2005), Pine Rivers Shire Council (2004), NASA (2004), Geoscience Australia (2006),

and ESSCC at the University of Queensland (2006). The topographic datasets

available early in the project from local sources (DME, Geoscience Australia, Pine

Rivers Shire Council) proved to be unsuitable as they were mainly of coarse

resolution. Furthermore, the resolution varied spatially (from 10 to 50 m contours)

across the southeast Queensland region. The DEMs analysed early in the project were

initially derived from traditional topographic maps and errors were found such as one

contour that was marked as 50 m and 100 m in separate locations. Therefore, these

maps were deemed unreliable and not fully digitised. At best they provided only a

broad digital model of the terrain. In order to integrate elevation data with other

datasets in a GIS, a digital elevation model (DEM) is required. To perform multi-scale

spatial analysis such as the measurement of orientation of channels or to extract

detailed longitudinal profiles or cross-sections of rivers, a reliable and high-resolution

DEM is required. Satellite Radar Tomography Mission data (SRTM: NASA, 2004)

became available from NASA during the course of the project providing a consistent

and, therefore, more suitable digital elevation model for the region. Nevertheless, the

resolution was still only 25 m and could not be relied upon for computer-generation of

a stream-network at the sub-catchment scale required. Therefore, a full stream

network was manually digitised and later ground-truthed and adjusted as necessary, in

order to ensure the network was of sufficient quality prior to performing detailed

analysis upon it. Later in the study, a more reliable digital dataset for the topography

of the region was obtained (Queensland Government, 2005) and replaced the use of

the SRTM data for the latter part of the research as it covered a broader area, was

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more flexible within the GIS programs and less memory intensive. The two elevation

models were comparable in quality.

Geological data Additional digital maps of southeast Queensland were obtained from the Department

of Natural Resources, Mines and Water (Queensland Government, 2003) that

provided coarse-resolution geological and drainage features. Detail and accuracy of

these maps limited their use depending on the scale required. Although geological

data is well represented, recent core logging suggests that there are significant

inaccuracies in the current geology maps (pers. comm. Brisbane City Council, 2006).

Nevertheless, it was the most complete geological representation available for the area

of study at a scale that was suitable for this work. The geological dataset included

fault, fracture and cleavage measurements across the region. However, the data was

focussed in disparate areas and did not include sufficient measurements in the Laceys

Creek catchment in particular. Therefore, it was necessary to expand the dataset and

field work was undertaken in the Laceys Creek catchment to provide additional rock

fabric orientation measurements for cleavage, joints and fractures.

Earthquake data Earthquake epicentre data available for southeast Queensland from Geoscience

Australia (2006) is relatively limited, and for the purposes of this study was

augmented by a more comprehensive dataset available from Earth Systems Science

Computational Centre at The University of Queensland (ESSCC 2006). The majority

of earthquakes in southeast Queensland have low magnitudes (< 2 M). The dataset

included all reported seismic ‘activity’ although for some of the reports, the epicentre

was uncertain and, therefore, not included in the analysis for this study. For

completeness, the remaining data were used in their entirety irrespective of

magnitude.

Geographic Information Systems (GIS) and choice of GIS products A geographic information system (GIS) is a computer-based tool that is designed to

allow geographically referenced data to be captured, stored, displayed and edited.

103

Spatial information can then be integrated and analysed within the system. MapInfo

and ESRI® ArcMapTM are commonly used GIS packages each with their own

advantages (e.g. Santos et al., 2000; Cartaya et al., 2006; Sarup et al., 2006; Singh and

Phadke, 2006). For example, direct digitising is more straightforward in MapInfo than

in ArcMap. Although ArcMap has more functions for multi-dimensional analysis than

MapInfo, the addition of the Vertical Mapper facility to MapInfo enhances its

capabilities. However, specific properties, such as DEMs, slope maps and shaded

elevation model maps, may be created in both products.

GIS provides a basis for collating, viewing and then analysing, statistically or

visually, georeferenced and spatial data that might have been collected at varying

scales, densities and the types of information may equally be disparate (e.g. Childs,

1991; Oguchi et al., 2003; Delcaillau et al., 2006; Palyvos et al., 2006; Tejero et al.,

2006). For example, topographic, geochemical and geophysical data can be imported

into GIS to view spatial extent and variation individually or to apply multiple-criteria

analysis upon them (Marinoni, 2005; e.g. He et al., 2007). GIS tools also have the

capability to perform detailed analysis of topographic data such as slope or orientation

of valleys and lineaments providing new maps for further interpretative analysis.

GIS can perform multiple scale analyses and provide a viewing platform for

detailed analysis of large, remote and inaccessible places. It has been employed for

surface analysis of acutely inaccessible places such as Mars (Baker, 2004) and

Jupiter’s satellite, Europa (Riley et al., 2006). GIS also has the capability of

performing a wide range of spatial analysis techniques, although it does not

automatically take into consideration surface area for its calculations. This may cause

some computational problems where surface area rather than plan area may affect the

results (Appendix 2). Despite the ability of GIS to perform multi-scale analyses, the

system is, to a great extent, limited by the input data: for example, generalisations of

the land surface are built into digital elevation models (DEM) and if they are greater

than the resolution of the landscape processes that are being studied, results may not

be fully representative and should be treated with caution (Pain, no date). Slope

angles, for example, may be inaccurate if the scale of DEM is not sufficient to

describe the landscape of the catchment under scrutiny. An appropriate scale for the

landscape and processes under scrutiny must be determined to ensure sufficient detail

lies within the digital data prior to analysis.

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Using variously obtained datasets within GIS it is possible to identify

geological linearity and associations with marked changes in terrain elevation,

drainage anomalies and alignment with known neotectonic structures. If these features

are taken separately, they cannot provide conclusive evidence of geological control

over landscape. However, where there is synchroneity and/or superposition of several

indices, and if such combinations do not imply other interpretations, then it may

signify geological control over the feature, and possibly a neotectonic fault zone

(Goldsworthy and Jackson, 2000; Ganas et al., 2005; Palyvos et al., 2006).

GIS is flexible with regard to the type of spatial data used, ability to combine

and integrate data of varying types and scales, extent of view and ability to vary the

scale of analysis. Therefore, GIS is a suitable tool for this project, as spatial analysis

at varying scales is required, combining elevation, drainage and geological datasets

together with the locations and magnitudes of earthquakes. Due to various conflicting

licensing issues throughout the course of this study, it was necessary to employ the

use of two GIS analysis packages: MapInfo and ArcGIS. Although ArcGIS was

initially equipped with more advanced features than MapInfo, both packages have

similar capabilities that were required for the analysis. However, MapInfo required

coupling with Vertical Mapper, a MapInfo ‘add-on’ that provides a vertical analysis

tool, to bring its capability in line with ArcGIS. A further ‘add-on’ was also employed

in MapInfo that enabled the program to measure and export the orientation of

polylines, necessary for the analysis of faults and stream orientations used in paper 1.

Neither ArcGIS nor MapInfo had an automated ordering system that would order the

network using the preferred ordering system devised specifically for this work.

Therefore, to ensure a suitable comparison was made when analysing the orientation

features across and throughout the network, streams were ordered manually and then

the orientations of each stream order were measured and exported separately.

As with broad scale studies (e.g. Scheidegger, 1979b; Beavis, 2000), analysis

at a fine-scale requires the orientation of stream channels to be compared with the

orientation of structures such as faults, joints and rock fabric. To increase resolution

of fine-scale channels, further drainage may be manually digitised where contour

deflections indicate concave-downhill patterns and ground-truthing may then be

undertaken by field work, aerial photography and comparison with existing maps.

Catchment and subcatchment boundaries may be digitised following topographic

105

highs around each drainage basin. To quantitatively measure the channels and their

orientations, channels may be ‘straightened’ following the method of Scheidegger

(1979b) by digitising axes from node to node throughout the network. The orientation

of each channel must be measured and although neither MapInfo nor ArcGIS has a

sufficient facility for this, ‘qik-orientate-345’ (Lawley, 1997), was available as a

‘freeware’ addition to MapInfo (Appendix 3) and this was used for this work.

Remote sensing Remote sensing is a method for analysing spatial information from a distance. Data

may be collected aerially and consist, for example, of images of spectral or

geophysical data. Many examples of remote sensing exist and have been utilised to

analyse a range of parameters over broad areas. An example in the southeast

Queensland region is the land-cover and land-use change monitoring of a rapidly

urbanising coastal environment – the Maroochy and Mooloolah River catchments

(Phinn and Stanford, 2001). Their study was designed to incorporate the input of

multiple resource monitoring groups at project planning, implementation and

completion phases. Various data types were integrated to provide a tool for a wide

group of resource managers and allow them to make better application of information

within the land development process. Although remote sensing is not a new

technology, it is becoming more popular since the development of Geographical

Information Systems (GIS). Using GIS, Allan and Peterson (2002) were able to model

the implications of land-use planning in Victoria, which resulted in a new decision

support tool.

Spatial analysis Spatial analysis is the study of data and information that relates to an area of interest.

In order to analyse particularly large areas, it is now common to use remotely

obtained datasets and this is referred to as remote sensing, and the most recent method

for such collection is by aeroplane or by satellite. Remote sensing in its various forms

has been used for over 100 years to identify geomorphological features and is

becoming an increasingly important tool. Early works include those of Hobbs (1901;

1904; 1911), who utilised broad-scale maps (‘111 miles to one inch’) to identify

106

physiographic lineaments and their relationship with regional faulting. A 3-

dimensional relief model of Australia was built (University of Melbourne) during the

1940’s that provided early information on the relationship between topography and

tectonics. This model revealed strong lineaments that, at the time, could not have been

discovered in any other way across an area as large as a continent (Hills, 1956). Since

that time, the use of traditional methods such as stereo-pairs and photo-mosaics have

been replaced by digital photographs, satellite images, more accurate topographic

maps and digital elevation and terrain models, that can now be amalgamated within

products such as GIS to further analyse the landscape. Other analysis tools such as

GOCAD®(Paradigm) and SiroSOM (Fraser and Dickson, 2007) may also be used for

spatial analysis depending on the user’s specific requirements. Structurally controlled

surface features such as scarps, aligned hills and drainage patterns have been

identified and analysed using remote sensing (Berger, 1985; Harding and Berghoff,

2000; e.g. Philip, 2007). Similarly, satellite imagery was successfully used to asses

recent tectonics in the Turkana Rift, North Kenya, when it was combined with both

drainage patterns and seismic reflection analyses (Vétel et al., 2004).

Methods of channel analysis Using the definition of Twidale (1980), the term ‘structure’ has been used in relation

to geomorphological control, to include rock-grain and texture, in addition to joints,

faults, bedding, cleavage and folds. Zernitz (1932) and Twidale (2004) presented

extensive reviews of drainage patterns and their meanings, and conclude that

geological control is the major influence over many patterns. Geologically controlled

drainage patterns commonly include trellis, rectilinear, dendritic, radial, centripetal,

parallel and sub-parallel, for example (Twidale, 2004), but dendritic drainage

indicates an overall lack of structural control (Zernitz, 1932). As discussed previously,

due to the location of the Great Divide and the Great Escarpment to the west and the

ocean to the east, it may be assumed that drainage would normally occur from the

highlands towards the coast, generally from west to east. Comparison of the location

and orientation of features such as faults, fractures or rock fabrics, with the location

and orientation of streams, valleys and slopes, may identify relationships between

those geological features and the morphology of the landscape. This has been

undertaken in several broad scale studies for example by Beavis (2000) and

107

Scheidegger (1979b). In order to facilitate such as study at a finer scale, the resolution

of mapped drainage must be increased to ensure the number of channels is of suitable

magnitude to be compared with the geological features such as cleavage and joint

systems. Although some programs can automatically digitise a drainage network, such

as the Soil and Water Assessment Tool – “SWAT” (USDA, 2008), the result will rely

on the level of detail in the underlying topographic model. To increase drainage

resolution where an automated system may not select sufficient streams, further

drainage may be manually digitised where contour deflections indicate concave-

downhill patterns and ground-truthing may then be undertaken by field work, aerial

photography and comparison with existing maps.

Stream ordering To determine whether different structural features typically control stream segments

of different magnitude, it is necessary to partition the channels into similar channel-

order ‘sets’ and group channel segments on the basis of similarity of scale and

position within the drainage network. Therefore, a hierarchical ordering system is

required. It is generally accepted that all finger-tip tributaries or channels in a

network, are designated as 1st order. Identification of first-order channel head

locations can be problematic (Heine et al., 2004) and lead to spurious orientation

measurements for these reaches, so the orientation data of first order channels should

be treated with caution.

Some channel-ordering methods, such as the Horton (1945) and Strahler

(1954) methods, may be manipulated in various ways. However, similarly derived

dimensionless numbers might also be treated in a similar way. Shreve (1966; 1967)

noted that Strahler’s and Horton’s Laws would be expected from any topologically

random distribution. This argument was later confirmed and it was established that,

from the properties the laws describe, no conclusion can be drawn to explain the

structure or origin of the stream network (Kirchner, 1993). However, ordering

systems continue to be used as ranking systems for practical purposes Scheidegger

(1965), Woldenberg (1967), Walsh (1972), and Orme (2002) proposed

mathematically derived ordering systems although the complex results lead to

operational difficulties (Gardiner, 1975). The most commonly used ordering systems

108

are those of Horton (1945), Strahler (1957) (now commonly referred to as the Horton-

Strahler method) and Shreve (1967) and each is discussed further, herein (Fig. 26).

In summary, the Horton (1945) method may designate a high order to any

scale of channel, from fingertip tributaries through to major rivers, which prevents

successful comparison between orders grouped in this way (Fig. 26a). The Strahler

ordering system (1957), derived from the Horton method, (now referred to as the

Horton-Strahler method) fails to allocate a new order at every node. By disregarding

tributaries in this way, the method effectively ignores the presence and influence

(discharge and capacity) of some channels in the system (Fig. 26b). The Shreve

(1967); numbering system, to some extent provides order numbers that relate to

channel magnitude or position, although it also leads to situations where similarly

positioned channels are assigned to substantially different orders and the relationship

between channels in each order may be vague in some parts of the network (Fig. 26c).

For the purposes of this study, a stream ordering system was required to

ensure that stream segments of equivalent orders are compared with structural and

rock fabric characteristics to identify the level of congruence and, thus, geological

control on that network. The controls on entrapment of a watercourse may, over time,

become concealed. However, the orientation of the channel may remain aligned with

the original plane or line of weakness. To ascertain recent or antecedent geological

control, it is important to identify the orders of channels that correspond to measured

and known physiography and structural features. It is, therefore, important to ensure

that the ordering system identifies similarly placed streams throughout the network.

For the reasons discussed above, previous ordering systems are unsuitable for this

work and a new ordering system has been developed and is presented in Paper 1.

109

110

Figure 26 Differences in resulting orders among commonly used stream ordering systems as discussed in the text: a) Horton (1945); b) Strahler (1957); c) Shreve (1967)

SUMMARY

The author wholly acknowledges that climate and surface processes influence the

shape of the landscape. However, for the purposes of this study, it is assumed that

those processes may enhance underlying structural and fabric anomalies where

mechanical and chemical weathering exploit sites of weaker and more susceptible

rock types. Various workers have identified that morphological features such as

gullies, valleys, hillslopes and ridges, crests and scarps, may follow repeating

alignment where geological or endogenic control exists. Therefore, one of the aims of

this research is to identify tectonic and endogenic influences on the landscape. It may

not be possible to fully discriminate between these influences, and the influences that

are, for example, climate driven because the processes act simultaneously: the latter

acting upon features produced by the former. To separate the effects of the processes

that occur in tandem would suggest they act alone, but as already acknowledged,

these processes act together. Without weakened, uplifted, folded, emplaced, variably

altered or different strength rocks, weathering effects would be minor.

The primary focus of this study is to discover how endogenic forces control

the existing landscape of southeast Queensland. Southeast Queensland is geologically

complex and is the result of many cycles of geological processes. Landmasses are

dynamic: over geological time they are continually moving, uplifting or being

downthrown; becoming folded, extended and compressed; becoming heated or buried

and metamorphosed; becoming accreted to other landmasses, eroded and redeposited.

This equates to the ‘rock-cycle’. However, the importance of these processes is often

taken for granted. If the driving force of plate tectonics were to cease, and weathering

processes were to continue, the landmasses would probably, almost entirely erode into

the ocean basins and surficial processes would rely on dune formation or impactors to

rejuvenate the landscape morphology. Therefore, the overarching driving force behind

the shape of our landscape is geological processes. They may be described as the

endogenic force that positions rocks upon which, exogenic forces may act.

This work integrates pre-existing datasets and uses a method that can be re-

applied to other areas, most importantly inaccessible places. In many regions, large,

pre-existing bodies of knowledge exist in the form of maps and datasets, which can be

digitised and used in a GIS allowing integration of each data-type for simultaneous

111

analyses. Newly acquired data can also be included in such analyses. Datasets may

include for example, maps, digital elevation, geology, and seismic data that although

in places may not be accurate or extensive, should at least be analysed alongside

existing maps and datasets. This would provide multiple-layer visualisation and

analysis that may be easily manipulated to change scales including more, or less data,

as required. As statistical analysis of circular data for clustered and multiple-feature

orientations is currently not reliable, graphical analyses of the data can be used

successfully for comparative studies. Numbering systems of streams do not lend

themselves easily to comparison of similar streams across a network and therefore an

improved method is required.

A modification to current analytical methods would integrate multiple

geological features, to compare their position and possible association with

physiography. This review has described some of the processes involved in

geomorphological change and has highlighted the significance of primary, or

endogenic controls, that establish the framework that is modified by secondary, or

exogenic processes. It is evident from previous work that there is a general acceptance

of an intrinsic relationship between geology and the landscape. Increasingly, more

work is being conducted to either quantitatively or qualitatively prove this

relationship and the extent to which landscapes are controlled by geology. Variations

in spatial and temporal scales should be considered, and analysis such as hindcasting

may be used as a support to predictive forecasting. Further work on this subject may

provide valuable insights, especially if a new approach is taken by integrating

multiple facets of the geological control, such as rock fabric and lithological variation,

joints, faults, folds and tectonics, at multiple scales.

Where geology has a significant influence over a landscape, a better

understanding of both the geomorphological and geological systems provides a

suitable framework upon which studies of anthropogenic influence can be based

(Preda and Cox, 2002). A measure of anthropogenic or climate-change impacting on a

landscape can be more easily discerned if the ‘natural’ level to which the landscape is

being controlled has first been identified. It may then be possible to more accurately

estimate how much erosion is anthropogenically or climatically driven if it is first

recognised that, for example, erosion due to uplift or faulting is naturally very high.

Similarly, if we identify that the landscape is tectonically and geologically inert,

112

producing little to no change in output over time, then major or sudden landscape

changes are more likely be either anthropogenically driven or caused by climate

change.

Although the influence that tectonics and geology in general has over the

landscape and in particular drainage channels is sometimes obvious, this is seldom

considered when the causes and impacts of surface processes are being studied. Long

term and often the more subtle effects of geology, may be taken for granted or not

considered as necessary parts of a landscape-change study. This may be because

surface processes such as erosion and weathering can be more easily observed ‘in

action’ and more easily measured on a short term basis, whereas geological processes

become part of the ‘background’ and are usually very slow. Surface process studies

would be better equipped to make a judgement on anthropogenic and climatic

influences if the internal driver of the landscape has also been considered. Both

anthropogenic and climatic changes will continue and will increase, and measurement

of their influences will require knowledge of the underlying system: therefore, this

study addresses the importance of geological influence over the landscape of

southeast Queensland as an example of a geologically complex, yet tectonically, a

relatively quiescent region.

113

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134

PAPER 1

TITLE The influence of geological fabric and scale on drainage pattern analysis

in a catchment of metamorphic terrain: Laceys Creek, southeast Queensland, Australia

AUTHORS Jane Helen Hodgkinson, Stephen McLoughlin, Malcolm Cox

School of Natural Resource Sciences Queensland University of Technology

Published in Geomorphology November 2006

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STATEMENT OF ORIGINAL AUTHORSHIP

Jane Helen Hodgkinson (PhD Candidate): reviewed previous work and literature; planned and conducted field work, collated datasets and conducted analysis, devised ordering system and interpreted data; wrote paper

Stephen McLoughlin (Principal PhD Supervisor): reviewed research program; discussed methods and ordering system; reviewed, discussed and edited paper

Malcolm Cox (Associate PhD Supervisor): reviewed, discussed and edited paper

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Abstract

The relationship between geological fabric and drainage patterns in the 81.8 km2

Laceys Creek sub-catchment of the North Pine River catchment, southeast

Queensland, Australia, is analysed using a new channel-ordination system. The

Laceys Creek catchment is situated on the South D'Aguilar Block, which underwent

metamorphism, faulting and uplift from the Late Carboniferous to Late Triassic. The

catchment drains exposures of two main rock units, the Neranleigh-Fernvale Beds

and the Bunya Phyllite. Both units are composed of metamorphosed deep-sea

sediments that accumulated as an accretionary wedge during late Palaeozoic

subduction of the palaeo-Pacific plate under the eastern margin of the Australian

craton. The new channel ordination system used in this study allows improved

classification of stream segments of equal prominence or rank in comparison to

previous schemes. A 10 m contour digital elevation model (DEM) was produced

within which drainage channels were digitised. Planar geological features, including

bedding, faults, joints and cleavage, were mapped in the field and collated with data

from previous geological mapping programs.

Regional and local trends of geological fabric are reflected in the variable

orientation of channels of different rank in the catchment. Cleavage and fractures are

the dominant planar features of the Bunya Phyllite and these correlate most closely

with the orientation of middle-order incised stream segments. In contrast, middle-

order channels on the Neranleigh-Fernvale Beds most closely correlate with bedding,

which dominates the fabric of this unit. Although anthropogenic factors exert local

influence and climatic processes exert broad influence on the catchment, this study

focuses on structural and lithological fabrics, which are the apparent dominant

controls on middle-order channel orientations. Identification of congruent patterns

between bedrock fabric and channel ranks is variable, depending on the scale and

number of channels included in the analysis. Many low-rank channels correspond

closely to the orientation of fine-scale bedding and foliation and these influences

may not be detected by coarse-scale mapping. Understanding the extent of geological

controls on the morphology of a catchment may assist geo-hazard identification, land

use planning and civil-engineering projects.

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Key words: Metamorphic terrain; Catchment; Channel orientation; Drainage pattern;

Channel ordination; Queensland.

1. Introduction

1.1 Background

The relationship between geology and landforms has long been established

(e.g. Hobbs, 1904, 1911; Zernitz, 1932; Twidale, 1980). Structure and slope are

accepted to be the primary controls on the spatial arrangement of channels. Some

rivers show correlation and repeating alignment with straight or gently arcuate

structural features such as faults, cleavage and fold axes to produce drainage systems

with a recognisable pattern (e.g., trellis, rectangular and parallel drainage networks).

In areas of poor outcrop, channel patterns can be a valuable guide to underlying

geological structures (Twidale, 1980). Initially following slope, rivers will later

adjust to structure as they incise into bedrock (Twidale, 2004). However, slope itself

may be controlled by active tectonism, implying that even low order channels, prior

to incision, may be geologically controlled.

Rock fabric has been shown to influence drainage patterns at very fine scales

(e.g. Twidale, 1972; Scheidegger, 1979a, b; Ackermann et al., 1997; Eyles et al.,

1997; Eyles and Scheidegger, 1999; Beneduce et al., 2004). It has long been assumed

the relationship occurs as a result of zones of weakness in the bedrock becoming

enhanced by weathering and erosion processes, although data mostly have been

insufficient to confirm this (Ericson et al., 2005). Where exposures are abundant and

regolith cover does not obscure structural details, it has been possible to accurately

map and measure large numbers of fracture traces but this method is less suitable for

assessing the structure-drainage relationship in catchments where regolith, vegetation

and land uses conceal natural bedrock features. Differential weathering of various

metamorphic rocks will form belts of hills and ridges depending on the resistance of

each rock unit (Strahler, 1966). Differential weathering of internal fabric, such as

cleavage, will be expressed by finer-scale controls on the landscape (Twidale, 1972).

Some previous studies have assessed diverse structural influences on drainage

pattern. High-quality aerial photographs have been used to demonstrate the

relationship between joints and channels in part of a granite-dominated catchment in

the Sierra Nevada, USA, where the high degree of bedrock exposure assisted

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correlation. In places, this relationship was evident irrespective of regional slope

(Ericson et al., 2005). At a fine scale, despite the presence of regolith and ground

cover, studies have shown a correlation between bedrock joints and gully orientation

and, based on investigations in New South Wales, the strength of this correlation is

strongly dependent on the bedrock lithology (Beavis, 2000). In the Macaronesian

Islands, stream orientations and ridge trends are similarly oriented, which suggests a

common tectonic control on the landforms (Scheidegger, 2002). On a coarser scale,

tectonic fabric was also found to exert a first-order control on landscape patterns in

the Chinese Himalayas (Scheidegger, 1998). Similarly, slopes and valley trends

were found to strongly correspond with Appenine and anti-Appenine lineaments in

central Italy (Alexander and Formichi, 1993). Tectonic controls appear to be the

main influences on many other large-scale landforms, particularly valleys and gorges

(Scheidegger, 2001). Although suspected for many decades, a clear relationship

between geological controls and trellis style channel networks was found to be weak

by some workers (Mock, 1971, 1976). More recently such a relationship has been

quantitatively demonstrated (Abrahams and Flint, 1983). Bedrock fractures and

metamorphic cleavage have been suggested as the likely controls on the incised

meanders of the Shenandoah River, USA, and the channel and gorge systems of the

meandering River Torrens, Mt Lofty Ranges, Australia, respectively (Twidale,

2004).

Such previous studies have clearly identified relationships among fracture

patterns, cleavage direction and stream orientation, but this does not imply that all

channels or valleys are endogenically controlled. The arrangement of non-random

channel orientations may be controlled by endogenic influences such as geological

structure or by ancient stress regimes (Scheidegger, 1979b). If channel orientations

prove to be random, exogenic forces such as climate are most likely the cause

(Scheidegger, 1998).

1.2 Purpose of this study

This study aims to identify the extent to which structural grain and

lithological fabric, collectively described herein as geological fabric, controls

channel alignment. The relationship between the drainage system morphology and

geological fabric in a high-energy, sub-tropical catchment dominated by low-grade

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metamorphic rocks in southeast Queensland, Australia is investigated (Fig. 1a, b).

The dominant rock units are phyllitic and are transected by a range of structural

discontinuities (faults and joints) that are variably orientated with respect to

cleavage. Geological fabric elements in the study area include: bedding, cleavage,

faults, and joints , hereafter cumulatively referred to as lineaments (their expression

in outcrop) or planar features (their two-dimensional representation). Geological

structures occur at a variety of scales, and consequently their effects on channel form

might be expected at varying magnitudes.

The study area is the Laceys Creek catchment (Fig. 1c), which has two primary

rock units of similar sedimentary origin but of different, albeit low, metamorphic

grade. Both rock types have been subjected to almost the same climate across the

catchment so differences in endogenic controls on channel form should be

quantifiable within each lithological unit. Despite the complex nature of the planar

geological features caused by multiple deformation events and the nature of the

metamorphic lithology, any relationship between drainage and structure should be

determinable by detailed mapping and analysis of preferred orientations of channel

segments. This study aims to identify whether stream pattern varies across the

catchment and whether the lithological fabric of each rock unit affects stream

orientation and the pattern of channels. It also aims to demonstrate the extent to

which channels are controlled endogenically and exogenically, and finally illustrate

how portrayal of network orientation is affected by varying the scale of the mapped

channels.

Many civil engineering and land management projects employ evaluation of only

coarse-scale lithological and structural properties of the bedrock but greater detail

may be required for specific local-scale projects. Changing the resolution of the data

may significantly alter their interpretation. Therefore, fine-scale channel mapping

and the effects of the underlying geology upon the position of those channels may

also be of assistance to local land-use and construction planning in the target

catchment.

2. The study area

The Laceys Creek catchment is the largest subcatchment of the North Pine River system and

is situated approximately 50 km north of Brisbane, southeast Queensland (Fig 1a, b). The catchment is

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located upstream of the artificial Lake Samsonvale, an important water resource for southeast

Queensland. The hilly to mountainous terrain of the catchment is sparsely populated, with fewer than

1000 residents. Although the catchment has not been widely developed, forest was cleared in 60% of

the catchment during the early 1900s and at present this area is used for grazing and rural-residential

land; the remaining 40% is forest reserve and state forest. Natural vegetation cover consists mostly of

Eucalyptus-dominated open sclerophyll forest with minor riparian closed-vine forest. The region

experiences predominantly summer rainfall, but this may be erratic and of variable intensity. The

catchment is located within the South D’Aguilar Block of the New England orogenic belt, which is

characterised by north-northwesterly trending geological assemblages (Fig. 2a) that represent volcanic

arc, forearc/backarc basins and subduction complexes (Murray et al., 1987; Coney, 1992; Little et al.,

1992; Holcombe et al., 1997a,b; Betts et al., 2002). The South D’Aguilar Block consists of steeply

dipping, north-northwesterly to south-southeasterly striking, pre-Permian meta-sediments and meta-

volcanics (Denmead, 1928; Belford, 1950; Bryan and Jones, 1962; Tucker, 1967; Wilson, 1973;

Cranfield et al., 1976). The Bunya Phyllite and the Neranleigh-Fernvale Beds are the two main

geological units in the Laceys Creek catchment (Fig. 2). They are of similar sedimentary origin but

have different fabrics. The Bunya Phyllite crops out in a north-northwest-trending belt on the

southwest flank of the Rocksberg Greenstone in the Pine Rivers catchment (Fig. 2).

Fig 1. Study area catchment (a) Location in relation to major Australian cities. (b) Location of North Pine River catchment in relation to other local geological provinces of southeast Queensland. (c) Map showing drainage channels of the North Pine catchment detailing Laceys Creek catchment, shaded grey.

141

The Bunya Phyllite overlies the Rocksberg Greenstone, and the transition is

represented by the intercalation of meta-sediments and meta-volcanics. The unit is

strongly foliated and consists of lutites and arenites metamorphosed to greenschist

facies. It is a dominantly pelitic suite of metasediments with some intercalated

metabasic volcanic rocks. Alternating micaceous and quartzose bands are transected

Fig 2. Geological setting. (a) Geology of the North Pine catchment and boundaries of the North Pine River and Laceys Creek catchments (Queensland Government, 2003). (b) Geology of the Laceys Creek catchment. Stream reaches have been straightened from source to outlet (Queensland Government, 2003).

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by veins of white quartz with accessory graphite and calcite. Grain size is generally

less than 0.01 mm and the mineral assemblage is primarily quartz, muscovite and

chlorite and is assigned to the lowest Barrovian-type greenschist subfacies (Winkler,

1967). The original sediments are interpreted as having been deposited in a relatively

deep-water marine environment and may represent oceanward facies equivalents of

the Neranleigh-Fernvale Beds. Cranfield et al., (1976) suggested the age of the

Bunya Phyllite is not younger than Carboniferous. Within the Laceys Creek

catchment, the Bunya Phyllite covers 12.9 km2 and forms rugged slopes with

elevations of 80 to 420 a.s.l.

The Neranleigh-Fernvale Beds are exposed against the southwestern margin

of the Bunya Phyllite and cover an area of 68.9 km2 in the Laceys Creek catchment

(Fig. 2). Exposures form rugged hills with elevations of 100 to 660 m a.s.l. The unit

consists of argillaceous rocks, conglomerates, radiolarian cherts, arenites, basic

volcanics and minor limestone (Cranfield et al., 1976). Arenites are well developed

within the Pine Rivers area, and thinly bedded shale and siltstone are widespread, in

some places sheared and phyllitic. Original bedding and cross-bedding are well

preserved. The representative lithologies and bedforms suggest deposition took place

in a relatively deepwater marine environment, experiencing periodic turbidity flows.

The unit has been regionally metamorphosed to the lowest Barrovian-type

greenschist subfacies but to a grade less than that of the Bunya Phyllite (Winkler,

1967). The mineral assemblage consists of quartz, sericite and chlorite. Triassic

intrusions, including the Mount Samson and the Samford granodiorites, have

thermally metamorphosed the Neranleigh-Fernvale Beds in the Pine Rivers area (Fig.

2a). An accurate age for the Neranleigh-Fernvale Beds has not been identified but is

placed between the mid-Devonian (Fleming et al., 1974) and mid-Carboniferous

(Green, 1973). The unit was subject to low-grade metamorphism towards the end of

the Carboniferous (Cranfield et al., 1976).

The Neranleigh-Fernvale Beds are considered to have been thrust over the

Bunya Phyllite although the exact stratigraphic relationship between these units has

not been clearly established. A major shear zone is located along their contact

(Cranfield et al., 1976). The beds have been folded and several north-northwest

trending fold axes have been mapped (Denmead, 1928; Belford, 1950; Cranfield et

al., 1976). However, due to a paucity of detailed work in this area, interpreting

precise structural relationships is difficult (Cranfield et al., 1976). During the Late

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Carboniferous New England orogenic event, the pre-Permian rocks were folded

along north-northwesterly trending axes. Further deformation occurred during the

Late Permian and Early Triassic, followed by block faulting and associated

emplacement of post-tectonic granitic intrusions several of which are within the

North Pine catchment. During the late Middle Triassic further folding took place

along north and northwest trending axes (Cranfield et al., 1976; Holcombe et al.,

1993, 1997a). The multiple episodes of deformation experienced by the pre-Permian

sediments and volcanics of the South D’Aguilar Block produced diverse bedding,

cleavage, fault and joint orientations within the units. The Paleogene saw

development of small intermontane sedimentary basins through eastern Australia,

including the Petrie Basin within the North Pine catchment, situated at the

southeastern edge of Lake Samsonvale (Fig. 2a). The Petrie Basin received 300 m of

sediment and is considered to be partly erosional and partly tectonically controlled

(Cranfield et al., 1976). The Paleogene sediments are largely undisturbed except

along rejuvenated basement faults such as the North Pine Fault (Fig. 2a).

Three of the main drainage pattern categories (e.g. Zernitz, 1932; Twidale,

2004) can be used to describe the drainage pattern of the Laceys Creek catchment.

Drainage on the Bunya Phyllite is generally dendritic. The drainage pattern on the

Neranleigh-Fernvale Beds is generally dendritic with a strong parallel influence and

angular junctions; a centrifugal drainage pattern is observed in the most proximal

part of the network.

Hill slopes are typically 20-25° in the upper portion of the study area,

becoming more gentle closer to the main perennial channel. The trunk channel of the

network has a mean slope gradient of ca. 1°. Overall, the incision of the channels

forms ‘V’ shaped valleys. Shallow rudosols and tenosols (Isbell, 1996) dominate the

catchment on the steep slopes, but thicker profiles are seen on very gently inclined

lower slopes and in depressions. Laterite occurs on some of the lower slopes and

flats.

3. Methods

Existing digital maps available for the area provide only coarse resolution and

greatly under-represent small channels. Analysing only the channels from those maps

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would lead to results biased to the orientation of larger channels only. To reduce this

effect, an alternative map of channel networks was compiled (Figs. 1c and 2).

NASA Shuttle Radar Topography Mission (SRTM) data (NASA, 2004) and

the MapInfo Professional 7.8 software were used to extract a 10 m contour digital

elevation model (DEM) of the catchment. Where contour deflections indicated

concave-downhill patterns, channels were digitised over the base map as a separate

GIS layer. A proportion of the channels digitised were randomly selected to verify

the accuracy of their positions, using aerial photographs, existing maps and field

observations using a compass and GPS. Catchment and subcatchment boundaries

were also digitised following topographic highs around each drainage basin. Digital

geological maps of lithological and structural data collated previously (Queensland

Government, 2003) were also included as additional GIS layers.

To quantitatively measure the channels and their orientations, channels were

‘straightened’ following the method of Scheidegger (1979a) by digitising axes from

node to node throughout the network (Fig. 2). The orientation of each channel reach

was then measured. Because identification of first-order channel head locations can

be problematical (Heine et al., 2004) and lead to spurious orientation measurements

for these reaches, the orientation data of first order channels were treated with

caution.

Standard statistical procedures cannot confidently be applied to directional

data due to the very nature of circularly derived measurements where 0° = 360°

(Jones, 1968). Statistical analysis of directional data has been explored to some

extent in a variety of scientific disciplines where orientation data naturally occur

(Krieger Lassen et al., 1994). Parametric orientation statistics in relation to earth

sciences have been discussed by Kohlbeck and Scheidegger (1985). Statistical

methods commonly seek to describe a mean value, deviation from that mean, or

closeness of fit between data sets. However, for the purposes of this study, it is more

important to seek correlations between the various datasets, which themselves may

display multiple clustering of data causing further complications to the analysis. In

an attempt to avoid the problems associated with circular data in standard statistical

procedures, simple statistical analysis was performed on selected segments of the

circular data where the selection did not incorporate orientations towards or either

side of 360°. For example, a portion of the dataset ranging from 90-180° was

analysed and subsequently narrowed to incorporate only those data within the 140-

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170° range. Normally it would be inappropriate not to apply the same method to an

entire dataset, but in this situation, it was not possible to do so as the problem of

analysing circular data returns when the portion of the selected dataset includes

360/0°. Additionally, this practice may intentionally exclude pertinent peripheral

data that may relate to minor trends present. Although the results of selective

statistical analysis are discussed, the current methodologies are not deemed to be

reliable as a quantitative analytical method for this field of study. A review of current

literature suggests that there is not yet a suitably rigorous technique to statistically

analyse circular orientation data. Therefore, visual comparison of channel orientation

patterns has been essential throughout this study. Channel orders with similar trends

were grouped together and a new group was formed where the dominant trend

showed significant change. Channel orders were grouped to both simplify diagrams

and to better indicate visually where trends change as orders progress through the

drainage network.

3.1 Ordering the channels

In order to partition the channels into similar channel-order ‘sets’, the catchment

channels were ordered, using a hierarchical numbering system. As this study seeks to

determine if different structural features typically control stream segments of

different magnitude, a stream ordering system is required that groups channel

segments on the basis of similarity of scale and position within the drainage network.

It is generally accepted that all finger-tip tributaries or channels in a network, are

designated as 1st order. This suggests the 1st order channels have something in

common and are comparable with one another and, therefore, may be analysed as a

set. To analyse the whole network, all channel sets, or orders, should be similarly

comparable. The ordering scheme used for this work also needs to ensure that every

channel order increases after each node, so that every successive reach is identified

and separable from the rest of the network for analysis.

Channel-order numbers of some schemes, such as the Horton (1945) and

Strahler (1954) methods, may be manipulated in various ways. Similarly derived

dimensionless numbers might be treated in a similar way. Shreve (Shreve, 1966,

1967) noted that Horton’s and Strahler’s Laws should be expected from any

topologically random distribution. A later review of the relationships confirmed this

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argument, establishing that, from the properties the laws describe, no conclusion can

be drawn to explain the structure or origin of the stream network (Kirchner, 1993).

However, for practical purposes, ordering systems continue to be used as ranking

systems (Orme, 2002). Some mathematically derived ordering systems, such as those

proposed by Scheidegger (1965), Woldenberg (1967) and Walsh (1972), provide

complex results that lead to operational difficulties (Gardiner, 1975). Therefore,

these methods have not been incorporated for this project. The three most commonly

used ordering systems are those of Horton (1945), Strahler (1957) (now commonly

referred to as the Horton-Strahler method) and Shreve (1967) and each was assessed

for suitability of channel ranking within this project.

In summary, the Horton (1945) method was unsuitable as a high order may

be designated to any scale of channel from fingertip tributaries through to major

rivers, and comparison between orders grouped in this way cannot be justified for

this study (Fig. 3a). The Strahler (1957) ordering system, a derivation of the Horton

method, now referred to as the Horton-Strahler method) was inappropriate as it does

not allocate a new order at every node, disregards some tributaries when orders are

designated and effectively ignores the presence and influence (discharge and

capacity) of some channels in the system (Fig. 3b). The Shreve (1967) numbering

system,

Fig 3. Differences among stream ordering systems: a) Horton (1945); b) Strahler (1957); c) Shreve (1967); d) new system described in this paper.

to some extent provides order numbers that relate to channel magnitude or position

and is more suitable for the present study than the Horton and Strahler methods.

147

However, it leads to situations where similarly positioned channels are assigned to

substantially different orders and the relationship between channels in each order is

inadequate to allow comparison in this study (Fig. 3c).

Since none of the schemes was fully suited to the requirements of this study,

a new numbering method was devised. As with the Horton, Strahler and Shreve

methods, fingertip tributaries are designated as 1st order (Fig. 4a), and the ordering

system is then ‘counted’ in a downstream direction. Once designated to an order, a

channel is then hidden, temporarily pruned or ‘greyed out’ depending on the

technique available on the GIS package. The next channels that appear to be fingertip

tributaries on the remaining network are designated the 2nd order (Fig. 4b). These

can then be hidden, removed or greyed out revealing the next order of channels that

again appear to be fingertip tributaries and are designated 3rd order (Fig. 4c). This

method is carried out systematically throughout the entire catchment network, always

treating the visible channels that appear to be fingertips as the new order (Fig. 4d-f).

Fig 4. Portion of the Laceys Creek catchment showing the methodology of the new channel ordering system. a) The fingertip tributaries are designated as order 1 (or 1st order); b) By greying out or removing the 1st order channels, those channels that now appear to be the fingertip tributaries are designated the 2nd order; c) By greying out or removing the 2nd order channels, those channels that would appear to be fingertip are designated the 3rd order; d) Similarly, 3rd order channels are removed or greyed out to reveal channels now designated as 4th order; e) The next channel that appears to be fingertip is designated as 5th order; f) The final order in this sub-catchment is designated as 6th order.

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This ordination system need not be numerical. Each order may be given a letter, or

for visual aids, a colour and be equally effective as the order descriptor remains

dimensionless. However, numbers provide a limitless supply of sequential

descriptors and are, therefore, possibly the most useful, coupled with varying channel

colours in a GIS. The order designated to each channel reach will be a relative

indication of influence upon that reach from others upstream (like the Shreve method

but unlike the Horton and Strahler methods). Although working on a similar

principle to the Shreve method, it allows for all orders to be accounted for in the

system, keeps the final order number low, and provides a more suitable method for

comparative studies across networks and between catchments. All orders can be

sequentially removed and remaining ‘fingertip’ channels are of equal rank and

therefore comparable. No other scheme achieves this while assigning every

successive reach to a consecutive separate order.

The number designated to each order is dimensionless, yet since it is relative

to others in the network, it is useful as a comparative tool regarding upstream

influence upon that particular order. It also allows groups to be removed from the

network in order to analyse the remaining network. Although this method creates a

scale-dependant system, at present a method for scale independency has not be

established. This method can be used to show the level to which analytical results are

scale dependant by sequentially removing orders of the same weighting, and viewing

the remaining catchment.

3.2 Rock fabric

Field work was carried out to measure the orientation of planar features to augment

data supplied by Queensland Government DNR (Queensland Government, 2003).

Given the paucity of outcrop within the Laceys Creek area, particularly on the Bunya

Phyllite, data was collected from additional sites (primarily road cuttings) close to,

but outside of the study area. Strike and dip of planar-features were measured using

the ‘right-hand-thumb along strike’ rule, where dip is recorded 90° clockwise from

strike. Strikes range from 1° to 360° requiring a circular rose diagram for visual

representation. Each planar-feature strike is a double-headed vector, causing the

opposite direction of each measurement to be equally relevant to this analysis. Both

orientations are incorporated in the portrayed data giving the rose diagrams 180°

symmetry (Krumbein, 1939; Jones, 1968; Kohlbeck and Scheidegger, 1985). The

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strike of each planar feature was sorted by both feature type and lithological unit in

which it appeared and rose diagrams were produced to visually express the datasets

as a circular distribution (Krumbein, 1939; Jones, 1968; Reyment, 1971).

Reference

All fingertip

tributaries

designated as 1st

order

Sequential

ordering (orders

present increase

in units of 1)

Every reach of the

network accounted

for by increase of

order number

Numbers treated

as designations

rather than values

Horton

(1945) NO YES1 NO YES

Strahler

(1957) YES YES NO YES

Shreve

(1967) YES NO YES NO

This paper YES YES YES YES

1Although numbers increase downstream on the whole, the Horton system reassigns entire streams with a higher order and as such, does not entirely fit these criteria (see also Fig. 3a). Table 1 Comparisons among the Horton, Strahler and Shreve schemes and proposed new method.

Channel-reach measurements were taken in the direction of flow, therefore,

each datum was within the range of 1° to 360° and these are represented on circular

rose-diagrams as unidirectional vectors. Rose diagram peaks are then used to identify

the mean orientations of each dataset (Müller-Salzburg, 1963). Orientations of all

channels were first grouped depending on underlying lithology. Rose diagrams were

constructed to show the orientation trends for each channel order, as well as for

clusters of channel orders. Rose diagrams were produced using all channels in the

network on each lithology and further diagrams were produced after removing low-

order and then low- and middle-order channels to assess the effects of scale on

network orientation analysis. The symmetrical rose diagrams of planar features were

compared with asymmetrical diagrams of channel orientations for each rock unit.

4. Results

Well preserved, thin (3-10 cm), turbidite beds, some containing planar- and

cross-lamination, are evident in the Neranleigh-Fernvale Beds. Moderate weathering

has occurred, including mechanical weathering by root wedging. Some preferential

weathering of the coarser fractions within the turbidites has formed corrugated

exposures. Slatey cleavage is locally evident but the planar surfaces are poorly

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defined. Crenulation cleavage, along which quartz is present, was observed.

Fractures are commonly filled with quartz. Two main trends of bedding planes are

evident across the catchment, striking approximately 100° and 138° from north and

dipping approximately 50° and 80° towards the southwest, respectively (Fig. 5a).

Fractures typically have northeast strikes and dip 40° to 90° to the southeast or

similar angles to the northwest (Fig. 5b).

Cleavage is well developed in the Bunya Phyllite, within the Laceys Creek

catchment. Fractures are common and bedding is seen rarely. Quartz veins are

located along some cleavage, fracture and bedding planes. Deformation of primary

foliation and of some quartz veins is evident. Cleavage planes strike approximately

140° and typically dip 65° towards the southwest (Fig. 6a). Fractures are generally

more vertically orientated than cleavage planes, striking predominantly northeast and

southwest (Fig. 6a). Much of the outcrop visible in road cuts is weathered where

water has penetrated along cleavage planes, altering minerals and mobilizing the clay

fraction.

Observations with respect to channels traversing the Neranleigh-Fernvale Beds

(Fig. 5b) include

The 1st to 3rd order channels trend mainly northeast, east and west with a few

to the north;

The 4th to 7th order channels trend mainly east to south-southeast and also to

the northwest with a few to the west;

The 8th to 15th order channels trend mainly east to southeast and northwest

to north-northwest with some channels to the northeast;

Channels of or above 16th order trend mainly north-northwest through north

to east.

The 1st to 3rd order channels display a strong trend, but do not clearly display a

correlation with the planar features measured (Fig. 5a, b). However, there is a

possible relationship with bedding orientation. Channels from 4th to 15th order show

a good correlation with bedding and a less-strong correlation with cleavage.

Channels of or above 16th order display a strong trend that may correlate with

fractures and possibly bedding although this relationship is weak.

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Examination of channel orientations on the Bunya Phyllite reveals the following

(Fig. 6b):

• The 1st order channels trend mainly northeast;

• The 2nd to 4th order channels trend mainly north-northwest, north-northeast

and southwest;

• The 5th to 9th order channels trend mainly to the southeast with some

towards the north-northeast, north and north-northwest;

• The 10th to 13th order channels trend towards the northeast, east and

southeast;

• Channels of or above 14th order trend strongly northeast with some towards

the east.

The 1st order channels on the Bunya Phyllite display trends that do not strongly

correlate with measured planar features, although some correlation with cleavage

may be present (Fig. 6a, b). Channels from 2nd to 9th orders have trends that

correlate with cleavage and bedding. Channels from 10th to 13th orders show some

correlation with cleavage. Channels from the 14th order do not strongly correlate

with orientations of planar features although a weak correlation with fractures may

be present and a strong trend is evident.

Cleavage and bedding plane orientations correlate better with lower-order

channels on the Bunya Phyllite than on the Neranleigh-Fernvale Beds. These planar

features correlate with the orientation of higher-order channels on the Neranleigh-

Fernvale Beds. On both units geological fabric exerts the least control on the lowest

order channels and the most control on low- to middle and middle (around 3rd to

15th) order channels. High (greater than 16th) order channels showed an average

orientation of northeast through north to north-northwest on the Neranleigh-Fernvale

Beds and approximately southeast on the Bunya Phyllite. The highest order channels

may be influenced by geological fabric to a limited extent but their strong disparate

trend suggests alternative controls.

Rose diagrams including all channels in the network on each lithology

revealed an average orientation mainly east-west with some north-south trends on the

Neranleigh-Fernvale Beds and approximately northeast through to south on the

Bunya Phyllite (Fig. 7). The rose diagrams show the average orientation of the

remaining network to alter direction after progressively more ranks of low and then

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middle order channels were deducted from the dataset, although this was most

apparent on the Neranleigh-Fernvale Beds.

Results from the trials of selective statistical analysis provided correlation

coefficients varying from strong through to weak depending upon the range and

position of the dataset selected. For example, a southeasterly channel orientation

trend is apparent in the 4th to 7th channel set on the Neranleigh-Fernvale Beds (Fig.

5b). Data ranging from 90-180° were analysed incorporating both cleavage and

channel orientations and resulted in a moderate statistical correlation. The dataset

was then narrowed to include only those data within the 140-170° range, which

statistically resulted in a very strong correlation. It is clear that the results are biased

by the data selection process and, therefore, provide no greater insights than visual

analysis.

6 Discussion

The strong trends displayed by 1st to 3rd order channels on the Neranleigh-

Fernvale Beds and first order channels on the Bunya Phyllite suggests there may be

additional endogenic controls on channel courses in the catchment. The poor

correlation between low order channels and planar features suggests these channels

may not yet have sufficiently down-cut into bedrock for fractures and foliation to be

influential. Planar features may be the main control on 4th to 15th order channel

orientation. The strong trends of channel orientation from the 16th order on the

Neranleigh-Fernvale Beds and from the 14th order on the Bunya Phyllite, do not

correlate with measured planar features, but may indicate control by larger scale

structural features or by processes or structures no longer evident in the environment.

The variation in channel orientation evident where the network involves

fewer data and less detail (Fig. 7), strongly implies that network analysis is scale-

dependant and that better accuracy is achieved where more channels are measured.

Analysis of each channel order under the new ordination scheme reveals correlations

with different geological or other environmental influences at different scales.

Although existing ordination systems have their own merits, the new method devised

for this project was found to be an effective alternative and may be employed by both

traditional manual methods and with GIS. The sequential removal or addition of

orders ensures that the scale of the drainage system is reduced or enhanced equally

across the network where scaling is required. Every sequential order is accounted for

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allowing direct comparisons to be made in the event that more than one catchment is

being studied. Escalating order numbers are avoided unlike the systems where orders

are derived by the addition of previous order numbers. Whilst still assigning every

reach to a new order, this method may be of benefit when working with extremely

complex or large catchments.

Fig. 5a Rose diagrams of channels grouped in similar orientations in Laceys Creek catchment on the

Neranleigh-Fernvale Beds

Fig. 5b Rose diagrams of planar feature orientations in Laceys Creek catchment

in the Neranleigh-Fernvale Beds

Strike of fault and fracture planes on Neranleigh-Fernvale Beds

Strike of cleavage planes on Neranleigh-Fernvale Beds

Strike of bedding planes on Neranleigh-Fernvale Beds

n=100 n=38 n=18

16th order channels and over

8th to 15th order channels

4th to 7th order channels

1st to 3rd order

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Fig. 6a Rose diagrams of channels grouped in similar orientations in Laceys Creek catchment

on the Bunya Phyllite

2nd to 4th

order channels

5th to 9th order channels

10th to 13th order channels

14th order channels and over

1st order channels

Fig. 6b Rose diagrams of planar feature orientations in Laceys Creek catchment

in the Bunya Phyllite

n = 9

Strike of bedding planes on Bunya Phyllite

Strike of fault and Strike of cleavage planes on Bunya Phyllite

fracture planes on Bunya Phyllite

n = 70 n = 26

155

Fig. 7. Comparisons among the Horton, Strahler and Shreve schemes and proposed new method.

The new channel ordination system allows channels of equal rank to be removed

and analysed sequentially for investigating the relative influence of structures and

fabric on channel orientation at different scales. On both lithologies in the Laceys

Creek catchment, combinations of planar-feature orientations correspond to the

orientation of low to middle-order channels but relationships are less well resolved in

the lowest and highest-order parts of the network.

As noted, lowest order channels show a strong trend, especially on the

Neranleigh-Fernvale Beds, but do not strongly correlate with planar bedrock

features, suggesting another influence such as neotectonic tilt. Shallow, low-order

channels forming at the surface and not yet incised to bedrock may be more

susceptible to recent geological changes than are older, higher order or incised

channels. The Australian continent is currently under a compressional stress regime

that may cause warping and reverse faulting of the crust. Following the construction

of the Australian stress map (Hillis and Reynolds, 2000), modelling has revealed a

roughly north-northeast south-southwest trending stress field in southeast

156

Queensland (Reynolds et al., 2002, 2003). Local work on recent, shallow earthquake

activity indicates that the principal compressional stress field in this region is

currently acting in a northeast-southwest direction (Cuthbertson, 1990), and this may

have influenced the orientation of the smallest and youngest channels. The highest

order channels also do not correlate with the measured planar features and may be

controlled by other geological structures such as deep-seated faults and fractures or

by conditions that are no longer prevalent.

Previous analyses of an area of uniform rock-type such as granite, with high

exposure, have revealed strong stream-fracture orientation relationships

(Scheidegger, 1979a; Ericson et al., 2005). A similar relationship (albeit on very

fine-scale channels) has also been shown to exist in areas of variable rock type where

regolith cover is substantial (Beavis, 2000). This study shows that, at multiple scales

within a whole catchment, there is correspondence between the orientation of planar

bedrock features and channels despite rock types of two metamorphic grades each

with broadly varying degrees of soil and vegetation cover. The correlations vary

between the two rock units investigated. This study also reveals evidence of the

evolution of the Laceys Creek drainage network and the extent to which geological

fabric is controlling the drainage pattern. Large-scale geological structures and

palaeo-controls are likely to be the dominant influences on highest order streams.

The middle orders are mainly controlled by the structural grain and lithological

fabric and the lowest orders, not yet incised to bedrock, may be influenced initially

by neotectonism and exogenic controls.

In summary, an assessment of the influence of rock architecture on drainage

patterns is strongly affected by the scale of analysis. Given the limitations of current

statistical methods when dealing with circular orientation data, visual analysis is

better suited to this study. However, the types of information derived from catchment

segment and geological fabric orientations would offer useful datasets for rigorous

analysis should an appropriate statistical procedure become available in future.

Identification of endogenic controls on channel orientation and scale by mapping and

analysis using the methods outlined above, may be of use for local scale land-use

planning and prediction of geohazards such as mass wasting, substrate stability and

stream avulsion.

157

Acknowledgements

We are grateful for the constructive input of both Dr Mike Daniels and an

anonymous reviewer. We are also grateful to Dr. Micaela Preda for assisting with

GIS and for helpful discussions, Dr. Andrew Hammond for useful input and advice

and Jonathan Hodgkinson for his field assistance and valued support.

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162

INTRODUCTION AND BACKGROUND TO PAPER 2

As the results from the first paper showed a correlation between faulting and

drainage of the higher order channels in the Laceys Creek catchment, this raised the

question whether there were further correlations between drainage channels and

mapped faults at a broader scale. Regional drainage and topography were compared

with the mapped faults and joints, and some correlation was evident, particularly in

the upper Brisbane River valley where major ancient fault systems exist and where

two major artificial reservoirs are presently located (Lakes Somerset and Wivenhoe).

As the reservoirs are built on known faulted valleys, a seismic monitoring network is

located at both Wivenhoe and Somerset dams to detect earthquakes that may

document premature releases of stress in the crust caused by the crustal loading and

pore-pressure changes induced by the water bodies (reservoir-induced earthquakes).

The relationship between the physical features and structure in the region

suggests the landscape is ancient in origin. For example, the upper Brisbane Valley is

located in a narrow downfaulted zone that may constitute a late Palaeozoic to early

Mesozoic remnant foreland basin or intra-cratonic graben (Campbell et al., 1999).

However, in order to identify whether those original primary processes are

continuing to impose controls on the landscape, the correlation between some known

physical features and recent earthquake epicentres was analysed. The datasets, as

previously mentioned, provided locations of epicentres that may have errors of up to

30 km in radius and this was taken into consideration during analysis, by allowing a

‘buffer’ around the location of each earthquake. Thus, where more than 3 ‘buffered’

earthquake epicentres revealed some clustering or linear patterns, these are described

in the following paper as ‘corridors’. The corridors do not necessarily imply the

positions of major fault planes, as the majority of earthquakes represented are of low

magnitude, but the linear alignments suggest that such patterns may be related to

narrow zones where stress is released periodically.

The earthquakes in the databases covering the past 100 years are mainly less

than magnitude 2 but these should not be considered representative of the

earthquakes in the region throughout geological time. The low magnitude

earthquakes experienced most frequently in this region over the past century are

unlikely to cause large, if any, surface displacement. However, they may be

responsible for continued weakening of the rocks, indicating the preferred locations

163

of less-common larger magnitude earthquakes, and they may define zones of

weakness that could eventually lead to preferred fluid drainage, weathering and

possibly erosion in these locations. The resulting corridors suggest that groups of

earthquakes may be causing small weaknesses in preferred locations across the

region. Paper 2 considers whether the earthquake corridors indeed show

correspondence with drainage features, and whether ongoing small-scale seismic

activity may be responsible for enhancing the topographic expression above existing

structural features. The database limitations are well known to the earthquake

engineering community, hence a thorough discussion of seismic data and its

limitations was not outlined at the conference at which the following paper was

presented. Limitations and further references relating to earthquake data are provided

in the literature review.

CAMPBELL, L. M., HOLCOMBE, R. J. and FIELDING, C. R. 1999. The Esk Basin - a Triassic foreland basin within the northern New England Orogen. In: Flood, P. G., ed. Regional Geology, Tectonics and metallogenesis, New England Orogen, NEO '99. pp. 275-284. Armidale Dept of Earth Sciences, University of New England.

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PAPER 2 TITLE The correlation between physiography and neotectonism in southeast Queensland AUTHORS Jane Helen Hodgkinson. Stephen McLoughlin, Malcolm Cox School of Natural Resource Sciences Queensland University of Technology Reviewed for DEST purposes and presented at the Australian Earthquake Engineering Society Conference, Canberra, ACT November 2006

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STATEMENT OF ORIGINAL AUTHORSHIP

Jane Helen Hodgkinson (PhD Candidate): reviewed previous work and literature; planned methodology, collated data and conducted GIS work; analysed and interpreted results, wrote paper and poster, presented both at conference

Stephen McLoughlin (Principal PhD Supervisor): reviewed and discussed methods and results; made suggestions regarding location of earthquake ‘corridors’; reviewed, discussed and edited paper Malcolm Cox (Associate PhD Supervisor): suggested need for a review of faults in the region; reviewed, discussed and edited paper

166

Abstract

We tested for correlation between recent earthquake epicentre data and the

distribution of major physiographic features, such as escarpments and river channels,

in southeast Queensland. Preliminary results indicate that many of the known

earthquake epicentres over the past century are distributed in several broad belts,

corresponding in location and orientation to major structural discontinuities or

narrow sedimentary basins bounded by faults. Other earthquake clusters show broad

correlation with linear segments of major river systems where no major faults have

been mapped. Several domains dominated by Palaeozoic-Triassic rocks, such as the

North and South D’Aguilar blocks, are represented by high terrain flanked by faults

that may have been active back to at least the mid-Mesozoic. Reactivation and

subsidence along some of these faults may account for the local accumulation of

thick sedimentary piles during the Paleogene. Modern earthquake epicentre

distributions along the margins of these blocks suggest that recent and on-going

tectonism may be enhancing the escarpments flanking the uplands. Unmapped,

concealed or deep-seated geological discontinuities may exist where earthquake

epicentres correspond to linear physiographic features but not to currently mapped

faults or joints. Identification of such concealed geological structures will be

important for developing accurate earthquake hazard maps into the future.

Introduction

Tectonism is one of the primary driving forces behind the structural and

physiographic modification of land masses. For example, tectonism is largely

responsible for terrain uplift and basin subsidence, which allow modification by

secondary processes such as weathering and erosion. As tectonics is generally

accepted to cause geomorphological change, it is logical to study geomorphological

features to identify the influences of tectonics on the landscape (for example Burrato

et al., 2003; Vannoli et al., 2004).

The Australian continent is situated within the Indo-Australia Plate.

Compared to plate boundary earthquakes, intraplate earthquakes are few and

shallow. However, the Global Seismic Hazard Map shows that Australian earthquake

activity is moderate to high, relative to other intraplate regions (GSHAP, 1992-

1997). The Indo-Australian Plate is presently under compressional stress (Hillis,

1998; Hillis and Reynolds, 2000) and modification of the land will occur in order to

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accommodate shortening of the continental mass where the stress exceeds the

strength of the crust. For example, Neogene-Quaternary reverse faulting and

compressional folding has clearly influenced landscape evolution in both central

western (for example, Clark, 2005), and southeastern Australia (for example,

Sandiford, 2003). Folds, faults, joints, shears and rock fabric alteration, resulting

from tectonic movement, have long been known to control the formation of a variety

of distinctive land surface features such as scarps and river channels (for example:

Hobbs, 1904; Hobbs, 1911; Zernitz, 1932; Strahler, 1960; Strahler, 1966; Twidale,

1980; Scheidegger, 1998; Scheidegger, 2002; Ericson et al., 2005; Hodgkinson et al.,

in press). The relationship between Australia’s geology and its earthquakes is poorly

understood and many earthquakes cannot be assigned to known structures (Clark and

McCue, 2003). Physiographic analysis in conjunction with recent seismic data will

assist identifying those landscape features that are likely to be tectonically controlled

and presently active; such analysis has the potential to refine zones hazardous to the

population and infrastructure.

For dipping faults, earthquake epicentres will appear more distant from the

surface trace with increasing hypocentral depth. As a consequence, epicentres may

not be expected to align precisely with surface features, such as mapped faults,

scarps and joint systems. Therefore, broad sectors in which earthquake epicentres are

located should be identified to determine potentially active fault zones. Earthquake

locations may also be inaccurate, particularly those identified from early records and,

therefore, care must be taken when relating them to local physiographic features.

Since the calculation of actual earthquake depth is typically inaccurate, this

parameter should be treated with caution. Using available data, this study aims to

provide evidence of tectonic control upon the landscape of southeast Queensland.

Background

Southeast Queensland’s geology is complex and derived from several cycles of

compressional and extensional tectonic activity since about 370 Ma. Palaeozoic to

modern sedimentary and igneous rocks are interspersed with large belts of

metamorphic rocks throughout the region. Many of the geological units (Queensland

Government, 2003) are bounded by faults. Extensive regolith, vegetation and

infrastructure conceals many of southeast Queensland’s geological discontinuities

including faults, joints and formation boundaries. Some areas appear to be relatively

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fault-free and, although this may be the case, the apparent dearth of these features

may be attributable to concealment by ground cover or the lack of detailed mapping.

Recent core logging in southeast Queensland has revealed discrepancies with the

published geological maps (geological map, Queensland Government, 2003;

Brisbane City Council, 2006 pers. comm.) and confirmed that faults and joints are

common in the region. Fault distributions have been analysed recently (Humphries,

2003) but little has been published regarding age constraints on fault activity. Childs

(1991) analysed Landsat images of the northern part of the region and showed that

the main ranges and drainage systems are strongly concordant with the bedrock

geology, and that faults also correspond with channel orientation. However,

Humphries noted that some major faults and a shear zone on geological maps were

not identifiable on the Landsat image, and may either lack surface expression or have

had unfavourable illumination for Landsat (Childs, 1991). The region’s elevation

ranges from sea-level to 1360 m a.s.l. and the area can be divided into three general

terrains: highlands (>300 m a.s.l.), hills (30-300 m a.s.l.) and lowlands (<30 m a.s.l.)

(Fig. 1). The greatest portion of southeast Queensland is situated in the hilly to

highland terrains. However, most of the population presently resides within the

coastal lowlands, especially within the expanding cities of Brisbane, Ipswich and the

Gold Coast. Three artificial reservoirs, Somerset, Wivenhoe and Samsonvale,

provide southeast Queensland’s main water supply: each is situated in known faulted

and seismically active zones.

Earthquake monitoring

In order to compare neotectonism and its geomorphological effects, detailed

earthquake data are needed. Earthquake monitoring in Queensland is generally sparse

by international standards and has only operated intermittently. Earthquakes have

been recorded since the late 1800’s. In 1937, Queensland’s first international

monitoring station was opened in Brisbane, followed by the Charters Towers station

in 1957. Subsequently, a seismic monitoring network developed slowly, broadening

considerably after 1977, when more detailed instrumental monitoring was

implemented around the large dams. Dam-site and other seismographs were

integrated into a state-wide network, monitored by The University of Queensland

(UQ) from 1993 (the QUAKES Centre) but since 1998, much of the operational

instrumentation has been progressively discontinued from service. Monitoring is now

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restricted to southeast Queensland. Since 2000, 22 Queensland Government

seismograph stations continue to collect data under commercial contract to

Environmental Systems and Services (ES&S, Victoria,). As well as temporal

discontinuities, data completeness is also affected by differences in the resolution of

monitoring, spatially.

Detail shown in Fig. 6

Fig. 1 25m DEM of southeast Queensland

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Fig 2 Main drainage systems and locations of southeast Queensland

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Fig. 3 Earthquake epicentre corridors superimposed onto slope map. Scarps highlighted in black

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Methods

Digital topographic data at 25 m intervals (Queensland Government, 2005) (Fig. 1),

geological and drainage (Fig. 2) maps for southeast Queensland were obtained from

the Department of Natural Resources, Mines and Water (DNRM&W)(Queensland

Government, 2003). Using the ArcGIS 9 software, a digital elevation map (DEM)

was produced and slope maps (Fig. 3) created from which scarp features were

extracted. Earthquake data retrieved from Geoscience Australia (2006) provided

information for 100 earthquakes recorded in the region since 1872. Further data were

supplied by the Earth Systems Science Computational Centre (ESSCC) at The

University of Queensland, increasing the total number of earthquakes recorded in the

region to 344 (Figs. 3,4,5). The digital maps were combined with seismic data for

identification of concordant patterns of geomorphological lineaments and earthquake

epicentres. Where 4 or more earthquake epicentres clustered or were well-aligned

within a 12-15 kilometre wide corridor, they have been considered to possibly have a

common source and be related to similar zones of seismic activity. Such clusters and

alignments are referred to here as ‘earthquake corridors’.

Results

Highlands and scarps

The highland areas are situated mainly in the west and north of the study area, and

generally trend in a northwest-southeasterly direction. A discrete area of highlands,

situated in the central region, is separated from the west by the Brisbane River

valley. Some highland terrain is situated in the southeast, associated with the Mount

Warning shield volcano. The physiography of the latter highland area does not

correspond to the predominant northwest-southeast geological trends in southeast

Queensland. Scarps are common across the region (Fig. 3). In places they coincide

with the orientation of highlands, geological units, faults and drainage.

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Fig. 4 Main drainage, structural features and earthquake epicentres in southeast Queensland

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Fig. 5 Data from ‘Fig. 4’ superimposed with earthquake corridors

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Drainage

Channel orientation in the region is predominantly northwest-southeasterly and

northeast-southwesterly (Fig 2.). These trends are particularly strong in the Brisbane

River system, which may be described as a trellis or rectilinear drainage pattern.

Secondary trends occur in an east-west orientation and other trends are evident at a

finer scale. Drainage in the southeast is radial, away from the centre of the Mount

Warning volcanic complex.

Geological discontinuities

High angle dip-slip faults, joints, thrusts and shear zones have been mapped

throughout the region (Queensland Government, 2003), although a large area in the

southwest and on the coastal plains in the east appears to have few faults. Fault

orientations in the remainder of the region strongly trend in a northwest-southeasterly

orientation although various other trends are also evident (Fig. 4).

Seismicity

Earthquakes occur throughout the region on all terrains (Figs. 3,4,5). As depth to

focus data are highly uncertain, earthquake epicentres only have been considered in

this analysis. Their distribution shows some concurrence with drainage, structural

features (Figs. 4,5) and scarp distributions (Fig. 3). The epicentres cluster most

prominently within a broad northwest-southeast trend but subsidiary southwest-

northeast and roughly east-west trends are also evident (Figs. 3,5).

Discussion

Physical relationships

There is some concurrence between the location and orientation of faults and rivers,

especially the Brisbane River system (Fig. 4). The presence of a scarp may be due to

surface displacement by faulting, mass wasting or by other surface processes such as

fluvial erosion. Some scarps appear to have no correlation with present drainage or

mapped faults and may represent features with historical controls such as retreating

coastal escarpments. A relationship between drainage system pattern and highland

location is present, although such definition would be expected due to normal down-

cutting of rivers between resistant rock units. The lowland areas primarily consist of

unconsolidated Cenozoic sediments, which may conceal faults or joints.

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Seismic and physiographic relationships

Earthquake epicentre and drainage patterns commonly concur throughout the region

(Figs. 4,5). North of Brisbane/Toowoomba, this association is also closely aligned

with faults. However, south of Brisbane/Toowoomba, virtually no mapped faults

coincide with earthquake and river-trends. In the north, this alignment suggests that

mapped faults may be active and controlling drainage channel orientation and

position. In the south however, where some earthquake zones align with drainage but

do not coincide with mapped faults, other faults may be concealed and/or not yet

mapped. Several scarps coincide spatially with earthquake-prone zones (Fig. 3) and

an apparent alignment between some scarps, faults and drainage channels, suggests

that these scarps may be fault and/or river controlled. Some earthquake epicentres

cluster in close proximity to mapped faults, such as those flanking much of the South

D’Aguilar Block (Figs. 4,7). However, some clusters do not appear to align with

currently mapped faults despite their linear spatial distribution. The proximity of

earthquake activity to channel location suggests that there may be a relationship

requiring further investigation.

Fig. 6 DEM detail (northwest of region) showing linear escarpments with mapped faults superimposed

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Fig. 7 Stable geological blocks and basins of southeast Queensland

Seismic zones lacking physiographic relationships

There are several earthquake-prone zones in the region that are commonly located in

flat or gently undulating terrain and free from scarps, large river channels and faults.

The earthquake epicentres in these areas may be associated with very deep faults that

presently have no surface expression, may be in areas that are poorly mapped due to

ground cover or may be beyond the resolution of the DEM. Equally, they may be

associated with mapped faults with very shallow angles of dip causing the surface

expression to be far enough away from the epicentre to appear unrelated. Data may

also inaccurately reflect the position of the epicentre.

General

Deep earth investigation such as drilling, reflection seismography or GPR, together

with more accurate measurements of hypocentre depths may assist in identifying the

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faults with which recent earthquakes are associated. Such work may also identify

unmapped faults where surface features and earthquakes suggest there is potential

faulting in the vicinity. For example, topography, river orientation and earthquake

activity suggests faulting occurs along the southern edge of the South D’Aguilar

Block. Many of the rock units throughout the region are bounded by faults implying

tectonism is responsible for their current position. Recent earthquake activity in the

vicinity of these faults suggests continued or sporadic movement of these units is

occurring.

Conclusions

This preliminary study suggests that geomorphological evidence, when combined

with geological and earthquake data, may be used to successfully identify zones of

current faulting. An important consideration in this study has been the scale of

viewing both temporally and spatially. Earthquake corridors suggested in our results

may not be apparent if each epicentre was viewed in isolation or at a less broad scale

in time and space. Although features such as channels and slopes may be controlled

by differential weathering, neotectonism may also be influential and this may pose a

greater threat than geohazard maps imply. The most widely used seismic hazard map

of southeast Queensland (McCue et al., 1998) is a classic representation of a

probabilistic earthquake model (defined by Cornell, 1968). The hazard designations

are a product of available data, which may be sparse, temporally and spatially.

Equally, the earthquakes may not be probabilistic in nature (Clark and McCue,

2003). Consequently, the map may not fully represent actual hazards in the area.

Therefore, more detailed, widespread, long-term monitoring programs would be a

valuable addition to future hazard assessment and mitigation, together with

deterministic seismic modelling. First motion studies are useful in determining the

dip orientation of dip-slip faults and whether normal or reverse. Accurate focal

depths would also better constrain fault locations. Broad ‘zones’ surrounding the

implied epicentre positions should be used to relate earthquakes to potential, local,

physiographic features, unless absolutely certain of the data accuracy. The most

densely populated area in southeast Queensland is situated within the lowlands,

which hosts a widespread veneer of unconsolidated Cenozoic sediments that may

conceal potentially active faults. Better collection and availability of structural data,

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in combination with high resolution digital terrain models, would enable more

thorough landscape analysis to identify potentially active fault zones, areas of

concealed faults and deep sediment zones which are conducive to seismic

amplification. Ultimately this would provide a better understanding of both

neotectonism and localised seismic hazard zones in southeast Queensland.

Acknowledgements

We wish to thank Dr Dion Weatherly and Col Lynam of ESSCC and QUAKES

Group at the ESSC Centre, The University of Queensland, for providing us with the

ESSCC Earthquakes Database and other useful references, and for interesting

collaborative discussions. We are also grateful for the valuable suggestions and

comments from Dan Clark and an anonymous reviewer.

References

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Childs, I., 1991. Earthquake risk, Landsat imagery and fault zones in the Bundaberg area of central eastern Queensland. Queensland Geographical Journal, Series 4, 6: 59-70.

Clark, D. and McCue, K., 2003. Australian paleoseismology: towards a better basis for seismic hazard estimation. Annals of Geophysics, 46(5): 1087-1105.

Clark, D., 2005. Identification of Quaternary faults in southwest and central western Western Australia using DEM-based hill shading. Geoscience Australia Record: 60p.

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Ericson, K., Migon, P. and Olvmo, M., 2005. Fractures and drainage in the granite mountainous area: A study from Sierra Nevada, USA. Geomorphology, 64(1-2): 97-116.

ESSCC, 2006. Earth Systems Science Computational Centre, Earthquake Database, University of Queensland, Brisbane.

Geoscience Australia, 2006. http://www.ga.gov.au/oracle/quake/quake_online.jsp. GSHAP and (Global Seismic Hazard Assessment Program), 1992-1997. Global

Seismic Hazard Map, http://www.seismo.ethz.ch/GSHAP/global/. Hillis, R.R., 1998. The Australian stress map. Exploration Geophysics, 29(3-4): 420.

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Hillis, R.R. and Reynolds, S.D., 2000. The Australian Stress Map. Journal of the Geological Society, 157: 915-921.

Hobbs, W.H., 1904. Lineaments of the Atlantic border region. Geological Society of America Bulletin, 15: 483-506.

Hobbs, W.H., 1911. Repeating patterns in the relief and structure of the land. Geological Society of America Bulletin, 22: 123-176.

Hodgkinson, J.H., McLoughlin, S. and Cox, M., in press. The influence of geological fabric and scale on drainage pattern analysis in a catchment of metamorphic terrain: Laceys Creek, southeast Queensland, Australia. Geomorphology, doi:10.1016/j.geomorph.2006.04.019.

Humphries, D., 2003. An analysis of post-Triassic faulting in southeast Queensland. BSc (Hons) Thesis, University of Queensland, Brisbane, 134 pp.

McCue, K.F., Somerville, M. and Sinadinovski, C., 1998. The new Australian earthquake hazard map, Proceedings of the Australasian Structural Engineering Conference, Aukland, NZ, pp. 433-438.

Queensland Government, D.N.R.M., 2005. South East Queensland 25 metre Digital Elevation Model - SEQ_DEM_100K.

Queensland Government, D.N.R.M.W., 2003. Queensland Geological Digital Data, CD ROM.

Sandiford, M., 2003. Neotectonics of southeastern Australia: linking the Quaternary faulting record with seismicity and in situ stress. Geological Society of Australia Special Publication, 22: 101-113.

Scheidegger, A.E., 1998. Tectonic predesign of mass movements, with examples from the Chinese Himalaya. Geomorphology, 26(1-3): 37-46.

Scheidegger, A.E., 2002. Morphometric analysis and its relation to tectonics in Macaronesia. Geomorphology, 46(1-2): 95-115.

Strahler, A.N., 1960. Physical Geography. John Wiley and Sons, New York. Strahler, A.N., 1966. The Earth Sciences. Harper International, 681 pp. Twidale, C.R., 1980. Geomorphology. Thomas Nelson, 406 pp. Vannoli, P., Basili, R. and Valensise, G., 2004. New geomorphic evidence for

anticlinal growth driven by blind-thrust faulting along the northern Marche coastal belt (central Italy). Journal of Seismology, 8(3): 297-312.

Zernitz, E.R., 1932. Drainage patterns and their significance. Journal of Geology, 40: 498-521.

182

PAPER 3 TITLE Drainage patterns in southeast Queensland: the key to concealed geological structures? AUTHORS Jane Helen Hodgkinson, Stephen McLoughlin, Malcolm Cox School of Natural Resource Sciences Queensland University of Technology Published in Australian Journal of Earth Sciences December 2007

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STATEMENT OF ORIGINAL AUTHORSHIP

Jane Helen Hodgkinson (PhD Candidate): reviewed previous work and literature; planned methodology, collated data, conducted GIS work and analysis, interpreted results; wrote paper

Stephen McLoughlin (Principal PhD Supervisor): reviewed and discussed methods, analysis and results; identified some drainage patterns and additional references; reviewed and edited paper

Malcolm Cox (Associate PhD Supervisor): reviewed and discussed results and reviewed and edited paper

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Abstract

Southeast Queensland’s geomorphology is characterised by northwest-southeast

trending trunk drainage channels and highlands that strongly correlate with the

distribution of geological units and major faults. Other geomorphological trends

strongly coincide with subsidiary faults and geological domains. Australia is

presently under compressional stress. Seismicity over the past 130 years records 56

earthquakes of >2 magnitude indicating continuing small-scale earth movements in

the Moreton region. Highlands in this region are dominated by Palaeozoic to Triassic

metamorphic and igneous rocks, and are generally 20-80 km from the coastline.

Coastal lowlands are largely dominated by Mesozoic sedimentary basins and a

veneer of surficial sediments. The eastern coast of Australia represents a passive

margin; crustal sag along this margin could be expected to produce relatively short,

high-energy, eastward flowing drainage systems. We performed a geomorphological

analysis to characterise the drainage patterns in southeast Queensland and identify

associations with geological features. Anomalous channel, valley and escarpment

features were identified, which failed to match the anticipated drainage model and

also lacked obvious geological control. Despite their proximity to the coast (base

level), these features include areas where drainage channels flow consistently away

from, or parallel to, the coastline. Although many channels do coincide with

geological structures, the drainage anomalies cannot be directly related to known

structural discontinuities. Anomalous drainage patterns are suggested to indicate

previously unidentified structural features and in some cases relatively young

tectonic control on the landscape. Recent seismicity data have also been analysed to

assess spatial correlations between earthquakes and geomorphological features. Our

results show that structure largely controls drainage patterns in this region and we

suggest that a presently unmapped and potentially active, deep-seated structure may

exist parallel to the coast in the northern coastal region. We propose that this

structure has been associated with uplift in the coastal region of southeast

Queensland since mid-Cenozoic times.

KEYWORDS: Drainage patterns; Anomalous drainage; Geological structure;

Geomorphology; Tectonic control

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INTRODUCTION

Fluvial drainage patterns have been studied broadly as a tool for a wide range of

theoretical and applied geological investigations (for example Strahler, 1966;

Schumm and Khan, 1972; Twidale, 2004). As stated by Hills (1963) and reiterated

by Twidale (2004), the greatest assistance that geomorphology can offer structural

geology may be derived from the interpretation of drainage patterns. Twidale (2004)

concluded that most river patterns are determined by geological structure and slope,

and anomalies in, and diversions from, these patterns are generally caused by active

faults and folds. Control of drainage patterns by geological structure and tectonics is

widely accepted and has been investigated extensively (for example Burnett and

Schumm, 1983; Ouchi, 1985; Mather, 1993; Jackson et al., 1998; Zelilidis, 2000;

Maynard, 2006).

Tectonic control of geomorphological features is broadly accepted (e.g.

Ollier, 1981). Recorded earthquakes are widespread in Australia but relatively few

can be assigned to known structures (Clark and McCue, 2003). Deep regolith cover

across much of the continent conceals many bedrock structural details. Low

resolution mapping and sparse seismic profiles have also constrained fault

identification in many areas. Additional methodologies are required to identify active

and ancient faults for geohazard mapping and geotechnical surveys.

Geomorphological analyses offer a means to identify many concealed structural

discontinuities.

Entrapment of drainage channels along faults is generally a function of

preferential weathering and erosion along zones of rock weakness and/or rotation of

fault blocks influencing the topography. Geomorphological evidence such as linear

trends of major drainage channels and steep slopes may be used to identify zones of

faulting. Analysis of drainage patterns and recognition of anomalies in these systems

has become a popular method to identify obscure geological structures and

neotectonism (for example Jackson et al., 1998; Goldsworthy and Jackson, 2000;

Burrato et al., 2003; Vannoli et al., 2004; Delcaillau et al., 2006; Hodgkinson et al.,

2006a). This is especially effective when combined with spatial earthquake data.

This study aims to characterise the drainage systems of southeast Queensland

and identify broad-scale anomalies in stream patterns and their potential geological

controls. A multidisciplinary approach is employed in which remote sensing

techniques are integrated with structural geology, earthquake records and

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geomorphological observations within a geographic information system (GIS). The

objective of this study is to improve the understanding of geological controls on the

landscape and the effects of neotectonism in the region.

SETTING

The study area is on the eastern edge of the Australian continent between 151° 53'E,

26° 11'S to 153° 31'E, 28° 30'S, and covers approximately 41,000 km2. It generally

corresponds to the region covered by the Moreton 1:500 000 Geology Map

(Whitaker and Green, 1980). The region is currently undergoing extensive

urbanisation and development, and represents one of the fastest population growth

centres in Australia (Australian Bureau of Statistics, 2006). The region has a sub-

tropical climate, commonly with hot, wet summers (November to February) and

warm, dry winters. Rainfall is often heavy and may contribute to extensive areas of

mass wasting on escarpments flanking the coastal plain. Water resources are limited

by strongly seasonal and highly variable rainfall, and artificial reservoirs provide the

majority of the region’s water supply. The largest reservoirs are situated in valleys

that are developed on faults or fault zones.

The geomorphology of southeast Queensland has been studied extensively

(e.g.: Marks, 1933; Watkins, 1967; Arnett, 1969; Arnett, 1971; Donchak, 1976;

Beckmann and Stevens, 1978; Murray and Whitaker, 1982 ; Lucas, 1987; Murray,

1987; Murray et al., 1987; Cuthbertson, 1990; Childs, 1991; Little et al., 1992;

Holcombe et al., 1993; Little et al., 1993; Holcombe and Little, 1994; Hodgkinson et

al., 2006a). In brief, highlands (mostly plateaux over 300 m a.s.l.) fringe the western,

southern and northern margins of the study area; an additional isolated, dissected

highland area occurs in the centre (Fig. 1). The remainder of the area, principally in

the east, can be described as foot hills and coastal plains. Escarpments are common

across the region. The main drainage systems of the region commonly display strong

northwest-southeasterly and northeast-southwesterly trends. Identified fault

orientations also strongly trend in a northwest-southeasterly orientation although

various other trends are also evident (Fig. 2). The Australian continent is currently

under compressional stress (Hillis, 1998; Hillis and Reynolds, 2000) and may

experience warping and reverse faulting of the crust as the landmass shortens.

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Fig. 1 Digital elevation model showing locations and main rivers in the study area. The Main Range in this area corresponds to the Great Divide and the Great Escarpment.

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Fig. 2 Faults and joint systems and main drainage in study area.

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Stress orientations and seismicity in Australia have been modelled and reveal a

north-northeast to south-southwest trending stress-field in the region of eastern to

southeast Queensland (Cuthbertson, 1990; Hillis, 1998; Hillis et al., 1999; Hillis and

Reynolds, 2000; Zhao and Müller, 2001; Reynolds et al., 2002; Hillis and Reynolds,

2003; Reynolds et al., 2003). A strong northwest trend is clearly evident within

structure and distribution of the rock units located in southeast Queensland and is

related to the late Palaeozoic – Early Mesozoic convergent margin setting. Seismicity

monitoring over the past 130 years has recorded 56 earthquakes of >2 magnitude in

the region, of which 17 were >3 magnitude and 2 were >5 magnitude (ESSCC 2006).

Many epicentres associated with these earthquakes align in discrete zones

(Hodgkinson et al., 2006a), some of which correspond to known structural

discontinuities.

Geological History

The Australian continent is situated wholly within the Indo-Australia Plate. The

geology of southeast Queensland (Fig. 3) developed primarily from a complex series

of compressional and extensional events from the late Palaeozoic onwards. During

the Late Carboniferous, when the Australian continent was part of Gondwana, an

Andean-type volcanic chain (the Connors-Auburn Volcanic Arc), a central forearc

basin (the Yarrol Basin) and an accretionary prism in the east (Wandilla Slope and

Basin) developed in association with a west-dipping subduction zone (Day et al.,

1978; Plumb, 1979; Murray and Whitaker, 1982; Day et al., 1983; Fergusson and

Leicht, 1993). These structures formed the northern sector of the New England Fold

Belt. Shortening and deformation of the accretionary prism and local obduction of

oceanic crust occurred (Day et al., 1978; Plumb, 1979), which led to low grade

metamorphism and uplift in the southeast Queensland sector of the New England

Fold Belt (for example Fleming et al., 1974; Cranfield et al., 1976; Holcombe, 1978;

Murphy et al., 1979; Murray et al., 1979).

During the Early Permian, andesitic volcanism resumed (Day et al., 1978;

Day et al., 1983). The convergent tectonic regime persisted through the remainder of

the Permian and most of the Triassic. Associated backarc and forearc subsidence

caused widespread shallow seas to form and new sediments were deposited on the

earlier Carboniferous metamorphosed terranes. Thick sediments accumulated in the

Esk Trough and Brisbane Valley in the Early Permian (Northbrook Beds) and

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Middle Triassic (Esk Group). The old accretionary wedge was intruded by small

intermediate to felsic plutons whilst offshore a new subduction zone became active

(Willmott, 2004). During the Middle to Late Triassic an extensional event lead to

further volcanics, granite intrusions and initiation of the Ipswich and Tarong basins

(Evernden and Richards, 1962; Webb and McDougall, 1967; Cranfield et al., 1976).

Uplift and the creation of mountainous terrain followed (Cranfield et al., 1976;

Plumb, 1979; Willmott, 2004).

From the Late Triassic to Early Cretaceous, extensional epicratonic basins,

such as the Clarence-Moreton, Nambour and Maryborough basins formed and

accumulated braided river, paludal and deltaic sediments (Day et al., 1983).

Approximately 120 million years ago, the eastern fringe of Gondwana began to break

up (Veevers and Evans, 1975; Powell et al., 1976; Branson, 1978; Veevers, 2001;

Willmott, 2004). More importantly, between 70 and 45 million years ago, crustal

doming led to fracturing of the crust and seafloor spreading along the eastern margin

of Australia, and the opening of the Tasman Sea. Significant uplift probably occurred

along the flanks of this rift system resulting in the inversion of the local Mesozoic

basins.

3a) 3b)

Fig. 3 a) Geology of southeast Queensland (after Queensland Government) (2003); b) stable blocks and basins of the Moreton district.

191

Passive continental margins such as the east coast of Australia, are commonly

characterised by broad, high elevation, low-relief plateaux flanking a dissected

coastal belt. Uplift caused by rifting initiates coastal erosion that may create seaward

facing escarpments and coastal plains (e.g. Ollier, 1982; Seidl et al., 1996; Ollier and

Pain, 1997). The Great Divide is considered to be the result of upwarping of the crust

during rifting. To the east of the Great Divide, the Great Escarpment of eastern

Australia, as described by Ollier (1982) can be traced almost continuously along the

east coast of Australia, although in some places such as immediately north of

Brisbane, the escarpment is obscure or absent. Localised subsidence in the Paleogene

saw the evolution of the small Petrie, Oxley and Booval basins, which accumulated

silt, clay, limestone, oil shale and basalt in lacustrine and paludal environments

(Cranfield et al., 1976). Neogene erosion produced the modern, relatively subdued,

topography in the Moreton district (Willmott, 2004). However, as Australia migrated

northwards during the Cenozoic, the study area is considered to have moved over

one or more hotspots causing localised felsic volcanism such as the Glasshouse

Mountains (Jensen, 1903; Jensen, 1906; Stevens, 1971; Willmott, 2004) and mafic

volcanism such as the Main Range and the Lamington Group volcanics (Stevens,

1965; Stevens, 1966) around 25-20 million years ago. Between approximately 6

million and 400,000 years ago, small basaltic volcanoes erupted in the Gayndah and

Bundaberg areas, although the origins of these are not well understood (Willmott,

2004): they do not conform to the southward younging age-trend of other hot spot

related volcanism of eastern Australia (Robertson, 1985; Sutherland, 1985;

Sutherland, 2003). Since this time, erosion and deposition has continued and

siliciclastic deposits have accumulated on flood plains, estuaries, deltas, spits and

sandbars. The coastal plain is largely developed on Triassic to Jurassic mudstones

and sandstones (for example the Kin-Kin Beds in the north and Landsborough

Sandstone in the central coastal region) and Devonian-Carboniferous metamorphics

(the Bunya Phyllite and the Neranleigh-Fernvale Beds in the Brisbane region).

Neogene deposits are found throughout the coastal area.

PREVIOUS WORK

Taylor (1914), related the river patterns of eastern Australia to structural geology,

explaining that westward migration (coastal retreat) of the Great Dividing Range

caused headwaters of westward-flowing streams to be captured and reversed. The

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physiography of the Brisbane River and surrounding catchments has been described

by several workers who generally concluded that local escarpments are shaped by

erosion and not faults; structural lines of faulting, jointing and zones of preferential

weathering in the area moderately coincide with drainage patterns (Marks, 1933;

Beckmann and Stevens, 1978). An extensive geomorphological review that covered

a large portion of our study area (Sussmilch, 1933), considered river channel

positions, although not drainage patterns per se. Sussmilch described the general

geomorphology and discussed the relationship between the complex series of horsts

separating the continuous high western plateau from the eastern coastal plain. In his

review, Sussmilch first described the Brisbane Gap, a low-lying area between the

D’Aguilar and ‘Tambourine’ (now Beenleigh) Blocks. He observed that the main

drainage through the Brisbane Gap does not flow along the central axis of this

domain and inferred that the ‘Gap’ was probably not solely an erosional feature. He

suggested that the Brisbane Gap is of tectonic origin and that the northern boundary

is a fault-scarp along the southern margin of the D’Aguilar Block and its southern

margin may also be a line of east-west faulting, previously suggested by Denmead

(1928). In his review, Sussmilch also observed that the Stanley River flows in a

general southwest direction to join the upper Brisbane River near Esk, despite it

starting close to the coast, but he did not provide an explanation for this atypical

‘counter-coastal’ drainage orientation.

Beckmann and Stevens (1978) suggested that due to back-cutting during

the late Miocene-early Pliocene, drainage was reversed along the majority of the

Stanley River. This may have been assisted by slight tilting to the west although

explicit evidence was not available to substantiate this hypothesis. They also

suggested that, at this time, several coastal rivers, such as the Caboolture and Pine

Rivers, may have previously flowed into the Brisbane River and now discharge

directly into Moreton Bay. A brief review of drainage in the Pine Rivers catchment

defined it as being fault controlled and suggested that the North Pine Fault, which

trends approximately northwest, is responsible for the elongate shape of the

northwest trending North Pine River catchment (Hofmann, 1980). In the Bundaberg

area, Landsat images clearly show a major north-northwest/south-southeast trend in

ridges and valleys across the region (Childs, 1991) and the main ranges and drainage

systems in that area also display a strong trend corresponding to geological structure.

The geomorphological evolution of southeastern Australia has been related to

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geological events that occurred episodically over a vast time scale. As tectonic

movement is part of a dynamic, on-going process, the continued interruption to

homogenous and consistent erosion will prevent the mature peneplain stage from

being reached and instead cause complex evolution of the landscape (Ollier, 1995).

The dynamic process, or ‘evolutionary geomorphology’, was found to be responsible

for the anomalous drainage pattern of the Clarence River on Australia’s east coast

(Haworth and Ollier, 1992); the ‘barbed’ drainage pattern suggests stream reversal

whereby part of the ancient west-flowing Condamine River has been trapped by the

east-flowing Clarence River.

Drainage character in relation to the Great Divide and Great Escarpment

has been described by several workers. In summary, drainage to the west of the Great

Divide is relatively simple and commonly dendritic whereas to the east more

complex patterns exist (e.g. Ollier and Haworth, 1994; Ollier and Pain, 1997).

Drainage between the Great Divide and the Great Escarpment is often highly

complicated (Ollier and Stevens, 1989). In some parts of eastern Australia, drainage

to the east of the Great Escarpment may rise near the coast and turn inland before

flowing out to sea (Ollier and Pain, 1997) and some rivers flow parallel to the coast,

possibly following major structural lineaments (Beckmann and Stevens, 1978).

However, some drainage east of the Great Escarpment in Queensland, is simple,

flowing directly to the Pacific (e.g. at Rockhampton, Ollier and Stevens, 1989).

It is clear that geological structure and physiography correlate strongly in

southeast Queensland (Jones, 2006). However, some rivers and escarpments in this

region show regular patterns that do not correspond to mapped structural features.

Preliminary work has shown that zones of low magnitude earthquakes occur

throughout the region and commonly correspond to the positions of features such as

rivers and faults (Hodgkinson et al., 2006a). Monitoring of seismicity in the region is

sparse by international standards, having only operated over short periods of time

since the late 1800’s. Earthquake monitoring and prediction modelling is currently in

progress at the Earth Systems Science Computational Centre (ESSCC) at the

University of Queensland.

Few geomorphological analyses have been undertaken to identify the

relationships between known faults, landscape features and neotectonism in the

region. Similarly, drainage patterns represented in southeast Queensland, and their

degree of correlation with known structures, have not previously been described.

194

195

This study aims to provide a regional-scale review of drainage patterns, and discuss

their relationship with known and potentially concealed geological features.

METHODS AND TERMINOLOGY

Along the eastern coast of Queensland throughout the Late Cretaceous and Cenozoic,

highlands lay to the west of the region and the lowlands and ocean lay to the east. In

this paper, we assume that drainage would be sourced from the highlands and flow

towards the coast (generally west to east). Deviations from this model are likely to be

controlled by processes and features such as zones of differential weathering, faults,

synforms or antiforms. Drainage trends that coincide with known geological

structures are classified in this paper as ‘predictable’ and drainage that shows a

distinctive pattern but is not associated with known geological features is described

as ‘anomalous’.

River systems of southeast Queensland were analysed and compared to

available geological data to identify both predictable (Zernitz, 1932; Twidale, 2004)

and anomalous drainage patterns. Digital topographic, geological and drainage maps

of southeast Queensland were obtained from the Department of Natural Resources,

Mines and Water (Queensland Government, 2003). Using ArcGIS 9 software, a

digital slope-map was created. Earthquake epicentre data were obtained from the

Earth Systems Science Computational Centre at The University of Queensland

(ESSCC, 2006). The digital maps and data were integrated and analysed in ArcGIS 9

to identify anomalous drainage patterns in the region and to identify correspondence

between gross drainage patterns and geological units, structures and earthquake

epicentres.

RESULTS AND DISCUSSION

A large number of rivers in southeast Queensland display patterns that suggest

controls by geological features such as lithotypes, faults or folds. To illustrate the

diversity and distribution of drainage patterns in the study area, several

representative examples have been selected and described here (Fig. 4a).

Fig.

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‘Predictable drainage patterns’

Examples of ‘predictable’ drainage patterns are expressed by some degree of

regularity in their tributary orientations. It is assumed that some aspect of the

bedrock geology or regional slope controls the development of these patterns.

Several distinct drainage patterns of this type are evident in the study region and

examples are presented here to illustrate their diversity. Patterns may vary depending

on the scale of analysis (Hodgkinson et al., 2006b). Few drainage systems display a

single type of drainage pattern throughout.

Dendritic drainage develops where multiple factors influence channel

formation or where drainage has evolved on a relatively uniform regional slope.

These areas may lack significant structural control (Zernitz, 1932) but the drainage

network is, nevertheless, predictable in its form. Dendritic drainage is fairly common

in the region although it is not represented in any large-scale river systems and

generally occurs in small systems or as sub-units of large drainage systems in which

other patterns predominate (Fig. 4b).

Parallel drainage patterns are common in broad-scale river systems such as

the upper reaches of the Brisbane River where faults commonly correspond to

drainage orientation (Fig. 4c). However, in the southwest of the area, where parallel

channels drain away from the crest of the Great Escarpment (Fig. 4d), the few known

faults are perpendicular to drainage. Many basement faults in the southwest of the

area may be concealed by Cenozoic basalts and thick regolith cover. Earthquake

epicentre corridors in the upper Brisbane Valley (Fig. 5) are typically parallel to the

channels suggesting that these faults remain active and may be influencing modern

drainage. Although not closely associated spatially, a strong parallel southwest-

northeasterly drainage trend is apparent across the region including (from south to

north) Teviot Brook, Logan River, the southern trunk of the Brisbane River, the

upper Stanley River, Yabba Creek and Kandanga Creek (Fig. 1). Parallel drainage is

also common at a finer scale, such as to the east of the D’Aguilar Range (Fig. 4e),

where channel orientation may be largely controlled by rock fabric (Hodgkinson et

al., 2006b) and faulting. Parallel drainage is also evident on the major sand barrier

islands where Quaternary parabolic dunes are the major influence on topography

(Fig. 4f).

A radial drainage pattern occurs on a broad scale, on the outer flanks of the

Mount Warning shield volcano in the southeast of the region (Fig. 4g) and at a finer

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scale in several highland sites such as Mt Nebo, Mt Glorious (Fig. 4h) and Mt

Perseverance (Fig. 4i). A centripedal drainage pattern occurs within the Mt Warning

shield volcano inner escarpment and basin (northern New South Wales) and is also

weakly developed at a smaller scale on the deeply weathered Samford batholith in

the east (Fig. 4j).

Angular and trellis (or rectilinear) drainage patterns occur across the region at

various scales. On a broad scale, the Brisbane River system can be described as a

combination of both styles, and the Mary River in the north, has similar features (Fig.

2). At an intermediate scale the North Pine River in the east (Fig. 4k) is also

rectilinear in style and numerous smaller rivers display this pattern throughout the

region. The Brisbane River and North Pine Rivers both closely follow faulted and

earthquake-prone zones. However, some linear reaches of the Brisbane River lack

mapped faults and these may be the sites of concealed structural features. The

numerous meanders of the Mary River (Fig. 4l) may be controlled by the strong

northwest-southeasterly and northeast-southwesterly trends of small faults in the area

(Fig. 2) but these are not significant enough to control the location and orientation of

the river system as a whole. There are relatively few recorded earthquakes along the

Mary River axis (ESSCC 2006) although earthquake epicentre corridors correspond

to some upper tributaries and a similarly orientated corridor (Fig. 5) is recorded off-

shore (ESSCC 2006; Hodgkinson et al., 2006a). Other parts of the Mary River

system are aligned with larger faults (Fig. 2).

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Fig. 5 Dominant earthquake corridors in the study area defined by the criteria of Hodgkinson et al. (2006a). As position and depth to earthquake may be inaccurate, broad ‘corridors’ were defined to allow for location errors. The corridors show there is some alignment of earthquakes, several of which correspond to known faults. Earthquake data span past 130 years. Data source: Earth System Science Computational Centre (ESSCC, 2006)

‘Anomalous drainage’

Although the Mary River drainage pattern (Figs. 2, 4l) has been described above as

rectilinear, suggesting structural influence, the northward course of the main channel

is not coincident with any known major structural feature and is, therefore,

anomalous. However, the shore-parallel course of the Mary River may have been

incised prior to down-warp, as has been identified in some other rivers, such as the

Shoalhaven River in New South Wales (Ollier and Pain, 1994), and may therefore

represent antecedent drainage. A strong element of westward drainage (away from

the coast) is evident in the eastern part of the Mary River catchment, the control of

which is not obvious and, therefore, anomalous. To the south of the Mary River

catchment, similar westward drainage persists and is controlled by a drainage divide

extending approximately 120 km in length and situated 10 - 30 km from the coast

(Fig. 6a). This drainage divide occurs at relatively low elevation (less than 100 m

above sea level in some places and not exceeding 200 m above sea level for the

majority of its length) from the area of the Mary River catchment in the north, to the

North Pine River catchment in the centre of the region (hereafter designated as the

‘coastal drainage divide’: Fig. 6a, b). Although the coastal drainage divide exceeds

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300 m above sea level in some places, the majority of the divide is less than 150 m

above sea level in elevation. The coastal drainage divide crosses several geological

units of varying lithology that are of Triassic to Jurassic age in the northern and

southern sectors of the divide, and of Permian age in the central part. No known

faults or other geological structures correspond to the position of the coastal drainage

divide and we, therefore, designate drainage immediately to the west of this feature

as anomalous.

To the west of the divide, several small river channels display evidence of

stream-capture and align with steams to the east of the divide where they may have

previously flowed (Fig. 6b). For example, in the upper eastern reaches of the

Brisbane River system, the Stanley River is sourced in the Blackall Ranges, flows

eastward towards the coastal drainage divide, then turns abruptly southwest over a

relatively fault-free area, towards the faulted and earthquake-prone area at the north

end of Lake Somerset, after which it joins the Brisbane River. The course of the

upper Stanley River, as it approaches the coastal drainage divide, aligns with the

course of Coochin Creek to the east of the divide. As well as anomalous drainage and

stream-capture, we propose that the upper section of the Stanley River has undergone

reverse drainage. Obi Obi Creek also initiates in the Blackall Ranges, flows in an

easterly direction then turns north at the coastal drainage divide (Fig. 6b). It flows

parallel to the divide for approximately 5 km then turns to the northwest and

continues in this direction until it joins the Mary River at Kenilworth. The east-

flowing reach of Obi Obi Creek aligns with the Mooloolah River to the east of the

divide. Faults or preferential weathering do not appear to control the changes in

direction of the creek and we propose this anomalous drainage is controlled by

flexure along the coastal drainage divide and capture of the upper Mooloolah River.

Similarly, to the north, Six Mile Creek commences by flowing towards the coast but

turns northwards and then northwest at the drainage divide and continues in this

direction until it reaches the Mary River, south of Gympie (Fig. 6b). To the east of

the divide, Ringtail Creek aligns with the east-flowing reach of Six Mile Creek. This

may represent a third case of eastward flowing stream headwaters being captured by

northward or westward flowing rivers. A linear depression runs from the highland in

the northwest, through the area of Kilcoy and towards the Bribie Island region, that

may be the pathway of an ancient drainage system (Fig. 7). This valley (hereafter

designated the ‘Kilcoy Gap’) begins with an orientation that is conformable to the

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northwest-southeast trend of faults in the upper Brisbane Valley but turns to the east

and descends through foothills towards the modern coastal plain and Bribie Island.

Several modern watercourses are situated within this depression including parts of

the upper Stanley River draining to the west, and Coochin and Mellum Creeks

draining to the southeast and east. Extensive unconsolidated sediments flank these

streams.

b)a)

.eps version

Fig. 6 a) Drainage networks in northeastern part of Moreton district showing the ‘coastal drainage divide’ (heavy line) and locations of Cenozoic volcanics; b) 3 examples of potentially reversed and captured drainage along the coastal drainage divide. See text for inferred causal mechanism.

The depression is largely developed on the Triassic Neurum Tonalite and the

latest Triassic to Early Jurassic Landsborough Sandstone. Several late Palaeozoic

volcanic and metasedimentary units are also exposed within the depression. One site

near the northern margin of the valley (grid ref. 152° 50E' 26", 26° 50' 5"S) reveals

previously unmapped, poorly consolidated, coarse-grained channel-fill deposits,

incisively overlying Palaeozoic andesite along a modern interfluve approximately

260 m above sea level. Sediments in this exposure are oxidized and have not been

dated but their relatively unconsolidated state suggests that they are Cenozoic in age.

The deposits provide evidence that at least one ancient river channel has been

preserved within this broad valley by topographic inversion (Fig. 8). However, the

201

scarcity of such sites suggests that erosion of similar channel fill deposits together

with a substantial quantity of volcanic and metamorphic bedrock has occurred in the

Kilcoy Gap region.

Fig. 7 Topographic map detailing the broad valley structure between t-Kilcoy and the Glasshouse Mountains (The ‘Kilcoy Gap’) and the righ

angled bend in the Brisbane River near Ipswich.

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The morphology of the Kilcoy Gap, suggests it may have been a drainage

system

. 6) is, for the main part, a

low-rel

descending from highlands in the northwest to the coast in the east. The

Stanley River, which is situated within this depression, presently flows away from

the coast and the coastal drainage divide, and it may have experienced reversal of

drainage within a previously major river channel. As mentioned above, Beckmann

and Stevens (1978), suggested the reversal of the Stanley River, the mechanism for

which they proposed was backcutting of the Stanley headwaters across a previous

divide near Kilcoy. However, backcutting alone is unlikely to have caused the

reversal of drainage and we suggest the process was combined with one of stream-

capture, enhanced by westward tilting. Beckmann and Stevens (1978) also suggested

tilting to the west but were unable to substantiate this. From this study, we invoke a

mechanism involving doming or tilting along the coastal drainage divide. The cause

of doming or flexure along this line may be the late Oligocene to early Miocene

emplacement of the Glasshouse Mountains volcanic plugs and a series of more

isolated coeval felsic and mafic intrusives along the coastal plain to the north. The

changes in direction of Obi Obi Creek and Six Mile Creek, together with the

alignment of their eastward flowing reaches with other streams east of the divide,

provide further evidence that flexure along the coastal drainage divide has forced

stream-capture and potentially stream reversal. Stream-capture is common elsewhere

along the eastern Australian highlands such as within the Clarence-Moreton Basin,

northern New South Wales (Ollier and Haworth, 1994).

Topographically, the coastal drainage divide (Fig

ief feature throughout its length. If the feature is not currently undergoing

uplift, given sufficient time it may eventually erode and retreat westwards allowing

coastal streams to re-capture the headwaters of some westward flowing systems.

Given that no major streams flow from the Great Divide to the coast, in the area from

Brisbane to the northern limit of the study area, we propose that the coastal drainage

divide described here, is a relatively young feature generated by Cenozoic uplift or

tilting. Two major mechanisms may be responsible for the uplift. Firstly, uplift may

have been generated along a deep-seated, unmapped fault, blind thrust, or gentle

flexure of the crust, caused by the current compressional tectonic regime. A series of

shore-parallel, gently undulating synforms and antiforms or block faulting caused by

compression would explain both the drainage divide and the shore-parallel drainage

orientation of the Mary River. Similar undulating topography associated with gentle,

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Late Cretaceous folding and faulting occurs in the central Maryborough Basin,

immediately north of the study area (Ellis, 1966). If this model is correct, the

processes that generated the coastal drainage divide may currently be inactive as few

earthquakes have been recorded in the vicinity of this feature. Although the coastal

drainage divide is not perpendicular to the first-order (plate-boundary controlled)

northeast-southwest stress orientation in the region (e.g. Cuthbertson, 1990; Hillis et

al., 1999), it may be attributable to local, second-order stress variations, which occur

throughout Australia, caused by structural, topographic and density variations in the

lithosphere (Hillis and Reynolds, 2003). Late Cenozoic stresses have caused

extensive flexures and faults in the landscape in diverse parts of the continent such as

the Flinders Ranges (Celerier et al., 2005), the Carnarvon Basin in Western Australia

(Hocking, 1990) and the Gippsland Basin, Victoria (Nelson and Hillis, 2005).

Secondly, some parts of the divide closely coincide with the location of small areas

of mid-Cenozoic felsic to mafic igneous intrusions (Fig. 6a). Thermal doming and

emplacement of magma may have caused uplift of the crust around these zones,

creating a linked meridional zone of flexure. The coastal drainage divide has a

topographic expression that is barely perceptible in places and does not precisely

coincide with the position of the volcanics for the majority of its length. The gently

scalloped or sinuous pattern of the divide over much of its length may be explained

by intense subtropical weathering and erosion during the past 20 million years.

Dramatic realignment of river segments is evident elsewhere in southeast

Queensland. The southern section of the Brisbane River shows an abrupt right-

angled change in orientation towards the northeast in the vicinity of Ipswich and then

passes in a relatively straight line towards the coast through the Brisbane Gap

(Sussmilch, 1933; Fig. 7). No mapped structural feature aligns with this sharp

reorientation. Although few faults are mapped in this area (e.g. Queensland

Government, 2003), the lower segment of the Brisbane River coincides with a zone

of low magnitude earthquakes (Fig. 5) and this may be evidence of a concealed

structural feature (Hodgkinson et al., 2006a). Denmead (1928) and Sussmilch (1933)

hypothesised that the Brisbane Gap is bounded by faults to the north and south.

However, Cranfield et al. (1976) suggested a single major fault [the hypothetical

Buranda Fault of Bryan and Jones (1954)] separates the D’Aguilar and Beenleigh

Blocks. Some older maps (e.g. Cranfield and Schwarzbock, 1971) include this

inferred structure, along the southern margin of the South D’Aguilar Block. A major

204

concealed fault in this location would explain both the linear NE orientation of the

lower Brisbane River and the lateral offset of the exposed Palaeozoic basement rocks

to the north (South D’Aguilar Block) and south (Beenleigh Block) of the river.

Several earthquake epicentres over the last 150 years, plot in this area (ESSCC 2006;

Fig. 5), suggesting that a major geological discontinuity indeed exists along this

corridor. Teviot Brook and the upper Logan River flow in a similar orientation to the

lower Brisbane River (Fig. 1), and may be aligned along parallel structural

discontinuities although they both lie in an area where few faults or earthquakes have

been recorded.

Not all stream-capture features and drainage patterns in southeast Queensland

were necessarily generated by differential weathering or neotectonism in the strict

sense. Some drainage patterns have clearly been influenced by the emplacement of

Quaternary coastal aeolian dune systems (Fig. 4f); other streams are likely to have

been diverted or initiated by the emplacement of Cenozoic mafic lava fields (Fig.

6a), and some watercourses may have migrated to their current positions simply due

to autogenetic factors. The lower reaches of the Noosa River provide a good example

of the last of these processes. Aerial photography reveals the existence of an ancient

large meandering channel located around 2 km to the east of the current position of

the lower Noosa River (Fig. 9). This feature likely represents the ancient position of

the lower Noosa River until an avulsion event in the relatively recent past redirected

the main channel into Lake Cooroibah and thence southwards to Tewantin. The

lower part of the Noosa, and other major southeast Queensland river valleys, are

characterized by broad floodplains (kilometres to 10s of kilometres wide). Hence

episodic avulsion events can result in wide-spaced repositioning of the major channel

within the lower alluvial valley. Therefore, it is important to consider drainage

patterns upstream, if assessing potential controls on river positions in southeast

Queensland.

205

Fig. 8 Road-cut at Cedarton showing fining-up (conglomerate to medium grained sandstone) channel fill deposits resting erosively on Permian andesites located on a modern interfluve interpreted to represent inverted mid-Cenozoic topography. Thick line represents basal erosion surface. Thin lines represents scour surfaces within the channel fill. Geologist for scale approximately 1.8 m.

a) b)

Fig. 9 Aerial photograph of Noosa River area a) showing current river channel flowing through Lake Cooroibah; b) ancient abandoned channel highlighted to the east of current river position.

CONCLUSIONS

The dominant controls on modern drainage patterns in southeast Queensland are

differential erosion of lithotypes and entrapment by geological structures, together

with late Cenozoic volcanism. These processes are also clearly evident in other parts

206

of eastern Australia (Holdgate et al., 2006). This study has identified a range of

drainage patterns at various scales across the region. Although short, high-energy

sub-tropical catchments with eastward flowing streams may be expected in a setting

such as southeast Queensland, it is evident that far more complex drainage patterns

and drainage histories exist in this region. Several anomalies in expected drainage

were noted. Some of these are readily explained by differential weathering and

erosion of bedrock lithotypes or by alignment with mapped ancient structural

features. However, the genesis of other drainage anomalies remains ambiguous.

Previous authors recognised that anomalous river orientations and drainage patterns

may be caused by active faults or folds or by catastrophic climatic, tectonic or

extraterrestrial events (Twidale, 2004) and that dendritic drainage patterns appear to

indicate a lack of structural control (e.g. Zernitz, 1932; Ollier and Haworth, 1994).

Both the scarcity of dendritic drainage, coupled with the multitude of other drainage

patterns identified in this study, suggests that geological structure imposes major

controls on drainage in this region.

Faults and other geological structures have a profound influence on the

geomorphology of the region. The Kosciusko uplift, which may have been

responsible for some uplift in this region (Sussmilch, 1933), has received little

attention in modern literature, but recent work in NSW has prompted a renewed

interest in the nature, timing and extent of this event (Kohn et al., 1999; Sharp,

2004). Further comparisons between the NSW highlands and southeast Queensland

may clarify the influence of this phase of tectonism. The lower course of the

Brisbane River, running parallel to the southern edge of the D’Aguilar Block, is in

close proximity to a belt of recent earthquakes and the drainage in this area may be

experiencing ongoing adjustments due to neotectonism. Other areas, such as along

the coastal drainage divide, require better structural and seismicity data before the

influence of neotectonics can be confirmed or excluded.

This study clearly shows that structural features and lithological variations

have played a major role in the development of the Moreton District drainage.

Therefore, although some antecedent drainage may persist, it is highly likely that

anomalous drainage features are also controlled by concealed structures or subtle

lithological differences. Future seismic traverses may resolve this issue and further

analysis of earthquake data such as focal mechanisms of recent and future

earthquakes in the region would better constrain this inference. Although the geology

207

of the area is relatively well-mapped by Australian standards, higher resolution

mapping may also provide a better understanding of the genetic controls on channel

orientation across the region.

ACKNOWLEDGEMENTS

We wish to express our appreciation for the rigorous reviews and valuable

suggestions of Dr Colin Pain and Dr Malcolm Jones. We thank Dr Dion Weatherley

and Col Lynam of ESSCC, University of Queensland, for important collaborative

discussions and for providing earthquake data. We are also grateful to Dr Andrew

Hammond for reviewing this paper and for enlightening debate, Bill Ward for

informative local field trips, and Jonathan Hodgkinson for invaluable support and

assistance in the field.

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Conclusions

The multi-criteria analytical approach used in this project has confirmed that

underlying geological features control large components of the southeast Queensland

landscape. In its entirety, the research covers a far greater area both in extent and

scope, has utilized more geological information, and compares more datasets than

previous studies. In turn, the work has yielded significant new findings for southeast

Queensland, in addition to providing a new stream-ordering system and

geomorphological knowledge that may be applied to other regions with similar

tectonic settings.

In summary, the significance of this work includes the following:

• The analysis presented in paper 1 is the first study of its kind that

encompasses a whole sub-catchment that is situated on two differing,

juxtaposed meta-sedimentary rock types. Additionally, an entirely new

stream-ordering system has been presented in paper 1 that, unlike other

ordering systems, importantly retains a topology that is meaningful in terms

of stream importance throughout the drainage system.

• An assessment of earthquake epicentre locations in relation to geological

structure of southeast Queensland is presented in paper 2, which is the first

assessment to have been performed utilising the most complete earthquake

database currently available. It is also the first analysis of its kind to have

been performed for this region in more than 15 years.

• The regional-scale geomorphological review of southeast Queensland

described in paper 3 has integrated a range of datasets using GIS at a scale

and extent that has previously not been achieved. The work has identified

some unique findings for the region that have applicability to understanding

landscape development in similar tectonic settings globally.

Paper 1 has been cited by Ribohni and Spagnolo (2008) as one of the few studies

globally that has dealt with the influence of both the different rate of rock uplift and

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the selective erosion processes along fault and fracture planes. The three published

papers provide a continuous study of multiple aspects of the endogenic controls of

geomorphology in southeast Queensland. Together, they provide methods, examples,

results and conclusions that may be used for geomorphological studies in other

geological and geographic settings globally.

Summary of results and major findings

This study has identified that the morphology of southeast Queensland is the

cumulative result of multiple tectonic events and the region is not analogous to all

other passive margin settings. The study has identified various geological events over

the past 350 million years that have influenced, and in some cases continue to

influence the evolution of the modern landscape in the region. Integration of the

analytical tools used here, with the different datasets and applied at multiple scales,

has shown that, although surface processes are on-going, geological controls from

various events in the past continue to leave their mark on the landscape.

Hypothesis 1

“Complex geological fabric of metamorphic rocks of southeast Queensland

has control over the orientation of streams at the sub-catchment scale”

The first hypothesis that was tested aimed to identify the extent to which streams

show alignment with the underlying rock fabric within a catchment that had

developed on two juxtaposed metamorphic rock types.

The findings identified that:

• the orientation of low order streams are the least strongly controlled by rock

fabric and faults;

• the orientation of middle order streams are mainly controlled by fine-scale

rock fabric features, particularly foliation and joints in phyllitic bedrock;

• the orientation of higher order streams are mainly controlled by major faults.

In conclusion from testing this hypothesis, low order streams tend to remain dendritic

until they have down-cut to reach bedrock and once this is achieved, the orientation

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of rock fabric such as cleavage and faults can control the location and orientation of

drainage channels. The channel controls and stream ordering system used in this

study are discussed below.

The control of streams by faulting is a well-known phenomenon and although

faults in southeast Queensland are typically ancient, it was important to ascertain

whether the present landscape may be controlled by active tectonism or only by

geological juxtapositioning generated by very ancient fault movements. Therefore,

the second hypothesis was tested.

Hypothesis 2

“The location of recent earthquakes in southeast Queensland align with

geomorphological features such as scarps, mountain ranges and valleys.”

The second hypothesis aimed to identify whether earthquake epicentres show spatial

alignment and if so, whether they correspond with any geological and

geomorphological features (including scarps, river valleys and highland lineaments).

The information was required in order to consider whether neotectonics currently

plays a role in the evolution of the landscape.

The findings identified that:

• low-magnitude earthquakes in the region cluster in preferred areas;

• there are several distinct corridors where earthquake epicentres align with

geomorphological and geological structures;

• additionally, the location of some earthquake epicentres occur in a linear

‘pattern’ that, although in some places correspond with ancient faults, in other

places do not align with known faults or other structural geology.

In conclusion from this part of the study, although the geomorphology of some

regions clearly corresponds with ancient controls such as the outcrop distribution of

Palaeozoic rock units and large, ancient fault systems, other areas may be influenced

by some neotectonic control - a function of stress induced by the present compressive

regime. Earthquakes presently occurring in the region are not likely to cause surface

rupture or displacement. Nevertheless, they may generate subsurface fractures within

the rock, which can influence the movement of fluids, enhance local weathering and

offer sites for preferential erosion. Additionally, although the low magnitude

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earthquakes may be releasing stress periodically along ancient faults, some

earthquake activity is also related to unknown structures that do not presently have a

recognised surface expression and may require further investigation to resolve their

character.

Hypothesis 3

“Drainage networks across southeast Queensland show repeating, aligned and

anomalous patterns that are controlled by a range of geological structures of

varying age.”

The ultimate aim of testing hypothesis 3 was to assess how the regional scale

drainage orientations and patterns of southeast Queensland have been influenced by

the location of earthquake corridors, and the distribution of geological structure,

lithostratigraphy, and igneous intrusions of various ages and origins.

The main findings identified that:

• drainage patterns of the majority of large river systems in the region are

characteristic of geologically controlled networks;

• drainage channel location in the region is commonly controlled by faults and

zones of differential weathering on regional and localised scales;

• some large drainage systems in the region align with earthquake corridors

and large ancient fault systems;

• uplifted blocks have caused steep highland drainage proximal to the coast;

• some low order streams have been diverted;

• there are many incised, meandering streams both in low- and highland areas;

• the ‘coastal drainage divide’, first described in this work, has a significant

effect on drainage in the region, north of Brisbane;

• a large valley is first described in this work (‘the Kilcoy Gap’) that displays

evidence of reversed drainage;

• despite the eastern Australian coast being a passive tectonic margin, drainage

patterns are generally atypical of such a setting.

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The results of paper 3 provide evidence to conclude that drainage patterns

have been influenced by structural and lithological features. These have been

emplaced by a long series of tectonic events since the late Palaeozoic that include

folding, faulting, metamorphism and volcanism within convergent margin

compressional, passive margin extensional, and intra-plate hot-spot volcanism

related tectonic regimes. The presence of many incised meandering streams, both in

low- and highland areas, suggests there has been relatively recent uplift. The coastal

drainage divide is identified by a lack of drainage directly to the coast from the

shore-parallel highlands. This feature, previously unidentified, lies to the east of both

the Great Divide and the Great Escarpment. It is generally of low-relief,

approximately 120 km in length, and is situated 10 to 30 km from the coast in the

northeast of the study region, and has a significant influence over drainage in the

region. Furthermore, some streams initially flow from the dominant highlands

towards the coast, then turn away from the coast where they approach the subtle

coastal drainage divide. This is discussed further, below. The divide crosses several

geological units of Jurassic, Triassic and Permian ages. No known structure or

geological unit corresponds to the position of this feature but various potential

structural controls are hypothesized below.

A major fault through the Brisbane region that was previously mapped (the

Buranda Fault) but later removed from published maps, may be worthy of further

investigation as its presence might explain a sharp, northeastward bend in the

Brisbane River in the Ipswich area, and may additionally explain the offset of

Palaeozoic rock units to the northwest and southeast of Brisbane. The Kilcoy Gap

first described in paper 3, may have previously drained directly to the coast and has

since experienced reverse drainage due to the mechanism that has generated the

coastal drainage divide. Primarily, paper 3 is an example of how a detailed and

regional-scale analysis of drainage patterns in relation to geology can identify both

the main controls over a landscape, and anomalies that may provide new information

towards understanding the evolution of an area’s physiography

Additional findings

To assess whether fine-scale geological features control morphology, paper 1

analysed rock fabric in relation to drainage patterns at a sub-catchment scale. This

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analysis required comparison of topologically similar streams across the network.

Testing of the available stream-ordering systems identified that they each

insufficiently identify topologically similar stream reaches and do not provide a

satisfactory solution for comparative analysis. Therefore, a new stream ordering

system was devised, presented and used for the analysis in paper 1.

Further to the main findings of paper 2, the results also indicate that there

may be a continuous accumulation and release of stress in some regions

preferentially to others, such as near water storage reservoirs, although there was no

clear indication whether the events were reservoir-induced or whether there is a bias

in the dataset due to the clustering of seismographs presently situated around dam

sites. As the findings may be significant for the purposes of hazard mapping, it was

concluded that further geological and geophysical mapping may identify additional

structural and lithological discontinuities where earthquakes cluster along zones with

no obvious surface morphological expression. Additionally, it was concluded that

more detailed earthquake monitoring would better constrain earthquake locations and

the correlation between epicentres and known structures may be improved.

Furthermore, small faults (typical of southeast Queensland) can eventually coalesce,

forming larger fault traces, along which, rivers are likely to preferentially flow. This

process may be slow and difficult to monitor in real-time, but does not preclude it

from being a geologically derived landscape control.

The work undertaken in paper 3 identified that, despite the eastern Australian

coast being a passive tectonic margin, there is a lack of regional subsidence and as

previously mentioned, the drainage patterns in the region are generally atypical of

such a setting. Some streams run parallel to, or away from the coast, rather than

flowing as short streams from the shore-parallel highlands directly to the coast as is

typical for such tectonic settings in other parts of the world. In paper 3, the results

also indicated that, although some river patterns correspond with and are controlled

by known geological structure, not all drainage is controlled in this way. Some

drainage patterns, although having linear or angular characteristics of geologically

controlled systems, do not correspond with known geological structure, suggesting

that they may be controlled by unmapped or concealed structures.

Papers 1, 2 and 3 provide multiple forms of evidence at varying scales that

suggest there are strong endogenic controls on landscape evolution in the study

region. Examples of the multiplicity of geological controls on surface processes can

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be found within small areas. For example, in the Laceys Creek catchment (paper 1),

the phyllitic texture of the rock has a strong influence on the orientation of streams of

a certain magnitude. Flow tends to be directed preferentially along the cleavage, later

incising deeper into the rock and retaining the same orientation as the rock foliation.

In a similar way, fluid preferentially flows along faults, even where the fault

produces no initial landscape expression. Fluid flow along such a plane, even

beneath a thick regolith can gradually cause weathering and widening, and this has

been identified in Laceys Creek (paper 1), and the North Pine and upper Brisbane

rivers (paper 3). A corridor of earthquakes occurs along the orientation of the

Brisbane River (paper 2), where rock weakening would be expected. These events

may lead to fractures, joints, and possibly small faults, causing the rocks to be less

resistant to water flow and leading to further erosion and widening by the river along

these planar orientations. Paper 3 more fully explored the relationships between

drainage patterns and the location of geological units, faults, structure, highlands and

valleys. At both coarse and fine scales, many parallel and angular stream patterns

exist in southeast Queensland. Although surface water naturally flows away from

areas of high relief, specific flow patterns also show evidence of geological control.

Radial drainage, for example, is well defined from the remnant crests of the Mount

Warning (Tweed) shield volcano, and from the peaks of Mount Perseverance and

Mount Glorious. Centripetal drainage has developed from steep highlands into the

eroded basin underpinned by the Samford Granodiorite that now forms the Samford

Valley. Paper 3 cites many other examples of geologically controlled stream patterns.

However, the geological control of streams that flow inland from the coastal drainage

divide described in paper 3 is not clear. Some of the streams close to the drainage

divide are strongly affected in that they show evidence of diverted drainage. These

are low order and therefore, very probably young, so this work concludes that the

control of the elevated topography may be relatively recent and is discussed at

greater length below. Paper 3 investigated geological control of topography and river

patterns in a broader sense, identifying strong correlations between stream and

highland distributions and known structure, and more importantly identified some

anomalies where geological control is probable but not yet conclusive. This is also

discussed at greater length below.

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Implications for future research

The new stream-ordering system that was presented in paper 1 was found to

be most beneficial for analysing the correlation between channels and small-scale

rock-fabric structures; in itself, the new ordering system is a substantial contribution

to this subject. Use of alternative methods in future research will depend on whether

topology is of importance to the study. Other methods typically designate a stream

order based on a counting system that may not reflect the true topological position of

the stream in the network. Furthermore, the stream order designated to a channel

reach might not be comparable to other streams in a similar position in the network.

The new stream ordering method introduced in paper 1 is better able to compare

topologically equivalent segments of a drainage system. This will benefit any future

study where comparison of similar order streams is being made across a network,

whether this is a comparison of physical properties, orientation or river stage. For

example, if evolution of 3rd, 4th and 5th order streams were being studied to identify

stream-bed gravel resources or expected flood magnitude of an area, it would be

necessary to ensure the orders are equivalent across the network. Otherwise,

variability of processes that operate within each stream order would be excessive.

Previous stream ordering systems that lack topological similarity would therefore not

be practical for this purpose. Comparison of network characteristics becomes more

meaningful by using the new ordering system. For example, for a study of flow

dynamics in streams during a flood cycle, it would be unlikely that all streams in a

catchment could be manually measured. After assigning stream orders across the

whole network using the new ordering system, just a small number of the selected

order streams could then be monitored, in the knowledge that all other streams of that

same order are topologically similar. The similarity allows the results to be used for

forecasting or prediction purposes. First ensuring that stream orders are topologically

equivalent would enable fewer streams to be monitored. If the alternative (previously

established) ordering systems are used, the results may be relatively meaningless.

The research presented in paper 1 is also unique as the study was conducted in a sub-

catchment on metamorphic rock with substantial ground-cover and little outcrop, in

addition to the study incorporating an entire sub-catchment. Previous studies of this

type have focussed on granites, in areas with extensive outcrop and covering only

portions of a drainage catchment.

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The results from this study highlight the importance of identifying the

orientation of fault and fracture planes, irrespective of earthquake magnitudes typical

of an area. This is particularly important because even small faults or joints provide

sites for preferential fluid flow that may eventually cause changes in the morphology

of the landscape. In locations where small seismic events cluster, this may indicate

that rocks are accumulating more stress, or that the rocks there are less able to retain

stress and this should also be considered in similarly focussed, future research.

Other observations and general discussion

Several scarps in southeast Queensland closely parallel the location of

drainage segments. However, some drainage channels, such as the North Pine River

and Brisbane River, are aligned with faults, but not situated close to an associated

scarp, as the stream has eroded and migrated away from the location of the fault.

Differential weathering has also accentuated the scarps where, for example in the

North Pine catchment, the fault divides the more resistant Rocksberg Greenstone and

the less resistant Bunya Phyllite, the latter of which has eroded more readily.

Therefore, although the fault may have been a primary control of the initial location

of the river, the river has then exploited the softer rock and differential erosion has

widened and deepened the location of flow through this area. Scarps spaced radially

around Mount Warning and parallel scarps along the top of the Main Range are

closely situated to stream channels and indicate that there has been down-cutting into

the hard volcanic rocks with little migration of stream channels. Scarps bounding the

edges of the Kilcoy Gap however, are not closely associated with drainage channels

or faulting and potentially represent the edges of an ancient drainage corridor

(alluvial plain), although to the north, the Maleny Basalt may have provided some

protection against erosion in this area. Multiple small, parallel scarps in the

northwestern part of the region, are parallel to the upper Brisbane River and the

Great Moreton Fault system, and may be fault or fracture controlled. Scarps in the

south-central region align in places with the upper Logan River, where differential

erosion has caused scarps along the interface between the Jurassic sediments and the

Cenozoic basalts. The Como and Glasshouse scarps do not coincide with drainage or

fault orientation and represent coastal scarp retreat that occurred at different times,

which is discussed further, below.

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In their review of the Great Escarpment, Ollier and Stevens (1989) stated that

complex drainage occurs between the Great Divide and the Great Escarpment and

simple drainage occurs to the east of the escarpment. The coastal drainage divide lies

to the east of the Great Escarpment. Therefore, according to this model, all drainage

to either side of the coastal drainage divide should be simple. Furthermore, as the

Great Escarpment is situated to the west of the Brisbane River for the majority of its

length, this would suggest that the latter should have a simple drainage pattern.

However, ‘simple’ drainage to the east of the Great Escarpment in southeast

Queensland, from highlands to shore, is not commonplace. This section of the Great

Escarpment is referred to by Ollier and Stevens (1989) as section IX (or the

Bellthorpe-Wilsons Peak section). In the very north of the Brisbane River catchment,

the river is situated between section IX ending to the river’s west and VIII -

Biggenden-Goomeri-Bellthorpe (Ollier and Stevens, 1989) commencing to its east.

This alone would suggest some complications should be expected in the drainage

patterns in this area. It is evident that drainage patterns in the area flanked by both

the Great Escarpment and the coastal drainage divide are very complex. This allows

for two possible scenarios: the first may be that the Great Escarpment in this region

has been mis-located on maps, and should correspond instead to the position of the

coastal drainage divide; or the second, more simple explanation, may be that the

coastal drainage divide is a supplementary feature with a separate origin to the Great

Escarpment but acting in the same way, with complex drainage to its west and simple

drainage to its east. If the former is not the case, and the coastal drainage divide is

simply acting in the same way as the Great Escarpment, its origin is probably

similarly related to back-tilting generating complex drainage to its west, although the

tilting process requires a driving mechanism that is not yet clearly defined.

Interpretation of the coastal drainage divide as a simple wave-cut escarpment at a

time of higher sea level would not cause back-tilting, so a more complex mechanism

for its formation is probable. The coastal drainage divide could be a small, secondary

escarpment possibly formed by a second pulse of thermal doming and rifting or

localised doming. Alternatively, the back tilting may potentially be caused by a deep

seated, unmapped fault, blind thrust or gentle flexure of the crust caused by the

current or recent compressional tectonic regime. As there is no evidence of the latter

proposed mechanism, thermal doming is more probable. This may be connected with

flexure and uplift of the crust related to the mid-Cenozoic emplacement of igneous

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bodies and hot-spot activity or later underplating. Volcanics related to the mid-

Cenozoic events are situated close to both the coastal drainage divide, in the north

(Mount Boulder and west of Eumundi) and the Maleny plateau (dated as

approximately 25.2 m.y.) in the south. The Glass House Mountains situated on the

coastal plain are postulated as having a genetic link with the Maleny basalts (Ewart

et al., 1980). The Glass House Mountains erupted approximately 25.4 Ma at a time

when the coastal plain was approximately 200 m above the present level prior to

erosion. At the time of emplacement, thermal doming would have been central to the

location of the volcanic activity, given that it was hot-spot-generated, this centre may

have moved over time, generating a roughly meridional elongate domal structure.

Coastward erosion, development of a scarp, and landward retreat of the drainage

network would have also caused the location of the coastal drainage divide to have

shifted to its present location. The Como and Glasshouse scarps that were previously

identified by other workers coincide closely, in places within 10s of metres, with the

coastal drainage divide but the scarps are situated slightly to the east of the drainage

divide proper. In essence, the crests of the coastal scarps appear to be spatially

related to the coastal drainage divide but are not fully coincident with it. Scarp retreat

through essentially flat to low-angle strata may not yet have had time to “catch” the

drainage divide itself. Clearly the origin of the Como and Glasshouse coastal scarps

requires further investigation but this study has provided the first viable hypothesis

for the origin of these features. The coastal drainage divide has previously not been

described as a single continuous feature; only by analysis of drainage channel

locations was the full extent of this geomorphological feature identified.

A further matter for consideration is that the Great Divide and Great

Escarpment are both associated with typical models of a passive margin tectonic

setting. The model dictates that the escarpment and divide in such a setting would

typically migrate away from the coast line. However, Forsyth and Nott (2003) have

suggested that Australia’s eastern highlands do not conform to this model, as divide

migration and subsequent stream diversions have not occurred in all places.

Furthermore, it is suggested that the continental divide already existed in some areas

during the Early to Middle Jurassic, prior to rifting in the Late Cretaceous (Nott and

Horton, 2000). From the discussion and research presented here, it is evident that

drainage in southeast Queensland is atypical of that expected in a simple passive-

margin setting. Forsyth and Nott (2003) cited examples of streams on the Cape York

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Peninsula, northern Queensland, that previously had been claimed by Pain et al.

(1998) as having been ‘captured’ due to formation and migration of the Great Divide.

Pain et al. suggested that the Barron and Pasco Rivers, for example, were linked with

streams that flow west and are situated west of the Great Divide. However, from

drilling surveys and additional field evidence, Forsyth and Nott (2003) confirmed

that the Barron and Pascoe Rivers are not related to those that are west of the divide.

Furthermore, they concluded that the Barron and Pascoe Rivers are structurally

controlled by faults, forcing each to make sharp turns before reaching the coast. This

drainage pattern is very similar to that of the Brisbane River. These two areas have

similar drainage patterns that starkly differ to the region in between – central

Queensland coastal region. In the central region, the Great Divide is situated far

inland and the Great Escarpment is close to the coast and approximately shore-

parallel. The drainage patterns are very different in that the central Queensland

region is dominated by two very large catchments, the Burdekin and Fitzroy, as

discussed by Jones (2006 p. 440), who identified that ‘scarp retreat (mostly through

relatively soft and gently folded Permian to Jurassic strata) is the most obvious

erosional mechanism affecting central Queensland catchments’. The central

Queensland catchments act in a very different way to those lying to the north and

south, where the Great Divide is closely coincident with the Great Escarpment. This

suggests that the location of the Great Divide is a stronger reflection of coastal

drainage development than the location of the Great Escarpment. In both Cape York

and southeast Queensland, where the escarpment is close to the coast, it is clear that

faulting strongly influences drainage.

As a comparison, the work of Bezerra et al. (2008) showed that the passive

margin of northeastern Brazil, which is now under compressive stress, has

experienced subsidence caused by the reactivation of tilted fault blocks. As already

stated, a consequence of rifting is back-tilting behind the great escarpment caused by

regional doming. However, rifting may also be accommodated by listric and strike

slip faulting. In southeast Queensland, it is clear that the Great Moreton Fault system

was already an active feature prior to rifting. This fault may have been reactivated

during Cretaceous-Cenozoic rifting, and a new perpendicular strike-slip fault (the

hypothesized Buranda Fault) may have offset the South D’Aguilar and Beenleigh

Blocks. Drainage that was previously captured along the Great Moreton Fault

system, now the upper Brisbane River may have been diverted along the transfer

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fault towards the ocean, through the disjunction between the two blocks of

Palaeozoic rocks. Unlike the northeastern Brazil region, southeast Queensland does

not appear to be subsiding, perhaps due to magmatic underplating, as discussed

further, below. The modern compressional stress regime may be reactivating faults in

the region, causing some further tilting and drainage diversion.

Jones (2006) showed that fluctuations in sea level can influence

sedimentation and drainage pattern development along the Queensland coast. Unlike

the rest of the eastern Queensland shelf edge, the central Queensland coast where the

Burdekin and Fitzroy Rivers discharge, has a broad shelf whose seaward margin is

not coast-parallel and here, large quantities of continental sediment have been

deposited from the two rivers. In particular, during late Miocene low sea-levels,

continental sediments were transported far out onto the shelf and are now located at

527 m below sea level in accumulations up to 177 m thick (Jones, 2006). At this

time, the coastline would have been several hundred kilometres offshore from its

present location and a lower base level would have encouraged more stream channel

down-cutting and erosion and if head-ward erosion took place, this would have been

coupled with enlargement of the catchments on-shore. Although fluvial sediments

that are delivered to the sea are commonly deposited close to the shoreline, changes

in the location of shoreline as sea-level changed, would have distributed the

sediments across the broad shelf. In contrast, southeast Queensland has a narrow

continental shelf and the Great Divide is closer to the present-day coast line. Here,

the growth of catchments may have been partly limited by the location of the Great

Divide. In southeast Queensland, a fall in sea-level would have resulted in less

terrestrial erosion than occurred further north, and instead there would have been

more erosion of the coastal plain and canyoning of the narrow shelf and slope.

Furthermore, the presence of the coastal drainage divide in southeast Queensland

highlights that in this area, where highland-parallel coastal drainage is not directly

from the highlands to the nearby shore, sedimentation will not be uniform along the

coastline. Rather, major depocentres are more likely to be focussed in isolated areas

along the shelf. Drainage patterns and sedimentation patterns at passive margins

generally, are therefore, likely to be influenced by localised ‘anomalous’ drainage,

where drainage is not simply from the coastward side of the great escarpment to the

shore and is clearly not ‘simple’ as previously suggested by several other authors.

Boyd et al. (2004) identified that the southeast Queensland continental shelf is both

227

narrow and severely sediment deficient in comparison with some other passive

margins such as the eastern margin of North America. They concluded that the

region has subsided very little since its formation but did not suggest why. The

continued buoyancy of the crust in southeast Queensland, perhaps due to crustal

underplating (discussed further, below), together with complex, shore-parallel

drainage and stream diversion along the coastal drainage divide, may have led to a

lack of sediment delivery to some parts of the coast and additionally, sediments may

be remaining onshore and stored as sediment veneers on the uplifted highlands and

plains or in small Cenozoic basins (e.g., the Pomona, Petrie, Booval and Oxley

basins).

The Tweed Shield Volcano (Mount Warning), of Miocene-Oligocene age, is

situated in the far southeast corner of the region, in alignment with the Great

Moreton fault. K-Ar ages of the volcano range from approximately 20.5-22.3 m.y.

(Jager 1977). The Tweed Shield Volcano is the largest volcano influencing southeast

Queensland. Its eruption would have had major affects on the geomorphology and

potentially on the structure of the region. Ewart et al. (1980) concluded that

Miocene-Oligocene volcanism of southeast Queensland is the product of magma

fractionation and intrusion at the crust-mantle boundary. The process involved

‘underplating’ in which large sill-like intrusions caused thickening of the crust by up

to 20 km under the volcanic regions and this has led to a reduction or prevention of

subsidence. A similar conclusion was also made by Wellman (1979a; 1979b; 1994)

who based studies upon magnetic and gravity anomalies and physiography. Having

studied picritic parental magmas, Cox (1980) developed a similar model for lower

crustal fractionation and thickening caused by intrusion of sill-like bodies, in the

Karoo province of southern Africa and the Parana lavas of South America. Up-

doming of the crust during the formation of the Tweed shield volcano is likely to

have caused adjustments to the drainage in the region as physiography changed.

Drainage from the Tweed shield volcano is radial and the western-most streams in

southern Queensland join the Logan River system, which flows around the outskirts

of the volcano before reaching the ocean. The eruption and associated tectonics of

the volcano may be linked to the location of faulting in the region, where natural

planes of weakness provided conduits through which lava could erupt. As stated

previously, the volcano is positioned in alignment with a southern extension of the

fault system that runs northwest-southeast along the boundary between the Esk

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Trough and the D’Aguilar Blocks and this plane of weakness may have provided a

focus for the eruption of the volcano. O’Brien et al. (1994) described this fault (after

Cranfield et al., 1976) as being continuous in a northwest-southeast orientation north

of the Ipswich Basin (Eastern Border Fault), and in a north-south orientation south of

the basin (West Ipswich Fault), therefore being distant from, and unconnected to the

volcano. However, on the Moreton Geology map compiled by the Geological Survey

of Queensland (Whitaker and Green, 1980), this is not identified as a continuous

fault and there may be a concealed and unmapped fault continuing as far as the shield

volcano. Cranfield et al. (1976) and O’Brien et al. (1994) described the Great

Moreton Fault System as a network of intersecting and braided faults. This may

suggest that, of the multiple associated fault planes in this system, many have yet to

be identified. Lavas from the Tweed shield volcano may have concealed any

evidence of major bedrock faulting around the volcano itself and would account for

the lack of structural detail currently mapped.

Hot-spot activity in southeast Queensland is associated with continued

underplating, crustal thickening and later eruptions of the Main Range and Mt

Warning to the west and south of the Glass House Mountains. Crustal doming

associated with hot-spot activity could also account for the back-tilting and drainage

anomalies along the coastal drainage divide, but it does not account for anomalously

high uplift in the D’Aguilar blocks. Regional uplift or doming that caused tilting and

uplift and present-day landward drainage, of the D’Aguilar blocks could be due to a

combination of crustal doming and the crust slowly uplifting in order to adjust to

isostatic equilibrium, where the thickened, fractionated crust underlies this region.

The recent work of Kirby et al. (2008) stated that indices, such as

anomalously steep channel profiles and evidence from the topography of long-term

uplift were, retrospectively, strong evidence that Sichuan Province of China was

seismically active. A surprisingly large earthquake of magnitude 7.9 struck the

Sichuan Province in May 2008, in a region where, although previously known to be

tectonically active, events were regarded as relatively infrequent and an earthquake

of such magnitude was not anticipated. Kirby et al. (2008) stated that indices such as

steepened channels and evidence of long-term uplift may be suitable for identifying

potential activity on blind or hidden faults or in regions where geodetic networks

indicate that little strain is accumulating in the upper crust. Furthermore, beneath the

Sichuan Province crustal thickening has occurred, driven by flow and deformation in

229

the lower crust, which may cause seismic activity despite no evidence of shortening

in the upper crust. Following the type of evidence and key indicators used by Kirby

et al. (2008) in the Sichuan Province, a potentially similar seismic geohazard may

exist in the southeast Queensland region. This is evidenced by the anomalous

drainage patterns amongst low order streams near the coastal drainage divide, incised

meanders in both low and high order streams, numerous terraces and steep

headwaters in some catchments draining the D’Aguilar blocks. Palaeodrainage

evidence also suggests continued and large-scale uplift of the D’Aguilar blocks. Also

similar to the Sichuan Province, crustal thickening has occurred in the southeast

Queensland region (for example Ewart et al., 1980) where flow at the crust-mantle

boundary may have underplated the crust.

Implications for evaluating the evolution of the landscape

Simple geomorphological models are unlikely to fit most landscapes that, like

southeast Queensland, have been the subject of a complex, geological history. The

results of this study show that where geological control is prevalent, the influence

upon the landscape is commonly long-term despite overprinting by numerous

subsequent geological events and broad changes in exogenic influences. Although

surface features (e.g. surficial sediments) may conceal a geological control such as a

fault, the affect of the fault on the landscape is generally still detectable. Surface

processes, such as differential weathering, may also enhance evidence of geological

control. This work has shown that a multi-criteria approach must be used for

landscape evolution analysis.

Considering the evidence presented in this thesis, and also discussed further

above regarding passive margin settings, it may be necessary to modify the

‘classical’ model of drainage in a passive margin tectonic setting. More work is

required in similar geological settings to clarify (1) the range of deformation styles,

(2) the character of modern stress regimes, and (3) the drainage architecture, to

clarify the range of variation in drainage development along passive continental

margins.

Evidence of past geological events in the present landscape

The geology of southeast Queensland continues to display some fabric from the Late

Carboniferous. During the Late Carboniferous, north-northeast – south-southwest

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compression caused deformation and uplift of an accretionary prism and the onset of

the uplift of the New England Fold Belt. Fabric evident in the present landscape from

this time includes the low grade metamorphism seen in the Rocksberg Greenstone,

Neranleigh-Fernvale beds and the Bunya Phyllite for example. As stated from paper

1, this fabric controls the orientation of some streams. The geomorphology is also

controlled by the structural fabric inherited from late Palaeozoic-early Mesozoic

time. At this time, compression in an east-west orientation caused mainly northwest-

southeast thrust and strike-slip faulting of the accretionary prism material, during the

Hunter Bowen orogenic episode. The structural discontinuities are clearly evident in

the present landscape as seen, for example, in the North and South D’Aguilar blocks

and the Beenleigh Block, although its ‘offset’ to the South D’Aguilar Block is not

explained by this event and as previously discussed, may have been caused by a

transfer fault during later rifting. Although further deformation continued through the

Middle Triassic, with folding occurring in a north-northwest orientation and igneous

emplacements such as the Mount Samson Granodiorite and the Samford

Granodiorite, these events did not alter the previously emplaced blocks and units

significantly. Extension during the Late Triassic – Early Cretaceous led to the

formation of basins such as the Clarence-Moreton, Maryborough and Nambour

basins and although these are significant in size, they do not sufficiently conceal or

alter the strong north-northwest – south-southeast trending units emplaced during the

Palaeozoic to early Mesozoic. During the late Mesozoic, north-northeast – south-

southwest extension led to the breakup of the eastern Australian margin, which led to

the opening of the Tasman and Coral seas. Strong and obvious morphological

evidence of this event is deficient in the region at present; nevertheless, it is possible

that during this event, the South D’Aguilar Block and Beenleigh Block and part of

the Great Escarpment were off-set. Small basins subsided and filled during the

Paleogene in association with local volcanism and possible uplift of adjacent

highland blocks. Volcanoes that erupted during the mid-Cenozoic, such as the Tweed

Shield Volcano, Main Range Volcanics, the Glass House Mountains and the Maleny

basalts, have made an obvious impression on the landscape. The Main Range

Volcanics for example, are potentially protecting the highlands in that region from

erosion; similarly so the Maleny basalts at the Blackall Range. Nevertheless, the

strong northwest-southeast trend of faults and blocks emplaced during the Palaeozoic

to early Mesozoic remains a dominant element of the landscape. The modern

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regional stress field is compressional in a northeast-southwest orientation. No large

scale surface ruptures, earthquakes or deformation have been observed in recent

times and there are no active volcanoes in the region. However, from the results of

paper 2, it is evident that the stress building from the present compressional regime is

being released as fairly frequent, low magnitude events, and this is potentially

occurring along some ancient faults such as the northwest-southeast trending Great

Moreton Fault system. Although the strong northwest-southeast geological trend

dominates the orientation of rock units in the area, and some rivers such as the

Brisbane and North Pine rivers appear to be strongly controlled by this trend, a

variety of the other, aforementioned regimes, presently control other drainage

patterns in the region. For example, the volcanic and igneous activity has led to

centripetal drainage (for example, on the Samford Granodiorite), radial drainage (for

example, around Mount Warning and Mount Glorious) and parallel drainage (for

example, flanking the Main Range Volcanics). The various phases of compression,

folding and metamorphism have led to parallel and angular drainage patterns, such as

that seen in the North Pine River catchment and the streams that feed the upper

Brisbane River. However, some drainage such as the anomalous drainage described

in paper 3, does not clearly fit with any specific regime described above. Although

the north-trending Mary River may be caused by an antecedent drainage regime, the

control of some small streams that first flow towards the coastal drainage divide and

then turn away, cannot be assigned to a known regime or event and their potential

control has been discussed above. In addition to the volcanics that crop out onshore,

some exist on the continental shelf, close to and a little way off-shore (Boyd et al.,

2004). Their presence, combined with the change in orientation of the coastline, from

north-south to northwest-southeast, causes northward longshore drift to diverge from

the coast and has created major sand islands in this area (Boyd et al., 2004). Features

such as the shoreline, major geological units and large faults (e.g., the Great Moreton

and North Pine faults), and the boundaries of geological units discussed above, are

all typically orientated northwest-southeast and despite there being several past

tectonic events reflected in the landscape of southeast Queensland, this dominant

trend has remained since Palaeozoic-early Mesozoic times.

In paper 3, evidence of inverted topography and remnant fluvial deposits

were presented, as seen in the Kilcoy Gap. Such deposits can provide hard evidence

of the location and orientation of palaeochannels. Additionally, it provides

232

information on landscape evolution, including the prevailing conditions during and

after deposition. Inverted topography occurs when, sediment initially deposited in a

depression, consolidates and becomes more resistant to erosion than the surrounding

rock. Once the surrounding rock is eroded, the sediments are left as remnants

capping high points in the landscape. Inverted topography may occur as a result of

armouring, covering or hardening of the stream fill, the former two, through deposits

of large and resistant boulders or basalt flows for example, the latter through

diagenetic processes forming ferricrete, silcrete or calcrete for example. Any of these

processes may provide resistance to weathering relative to the surrounding rocks that

may erode leading to elevation of the previously low-lying stream channel deposits.

Inversion of relief is an important contributor to landscape development although, as

stated by Pain and Ollier (1995), there is often a reluctance to accept this point of

view. Nevertheless, numerous examples exist globally. A particularly large and well-

defined example of this can be seen in the southern Pyrenees, Spain, where the Sis

conglomerate (Vincent, 2001) represents an enormous palaeovalley fill that now

stands elevated by several hundred metres above the older, exposed, underlying

sediments. The presence of inverted topography is particularly important for

providing evidence of variations in tectonic, climatic and pluvial conditions over

time. Inversion of relief has also proven to be a significant method for landscape

analysis of Mars (Pain et al., 2007). Several geomorphic features on the Martian

surface have been identified as representing inverted relief, including some inverted

impact craters. The study of Mars showed that several landscape evolution processes

have occurred there, including diagenesis, weathering and the movement of liquid

both at the surface and in shallow aquifers. Inverted topography in Australia has been

identified in many locations. For example, silcrete derived inversion is evident in the

Cape York Peninsular (Pain and Ollier, 1995) and the Kirup Conglomerate, Western

Australia (Pain and Ollier, 1995), both of which identify changes in groundwater and

overland flow conditions probably linked with climatic changes in the region. The

preservation of the inverted Haunted Hill Gravels in southern Victoria has been

valuable in identifying the provenance of sediments and pulses of tectonic activity of

the area (Bremar, 2002; Kapostasy, 2002). Preservation of palaeochannel deposits

may also conserve concentrations of economic deposits such as gold or sapphires

within the channel-fill. In Western Australia, ferricrete and nodular iron ore of the

Robe River deposit extends tens of kilometres along palaeovalleys (for example

233

McLeod, 1966; Pain and Ollier, 1995). In southeast Queensland, the Oakdale

Sandstones (Derrington et al., 1959; Cribb et al., 1960) of Cenozoic age, which

consist of sand, shale, conglomerate and coal seams, are capped by rhyolites and

basalts and are thought to be of Pliocene age. Similarly the channel fill deposit

described in paper 3 that is seen in the Kilcoy Gap is situated close to the Maleny

basalts and may have been covered with a thin veneer of basalt providing initial

protection from erosion. Basalt from the eruption of the Tweed Shield volcano

flowed down pre-existing stream channels and differential weathering has now led to

preserved basalt-capped river courses as headlands and ridges such as at Burleigh

Heads. The preservation of palaeochannel deposits helps to pinpoint the positions of

ancient drainage systems and to evaluate the relative incision and altitude of the

landscape in the past. In the case of the deposits preserved in the Kilcoy Gap, the

very coarse fluvial sediments indicate that this was the site of a major drainage

corridor of probable Paleogene age.

National and international significance

Although surface processes, regional tectonic processes and anthropogenic influence

may be cited as controlling elements of terrain morphology, the findings in paper 1

have confirmed that the landscape may be controlled at a fine scale and by multiple

endogenic controls. This is specifically relevant to understanding landscape

evolution in other metamorphic regions both within Australia and internationally.

Additionally, it highlights the significance of controls on modern drainage by the

foliation and structural discontinuities characterizing ancient accretionary terrains.

Understanding these influences has relevance to landscape interpretation in other

parts of the eastern Australian coast such as the Narooma accretionary complex in

New South Wales and accretionary regions such as western North America and

southern Europe. The channel ordering system presented in paper 1 may be applied

to any drainage system at any scale. In other similar settings, it would be possible to

repeat the methods used in papers 1 and 3 in order to identify the level of geological

control that the underlying rocks have on the orientation of the streams. This can be

used to establish a base-line before determining if there is any anthropogenic

influence on the landscape. More simply though, it can assist in understanding

whether rock fabric has a role in drainage orientation or whether the drainage is not

strongly influenced by geology but instead by surface processes.

234

Many areas of the world lack well-constrained or long-standing earthquake

monitoring systems and paper 2 describes and tests a simple and effective method for

a preliminary assessment of the relationship between earthquakes, the structural

geology of an area, and its landscape. The findings of paper 2 emphasise the need for

a more closely spaced earthquake monitoring system and for more continuous data

collection for similar studies to be effectively carried out. However, the paper also

identifies that it is possible to associate shallow earthquake events with known fault

systems or geomorphological features such as scarps, highland margins or hill-crest

alignments, to assess whether structural features are currently active and influencing

landscape form. As there is some evidence from extremely well monitored

earthquake-prone regions that low magnitude earthquakes may cause surface rupture,

it is important that other regions experiencing similar magnitude earthquakes are

more closely monitored to examine the cause and effect of activity in the region.

The findings of paper 3 provide a regional assessment of how multiple

geological influences of ancient and more recent origin have affected the modern

form of the landscape. The results will supplement studies of other passive

continental margins, such as the coastline surrounding the Red Sea, the east coast of

America and the west coast of Europe, to determine the consistency of drainage

patterns and evaluate the dominant mechanisms involved in landscape evolution in

such settings. Furthermore, as southeast Queensland also contains elements of

compressional and accretionary terrains, the patterns identified herein may be

particularly applicable to passive margins developed upon older accretionary terrains

such as the northern Gulf Coast Basin set against the Palaeozoic rocks of the

Ouachita Mountains of the United States. The rifted margin of southern Africa set

against the deformed Palaeozoic rocks of the Cape Fold Belt represents another

region where similar drainage patterns might be expected.

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Table 1 Evolutionary model of southeast Queensland and the relationship with knowledge

identified and discussed in this thesis

236

Table1- continued

237

Evolutionary model

Based on the three components of the study, the geological events that are the

controlling factors in the landscape evolution of southeast Queensland are summarised

in Table 1. This table also provides a relative time-line for these events and highlights

the importance of the multiple processes that have taken place and emphasises why

the morphology of southeast Queensland is not typical of a passive margin setting.

Précis of main findings

In summary, the main findings of this study include the following:

• The study has integrated a range of datasets using GIS at a scale and extent

that has previously not been achieved.

• An entirely new stream-ordering system has been presented.

• The earthquake analysis indicates that low-magnitude earthquakes in the

region cluster in preferred areas, some of which align in ‘corridors’ that

correspond with known structure and physiographic features, such as

highlands, scarps and valleys.

• Some epicentres occur in linear patterns that do not align with known faults;

some of these align with valleys and scarps.

• Low-magnitude earthquakes presently occurring in the region are not likely to

cause surface rupture or displacement.

• Some large drainage systems in the region align with earthquake corridors and

large ancient fault systems suggesting that the ancient faults where river

systems have developed may also host recent earthquakes.

• The earthquake analysis is the first of its kind to have been performed for this

region in more than 15 years.

• Low order streams remain dendritic until they have down-cut to reach

bedrock. The orientation of cleavage and faults can control the location and

orientation of drainage channels after down-cutting has been achieved.

• The majority of large river systems in the region display drainage patterns that

are characteristic of geologically controlled networks; these patterns are

commonly controlled by faults or by zones of differential weathering.

238

• Steep, highland drainage close to coastal zones has been caused by uplifted

blocks.

• Some low-order streams have been diverted suggesting recent structural

control.

• Incised meandering streams of both high- and low-orders are common,

indicating relatively recent uplift has taken place.

• First described in this work, the ‘coastal drainage divide’ has a significant

effect on drainage in the region, north of Brisbane, as it causes a distinct lack

of drainage directly to the coast from the shore-parallel highlands.

• Also first described in this work ‘the Kilcoy Gap’ displays evidence of

reversed drainage.

• Despite the eastern Australian coast being a passive tectonic margin, drainage

patterns are generally atypical of such a setting as they display evidence of

past events including convergent margin compressional, passive margin

extensional, and intra-plate hot-spot volcanism related tectonic regimes.

Future work

The remote-sensing and analytical methods used in this study can be applied to any

other location, where similar datasets are available. It would be valuable to carry out

similar studies in other passive margin and convergent margin settings in order to

clarify the diversity and commonalities of drainage patterns developed in such settings

globally.

The stream numbering method presented in paper 1, may be used to identify the

level of control geology has over other catchments although further work could take

into account the different phases of folding and faulting. More detailed geological

mapping of southeast Queensland may identify other faults and structures that might

correlate with, or better constrain, earthquake corridors described in paper 2;

similarly, geological mapping may provide field evidence for the existence of the

previously described Buranda Fault through the Brisbane Gap, suggested in this work

as having been caused during rifting.

Future work may also incorporate further tests of the hypotheses posed in paper

3, regarding the factors controlling the ‘coastal drainage divide’. Such tests may

require the use of geophysical methods, provenance studies, bore-hole logging and

239

detailed geological mapping. These studies might also provide additional evidence for

the eastward-flowing palaeochannel situated within the Kilcoy Gap.

Other future work may include repeating the methods presented here in

different areas to test whether geology provides the dominant controls on the

landscape or whether exogenic processes are dominant. In particular, the methods

presented in paper 1 can provide a useful assessment of which order of streams

correspond with various rock fabrics, and may be a guide to the extent to which

control is endogenic or exogenic in a small catchment or on multiple or complex

combinations of rock types.

The methods used in paper 2 can be used to identify whether recent

earthquakes are occurring close to, or in association with, known geological

structures, although a larger spatio-temporal database from a more extensive

monitoring system would be beneficial. It would be important to investigate the

potential seismic geohazards in the region, by more extensive earthquake monitoring,

detailed examination of gravity anomalies, analysis of upper crustal strain rates and

more precise confirmation of the status of the lower crust.

The methods used in paper 3 are suitable for remotely studying large areas,

particularly inaccessible regions. In isolation, the methods can each provide a limited

measure of the geological controls exerted over the landscape, but used together they

provide multiple indices to delineate the degree of geological influence and reduce

uncertainty in interpretations.

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Wellman, P., Williams, J.W. and Maher, A.R., 1994. Interpretation of gravity and magnetic anomalies in the Clarence-Moreton Basin region. In: A.T. Wells and P.E. O'Brien (Editors), Geology and petroleum potential of the Clarence-Moreton Basin, New South Wales and Queensland: Bulletin 241. AGSO, Canberra, pp. 217-229.

Whitaker, W.G. and Green, P.M., 1980. Moreton Geology 1:500 000 map. Department of Mines, Queensland.

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APPENDICES

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244

APPE

ND

IX 1

152

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246

APPENDIX 2 A GIS and map-analysis deficiency

Fig. 1

Fig. 2

As with other similar geomorphological studies, this work is based on plan view areas and not surface area. A potential deficiency in spatial calculations and morphometric methods with regard to land-surface area was identified at an early stage of this study. The deficiency is described here for completeness, as surface area calculations were not required and did not affect analyses conducted here. An area on a map is measured in plan view. For example, in Fig. 1, area A, will have the same measured area as that labelled B: slope is not accounted for. Therefore actual surface area is rarely considered. Similarly shown in Fig. 2, area A and B in plan view would measure the same size (shown by adjoining dotted lines) although the surface area of A is clearly greater than that of B.

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Bearing this in mind, calculations that consider area may provide differing results if plan area and surface area were compared. For an example, calculating wetness, if two areas each of 1 km2 in plan view were to receive identical amounts of rainfall, they will become wetted to different degrees depending the slope of each; a steeper slope would become less wet than a gently sloped or flat area, because the rain falling on the steeper slope would be more ‘thinly spread’ across the larger surface area than the flatter area. Drainage density, another common geomorphological consideration, is equally affected by the area measured. For example, Strahler (1966 p. 506-7) uses four ‘1 square mile’ maps, each with different slopes and drainage densities. Although the discussion identifies potential reasons for varying densities, it does not consider the differences in each surface area. Although surface area currently is not calculable in GIS, the slope for each pixel may be. Therefore, by taking the known size of the pixel and the angle of its slope, the surface-area of each pixel may be computable using cosine (confirmed by Dr. Micaela Preda, pers. comm.). The success of computations for large areas, such as those used in this study, is unlikely to be successful due to the amount of data involved, although average slopes may be utilised if required to decrease data intensity. Reference STRAHLER, A. N. 1966. The Earth Sciences, Harper International p. 681.

APPENDIX 3

Other software products used

Circular data

In order to present and analyse circular data graphically, data must be exported from

‘qik-orientate-345’ (Lawley 1997) into Microsoft® Office Excel. The data may then

be transferred to Stereonet for Windows v1.2 (Allmendinger 2002), to produce 360°

rose diagrams for visual analysis.

Images

Adobe Illustrator 10 was used to augment and enhance maps for presentation

purposes.

References ALLMENDINGER, R. 2002. Stereonet for Windows v 1.2, rwa1@cornell.edu. LAWLEY, R. 1997. qik-orientate-345. r.lawley@bgs.ac.uk, Geo Trek Corp.

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APPENDIX 4

Statistical analysis of planar features in Laceys Creek

The orientations of bedding, cleavage, faults and fractures within the Laceys Creek

catchment were analysed with respect to channel orientations in an attempt to asses

their concurrence with one another. Using the statistical analysis package SPSS,

correlation coefficients were produced and are presented here in Tables 1 and 2.

High correlation coefficients, and very low significant figures imply a strong

relationship. The correlation coefficients revealed by the analysis are not

particularly high. Where very low significant figures were calculated by SPSS, the

corresponding correlation coefficient is highlighted in bold.

The results suggest that there are some cases of correlation between the

orientations of the network and those of the planar features, although these

instances are sporadic and difficult to clearly quantify in this way. From these

analyses, it is evident that there are more instances of channel correlation with

bedding planes than with other planar features on the Neranleigh-Fernvale Beds

(Table 1). However, there are more instances of channel correlation with cleavage

planes than with other planar features on the Bunya Phyllite (Table 2).

Statistical methods commonly seek to describe a mean value, deviation from that

mean, or closeness of fit between data sets. However, for the purposes of this

study, it was more important to seek correlations between the various datasets,

which themselves may display multiple clustering of data due to the heterogeneous

nature of the landscape, causing further complications to the analysis.

The clustering of data for both channel orientations and planar features may

explain the low correlation coefficient values. Analysis of the datasets needs to

recognize correlations between multiple clusters rather than identify the closeness

of fit for the entire dataset. Ordinary statistical procedures cannot confidently be

applied to this, or any other directional data due to the very nature of circularly

derived measurements where 0° = 360° (Jones, 1968). Statistical analysis of

directional data is a relatively new approach but has been explored to some extent

in a variety of scientific areas where orientation data naturally occur (Krieger

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Lassen et al., 1994). Parametric orientation statistics in relation to earth sciences

have been discussed by Kohlbeck and Scheidegger (1985).

Table 1

Channels

excluded Bedding Cleavage

Faults and

fractures

Bedding

and

cleavage

Bedding

and

fractures

Cleavage

and

fractures

Bedding,

cleavage

and

fractures

1st 0.090 0.046 -0.011 0.115 0.050 0.100 0.096

1-2nd 0.209 -0.060 -0.141 0.163 0.152 -0.052 0.163

1-3rd -0.260 -0.111 0.128 -0.243 -0.238 0.018 -0.243

1-4th -0.033 -0.259 -0.201 -0.033 -0.033 -0.182 -0.033

1-5th 0.048 -0.045 0.172 0.048 0.048 -0.102 0.048

1-6th -0.162 -0.099 -0.046 -0.162 -0.162 -0.164 -0.162

1-7th -0.249 -0.216 0.054 -0.249 -0.249 -0.244 -0.249

1-8th -0.046 0.200 -0.153 -0.046 -0.046 0.046 -0.046

1-9th -0.224 0.214 -0.088 -0.224 -0.224 0.066 -0.224

1-10th -0.177 0.060 -0.084 -0.177 -0.177 0.001 -0.177

1-11th -0.073 0.064 0.012 -0.073 -0.073 0.056 -0.073

1-12th 0.069 -0.050 -0.294 0.069 0.069 -0.034 0.069

1-13th -0.100 0.168 -0.186 -0.100 -0.100 0.147 -0.100

1-14th -0.030 0.170 -0.108 -0.030 -0.030 0.182 -0.030

1-15th 0.058 0.126 0.265 0.058 0.058 0.132 0.058

1-16th 0.216 -0.007 -0.099 0.216 0.216 -0.007 0.216

1-17th 0.144 0.031 -0.090 0.144 0.144 0.031 0.144

1-18th 0.037 0.106 0.372 0.037 0.037 0.106 0.037

1-19th 0.036 -0.212 -0.191 0.036 0.036 -0.212 0.036

1-20th 0.345 -0.064 -0.086 0.345 0.345 -0.064 0.345

1-21st -0.066 0.055 -0.140 -0.066 -0.066 0.055 -0.066

1-22nd 0.140 -0.118 0.001 0.140 0.140 -0.118 0.140

1-23rd -0.106 0.066 0.233 -0.106 -0.106 0.066 -0.106

1-24th 0.018 -0.098 0.379 0.018 0.018 -0.098 0.018

1-25th -0.113 0.231 0.274 -0.113 -0.113 0.231 -0.113

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Table 2

Channels

excluded Bedding Cleavage Fractures

Bedding

and

cleavage

Bedding

and

fractures

Cleavage

and

fractures

Bedding

cleavage

and

fractures

1st 0.102 0.382 -0.190 0.470 0.001 0.133 0.155

1-2nd 0.185 0.539 -0.125 0.511 0.058 0.539 0.539

1-3rd 0.068 0.548 -0.229 0.476 0.076 0.548 0.548

1-4th -0.051 0.536 -0.166 0.150 0.048 0.536 0.536

1-5th -0.208 0.552 0.167 -0.227 -0.002 0.552 0.552

1-6th -0.352 0.272 0.114 -0.329 -0.013 0.272 0.272

1-7th -0.587 0.020 0.229 -0.460 -0.242 0.020 0.020

1-8th -0.078 0.100 0.410 -0.397 -0.180 0.100 0.100

1-9th -0.345 -0.059 0.360 -0.530 -0.355 -0.059 -0.059

1-10th -0.347 -0.053 0.389 -0.553 -0.358 -0.053 -0.053

1-11th -0.147 -0.275 0.348 -0.481 -0.440 -0.275 -0.275

1-12th -0.125 -0.250 0.266 -0.485 -0.480 -0.250 -0.250

1-13th -0.363 -0.181 0.214 -0.618 -0.537 -0.181 -0.181

1-14th 0.138 0.189 -0.064 -0.305 -0.256 0.189 0.189

1-15th 0.286 0.421 0.144 -0.164 -0.118 0.421 0.421

References Jones, T.A., 1968. Statistical analysis of orientation data. Journal of Sedimentary Petrology 38, 61-67.

Kohlbeck, F.K., Scheidegger, A.E., 1985. The power of parametric orientation statistics in the Earth

Sciences. Mitteilungen der Österreichischen Geologischen Gesellschaft 78, 251-265.

Krieger Lassen, N.C., Juul Jenson, D., Conradsen, K., 1994. On the statistical analysis of orientation

data. Acta Crystallographica A50, 741-748.

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