facies term
Post on 25-May-2015
1.164 Views
Preview:
DESCRIPTION
TRANSCRIPT
FaciesFacies And And FaciesFacies Analysis Analysis
Page 2
Content
1. Introduction- Definition and History of facies
2. Types of facies- Lithofacies, ichnofacies, biofacies, seismic facies.
3. Facies sequence and facies association
4. Facies tools
5. Sedimentary log
6. Facie model 7. Facies analysis and environment
8. Applications and limitations of facies
Page 3
Definition and History of Facies
Facies is the aspect, appearance, and characteristics of a rock unit, usually reflecting the conditions of its origin; especially as differentiating it from adjacent or associated units.
The word facies was first introduced by a Swiss geologist, Amanz Gressly in 1838, as part of his contribution to the foundation to mordern stratigraphy.
Facies analysis refers to the interpretation of rocks and sediments for the purpose of reconstructing the processes that were responsible for the original deposition
Walther`s law of facies succession
In 1894, a German geologist in the person of Johannes walther proposed that Facies that occur in conformable vertical successions of strata also occur in laterally adjacent environments. Thus, facies boundaries may shift so that the deposits of an adjacent environment may lie directly atop those of a laterally related environment
Page 4
Types of facies
Lithofacies: These facies are characterized by sedimentary attributes, such as grain-size, sedimentary structures, bedding, color
Biofacies: These facies are Characterized by fossil content (body fossils ) such as shell and tooth.
Seismic facies: These facies are Characterized by seismic reflection amplitude and continuity. (Interpreted in terms of large-scale lithologic characteristics).
Ichnofacies: The assemblage of trace fossils like foot prints and burrow traces.
Page 6Page 6
LithofaciesLithofacies Biofacies
iichnofacies Seismicfacies
Facies Sequence and Facies Association
Facies association that reflect a particular depositional environment is said to be formed when a group of different individual facies caused by different processes all occur in the same environment. These facies all share the same environment.
Facies sequence or facies succession is a facies association in which facies occur in a particular order. They occur when there is a repetition of a series of processes as a response to regular changes in conditions.
Page 7
Page 8
Page 9
Facies b and c form
a facies sequence
Page 10
Facies Tools
Facies tools are devices from which data associated with facies analysis are acquired. They include :
Outcrops
Core samples
Wire line log
Seismic section
Page 11
FACIES TOOLS
Page 12
AN OUTCROP
A WIRE LINE LOG
A CORE SAMPLE
A Seismic section
Page 13
Sedimentary Log
Sedimentary log also referred to as litholog is a graphical representation of a series of beds in a sediment or sedimentary rock.
Litho logs consist of the following sections: Vertical and horizontal scale section
Lithology section
Facies name and facies code section
Process interpretation section
Environment interpretation section
Page 14
A sedimentary log
Page 15
Facies model
Facies model is the general summary given to a depositional system. It`s usually an interpretative device erected to explain a facie assemblage.
Facies models could take the following form:
2D VERTICAL SUCCESSION DIAGRAM 3D BLOCK DIAGRAM 4D MODEL(SIMPLY 3D ADDED WITH PREVAILING PROCESSES)
Page 16
Page 17
3D BARRIER ISLAND BLOCK DIAGRAM
2D VERTICAL SUCCESSION DIAGRAM FOR A DELTA ENVIRONMENT
Page 18
4d facies model (adds understanding of process)
Facies analysis and environment
Deltaic facies and environment:
Delta can be classified based on energy into:
river dorminated delta wave dorminated delta tide dorminated deltaDeltas are generally characterized by top set bed, fore set bed,
and bottom set bed
Page 19
Page 20
River dorminated delta
These are deltas in which river activities are prevalent at the delta , with the effects of wind and tides being minor at the delta front. Examples include : Mississippi delta
River dominated deltas are usually characterized by :
distributary channel interdistributary bay
Page 21
)
Page 22
River dominated: birds-foot delta(Mississippi-type)p
prodelta
Delta front
Delta plain
Mississippi delta
Prograding mouth bar succession Clean sand, low- & high-angle 3D strat.
… representing beach & dune deposits Well-sorted sand, planar & ripple x-lam.,
tangential x-bedding (bar crest); poorly sorted sand/silt, cut & fill,
small-scale trough x-bedding (bar back);
large channel fills near top (distributary channel) Interbedded mud/sand, wave & current ripple x-lam.,
parallel/lenticular lam., bioturbation, contorted bedding, possible cut & fill
… representing distal mouth bar deposit
Finely laminated mud, bioturbation, marine fauna, contorted bedding
… representing prodelta deposit
Silty/sandy slump sheet … representing redeposited
(distal) mouth bar sediment Homogenous mud, finely laminated or bioturbated, marine fauna
… representing shelf deposit
Page 23
Distributary channel fill facies
Page 24
Ripple-laminated, fine-grained sand- & siltstone,
plant-rich & with palaeosol-coal units
… representing filling of shallow channel after avulsion Trough & planar x-bedded sandstone
with unidirectional palaeocurrents
… representing migrating dunes/bars in channel
Massive, locally x-stratified sandstone with internal
erosion surfaces & some soft-sediment deformation
… representing main channel subject to flooding Basal coarse lag deposit above erosional surface
… representing channel avulsion & erosion
into delta front progradation succession
Wave dorminated delta
Page 25
These deltas are dominated by wave action at the delta front .
Examples inlcude : Nile delta
A wave-dominated delta formed where wave activity reworks the sediment brought to the delta front to form coastal sand bars and extensive mouth-bar deposits.
Wave dorminated delta
Page 26
Wave-dominated delta front succession
Medium-grained sand, plane-parallel lam. & low-
angle x-strat., passing into sand/mud with plant roots
... representing beach to non-marine deposit
Fine- to medium-grained, cross-bedded sand
... representing wave-modified mouth
bar deposit on upper shoreface Fine-grained, bioturbated sand with
HCS & plane-parallel lamination
... representing wave-swept lower shoreface deposit
CU mud to sandy mud to sand with pervasive
bioturbation, storm beds & hummocky x-strat.
... representing regressive shelf deposit
Page 27
Tide dominated deltas
These deltas are dominated by tidal activities
Coastlines with high tidal ranges experience onshore and offshore tidal currents that move both bed load and suspended load. A delta building out into a region with strong tides will be modified into a pattern that is different to both river- and wave-dominated deltas
Examples include: Gnages delta,
These deltas are characterized by : tidal flat tidal sand bar tidal channel
Page 28
Page 29
Alternating sand-silt-mud, x-lam., “flaser-linsen”
bedding, small channel fills, brackish-water fauna
... representing tidal flat facies on delta plain
Erosive, FU sand with herringbone x-strat., mud
drapes, tidal bundles, ripple x-lamination ... representing tidal
channel on delta plain
Bidirectional x-bedded sand, mud drapes, tidal
bundles, reactivation surfaces, scours/channel fills
... representing migrating tidal current ridges &
inter-ridge channel fills on delta front
Bioturbated mud passing into interbedded
mud-silt-sand, marine fauna
... representing open shelf to prodelta succession
Page 30
Page 31
Tidal flat and channel in Ord river delta
Why is Facies analysis essential to a sedimentologist?
Advantages and Application:- 1. simplifies and standardizes observations-permits rapid logging of field sections and drill core. 2.Facies analysis is useful in hydrocarbon exploration. 3. it is also useful in paleogeography. 4. it also finds its importance in paleoecological reconstruction. 5.Facies analysis is also useful in groundwater exploration
Page 32
Disadvantages include:
1) Discourages observations of the rare or unusual-may lead to inappropriate simplifications
Page 33
Thank You
For listening
top related