open file 2003-7 52 45' lake quaternary geology of the...
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Mb//F bRh
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csCb-Rx
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Fp-M
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F b-EG
F fG
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L b/FG G
L p//MbG
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Mb//F w-EG
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-VG
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Mb-V
Mh
Mh//F b-EG
Mh-E
Mj
Mj//F b -EG
Mj/F b -VG
Mm
Mmb//F bG
Mmu
Mp
Mpm//F vG
Mr
MuMu/F b-V
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Mub
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Mwh
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Op/F pA
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DESCRIPTION OF STUDY AREA
The study area is located approximately 50 kilometres southeast of Quesnel, near the township of Likely,British Columbia. The region is known for its long history of placer mining that began during the 1860's.During this time, the township of Quesnel Forks, located at the confluence of the Quesnel and Cariboo Rivers,was a major centre, housing more than 5000 people at its peak. Today, many of the original buildings are stillleft standing.
The mapped area lies on the eastern edge of the Interior Plateau at the boundary of the Quesnel Highlands andthe Fraser Plateau. The distinction between the highland and plateau regions is somewhat arbitrary. In general,the area is characterized by flat and gently rolling topography with large undissected uplands (Holland 1976).The highest point within the study area is approximately 1560 metres asl and the lowest point is 600 metres asl.On average, the plateau lies at 940 metres asl.
The major drainage in the region is provided by the Quesnel and Cariboo Rivers, which drain the Quesnel andCariboo Lakes (northeast of mapped area), respectively. The Quesnel River valley is an east-west trendingtopographic low that is on average 280 metres deep and approximately 1.5 kilometres wide. Flow within thevalley is to the west. The river drops 90 metres in elevation over a distance of 32 kilometres. The CaribooRiver valley also trends east-west and is similarly incised, though narrower.
Sub-boreal spruce zone occupies the majority of the region up to an elevation of 1300 metres asl, whereas athigher altitudes the Engelmann spruce-subalpine fir zone dominates (Meidinger and Pojar 1991). The primarysoils belonging to these zones are luvisols, podzols, and brunisols. Seasonal extremes typify the climate withsevere snowy winters contrasting relatively warm, moist summers. The area experiences a moderate annualprecipitation (Meidinger and Pojar 1991), on average 690 mm per year with approximately 70% being rain.
Thick glaciogenic sediments mantle most of the surface. Bedrock of the Quesnel Terrane outcrops are mostcommon in the north-east and southern areas of the map sheet, as well as in the major valleys on south facingslopes.
QUATERNARY HISTORY
The stratigraphic record and surficial geology of the study area is primarily the product of the Fraser Glaciationand associated depositional environments. Subordinate amounts of older sediment exist but are rare or occurbelow the current river level and are not exposed. Till and ice-contact sediment record the presence of glaciersand possible inundation of the Quesnel River valley prior to the late Wisconsin, > 59 ka BP(Clague 1992),during the climax and onset of deglaciation.
After glaciers had completely receded, a period lasting at least several thousand years of warmer, ice-freeclimate ensued (Clague . 1990). This period is known as the Olympic Interstade. During this time, theancestral Quesnel and Cariboo River valleys became incised to a similar level as found today (Clague 1991).
By the Late Wisconsin, the climate had once again cooled and glaciers began to expand from the highlands,such as the Cariboo Mountains to the east, where they had previously been confined. This was the start of theFraser Glaciation. Drainage in the major valleys became obstructed by outwash sediments, advancing glacialice, or some other mechanism.
The inundated valleys acted as sediment traps for sediment shed from advancing glaciers, filling the valley to atleast 730 m asl ( 100 m above current river level). As glaciers approached, the sediment deposited in thelake(s) became coarser. At some point the lake(s) became over-deepened, shortly before glaciers advancedthroughout the region.
Glacial flow during the peak of the Fraser Glaciation is recorded by the abundant subglacial bedforms foundthroughout the study area, though less common in the northeast corner. Drumlinoid ridges, flutings and striaeshow a northwest-southeast orientation of ice flow whereas drumlins and craig and tails indicate flow to thenorthwest.
Deglaciation likely occurred as suggested by Fulton (1991) with alpine areas initially becoming free of ice andsubsequently leaving detached, stagnating ice at lower elevations. As ice down-wasted, meltwater channelsformed along ice margins, many of which can be seen on the plateaus. The presence of a large meltwaterchannel that connects the Cariboo River to Quesnel Lake, near the town of Likely, may be an indication that thelower reach of the Cariboo River valley was obstructed by ice or valley fill.
Evidence for recessional phase lakes and fluvial systems is scattered about the plateaus, though concentratedalong the main drainage courses. As the drainage system became more well established, it began to erodethrough valley fill sediment, creating the succession of glaciofluvial terraces found in the major valleys.
Throughout the Holocene, denudation continued and eventually established the current drainage system.
et al
ca.
REFERENCESBichler, A.J. 2003. Landslides, stratigraphy and surficial geology of the Hydraulic map sheet (NTS 93A/12).
University of Victoria, Victoria.
British Columbia Resources Inventory Committee, 1996. Guidelines and standards for terrain mapping inBritish Columbia, British Columbia Ministry of Forests, Victoria.
Clague, J.J., 1991. Quaternary stratigraphy and history of Quesnel and Cariboo river valleys, British Columbia:implications for placer gold exploration. Current Research, Part A(Geological Survey of Canada, Paper91-1A): 1-5.
Clague, J.J., Hebda, R.J. and Mathewes, R.W., 1990. Stratigraphy and paleoecology of Pleistocene interstadialsediments, central British Columbia. Quaternary Research, 34: 208-226.
Fulton, R.J., 1991. A conceptional model for growth and decay of the Cordileran Ice Sheet. Geographiephysique et Quaternaire, 45(No. 3): 281-286.
Holland, S., 1976. Landforms of British Columbia, a physiographic outline, Bulletin 48. B.C. Ministry ofEnergy, Mines and Petroleum Resources, 138 pp.
Howes, D.E. and Kenk, E., 1997. Terrain classification system for British Columbia. Version 2, BritishColumbia Ministry of Environment, Lands and Parks, Victoria.
Levson, V.M. and Giles, T.R., 1993. Geology of Tertiary and Quaternary gold-bearing placers in the Caribooregion, British Columbia (93A, B, G, H), British Columbia Ministry of Energy and Mines, Victoria.
Meidinger, D. and Pojar, J., 1991. Ecosystems of British Columbia. no. 6, B.C. Ministry of Forests.
ACKNOWLEDGMENTS
Funding and logistical support for field checks of terrain polygons was provided by the British ColumbiaGeological Survey Branch. Fieldwork was carried out with the assistance of Adrian Hickin, Hart Bichler, PaulGrant and Roger Paulen. In addition, mapping and stratigraphy has benefited from the technical advice ofVictor Levson and John Clague.
RECOMMENDED CITATION
Bichler, A.J. and Bobrowsky, P.T., 2003. Quaternary geology of the Hydraulic map sheet (NTS 93/A12),British Columbia. British Columbia Geosciences, Research and Development Branch, Open File 2003-7, scale 1:50 000.
Quesnel
Lake
Polly
Lake
Likely
Cariboo River
Quesnel River
Maud
Lake
Le
Bourdais
Lake
Morehead Lake
Little Lake
Joan Lake
Cham
berLake
Opheim
Lake
Jaco
bie
Lake
Bootjack
Lake
TrioLake
JackpineLake
RollieLake
Wolverine Lake
INTRODUCTION
Surficial geology of the Hydraulic map sheet (NTS 93A/12) was mapped in partial fulfilment of a Master's ofScience thesis being conducted at the University of Victoria and in association with the British ColumbiaGeosciences, Research and Development Branch and the Geological Survey of Canada. The region wasmapped at a scale of 1:50 000, using 1:40 000-scale, black and white, vertical aerial photographs(15BCB960011, 15BCB98020, 15BCB98021 and 15BCB98023).
Mapping methodology followed the Guidelines and Standards for Terrain Mapping in British Columbia (BritishColumbia Resource Inventory Committee 1996) and the Terrain Classification System for British Columbia(Howes and Kenk 1997). The study area was divided into terrain units based on the surficial material,geomorphic attributes, and geologic/geomorphic processes found within their boundaries. Each enclosedterrain unit, or terrain polygon, represents a homogeneous parcel of land with respect to its inherent attributes.
Three hundred and twenty eight terrain polygons were identified of which 104 were ground-truthed by 137 fieldstations. This yields approximately 32% of the polygons verified and corresponds to a Terrain Survey IntensityLevel (TSIL) C as described by the British Columbia Resource Inventory Committee (1996). For all fieldstations, location and a description of the surficial material including its type, texture, thickness and geomorphicexpression were recorded.
Fieldwork for surficial mapping and stratigraphy was conducted in 2001, making use of an extensive networkof logging roads in addition to using a boat along the Quesnel and Cariboo Rivers. Most of the majorstratigraphic sections are located along these rivers, as well as within an excavated, buried channel (Bullion Pit)that contains the most complete known stratigraphic sequence in the region (refer to Clague . 1990). Intotal, 21 stratigraphic sections were logged in detail and are discussed by Bichler (2003).
et al
Tertiary
Pre-Late Wisconsin
Late Wisconsin
Holocene
Fluvial gravel:
Penultimate till:
b
Recessional ice contact and glaciofluvial:
c d
Interglacial sediment:e et al
Advance glaciolacustrine:
A f
Fraser till:D h
C
Recessional glaciofluvial:E
Fluvial/glaciofluvial gravel:
Other modern sediments:
These sediments were commonly sought after by placer miners duringthe past several decades.
This is the oldest till in the region. It is a very well-compacted, clayey, silt diamictoncontaining 25% to 35% clasts. Clasts are subrounded to angular and range up to boulder in size. Clasts arecommonly faceted and striated. It is interpreted as belonging to the penultimate glaciation and has beendescribed at only two locations in the study area, at the Bullion Pit (unit ) and at section AJB02-S12.
Sediments of these types are sandy gravel interbedded with mediumto coarse sand and diamicton at its base. Generally, they exhibit crude stratification and imbrication withintertonguing lithologies and deformation structures. Clasts are subrounded to angular and range up to boulderin size. These sediments were laid subaqueously in close proximity to receding glaciers. More typical fluvialcharacteristics increase up-stratigraphy. These units (unit and ) are found directly overlying penultimate till
at the Bullion Pit and at section AJB02-S12.
The only known location of interglacial sediment within the study area occurs at theBullion Pit (unit ) and is described and dated by Clague . (1990). It consists of interbedded peat andorganic-rich silt, sand and gravel. Radiocarbon dates obtained from woody debris range from 46 300 ± 1740 to36 840 ± 430 years before present.
This unit is the most extensive unit found in the major valleys and can be more than100 m thick. It is characterized by sub-horizontal, rhythmically bedded sand, silt and clay in a coarseningupwards sequence (AJB01-L9, unit ; Bullion Pit, unit ). In places, the sediments are coarser, composed ofinterbedded gravel, sand and silt. This is particularly true for the Cariboo River valley. In a complete sequence,the upper, coarser beds become more steeply dipping and resemble foreset beds of a deltaic environment. Theunit is often capped by fine-grained sediment, either rhythmically bedded or massive clay or silt
. Near the upper surface of the silt or clay cap, dropstones are commonly found.
The youngest till is well-compacted, silty, clay diamicton that may contain small, amorphouspockets of sand (AJB01-L9, unit ; Bullion Pit, unit ). It typically consists of 30% to 35% clasts. The clastsrange up to large boulder in size, are subrounded to angular in shape and are commonly faceted and striated.Where it conformably overlies glaciolacustrine sediment, it may contain intertonguing, poorly sorted, gravellenses and have a sandier matrix (AJB01-L9, unit ).
In the most complete sections, steeply dipping gravel overlies till (AJB01-L9, unit). In general, the sections are well bedded, moderately sorted, pebble, cobble gravel with a coarse sand
matrix. Locally, the gravel may have an open framework and be clast supported. Clasts range from
subrounded to subangular in shape.
Older sediments were eroded by river systems fed by receding glaciers and haveformed a series of successively lower glaciofluvial terraces within the valleys. The highest, most well definedterraces occur approximately 70 m above the current river level. These terraces are composed of moderately topoorly sorted cobble gravel with a sand matrix. Clasts are typically rounded to subangular and range in size tolarge boulder. Imbrication consistent with the modern drainage direction is commonly found within these
sediments.
The most recent deposits in the region include organic, fluvial and colluvialsediments. Organic deposits are found primarily in fens and bogs; fluvial sediment alongside active drainagecourses; and colluvium on steep valley slopes or valley bottoms where mass wasting processes have transported
This unit is present at the base of the Bullion Pit (unit ). Most often the unit is foundunconformably overlying bedrock and are typically: strongly cemented, well stratified, well imbricated andwell rounded (Levson and Giles 1993).
(AJB01-L9,
unit ; Bullion Pit, unit )
a
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(F)
(M)
(F )
(L)
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(L )
(M)
(F )
(F, F )
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/Mb
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Subclasses
QualifierTexture
SurficialMaterial
SurfaceExpression
StratigraphicRelation
Delimiter
GeomorphicalProcesses
SurficialMaterial
C
F
L
O
R
A
M
Anthropogenic
Colluvium
Fluvial
Lacustrine
Morainal
Organic
Bedrock
Delimiter
/ Surficial material in front of symbolis more extensive than the followingmaterial if no surficial materialprecedes symbol, then it indicates apartial covering of the followingmaterial
or
// Surficial material in front of symbolis much more extensive than thefollowing material
Surficial material in front of symbolis approximately equally extensive asthe following material
SurfaceExpression
a
b
f
h
j
k
m
p
r
s
t
u
v
w
Moderate slope
Blanket
Fan
Hummocky
Gentle slope
Moderately steepslope
Rolling
Plain
Ridges
Steep slope
Terrace
Undulating
Mantle of variablethickness
Veneer
StratigraphicRelation
Indicates a stratigraphic relationship;read as a fraction, the materialindicated in the numerator is foundoverlying the material described bythe denomenator
Texture
c
s
g
z
Clay
Gravel
Silt
Sand
Qualifier
G
A
Indicates the material has a glacialdepositional origin
Indicates that the depositionalenvironment in which the materialwas deposited is still active
GeomorphicalProcesses
E
F
M
R
V
Channeled by meltwater
Slow mass movement
Meandering channel
Rapid mass movement
Gully erosion
Subclasses
e
x
Earthflow
Slump-flow
(Modified from Howes and Kenk 1997)
C
F
LG
M
O
A
Quaternary
Holocene
FG
Pleistocene
R
Pre-Quaternary
ORGANIC: Thick accumulations of water-saturated, organic rich peat thatoccurs often as a level blanket of fibric material found in bogs, fens and otherlow-lying, poorly drained areas.
ANTHROPOGENIC: Surficial material that has been modified by humanactivities so that its natural physical properties (e.g. internal structure,compaction, cohesion) are no longer evident. Making up most of thesematerials are mine tailings as well as washed sand and gravel from placermines.
FLUVIAL: Cobble gravel with sand matrix associated with the avulsion ofwater courses. Sediment is deposited in gravel bars and low fluvial terraces.In subordinate valleys, fluvial sediments, consisting of fine to coarse sandfound within the floodplains.
COLLUVIUM: Poorly sorted, sandy to gravelly diamicton with weak toweakly moderate compaction. Where colluvial deposits are the result ofmass wasting of glaciolacustrine sediment, they tend to be clay or silt richand contain organic debris. At the base of steep rock cliffs, colluvium istypically talus, composed of angular, cobble or boulder clasts.
GLACIOLACUSTRINE: Thick accumulations of interbedded sand, silt,and clay. May also occur as rhythmically bedded silt and clay. In largeexposures, a general coarsening upwards succession is observed, oftencapped by a massive unit of clay or silt. This succession most notablyoccurs in the major valleys, underlying fluvial and glaciofluvial terraces.
GLACIOFLUVIAL: Typically moderately sorted, weak to moderatelycompacted, cobble or boulder cobble gravel with a sand matrix. Clasts arerounded to subrounded. They are found as well-defined terraces in themajor valleys up to approximately 70 m above river level or as irregulardeposits at higher elevations on valley slopes or on plateaus. They areassociated with melt-water channels or drainage courses.
MORAINAL: Poorly sorted, moderate to well compacted, clayey to siltydiamicton. Clasts are subrounded to subangular, range from pebbles toboulders and may be faceted and/or striated. Interpreted as lodgement till.Irregular sand and gravel lenses may be present where till was deposited
r in association with flowing water. At higher elevations, inthe northeast region of the map sheet, less compact, boulder rich ablation tillexists.
subaqueously o
BEDROCK: Quesnel Terrane, upper Triassic to lower Jurrasic rocks relatedto a volcanic arc.
SYMBOLS
Paved
Gravel
Roads
Contour(60 m interval)
River/Stream
Geographical Features
Striae(bi-directional)
Drumlin(uni-directional)
Fluting(bi-directional)
Craig and Tail(uni-directional)
Melt Water Channel
Ice Flow/ContactFeatures
Sharp
Clear
Gradational
Terrain Boundaries
StratigraphicSection
Mapping ControlPoint
Fieldwork Stations
G1
L1
SURFICIAL GEOLOGY
Qu
esnel
Lake
Quesnel R.
Cariboo R.
Polly
Lak
e
Quesnel R.
Likely
485815BCB96001
17716715BCB98021
15BCB9802341
51
15BCB9802382
72
15BCB9802056
46
AERIAL PHOTOGRAPH FLIGHT LINES
SURFICIAL GEOLOGY
Much of the surficial material in the study area can be attributed to the Fraser Glaciation of the Late Wisconsin.Over the plateau, till is the most dominant surficial material. Morainal terrain units make up 86% of the entiremapped area. Till typically occurs as a thick blanket (>1 m thick) that masks local topography. It is poorlysorted, moderate to well-compacted, silty clay diamicton. At surface the till is often heavily washed, with thefine-grained component removed by weathering and erosion. These deposits are interpreted as lodgement till,except at higher elevations north of the Quesnel River in the eastern part of the map sheet where till is lesscompact, boulder rich, and has a sandy matrix. There, deposits are interpreted as ablation till.
Many streamlined landforms occur in association with ground moraine, in which flutings are most common,especially in the northeast map quadrant. Flutings are up to 1.5 km in length and 100 m wide. They are readilyidentifiable from airphotos where flute ridges are forested and depressions between adjacent flutes aredominated by fens. Within logged areas, these depressions show a dark tonal change that is indicative of
organic rich soil and high moisture content. Flutings have a mean bi-directional orientation of 315 or 45 . In
the southeastern region, their orientation has a stronger east-west component ( 300 ), with an increasing
north-south orientation in the northwest ( 330 ).
Drumlins, drumlinoid ridges, and craig and tail features are less common but occur in similar regions as
flutings. These features have orientations on average 308 but also range from 300 to 330 . These streamlinedforms are generally shorter than flutings, up to 500 m in length, and have similar widths.
Glaciofluvial sediments comprise 6% of the study area and are concentrated within the major valleys. They aretypically moderately sorted, weak to moderately compacted, cobble or boulder gravel with a sand matrix.These sediments are found in a succession of well-defined terraces ranging in height from a metre above thecurrent river level to 70 m high. The gravel that occurs at the surface of the terraces is up to 5 m thick. Atsome locations, glaciofluvial gravel is found at higher elevations on valley sides in the form of hummockyblankets up to 10 m thick. Also found within valleys are glaciofluvial fans that are composed of sedimentssimilar to those in the terraces, but are sandier. In upland regions, glaciofluvial sediment is dominantly sandy,pebble gravel that occurs in isolated areas, associated with meltwater channels.
The remaining 8% of the region consists of minor amounts of glaciolacustrine sediment, organic material (i.e.,fens and bogs), colluvium, modern fluvial deposits and anthropogenically disturbed stratum. It is important tonote that though glaciolacustrine sediment only covers a very small percentage of the surface (<1%), itunderlies virtually all terraces found within the major valleys.
º ºº
º
º º
ca.
ca.
º
STRATIGRAPHY
The stratigraphy of unconsolidated sediments is summarized based on observations made during fieldwork, aswell from previous studies (e.g. Clague 1990, Clague 1991, Levson and Giles 1993). Two stratigraphiccolumns are provided that illustrate the succession of units described herein
et al.(see accompanying columns
AJB01-L9 and Bullion Pit).
BR
ITIS
H COLUM
BIA
GE
OLOGICAL SURV
EY
Ministry of Energy and MinesMines and Minerals DivisionGeosciences, Research andDevelopment Branch
2000 0 2000 4000 m
Scale 1:50 000
Universal Transverse Mercator Grid Zone 10North American Datum 83
QUATERNARY GEOLOGY OF THEHYDRAULIC MAP SHEET (NTS 93 A/12)
BRITISH COLUMBIA
OPEN FILE 2003-7
A.J. Bichler, University of VictoriaP.T. Bobrowsky, Geological Survey of Canada
sand pe
bble
cobb
le
boulde
rclay si
lt f m c
UnitNumber Lithology
780E
620
660
700
740
Elevation(m asl)
D
C
A680
760
720
640
AJB01-L9
36, 840 �����
�����
to
46,300
36, 840 to
46,300
�����
�����
Bullion Pit
sand pe
bble
cobb
le
boulde
rclay si
lt f m c
UnitNumber Lithology
860h
760
780
820
Elevation(m asl)
g
f
e
840
800
d
c
b
a
880
B
FG
M
FG
LG
L
LG
M
LG
M
FG
LG
M
Digital base map from British Columbia Ministry of Environment, Lands and ParksModified from 1:20 000 TRIM digital data
53 30'º
121
30'
º
52 45'º
122
00'
º