open file 2003-7 52 45' lake quaternary geology of the...

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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 still left standing. The mapped area lies on the eastern edge of the Interior Plateau at the boundary of the Quesnel Highlands and the 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 and Cariboo Lakes (northeast of mapped area), respectively. The Quesnel River valley is an east-west trending topographic low that is on average 280 metres deep and approximately 1.5 kilometres wide. Flow within the valley is to the west. The river drops 90 metres in elevation over a distance of 32 kilometres. The Cariboo River 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 at higher altitudes the Engelmann spruce-subalpine fir zone dominates (Meidinger and Pojar 1991). The primary soils belonging to these zones are luvisols, podzols, and brunisols. Seasonal extremes typify the climate with severe snowy winters contrasting relatively warm, moist summers. The area experiences a moderate annual precipitation (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 most common in the north-east and southern areas of the map sheet, as well as in the major valleys on south facing slopes. QUATERNARY HISTORY The stratigraphic record and surficial geology of the study area is primarily the product of the Fraser Glaciation and associated depositional environments. Subordinate amounts of older sediment exist but are rare or occur below the current river level and are not exposed. Till and ice-contact sediment record the presence of glaciers and 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-free climate ensued (Clague . 1990). This period is known as the Olympic Interstade. During this time, the ancestral 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 the Fraser Glaciation. Drainage in the major valleys became obstructed by outwash sediments, advancing glacial ice, or some other mechanism. The inundated valleys acted as sediment traps for sediment shed from advancing glaciers, filling the valley to at least 730 m asl ( 100 m above current river level). As glaciers approached, the sediment deposited in the lake(s) became coarser. At some point the lake(s) became over-deepened, shortly before glaciers advanced throughout the region. Glacial flow during the peak of the Fraser Glaciation is recorded by the abundant subglacial bedforms found throughout the study area, though less common in the northeast corner. Drumlinoid ridges, flutings and striae show a northwest-southeast orientation of ice flow whereas drumlins and craig and tails indicate flow to the northwest. Deglaciation likely occurred as suggested by Fulton (1991) with alpine areas initially becoming free of ice and subsequently leaving detached, stagnating ice at lower elevations. As ice down-wasted, meltwater channels formed along ice margins, many of which can be seen on the plateaus. The presence of a large meltwater channel that connects the Cariboo River to Quesnel Lake, near the town of Likely, may be an indication that the lower 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 concentrated along the main drainage courses. As the drainage system became more well established, it began to erode through 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. REFERENCES Bichler, 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 in British 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, Paper 91-1A): 1-5. Clague, J.J., Hebda, R.J. and Mathewes, R.W., 1990. Stratigraphy and paleoecology of Pleistocene interstadial sediments, central British Columbia. Quaternary Research, 34: 208-226. Fulton, R.J., 1991. A conceptional model for growth and decay of the Cordileran Ice Sheet. Geographie physique et Quaternaire, 45(No. 3): 281-286. Holland, S., 1976. Landforms of British Columbia, a physiographic outline, Bulletin 48. B.C. Ministry of Energy, Mines and Petroleum Resources, 138 pp. Howes, D.E. and Kenk, E., 1997. Terrain classification system for British Columbia. Version 2, British Columbia 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 Cariboo region, 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 Columbia Geological Survey Branch. Fieldwork was carried out with the assistance of Adrian Hickin, Hart Bichler, Paul Grant and Roger Paulen. In addition, mapping and stratigraphy has benefited from the technical advice of Victor 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 C a r i b o o R i v e r Q uesnel Ri v e r Maud Lake Le Bourdais Lake Morehead Lake Little Lake Joan Lake Chamber Lake Opheim Lake Jacobie Lake Bootjack Lake Trio Lake Jackpine Lake Rollie Lake W o lve ri n e La k e INTRODUCTION Surficial geology of the Hydraulic map sheet (NTS 93A/12) was mapped in partial fulfilment of a Master's of Science thesis being conducted at the University of Victoria and in association with the British Columbia Geosciences, Research and Development Branch and the Geological Survey of Canada. The region was mapped 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 (British Columbia 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 enclosed terrain 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 field stations. This yields approximately 32% of the polygons verified and corresponds to a Terrain Survey Intensity Level (TSIL) C as described by the British Columbia Resource Inventory Committee (1996). For all field stations, location and a description of the surficial material including its type, texture, thickness and geomorphic expression were recorded. Fieldwork for surficial mapping and stratigraphy was conducted in 2001, making use of an extensive network of logging roads in addition to using a boat along the Quesnel and Cariboo Rivers. Most of the major stratigraphic 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). In total, 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 during the past several decades. This is the oldest till in the region. It is a very well-compacted, clayey, silt diamicton containing 25% to 35% clasts. Clasts are subrounded to angular and range up to boulder in size. Clasts are commonly faceted and striated. It is interpreted as belonging to the penultimate glaciation and has been described 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 medium to coarse sand and diamicton at its base. Generally, they exhibit crude stratification and imbrication with intertonguing lithologies and deformation structures. Clasts are subrounded to angular and range up to boulder in size. These sediments were laid subaqueously in close proximity to receding glaciers. More typical fluvial characteristics 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 the Bullion Pit (unit ) and is described and dated by Clague . (1990). It consists of interbedded peat and organic-rich silt, sand and gravel. Radiocarbon dates obtained from woody debris range from 46 300 ± 1740 to 36 840 ± 430 years before present. This unit is the most extensive unit found in the major valleys and can be more than 100 m thick. It is characterized by sub-horizontal, rhythmically bedded sand, silt and clay in a coarsening upwards sequence (AJB01-L9, unit ; Bullion Pit, unit ). In places, the sediments are coarser, composed of interbedded 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. The unit 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, amorphous pockets of sand (AJB01-L9, unit ; Bullion Pit, unit ). It typically consists of 30% to 35% clasts. The clasts range 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, gravel lenses 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 have formed a series of successively lower glaciofluvial terraces within the valleys. The highest, most well defined terraces occur approximately 70 m above the current river level. These terraces are composed of moderately to poorly sorted cobble gravel with a sand matrix. Clasts are typically rounded to subangular and range in size to large 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 colluvial sediments. Organic deposits are found primarily in fens and bogs; fluvial sediment alongside active drainage courses; 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 found unconformably overlying bedrock and are typically: strongly cemented, well stratified, well imbricated and well rounded (Levson and Giles 1993). (AJB01-L9, unit ; Bullion Pit, unit ) a B g (F) (M) (F ) (L) G (L ) (M) (F ) (F, F ) G G G /Mb csL G -Rx Subclasses Qualifier Texture Surficial Material Surface Expression Stratigraphic Relation Delimiter Geomorphical Processes Surficial Material C F L O R A M Anthropogenic Colluvium Fluvial Lacustrine Morainal Organic Bedrock Delimiter / Surficial material in front of symbol is more extensive than the following material if no surficial material precedes symbol, then it indicates a partial covering of the following material or // Surficial material in front of symbol is much more extensive than the following material Surficial material in front of symbol is approximately equally extensive as the following material Surface Expression a b f h j k m p r s t u v w Moderate slope Blanket Fan Hummocky Gentle slope Moderately steep slope Rolling Plain Ridges Steep slope Terrace Undulating Mantle of variable thickness Veneer Stratigraphic Relation Indicates a stratigraphic relationship; read as a fraction, the material indicated in the numerator is found overlying the material described by the denomenator Texture c s g z Clay Gravel Silt Sand Qualifier G A Indicates the material has a glacial depositional origin Indicates that the depositional environment in which the material was deposited is still active Geomorphical Processes 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 L G M O A Quaternary Holocene F G Pleistocene R Pre-Quaternary ORGANIC: Thick accumulations of water-saturated, organic rich peat that occurs often as a level blanket of fibric material found in bogs, fens and other low-lying, poorly drained areas. ANTHROPOGENIC: Surficial material that has been modified by human activities so that its natural physical properties (e.g. internal structure, compaction, cohesion) are no longer evident. Making up most of these materials are mine tailings as well as washed sand and gravel from placer mines. FLUVIAL: Cobble gravel with sand matrix associated with the avulsion of water courses. Sediment is deposited in gravel bars and low fluvial terraces. In subordinate valleys, fluvial sediments, consisting of fine to coarse sand found within the floodplains. COLLUVIUM: Poorly sorted, sandy to gravelly diamicton with weak to weakly moderate compaction. Where colluvial deposits are the result of mass wasting of glaciolacustrine sediment, they tend to be clay or silt rich and contain organic debris. At the base of steep rock cliffs, colluvium is typically 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 large exposures, a general coarsening upwards succession is observed, often capped by a massive unit of clay or silt. This succession most notably occurs in the major valleys, underlying fluvial and glaciofluvial terraces. GLACIOFLUVIAL: Typically moderately sorted, weak to moderately compacted, cobble or boulder cobble gravel with a sand matrix. Clasts are rounded to subrounded. They are found as well-defined terraces in the major valleys up to approximately 70 m above river level or as irregular deposits at higher elevations on valley slopes or on plateaus. They are associated with melt-water channels or drainage courses. MORAINAL: Poorly sorted, moderate to well compacted, clayey to silty diamicton. Clasts are subrounded to subangular, range from pebbles to boulders 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, in the northeast region of the map sheet, less compact, boulder rich ablation till exists. subaqueously o BEDROCK: Quesnel Terrane, upper Triassic to lower Jurrasic rocks related to 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/Contact Features Sharp Clear Gradational Terrain Boundaries Stratigraphic Section Mapping Control Point Fieldwork Stations G1 L1 SURFICIAL GEOLOGY Q u e s n e l Lake Quesnel R. Cariboo R. Polly L a k e Quesnel R. Likely 48 58 15BCB96001 177 167 15BCB98021 15BCB98023 41 51 15BCB98023 82 72 15BCB98020 56 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 entire mapped area. Till typically occurs as a thick blanket (>1 m thick) that masks local topography. It is poorly sorted, moderate to well-compacted, silty clay diamicton. At surface the till is often heavily washed, with the fine-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 less compact, 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 readily identifiable from airphotos where flute ridges are forested and depressions between adjacent flutes are dominated 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 streamlined forms 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 are typically 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 the current river level to 70 m high. The gravel that occurs at the surface of the terraces is up to 5 m thick. At some locations, glaciofluvial gravel is found at higher elevations on valley sides in the form of hummocky blankets up to 10 m thick. Also found within valleys are glaciofluvial fans that are composed of sediments similar 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 to note that though glaciolacustrine sediment only covers a very small percentage of the surface (<1%), it underlies virtually all terraces found within the major valleys. º º º º º º ca. ca. º STRATIGRAPHY The stratigraphy of unconsolidated sediments is summarized based on observations made during fieldwork, as well from previous studies (e.g. Clague 1990, Clague 1991, Levson and Giles 1993). Two stratigraphic columns are provided that illustrate the succession of units described herein et al. (see accompanying columns AJB01-L9 and Bullion Pit). B R I T I S H C O L U M B I A G E O L O G I C A L S U R V E Y Ministry of Energy and Mines Mines and Minerals Division Geosciences, Research and Development Branch 2000 0 2000 4000 m Scale 1:50 000 Universal Transverse Mercator Grid Zone 10 North American Datum 83 QUATERNARY GEOLOGY OF THE HYDRAULIC MAP SHEET (NTS 93 A/12) BRITISH COLUMBIA OPEN FILE 2003-7 A.J. Bichler, University of Victoria P.T. Bobrowsky, Geological Survey of Canada sand pebble cobble boulder clay silt fmc Unit Number Lithology 780 E 620 660 700 740 Elevation (m asl) D C A 680 760 720 640 AJB01-L9 36, 840 ± 940 ± 940 to 46,300 36, 840 to 46,300 ± 940 ± 940 Bullion Pit sand pebble cobble boulder clay silt fmc Unit Number Lithology 860 h 760 780 820 Elevation (m asl) g f e 840 800 d c b a 880 B F G M F G L G L L G M L G M F G L G M Digital base map from British Columbia Ministry of Environment, Lands and Parks Modified from 1:20 000 TRIM digital data 53 30' º 121 30' º 52 45' º 122 00' º

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Page 1: OPEN FILE 2003-7 52 45' Lake QUATERNARY GEOLOGY OF THE ...cmscontent.nrs.gov.bc.ca/geoscience/Publication... · Mbu Mbu Mbu Mh Mh Mh Mh Mh-E Mh-E Mh-E Mh-E Mj Mj Mj Mj Mj Mj Mbj Mj

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G

G.

F h

csL

G

G

F j

csL

G

G.

F t

L

G

G

Ma

LG

Ma

LG -V

Mb

csLG

-VR

MbRh

MbRr

Mb//F bRh

G

Mb/Cb

LG

Mj

csL.

G

MvRh

MwRh

MwRha

MwRr

MwRh

-E

Cb/Mb/LG

Cb

LG

/MwrRh

/MwRha

/MwRh

/MmRh

/MbRh

/MvRh

CvRk

A

Cb

Cb/FG

Cb/Fb/Mb

G

Cb/Mb

Cb/Mb-V

Cb/Ms

Cb-FCbh

Cb-R

Cs

Cs/Mb

Cs/Mb-V

csCb-Rx

Cvs-E

Cw/FG

F p/L -MA G

Fp-M

A

Mb/F bG

F b/CbG

F b/MbG

F b/Mb-VG

F b-EG

F fG

F htG

F tG

F t/MbG

L b/FG G

L p//MbG

Ma

Mb

Mb//F bG

Mb//F b-EG

Mb//F w-EG

Mb//Op

Mb/Cb

Mb/Cb-V

Mb/F bG

Mb/F

-VG

Mb/L

-VG

Mb/Op

Mba

Mba/F bG

Mb-E

Mbh//F bG

Mbj

Mbk/Cv

Mbm

Mbu

Mbu-E

Mbu-V

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

G

Mub

Mu-E

Mw

Mw//R

Mw//Rh

Mwh

Mws/Cs

Rs/Cv

Rs/Cv

zsCb-R zsCb-Rx

Mp

Mp

Op

Op

Op

Op

Op

Op

Op

Op

Op

O/F p-MA

Op

Op

Op

Op

Op/F pA

Op

Op/F pA

Op

Op

Op

Op

Op

Op

Op

Op

Op

Op

Op

/MbRh

/MvRh

/MwRh

/MwRh

/MwRh

F t

csL

G

G F t

L

G

G

F t

L

G

GF t

L

G

G

F t

L

G

G

F t

L

G

G

F t

L

G

G

F t

csL

G

G

F t

csL

G

G

F t

csL

G

G

F t

csL

G

G

F t

csL

G

G

F t

csL

G

G

F t

csL

G

G

F t

csL

G

G

F t

csL

G

G

F h

csL

G

G

F h

csL

G

G

Ft

Ft

FtF h

csL

G

G

F h

csL

G

G

F h

csL

G

G

F h

csL

G

G

F h

csL

G

G

F h

csL

G

G

F h

csL

G

G

MbRh

MbRh

MbRh

Mb/F t

sgL

G

G Mb/F t

sgL

G

G

A

A

A

A

A

A

A

Cb

Cb/Mb

Cb/Mb

Cb/Mb

Cb/M

b

Cb/Mb-V

Cs/Mb

Cs/Mb

F p/L -MA G

Fp/L

-MA

G

F fG

F fG

F fG

F fG

F fG

F fG

F fG

F fG

F fG

F fG

F fG

F fG

F fG

F fG

F fG

F htG

F tG

F tG

F tG

F tG

F tG

F tG

F tG

Ma

Ma

Ma

Ma

Ma

Mb

Mb

Mb

Mb

Mb

Mb

Mb

Mb

Mb

Mb

Mb

Mb

Mb

Mb

Mb

Mb Mb

Mb

Mb

Mb Mb

Mb

Mb

Mb

Mb-E

Mb-E

Mb-E

Mb-E

Mb-E

Mb-E

Mb-V

Mb-V

Mb-V

Mb-V

Mb-V

Mb//F bG

Mb//F bG

Mb/Cb

Cb/Mb-V

Mb/F bG

Mb/F bG

Mb/F bG

Mb/Op

Mbu

Mbu

Mbu

Mh

Mh

Mh

Mh

Mh-EMh-E

Mh-E

Mh-E

Mj

Mj

Mj

Mj

Mj

Mj

Mbj

Mj

Mm

Mm

Mm

Mm

Mm

Mm

Mm

Mm

Mbr

Mr

Mr

Mr

Mu

Mu

Mbh

Mu

Mu

Mu-E

Mw

Mw//R

Mw//Rh

Mw//Rh

Mwh

Rs/Cv

Rs/Cv

Rs/Cv

zsCb-R

x

Cb/M

b/F

b-V

G

G44

G45

G46

G47

G28

G64

G80

G82

G81

G63

G29

G84

G35

G87

G40

CbMb

LG -V

CbMb

LG -V

CbMb

LG -V

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

B g

(F)

(M)

(F )

(L)

G

(L )

(M)

(F )

(F, F )

G

G

G

/Mb

csLG -Rx

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