SURFICIAL GEOLOGY - Central Saanich

SURFICIAL GEOLOGY 

SURFICIAL GEOLOGY AND GEOMORPHOLOGY OF 

CENTRAL SAANICH PENINSULA, SOUTHEASTERN 

VANCOUVERISLAND 

1 2 3 

David Huntley, Katrina Bennett , Peter Bobrowsky and John 

4 

Clague 

1.WesternGeographicResearch,505-350DouglasStreet,Victoria,B.C. 

2.LatitudeGeographicsGroup,257MarketSquare,Victoria,B.C. 

3.BritishColumbiaGeologicalSurvey,MinistryofEnergyandMines,Victoria,B.C. 

4.DepartmentofEarthSciences,SimonFraserUniversity,Burnaby,B.C. 

INTRODUCTION 

ThissectionsummarisesthesurficialgeologyandQuaternaryhistoryof 

central Saanich Peninsula. The map, figures and text also provide 

baselineinformationforinterpretingthedistributionofgroundwaterand 

aggregateresources,potentiallyunstablelandareas,soilsandvegetation 

cover. Fieldwork and research was undertaken for Ocean Drilling 

Programleg169S andtheResourceAtlasProjectoftheEnvironmental 

AdvisoryCommissionoftheMunicipalityofCentralSaanich. Support 

wasprovidedbytheCentreforEarthandOceanResearch,Universityof 

Victoria, the British ColumbiaGeological Survey Branch andMinistry 

ofEnvironment,LandsandParks,theGeologicalSurveyofCanadaand 

NationalScienceandEngineeringResearchCouncilofCanada. 

Landformsandsurficialsedimentsweremappedfromobservationsat39 

fieldsites and from 1:23 000 and 1: 70 000 scale air photographs. 

Surficial units were defined on the basis of landform associations, 

texture, sorting, fissility, colour, sedimentary structures, consolidation 

andcontactrelationships.Icedispersalpatternshavebeeninferredfrom 

striae,flutes,drumlins,rochesmoutonnes,andlong-axisorientationsof 

clastsintill.Meltwaterflowdirectionswereinferredfromforeset-cross 

and ripple-bedding, clast imbrication and channel orientations. 

Additionalinformationwascompiledfromearlier regionalstudies(e.g. 

Fyles 1963, Halstead 1966, 1968, Clague 1976, 1977, Alley and 

Chatwin, 1979,Hicock andArmstrong 1983,Bornhold et al.1997 and 

1998); 1:63,360 and 1:50,000 scale surficial geology maps (Halstead 

1966,BlythandRutter1993,Huntleyunpublishedmapping);1:250,000 

and 1:100,000 scale geology maps (Muller 1980, Massey et al.1994); 

soils reports and accompanying 1: 100,000 and 1:20,000 scale maps 

(Jungen 1985, Jungen et al. 1985); and the Ministry of Environment, 

LandsandParkswaterwellandlakedatabases. 

PHYSIOGRAPHY,GEOLOGYANDGEOMORPHOLOGY 

Central Saanich Peninsula lies on the southeastern margin of the 

Nanaimo Lowland and Vancouver Island Ranges (Holland 1980). The 

peninsula is bordered to the east by Cordova Channel and by Saanich 

Inlet to the west. The area is mainly underlainby fractured and faulted 

volcanicandigneousrocksrangingfromTriassic(ca.230ma)toJurassic 

(ca. 170 ma) inage (Muller 1980, Massey et al. 1994). Mount Newton 

(307 masl), thehighestpointinthe study area, is underlainbyJurassic 

granodiorite. Steep, rollinguplandsof the Partridge Hills areunderlain 

byJurassicbasalts. Undulatingandgentlyrollinglowlandterraininthe 

vicinityofBrentwoodBay,KeatingandIslandViewBeachisunderlain 

by Triassic basalts and breccia and granodiorite. Permian to Triassic 

limestonesarefoundsouthofBrentwoodBay. 

Bedrockismantledbyasurficialsedimentcoverthatrangesinthickness 

fromlessthanametreonsteepuplandslopestogreaterthan40metresin 

some lowland areas. Seven surficial units are identified (informally 

designated units 1to 7, Table G2 and G3). Units are correlated with 

previously defined sequences in adjacent coastal areas by stratigraphic 

position, sedimentology,surfaceexpressionandlandformassociations. 

The dominantlandformsanddepositsare LateWisconsinan in age(ca. 

29to10ka),andrecordtheadvance,maximumandretreatphasesofthe 

last (Fraser) glaciation. Soil textures and hydrologic characteristics 

reflectunderlyingsurficialunitsandbedrock(TableG2). 

QUATERNARYSTRATIGRAPHYAND GEOMORPHOLOGY 

Pre-LateWisconsinan 

Theoldestsurficialsedimentsare exposedinaseacliff betweenIsland 

ViewBeachand Cowichan Head (Figure G-1, logA;refer toTable G1 

for key to faciescodes used instratigraphic columns).Abasal unit, the 

Muir Point Formation, consists of non-glacial marine, alluvial, fluvial 

andcolluvial sediments, inferred todate to the Sangamonian stage (ca. 

120ka;HicockandArmstrong1983). Unit1isoverlainbyglaciofluvial 

outwash, till and fossiliferous marinebeds assigned to the Dashwood 

Drift.The age of unit 2is uncertain,butisprobably EarlyWisconsinan 

(ca. 80 to 65 ka; Fyles 1963, Hicock and Armstrong 1983). Unit 3 

includesoxidisedfluvialsandandgravel,andorganic-richestuarinesilt 

and clay. These deposits are older than 23 ka and are assigned to the 

MiddleWisconsinanCowichanHeadFormation(ArmstrongandClague 

1977). 

Late Wisconsinan - Fraser Glaciation (glacial-advance 

phase) 

Fraser Glaciationadvance-phase sediments,termed QuadraSand, were 

deposited after 29 ka (Halstead 1966, 1968, Clague 1976, 1977). Two 

facies are recognised in the study area. Unit 4a is an ice-distal facies 

consistingofwell-sortedsand,withgravel,siltandclay.Itisrestrictedto 

theeastside ofSaanichPeninsulaand islandseastof Cordova Channel 

(Figure G-1, log A). Unit 4b,informally referred to as the Saanichton 

gravel (Halstead1968), isanice-proximal facies consisting of massive 

G-1 

SURFICIALGEOLOGYAND GEOMORPHOLOGY 

to stratified gravel and sand (Figure G-8). Palaeoflow indicators are 

consistent with meltwater and sediment transport from Koksilah and 

Cowichan valleys toward Saanich Peninsula (Figure G-2, log B). 

Advance-phase glaciofluvial outwash in central Saanich Peninsula 

occursuptoapproximately100masl. 

Late Wisconsinan - Fraser Glaciation (glacial-maximum 

phase) 

Glaciallysculptedbedrock,oldersedimentsandadvance-phasedeposits 

areunconformablyoverlainbymorainaldepositscomprisingtheVashon 

Drift (Hicock and Armstrong 1985). Deposition of glacial maximum 

sediments occurred between ca. 23 and 18 ka (Clague et al. 1980). 

Morainal deposits include diamictons interpreted as lodgement and 

melt-out tills (unit 5a), and interstratified glaciofluvial gravel and sand 

(unit5b).InthePartridgeHillsandontheflanksofMt.Newton,moraine 

is extensively colluviated and best preserved in glacially-scoured 

bedrock depressions (Figure G-3, log C). Along valley floors and in 

lowland areas, unit 5forms an extensive drumlinised ground moraine 

overlyingolderunitsandstreamlinedbedrock(FiguresG-8,FigureG-1 

and G-2 logs A, B). Till textures reflect underlying materials. In the 

SaanichtonandKeating areas, tillshaveasand-richmatrixthatreflects 

derivationfromunderlyingQuadraSandandearlierunits.Inthevicinity 

ofMountNewton, BrentwoodBayand PartridgeHills,tillsarederived 

from bedrock and matrices are predominantly clay and silt-rich. The 

distributionandorientationofstriae,crag-and-tails,drumlins,andflutes 

indicate that iceflow was directed southward toward the Victoria area. 

Tillclastsanderraticbouldersarepredominantlylocallyderivedorhave 

provenances in the Koksilah andCowichan valleys. Exotic clasts have 

sources in central Vancouver Island and coastal mainland British 

Columbia. 

LateWisconsinan-FraserGlaciation(glacial-retreatphase) 

Fraser Glaciationretreat-phase sequences, termed Capilano Sediments 

(Fyles1963,Halstead1966,1968,HicockandArmstrong1985),include 

colluvial(unit6a),glaciofluvial(unit6b),glaciolacustrine(unit6c)and 

glaciomarine deposits (unit 6d). In upland areas and on valley sides, 

bedrockandmorainaldepositsareoverlainbydiamictonsinterpretedas 

ice-contactandproglacialmass-movementdeposits(FigureG-4logD). 

TerracedgravelsandcolluviumonthesouthflankofMountNewton,and 

Figure G-1. Figure G-2. Figure G-3. 

Figure G-4. 

Municipality of Central Saanich ResourceAtlas


ameltwater spillway in the Durrance Lake valley indicate astable 

recessionalicesurfaceovercentralSaanichPeninsulaatabout150masl. 

Theorientationofthesefeaturesisconsistentwithsoutheasttransportof 

meltwaterandsedimenttowardCordovaChannel.Below80masl,older 

units, moraine and bedrock are draped by raised glaciomarine debrisflowdiamictons,sandandgraveloutwash,andmassivetorhythmicallybeddedsilt-clay(FigureG-1,logA).Morainaldepositsarealsoterraced 

and winnowed,indicatingreworkingbysurfacerunoffandwaveaction 

(Figure G-9). The elevation range of unit 6d and wave-cut terraces 

delimits the extent of marine transgression over central Saanich 

Peninsula during deglaciation. Raised glaciomarine deposits are 

correlative to the earliest deglacial sediments in ODP cores1033 and 

1034,anddatebetween12and15ka(Mathewsetal.1970,Clagueetal. 

1982,Bornholdetal.1997and1998,Huntleyetal.inpress). 

Figure G-5. Figure G-6. 

Holocene(post-glaciation) 

Post-glacialsequences,termedSalishSediments(Fyles1963, Halstead 

1968), includecolluvial (unit 7a), fluvial (unit 7b), lacustrine (unit 7c) 

and marine deposits (unit 7d). On steep slopes, deglacial and older 

exposedsedimentsarepartlyreworkedbymass-movement,andlocally 

overlainbypostglacialcolluvium(FigureG-4,logD).Glaciomarineand 

morainal sediments are incised by streams. Mass-movement in the 

vicinityofSaanichtonislikelyattributedtoactivestreamincision.West 

of Sannichtonand Keating, eroded sediment is deposited along valley 

floors, in lakebasins, and inSaanich Inlet (Figure G-5 to G-7). Tothe 

east,mostsedimentisdepositedinCordovaChannelandHaroStrait.In 

situfossiltreestumpsexposedintheintertidalzoneatIslandViewBeach 

indicates marine transgression on the east coast of Saanich Peninsula 

overthelast2ka(Mathewsetal.1970).Sedimenterodedfromseacliffs 

at Cowichan Head is transported northward by long-shore drift and 

deposited mostly on Island View Beach. The intertidal zone bordering 

BrentwoodBayandSaanichInletisdominatedbysteepbedrockslopes, 

andismantledbyathincolluvialcover.Theoldestpostglacialsediments 

in Saanich Inlet are diatomaceous muds and massive clays deposited 

undermoderatelyoxygenatedconditionswhensea-levelwaslowerthan 

present. The Mazama ash is adistinctive horizon in marine and lake 

sequences dating to about 7.6ka. Above the ash layer, varved 

diatomaceous muds were deposited under low-energy and anoxic 

conditions (Bornhold et al. 1997 and 1998). Interbedded with these 

sediments are massive muds, interpreted to be mass-flow deposits 

emplacedduringstormsandearthquakes(Blais-Stevensetal.1997). 

Figure G-7. 

Table G-1. Key tofacies codesused 

in stratigraphic columns. 

Facies code Description 

Dcm Diamicton, clast-supported, massive 

Dcs Diamicton, clast-supported, stratified 

Dmm Diamicton, matrix-supported, massive 

Dms Diamicton, matrix-supported, stratified 

Bm Boulders, massive 

Gm Gravel, massive 

Gs Gravel, stratified 

Gf Gravel, foreset-bedded 

Gt Gravel, trough cross-bedded 

Sm Sand, massive 

Sp Sand, planar 

St Sand, trough cross-bedded 

Sr Sand, ripple-bedded 

Fm(d) Silt and clay,massive(with dropstones) 

Fl(d) Silt and clay,laminated (withdropstones) 

G-2 

SURFICIALGEOLOGYAND GEOMORPHOLOGY 

Figure G-8. Vashon 

Drift,lodgement till 

(5a [sdMb]) 

unconformably 

overlying 

drumlinised Quadra 

Sand, glaciofluvial 

outwash (4b [gsFb]) 

exposed in the 

vicinity of Keating 

townsite. Seealso 

Figure G-2,log317, 

and map legend for 

description of 

terrain units. 

Figure G-9. Capilano Sediments, glaciomarine suspension and 

debris flow deposits (6d[zdMw]). Hagan Creekvalley,view 

toward Brentwood Baytownsite. See map legendfor 

description ofterrain units. 



Map Legend A-Surficial Materials 

For Map G1. Surficial geology material, Central 

Saanich.1998 (recordedon Map G1 as uppercase 

symbols). 

W Marine deposits:massive to stratifiedclay, silt, sand and 

gravel; generallymoderatelytowell-sorted,deposited in 

saltand brackishwater by settlingfromsuspension and 

submarine gravityflows, including turbiditycurrents, wave 

actionand longshore drift; may containshells and other 

organic material. 

O Organic deposits:peat and other vegetative materials; 

formed by theaccumulationof organic matter in 

depressions orlevelareas; includesbogs, fensand swamps. 

L Lacustrine deposits:massivetostratified fine sand, siltand 

clay;depositedfromsuspension and subaqueous gravity 

flows, includingturbidity currents and waveactioninfresh 

water.. 

F Fluvialdeposits:gravelto silt-size sediment;generally 

well-sorted and stratified; clastswell-rounded;deposited 

byrivers, streams and creeks. 

C Colluvialdeposits:massive tostratified, clast- and matrixsupporteddiamicton 

or rubble; resulting fromtheme 

chanicalor chemical weathering ofbedrockand surficial 

sediment, andthe down-slopemovement ofmaterialsby 

gravitational processesincluding creep, solifluxion, sliding, 

debris-flow, avalanching, topple androckfall. 

WG Glaciomarinedeposits:diamicton, sand, siltand clay 

depositedfromsuspension and submarine gravity flows, 

including turbidity currents, inproximity toglacier ice; 

alsoincludesice-rafted stones, till-like diamictonsand 

interstratifiedglaciofluvialmaterials;wave-cutterraces, 

abrupt changesin texture anddistortedbedding common; 

marine shellsand other organic materialmaybe present. 

LG Glaciolacustrine deposits: well-stratified sand, siltandclay, 

including minor gravel and diamicton;deposited deposited 

fromsuspension and subaqueousgravity flows, including 

turbidity currentsandwave action in lakesadjacent to 

glacial ice; slump structures,irregular topographyand 

kettlesindicative of collapsefrommeltingof buried ice 

maybe locallypresent. 

Table G-2. GeneticParent MaterialsandSoils Relationships. 

Ta ble G-2 Genetic Parent Materials and Soils Rela tionships 

FG Glaciofluvial deposits:massive to stratified boulders,cobbles, 

pebble-gravel, sand, siltand diamicton; sortinggoodto poor; 

depositedby riversandstreamsflowing from, or incontact 

with glacialice;includingspillways, outwash plains,kames 

andraised deltas;evidence for ice collapse including 

slumping, kettlesandirregular topography. 

M Morainal deposits: massiveto stratified, matrix-supported 

diamicton, till;sub-rounded andfaceted boulders, cobbles and 

pebblesin aclay, siltandsand matrix;interstratified with 

minor gravel, sand andsilt;depositedeither directlyby 

lodgement, basal meltout; subglacial meltwater;or sediment 

gravity-flow processes,including debrisflowsassociated with 

ice melting; overlies drumlinised olderglacialnonglacial 

sedimentsand glaciallysculpted bedrock;may contain kettle 

depressions. 

G-3 

SURFICIALMATERIALSANDTEXTURES MAPLEGEND 

Unit Parent material Soil texture Soil classification Soil Names Drainage 

and Types classification 

unit 7d marine sands and gravels Regosols, saline phases Coastal Beach, well- to poorly-drained 

mud, rock Regosols, saline phases Tidal Flats, Rocky Coast well to poor 

unit 7c lacustrine/organic humic Terric Humisol Metchosin very poorly-drained 

unit 7b fluvial gravely, sandy loam Gleyed Dystric Brunisol Brigantine imperfectly-drained 

unit 7a colluvial/till gravely sandy loam Orthic Dystric Brunisol Rumsley, Mount Newton moderately well-drained 

gravely sandy loam Duric Dystric Brunisol Shawnigan moderately well-drained 

unit 6d glaciomarine gravely loam and silty Duric Dystric Brunisol Dashwood moderately well-drained 

gravely sandy loam Duric Sombric Brunisol Langford moderately well-drained 

silt, clay loam Orthic Sombric Brunisol Saanichton moderately well-drained 

silty clay loam Orthic Humic Gleysol Tolmie; Cowichan poorly-drained 

unit 6c glaciolacustrine/organichumic Terric Humisol Metchosin very poorly-drained 

unit 6b glaciofluvial gravely, loamy sand Orthic Dystric Brunisol Qualicum well-drained 

unit 6a proglacial colluvial/till gravely sandy loam Orthic Dystric Brunisol Rumsley, Mount Newton moderately well-drained 

gravely sandy loam Duric Dystric Brunisol Shawnigan moderately well-drained 

unit 5 moraine gravely sandy loam Duric Dystric Brunisol Shawnigan moderately well-drained 

unit 4 glaciofluvial gravely, loamy sand Orthic Dystric Brunisol Qualicum well-drained 

unit 3 fluvial, lacustrine, marineexposed in sea-cliff Orthic Regosol Steep slope well-drained 

unit 2 glaciomarine, moraine exposed in sea-cliff Orthic Regosol, ancient phase poorly-drained 

unit 1 fluvial, lacustrine, marineexposed in sea-cliff Orthic Regosol, ancient phase poorly-drained 

and wave-cut platform 

Surficial Material Textures 

(recorded on Map G-1 as lower case 

symbols) 

cz clays with silts 

sd mixedfragmentwithsands 

d diamicton, mixed fragments 

sg gravelswith sands 

dz silts with mixed fragments 

sz silts with sands 

hz silts with humic materials 

zc clays with silts 

zd mixedfragments withsilts 

zh humicmaterialswithsilts 

s sands 



Legend Map G-1-Surficial MaterialsandTextures Map G-1. 

Map coloursindication the type of surficial material present: 

Colluvium 

Fluvial 

Morainal 

Organic 

Marine 

Glacio-marine 

GEOMORPHIC SYMBOLS 

trimline 

crag-and-tail 

drumlin 

flute 

striation 

erratic boulders 

meltwaterchannel 

(flow directionknown) 

C 

F 

M 

O 

W 

WG 

meltwaterchannel 

(flow directionuncertain) 

terrace 

gully 

mass-movement 

(flow directionknown) 

surface seepage, spring 

drownedtrees 

See previous page foradescription forthemap symbols. 

Note: SurficialmaterialsL-Lacustrine, LG -Glaciolacustrine, FG - 

Glaciofluvialare notdisplayedon thismapbutdo occur in the studyarea 

at some locationsbelowthe surface. The stratigraphiclocations of some 

of these depositsoccur inthe GroundwaterAquifer section onthe crosssections;andtheyare 

alsorecorded inthe Surficial GeologyAppendix.. 

464 000 469 000 

Map G-1 Surficial GeologyMaterials of Central Saanich. 

1000 m 0m 

1000 m 

Scale 1:40000 

2000 m 

G-4 

SURFICIALMATERIALSANDTEXTURESMAP 

464 000 469 000 474 000 

Map Notes: This map displaysthe materialswhich lie at the 

surface of the land. Thisis onlyone type of display derived 

fromthe data base. In many areas, layers orstratasof other 

materials occuratdepth such as materials which identify 

gravellyaquifers. 

Municipality of Central Saanich ResourceAtlas 

474 000


QUATERNARYHISTORY 

In this section, the late Pleistocene and early Holocene history of the 

centralSaanichPeninsulaisdiscussedinaregionalcontext.FiguresG- 

10 to G-16 show a conceptual model that depicts the changing 

palaeogeography of southeastern Vancouver Island, showing central 

Saanich Peninsula from ca. 19to 4ka (calendar years before present). 

During this geomorphically dynamic interval, Saanich Inlet evolved 

from aglacierised fjord basin into amarine inlet dominated by nonglacial 

processes. At the same time, significant changes in sediment 

delivery rates,sea-level, water temperature, geochemistry and ecology 

occurredonthepeninsula. 

Changes in ice margins, drainage patterns and shoreline geometry are 

inferredfromthedistributionandelevationrangeofmoraine,proglacial 

colluvium, glaciofluvial and glaciomarine landforms (Huntley et al. in 

press). Landform and sediment assemblagesin the area aresimilar to 

thoseobservedincontemporarypalaeoglacialenvironmentsandmodern 

fjords dominated by retreating tidewater glaciers. The chronology of 

major geomorphic events and sea-level changes is constrained by 

radiocarbon dates from late Pleistocene and Holocene sequences in 

Saanich Inlet, adjacent parts of southern Vancouver Island and the 

Pacific northwest (Mathews et al. 1970, Alley and Chatwin, 1979, 

HicockandArmstrong1985,Bornholdetal.1997,PorterandSwanson 

1998). 

Legendfor Quaternary 

History Diagrams 

Glacierice (with estimated 

ice thickness in metres) 

Deglaciated terrain 

Glaciofluvial outwash 

Sea and lake water 

Iceflow direction(determined 

from paleo-iceflow indicator) 

Meltwater flow 

(current direction known) 

Meltwater flow 

(current direction uncertain) 

Lateglacial-maximumphase(ca.19to17ka) 

Before 17 ka, central Saanich Peninsula was covered by an ice sheet 

flowing from montane sources on Vancouver Island and the adjacent 

BritishColumbiamainland.Bedrockandoldersedimentswereoverlain 

by subglacial morainal deposits consisting of lodgement till, melt-out 

till, and glaciofluvial sediments (Figure G-1). Streamlined bedforms 

indicate that during this phase, ice and subglacial meltwater-flow was 

directed south-to southeasttoward Juan de Fuca Strait and Haro Strait 

(Figure 2a). In the northwest, cirque headwalls above 1200 masl have 

been modified by frost-shatter and solifluxion. This relict periglacial 

terrain isinterpretedtorepresentaminimumlimitto glaciationpriorto 

the onset of deglaciation (Huntley et al. in press). Ice thicknesses over 

Saanich Peninsula at this time ranged from 800 to 1000 m. In Saanich 

Inlet,icethicknesswasgreaterthan1500m(FigureG-10). 

G-5 


FigureG-10. Late glacial maximum phase ( ca. 19 to 15 ka). 

Figure G-11. Early deglacialphase ( ca. 

15to 14 ka). 

Earlyglacial-retreatphase(ca.16to15ka) 

Deglaciationbeganbefore16ka(PorterandSwanson1998).Mountains 

anduplandsweredeglaciatedearlyastheregionalequilibriumlinerose 

above the elevationof localcirquebasins.As aresult, remnant ice was 

confined to valleys and coastal lowlands (Figure 2b). In proglacial 

settings, exposed glacial debris was extensively remobilised by 

meltwaterandmass-movement.Meltwateranderodedsedimentdrained 

southeast across Saanich Inlet. Hydrologic continuity between ice-free 

areas was likely maintained by eskers, subglacial sheet-flow and 

supraglacial channels. Glacio-isostatically depressed lowlands were 

inundatedastheeustaticsea-levelrose.Asicethinned,tide-waterglacier 

margins partly floated and retreated to grounding lines in southern 

SaanichInlet,SatelliteChannel,andoverSaanichPeninsula(Huntleyet 

al. in press). Ice, meltwater and sediment drained to alarge calving 

embaymentformedinHaroStrait,southernStraitofGeorgiaandeastern 

JuandeFucaStrait(FigureG-11). 



Figure G-12. Middle deglaciation ( ca. 14 to 13 ka). 

Figure G-13. Late deglacial phase ( ca. 13 to 12 ka). 

Middleglacial-retreatphase(ca.14to13ka) 

Alongvalleyfloors,ephemerallakeswereimpoundedbydebris-covered 

stagnant ice and retreat-phase glaciofluvial outwash. Meltwater and 

sediment were directed into interlobate basins formed along the lower 

reaches of Cowichan and Koksilah rivers, and an embayment 

encompassingSaanich Peninsula and Saanich Inlet(Figure G-12). Icecontact 

deltas graded to between 100 and 80 masl delimit stable 

recessional grounding-line positions for tide-water glaciers in Saanich 

Inlet, Satellite Channel, Cowichan and Koksilah valleys, and over 

SaanichPeninsula.Below80masl,glaciomarinedebris-flows,sandand 

gravel outwash, and clay-silt rhythmites draped winnowed till and 

bedrock (Figure G-2). Raised glaciomarine deposits are correlative to 

earliestdeglacialsedimentsinODPcores1033and1034(Bornholdetal. 

1997). The elevation range of unit 6d delimits the extent of marine 

overlap attributed to glacio-isostatic depression and eustatic sea-level 

rise. The 80 mmarine transgression limit is probably equivalentto the 

post-14ka75mmarinelimitnearVictoria(Mathewsetal.1970,Clague 

etal.1982). 

Lateglacial-retreatphase(ca.13to12ka) 

By 13 ka, inland southeastern Vancouver Island was ice-free down to 

approximately400 masl (Alley and Chatwin 1979). In uplands and on 

valleysides,glacialdepositscontinuedtobereworkedbymeltwaterand 

mass-movement. Proglacial lakes drained as ice downwasted and 

outwash was degraded (Figure G-13). Extensional deformation 

structuresinglaciolacustrinesedimentsareattributedtochannelincision 

during rapid lake drawdown (Huntley et al. in press). Coarse outwash 

overlyingtruncateddeltaicandlakesedimentslikelyrepresentdeglacial 

flooddepositsrelatedtolakedrainage. 

G-6 


FigureG-14. Postglacial phase ( ca. 12 to 10 ka) 

Earlypost-glacialphase(ca.12to10ka) 

The flux of meltwater and sediment into Saanich Inlet decreased 

markedlyafter12kaasstagnant,debris-coveredvalleyicedisappeared 

(FigureG-14).SoutheastVancouverIslandwasdeglaciatedbefore11ka 

(AlleyandChatwin1979),anddeglaciatedslopesbecamevegetatedand 

stabilised. Plant macrofossils in early postglacial lake sediments 

indicate the presence of lodgepole pine and grass. This vegetation 

assemblage indicates relatively cool conditions (Hebda 1995). Raised 

wave-cutplatformsandstrandlinesindicatethatglacio-isostaticrebound 

continued after deglaciation, and that periodically, rate of rebound and 

sea-levelriseweresimilar.Between12and10ka,relativesea-levelwas 

closetothemoderndatum(Mathewsetal.1970,Clagueetal.1982),and 

theshore-lineofSaanichInletwassimilartopresent(Figure2e). 



Figure G-15. EarlyHolocene ( ca. 10 to 8ka) 

FigureG-16. Middle Holocene ( ca. 8to 4ka). 

EarlyHolocene(ca.10to8ka) 

Glacio-isostaticreboundcontinuedduringtheearlyHolocene(Clagueet 

al. 1982). During this interval, Pleistocene valley fill was intensively 

dissected by degrading postglacial streams as relative sea-level fell. 

UnconformitiesinearlyHoloceneandlatePleistocenemarinesediments 

and submerged terraces in Juan de Fuca Strait around 50 mbsl likely 

representaminimumelevationforamarinestandca.9to8ka(Clagueet 

al. 1982).As sea fellbelow presentdatum, the palaeogeography of the 

SaanichInletbasin changedsignificantly (Figure G-15). Baysentering 

the inlet were reduced in size and the entrance to Satellite Channel 

became constricted. The land area of Saanich Peninsula increased to 

include parts of Cordova Channel and James Island. These changes 

probably had an impact on oceanographic conditions within Saanich 

Inlet. Lake elevations were at their minimum stands during the early 

Holocene.Vegetationassemblages,dominatedby grass, alder, Douglas 

fir and oak, correspond to axerothermic interval observed in southern 

British Columbia and the Pacific Northwest (Hebda 1995, Pellattet al. 

1998). Charcoal in peat deposits indicates that southern Saanich 

PeninsulawasdisturbedbyfireduringtheearlyHolocene. 

MiddleHolocene(ca.8to4ka) 

After 8ka, eustatic sea-level rise was dominant (Clague et al. 1982). 

EarlyHolocenecoastalslopesweredrownedanderodedbywaveaction 

astheseatransgressed.ThelowerreachesofChemainus,Cowichanand 

Koksilahvalleyswere aggradedasthemodernCowichandeltaformed. 

Lakes surrounding Saanich Inlet were slowly infilled with silt-rich 

gyttja. Tephra, inferred to be Mazama ash, forms adistinct regional 

markerhorizondatedtoaround7.6kaforcoresrecoveredfromSaanich 

Inlet and lakes in the region (Bornhold et al. 1997, Huntley et al. in 

press). After 7.6 ka, Douglas fir, western hemlock, red cedar became 

dominant, reflecting the transition to amild and wet climatein the late 

Holocene (Hebda 1995, Pellatt et al. 1998). Modern drainage and 

sedimentation patterns were established in the study area after 4ka as 

relativesea-levelapproacheditspresentelevation(Mathewsetal.1970, 

Clagueetal.1982,FigureG-16). 

G-7 


Table G-3. Relationship of glacial eventsthroughtime 

togenetic materials andfacies units*. 

Stratigraphicunit Faciesunit Genesis Age(ka) 

Holocene unit 7d Nonglacialmarine,estuarine, ca.11katopresent 

SalishSediments lagoonal andbeachdeposits 

unit 7c Lacustrinedeposits ca.11katopresent 

unit 7b Channel, floodplainand ca.11katopresent 

deltaic deposits 

unit 7a Nonglacialhillslopecolluvium, ca.11katopresent 

talus andother 

mass-movement deposits 

LateWisconsinan unit 6d Ice-contact submarine debris ca. 14to 11ka 

Fraser Glaciation flows,glaciomarinesuspension 

Capilano Sediments andraisedbeachdeposits 

Retreat phase 

unit 6c Subaerial ice-contact and ca. 14to 11ka 

proglaciallakedeposits 

unit 6b Ice-contact andproglacial ca. 14to 11ka 

channel, braidplain, kame 

terraceanddeltadeposits 

unit 6a Ice-contact andproglacial ca. 15to 11ka 

colluvium,talus andother 

mass-movement deposits 

VashonTill unit 5b Subglacialfluvialdeposits ca. 23to 11ka 

Glacialmaximum phase 

unit 5a Lodgementtill, locally ca. 23to 12ka 

streamlinedandmelt-out till 

QuadraSand unit 4c Ice-contact andproximal ca. 29to 15ka 

Advance phase hillslopecolluvium, talus and 

other mass-movement deposits 

unit 4b Ice-proximalglaciofluvialfan- ca. 23to 17ka 

apron andbraidplain deposits 

unit 4a Ice-distalglaciofluvialfan- ca. 29to 23ka 

apronandbraidplaindeposits 

Olympia NonglacialInterval unit 3 Nonglacialmarine,estuarine, ca. 65to 23ka 

to earlyFraser Glaciation lagoonal andfluvialdeposits 

Cowichan Head Formation 

DashwoodDrift marine deposits 

Sangamonian Interglaciation unit 1 Marine, alluvial, fluvial ~125ka 

MuirPointFormation 

unit 2 

andcolluvial deposits 

*Ages of surficial units are shown in radiocarbon yearsbefore 

present. These depositsare discussed in the Quaternary 

Stratigraphy and Geomorphology section,and withinthe 

GroundwaterAquifer section with respectto texturalgroups as 

aquifers . 



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G-8 

Municipality of Central Saanich ResourceAtlas 

REFERENCES

SURFICIAL GEOLOGY - Central Saanich

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