SURFICIAL GEOLOGY - Central Saanich

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SURFICIAL GEOLOGY 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. Municipality of Central Saanich ResourceAtlas
SURFICIAL GEOLOGY 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 Municipality of Central Saanich ResourceAtlas
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SURFICIAL GEOLOGY - Central Saanich

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