Year: 2016
Type: report
Abstract: Map unit thickness is typical range; in some areas the map units may be thicker or thinner than the given range]HOLOCENE AND LATE WISCONSIN Flood-plain and channel alluvium-Yellowish-brown, olive-brown, grayish-brown, brown, olive, yellowish-gray, brownish-gray, olive-gray, gray, black, or mottled clay, silt, sand, and gravel.Calcareous or noncalcareous; partly or completely oxidized.Clasts are angular to well rounded.Clast composition reflects that of other surficial materials and bedrock in the drainage basin.Fossiliferous (gastropod, pelecypod, and vertebrate remains; wood fragments and plant detritus) in some places.Included in other map units in many areas.Includes some sheetwash alluvium, alluvial-fan deposits, alluvium beneath low terraces, outwash and ice-contact sand and gravel, lake deposits, and bedrock outcrops.Alluvium in some areas is dominantly redeposited outwash, ice-contact deposits, and lake deposits.Thickness 1-6 m, locally >20 m Flood-plain alluvium-Chiefly poorly-sorted to well-sorted clay, silty clay, silty clay loam, clayey silt, and silt with scattered granules and pebbles; locally, loam, sandy clay loam, sandy loam, or fine sand.Moderately to well stratified.Commonly has either obscure bedding or pronounced horizontal bedding; weakly laminated in some places.Clay, silt, sand, or gravel lenses or small channel fills of sand and gravel are common.Dense and compact in most places.Clayey alluvium is moderately plastic, soft, and sticky where moist and hard where dry.Textures may vary abruptly, laterally and vertically.Local thin buried soils (humic horizons).Concentrations of detrital lignite (bedrock) fragments as large as 1 cm are common in crossbedded sand.Where flood-plain alluvium directly overlies lake clay, silt, and sand or sheetwash alluvium, in some places it is difficult to distinguish the deposits Channel alluvium-Chiefly loose, stratified, poorly-sorted to well-sorted, pebbly, fine to medium sand and (or) coarse sand and gravel; locally very poorly sorted sandy shale-fragment gravel.Cobbles and boulders are common to abundant in some areas.Generally crossbedded or has crude horizontal bedding or lenticular bedding; local festoon bedding.Locally fossiliferous (chiefly vertebrate remains) Flood-plain and channel alluvium-Deposits in the northwest part of the quadrangle, similar to map unit al, preserved as terrace remnants higher than the postglacial alluvium.The deposits were derived from erosion of Tertiary bedrock and erosion and redeposition of Tertiary and Quaternary sand and gravel (see map unit xsh).Clasts are chiefly quartzite, argillite, chert, chert conglomerate, and sandstone.Rare redeposited clasts of erratic igneous and metamorphic rocks from the Canadian Shield are present in terrain possibly glaciated during the early Pleistocene or late Pliocene (see symbol "Limit Of Residual Erratic Glacial Boulders On Dissected Bedrock Surfaces") or where they were ice rafted in one or more Pleistocene glacial lakes.Thickness 1-2 m Lake clay and silt-Pale-yellow, grayish-yellow, bluish-green, yellowish-brown, olive-brown, grayish-brown, brown, olive, yellowish-gray, brownish-gray, olive-gray, bluish-gray, gray, olive-black, bluish-black, black, or mottled, calcareous clay and silt.Generally stratified; well sorted; massive or weakly bedded.Commonly laminated, locally varved, clay and silt.Generally clay in lower part and massive or horizontally-bedded silty clay and silt in upper part.Upper part generally is clast free; in some places, iceberg-rafted granules, pebbles, cobbles, and boulders are common in lower part.Clasts generally are absent on the surface.Contains local thin, discontinuous beds, lenses, or stringers of sand or fine gravel; pockets or pods of iceberg-rafted granules and pebbles, or isolated rafted erratic cobbles or boulders.Interbedded with sand, fine gravel, till, or flowtill in some places; some rare ice-rafted clasts of till are 1-2 m in diameter.Graded beds, silt blebs and nodules, or rip-up clasts of till or lake silt and clay are present locally.Strongly contorted in the northwest part of the quadrangle; slump structures, load structures, and folds in some places.Generally not faulted.Dessication cracks are common in some places.Commonly oxidized in upper 1-2 m; local iron oxide stains.Soft to very firm; locally cohesive and compact.Very plastic and sticky when moist; hard when dry. Locally gritty.Dry clay and silt commonly breaks into chips or blocks.Clay minerals are dominantly montmorillonite.Selenite (gypsum) crystals <6 mm in length are present locally in fractures and are abundant in saline lake sediment.Secondary calcium carbonate concretions locally are present in upper part.Gullies are common in some places.Deposit is susceptible to landslide processes (chiefly slump) in exposures.Most deposits are offshore deposits of former lakes.Present beneath flat plains and in small basins formerly occupied by glacial and postglacial lakes and ponds.Flat to rolling or hummocky surface topography.Thin and discontinuous in some areas.Overlapped by flood-plain alluvium adjacent to some streams; overlapped by sheetwash alluvium adjacent to some bedrock outcrops.Includes lake silt and sand where lake clay, silt, and sand have not been distinguished.Includes some till with a thin veneer of silt and clay.Includes some ice-contact and outwash sand and gravel, small lake delta deposits, and bedrock outcrops.In some places, lake clay and silt are overlain by eolian silt and sand, alluvial-fan deposits, or flood-plain alluvium.Thickness 1-5 m, locally >15 m Lake sand and silt-Grayish-yellow, yellowish-brown, grayish-brown, brown, yellowish-gray, olive-gray, brownish-gray, gray, or mottled, calcareous silt and sand mixed with minor clay and gravel.Generally well stratified and well sorted.Typically horizontally-bedded or massive, fine or medium sand containing scattered granules or small pebbles.Commonly interbedded or intercalated with massive, bedded or laminated, silt containing dropstones; in some areas, chiefly laminated silt and fine sand.Commonly slumped and contorted on hillslopes.Detrital fragments of lignite (bedrock) are abundant in many areas, concentrated in sand crossbeds.Clasts are chiefly subrounded and rounded erratic limestone, dolomite, and igneous and metamorphic rocks and local sandstone and shale that were ice rafted or reworked from till.Present beneath lake plains and in small basins formerly occupied by glacial and postglacial lakes.Surface relief 1-4 m.Includes some lake clay and silt, flood-plain and channel alluvium, and till.In many places, overlies lake clay and silt.Thickness 1-8 m, locally >10 m Swamp deposits-Brown, bluish-gray, olive-gray, gray, or black muck, mucky peat, and organic residues mixed with fine-grained mineral sediment.Soft to dense and tough; commonly plastic where moist.Obscure horizontal bedding.Mapped only in one area where extensive, northeast of Medicine Lake.Elsewhere included in other map units.Thickness 1-3 m Dune sand-Yellow, yellowish-brown, olive-brown, grayish-brown, brown, brownish-gray, gray, or mottled windblown sand in dunes.Generally calcareous.Typically loosely compacted, stratified, well-sorted fine to coarse sand.Faint parallel or irregular bedding or pronounced crossbeds; local foreset beds.Chiefly subrounded to well-rounded quartz grains; grains are frosted or clear.Typically oxidized to depths >1 m; locally stained by iron oxides.In some places, contains thin, weakly developed, buried soils (humic horizons).Some dunes are irregular hummocks; most are parabolic dunes or elongate blowout dunes.Surface relief generally is 2.5-5 m; maximum relief is >10 m.Dunes are mostly stable, with grass cover; local blowouts.Includes some eolian sheet sand and flood-plain and channel alluvium.Thickness 1-10 m Eolian silt and sand-Yellowish-brown, olive-brown, grayish-brown, brownish-gray, gray, or mottled windblown silt and sand.Calcareous.Well stratified; well sorted.Faint beds or cross-beds.Very friable; slightly hard; subangular blocky structure.Not sticky or plastic when moist.Chiefly well-rounded quartz grains; less abundant feldspar grains.Quartz grains are frosted or clear.Undulating surface topography.Typically oxidized to depths >1.5m.Thickness 1-3 m; maximum >4 m Colluvium, 2 sheetwash alluvium, 1 and glaciofluvial-fill deposits-Complex map unit in meltwater channels and lake sluiceways.Channel sides are sharply defined to indistinct.Valley sides are chiefly colluvium, sheetwash alluvium, till, and bedrock outcrops.Large boulders or lag deposits of cobbles and boulders are present on valley sides in some places.Gullies are common locally on valley sides.Basal part of fill is generally glaciofluvial sand and gravel (map unit gg) or reworked glaciofluvial deposits.Flood-plain and channel alluvium (map unit al) is inset into some fill deposits.Flood-plain deposits overlap the fill deposits in some places.Sheetwash alluvium (map unit wla) commonly overlaps the fill deposits on foot slopes on valley sides; in some places, it mantles most of the fill on the valley floor.Mapped in the east central part of the quadrangle.Combined thickness of fill and overlapped alluvium is 1-10 m Colluvium-Yellowish-brown, olive-brown, brown, olive, yellowish-gray, brownish-gray, gray, or mottled debris transported and deposited by mass-movement processes.Calcareous or noncalcareous.Loose to compact.Nonsorted or poorly sorted; nonstratified or faintly stratified.Commonly massive.Where derived from glacial deposits, material is typically boulders, cobbles, pebbles, and granules of erratic quartzite, limestone, dolomite, and igneous and metamorphic rocks and local bedrock in a clayey to sandy matrix.Lignite (bedrock) fragments are ubiquitous in most of the colluvium.Thickness 1-5 m Sheetwash alluvium-Similar to map unit wla.Thickness 1-4 m Glaciofluvial-fill deposits-See map unit gg.Thickness 0.5-1m HOLOCENE, LATE PLEISTOCENE,
DOI: 10.3133/ofr20161142
Language: English
Subfield: Earth-Surface Processes
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W2520554530