Facies architecture within a regional glaciolacustrine basin: Copper River, Alaska

摘要: Abstract This paper defines the principal architectural elements present within Pleistocene, glaciolacustrine basin-fill of Copper River Basin in Alaska. The drains an intermontane basin via a single deeply incised trench through Chugach Mountains to Gulf was blocked by ice during last glacial cycle and large ice-dammed lake, referred as Lake Atna, filled much Basin. Facies analysis floor allows series associations be defined consistent with basinward transport sediment deposited along calving margins at edge. Basinward involves continuum gravity driven processes, including slumping, cohesive debris flow, hyperconcentrated/concentrated density flows, turbidity currents. results deposition subaqueous fans, which two main types are recognised. (1) Large, stratified, extend over least 5 km exposed centre. These fans composed multiple lobes, mega-channels, giving fan architectures that dominated horizontal strata large, cross-cutting channel-fills. Individual lobes channel-fills consist combinations of: diamict derived from iceberg rainout ice-marginal release subglacial sediment; units fining upward gravels grade vertically into parallel laminated rippled fine sands silts, range flows currents discharge meltwater; rhythmites grading diamicts sediment-density re-mobilising either or sediment. (2) Small, complex, proximal less than 2 km, southern part basin. coalescing prograding gravel both directly meltwater flows. cross-cut sand gravel-filled troughs channels cut outwash, overlie overlain sheets are, therefore, characterised laterally variable facies, architecture. Water depth, proglacial topography, stability portals supply may all important determining type any one location. We suggest is packages containing individual separated diamict. Each package turn next palaeo-landsurface shaped interstadial/interglacial fluvial processes volcanic