Late Pleistocene coastal loess deposits of the central west coast of North America: terrestrial facies indicators for marine low-stand intervals
Coastal loess deposits measured in sea cliffs, bay cliffs, road cuts and boreholes (62 sites) are compiled for the states of Washington, Oregon, and California in the central west coast of North America (1700 km in length). The loess-enriched deposits are recognized by (1) substantial abundances of silt (30–90% by weight) and (2) depositional settings in uplifted marine terraces or dune fields that are situated well above alluvial floodplains at the coast. Total loess thickness above the MIS5a marine terrace, or 80 ± 20 ka basal TL age, ranges from 0.1 to 8.0 m in 46 dated sites. Loess deposits reach maximum thickness (5–8 m) in the vicinities of glacial outwash plains in the highest latitudes. Loess thickness in the middle and lower latitudes increases with proximity to 1) large river mouths (>3 × 106 mt yr−1 modern suspended sediment discharge) and 2) broad shelf widths (>10 km distance from 0 to −100 m depth). Coastal loess deposits dated by TL or radiocarbon (37 samples) range from ∼250 to 11 ka in age, but generally fall into the MIS4-2 marine low-stand intervals (32 dates between 77–15 ka). The coastal loess facies represent marine low-stand intervals in coastal Quaternary sequences from the central west coast of North America.