Late Pleistocene Ice-Proximal Glaciomarine Subaerial Delta and Submarine Outwash Fan Lithofacies, Fraser Lowland, British Columbia, Canada: ABSTRACT

Abstract

Field study of sedimentary textures, structures, and lithofacies of upper Pleistocene sediment deposited when glaciers retreated from a fjord indicate local depositional history and environment. Three discrete lithofacies sequences are inferred to be ice-proximal deltaic and submarine outwash-fan deposits of a glaciomarine environment. Two delta-plain sequences are composed of planar-stratified and large-scale trough-cross-bedded sands and clast-supported gravels. Delta-front facies comprise interstratified sands, silty sands, and pebbly sands that contain ripple and climbing-ripple cross-stratification. Mud drapes on ripples indicate that traction currents were episodic but frequent. Nonrippled sands are reverse to normally graded or normally graded low-density gravity-flow deposits or discontinuous underflow deposits. Structureless sands resulted from grain flow or settled from a turbid overflow plume. Prodeltaic facies dominated by muds are rhythmically interstratified with sand and are deposited from turbid overflow plumes. Other coarser-grained sands are turbidites associated with slumps, slide blocks, and debr s-flow deposits shed off the delta front. The submarine outwash-fan sequence comprises scour channels End_Page 477------------------------------ infilled by matrix-supported gravel overlain by mass-flow deposits of planar-interstratified sand and mud. Channel infills are overlain by stratified matrix-supported gravels and sands and structureless clast-supported gravels deposited by debris flows which deformed underlying sands. Inasmuch as submarine outwash-fan sequences characteristically contain matrix-supported gravels, planar-interstratified sand and mud infill of channels and lack large-scale trough cross-bedding, they can be distinguished from deltaic sequences. End_of_Article - Last_Page 478------------