Abstract

During Albian time the Western Interior Sea formed an embayment of the northern Boreal Sea and paleogeography, depositional processes and relative sea level were controlled by a global sea level rise and active thrusting within the Cordillera. Along the Sikanni Chief River in northeastern British Columbia, the Buckinghorse Formation is exposed as an over 1000 m thick marine mudstone package that was deposited in the western foredeep of the Western Canada Sedimentary Basin. The section appears lithologically relatively uniform, however, close examination allowed recognition of seven lithofacies responding to subtle changes in shelf to upper offshore depositional environments. On regional wireline log cross-sections seven major flooding surfaces that subdivide the Buckinghorse Formation into six depositional sequences are widely correlative. These are independent from lithofacies. A new informal foraminiferal subzonation is proposed and correlated to the existing standard zonation based mainly on the intensely studied Peace River region to the south. In the northern continuous offshore setting foraminiferal assemblages responded with gradual faunal changeover. Each marine transgression brought new, mainly Boreal taxa to the basin. The “Viking” marker, described and faunally distinguished in the Hudson Hope area within the Hasler shale, is identified in the Sikanni Chief River area as a distinct silt to fine sandstone interval with a change from the Haplophragmoides gigas Zone to the Miliammina manitobensis Zone. On well logs this horizon is a major flooding surface, correlated with the top of the Paddy Member.

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