Four Pleistocene formations in southwest British Columbia: their implications for patterns of sedimentation of possible Sangamonian to early Wisconsinan age

Abstract

Semiahmoo and Dashwood drifts were deposited during the penultimate glaciation, and Highbury Sediments and Muir Point Formation during the last interglacial. These sediments are defined and described, and stratotypes are established for them.Based on arboreal pollen assemblages, lithologic similarity, and relative stratigraphic position, Semiahmoo Drift of the Fraser Lowland is tentatively correlated with Dashwood Drift of Vancouver Island. Stone provenance, till fabrics, glaciotectonic structures, cross-bedding, and stone imbrication indicate that regional ice and meltwater flowed out of major fiords in the Coast Mountains and into the ancestral Strait of Georgia during the penultimate glaciation. Ice flowed southeastward against the east coast of Vancouver Island, and down the axis of the strait. Pollen and molluscs in Semiahmoo and Dashwood fossiliferous muds give evidence of transition from glaciomarine to marine conditions at the close of the penultimate glaciation.Highbury Sediments of the Fraser Lowland perhaps correlate with the Muir Point Formation of Vancouver Island, based on lithologic similarity and relative stratigraphic position. Stone provenance and paleocurrent data indicate that stream flow during the last interglacial issued from nearby mountains and onto coastal floodplains that shelved into the ancestral Strait of Georgia and Juan de Fuca Strait. Abundant Pseudotsuga and Tsuga heterophylla pollen indicate that climate during that time was at least as warm as the present.