Cordilleran Ice Sheet lobal interactions and glaciotectonic superposition through stadial maxima along a mountain front in southwestern British Columbia, Canada

Glaciotectonic structures in subglacial till and substrate, as well as stone fabric, provenance and surface features in till, indicate that complex interactions of late Wisconsinan glacial lobes occurred along a mountain front in the western Fraser Lowland of southwestern British Columbia. Tills of this study represent subglacial deposition through the maxima of two stades in the Fraser Glaciation, the Coquitlam and the Vashon. Through each stadial maximum, temperate glacial ice was grounded and commonly overrode proglacial outwash while superimposing deformations in subglacial till during three phases: (1) pre-maximum glacier flow down valleys and into lowland piedmont ice, (2) coalescent piedmont ice during stadial maxima when flow was westward along the mountain front and across valley mouths, and (3) post-maximum glacier flow down valleys into lowland piedmont ice but prior to general deglaciation. Valley glaciers appear to have shifted flow directions during phases 1 and 3. During stadial maxima (phase 2), Fraser Lowland piedmont ice may have been part of an outlet glacier-ice stream complex that terminated in salt water over the continental shelf.