The Quaternary stratigraphic record of British Columbia—evidence for episodic sedimentation and erosion controlled by glaciation

The terrestrial Quaternary stratigraphic record of British Columbia is largely a product of brief depositional events separated by long periods of nondeposition and erosion. Thick, stratified Quaternary sediments are present mainly in valleys and coastal lowlands and accumulated during periods of growth and decay of the Cordilleran Ice Sheet. At glacial maxima, till was deposited over large areas of low and moderate relief. However, at the same time, much of the landscape was eroded by glaciers. Sedimentation has been more restricted and has occurred at lower rates during nonglacial periods than during glaciations. On land, the only important sediment accumulation sites during nonglacials have been lakes, floodplains, and fans. However, large amounts of sediment have accumulated offshore, especially in fjords and basins such as the Strait of Georgia. Because of the restricted aspect of sedimentation during nonglacials, the stratigraphic record of these periods is meagre. In most places, tlue nonglacial units are thin and discontinuous, or they are absent altogether. Commonly, a nonglacial period is recorded only by an unconformity produced when streams incised valley fills shortly after the end of the preceding glaciation.