PROGRESS IN UNDERSTANDING THE NATURE AND TIMING OF PRE-FRASER (EARLY WISCONSINAN AND OLDER) PLEISTOCENE GLACIATIONS IN THE CANADIAN CORDILLERA OF SOUTHERN BRITISH COLUMBIA, CANADA

During the Pleistocene the Canadian Cordillera experienced many glaciations separated by lengthy nonglacial intervals. Sedimentary evidence for some of these events is recorded in the deep valleys and basins within the interior, or along the coast, of southern British Columbia. Defining events older than the last (Fraser) glaciation with relative certainty has, however, been problematic due to a paucity of suitable dating methods for this time period. As a result pre-Fraser glaciations have, in many cases, been defined solely on the basis of basic sedimentology and by employing counting-down-from-the-top stratigraphy. Over the past 20 years a better understanding of subglacial processes and glacial geology (sedimentary and structural properties of glacigenic diamictons), together with the refinement of chronological methods, such as optical dating, and novel applications of more established methods, have improved our understanding of the character, timing, and extent of Cordilleran glaciations. In this talk I will discuss using examples how some dating methods have been applied in standard and novel ways, together with detailed sedimentological analyses, to establish, with relative confidence, the existence of pre-Fraser glacial events in the southern Canadian Cordillera, and to put limits on when they occurred.