ABSTRACT: Radiocarbon geochronology of southern British Columbia

CGRG Bibliography of Canadian Geomorphology
Search Results

Author :

Date :

Title :

Publication :

Issue :

Page(s) :

Abstract

The radiocarbon-dated Quaternary history of southern British Columbia extends over the past 52,000 years. This interval has been subdivided into 3 major geologic-climate units: Olympia Interglaciation, Fraser Glaciation, and Postglacial. In southern British Columbia the Olympia Interglaciation began more than 52,000 years ago and ended about 19,000 years BP. Meagre information available from the west coast suggests that the climate during this period was cool and damp but probably not too different from present. Bison and Equus bones collected from deposits of this age in the interior of British Columbia indicate that the climate was such that it could support large herbivorous animals. The Olympia Interglaciation sedimentary framework, the processes active and the deposits formed, were similar to those of the same area at present. Three major depositional cycles have been recognized: (1) an early period of deposition at base levels higher than present, (2) a period of low base levels, and (3) a late episode of deposition at base levels above those of present day. Fraser Glaciation ice did not occupy the lowlands of southern British Columbia until later than l9,000 years ago, but probably began to build-up in the mountainous areas before that time. Parts of the west coast were ice-free about 13,000 years ago and all of southern British Columbia was probably as free of ice as at present by 10,000 years BP. From the time of deglaciation to about 8,000 years ago, isostatic movements tended to control local sea level and to mask eustatic changes. The apparent sea levels were high, due to isostatic depression at the time of Fraser deglaciation. Isostatic adjustments caused local sea levels to fall during deglaciation, rise again about 11,000 years ago and fall below the present level about 8,000 years BP. At that time, it appears that approximate isostatic equilibrium was achieved and the later sea level history is largely one of changes in response to worldwide eustatic fluctuations. The Postglacial record of southern British Columbia includes four dated ash falls: (1) Mazama, about 6,600 year BP; (2) St. Helens Y, about 3,300 years BP; (3) Bridge River, about 2,400 years BP, and (4) St. Helens W. (?), later than 1,200 years BP. The climate was cold 12,000 years ago, but it warmed sufficiently to be similar to the present when most of southern British Columbia was deglaciated. A thermal maximum about 6,000 years ago was followed by a cooler period which persisted until present. Glacial advances took place 3,000 to 2,500 years ago and in the past few centuries. During this most recent advance, the alpine glaciers of southern British Columbia were more extensive than at any time since the end of Fraser Glaciation about 10,000 years ago.

Bibliography of Canadian Geomorphology