ABSTRACT: Late Cenozoic geology of the northern Rocky Mountain Trench, British Columbia

CGRG Bibliography of Canadian Geomorphology
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Abstract

Detailed sedimentological analysis of unconsolidated sediments along the Finlay River in the northern Rocky Mountain Trench was undertaken as part of a stratigraphic study of the Quaternary of northeastern British Columbia. Fifteen sediment types were identified and classified within four broad textural groups: diamicton, gravel, sand, and fines. The diamicton group consists of: (1) structureless diamicton; (2) diamicton with clastic intrabeds; and, (3) stratified diamicton. Gravels are represented by the following sediment types: (1) massive gravels; (2) normal/inverse graded gravels; (3) stratified gravels; (4) disrupted gravels; and, (5) inclined gravels. The sand group consists of: (1) structureless and graded sands; (2) horizontally laminated sands; (3) trough-cross stratified sands; (4) planar cross-stratified sands; and, (5) ripple laminated sands. Fines are represented by two sediment types, silt and clay. Paleomagnetic samples (discontinuous suite) were removed from several bluff exposures. Analysis of these samples indicates normal polarity was in existence during their deposition (late Pleistocene). Fossils retrieved from the study area include one trace fossil (annelid burrow), several freshwater snail shells, and numerous wood fragments (Picea sp.). C14 dating of the wood specimens provided a number of dates ranging from circa 15,000 to 40,000 years B.P. The C14 dates correlate well with the amino-acid racemization values obtained from the same samples. The results of this study indicate that the northern Rocky Mountain Trench was glaciated twice during the Quaternary. The penultimate glaciation was probably pan-provincial, owes its source area to the coastal mountains of B.C., and extended eastward across the Rocky Mountains into the foothills regions. The timing and duration of this glaciation could not be established, but definitely occurred before 44,000 years B.P. A nonglacial interval starting before 44,000 years B.P. and ending approximately 15,000 years B.P. followed the penultimate glaciation. Pollen data from this interval indicate a northern boreal environment typified the area (dominated by black and white spruce). The second and final glaciation began approximately 15,000 years ago, ended before 10,000 years B.P. and corresponds to the Late Wisconsinan. This glaciation was localized in extent and probably consisted of a confined valley glacier, whose furthest eastward progression is marked by the Portage Mountain moraine. This study concludes that an extensive ice-free-corridor was in existence throughout the Quaternary.

Bibliography of Canadian Geomorphology