Abstract

During late Wisconsin time an assemblage of fossiliferous till-like stony clays and associated clays, silts sands, and gravels with an aggregate thickness of 500 feet was deposited in the Lower Fraser Valley of British Columbia. The authors believe these sediments were deposited in the sea during and following the wasting and retreat of a major Cordilleran ice sheet, and during subsequent uplift of the land above sea level. The agents of transportation probably were ice, including shelf-, berg-, and sea ice; glacial meltwater; and sea water. The writers believe the till-like stony clays, called glacial till by previous workers, had more than one origin, as follows: (1) The stony clays are in part marine drift; that is, the stones and some of the finer materials were transported by ice, and the remainder of the finer materials, predominantly clay, were transported by meltwater and sea water. Three modifications of this theory depend largely on how the stones were transported. These are (a) shelf-ice theory, (b) berg-ice theory, and (c) sea-ice theory. (2) The stony clays were in part deposited as a result of submarine erosion in the littoral and sublittoral zones from the action of submarine slides or slopewash, sea currents, and turbidity currents on pre-existing sediments, mainly till and till-like mixtures, during uplift following maximum advance of the ice sheet. The authors have termed this the submarine slopewash theory. The marine drift and slopewash theories are combined in a composite theory which also explains the origin of the associated sediments.

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