Abstract

Exposures in the Prophet River valley in northeast British Columbia provide a unique glimpse into the Quaternary history of the northwest Canadian Boreal Plains. The region shows evidence of Late Wisconsinan Laurentide glaciation in the form of widespread till, containing abundant erratic clasts derived from the Canadian Shield. Vertical sections along the Prophet River expose non-glacial and advance glacial sediments below this till. Pre-Late Wisconsinan non-glacial or interglacial floodplain sediments are interbedded with fluvial gravels at many sites. Macrofossils within horizontally laminated organic-rich black clay and silt indicate deposition on the floodplain of the paleo-Prophet River within an oxbow lake. The climate during deposition is interpreted to be similar to present, supporting a dominantly spruce forest. Wood obtained from eight sites provided non-finite radiocarbon ages, and one sample provided an age of 49 300 ± 2000 BP, which is also considered non-finite. Glaciolacustrine clays and silts, deposited during impoundment of eastward-flowing drainage by the advance of the Laurentide Ice Sheet (LIS) in the Late Wisconsinan, overlie the non-glacial sediments throughout the valley. A blanket of clast-poor, clay-rich till up to 20 m thick, and deposited by the LIS, drapes the glaciolacustrine sediments. Since deglaciation, the Prophet River has incised the valley and formed fluvial terraces at different levels above the modern river.

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