| Summary: | The study area in northeast British Columbia extends from the Rocky Mountains in the west to the Fort Nelson Lowland in the east, and includes the westernmost extend of the Laurentide Ice Sheet (LIS) and the easternmost extend of the Cordilleran Ice Sheet (CIS) in the Late Pleistocene. Surficial mapping conducted over portions of the Fontas and Fort Nelson map areas (NTS 094I/SW and 094J/SE, respectively) provides information on sediment distribution and characteristics as well as glacial history. This information has direct implications for geotechnical investigations, aggregate resources and diamond exploration in the region. Non-glacial pre-Late Wisconsinan sediments occur at multiple sites along the Prophet River, providing a pre-glacial or interglacial history for the area. Geochemical analysis and clast lithologies were used to differentiate between sediments derived from the LIS to the east, and Montane/CIS glaciers to the west. The Quaternary stratigraphy of the Prophet River valley indicates the presence of a paleo-Prophet River valley system. Nonglacial deposits in the paleovalley include overbank fines and floodplain sediments interbedded with fluvial gravels. Macrofossils within horizontally laminated organic-rich black clay and silt are interpreted to indicate deposition in the floodplain of the paleo-Prophet River within oxbow-lakes and possibly also sag ponds. The climate is interpreted to be similar to present within a dominantly spruce forest. Wood found at one site provided a radiocarbon date of 49 300±2000 BP, while wood obtained from five other sites provided non-finite radiocarbon ages. In the Late Wisconsinan, the LIS advanced west-southwest into the study area, blocking existing east-flowing regional drainage, and forming an ice-dammed proglacial lake in the Prophet River valley. Ice overrode these sediments and deposited clast-poor clayey-silt till over the entire region. Thicknesses range from less than one metre to greater than twenty metres in the Prophet River valley. In river-cut ...
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