PALEOGEOGRAPHY OF THE UPPER PURCELL SUPERGROUP, NORTHERN PURCELL BASIN, SOUTHEASTERN BRITISH COLUMBIA, CANADA

The 1.4 Ga Upper Purcell Supergroup was deposited in a marine to lagoonal setting. Measured sections and maps completed during the summer 2006, in combination with existing maps, permits a test of previous stratigraphic correlations. Replacement of Dutch Creek Formation to the west by the La France Creek Group reflects the westward thinning and increased sand-content of this unit. The Dutch Creek Formation is replaced to the south by the Gateway—Roosville formations. A micaceous north-tapering sandstone unit, the Phillips Formation separates the Gateway and Roosville formations, and provides a record of syn-depositional change in the architecture of the Purcell basin. Pinch out of the Phillips Formation to the north points to decreasing accommodation space due to reduced subsidence to the north. East-west striking thrust faults may have originated as south-dipping growth faults that accommodated the increased subsidence to the south. Westward thinning of the Dutch Creek Formation is attributable to Cretaceous strain and does not indicate proximity to the ancient west-margin of the basin.