Abstract

The architecture, distribution and facies of sandstone bodies in the Gog Group of the southern Rocky Mountains of Western Canada record the dynamics of sand movement on the broad continental shelf of West Laurentia during the Early Cambrian phase of worldwide transgression. These sandstones represent early deposits of a passive margin under high rates of sediment supply; accommodation was sustained by high rates of thermal subsidence plus sea-level rise. This study focuses on the stratigraphy and sedimentology in the Bow Valley region, specifically the sector from Mount Assiniboine northwest to the North Saskatchewan River. The objectives are to: 1) revise the existing stratigraphic nomenclature; 2) provide a general facies description and paleoenvironmental analysis of the constituent units; and 3) place the depositional setting in the context of the evolution of the Western Canada Sedimentary Basin.

The Gog Group in this area has historically comprised four units: the Fort Mountain Lake Louise, St. Piran and Peyto formations. North of Bow Pass, an additional unit, the Jasper Formation, occurs below the Fort Mountain Formation and is related to accommodation created by active rift-faulting during the latest Neoproterozoic. In the Lake Louise and Lake O’Hara area, four new formal subdivisions within the St. Piran Formation are proposed: Lake O’Hara, Lake Oesa, Lake Moraine and Wiwaxy Peaks members.

A wide range of subenvironments is recognized. The Fort Mountain Formation and the uppermost part the Lake O’Hara and Moraine Lake members record shallow-subtidal sedimentation. The correlative interval at Mount Assiniboine appears to have been deposited closer to the source area, and paleocurrents reveal sediment transport towards the north, parallel to the shoreline. The Lake Louise Formation was deposited in a protected low-energy, inner-shelf setting, while most of the Lake O’Hara Member records inner-shelf compound dunes and sand sheets. The Lake Oesa Member, which erosively overlies the Lake O’Hara Member, represents deposition in a tidal-flat environment. It is capped by a transgressive shoreface consisting of the lowermost deposits of the Moraine Lake Member. A record of sedimentation in inner-shelf conditions dominates the middle part of this unit, but with facies indicative of deposition in shallow-subtidal conditions in the upper part. The Wiwaxy Peaks Member represents an inner-shelf sand-ridge complex, followed by development of a shoreface environment. The overlying limestone-dominated Peyto Formation records deposition on a carbonate ramp related to a decrease in siliciclastic sediment supply.