Stratigraphy and sedimentology of the Chancellor succession (Middle and Upper Cambrian) southeastern Canadian Rocky Mountains.

Abstract

The Chancellor succession accumulated in a deep-water trough bordering a wide, epeiric shelf during Middle and Late Cambrian time. The Chancellor is divisible into seven major lithostratigraphic units, which are correlative with an eastern shelf assemblage comprising eight cabonate and siliciclastic formations. The deep-water carbonate and siliciclastic sediments in the Chancellor are divisible into five basic lithofacies, each of which has several variants due to a variety of depositional and diagenetic factors. Sediments in the argillite lithofacies were deposited by dilute, muddy and silty turbidity currents and hemipelagic settling. The ribbon calcilutite lithofacies was probably deposited in a similar manner, but owes its final appearance to diagenetic enhancement of rhythmic, primary variations in sediment composition. Both of these lithofacies contain a variety of synsedimentary deformation structures indicative of slope instability. The ribbon calcisiltite lithofacies is composed of interbedded silty carbonate and terrigenous mud turbidites. The calcarenite lithofacies is the product of high-concentration turbidity flows. It locally occupies large, channel-like features ("megachannels"), which are inferred to be slide scars incised into the upper slope. Most of the sediments assigned to the conglomerate lithofacies show evidence of matrix strength, and were laid down by debris flows. This lithofacies includes spectacular megaconglomerates containing Epiphyton boundstone blocks up to 50 m in maximum dimension. Periplatform talus blocks of similar size are scattered throughout the Chancellor. During most of Chancellor time, silt- and sand-sized material either bypassed the upper slope or was confined to the shelf. The high proportion of carbonate and siliciclastic turbidites in the Duchesnay and Oke units (middle Chancellor) is a direct reflection of an abrupt, regressive shift in the position of the cratonal shoreline. Spectacular cross-strike exposures have revealed that the Eldon-Pika margin and adjoining upper slope strata (Tokumm and Vermilion sub-units) are traversed by at least three megatruncation surfaces. (Abstract shortened by UMI.)