Biostratigraphy of the sekwi and rockslide formations (lower to middle Cambrian; Wrigley lake and Sekwi mountain areas; NTS 95M and 105P, Northwest Territories, Canada); implications for basin development and regions correlation

Abstract

The lower and middle Cambrian, carbonate-dominated Sekwi and Rockslide formations were deposited in the Selwyn basin, a Neoproterzoic-Paleozoic depositional entity that occupied most of the ancestral western margin of Laurentia and spans parts of modern-day Yukon and Northwest Territories. Biostratigraphic data and limited chemostratigraphic data (δ13Cvpdb) from two Sekwi Formation sections in the Sekwi Mountain map-area (NTS 105P) are used to refine the current understanding of the spatial and temporal distribution of trilobite faunas in the area and to correlate the Sekwi Formation with other units throughout the Canadian Cordillera. Two species-based trilobite biozones (in ascending order: the Nevadia addyensis and Nevadella eucharis zones) previously best known from Arizona, California, and Nevada are documented in the lower Sekwi Formation, and a new genus-based assemblage zone, the Elliptocephala Zone, is proposed for the lower Dyeran of the Selwyn basin and surrounding areas. Trilobite data from three sections in the Wrigley Lake area (NTS 95M) are used to determine the chronology of basin events adjacent to the Redstone arch during the early and middle Cambrian, and lithostratigraphic data from other locations in the same map area is discussed to illuminate the nature of the basin events. There is evidence for two tectonic events during the late (traditional) early Cambrian and earliest middle Cambrian: (1) Event I, a regional uplift that eroded strata proximal to the Redstone Arch, and (2) Event II, a regional deepening event that heralded the onset of Rockslide Formation deposition. Trilobite biostratigraphy remains a mainstay of correlation in the Cambrian and is a powerful tool. However, further refinement is needed for the current biostratigraphic synthesis of the Cambrian of Laurentia, and biostratigraphy is enhanced when combined with chemostratigraphic curves.