SUBSURFACE ANALYSIS AND CORRELATION OF CAMBRIAN FORMATIONS BENEATH THE COLVILLE HILLS, NORTHERN MAINLAND NORTHWEST TERRITORIES

Cambrian formations across much of the mainland Northwest Territories were deposited in a semi-enclosed, epicontinental basin, with a present-day zero edge that onlaps the Canadian Shield. A new sequence-stratigraphic model for the basal Cambrian succession beneath the Colville Hills helps with basin modelling and deciphering the syndepositional history of faulting.

The Mount Clark Formation (Early Cambrian) unconformably overlies Proterozoic strata and is dominated by medium-grained, well-sorted, quartz. The arenites commonly contain trace fossil assemblages classified as the Skolithos Ichnofacies. Glossifungites Ichnofacies-demarcated discontinuities are locally observed. Coarse-grained facies of the Mount Clark Formation represent the high-energy upper shoreface to foreshore while fine-grained, moderately to intensely bioturbated facies represent the lower shoreface, and are characterized by the proximal Cruziana Ichnofacies.

The Mount Clark Formation is overlain gradationally and diachronously by the Mount Cap Formation (Early to Middle Cambrian), the lower part of which consists of intensely bioturbated heterolithic sandstones and mudstones that represent proximal offshore to middle shoreface paleoenvironments and commonly preserve expressions of the Cruziana to Skolithos Ichnofacies, respectively. Carbonate beds in the lower part of the Mount Cap are largely dolomitized and intensely bioturbated. In the lower part of the Mount Cap, a maximum flooding surface (MFS) can be correlated throughout a considerable portion of the study area. In core, this surface is sharp to abruptly gradational, shifting upward from a moderately bioturbated green shale to a barren dark grey shale inferred to represent a transgression and concomitant decrease in total dissolved oxygen. Up-section are sparsely bioturbated to barren shales. Four regionally correlatable carbonate beds and an additional MFS are observed upwards in wireline. Using these five markers, syndepositional extensional faulting during deposition of Mount Cap strata is evident and is capped by a regional MFS. The upper Mount Cap consists of calcareous shale interbedded with carbonates.

The Mount Cap Formation is unconformably overlain by the Saline River Formation, a succession of shale, carbonate, and evaporites.