Early Cambrian tidal sedimentary environments, western Victoria Island, Arctic Canada

Abstract

The currently unnamed early Cambrian (Series 2, Stage 4) sandstone unit is exposed in the Minto Inlier of western Victoria Island, Canadian Arctic Islands, and forms the base of the Phanerozoic succession. Coeval with other sandstones of this age in Laurentia, it was deposited in a shallow-marine embayment on the passive margin during the initial phase of the early Paleozoic transgression. Four facies associations are recognized: (1) outer embayment sand dune complex characterized by laterally continuous, planar cross-stratified, medium- to coarse-grained sandstone; (2) inner embayment sand flat consisting dominantly of fine- to medium-grained bioturbated sandstone and fine- to medium-grained sandstone interbedded with laminated mudstone; (3) coastal lagoon characterized by laterally continuous, medium-grained oolitic ironstone and fine- to medium-grained bioturbated sandstone; and (4) offshore muddy shelf consisting dominantly of laminated mudstone with discontinuous seams of medium- to coarse sand. Bioturbation in the form of a typical early Cambrian suite of shallow-subtidal ichnofossils predominated in the inner embayment and coastal lagoon settings, representing a low-diversity Cruziana ichnofacies. Oolitic ironstone horizons in the coastal lagoon setting mark periods of low sedimentation rates when iron became concentrated and calcite was the primary cementing agent. Dunes are, for the most part, non-bioturbated or contain just a few individual burrows belonging to Skolithos, representing the Skolithos ichnofacies. The dominantly tabular, sheet-like geometry of the sandstones characterizes a comparatively lower energy regime than what has been found in typical complex dune geometries in modern and ancient examples and is attributed to sediment deposition under essentially uniform current speeds at consistent water depth conditions on a low-gradient shelf. Paleocurrent measurements and thickness variation suggest that deposition was affected by undulating topography on the Proterozoic basement within facies association 1 and 2, as well as by syndepositional faulting in some areas. The coastline is envisaged as a complex of bays and lagoons. The embayment opened to the northwest where sandbars developed offshore; stratigraphic thinning towards both the south and northeast indicates the direction of the paleoshoreline. Approximately shoreline orthogonal paleocurrents are considered indicative of a tidal origin. The lack of hummocky cross-stratification suggests there was no influence of major storms in this region.