New insights into the Bedrock and Quaternary Geology of St. George’s Bay from a vertical integration of marine datasets, offshore western Newfoundland

Abstract

St. George’s Bay lies south of Port au Port Peninsula on the west coast of Newfoundland, Canada. The Carboniferous Bay St. George subbasin extends beneath the bay and onshore to the southeast. The subbasin is an extension of the Magdalen Basin, a Carboniferous basin with probable resource potential, part of the broader Maritimes Basin. The onshore geology of the subbasin is relatively well understood. Marine datasets from the less well known offshore portion include high-resolution bathymetry, aeromagnetic data, shallow and industry wells, and both shallow and deeper (conventional) two-dimensional seismic data. Quaternary features were previously documented in inner St. George’s Bay where the surficial cover is thick. In the outer part of the bay, bedrock ridges are draped by iceberg-turbated glaciomarine mud and moraines. Beneath this cover, reinterpreted palynological analyses in the A-36 well reflect only Visean Codroy Group. The uppermost Codroy Group of this well may correlate with nearby red sandstones from shallow marine bedrock drill cores; however, younger Carboniferous rocks may also be present. Reflectors mapped using conventional seismic data mark the base Codroy Group and the top of a salt unit in the Codroy Group. Salt-cored anticlines and synclines are associated with halokinesis, and with a fault system with both dip-slip and dextral-slip components. Multibeam bathymetry and the second vertical derivative of the magnetic field delineate the folds as curvilinear, en echelon, and, in some cases, doubly plunging. Beneath the subbasin, seismic and aeromagnetic data indicate Proterozoic basement blocks and an offshore extension of the early Paleozoic Romaines Brook Fault. The Carboniferous structures suggest an environment of dextral transtension that reactivated early Paleozoic structures aligned with pre-existing weaknesses in basement.