Carbonate sedimentation in an evolving Middle Ordovician foreland basin, western Newfoundland

Abstract

Table Head and Goose Tickle group strata in western Newfoundland are a deepening-upward, carbonate to clastic sequence deposited on the convergent, paleosouth-facing, North American continental margin during Middle Ordovician time. Preceding passive margin platform growth was abruptly terminated by widespread, early Middle Ordovician block-faulting and differential uplift (St. George Unconformity) caused by migration of a peripheral bulge across the platform interior. Subsequent sea level rise led to widespread peritidal, then shallow subtidal, carbonate deposition (Table Point Formation) on a tectonically unstable platform that formed the western flank of the evolving Taconic foreland basin. Synsedimentary faulting and differential subsidence profoundly influenced sedimentation, leading to marked variations in thickness and abrupt lateral and vertical changes in platformal carbonate lithofacies. Episodic seismicity and changes in slope triggered gravitational slides and flows. This platform was in turn tectonically drowned by extensional faulting and differential collapse as it became part of the outer trench slope of the subduction zone. Thin-bedded, hemipelagic and turbiditic limestone and shale (Table Cove Formation) accumulated on discontinuous, gently-dipping carbonate slopes and basin margins of variable duration and facing direction. Massive, polymictic, carbonate debris flow conglomerate, calciturbidite and shale (Cape Cormorant Formation) were deposited in an isolated basin adjacent to a high relief fault scarp that exhumed several hundred metres of buried, older, passive margin platformal carbonate. Laminated black shale (Black Cove Formation) accumulated in remote, sediment-starved basins, and on the tops of isolated, rapidly foundered, relict platforms. As the (collapsed) platform entered the trench it was buried by siliciclastic flysch (American Tickle Formation and Mainland Sandstone) derived from an advancing accretionary prism. Terrigenous mud, silt and sand, transported mostly by turbidity currents travelling southwest parallel to the trench axis, accumulated in topographic depressions controlled by antecedent structural domains. Contemporaneous reverse faulting generated new escarpments in the trench, sourcing limestone debris flow conglomerates and calciturbidites deposited in intra-trench depressions (Daniel's Harbour Member).