Phanerozoic vertical motions of Hudson Bay

We analyze the sedimentary record of the Hudson Bay basin, an intracratonic basin which is widely believed to have been formed by convective downwelling within the mantle. This belief largely stems from the coincidence of a long-wavelength negative gravity anomaly and an approximately circular basin which is filled with about 2 km of predominantly Paleozoic sedimentary rocks. Our starting point is a set of wells and seismic reflection profiles which demonstrate that the basin subsided rapidly from Ordovician to Devonian times. One- and two-dimensional subsidence modeling show that water-loaded subsidence occurred in two stages and is too rapid to be accounted for by thermal contraction alone. Instead, we suggest that basin subsidence is consistent with minor phases of lithospheric thinning which occurred during Ordovician–Silurian and Early–Middle Devonian times. Stretching factors for these minor extensional episodes vary from 1.05 to 1.2 with vertical strain rates of 2–10 Ga–1. Our interpretation of the subsidence record is corroborated by limited evidence for syn-rift normal faulting and crustal thinning inferred from legacy seismic reflection and refraction data sets. Subsidence modelling also suggests that about 1 km of expected thermal subsidence is missing. This discrepancy suggests that the basin was uplifted and denuded at least once, but possibly several times, between Late Devonian and Middle Cretaceous times (i.e., 360–100 Ma) and between Cretaceous and Quaternary times. We conclude that the Hudson Bay basin was not generated by convective downwelling that initiated in Paleozoic times and that remained coupled to the lithospheric plate.