Abstract

The lower Paleozoic rocks of the Hudson Platform are contained within four principal tectonic elements: the Hudson Bay, Moose River and Foxe basins, and the Foxe Channel/Hudson Strait graben system. The rocks, with a composite thickness of 2500 m, range in age from Cambro-Ordovician to Early Silurian in the northeastern part of the platform (Foxe Basin-Foxe Channel/Hudson Strait Graben), and from Late Ordovician to Late Devonian in its central and southern parts (Hudson Bay and Moose River basins). The rocks are mainly carbonates and evaporites, with shale, siltstone and sandstone comprising a significant proportion of the overall succession.

Lithological and biostratigraphic similarities of certain of the sequences with their counterparts in the St. Lawrence, Arctic and Interior platforms indicate a broad connection of the sea at periodic intervals of Ordovician, Silurian and Devonian time. The distribution of sea and marine deposition on the craton were continuously changing processes due to global tectonic mechanisms and possible related changes in structural attitude of the orthogonal basement arch systems that transected the craton in the Paleozoic. Basement highs that significantly affected shorelines and depositional processes on and adjacent to the Hudson Platform were the northeast-trending Keewatin, Transcontinental and Fraserdale arches, and the northwest-trending Baffin, Boothia-Bell and Severn arches, along with a major arch system now deeply buried beneath Devonian rocks in the central part of Hudson Bay Basin. Positive relief on these elongated structural elements in early Middle Ordovician (Whiterockian/Chazyan) apparently led to the inception of Foxe Basin and an unnamed basin in eastern Hudson Strait-Ungava Bay that opened on northern Labrador Shelf. Further epeirogeny in Late Ordovician (Edenian), and again in the Richmondian-Gamachian, apparently contributed to the inception of Hudson Bay and Moose River basins, respectively; with subsequent episodes of epeirogeny resulting in the acceleration of basin development in both of these regions in Silurian and Devonian times, and in the Early Cretaceous.

The timing of marine transgression, regression, and periods of accelerated subsidence and structural deformation of Paleozoic terrain in the Hudson Platform coincides closely with similar events in the foreland basins of St. Lawrence, Arctic and Interior platforms. They may, therefore, have been triggered and controlled by common forces of plate tectonic origin in the Appalachian, East Greenland, Innuitian and Cordilleran regions operative in the south, east, north and west sides of the North American continent, respectively.

Fault-bounded blocks, salt dissolution structures and biohermal facies that have wide occurrence in Hudson Platform have many characteristics in common with structures that contain oil and gas along the Algonquin-Findlay Arch trend in southwestern Ontario. Some of the potentially prospective structural and stratigraphic traps have been drilled in Hudson Bay Basin, but thus far, none of the wells have been successful in obtaining commercial quantities of either of those commodities.