Hudson Bay occupies a large structural basin, known as the Hudson Bay basin, that lies within the Canadian Shield. The collection and interpretation of outcrop, seismic and drillhole data for exploration for oil and gas reservoirs within the Hudson Bay basin found that it is filled by, at most, of Ordovician to Devonian limestone, dolomites, evaporites, black shales, and various clastic sedimentary rocks that overlie less than of Cambrian strata that consist of unfossiliferous quartz sandstones and conglomerates, overlain by sandy and stromatolitic dolomites. In addition, a minor amount of terrestrial Cretaceous fluvial sands and gravels are preserved in the fills of a ring of sinkholes created by the dissolution of Silurian evaporites during the Cretaceous Period.