Jens Munk Archipelago: Ordovician‐Silurian Islands in the Churchill Area of the Hudson Bay Lowlands, Northern Manitoba

The name “Jens Munk Archipelago” is proposed for a cluster of small monadnocks that rise a maximum of 45 m above present sea level on the shores of Hudson Bay in the Churchill area of northern Manitoba. Resistant Precambrian quartzite formed shoals and islands during the Late Ordovician and Early Silurian periods. Outcrop control in the present tundra environment of the Hudson Bay Lowlands is spotty at best, but the quartzitic monadnocks are fringed by Upper Ordovician and Lower Silurian ramp deposits, mainly carbonate in composition. Five isolated outliers of Ordovician-Silurian strata are described, and the location of four other potential outliers is indicated. Ramp dip at any one site generally ranges from 10 to 15, and the surviving ramps on opposite flanks of paleoislands suggest preservation of near synsedimentary conditions. Extensive conglomerates of reworked quartzite are most abundant on a northern exposure within the islands. Ripple marks and oriented cephalopod debris are related to a vigorous long-shore current generated by northeasterly trade winds that emanated from a subtropical high-pressure cell in the Northern Hemisphere. A paleogeographic reconstruction links the Jens Munk Archipelago of Manitoba to a larger landmass with a Precambrian quartzite core centered over northern Saskatchewan. The general paleoecology of the Jens Munk Archipelago conforms to patterns of windward and leeward facies preserved on other paleoislands of various ages.