 A slightly older but possibly related geologic feature is the Mackenzie Large Igneous Province in Canada, which extends from the Arctic in Nunavut to near the Great Lakes in Northwestern Ontario.The Proterozoic Nonesuch Shale formation in the Keweenawan Rift contains enough organic carbon (greater than 0.5%) to be considered a potential source rock for petroleum.Oil identified as Precambrian has been found seeping out of the Nonesuch Shale in the White Pine mine in Michigan.