The omar story: The role of omars in assessing glacial history of west-central north America

The direction of Wisconsinan glacial dispersion of distinctive Proterozoic erratics derived from the Belcher Group in southeastern Hudson Bay is shown to have been northwestward, westward and southward for hundreds of kilomet res across Hudson Bay, Northern Ontario, western Canada, and several adjoin ing northern States. The most distinctive of these erratics, termed "omars" , are composed of massive siliceous wacke characterized by buff-weathering calcareous concretions; these erratics were derived from the Omarolluk Form ation of the Belcher Group, exposed in the Belcher Islands of eastern Hudso n Bay, and probably underlying much of the southern part of this inland sea . Far less common but equally distinctive are erratics of red oolitic jaspe r that were derived from the Kipalu Formation of the Belcher Group. In para llel with the now widely accepted field term "omar", we introduce the term "kipalu" for such erratics of oolitic jasper. A map showing the distributio n cf the distinctive erratics, in relation to indicators of Wisconsinan gla cier movement, provides the basis for inferring at least two discrete glaci ations that produced several major ice lobes. This paper summarizes the fie ld observations of numerous Canadian and American earth scientists, traces the evolution of thought on provenance of the distinctive erratics, and out lines the criteria for distinguishing "true" oma rs from erratics derived f rom other bedrock sources of concretion-bearing wackes.