Glacial dispersal of boulders in the James Bay Lowlands of Quebéc, Canada

Abstract

Paleozoic fossiliferous limestones from the Hudson Bay area were dispersed southeastward a total distance of 110 km in the Québec part of theJames Bay Lowlands during the surging Cochrane flow event of the Laurentide Ice Sheet. The dispersal by the surging ice appears comparable to non‐surging ice dispersal events elsewhere in terms of the dispersal index and the half distance of transportation; however, the total distance of transportation of the limestone clasts and their relatively high abundance far away from their source suggest that part of the transport of the debris during the surge was englacial, with the load later deposited as a surface mantle, or that the flow of the surging ice was limited to rapid basal sliding, with little or no internal shear within the ice mass. The glacial transport characteristics of earlier non‐surging flow events in the same area were determined using the Total Transport Distance (TTD) method of measurements. Based on an indirect measurement of the half distance of transportation, the Selbaie till is characterized by longer transport distance than the Matheson till, and the Nouveau‐Québec till has the shortest transport distance of all the tills of the area.