Low δ18O values of formation waters, collapse structures related to salt dissolution, hydrodynamic blowout structures, and biodegradation of oils all suggest a significant influx of fresh water into the Williston basin along the outcrop belt in southern and central Manitoba during Pleistocene glaciation. The thickness of the continental ice sheet over Manitoba would have provided sufficient potentiometric drive to reverse the regional-scale flow system of the Williston basin. The dynamic nature of the flow system suggests that modern-day pressure distributions may not be good proxies for ancient petroleum migration pathways as is commonly assumed.

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