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The Sweetgrass arch has been part of the stable platform known as the Alberta shelf throughout its tectonic history. This resulted in major periods of emergence interrupted by periods of shelf marine and/or fluvial deposition. The present-day Sweetgrass arch has been in a position coincident or proximate to a marine to nonmarine transition throughout geologic history. Approximately one half of geologic time is represented in the stratigraphic record of the Sweetgrass arch. The remainder of geologic time was occupied by major hiatal periods leaving significant unconformities in the sedimentary column.
Sedimentary history of the Sweetgrass arch is recorded in a stratigraphic column averaging less than 5,000 ft (1,500 m) thick. This thickness grades eastward into a Williston basin stratigraphic column of up to 15,000 ft (4,500 m) and westward into a depositional thickness of more than 100,000 ft (30 km) in portions of the Cordilleran geosyncline.
This discussion will relate tectonic history of the Sweetgrass arch to the sedimentary record, relate tectonic events in the Sweetgrass arch to those in surrounding areas and to the classic orogenic episodes of Rocky Mountain geology, draw some conclusions with respect to tectonic influence on oil and gas accumulations in the Sweetgrass arch, and examine implications for future energy exploration in the Sweetgrass arch.
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