Stratigraphic Record of the Transition from Cratonic Basin to Foreland Basin

Shaohua Li and Charles M. Henderson
University of Calgary, Calgary, AB

The Upper Jurassic Vanguard Group in southwestern Saskatchewan records the first orogenic clastic wedge in the Canadian part of Williston Basin. It also reflects the initial connection of the Alberta Trough and the Williston Basin after a long period of separation by the Sweetgrass Arch. This significant transition should have left traceable sedimentological and biostratigraphic evidence within the sediments. Integration of sequence stratigraphy and biostratigraphy should allow resolution of the stratigraphic relationship between the Vanguard Group in Saskatchewan and its equivalent in Alberta.

A significant amount of oil and gas has been found from geographically restricted Upper Jurassic strata in the Western Canada Sedimentary Basin. The complexity of tectonic and eustatic controls on the sedimentation and distribution of the reservoirs is highlighted by the locally present Roseray sandstones in southwestern Saskatchewan and Swift Formation in southeast Alberta and north-central Montana. Understanding of these controls will provide a powerful tool to predict potential reservoirs as well as to demonstrate the influence of the western orogenic activity on interior sedimentation.

Apart from the regional effects of the Columbian Orogeny, the active Sweetgrass Arch plays a direct role on the sedimentary pattern on both sides-in the Alberta Trough and in the Williston Basin. Even after these two depositional areas have been connected by the transgressive seaway, they still show very distinct depositional patterns because of their relative location to the source areas as well as their basin geometry and bathymetry.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005