STRATIGRAPHY AND SEDIMENTOLOGY OF THE DINOSAUR PARK– BEARPAW FORMATION TRANSITION (CAMPANIAN) IN THE CYPRESS HILLS REGION, SOUTHWESTERN SASKATCHEWAN, CANADA

The Belly River Group comprises an eastward-thinning paralic to non-marine Campanian clastic succession in the Western Canadian Sedimentary Basin. Three formations are formally recognized in the western Canadian Plains. In ascending order, these are the Foremost (paralic to non-marine), Oldman (alluvial to paralic), and the Dinosaur Park (alluvial, estuarine, and paralic) formations. The Foremost Formation, which interfingers with the underlying marine Lea Park Formation, whereas the transgressive Dinosaur Park Formation interfingers with sediments of the overlying marine Bearpaw Formation.

Previous regional surface and subsurface correlations of the Dinosaur Park Formation confirm its presence in the Cypress Hills of Saskatchewan. Detailed sedimentology and ichnology have been utilized to determine stratigraphic relationships of units, and distinguish between fluvial, marginal marine, and open marine environments. This study focuses on the transition from the upper Dinosaur Park Formation into the Bearpaw Formation using core, outcrop, and subsurface well log data. Fitting the Group into a sequence stratigraphic context across southwestern Saskatchewan and southern Alberta provides opportunity to understand the effects of sea level changes from the coastal plain into terrestrial, inland deposits not in direct contact with marine waters.

A gradual shift from fluvial to fluvio-estuarine conditions is marked by inclined heterolithic stratification and a gradual increase in fine-grained bioturbated sandstone. Inclined heterolithic stratification represents lateral accretion in sinuous channels of the Dinosaur Park Formation, which in the Saskatchewan examples are more clearly tidally influenced than the IHS-containing channels of Alberta (e.g., at Dinosaur Park). Diminutive burrows of a brackish water suite consisting of Teichichnus, Planolites, Palaeophycus, and Cylindrichnus have been identified within facies near the Dinosaur Park-Bearpaw transition. Overlying Bearpaw facies above the contact consist of fully bioturbated shales with in situ marine mollusc shells. This facies association coarsens upward into fine-grained cross-bedded and well bioturbated stacked sandstones.