High Resolution Sedimentology of the Upper Jurassic Nikanassin Formation, in the Grande Cache Area of Alberta

Summary Several excellent outcrops of the Upper Jurassic Nikanassin Formation can be examined along Highway 40, close to Grande Cache. Two outcrops exposed within the Stearn Anticline allow the chance to compare and contrast a dominantly braided portion of the Nikanassin with a clearly meandering portion of the same Formation. The close proximity of the outcrops allows the chance to compare two strikingly different fluvial depositional settings, and to draw conclusions on how and more importantly why these differences occur. The larger scale bedforms of the braided section are interpreted as downstream accreting macroforms, in contrast to the lateral accretion surfaces of the meandering system. The proportions of the fluvial channel and crevasse splay lithofacies components are also very different. Diagnostic criteria are developed for the two depositional settings, and interpretations are put forward to explain why these differences occur, and their potential impact on sand distribution.