Mississippian Cyclic Sedimentation, Sunwapta Pass Area, Alberta, Canada

Abstract

Two sections of the cyclic Banff formation in the Banff-Jasper area were measured in detail and studied for the purpose of determining whether the nature of the cycles would be of value in making detailed correlations between these two areas. If successful, this method of correlating the Banff could then be extended into other areas. Fundamentally, the Banff cycles consist of alternations of limestone and shale or silty shale. Five common types of alternations are described. No consistent trend of succession of these cycle types was found in the two sections which could be useful for correlation. These simple limestone-shale cycles were found to be part of a more complex unit which recurs persistently throughout the section. This larger, complex cycle has been termed the megacycle. These megacyclic units were found to be useful in correlating the sections at Sunwapta Pass and Mount Coleman. The number of megacycles from the base of the Banff to the first development of the massive limestone facies of the overlying Dessa Dawn formation varies with the different sections. A study of the megacycles in these sections and sections northwest at Medicine Lake and Wapiti Lake, substantiated by faunal evidence, indicates that the Dessa Dawn facies begins higher in the section in the Sunwapta-Coleman area. The Banff formation is considered to have been deposited in a slowly subsiding trough off a land area of very low relief. That the over-all subsidence of the trough increased with time is demonstrated by the gradual increase of calcareous material in the section, culminating in the deposition of the massive, crinoidal limestones of the Dessa Dawn and Rundle formations.