--> --> Abstract: High-resolution Stratigraphic Correlation of the Late Cretaceous Pierre Shale Using Bentonite Beds, by J. L. Bertog; #90925 (1999)

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BERTOG, JANET L., University of Cincinnati, Dept. of Geology, Cincinnati, OH

Abstract: High-resolution stratigraphic correlation of the Late Cretaceous Pierre Shale using Bentonite Beds

Sequence stratigraphy has become an important tool in anticipating lateral and vertical facies distribution and in constructing age models by correlation to the global sea level model. However, this model is limited to the recognition of individual widespread unconformities. In the deepest part of the basin, the bounding unconformities may not be present, and the conformable facies changes may be difficult to discern. Therefore, correlation based on sequence packages from the basin margin to the foredeep may be difficult. Within the Late Cretaceous Western Interior seaway, an independent method of detailed correlation is available in the form of widespread bentonite (volcanic ash) beds, which are synchronous markers within the basin. These bentonite beds can be used for high-resolution correlation in order to evaluate lateral and vertical facies changes in a sequence stratigraphic framework. The full chronostratigraphic potential of these bentonite beds has yet to be realized, and it is the purpose of this proposed research to develop that potential using well-established methods of high-resolution bentonite correlation.

The proposed research will investigate the third-order Claggett Cycle within the Western Interior, which has been correlated to the Exxon global sequences. This sequence is middle Campanian in age. The sequence consists of an organic-rich oil shale in the center of the basin and interbedded oil shale and coarser sandstone and conglomerate along the western margin. Over 20 bentonites are recognized within this sequence. These bentonites will provide opportunity for high-resolution correlation of the facies within this sequence. 

AAPG Search and Discovery Article #90925©1999 AAPG Foundation Grants-in-Aid