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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