ABSTRACT: K-Bentonite and Sequence Correlations of Upper Black River and Lower Trenton Limestones from Lake Simcoe, Southern Ontario Canada to Watertown, Northern New York State

Sean R. Cornell, and Carlton E. Brett, Department of Geology, University of Cincinnati, OH; e-mail: cornelsl@email, uc.edu, [email protected]

Recent studies of the Black River to Trenton transition in the study area has resulted in regional (~300 km E-W) correlation of meter scale intervals, distinctive marker beds and K-bentonites. We recognize two depositional sequences leading up to and spanning the traditional Black River-Trenton boundary. The first sequence starts within the lower Lowville, above the "MX" K-bentonite. The transgressive sytems tract (TST) is recorded as the transition from dolomitic and vugy limestones through laminated, thin mudcracked micrites to more massive clean birdseye micrites. A sharp flooding surface above the "MH" K-bentonite records the change from shallow subtidal to deeper shelf (recorded by burrow mottled wackstones of the upper Lowville), which is internally divided into 8-10 regularly spaced small scale shallowing upward cycles. Overall it appears to show a progradational pattern and thus represents the HST. The late HST of this sequence is marked by the Glenburnie Shale (a stromatolitic and mudcracked interval).

The Glenburnie is abruptly overlain by conglomeratic grainstones delineating the boundary between the two sequences. The TST of the second sequence is represented by the Watertown and Selby, and the HST by the Napanee to Kirkfield and are separated by a sharp flooding surface. Correlation of marker beds including four fingerprinted K-bentonites suggest these intervals are synchronous across the study area.

Surprisingly and contrary to the suggestions of many previous workers, the upper Black River Group demonstrates that (despite local facies changes and the confusing multiplicity of local names), these beds show a considerable regularity and predictability with no evidence for diachroneity as previously asserted.

Search and Discovery Article #90907©2000 AAPG Eastern Section Meeting, London, Ontario, Canada