Middle Devonian Bentonite in Michigan Basin: DISCUSSION

We agree with Baltrusaitis that the thin bentonite bed that he has described as the Kawkawlin Bentonite in the Michigan basin and the Tioga Bentonite Bed that others have described in New York and in the Appalachian and Illinois basins represent one and the same ashfall. However, contrary to his view, we believe that the bentonite bed described by Droste and Vitaliano on the flank of the Michigan basin in northern Indiana is also the Tioga and thus is equivalent to the Kawkawlin. The relations of the northern Indiana bentonite bed to standard conodont zones, the bed's position in a Middle Devonian physical stratigraphy thoroughly studied throughout Indiana, and the mineralogy and petrography of the bentonite all seem to indicate that the northern Indiana bentonite should not be considered as a lower (than Tioga and Kawkawlin) bentonite that would have no known equivalent elsewhere.