A reevaluation of the Burnt Bluff Group (Llandovery, Silurian, Michigan Basin) from subsurface and outcrop data: Development of a time-transgressive depositional model
P.J. Voice, W.B. Harrison, III, G.M. Grammer, "A reevaluation of the Burnt Bluff Group (Llandovery, Silurian, Michigan Basin) from subsurface and outcrop data: Development of a time-transgressive depositional model", Paleozoic Stratigraphy and Resources of the Michigan Basin, G. Michael Grammer, William B. Harrison, III, David A. Barnes
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Previous work shows that the Burnt Bluff Group was deposited as a series of shallow- to moderate-water-depth facies in a tropical marine setting in the Michigan Basin during the Llandoverian. New interest in the unit for both hydrocarbon resources (subsurface) and aggregate resources (outcrop) is driving research in this poorly understood unit. New cores, as well as investigation of the outcrop belt in the Upper Peninsula of Michigan, allow further elaboration of the depositional model. The traditional interpretation of the Burnt Bluff Group consists, in stratigraphic order, of the open-marine deposits of the Lime Island Formation, the restricted lagoonal–tidal flat Byron Formation, and the open-marine deposits of the Hendricks Formation. The contacts with the underlying Cataract Group and overlying Manistique Group are gradational. Identification and description of facies in both cores and outcrop sections provide new constraints on the stratigraphic nomenclature of the Burnt Bluff Group. New outcrop and core data require the revision of the depositional model for portions of the group because typical Byron-like facies are found interbedded with Hendricks-like facies in both the Byron and Hendricks Formations. Limited age data from published research combined with the new facies model for the Burnt Bluff Group suggest that the unit was deposited as a time-transgressive package on a carbonate ramp during the Llandoverian.