Petrology, Stratigraphy, and Depositional Environments of Burnt Bluff Group in Michigan: ABSTRACT

Abstract

Recent discoveries of sizable natural gas deposits (production at least 1 MMCFGD/well) in 3 widely separated areas of Michigan have touched off exploration interest in the lower Middle Silurian Burnt Bluff Group. The Burnt Bluff and Manistique Groups are stratigraphically equivalent to the better known Clinton Group. Analyses of core samples, outcrop samples, and wireline logs allow for a preliminary reconstruction of facies relationships and depositional environments. Where thickest, in northeastern Michigan, the Burnt Bluff Group can be divided into 3 formations: Lime Island Dolomite, Bryon Dolomite and Hendricks Dolomite. To the southwest the group thins dramatically to a single lithologic unit. The Lime Island and the Hendricks Dolomites represent shallow subtidal facies with abundant large, whole bioclasts of corals, stromatoporoids, and brachiopods. The Bryon Dolomite is a thinly laminated intertidal and supratidal carbonate with desiccation cracks, algal laminae, and anhydrite nodules. Presently, natural gas production is found only in slightly dolomitized portions of the subtidal bioclastic facies in the Burnt Bluff. Porosity development is the key to production and is primarily solution-enlarged interparticle porosity restricted to the Hendricks and Lime Island Dolomites. End_of_Article - Last_Page 263------------