AAPG Annual Convention and Exhibition

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Salina Group Lithofacies in the Michigan Basin: Development of an Improved Depositional Model From Core Analysis


A series of newly archived cores at the Michigan Geological Repository for Research and Education have allowed the first detailed observations of the entirety of the Salina Group in southeastern Michigan. Prior to these acquisitions, due to the inclination of industry, the known curated cores available focused on the Salina A- and F-units. New cores as well as rediscovered historic cores have provided new insights into Salina Group stratigraphy, due to the more complete sampling of the entire Salina Group. The Salina Group were deposited during the Upper Silurian and represent a series of deposits in a restricted marine basin, punctuated by periods when the basin was connected to the open ocean. In the subsurface of the Michigan Basin, the Salina Group has been subdivided, on the basis of wireline log and cuttings data, into the A-0 through G units. Major evaporite units in the Salina Group include the A-1 and A-2 evaporites, the B-Unit, the D-Unit and the F-Unit. All of these units reached halite saturation and are characterized by interbedded dolomudstones, anhydrites and rock salts. In the central basin, the A-1 unit reaches sylvite saturation, and sylvinite deposits are found and have been economically exploited in the past. Thick shales with interbedded anhydrite and dolomite are found in the C-, E-, and G-Units. In the southernmost Upper Peninsula, the Salina Group undergoes lateral facies changes to the dominantly shale Pte. aux Chenes Formation. The Salina Group hosts important rock salt and sylvinite reserves. The lower Salina units serve as seals for important hydrocarbon reservoirs in the Niagaran pinnacle reefs and A-1 carbonate. Significant volumes of natural gas and liquefied petroleum gas are hosted in salt caverns in the A-2 and B salts. An overview of the Salina Group lithofacies will be presented with review of their distribution in the subsurface of Michigan, including interpretation of depositional environments and patterns in sedimentation. Detailed understanding of the lateral distribution and physical properties of the units of the Salina group will enhance our understanding of its value as reservoir seals and salt storage cavern resource.