Eastern Section Meeting

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Late Stage High Temperature Dolomitization in the Ordovician of the Michigan and Illinois Basins – Why the Difference?


The Ordovician Black River and Trenton Groups are composed of a series of stacked marine carbonate depositional cycles that are stratigraphically and volumetrically important components of the sedimentary fill in the Michigan and Illinois Basins. The Michigan and Illinois Basins are similar in size, ~80,000 square miles and ~60,000 square miles respectively, and are considered interior cratonic basins. Each basin is interpreted to have originated from failed Precambrian rift systems. The maximum thickness of the sedimentary section is approximately 21,000 feet in the Illinois Basin and approximately 16,000 feet in the Michigan Basin. Yet there is a striking difference in reservoir development potential in the Black River and Trenton stratigraphic packages in the two basins. The Black River and Trenton oil and gas reservoirs of the Michigan Basin are believed to have been largely formed by periodic structural movement and late-stage, high temperature dolomitization processes. Although late-stage dolomitization has been observed in the Trenton Formation of the Illinois Basin it has not proven to be a significant reservoir forming/preserving diagenetic process in the majority of the Basin. A regional map of Trenton dolomite thickness in Indiana suggests that the extensive, late-stage, subsurface dolomitization observed in the Trenton Formation located on the northern edge of the Illinois Basin were formed from dolomitizing, subsurface fluids that moved south out of the Michigan Basin. Differences in the structural evolution of the two basins and the response of sedimentary basin filling to structural movements are interpreted to be responsible.