Selective Dolomitization of the Black River Group and Its Relationship to the Massive Dolomites of the Overlying Trenton Formation in North and East Central Indiana
Dennis R. Prezbindowski
Petroleum Consulting, Inc., Syracuse, IN, [email protected]
The Black River Group is composed of a series of stacked marine carbonate depositional cycles that were deposited as part of a major marine transgression on to the erosional unconformity at the top of the Cambrian Knox Group in northern and eastern Indiana. Knox erosional remnants have been demonstrated to have as much as 160 feet of local relief in the area. Although the paleotopographic relief was reduced as deposition of the Black River carbonates occurred, sufficient relief was present to form local high energy carbonate deposits associated with underlying Knox highs in the Black River and overlying Trenton carbonates. The high energy capping carbonate facies, with remnant primary and secondary porosity along with cross-cutting faults, were the preferred flow paths for the late-stage dolomitizing fluids that moved out of the Michigan Basin. This process resulted in the development of complex, highly variable dolomite reservoir units in the Trenton and Black River Formations. The broad geographic and stratigraphic extent of the Trenton dolomites, as compared to the limited stratigraphic and geographic distribution of the Black River dolomites suggests that the capping Maquoketa Shale was a major basin aquitard. The Maquoketa Shale forced the high temperature, reactive, basinal fluids to flow laterally out of the basin through the underlying Trenton carbonates towards the crest of the Kankakee Arch that separates the Michigan and Illinois Basins. A limited volume of downward moving basinal fluids through faults can account for the limited and complex distribution of Black River dolomite facies in east central Indiana.
AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012