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Using Modern Analogs to Understand the Genesis of Ancient Carbonates: Trenton/Black River Formations, Michigan Basin

Voice, Peter J., Anthony E. Sandomierski, William B. Harrison III, and G. M. Grammer
Carbonate Sedimentology Laboratory, Western Michigan University, Kalamazoo, MI

In modern carbonate depositional settings, carbonate mud is generated as a result of several processes, including disintegration of calcareous algae, micritization of carbonate grains, inorganic precipitation, and direct precipitation of mud-sized tests of calcareous phytoplankton. In Florida Bay, mud production occurs in shallow protected waters inland of the Florida Keys, and is thought to form from the breakdown of calcareous thalli of codiacean algae including species of Rhipocephalus, Udotea, and Penicillus. Mud accumulates to form banks through the baffling of currents by the sea grass, Thallassia. Skeletal sand shoals composed of the remains of Halimeda, mollusks, and minor input of corals are found in lateral relationship with the mud banks. The activities of burrowing, mud-ingesting arthropods convert carbonate mud to sand-sized peloidal grains. Burrows may obscure the primary depositional fabric of the sediment but can also enhance the porosity of a unit.

The Trenton/Black River Formations (Ordovician) of the Michigan Basin were deposited on a shallow carbonate shelf and are characterized by bioturbated peloidal wackestones and mud-lean packstones with local cross-bedded skeletal grainstones. Vascular plants such as Thallassia were not present during the Silurian, however, crinoids served the role of current bafflers in the development of mud banks. In addition, the activities of arthropods and worms likely contributed to the stabilization of mud banks by pelletizing the mud. Understanding the genesis and stabilization of mud-rich facies in modern carbonate depositional environments can be useful in understanding both the origin and the distribution of ancient muddy carbonates, and may help to predict reservoir trends on both regional and local scales.

AAPG Search and Discovery Article #90031©2004 AAPG Eastern Section Meeting, Columbus, Ohio, October 3-5, 2004