Depositional Patterns and Diagenetic History of Trenton-Black River Formations in Michigan Basin: ABSTRACT

Abstract

The Trenton-Black River formations (Middle Ordovician) exhibit depositional facies and regional thickness variations indicative of normal marine, carbonate platform accumulation adjacent to a deeper water, basinal environment. Thickening of both formations occurs in the southeast part of the Michigan basin, possibly in response to basement movement accompanied by a shift in the basin depocenter. Early mixed-water diagenesis introduced the first generation of replacive dolomite, which varied in minor element composition and abundance depending on proximity to structural highlands southwest and southeast of the Michigan basin. A ferroan cap dolomite is interpreted to be partly representative of this early dolomite stage. Later stage replacive dolomite and dolomite cements are commonly associated with large fracture systems active during the Paleozoic. Although ferroan dolomitization is common throughout the Trenton and Black River formations, it is most extensive within these fracture zones, which also host significant oil and gas deposits in several locations. In addition, several accessory minerals are associated with late-stage dolomite cements, including pyrite, calcite, anhydrite, barite, celestite, sphalerite, and fluorite. The trade occurrence of these minerals in association with late-stage ferroan dolomite cements indicates that the Trenton-Black River formations in southern Michigan have undergone hydrothermal alteration analogous to a typical Mississippianmore » Valley-type deposit. Evidence based on the stratigraphic distribution of this mineralization indicates that the lower Paleozoic and Precambrian basement rocks were important sources for iron, sulfur, and other trace metals deposited in the Trenton-Black River during the late Paleozoic.« less