ABSTRACT

Silurian dolomite that crops out in a quarry at Maumee, Ohio USA, forms a thick reef complex roughly 600 m in diameter and about 68 m thick. It is composed, in ascending stratigraphic order, of the Lockport Dolomite and the Greenfield Dolomite. The Lockport Dolomite at Maumee contains multistory stromatolite, thrombolite, and coral-microbialite reefs. Such reefs have never been reported previously in this unit in Ohio and Indiana. Thrombolite and stromatolite reefs are interpreted to have formed in a subtidal setting possibly within a hypersaline lagoon. Wave stress affected the coral-microbialite reefs by limiting the number of metazoans and promoting the formation of fibrous cement inferred to have been marine precipitates originally in the form of magnesian calcite. Thrombolites an stromatolites form 20-60% by volume of coral-microbialite reefs, and they contributed substantially to the syndepositional stabilization of these reefs by serving as binders and encrusters of metazoans, especially branching corals. Such stabilization sharply limited the amount of sediment available for the formation of flank beds next to coral-microbialite reefs.

Evolution of the Maumee reef complex (MRC) involved two shallowing-upward sequences, each of which was terminated by subaerial exposure. The older interval of subaerial exposure is represented by an intraformational unconformity within the Lockport Dolomite. The younger unconformity at the top of the Lockport Dolomite is correlated with the base of the A-1 evaporite in the Michigan Basin.

Parts or all of patterns shown by coral-microbialite reefs and microbialite reefs in the MRC may provide an analogue for better understanding the nature and evolution of pinnacle reefs and patch reefs in the Michigan Basin region and other reefs elsewhere.