EARLY SILURIAN (LLANDOVERY) STROMATOPOROID DIVERSITY: BRASSFIELD FORMATION, WEST-CENTRAL, OHIO

The Early Silurian was a time of recovery for many organisms affected by Late Ordovician extinction events. Stromatoporoids were no exception. Their recovery and subsequent proliferation played a role in the formation of mid-continent, USA, carbonate build-ups. A collection of stromatoporoids from the Early Silurian Brassfield Formation in west-central Ohio was systematically studied. These data, in conjunction with a microfacies analysis, indicate notable species recovery during times of relatively stable conditions.

Remarkably high diversity occurred within two intervals. An early interval of poor-to-moderately sorted bryo/pelmatozoan pack/grainstone, and a later interval of moderate-to-poorly sorted pelmato-bryozoan pack-grainstone. The former represents a microfacies that contains a higher proportion of bryozoans and packstones to that of pelmatozoans and grainstones, whereas the latter microfacies displays a gradational change between pelmatozoans and bryozoans, and packstones and grainstones.