Paleontology and sedimentology of calcifying microbes in the Silurian of the Ohio-Indiana region: An expanded role of carbonate-forming microbial communities

The Silurian rocks within Ohio and Indiana contain carbonates deposited under the mineral-precipitating activities of benthic microbes. Fossil microbes occur with varying degrees of preservation, and an assortment of lithologies contains evidence of microbial influence on the precipitation of micrite and cement. Features indicative of microbial activity include micritic coatings around skeletal grains; laminated, clotted, and micropeloidal fabrics; micrite in forms having independence of gravitational control; and fibrous calcite cement adjacent to well-preserved organic material. The variety of microbial products and their preservational states illustrate that numerous taphonomies and pathways for microbial calcification existed.; Fossils of the calcifying microbes Girvanella, Renalcis, and Rothpletzella occur in well-preserved rocks of the Brassfield Formation (Llandovery) cropping out at the Oakes Quarry Park in Fairborn, Ohio. The quarry also contains mottled mudstones and wackestones surrounding cm-scale growth framework cavities containing veneers and pendants of microbially-precipitated micrite.; Bioherms in the Waldron Shale (Wenlock) in Bartholomew County, Indiana are considered incipient reef cores and consist of skeletal fossils that encrusted, and were encrusted by, micrite with massive or laminated microtextures. The microfabrics and steep-angled forms of the Waldron Shale bioherms strongly suggest that they developed via synsedimentary lithification of micrite produced by calcifying microbes.; Salina Group (Ludlow) rocks that crop out in the Duff Quarry near Huntsville, Ohio contain a paucity of megafauna and an abundance of microbialites indicating that microbial colonies overwhelmingly dominated the biota in that depositional setting. A shallowing-upward sequence of dolomitic boundstones comprises a variety of microbial geometries and textures that developed within a relatively narrow depth range in a peritidal setting.; Analysis of the Silurian rocks within the Ohio-Indiana region indicates that: (1) although the region's carbonates have commonly undergone extensive dolomitization and recrystallization, abundant lithologic evidence, which is consistent with recent research on microbialite diagenesis, exists for the mediation of local sediments by microbial communities; (2) microbial communities during the Silurian inhabited sedimentary regimes ranging from subtidal normal marine to peritidal; and (3) despite the apparent global reduction in microbialite development during the post-Ordovician, communities of calcifying microbes continued to flourish locally throughout the Silurian.