File:Fossiliferous limestone (Columbus Limestone, Middle Devonian; Olentangy River at Lazarus Run confluence, Delaware County, Ohio, USA) 5 (29731912282).jpg

Fossiliferous limestone in the Devonian of Ohio, USA.

The Columbus Limestone is a significant carbonate unit in the Devonian of central and northern Ohio. It's actually part of a much more widespread sheet of Devonian carbonates that extends from New York State to the Midwest. The Columbus Limestone represents deposition in a subtropical, shallow-water, carbonate platform environment. The rocks are principally micritic limestones, fossiliferous wackestones, and fossiliferous packstones. Some chert nodules are present in the unit, but were not observed at the locality shown above. Fossils are typical Paleozoic shallow marine invertebrates - favositid corals, rugose corals, stromatoporoids, brachiopods, crinoids, blastoids, bryozoans, trilobites, bivalves, gastropods, cephalopods, rostroconchs, and tentaculites. Microfossils include conodonts and charophyte oogonia. Other fossils in the Columbus Limestone include vertebrates (fish), land plants (rare), and trace fossils. Some fossil horizons in the Columbus Limestone are partially silicified.

At the locality shown above, the thick-bedded Columbus Limestone (= at & above water level) is overlain by the thin-bedded Delaware Limestone (= top left of photo). The contact is a prominent disconformity (a type II sequence boundary). Biostratigraphic studies have shown that one conodont biozone is missing at the Columbus-Delaware contact in central Ohio, probably representing ~1 to 3 million years. The base of the Columbus Limestone (not visible here) is a major, continent-wide unconformity representing the Tippecanoe-Kaskaskia megasequence boundary (a type I sequence boundary).

Stratigraphy: uppermost Columbus Limestone, Eifelian Stage, lower Middle Devonian