THE FALLS OF THE OHIO DEVONIAN CORAL BEDS: AN INVESTIGATION OF PALEOECOLOGICAL ASSOCIATIONS

Throughout the Phanerozoic, preserved reefs demonstrate the relationships between ancient organisms in a way that many other fossil deposits do not. Corals or other framework builders are often in life position with encrusting organisms, trace fossils, and associated organisms preserved. In addition, because reefs or reef-like deposits are preserved throughout the Phanerozoic, it is possible to use these well-preserved structures to study changes in ecological complexity through time. The purpose of this study is to compare the paleoecologic differences between the middle Devonian coral beds located at the Falls of the Ohio State Park to reef and reef-like deposits that occur earlier and later in geologic time.

Located in southern Indiana, the Falls of the Ohio State Park is world-renowned for the highly-diverse and well-preserved middle Devonian coral. These limestone fossil beds are sometimes considered a coral reef or bioherm, but previous studies are divided on the true biologic association. Despite the fact that The Falls of the Ohio State Park is an often visited public site of paleontological importance, these fossil beds have not been formally studied for several decades, and have never been investigated with modern quantitative paleontological methods.

The stratigraphic unit studied here is the Jeffersonville Limestone and it is conventionally divided into 5 biozones. These are determined based on faunal differences and are known as the Coral Zone, Amphipora Zone, Brevispirifer gregarious Zone, Fenestrate Bryozoan-Brachiopod Zone, and the Paraspirifer acuminatus Zone. This study focuses on the most coral-rich and lowest stratigraphically, the Coral Zone. This horizon is exposed in a continuous bedding plane over several acres in the late summer and fall when water levels in the Ohio River subside.

The methodology in this study involved censusing faunal elements using 1m² quadrat sampling along a series of transects in the exposed Coral Zone beds. Mean richness, colony size and associations between organisms were classified at multiple scales (within and among quadrats and transects). These findings were compared to other studies of fossil reef and reef-like associations as well as to modern reefs to determine whether it is accurate to refer to the coral associations at the Falls of the Ohio as a true reef.