Late Ordovician Paleontology, Sedimentology
and Stratigraphy in Ohio, Indiana and Kentucky
A Keck Geology Consortium Project
June 19 - July 16, 1999
A hardground encrusted with bryozoan reef mounds is located south of Maysville, Kentucky, in the Coryville portion of the Grant Lake Formation (Cincinnatian, Upper Ordovician). This hardground was believed to be destroyed between 1992-1998 due to road construction (Cuffey, 1998), but recent visits to this location show hardground exposure for 111 meters on the east side and 10.7 meters on the west side of US Route 68. The first research on these bryozoan reef mounds was conducted by Kissling and Turonis (1977) who described this hardground as hosting bryozoan minibioherms. Cuffey (1998) also conducted research on these reef mounds before road construction. Additional research will produce a more complete depositional sequence of the strata surrounding this hardground and create a better paleoecological reconstruction.
Hardgrounds are described as synsendimentarily lithified carbonate sea-floors (Wilson and Palmer, 1992). The appearance of a hardground in the rock record is marked by the presence of borers and encrusters. This Maysville hardground is unique due to the large bryozoan mounds which have encrusted both the top and bottom surfaces of the hardground up to 8 cm in height. In addition, borings enter the hardground from both the top and bottom and through the bryozoans that encrust both the top and underside of the hardground. This hardground is located within a stratigraphic sequence of limestones and shale. Study of this sequence could reveal the paleoenvironmental conditions of the hardground development and bryozoan growth.
How does this hardground fit into the stratigraphic sequence of events at this outcrop? Can distinct cycles be seen within the stratigraphic section? Why is the hardground different from the other sediments above and below it? What were the environmental conditions that led to the creation of this stratigraphic layer as a hardground? What type of hardground is it and are there similar examples either in literature or in the collections at the College of Wooster? Why does it have a sparry matrix? Why is pyrite abundant in thin section? Can sulfate reduction be used to explain the presence of the pyrite and the cementation? How do the faunal fragments inside the borings compare with those found in the hardground matrix? Why are some grains iron-rich?
What types of encrusters are present? Why do bryozoans encrust both above and below the hardground? Why are small caves present in this location? Can these caves be compared to Kobluk's (1977,1978, and 1980) examples?
What is the sequence of events among the hardground, bryozoans, and
borings? If the boring does not extend into the bryozoan, is it a boring
or burrow? Why do some borings go up and some go down?
