REWORKED CONODONTS: TILLS, SINKHOLES, AND TERRA ROSSA

Conodonts were recovered from several different types of nonmarine sediments into which they were redeposited and were found to provide a variety of useful geologic information. For example, in order to evaluate the potential of conodonts to help refine glacial stratigraphy, samples were collected from one Wisconsin and three Illinoian tills in west-central Indiana. Generically, identifiable conodonts from the Wisconsin till were many times more abundant than those from the Illinoian but were more restricted in the ages represented. The Wisconsin conodonts ranged in age from possible Silurian, as suggested by long-ranging Panderodus, to Early Mississippian; the Illinoisan ages were Ordovician into Pennsylvanian. These variations suggest that major subdivisions of the Pleistocene should be recognizable and that there is the possibility of separating smaller units and of determining ice direction based on the rocks represented.

In central Missouri, samples were collected from five more or less vertical Pennsylvanian solution fills and one sink hole in the Burlington Limestone (Mississippian). In the five fills Gnathodus texanus dominated and all specimens were compatible with a Middle Mississippian age, strongly suggesting the former presence of the Keokuk Limestone as a phantom formation above the Burlington. The ages of the conodonts from the sinkhole, however, indicate considerable transport, which has not yet been interpreted. Conodonts include specimens of Ordovician (4), Devonian (2), Middle Mississippian (3), and Pennsylvanian (1) age. In north-central Indiana a large sinkhole formed during mid-Tertiary time on Silurian rocks with clays sealing the sink. Conodonts from the red clay show that it was essentially in situ because all the conodonts, including Pterospathodus, found in it are present in the underlying bedrock.

One sample was taken from a fresh cut in terra rossa in southern Indiana. It yielded seven Pa elements of Cavusgnathus and one M element of Kladognathus, both present in the underlying Upper Mississippian limestone. I interpret this sample as having been formed in situ although there is some thought of downhill transport for terra rossa development.