Geologic applications of Late Pennsylvanian ichthyoliths form the midcontinent region.

Abstract

Ichthyoliths (microscopic fish skeletal debris comprised mainly of teeth, dermal denticles and mucous membrane denticles) are abundant and diverse in a wide range of lithologies and often occur in horizons which are otherwise unfossiliferous. However, very few studies have dealt with Late Paleozoic ichthyoliths due to the problems in identifying them. Through the use of a coded system of identification, I have been able to overcome these taxonomic problems and utilize ichthyoliths. This study was conducted to assess the applicability of Late Pennsylvanian ichthyoliths in geology by comparing their geographic and stratigraphic distributions with those of the conodonts from the Shawnee and Lansing groups.

Ichthyoliths from 16 localities extending from northern Oklahoma to Iowa were examined to determine their geographic and biostratigraphic distributions. Nearly 25,000 ichthyoliths comprising 156 different types were identified and used in the analyses. The results show that the distribution of ichthyoliths closely reflects that of conodonts in the Shawnee and Lansing groups. Different ichthyolith faunas were recovered from rock sequences of different ages, indicating a strong potential of ichthyoliths for biostratigraphic correlations. Initial studies to determine the reactions of ichthyoliths to thermal gradients show that they undergo not only color changes but structural alterations as well. Their thermal changes suggest an important use of ichthyoliths for hydrocarbon exploration. The results of this study indicate that Late Paleozoic ichthyoliths can provide useful information regarding biostratigraphy, geographic variation and geothermometry.