A reinvestigation of the paleobotanical evidence for the age of the Erin Shale

Abstract

The age of the Erin Shale, Clay County, Alabama, has been variously interpreted based primarily upon the acceptance or rejection of the original Carboniferous age assignment. The failure to confirm the in-place occurrence of the reported Pennsylvanian megafossils, coupled with both regional and detailed mapping, has led to the recent placement of the Erin Shale in a stratigraphically equivalent position with the Lay Dam Formation of inferred Early Devonian age. An investigation of the previously illustrated Carboniferous fossils reportedly collected from the Erin Shale and suites of rock specimens collected during the present study has added new pieces to the Erin puzzle but has not resolved the age asignment problem. Petrographic and x-ray diffraction powder analyses of the adhering matrix on Lepidostrobus hobbsii D. White and phyllites collected from the Erin outcrop belt indicate that these rocks are similar if not indistinguishable. Identifiable coal fragments exist in the Erin as do poorly preserved, unassignable fossil plant fragments. Much additional work is needed to fully define the fossiliferous nature of the Erin.