MACROFLORAL EVIDENCE FOR AN UNCONFORMITY AT THE MID-CARBONIFEROUS BOUNDARY IN THE CENTRAL APPALACHIAN BASIN

The presence and duration of an unconformity at the mid-Carboniferous boundary in the central Appalachian basin (CAB) have been debated for over 100 years. Based on early reports suggesting that the most complete Pennsylvanian section in North American occurred in West Virginia, various conceptual depositional models were advanced postulating continuous sedimentation across the mid-Carboniferous boundary in southern West Virginia. These models suffered from a lack of biostratigraphic control due to a limited knowledge of Late Mississippian macrofloras and the lack of Early Pennsylvanian marine faunas. Critical analysis of macrofloral data from extant collections, published records and new collections identified a substantial unconformity between Late Mississippian (Bluestone Formation) and Early Pennsylvanian (Pocahontas Formation) strata in the CAB. Lyginopteris stangerii, Mariopteris laciniata and associated taxa in uppermost Bluestone paleoflorules indicate a lower Namurian (Arnsbergian) age for the youngest Mississippian strata in the CAB. A Langsettian (lower Westphalian) age for Pocahontas Formation strata, excluding basal beds, is supported by the presence of Lyginopteris hoeninghausii and associated elements. The common occurrence of Diplotmema composita D. White [Eusphenopteris straeleni (Stockmans and Willière) Van Amerom] in basal Pocahontas paleoflorules suggests a latest Namurian age for oldest post-unconformity strata. The duration of the mid-Carboniferous unconformity in the CAB is comparable in duration to the one recognized throughout the Pennsylvanian Paleoequatorial Belt. This widespread unconformity is attributed to a glacio-eustatic sea level drop associated with the onset of widespread Gondwanan glaciation.