THE AGE OF THE DUNKARD: HAVE WE LEARNED ANYTHING IN 120 YEARS?

The age of the youngest strata in the Appalachian Basin, the Dunkard Group, has been contested since the late 1800s. Age estimates range from Late Pennsylvanian to Early Permian, depending on the biostratigraphic data addressed. Dunkard strata are an erosional remnant preserved within the Pittsburgh-Huntington Synclinorium, a distribution incorrectly termed “The Dunkard Basin.” These rocks comprise a clastic succession with minor non-marine carbonates and discontinuous muckpuddle coaly beds that continue the overall Late Pennsylvanian drying of Euramerica. This presentation will review the historic macrophyte data associated with this 120 year old controversy and discuss why these data remain enigmatic.

Overall, the Dunkard Group contains a Late Pennsylvanian (Stephanian) fossil flora with sporadic occurrences of taxa suggestive of the Early Permian. Palynomorphs extracted from Dunkard coaly beds generally support a Late Pennsylvanian, possibly transitional Permian, age. Fossil macrophytes have proven more problematic to interpret. Three distinct paleofloras have been recognized that occupied different niches during the Late Carboniferous-Permian transition. Early workers placed utmost importance on the first occurrences of Permianesque forms such as Callipteris (Autunia) conferta, Taeniopteris jejunata and Walchia. These xerophytes, first reported from the older Conemaugh Group, lived contemporaneously in extrabasinal environmental settings with the relic late Westphalian-like wetlands floras and replaced the “normal” lowland Stephanian flora during drier, interglacial periods. As a result, Dunkard paleofloras provide a mixed and confusing biostratigraphic signal. Vertebrate and invertebrate fossils known from Dunkard strata, mainly non-marine bivalves, branchiopods, serpulid worms, and rare Lingula, are of limited biostratigraphical utility. Until more definitive fossils are found, the exact age of the Dunkard cannot be resolved closer than transitional “Permo-Carboniferous.”