WALCHIAN CONIFERS FROM THE MID-LATE PENNSYLVANIAN CONEMAUGH GROUP IN THE APPALACHIAN BASIN: STRATIGRAPHIC AND DEPOSITIONAL CONTEXT, AND PALEOCLIMATIC AND PALEOGEOGRAPHIC SIGNIFICANCE

Walchian conifer macrofossils first appeared in North America during the Middle Pennsylvanian, but are rare until the Permian. An abrupt climate change occurred at the Westphalian-Stephanian boundary that was characterized by global warming, stronger seasonality, and shorter wet phases. It coincided with the regional extinction of most tree lycopsids and the appearance of widespread, high chroma, calcic vertisols and aridosols. Only four occurrences of Walchia have been reported from the Pennsylvanian of the Appalachian Basin (Ohio: 7-11 mine; Pennsylvania; and West Virginia: Charleston, Cedar Run). This paper uses recently acquired outcrop data to more fully document and reevaluate the depositional and stratigraphic context of the West Virginia assemblages and their paleoclimatic and paleogeographic implications.

The Cedar Run Walchia assemblage occurs in olive mudshale of an abandoned fluvial channel-fill 15.8 m above the base of the Ames Limestone, indicating a Stephanian/Earliest Virgilian age. It consists of branches and branchlets of Walchia, Walchistrobus, Lepidophylloides, Cordaites, and rare neuropteroid pinnules. The channel-fill is a component of the Grafton Sandstone IVF previously described from the study area. Correlation of paleosol-bounded, marine-cored cyclothems with their updip, nonmarine equivalents at Charleston indicates the Walchia previously reported at the Mahoning Coal horizon, occurs between the Brush Creek and Bakerstown Coals, and is Early Stephanian/Missourian and not Westphanlian D, similar to the revised age for the 7-11 mine Walchia.

Late Pennsylvanian, upland conifer communities were comprised of Walchia, Cordaites, and Sigillaria which produced a forest canopy with seed ferns as an understory. The Cedar Run assemblage was probably transported into the valley from adjacent, well-drained uplands formed during valley incision, and deposited during the early TST. It is also possible that Walchia expanded into the valleys when drainage became ephemeral during more arid phases. The revised correlations of Appalachian Walchias are more in synch with other paleoclimatic indicators, indicating their appearance closely followed, rather than predated the abrupt climate change and extinctions at the Westphalian-Stephanian boundary.