EXCEPTIONAL PRESERVATION OF AN IN SITU MIDDLE PENNSYLVANIAN FOREST: LEVEE BANK TO INTERDISTRIBUTARY LAKE ENVIRONMENTS OF THE LOWERMOST VOWELL MOUNTAIN FORMATION, MORGAN COUNTY, TENNESSEE

An exceptionally preserved fossil forest occurs within the Vowell Mountain Formation near Wartburg, Tennessee. Approximately 300 meters of highwall exposure, excavated during strip mining of the underlying Pewee coal (Red Mountain Formation), contains more than thirty arborescent lycopsids and sphenopsids in growth or near-growth positions. This locality is spectacular for both the relative proximity of fossil trees and their species heterogeneity and represents an exciting opportunity to examine community ecology within a Middle Pennsylvanian lowland forest.

Fossil trees occur within an upper delta plain facies assemblage that contains discrete channel, levee, interdistributary lake, and crevasse splay deposits. Upright, arborescent lycopsids occur with their bases within both interdistributary lake deposits (primarily Lepidodendron) that directly overlie the Pewee coal horizon and within laterally adjacent levee sands (mixed lycopsid species) that occur up to several meters above the Pewee coal. Calamites appears primarily within topographically highest levee bank sands, nearly 4 meters above the Pewee coal, suggesting a preference for dryer envrionments. All trees are preserved as either external molds or as both internal casts and external molds. Lycopsid species average 35-75 cm in diameter, and have preserved heights of 2.5-3.5 meters. Calamitean species average 10 cm in diameter and have estimated preserved heights of ~3.5 meters. Leaf litter within interdistributary lake and levee deposits mimics ecologic patterns of arborescent growth, with lacustrine deposits preserving a nearly monotypic lycopsid flora and levee bank sands preserving mixed floral elements that include sphenopsid, conifer, pteridosperm, and Cordaites.

Rapid burial of the forest community occurred via crevasse splay deposition. The initial levee breach resulted in 35-50 cm of sand accumulation, and additional pulses of this splay resulted in up to 120 cm of additional accumulation and was associated with slumping in mid-levee regions that resulted in the en echelon fracture and tilting of arborescent lycopsids. In off-levee regions a second, distinct package of crevasse splays completed the burial process prior to channel migration across the region.