A palynological study of shales and “coals” of a Devonian‐Mississippian transition zone, central Pennsylvania

Abstract

A section of Catskill Formation (Devonian) carbonaceous shales including pockets and small beds of pyritic, vitrinitic, high‐volatile A bituminous “coal” ( >40 percent ash) was uncovered during construction of Interstate Highway 80 in Centre County, Pennsylvania. The carbonaceous sediments are up‐section from reddish mudstone and gray sandy siltstone containing poorly preserved plant fossils, and the whole sequence is presumably deltaic. Stratigraphically about 50 feet above the coal, well‐preserved lepidodendrid ("Knorria") stem casts occur. About 2000 feet west and 140 feet stratigraphically above the principal study locality, typical Pocono (Mississippian) lithology is observed in another road cut. The carbonaceous shales and coals of the primary study locality contain abundant spores, mostly Hymenozonotriletes lepidophytus Kedo, H. famenensis Kedo, and H. pusillites Kedo. Similar associations of miospores occur at the Carboniferous‐Devonian boundary in Canada, western Europe, and the USSR, probably indicating that the zone can be used as an intercontinental marker horizon. As is true elsewhere, H. lepidophytus decreases in size and then disappears toward the top of the Devonian sequence. In the presumed Mississippian locality above and west of the “coal” site, only H. pusillites of this trio remains, as has been found on the Carboniferous side of the boundary elsewhere in the world. Size studies of H. lepidophytus within a small vertical sequence of the shales and coals show variations from sample to sample, which may indicate hydrodynamic effects during transport and deposition of the sediments.