Abstract

To better determine the relative contributions of wind/wave versus tidal processes along the westward prograding Catskill shoreline of eastern North America, seven stratigraphic sections comprising the marine-nonmarine transition were measured along a NNE-SSW line across central Pennsylvania over a distance of 279 km. The interval includes the upper Lock Haven Formation and equivalents up to the base of the Sherman Creek Member of the Catskill Formation. Each section, excepting Entriken, yielded a Diaphanospora reticulata palynomorph assemblage, implying that six of the sections are isochronous and of middle Frasnian age. Thus, the shoreline lay along the NNE-SSW trend of the outcrop belt. The sections contain approximately similar vertical sequences, starting with thick intervals of olive-grey hackly mud shales with a sparse brachiopod fauna that pass by way of hummocky-stratified, very fine sandstones into intervals up to 25 m thick of fine, often large-scale trough or planar cross-stratified sandstones. This assemblage is interpreted as a shelf sand ridge complex and associated inter-ridge seafloor constructed by wind/wave-driven flows. These are separated from shoreline deposits by a mixed mud shale, bioturbated fine sandstone interval interpreted as shoreface deposits. The shoreface deposits are replaced landward by either progradational sequences of transgressive bioturbated shoreface sands overlain by tidal flat muds, or by fining upwards sequences composed in ascending order of large-scale trough or planar cross-stratified fine to medium grained channel-filling sandstone, inclined heterolithic strata with flaser or lenticular bedding and asymmetrical ripple forms, and red laminated siltstones and mudstones with mudcracks and root traces. This sequence is interpreted as the product of tidal channel migration through muddy tidal flats. These interfinger with large-scale cross-stratified quartzose sandstone bodies interpreted as estuarine sand shoals. The tidal features are interpreted to indicate at least a mesotidal range for the shoreface and inshore environments. Thus, the Catskill shoreline across Pennsylvania was shaped by a mixture of offshore wave/wind and onshore tide-dominated sedimentation.