Landslide Facies and the Paleoslope in the Catskill Delta: ABSTRACT

Abstract

Non-red arenaceous strata of the Middle and Upper Devonian Fort Littleton Formation constitute the marine portion of the northern flank of the Catskill delta in Pennsylvania and New York. Lithostratigraphic units within the Fort Littleton thicken and become coarser toward the source in the south-southeast; laterally equivalent lower redbeds of the Catskill Formation occupy successively lower stratigraphic positions in the same direction. Submarine landslide deposits in the upper several hundred feet of the Fort Littleton below the redbeds consist of transported load-structures and angular blocks up to twelve feet long. The base of the landslide facies roughly marks the position of the foot of the paleoslope, that is, the juncture of rocks deposited on unstable slopes with undisturbed strata of the floor environment. Like the base of the Catskill facies, the landslide facies occurs at progressively lower positions toward the south-southeast and, in turn, is laterally equivalent to the distal floor facies, which is End_Page 340------------------------------ devoid of landslide structures. Regional variation in stratigraphic position of the base of the landslide facies established the fact that the foot of the paleoslope migrated north-northwestwardly through time. In strata of the landslide facies, directional-current structures show transport from south to north whereas rocks of the floor facies display evidence of paleocurrents moving from east to west, suggesting that gravity-driven paleocurrents were deflected by velocity loss from northwardly to westwardly flow at the foot of the paleoslope. Distinctive siltstones were deposited by the deflected currents against the foot of the paleoslope. The landslide facies is characterized by landslide deposits, reddish and greenish colors, subgraywackes, conglomerates, good fissility, fragmental fossils, ripple marks, and load-structures whereas the floor facies is defined by brown and gray colors, graywackes, poor fissility, sole marks, and trace fossils. End_of_Article - Last_Page 341------------