KARST OF THE DEVONIAN CATSKILL FORMATION, NORTHEASTERN PENNSYLVANIA

The Upper Devonian Catskill Formation of Pennsylvania’s northern tier is comprised of a series of stacked, fining-upward siliciclastic sequences. The basal sandstones tend to overlie intra-formational conglomerates, a poorly-sorted hodgepodge of coarse to pebbly, non-calcareous and calcareous clasts of largely paleo-pedogenic origin, mixed within a calcareous, finer-grained sandy matrix. These units occur as individual beds 2-3 m in thickness. Although the majority of upper bedding contacts are sharp, they commonly become gradational where the assorted clasts are incorporated into overlying sandstones.

Dissolution is directed along the surfaces of regionally predominant north-south, east-west joint sets as well as along near-horizontal bedding partings. Acid formation through the oxidation of pyrite associated with carbonized fossil plant material, and probable biogenic weathering through physical and chemical interaction of encrusting lichens contributes towards the enhanced weathering.

Small caves and a variety of dissolution features can be identified, as well as enhanced development of secondary porosity along the discontinuities of the weathered zones. The weathering progression is also tied into mass-wasting processes where void growth undermines more competent, non-calcareous bedrock, encouraging roof breakdown and eventual secondary development of “colluvial” caves.

The nearly horizontal attitude of the bedrock has confined the occurrence of these karstic features to the rims and moderate- to steep-sided slopes of incised stream valleys. It is suggested that these karstic beds may extend into topographic lowlands but are masked by glacial till and outwash that covers much of northeastern Pennsylvania.