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Geology at Red Hill

Red Hill, a 1 km long roadcut exposure located in Clinton County Pennsylvania, has been identified as part of the Duncannon Member of the Catskill Formation. Red Hill is a relatively isolated outcrop that is at least 45 km removed from the nearest substantial exposure of Late Devonian sediments. Palynological dating (using fossil plant spores) indicates that the fossil-rich rocks date to the upper Fa2c part of the Upper Famennian stage of the Late Devonian and were probably deposited 361 million years ago.

The paleoenvironment was tropical to sub-tropical with an estimated paleolatitude of 20° S. A paleosol (fossil soils) investigation revealed an alternating pattern of aridisols and vertisols that indicates extended periods of arid conditions interspersed with more mesic conditions characterized by moderate precipitation (821 +/-141 mm/yr) and a pronounced dry season. The fossiliferous deposits formed during the wetter part of the climatic cycle.

The sedimentary rocks at Red Hill are fluvial (i.e., they were deposited by a river). Red mudstones account for most of the rocks found at Red Hill, and give the site its characteristic color. Lenses of greenish-gray mudstones and fine- to very fine-grained sandstones are also present. The arrangement of these rocks in finning-upwards cycles of 5-10 m indicate that Red Hill was the site of a wide, meandering, lowland river. The paucity of coarser sandy sediments indicate that currents were generally sluggish. In addition, much of the red mudstones showed evidence of repeated drying and wetting, suggesting a pattern of advancing and receding floodwaters. Given the paucity of coarse sands, flooding at Red Hill was probably not destructive. Instead, it may have been seasonal and a source of ecosystem enrichment.

Taphonomic observations indicate that the plants and animals at Red Hill lived near where their remains were fossilized. Most vertebrate remains were recovered from shallow channel margins and were usually disarticulated, but associated (i.e., the bones were not joined, but were found together). They also don't show signs of extensive reworking and transport. Plant material was most common in a reduced lens (greenish-gray mudstone) which was probably a pond lying on the floodplain. The presence of well-preserved rooting structures suggest that at least some of the plants grew in or adjacent to the pond.

The Duncannon Member of the Catskill Formation is part of a larger geological unit often referred to as the Catskill Delta, a complex of Middle to Late Devonian alluvial, deltaic and marine deposits produced by the erosion of the Acadian Orogeny. The Catskill Delta lies in the present day Central Appalachians, with alluvial deposits extending from southeastern New York through Pennsylvania, Maryland, West Virginia and northwestern Virginia; associated marine deposits extend westward into Ohio and southward into Tennessee. A series of rivers (including the one at Red Hill) generally flowed in a northwest direction from the Acadian Uplands across a broad coastal plain and into the Catskill Sea, an inland sea covering part of western paleocontinent of Euramerica.

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Web:

E. Copeland & M. Lindholm's website on the Acadian Orogeny:
www.student.brynmawr.edu/students/mlindhol/

Paleontological Research Institute's pdf on the Acadian Orogeny:
www.priweb.org/ed/TFGuide/NE/geo_history/ history_files2/history_pdfs/ne_geohistory4.pdf

Scientific Papers:

Daeschler, E.B. and W. Cressler. 1997. "Paleocology of Red Hill: A Late Devonian tetrapod site in Pennsylvania (abstract)." J. Vert. Paleo. 17(3) Supplement: 41A.

Retallack, G. 2004. "Paleoenvironments of Late Devonian tetrapods from Pennsylvania." Journal of Vertebrate Paleontology Abstracts 24(suppl.3): 103A.

Traverse, A. 2003. "Dating the earliest tetrapods: A Catskill palynological problem in Pennsylvania." Cour. Forsch. -Inst. Senckenberg 241:19-29.

Woodrow, D.L. 1985. "Paleogeography, paleoclimate, and sedimentary processes of the Late Devonian Catskill Delta." pp. 51-63 In: D.L. Woodrow and W.D. Sevon (eds.). The Catskill Delta. Geological Soc. America Special Paper 201

Woodrow, D.L., R.A.J. Robinson, Anthony R. Prave, A. Traverse, E.B. Daeschler, N.D. Rowe and N.A. DeLaney. 1995. "Stratigraphic, sedimentologic, and temporal framework of Red Hill (Upper Devonian Catskill Formation) near Hyner, Clinton County, Pennsylvania: site of the oldest amphibian known from North America. Field Trip Guide." 60th Annual Field Conference of Pennsylvanian Geologist: 1-8.

Image Credits:

The Catskill Delta image is copyrighted © 2002, Dennis C. Murphy (See Terms of Use.)