EPISODIC STORM AND TECTONIC INFLUENCES ON A SHALLOW MARINE SHELF: THE LOCK HAVEN FORMATION (UPPER DEVONIAN), FORKSVILLE, PA

The upper part of the Lock Haven Formation, Upper Devonian (Frasnian-Famennian) in Forksville, Pennsylvania can be characterized as a shallow marine shelf (muddy offshore deposits and sandy shoreface) that was episodically influenced by tidal, storm, and tectonic events. The two dominant lithofacies contain flaser and wavy bedding, discontinuous hematite cemented coquinoid sandstone beds and erosional surfaces. Additionally, the muddy offshore deposits, platy bluish-gray shaley siltstone containing ripples and flaser bedding, exhibits intervals of severe bioturbation and soft sediment deformation. Storm activity in the sandy shoreface, a predominantly planar bedded medium-grain, light olive gray sandstone, is represented by hummocky cross stratification, shale intraclasts, and transported terrestrial plant debris. A possible bentonite bed is located stratigraphically between the two lithofacies.

Some of the organisms living in and on the muddy shelf include bivalves Leptodesma, Paracyclas, and Glossites, while brachiopods spiriferids, atrypids, and rhychonellids, and straight cephalopods were mostly found in the sandy shoreface deposits. In addition to these organisms, abundant burrows such as Arenicolites, Rhizocoralium, Cruziana-like traces, and other horizontal burrows were found mostly in the sandy shoreface. Abundant Cruziana-like traces were typically found associated with carbonized plant fragments, and some appear to have a subparallel alignment/orientation; no trilobites have been found. There is significant bioturbation in some of the beds in the muddy offshore facies.

The transition between the Lock Haven and overlying Catskill Formation is one marked by rapid sedimentation and progradation. This shallow shelf environment was influenced by tidal activity, and it experienced periodic storm activity and possible volcanic eruptions. Storm activity stirs up and transports nutrients within the basin resulting in an increased amount of bio-activity. Bioturbation in the offshore facies is related to resource mining while crawling traces dominate in the more energetic shoreface environment.