TRACE FOSSIL RESEARCH IN THE DELAWARE WATER GAP NATIONAL RECREATION AREA, NEW JERSEY

The Lizard Creek Member of the Shawangunk Formation (Silurian), comprising interbedded, quartz-rich sandstones, siltstones, and shales deposited in a diversity of marginal marine environments (e.g., tidal channel, barrier bar, tidal flat, lagoon), revealed specimens of Arenicolites ichnosp., Arthrophycus alleghaniensis, Chondrites cf. arbuscula, Monocraterion tentaculatum, Palaeophycus tubularis, Planolites beverleyensis, Protovirgularia ichnosp., Rosselia socialis, and Skolithos verticalis.

Interbedded calcareous sandstones, siltstones, and quartzose limestones making up the type section of the Upper Silurian Wallpack Center Member (Decker Formation) yielded Cruziana ichnosp., Diplichnites ichnosp., Lockeia siliquaria, Palaeophycus heberti, Planolites beverleyensis, Protovirgularia rugosa, and bilobate trails. The traces compare favorably to the Cruziana ichnofacies, and combined with the shelly fossils present indicate a shallow marine moderate to low energy environment, punctuated by periodic, higher energy (likely storms) conditions. In contrast, the Skolithos ichnofacies, consisting of vertically oriented burrows of Skolithos verticalis and associated shelly material, records limited exploitation by suspension feeders in a shallow marine environment during higher energy conditions.

Shallow, sub-tidal, interbiohermal argillaceous to arenaceous limestones comprising the Lower Devonian Shawnee Island Member (Coeymans Formation) yielded two ichnocoenoses. The Skolithos ichnocoenosis, consisting of Skolithos linearis, S. verticalis, and S. ?pusillus, reflects higher energy conditions, while the Planolites ichnocoenosis, including Chondrites affinis, Chondrites ichnosp., Palaeophycus tubularis, and Planolites beverleyensis, indicates trace-making during low to moderate energy levels.

Sub-tidal, arenaceous to shaly siltstone deposits of the Lower Devonian Esopus Formation yielded burrows of Skolithos. Interestingly, many specimens are seen to cut directly across earlier formed Zoophycos burrows.

Overbank flood and crevasse splay deposits of the Upper Silurian Bloomsburg Red Beds yielded the first occurrence in New Jersey of an ancestral horseshoe crab (suborder Synziphosurina). The monospecific presence of the associated trace fossil Skolithos suggests a brackish water origin for the synziphosauran-bearing strata.