TRACE FOSSILS, INCLUDING THAT OF A MYRIAPOD-LIKE ARTHROPOD TRACEMAKER, FROM SILURIAN AND DEVONIAN STRATA OF NEW JERSEY

The type section of the Wallpack Center Member of the Upper Silurian Decker Formation includes 25 m of calcareous sandstones interbedded with quartzose limestones and thin siltstones, representing mainly shallow subtidal, offshore bar deposits. Ichnologic analysis defines two contrasting ichnofacies. The trace fossil assemblage Aulichnites, Cruziana, Diplichnites, Palaeophycus, Planolites, and Protovirgularia exhibits horizontal to sub-horizontal shallow burrows, as well as locomotion traces, and a trackway. Likely producers such as arthropods, mollusks, and worm-like forms generated feeding, dwelling and crawling traces while foraging for food in organically enriched lime muds. The ichnotaxa and their associated traces compare favorably with the Cruziana ichnofacies. All of the trace fossils are restricted to the lower portion of the type section, and occur on the soles of sporadically rippled calcareous sandstones and thin siltstones overlying quartzose limestones. Periodically, organism foraging in the lime muds was interrupted by an influx of sands and silts which covered the traces. Of exceptional importance is the presence of a myriapod-like arthropod trackway (Diplichnites), produced in very shallow water. It represents one of the earliest known occurrences of its kind, and the first reported from New Jersey. A low diversity Skolithos ichnofacies, including the trace fossils Skolithos and Monocraterion, is also present. It is restricted to laminated and cross-stratified calcareous sandstones in the lower portion (Monocraterion) and upper portion (Skolithos) of the type section. Vertical to inclined burrows were likely occupied by annelid suspension feeders. The presence of these ichnotaxa denote a relatively high-energy setting.

Preliminary investigation of the Lower Devonian Oriskany Group (Ridgely Sandstone), indicates the presence of the trace fossil Planolites on the soles of thin siltstones interbedded with brachiopod-rich, bedded to cross-bedded coarse quartz sandstones and conglomerates. The strata reflect shallow water beach or barrier beach deposits. In addition, the Buttermilk Falls Limestone (Middle Devonian) has yielded evidence of the trace fossil Helminthopsis, associated with thin clayey and silty limestones. Deposition likely occurred in well-oxygenated subtidal waters.