Lower Devonian trace fossils from shallow marine deposits, Shawnee Island Member of the Coeymans Formation, northwestern New Jersey

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Shallow, sub-tidal, interbiohermal deposits of medium- to medium-dark-gray argillaceous to arenaceous limestones comprising the Shawnee Island Member of the Coeymans Formation (Lower Devonian), near Wallpack Center, New Jersey, have yielded a variety of trace fossils. Specimens of Skolithos linearis, S. verticalis, and S. ?pusillus, reflecting vertical dwelling burrows, are associated with large-scale, low-angle, cross-stratified, and trough cross-stratified units, and can be referred to the Skolithos ichnocoenosis. The Skolithos ichnocoenosis records exploitation by opportunistic suspension feeders during higher energy conditions. In contrast, the Planolites ichnocoenosis consists largely of horizontal traces, including Chondrites affinis, Chondrites isp., Palaeophycus tubularis, and Planolites beverleyensis, present on horizontally laminated deposits. Trace-making, largely by deposit- and suspension-feeding opportunistic organisms, occurred during low to moderate energy levels. Field evidence indicates, however, that Skolithos and Planolites ichnocoenoses trace-making was subject to periodic, high-energy (storm-generated) conditions. Fossil layers, dominated by crinoid columnals, lie stratigraphically above most of the trace-fossil units. These mark a rapid influx of biogenic debris as well as an end to trace-making activities.

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Northeastern Geology and Environmental Sciences

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