MACROFOSSILS AS PALEO-ENERGY INDICATORS IN A MIXED-SEDIMENT TIDAL FLAT SEQUENCE

The distribution and taphonomy of mollusks recovered from three 5-7-m-long sediment cores at Sewell Point, Cape May offer insight into the evolution of a back-barrier wetland. The stratigraphy of the site indicates rapid paleo-lagoon infilling over the past millennium, culminating in supratidal wetlands. Six shells of the eastern mudsnail (Ilyanassa obsoleta) recovered from each 3-cm-diameter core demonstrate the high population density of this gastropod. Its intertidal habitat range makes it a potentially valuable sea-level and paleo-environmental indicator. Three radiocarbon-dated mudsnail shells, along with saltmarsh rhizomes, exhibit a younging trend consistent with tide-dominated sediment accretion on the landward flank of the barrier. The oldest shell recovered at 5.39 m below present mean high water (MHW) level yielded a calibrated age of AD 1047-1210, indicating intertidal to subtidal conditions during the lagoon infilling. A younger specimen at 3.99 m dating to 1495-1650 exhibited sponge borings which suggest deposition in a low-energy backbarrier environment. At 2.95 m, a partially fragmented shell from 1523-1670 was recovered from a matrix of 70% sand. Based on the sedimentological context and taphonomy, this I. obsoleta was likely minimally reworked and transported by a storm event in the late 1500s. Just above this interval, an abraded oyster shell dated to 810-1006 suggests a more intense reworking. Both macrofossils and vegetation remains provide a composite chronology that closely follows the regional sea-level trend. The local MHW envelope is slightly depressed, possibly due to compaction by Cape May Harbor dredge spoil in the early 1900s. This study demonstrates that the macrofossils can be used as paleo-energy indicators in a back-barrier sequence that lacks clear lithological contacts due to the absence of mature peat and identifiable overwash horizons.