Paleoenvironmental evidence for latest Pleistocene sea-level fluctuations on the New Jersey outer continental shelf: combining high-resolution sequence stratigraphy and foraminiferal analysis

Abstract

Foraminiferal assemblages in vibracored sediments within ∼5 m of the seafloor document high-resolution sea-level fluctuations and confirm the complex Quaternary depositional history of the New Jersey margin. Biostratigraphic data have been integrated with ongoing 2-D/3-D high-resolution seismic analyses to interpret paleoenvironments of surficial stratigraphy beneath the modern middle-to-outer shelf. Cluster analysis of foraminiferal assemblages sampled every 20 cm (average) define four sample groups (A–D) dominated by benthic species. Group A, characterized by Cibicides lobatulus, is a middle-to-outer-shelf assemblage (∼60–100 m water depths). Group B is composed of middle-shelf species (∼30–60 m water depths) and is characterized by low abundances and a fairly uniform distribution of foraminifera, which suggests reworking and/or a high rate of sediment accumulation. Group C, dominated by Elphidium excavatum, is an inner-to-middle-shelf assemblage (∼10–40 m water depths). Group D, present in only one core and dominated by Ammonia beccarii, represents marginal marine environments (∼0–10 m water depths, with fluctuations in salinity). In general, the modern sedimentary veneer (i.e., the upper ∼20 cm) is characterized by the deeper-water fauna of group A. Sediments below these modern deposits are characterized by groups B and C, reflecting shallower water depths and variable sediment-accumulation rates on the inner and middle shelf. Taken together, the group succession in the cores suggests an overall SE-to-NW (landward) transgression in these latest Pleistocene–Holocene deposits. Seismic analysis indicates that one core (27) penetrates the flank of a buried channel, including its fill and the pre-channel section. Within the channel, three alternations of groups C and D suggest fluctuations between marginal-marine and middle-shelf paleoenvironments; high-frequency, perhaps very small (<10 m?) changes in base level are indicated. Using previously published AMS 14C dates, these fluctuations can be constrained as having occurred between 45,000 yr B.P. (channel incision) and 12,500 yr B.P. (channel filling), suggesting the non-uniform nature of the last Wisconsinan deglaciation.