SEQUENCE STRATIGRAPHIC INTERPRETATIONS FROM BENTHIC FORAMINIFERA: INSIGHTS ON NJ MARGIN ARCHITECTURE, IODP EXP. 313

Integrated Ocean Drilling Program Expedition 313 (IODP Exp. 313) drilled a critical nearshore segment of the New Jersey margin transect that extends from the onshore coastal plain (ODP Legs 150X & 174AX) to the continental slope (ODP Legs 150 & 174A). The transect is designed to unravel the complex relationships between eustatic change and margin sedimentation. Exp. 313 retrieved sedimentary successions from the region that is most sensitive to sea-level change, the inner continental shelf.

Benthic foraminifera are the only seafloor-dwelling microfossils that occur consistently in Exp. 313 marine facies. Different benthic foraminiferal species typically colonize certain water depth ranges, with key depth-indicator species providing an invaluable tool for reconstructing paleobathymetry. The paleodepth history of a site can be determined by documenting benthic foraminiferal changes. In additional, higher planktonic foraminiferal abundances typically indicate deeper waters. Patterns in foraminiferal data indicate shallowing- and deepening-upward successions within a sequence, providing the basis to define systems tracts, and hence, sequence stratigraphic relationships. For instance, a sequence with shallow-water foraminifera overlain be deeper-water foraminifera indicates lowstand systems tract (LST) deposits overlain by transgressive systems tract (TST) deposits. TST biofacies overlain by shallow-water foraminifera in the same sequence indicates highstand system tract (HST) deposits.

We integrate benthic foraminiferal assemblage data and % planktonic foraminifera in a seismic framework to define sequence stratigraphic systems tracts within several lower to lower-middle Miocene (~23-13 Ma) prograding clinoforms sampled at Exp. 313 Sites 27A, 28A, and 29A (~33m present depth). Paleodepths fluctuate from 0 to >100m across rollover structures. The most distal Site 29A is dominated by LST and TST deposits, with minor HST sediments. Proximal Site 27A is dominated by TST and HST deposits, with limited LST sediments. The thickest portion of clinoforms (near the rollover) tend to be dominated by TST and HST deposition (Sites 27A and 28A), with parasequence deposition in the thick, lower portion of the clinoform between the rollover and the toe of the clinoform (Site 29A).