PRELIMINARY EXAMINATION OF STRATIGRAPHY AND FORAMINIFERA OF THE PALEOGENE OF CENTRAL DELAWARE

This project is an examination of the Paleogene stratigraphy and foraminifera of subsurface central Delaware, specifically the Vincentown, Manasquan, and Shark River Formations. The Rancocas Aquifer is a permeable clean sand within the Vincentown Formation that varies in thickness and permeability, transitioning downdip into less permeable muddy sands and sandy muds. These facies changes occur from north to south over a relatively short distance (~10 km) in north-central Delaware; however, the nature of this change is not well understood. The overlying unit is the Manasquan Formation, which consists of a pale gray silty clay with a basal glauconite-rich bed and was deposited during the early Eocene. The Shark River Formation is a green and dark-gray glauconitic clayey silt and clay that contains evidence of extensive burrowing and is inferred to be middle Eocene in age. The Marlboro Clay is associated with the Paleocene-Eocene boundary interval and the concomitant Paleocene-Eocene Thermal Maximum (PETM) at other sites in the region, but has not yet been identified in the subsurface of Delaware. Samples from wireline cores drilled in southern New Castle County and northern Kent County allow a detailed evaluation of the north–to-south facies changes in these formations. The analyses combine planktonic and benthic foraminiferal records, lithologies, and sequence stratigraphy to understand sea-level changes and climate changes recorded within these strata. Initial interpretations show a southward fining of the Vincentown lithology, suggesting a transition from nearshore to offshore shelfal environments. The foraminifera in the Manasquan and Shark River Formations appear to record deposition in an offshore shelfal setting.