PALEOGENE-NEOGENE STRATIGRAPHY OF A NEW CONTINUOUSLY CORED HOLE AT SANDTOWN, DELAWARE

Recent drilling at Sandtown, Delaware, provides an exceptional, nearly continuous core record of Paleogene and Neogene formations and aquifers in the Middle Atlantic Coastal Plain. The borehole was drilled in May-June 2023 to a depth of 766 ft with 85% core recovery. Detailed on-site lithologic descriptions, core photographs, geophysical logs, and spot samples for biostratigraphy allow for a preliminary interpretation of stratigraphy. The upper Paleocene Vincentown Formation consists of bioturbated, glauconitic, micaceous sandy silty clay and clayey silt. Above a marked contact, sediments provisionally assigned to the Marlboro Clay are potentially associated with the Paleocene/Eocene Thermal Maximum. Unusual for the Marlboro is a thin basal glauconite sand with associated clay rip-up clasts, transitioning through slightly sandy silty clay, and culminating in an upper interval of more typical bioturbated silty clay with common foraminifera. Above a distinct contact, the lower Eocene Manasquan Formation has a basal glauconite sand overlain by bioturbated silty clay and clayey silt with abundant glauconite and foraminifera and a few cemented zones. The overlying Shark River Formation has muddy glauconite sand and glauconite-rich clay at the base, passing upward into foraminifera-rich silty clay and clayey silt. The section gradually coarsens upward into the middle Eocene Piney Point Formation, which is bioturbated, shelly, glauconitic, poorly sorted sand that is part of a regionally important aquifer. A marked unconformity separates the Eocene and Miocene (possibly with a thin indeterminate unit between). The lower Miocene Calvert Formation consists of shallow marine sands that are important aquifers and interbedded muds that act as confining beds. The lower Calvert is predominantly dark brown, bioturbated micaceous silt. Above that, most of the Calvert is shelly, very fine to medium (and less commonly coarse) sand interrupted by a few zones of finely laminated clayey silt and very fine sand. This site fills a gap in regional core coverage and will enhance understanding of interstate stratigraphic equivalency. In-progress analyses of lithostratigraphy, ages, and environments are expected to provide insights into the imprint of global climate change on the Middle Atlantic stratigraphic record.