Early Paleogene palynology of the Delaware Coastal Plain: a nearshore-to-offshore transition
Date
2022
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Publisher
University of Delaware
Abstract
The examination of the stratigraphy and dinocyst palynology in the subsurface of the Coastal Plain of Delaware was used to correlate three Paleocene-Eocene formations, the Vincentown, Manasquan, and Shark River Formations. This interval includes a unit of glauconite-quartz-shell-rich sands in central Delaware that comprises the regionally important Rancocas/Aquia aquifer. Lithologies change over a short distance (~10 km) southeastward from very permeable clean aquifer sands to much less permeable muddy sands and sandy muds, representing a transition from nearshore, clear, warm-water, carbonate-rich sand shoals to mud-dominated deeper-water, offshore shelfal environments. ☐ The age and correlations of these formations were evaluated using samples from three boreholes drilled with continuous wireline coring: Blackbird, Smyrna, and Woodland Beach. Fossil dinoflagellate cyst assemblages confirmed that the Vincentown Formation was deposited in the late Paleocene, with the overlying Manasquan and Shark River Formations forming during the early Eocene. Key taxa in determining age include Areoligera gippingensis, Cribroperidinium giuseppei, and Stenodinium meckelfeldensis. The Paleocene-Eocene Thermal Maximum (PETM) global warming event was absent from the rock record in the study area. Lithological logs demonstrate a trend of changes from clean permeable sands up-dip to silty sand and sandy silt lithologies in equivalent units downdip, supporting the hypothesis that a nearshore to offshore transition occurs in the study area in the Vincentown Formation. The Manasquan Formation is predominantly silt and clay where present, with the overlying Shark River formation consisting of interbedded clayey silts and sands. Changes in dinocyst assemblages help track paleo oceanographic changes, also suggesting changes from a shallow coastal setting up-dip to a neritic or outer marine setting downdip in the Vincentown formation, to general neritic or open marine conditions in the Manasquan Formation, to a coastal or inner neritic setting in the Shark River Formation.
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Keywords
Biostratigraphy, Dinoflagellate, Paleogene, Palynology