Paleocene-Eocene dinoflagellate biostratigraphy in the central Delaware coastal plain
Dinoflagellate cyst palynology and lithostratigraphy from three continuously cored boreholes (Blackbird, Smyrna, and Woodland Beach), supplemented by calcareous nannofossil biostratigraphic data, were used to refine the age and correlation of three Paleocene-Eocene formations in northern Delaware: the Vincentown, Manasquan, and Shark River. Lithologic logs reveal significant facies changes in the upper Paleocene Vincentown Formation over a short distance (*9 km) southeastward, transitioning from very permeable glauconite-quartz-shell-rich sands that form the regionally important Rancocas/Aquia aquifer to much less permeable muddy sands and sandy muds. These lithologic changes represent a shift from nearshore, clear, warm-water, carbonate-rich sand shoals to mud-dominated deeper-water, offshore shelfal environments. Dinocyst assemblages including Areoligera gippingensis, Cribroperidinium giuseppei, and Stenodinium meckelfeldensis confirm the Paleogene ages and track these paleoceanographic changes from shallow coastal settings updip to neritic or outer marine settings downdip. The Vincentown Formation is unconformably overlain by the lower Eocene Manasquan Formation, which consists predominantly of silt and clay with relatively consistent lithology across the study area, representing general neritic or open marine conditions. Lithology, dinoflagellate cyst assemblages, and calcareous nannofossil data indicate that the Marlboro Clay and its record of the onset of the Paleocene-Eocene Thermal Maximum (PETM) global warming event is absent from the Paleocene-Eocene transition at these sites, with an unconformity marking the boundary between the Vincentown and Manasquan formations. The youngest unit examined, the Eocene Shark River Formation, unconformably overlies the Manasquan Formation and consists of interbedded clayey silts and sands, with dinoflagellate assemblages suggesting a return to coastal or inner neritic settings. Calcareous nannofossil zones recognized from the Woodland Beach core corroborate the depositional ages determined using dinoflagellates throughout the sequence, confirming the chronostratigraphic framework for these important coastal plain units.