Calcareous nannofossil assemblage changes in the Surprise Hill core and their implications for floral response to the Paleocene-Eocene Thermal Maximum across the Salisbury Embayment of Virginia, USA
We present Paleocene-Eocene calcareous nannofossil biostratigraphy and paleoecology for the Surprise Hill core, U.S. Atlantic Coastal Plain, Virginia. Calcareous nannofossil datums ranging from Zone NP3 to NP14 were identified. The Danian-aged Brightseat Formation rests unconformably atop the Lower Cretaceous Potomac Group at 211.4 m and disconformably underlies the Aquia Formation at 208.8 m. The absence of Zone NP7 suggests a hiatus is present in the Aquia Formation (Zones NP5 – NP9a). The contact between the Marlboro Clay and the overlying Nanjemoy Formation (Zones NP10 – NP14) at 189.5 m is truncated. The Paleocene-Eocene transition is marked by a shift from glauconitic sands of the Aquia Formation to pelitic muds of the Marlboro Clay at 202.7 m. A 3–3.5‰ negative δ 13 C excursion of benthic foraminifer and a thin dissolution interval (201.6–202.5 m) are recorded in the basal Marlboro Clay. Nannofossil response to the Paleocene-Eocene Thermal Maximum (PETM) include (1) a bloom in taxa with affinities for changing salinity conditions just prior to the PETM basin wide ( Hornibrookina australis arca ), (2) a decline in taxa with ecological affinities for cool, eutrophic waters ( Chiasmolithus bidens ) during PETM, (3) fluctuations in mesotrophic to eutrophic, opportunistic taxa (e.g., Neochiastozygus junctus ) during PETM, (4) successive turnovers in species of Toweius spp. during core-PETM and its recovery. Our findings suggest that overall nannofossil assemblages in the southernmost portion of the Salisbury Embayment responded similarly to assemblages from South Dover Bridge, but had differing response to local changes in nearshore paleoecology.