TERRESTRIAL AND MARINE EVIDENCE FOR CLIMATE CHANGE ACROSS THE PALEOCENE-EOCENE BOUNDARY: DOCUMENTATION FROM THE SOUTH DOVER BRIDGE CORE, MARYLAND

The continuously cored South Dover Bridge core (Talbot County, Maryland) yielded a nearly 112 meter-thick section of Paleocene and Eocene sediments comprising, in ascending order, the upper Aquia Formation, the Marlboro Clay, and the Nanjemoy Formation. This interval includes a complete Paleocene/Eocene Thermal Maximum (PETM) section. Sediments throughout this section have been analyzed for bulk ∂C¹³ and ∂O¹⁸ isotopes, bulk percent CaCO₃, calcareous nannofossils and palynomorphs. Calcareous nannofossil and dinoflagellate assemblages in the underlying Aquia Formation are typical of the region with terrestrial palynomorph assemblages dominated strongly by Pinus. Juglandaceous pollen abundance abruptly increases fourfold at 204.0 m, just below the Aquia/Marlboro contact, and this is followed by a sharp increase in fern spore abundance at 203.6 m. Both Juglandaceous pollen and fern spores are abundant upward through the sample at 202.8 m; above this depth nonmarine palynomorphs are very sparse. Marine palynomorphs are well represented in all samples. The Paleocene-Eocene boundary is at the rapid transition from the glauconitic sands of the Aquia Formation below to the dense Marlboro Clay above (203.9 m). A calcareous nannofossil assemblage unique to the Carbon Isotope Excursion (CIE) is identified, and the presence of the calcareous nannofossil Rhomboaster spp.-Discoaster araneus assemblage from 201.3-187.8 m, coupled with the conspicuous presence of the dinocyst Polysphaeridium zoharyi in some samples, may provide insight into locally warmer or more variable paleoenvironments. Specimens of the dinoflagellate PETM marker species Apectodinium augustum also are present in the lower part of the Marlboro Clay. Nearly continuous sedimentation occurred across the PETM, but the absence of the calcareous nannofossil Rhomboaster contortus combined with the first occurrence of the dinoflagellates Dracodinium varielongitudum (187.8 m) and Achilleodinium biformoides (186.1 m) at the Marlboro Clay/Nanjemoy Formation contact suggests that an unconformity is present and that the basal Nanjemoy Formation is missing. Palynofacies analysis indicates a series of possible climatic changes associated with a dissolution zone and the Marlboro Clay/Nanjemoy Formation contact.