MIDDLE MIOCENE PALEOCEANOGRAPHY DESCRIBED BY BENTHIC FORAMINIFERA FROM MARYLAND AND VIRGINIA SHELF DEPOSITS

Sedimentary records from the Maryland and Virginia Coastal Plain contain valuable quantitative paleoecological data from the Miocene Climatic Optimum (MCO) and the Middle Miocene Climate Transition (MMCT). These records occur as marine sedimentary packages deposited during intervals of high sea level, reflecting eccentricity-scale variability in glacio-eustatic sea level and confirming episodes of Antarctic ice sheet growth and decay. Each sedimentary package is unique in that it reflects the magnitude, speed and duration of sea level change and the resulting environmental conditions. Many of these records are contained within the iconic Calvert Cliffs in southern Maryland along the western shore of the Chesapeake Bay. Ongoing work aims to correlate the Calvert Cliffs outcrops with the BG&E, Haynesville and Solomons Island cores to create a composite section of the most complete record of the MCO and MMCT in the Atlantic Coastal Plain. These records will be used to establish refined estimates of sedimentation rates and the duration of hiatuses as well as for reconstructions of local and regional paleoceanography and productivity, to include changes in ocean circulation and upwelling strength. Here we focus on the benthic foraminiferal assemblage data from the Baltimore Gas & Electric (BG&E) and Haynesville cores and the Calvert Cliffs outcrops. We examine these data in terms of the climate framework established by age-diagnostic diatom and planktic foraminiferal species, alkenone stratigraphy, and orbital (eccentricity-scale) tuning. We also consider the lateral correlation of sedimentary units between cores and outcrops in very close proximity. Cluster analyses of benthic foraminiferal assemblages show variability within the MCO, with sedimentary packages alternating between two main assemblages that record differences in water depth, coastal upwelling strength, and bottom water oxygenation. The cluster pattern across the MCO at the three sites yields a reconstruction of paleoenvironments through time and insight into how biologic communities are affected. These data will help in better understanding the variable regional paleoceanography among different warm intervals of the MCO, providing examples of the effects of differing rates and magnitudes of sea level rise on the mid-Atlantic region.