FORAMINIFERAL SIGNALS IN ATLANTIC COASTAL PLAIN SEDIMENTS

Changes in climate over millennial and longer time intervals are best observed in deep sea sediment cores where orbital resolution studies can illuminate climate extremes and transitions. Coastal plain outcrops and sediment cores, however, can capture climate change data during warm intervals when sea levels were high in higher resolution due to high nearshore sedimentation rates. While marine coastal plain deposits are usually discontinuous, they contain excellent snapshots of extreme climate states that capture the magnitude and speed of dynamic changes in shallow water ecosystems.

We sampled marine outcrops and sediment cores from the Atlantic Coastal Plain of Virginia and Maryland, USA, for the Paleocene-Eocene Thermal Maximum (PETM), Miocene Climate Optimum (MCO), middle Miocene Climate Transition (MMCT) and mid-Piacenzian Warm Period (MPWP). Specifically, we studied the Paleocene Aquia Formation and Eocene Marlboro Clay in the South Dover Bridge (SDB) and Mattawoman Creek-Billingsley Road (MCBR) cores, the middle Miocene Calvert Formation in the Calvert Cliffs outcrops and the Baltimore Gas & Electric (BG&E) core, and the mid-Piacenzian Yorktown Formation in the Rushmere outcrops and the Holland Ball Park and Dory cores. Although high resolution age models are often difficult to attain from coastal plain sediments, we were able to do so by combining calibrated first and last appearances of age-diagnostic species with alkenone biomarkers, used as a tool for stratigraphic correlation.

Results from the PETM, MCO/MMCT, and MPWP include improved age models as well as estimates of sea surface temperature, ocean acidification, productivity and sea level. We have 1) documented surface ocean warming and acidification in two discrete pulses at the PETM onset, 2) generated the first MCO and MMCT sea surface temperature data and documented high primary productivity associated with the MCO along the US mid-Atlantic Coastal Plain, and 3) characterized benthic foraminifer community changes associated with the PETM, MCO/MMCT, and MPWP, leading to a better understanding of the mid-Atlantic shallow marine ecological response to different rates and magnitudes of temperature and sea-level rise. Our results show that, though discontinuous, marine sedimentary records from the Atlantic Coastal Plain contain valuable quantitative paleoecological data. These data are especially useful to better understand regional and global responses to climate change because the initial response is often first recorded on the shallow shelf.