QUANTIFYING THE IMPACTS OF THE MID-MIOCENE CLIMATE OPTIMUM AND MID-MIOCENE CLIMATE TRANSITION ON THE BENTHIC FORAMINIFERAL COMMUNITIES OF THE CHESAPEAKE GROUP, CALVERT CLIFFS, MD

The mid-Miocene Climate Optimum (MMCO) was characterized by global temperatures averaging 6°C higher than present-day and was followed by the mid-Miocene Climate Transition (MMCT) when global temperatures fell 6°C. The impact of these conditions on shelf and coastal environments like the Chesapeake Group has not been well documented. The Chesapeake Group, exposed at the Calvert Cliffs, MD, is a shallowing-upward sequence of shelf to paralic environments deposited during multiple transgressive and regressive events. The benthic foraminifera of targeted beds, also known as Shattuck Zones, composing the Calvert Formation (Shattuck Zones 4-16A) and lower Choptank Formation (Shattuck Zones 16B-18) were sampled to understand the impact of climate change on foraminiferal communities and shelf environments.

Three laterally replicated vertical transects of targeted strata were sampled at decimeter to meter scale (total of 21 samples per transect). Approximately 300 foraminifera were picked from the 63 μm to 710 μm fraction of each replicate sample and identified. Numerical analysis defined benthic foraminiferal communities and intra- and inter-zone changes of communities. Paleoenvironmental interpretations of Shattuck Zones were made based on the benthic foraminiferal assemblages and compared to previous paleoenvironmental interpretations.

Species diversity (measured using Shannon index), species richness (S), and density of foraminifera peak during the MMCO (Shattuck Zones 11-12) and are lowest at the beginning of the MMCT at the boundary between the Calvert Formation and Choptank Formation (Shattuck Zone 17).This study furthers the knowledge of the impact of known climate change on shallow shelf benthic foraminiferal communities over ~ 6 million years and over multiple transgressive and regressive events.