FORAMINIFERAL AND SEDIMENTOLOGICAL ANALYSIS OF MID-MIOCENE SHATTUCK ZONES 10 THROUGH 17 FROM THE CALVERT CLIFFS, MARYLAND

The Middle Miocene was a time of significant global warmth associated with the mid-Miocene Climate Optimum (MMCO). Based on geochemical and geomorphological evidence, mid-latitude temperatures during this time were likely 6°C warmer than present, and global sea level was ~48 m higher than present day levels. To understand the response of marine communities and shelf environments to these conditions, benthic foraminiferal communities from the Miocene Calvert Formation and lower Choptank Formation of the Calvert Cliffs in Maryland, originally studied by G.B. Shattuck in 1904, are being examined at orbital scale resolution.

The Calvert Cliffs provide a well-studied exposure of mid-Miocene fossiliferous deposits that span about ten million years according to biostratigraphic and paleomagnetic data. They are composed of the Calvert Formation (Fairhaven and Plum Point members), the Choptank Formation, and the St. Mary’s Formation. These units generally show a shallowing upward record from inner shelf to marginal-marine environments, composed of distinct beds (termed Shattuck Zones) representing a series of transgressive and regressive events occurring during the MMCO. The lower Choptank Formation is interpreted to have been deposited under cooler climate conditions compared to the Plum Point Member. Fifty-one samples were taken for foraminiferal and grain-size analysis from Shattuck Zones 10 through 17, usually six samples per zone collected at three separate locations. Shattuck Zones 10 through 16A are part of the Plum Point Member and Shattuck Zones 16B and 17 are assigned to the Choptank Formation.

Previous studies have addressed how Cenozoic benthic foraminiferal communities of the mid-Atlantic coastal plain of the US have changed over more than 55 million years. This study advances knowledge of the impact of climate change on shelf environments, and the response of benthic foraminiferal community composition and structure over several transgressive-regressive cycles on a much finer scale.