MIOCENE NERITIC BENTHIC FORAMINIFERAL COMMUNITY DYNAMICS, CALVERT CLIFFS, MARYLAND, USA: SPECIES POOL, PATTERNS AND PROCESSES

Abstract: The presence/absence and abundance of benthic foraminifera in successive discrete beds (Shattuck “zones”) of the Miocene Calvert and Choptank formations, exposed at the Calvert Cliffs, Maryland, USA, allows for investigation of community dynamics over space and time. The stratigraphic distribution of benthic foraminifera is documented and interpreted in the context of sea-level change, sequence stratigraphy, and the previously published distribution of mollusks. Neritic benthic foraminiferal communities of four sea-level cycles over ∼4 million years of the middle Miocene, encompassing the Miocene Climatic Optimum and the succeeding middle Miocene Climate Transition, are dominated by the same abundant species. They differ in the varying abundance of common species that occur throughout most of the studied section and in the different rare species that appear and disappear. Transgressive systems tracts (TSTs) have higher species diversity than highstand systems tracts (HSTs) but much lower density of specimens. In contrast to some previous research, all beds in the studied section are interpreted as being from the inner part of a broad, low gradient shelf and were deposited at water depths of less than ∼50 m. It is suggested that species are recruited from a regional species pool of propagules throughout the duration of TSTs. Recruitment is curtailed during highstands leading to lower diversity in the HSTs.