Marine diatom sequence in Miocene strata of the Chesapeake Bay region, Maryland

The Calvert and Choptank Formations exposed along the west shore of Chesapeake Bay in Maryland have been correlated with strata of early and middle Miocene age. The stratigraphic ranges of marine diatom marker species indicate a distinct diatom sequence in the deposits. A few diatoms that mark deep-sea Miocene deposits are found sparingly in these shallow neritic assemblages. Seven diatom zones based on well-recognized events in the diatom biostratigraphy are proposed for the mid-Atlantic region of the eastern United States. A suggested correlation of these zones is made with some of the deep-sea diatom zonations in the Atlantic and Pacific Ocean basins.