Miocene Radiolarian Biostratigraphy, U.S. Mid-Atlantic Coastal Plain

Abstract

Cenozoic radiolarian biostratigraphy was developed in low-latitude pelagic sections where these microfossils are abundant, diverse and well preserved. Radiolarian faunas, ifpreserved, are usually less abundant and diverse in shelf sediments than in deep-sea sediments. Such an assemblage occurs in the neritic Calvert, Choptank, and Eastover formations (Chesapeake Group) of the mid-Atlantic Coastal Plain. Although many biostratigraphically important forms are sparse or absent in these middle-latitude, shallow shelf sediments, the standard radiolarian biostratigraphic zones can be recognized. The Calvert Formation is of early to middle Miocene age (Stichocorys wolffii to Dorcadospyris alata zones), the Choptank Formation of middle Miocene age (Diartus petterssoni Zone), and the Eastover Formation of latest Miocene or early Pliocene age (Stichocorys peregrina or Spongaster pentas zones). These results suggest that radiolarians may be valuable for biostratigraphic purposes over a wider spectrum of facies than was previously recognized.