About This Item
Share This Item
Miocene diatomaceous units are known from various outcrop and subsurface studies of the Atlantic continental margin. These are generally thought to reflect depositional environments dominated by nearshore processes. Many sections, however, contain microfossil assemblages with abundant pelagic forms, suggesting strong oceanic influence on the deposition of certain intervals.
Radiolarians and silicoflagellates are among pelagic microfossils valuable in providing biostratigraphic age information where calcareous forms are sparse. Lower and middle Miocene radiolarians (Calocycletta costata and Dorcadospyris alata zones) are present in the Calvert Formation (Maryland), whereas only lower Miocene (C. costata zone) forms occur in the Kirkwood Formation (New Jersey). Silicoflagellates from the Corbisema triacantha zone occur in both sections.
This biostratigraphic information is useful in analyzing the marine influence on the Atlantic margin in terms of Miocene paleo-oceanography. The diatomaceous interval falls within the major Miocene high stand of sea level on the Vail et al curve. Furthermore, the third-order cycles proposed on this sea-level curve appear to be consistent with the depositional history of the Calvert Formation. The earlier termination of diatomaceous sedimentation in the Kirkwood is possibly due to local detrital influx.
The effect of enhanced circulation in the northwestern Atlantic following closure of eastern Tethys at Arabia and western Tethys at Gibraltar, in the early and middle Miocene, is possibly reflected in the deposition of the diatomaceous units as well.
End_of_Article - Last_Page 1668------------