10. UPPER CRETACEOUS TO MIOCENE PLANKTONIC FORAMINIFERAL BIOSTRATIGRAPHY: RESULTS OF LEG 150X, THE NEW JERSEY COASTAL PLAIN DRILLING PROJECT1Chengjie Liu,2 James V. Browning,2 Kenneth G. Miller,2,3 and Richard K. Olsson2 |
ABSTRACTPlanktonic foraminiferal biostratigraphic study of Leg 150X boreholes at Island Beach, Atlantic City, and Cape May provides good biostratigraphic control for Eocene and older strata, limited control on Oligocene strata, and little control on Miocene strata. Upper Cretaceous to Eocene assemblages are open marine faunas, and most of the standard tropical/subtropical planktonic foraminiferal zones are represented in the Leg 150X boreholes. Oligocene planktonic foraminiferal assemblages are low in diversity, many marker taxa are absent, and standard planktonic foraminiferal zonations are difficult to apply. This reflects a shallow depositional paleoenvironment and local/global climatic cooling. Some lower Miocene intervals contain foraminifers, although the shallow depositional environment (inner neritic) excludes most marker taxa. Sediments younger than middle Miocene lack age-diagnostic foraminifers. The presence of most Late Cretaceous to Eocene zones indicates that hiatuses are short in duration. The turning point is during the Eocene/Oligocene transition: since the beginning of the Oligocene, depositional breaks are more frequent and their duration is longer. This may reflect larger, more rapid sea-level changes, consistent with increasing ice volume. |
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