Quantitative middle-late Miocene analysis of planktonic foraminifera of the North Pacific DSDP Sites 310, 173, 296, and 292 and the Southeast Pacific Site 319 reveal strikingly similar abundance distributions and foraminiferal datum levels permitting correlations between all sites. The following first (FA) and last (LA) appearances appear to be isochronous in tropical, subtropical, and temperate faunas: Globigerina nepenthes FA, G. druryi FA, Globorotalia mayeri LA, G. siakensis LA, Globoquadrina dehiscens LA, Globigerinoides kennetti FA and LA, and G. obliquus extremus FA. Isotope analysis is available for Site 310 and indicates a depletion in carbon at about 6.2 Ma following the extinction of G. kennetti and the first appearance of G. obliquus extremus. An increase in dissolution of calcium carbonate is apparent in the interval preceding the carbon shift at Site 310 and two further dissolution intervals are present lower in the section within paleomagnetic Epochs 7-8 (N16) and 12 (N14). Similar dissolution intervals have been observed in these same biostratigraphic intervals at DSDP Sites 296, 292, and 319. These dissolution intervals are often associated with a short hiatus and are marked by major faunal changes apparently due to climatic cooling.
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