Resumen de Stratigraphic occurrences of the Miocene Planktonic Foraminifer Globoquadrina dehiscens in Early Miocene sediments of the Indian Ocean

James P. Kennett, M.S. Srinivasan

• The Miocene planktonic foraminifer, Globoquadrina dehiscens (Chapman, Parr, and Collins) disappeared towards the end of the Late Miocene from temperate to tropical regions of the Pacific area. The occurrences of Globoquadrina dehiscens in Early Pliocene marine sediments from the Great Australian Bight (southern Indian Ocean), at Car Nicobar Island (Northern Indian Ocean) and in the South Atlantic indicates that this important planktonic species survived longer in certain Indian and South Atlantic areas than in the Pacific despite partial interoceanic exchange of water masses. The presence of G. dehiscens in Early Pliocene sediments of the Indian Ocean represents another example of a planktonic species surviving longer in certain regions after disappearing elsewhere. The extinction of G. dehiscens has been previously regarded as a reliable time-stratigraphic datum for distinguishing the Miocene-Pliocene boundary. However, its presence in these Early Pliocene sediments indicates a diachronous disappearance on a world-wide basis