Late Miocene to Pleistocene Biostratigraphy of Equatorial Pacific Sediments.

摘要

Combined foraminiferal, diatom, radiolarian, and paleomagnetic studies of tropical deep-sea-sediment cores permit establishment of multiple criteria for recognizing the Miocene/Pliocene and Pliocene/Pleistocene boundaries which can be used for correlation with the stratotype localities in Italy. The Miocene/Pliocene transition occurs at the top of Magnetic Epoch 5 at an age of about 5.1 m.y B.P., and the Pliocence/Pleistocence boundary during the Olduvai Event of the Matuyama Reversed Epoch at about 1.8 m.y. B.P. Stratigrapically significant foramiferal events are: (1) first appearance of G. crassformis and related species in the lower Tabianian of Italy and between the Nunivak and Cochiti events in deep-sea cores; (2) extinction of G. margaritae near the top of the Tabianian Stage in Italy and near the base of the Gauss Epoch in deep-sea cores; and (3) extinction of G. obliquus near the Pliocene/Pleisticene boundary at le Castella, Italy, and in the Olduvai Event in deep-sea sediments. The latest Miocene and earliest Pliocene interval is characterized by a sigificant diatom overturn involving extinctions and several evolutionary and ecological first appearances. Of special note is the first appearance duringg latest Micocene of Thalassiosira convexa and T. usatschevii and the last appearance of Nitzschia miocenica just before the Miocene/Pliocene transition. Sigificant changes also occur among the Radiolaria near these two boundaries.