LATE PLIOCENE CLIMATIC-CHANGE AND THE GLOBAL EXTINCTION OF THE DISCOASTERS - AN INDEPENDENT ASSESSMENT USING OXYGEN-ISOTOPE RECORDS

High-resolution records (2-7 kyr) of Upper Pliocene Discoaster abundan ces obtained from six ODP/DSDP sites oxygen isotope stratigraphy. Four Atlantic Ocean sites (DSDP Sites 552 and 607, and ODP Sites 659 and 6 62) comprise a transect from 56 degrees N to 1 degrees S and provide a record of latitudinal variations in Discoaster biogeography. Low-lati tude sites in the Atlantic (ODP Site 662), Pacific (ODP Site 677), and Indian (ODP Site 709) oceans provide additional information about var iability in Discoaster abundance patterns within the equatorial region . A common chronology, based on the astronomical time scale developed for ODP Site 677, has been established for all the sites. By integrati ng oxygen isotope data and Discoaster abundance records at each site w e are able to independently evaluate the temporal and spatial distribu tion of D. brouweri and D. triradiatus in the 500 kyr prior to the ext inction of the discoasters near the base of the Olduvai subchron. Majo r decreases in abundance are evident during some of the more intense l ate Pliocene glacial events. In particular, glacial isotope stages 82, 96, 98 and 100 are associated with distinct abundance minima. At thes e times, large-scale changes in surface hydrographic conditions appear to have suppressed Discoaster numbers on a global scale. The increase in abundance of D. triradiatus, which precedes the extinction of the discoasters by around 200 kyr, may also be related to the intensificat ion of environmental pressures that accompanied the build-up of Northe rn Hemisphere ice sheets during the late Pliocene. In spite of contras ting geographic and oceanographic settings, the various D. brouweri an d D. triradiatus records are remarkably similar. This demonstrates tha t the acme and extinction events are excellent biostratigraphic datums . The simultaneous extinction of D. brouweri and D. triradiatus at 1.9 5 Ma were synchronous events at both a regional scale within the Atlan tic, and on a global scale between the three major oceans. However, th e start of the D. triradiatus acme appears to have been diachronous, o ccurring some 40 kyr earlier in the Atlantic than in the Indo-Pacific, and hence the stratigraphic usefulness of this datum is regional rath er than global. (C) 1997 Elsevier Science B.V.