HIGH-RESOLUTION STRATIGRAPHY AND THE RESPONSE OF BIOTA TO LATE CENOZOIC ENVIRONMENTAL-CHANGES IN THE CENTRAL EQUATORIAL PACIFIC-OCEAN (MANIHIKI PLATEAU)

An undisturbed 16 m late Pliocene-Pleistocene sediment core spanning 2 .6 Myr of deposition was recovered from the Manihiki Plateau by the Ge rman research vessel Sonne in 1990. This core 34KL complements the hea vily disturbed late Pliocene-Pleistocene core sections of DSDP Site 31 7, and is well suited for stratigraphic correlation. The sediments con sist of calcareous microfossils (93-97% CaCO3), minor portions of sili ceous microfossils and detrital minerals. Ah important calcareous micr ofossil zones could be identified and correlated with the magnetostrat igraphic and isotope stratigraphic events, stages and periods. Due to the high degree of silica dissolution, the late Quaternary radiolarian Buccinosphaera invaginata Zone is the only siliceous fossil zone whic h could be identified. An interval with Globigerinoides gomitulus/pink was found within the middle Pleistocene which is clearly distinguishe d from the Globigerinoides ruber/pink interval of the late Pleistocene . The magnetostratigraphic Gauss-Matuyama and Matuyama-Brunhes boundar ies as well as the Olduvai and Jaramillo events were clearly identifie d. The delta(18)O curve displays the 100 kyr (Milankovitch) and the 41 kyr (Laplace) cyclicity periods. The beginning of the Laplace Period and the last occurrence of the calcareous nannofossil Discoaster brouw eri, which marks the end of the Pliocene, fall within the base of the Olduvai Event, There is also a marked drop in sedimentation rates arou nd this time, which seems to be a regional phenomenon. Prominent 3.5 k Hz subbottom reflectors at 8 ms and 15 ms reflection time are related to lithologic changes near the Mid-Pleistocene Revolution (MPR) and th e beginning of the Laplace Period or the Pleistocene, respectively. It is possible to trace these reflectors laterally to the eroded eastern edge of the Manihiki Plateau where they can be tied to older strata.