(Table 1) Stratigraphic datums from ODP Site 130-806

A 2 m.y. oxygen isotope record of Globigerinoides sacculifer from the Ontong Java Plateau, based on cores from Ocean Drilling Program Leg 130, is dated by matching variations to an orbital template. The procedure allows us to present the most complete Quaternary record available for the western equatorial Pacific. The template-generating algorithm describes a balance between growth and melting of ice. Following basic Milankovitch theory, ice growth is taken as constant, while melting is taken to depend on summer insolation, current ice mass, and average past ice mass. Template settings must be changed once, between 1 and 1.2 Ma, to reflect a major shift in climate. Template fits are strikingly good over much of the record and can be used to detect and fill gaps from core breaks and other disturbances. One result of template dating is an exact age for the Brunhes-Matuyama magnetic reversal boundary, at 790+/-5 ka, as well as several other precise dates (900 ka for the middle Pleistocene climate shift; 1070, 1240, and 1450 ka for isotope stages 31, 37, and 47, respectively). Sedimentation rates fluctuate between 18 and 28 m/m.y., a ca. 400 ka cycle being the most prominent. Major anomalies arise within the transitional regime (1.2 to 1 Ma). The origin of the cycles is unknown; we propose productivity variations in the western equatorial Pacific.

(Table T2) Stable carbon and oxygen isotopes of DSDP Leg 30, Leg 33, ODP Leg 130 and Leg 192 sites, Ontong Java Plateau

Stable isotopic analyses of bulk carbonates recovered from Ontong Java Plateau during Ocean Drilling Program (ODP) Leg 192 (Holes 1183A and 1186A) show an ~0.5 per mil increase in d18O values from the upper Campanian/lower Maastrichtian to the upper Maastrichtian. This shift is consistent with widespread evidence for cooling at this time. Similar shifts were found at other localities on Ontong Java Plateau (Deep Sea Drilling Project [DSDP] Sites 288 and 289 and ODP Site 807) and at DSDP Site 317 on Manihiki Plateau. These data extend evidence for Maastrichtian cooling into the southwestern tropical and subtropical Pacific. The record of apparent cooling survives despite a significant diagenetic overprint at all sites. Comparing average Maastrichtian d18O values among sites suggests that diagenesis caused d18O to first be shifted toward higher values and then back toward lower values as burial depth increased. Carbon isotopes at the six sites show no apparent primary shifts, but at four sites, the Cretaceous/Tertiary boundary interval coincides with a negative excursion attributed to alteration of sediments near the boundary.