The drilling campaign of ODP Leg 130 on Ontong Java Plateau resulted in the recovery of complete Neogene sections at several depths, providing materials for detailed biostratigraphic and paleoceanographic studies in the western equatorial Pacific. The acquisition of extensive logging records and high-resolution physical-property data allow detailed correlation from hole to hole and from site to site and provide the basis for a paleoceanographic interpretation of acoustic reflectors.
We drilled 16 holes at 5 sites on the north-eastern flank of the plateau (Sites 803 through 807). All sites are close to the equator, at water depths ranging from 2,500 m to 3,900 m. Sites 803 and 807 penetrated into basement (26 m and 149 m, respectively). The K/T boundary was recovered at both of these sites.
Neogene sedimentation rates decrease with depth, as expected, but this decrease is much greater than calculated from carbonate content, under the assumption that carbonate dissolution is the sole cause of the decrease. At any one site, sedimentation rates vary by a factor of more than two, with a striking maximum in the latest Miocene to early Pliocene, and strong minima in late early to early middle Miocene and in the Pleistocene.
Many acoustic reflectors correlate between sites, within the limits of stratigraphic resolution. This suggests paleoceanographic events as a cause, generating changes in physical properties of sediments at the time of deposition. Many of the reflectors occur at carbonate reduction events (CRE's). Some apparently are the product of diagenetic enhancement of property changes, as, for example, within the ooze/chalk transition (which is diachronous).
The interval corresponding to the Cretaceous/Tertiary (K/T) transition in the area is characterized by the presence of a deep CCD. The sequence at one site is calcareous; that at the other, is not. The fact that the two K/T sections recovered occur in sequences with major hiatuses suggests special conditions for preservation during the transition. We propose early cementation caused by high silicate concentrations in an ocean with greatly reduced productivity.
The basalt cored at Sites 803 and 807 is predominantly aphyric to sparsely olivine or plagioclase phyric; the last flows are Albian to Aptian in age. At Site 807, pillow lavas buried sediments. One very thick flow (∼28 m) was penetrated here, possibly a flood basalt, indicative of massive outpourings on Ontong Java Plateau during the middle Cretaceous.