Shatsky Rise is a medium-sized large igneous province in the west-Central Pacific Ocean (Fig. F1) and is possibly the oldest existing oceanic plateau. The rise consists of three prominent topographic highs. Sites 1209, 1210, 1211, and 1212 were cored on the Southern High (Bralower, Premoli Silva, Malone, et al., 2002). Eight sites on the Southern High of the rise were drilled during Deep Sea Drilling Project (DSDP) and earlier Ocean Drilling Program (ODP) legs (Sites 47, 48, 49, 50, 305, 306, 577, and 810). Of these, ODP Sites 577 and 810 provided interpretable Neogene magnetic stratigraphies.
Sites 1207 and 1208, from the Northern and Central Highs, provided unexpectedly expanded late Miocene (12.5 Ma) to Holocene sequences. These locations had not been cored during previous DSDP/ODP expeditions. The initial age model for all of the sites was based on correlation of the sequence of polarity zones to the geomagnetic polarity timescale (GPTS) (Cande and Kent, 1992, 1995). Mean sedimentation rates at the five sites vary from 1 to 4 cm/k.y. Latitude and longitude of the sites and basal ages of the Neogene sediments are given in Table T1. Neogene sediments at the sites consisted mostly of light gray to pale orange nannofossil oozes with varying amounts of clay, radiolarians, and diatoms. Magnetic susceptibility is low (<2 x 10–5 SI) at all the sites and shows a decreasing trend from the Quaternary to the late Miocene. Composite sections were constructed shipboard for four of the sites (1209, 1210, 1211, and 1212) using multisensor track (MST) data including magnetic susceptibility and gamma ray attenuation (GRA) bulk density and also reflectance data. Sites 1207 and 1208 were not double-cored, and depths at these sites are in meters below seafloor (mbsf). The magnetic stratigraphy from the six sites (1207–1212) was based on shipboard pass-through magnetometer measurements and discrete samples measured postcruise.
Sediments from five of the sites (1207–1211) showed a prominent cyclicity in reflectance data for parts of the sections, and this is the basis for the construction of an astronomically tuned age model for the 0- to 8-Ma interval. The astronomically calibrated polarity timescale has been well established for the 0- to 6-Ma interval (Shackleton et al., 1990, 1995; Hilgen 1991a, 1991b). Hilgen (1991a, 1991b) produced his astronomically calibrated polarity timescale for the 2- to 5.23-Ma interval using sapropel occurrences and carbonate content in Mediterranean sections. These polarity chron ages were incorporated into the GPTS of Cande and Kent (1995).
In this study we produced an astronomically calibrated magnetic reversal stratigraphy for the 0- to 8-Ma interval. This is in good agreement with Hilgen (1991a, 1991b) and Shackleton et al. (1995) in the 0- to 6-Ma interval. In the 6- to 8-Ma interval, polarity chron ages are in better agreement with the Shackleton et al. (1995) timescale, differing by up to ~200 k.y. from that of Hilgen et al. (1995) and the new Astronomically Tuned Neogene Time Scale (ATNTS2004) of Lourens et al. (in press).