BACKGROUND AND OBJECTIVES

Site 1208 is located in lower bathyal (3346 m) water depth close to center of the Central High of Shatsky Rise. According to the reconstruction of Nakanishi et al. (1989), basement underlying the site was formed in Magnetochron CM15 in the Berriasian (~136 Ma). The paleodepth of this site was ~1400 m in the early Maastrichtian based on the estimate of Barrera et al. (1997) for Site 305. However, the site probably subsided at a faster initial rate than typical crust (e.g., McNutt et al., 1990). Since this site lies ~4° north of sites on the Southern High, it likely crossed the equatorial high productivity zone several million years earlier (R. Larson, pers. comm., 2001), and thus the uppermost chert horizon is predicted to lie in an older part of the stratigraphic section (Fig. F1).

The Central High has not been drilled before; thus, the stratigraphy was unknown prior to our drilling of Site 1208. The site is located on seismic line TN037-8 (Fig. F1). The ages of reflectors and the major seismic units cannot be correlated with the Southern or the Northern Highs with any degree of certainty. Site 1208 drilling was designed to provide knowledge of the stratigraphy of the Central High as well as correlation of units and reflectors with the Southern and Northern Highs. Tentative predrilling correlation with the Southern High seismic units of Sliter and Brown (1993) suggested relatively thick seismic Units 1 and 2 (Neogene and Paleogene) characterized by predominantly weak, largely horizontal reflectors, and relatively thin Unit 3 (Upper Cretaceous). The Upper Cretaceous to Holocene sequence was expected to contain a number of disconformities as suggested by parallel but prominent reflectors. An angular unconformity indicates erosion of part or most of the mid-Cretaceous sequence (Fig. F1). The total thickness of the sedimentary record at Site 1208 was estimated at ~785 m using velocity data for the different units from Site 305.

Site 1208 lies in the middle of the Shatsky Rise depth and latitudinal transects. The site will be included in broad leg-based objectives that include

1. Reconstructing changes in the properties of surface and deepwaters through the Cretaceous and Paleogene. This will help to constrain the character and stability of intermediate- and deepwater circulation, vertical thermal gradients, and basin fractionation during ancient intervals of extreme warmth as well as during transitions from and to cooler intervals.
2. Shedding light on the origin of transient climatic events such as the Eocene/Oligocene boundary and the PETM. The depth transect will also help address questions concerning the nature of chemical (i.e., CCD, nutrients, and oxygenation) and physical oceanographic changes (temperature gradients) during these events.
3. Determining the significance of unconformities in the stratigraphic section. Are they related to local changes in currents or to regional/basinal changes in the CCD?
4. Charting changes in biotic assemblages and relating them to environmental changes over long time periods as well as during transient climatic events.
5. Understanding the origin of orbital cycles in the sedimentary record. Using petrography, geochemistry, and fossil assemblages to determine whether these cycles reflect changes in productivity or dissolution.
6. Using the Neogene section, which is expected to be clay-rich, to reconstruct eolian dispersal patterns and sources of wind-blown material (e.g., Chinese Loess Province).