BACKGROUND AND OBJECTIVES

Site 1209 is located in middle bathyal (2387 m) water depth close to the most elevated, central part of the Southern High of Shatsky Rise. According to the reconstruction of Nakanishi et al. (1989), basement underlying the site was formed in the latest Jurassic within Magnetochron M20 (~145 Ma). Site 1209 is the shallowest site in the Leg 198 transect. The paleodepth of this site was ~550 m in the early Maastrichtian based on the estimate of Barrera et al. (1997) for Site 305. However, subsidence likely occurred more rapidly than typical crust (e.g., McNutt et al., 1990).

The site is located on seismic line TN037-14A (Fig. F1). This profile is difficult to correlate with other profiles on the southern and western flanks of the Southern High that have drill hole control. A tentative predrilling correlation with the Southern High seismic units of Sliter and Brown (1993) suggests a moderately thick Unit 1 (Neogene), an expanded Unit 2 (Paleogene), and a moderately thick Unit 3 (Upper Cretaceous). The site is close to the point where the stratigraphic sequence appears to be most complete; however, the section is expected to contain a number of minor disconformities as indicated by prominent, horizontal reflectors. The total thickness of the sedimentary section at Site 1209 is estimated at ~1147 m.

The major goals of Site 1209 drilling are to core a shallow, relatively expanded Paleogene and uppermost Cretaceous section. Our drilling strategy was to double APC/XCB core the sequence down to the first thick chert horizon, then to drill through the Neogene to core the Paleogene and uppermost Cretaceous in a third hole. The site will be included in broad leg-based objectives that include

1. Reconstructing changes in the properties of surface and deep waters through the Late 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 abrupt climatic events such as the Eocene/Oligocene boundary, the PETM, late Paleocene and early Eocene hyperthermals, and the mid-Maastrichtian event. The depth transect will also help address questions concerning the nature of chemical (i.e., CCD, nutrients, and oxygenation) and physical oceanographic changes (i.e., temperature gradients) during these events.
3. Studying changes in biotic assemblages through time and relating them to fluctuations in temperature and nutrients over long time periods as well as during transient climatic events.
4. Understanding the origin of orbital cycles in the sedimentary record and determining the origin of these cycles using biotic and geochemical data.
5. Using independently generated biostratigraphy, magnetostratigraphy, and orbital stratigraphy to improve the Paleogene and Late Cretaceous timescale.