Site 1221 (12°01.999´N, 143°41.572´W; 5175 meters below sea level (mbsl); Fig. F1) forms an equatorial component of the 56-Ma transect drilled during Leg 199 and is situated about three-quarters of the way between the Clipperton and Clarion Fracture Zones in typical abyssal hill topography. On the basis of regional magnetic anomalies, we anticipated the basement age at Site 1221 to be equivalent to Chron C25n (~56 Ma) (Cande et al., 1989), about the same age as Site 1220. At the outset of drilling at Site 1221, our estimate for total sediment thickness was ~150 meters below seafloor (mbsf) (Fig. F2).
Based upon a fixed hotspot model (Gripp and Gordon, 1990, for the 0- to 5-Ma Pacific hotspot rotation pole; Engebretson et al., 1985, for older poles), Site 1221 should have been located about 1° south of the equator at 56 Ma (in an equatorial position at ~50 Ma) and ~2°N at 40 Ma. Thus, Site 1221 should have been situated underneath the South Equatorial Current in the early Eocene. A nearby piston core (EW9709-14PC) taken during the site survey cruise recovered >11 m of red clay with the base of the core containing a calcareous radiolarian ooze dated as early Oligocene age on the basis of radiolarian biostratigraphy (Lyle, 2000).
Site 1221 will be used to study equatorial ocean circulation from the late Paleocene through the late Eocene during the early Cenozoic thermal maximum. Sediment records from this site will help to define the carbonate compensation depth (CCD) during the Paleocene-Eocene and Eocene-Oligocene transitions. In this and other respects, Site 1221 will act as an interesting analog to Site 1220. The two sites are situated on similar age crust and exhibit similar seismic-stratigraphic sequences, but Site 1221 is thought to have crossed the equator ~5 m.y. earlier than Site 1220, during latest early Eocene time (~50 Ma).
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Ms 199IR-114