Site 1219

Abstract

ite 1219 (7°48.019´N, 142°00.940´W; 5063 meters below sea level [mbsl]; Fig. F1) is the southernmost site to be drilled on the 56-Ma transect during Leg 199 and is situated ~3° to the north of the Clipperton Fracture Zone on abyssal hill topography. The age of basement at Site 1219 was poorly constrained prior to Leg 199 because little reliable magnetic anomaly data are available between the Clipperton and Clarion Fracture Zones (Cande et al., 1989). At the outset of Leg 199, based on one interpretation of the location of magnetic Anomaly C25r (~57 Ma) (Petronotis et al., 1994), previous drilling, and assumed spreading rates, we estimated the age of basement at Site 1219 to be ~55 Ma. Site 1219 is the only site to be drilled during Leg 199 that features all of the seismic horizons identified for a Paleogene equatorial seismic stratigraphy (Lyle et al., this volume), and an estimate of sediment thickness at Site 1219 prior to drilling (based upon the seismic reflection profile; Fig. F2) was 270-290 meters below seafloor (mbsf), depending on which reflection was chosen as basement. Based upon a fixed hotspot model (Gripp and Gordon, 1990, for 0- to 5-Ma Pacific hotspot rotation pole; Engebretson et al., 1985, for older poles), Site 1219 should have been within 2° of the equator between 40 and 21 Ma and should have crossed the equator at 29 Ma. Thus, the sediments should record equatorial conditions from the late middle Eocene to the early Miocene. In addition, Site 1219 should provide an analog for Site 1218, except that it is on older deeper crust. Site 1219 will be used to study near-equatorial ocean circulation from the late Paleocene to the late Eocene including deepwater flow and sea-surface properties. Sediment records from this site will help to define the carbonate compensation depth (CCD) and lysocline during the Eocene-Oligocene transition and near the Oligocene/Miocene (O/M) boundary. Based on the results from a site survey piston core (EW3709-12PC; Lyle, 2000) taken a few kilometers to the southwest, we anticipated that Site 1219 passed below the CCD in the early Miocene. The basement at Site 1219 should have formed in the Southern Hemisphere, and changes in magnetic inclination at this site will be important to define the position of the equator in the early Eocene