Site 1215

Abstract

Site 1215 (26°01.77´N, 147°55.99´W, 5396 meters below sea level [mbsl]; Fig. F1) is the northernmost of seven sites drilled on the 56-Ma-crust transect during Ocean Drilling Program (ODP) Leg 199. It will be used to investigate paleoceanographic processes in the northern subtropical early Eocene Pacific Ocean. Site 1215 is situated north of the Molokai Fracture Zone on typical abyssal hill topography in an area of thin but continuous sediment cover (Fig. F2). Based on magnetic lineations, basement age at Site 1215 should be in the youngest part of Anomaly An26R, or ~58 Ma (Cande et al., 1989; timescale of Cande and Kent, 1995). The Cenozoic history of sedimentation in this region was poorly constrained prior to Leg 199 drilling because the nearest Deep Sea Drilling Project (DSDP) or ODP drill site (DSDP Leg 5) is >1000 km away. Based on data from these early rotary coring activities (together with magnetic anomaly maps, a program of shallow-penetration piston coring, and seismic profiling), we expected the sedimentary sequence at Site 1215 to comprise red clays (a mixture of wind-blown dust and authigenic precipitates) overlying a basal carbonate section deposited when the site was near the ridge crest in the late Paleocene and early Eocene. The broad paleoceanographic objectives of drilling the sedimentary sequence anticipated at Site 1215 are as follows: (1) to help define the shift in the Intertropical Convergence Zone through the Paleogene by following the change in eolian-dust composition and flux through time (red clays); (2) to help define the North Equatorial Current and North Pacific subtropical gyre processes (basal carbonates); and (3) sampling of the Paleocene/Eocene (P/E) boundary, one of the most climatologically critical intervals of Cenozoic time. Recovery of deep-sea sediments from this time interval was a high priority because the P/E boundary has never been sampled in the central tropical Pacific Ocean. Results from Site 1215 will also provide important information to test whether there was significant motion of the Hawaiian hotspot, with respect to the Earth's spin axis, during the early Cenozoic. At 56 Ma, the backtracked location based upon a hotspot reference frame (Gripp and Gordon, 1990, for 0- to 5-Ma Pacific hotspot rotation pole; Engebretson et al., 1985, for older poles) is ~11°N, 117°W. If significant hotspot motion or true polar wander occurred since 57 Ma (Petronotis et al., 1994), this drill site could have been much closer to the equator