Site 1264 (proposed Site WALV-8A; seismic lines GeoB 01-031, common depth point [CDP] 7884, and GeoB 01-046, CDP 1047) is located at a water depth of 2507 m near the crest of a north-south–trending segment of Walvis Ridge (Fig. F1). The site is ~52 m deeper than Deep Sea Drilling Project (DSDP) Site 525 to the southwest, where a 574-m-thick sedimentary sequence was recovered during previous drilling (Moore, Rabinowitz, et al., 1984). All sediments in the sequence are rich in biogenic carbonate. The Neogene section at Site 525 is truncated by a hiatus at 270 meters below seafloor (mbsf) so that upper Oligocene sediments overlie middle Eocene sediments. The upper Oligocene–Pleistocene sequence consists of nannofossil- and foraminifer-bearing nannofossil ooze. The Paleogene section includes nannofossil- and foraminifer-bearing nannofossil ooze and chalk and extends to 452 mbsf. DSDP Site 525 was drilled using a combination of the hydraulic piston corer and rotary drilling.
Our main objective for this site was the recovery of undisturbed upper Oligocene–Pleistocene sediments with the emphasis on the recovery of Neogene sediments to complement the recovery of a Paleogene section at nearby Site 1263. The combined sections from Sites 1263 and 1264 thus cover the Cenozoic at the shallow end of the Leg 208 depth transect. We planned to recover 100% of the sedimentary section in multiple holes to make it possible to establish a cyclostratigraphy and develop an astronomically tuned timescale. We aimed to fully document the thermal and chemical evolution of the South Atlantic during the Neogene, including the early Miocene Climatic Optimum.
To this end, Site 1264 was located in an area where total sediment thickness is estimated to be 621 m (velocity = 1.9 m/ms; 650 ms two-way traveltime [TWT] below seafloor). The seismic profiles show a series of reflectors (RO/M, R1, RP/E, and RK/P) that can be traced from Site 525 to Sites 1264 and 1263 and indicate that the Eocene/Oligocene (E/O) unconformity (R1) disappears laterally away from Site 525 (Figs. F2, F3). The E/O unconformity at Site 525 is represented in seismic line GeoB 01-031 as a zone of high amplitude and truncated reflectors. This zone tapers or fades toward Sites 1264 and 1263. At Site 1264, the shallowest of the distinct reflectors, RO/M (250 ms TWT below seafloor), is just below the Oligocene/Miocene (O/M) boundary. Deeper in the profile, RP/E (484 ms TWT below seafloor) represents the Paleocene/Eocene (P/E) boundary and RK/P (580 ms TWT below seafloor) represents the Cretaceous/Paleogene (K/P) boundary. The correlation of reflectors from DSDP Site 525 suggests the E/O boundary is at ~380 mbsf (velocity = 1.8 m/ms; 400 ms TWT below seafloor), indicating a thick upper Paleogene–Neogene sequence at Site 1264.
Coring in two holes at Site 1264 yielded a 280-m-thick sequence of carbonate-rich lower Oligocene to Pleistocene pelagic sediments (see "Site 1264" in "Site Summaries" in the "Leg 208 Summary" chapter). With the exception of a condensed interval in the middle Miocene and an unconformity in the upper Miocene, the 273-m-thick section is stratigraphically complete and exhibits subtle bedding cycles (expressed in core logs) throughout. The O/M boundary was recovered intact at 230 mbsf.
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