Site 1262 (proposed Site WALV-12A) is located in the Angola Basin near the base of the northwestern flank of Walvis Ridge. At a water depth of 4759 m, the site is 500 and 200 m deeper than the previously drilled Deep Sea Drilling Project (DSDP) Site 527 to the south and Site 523 to the southwest, respectively. Drilling at Site 527 yielded a 341-m section of Neogene, Paleogene, and Maastrichtian sediment (Moore, Rabinowitz, et al., 1984), whereas drilling at Site 523 retrieved a 150-m section of Neogene and upper Paleogene sediment (Hsü, LaBrecque, et al., 1984). Sediments vary from clays to carbonate-rich oozes and chalks. The Pliocene–Pleistocene section consists of nannofossil oozes and extends to <100 meters below seafloor (mbsf). The Oligocene–Miocene sequence, yielding carbonate-poor clays, is condensed and contains an unconformity. The Paleocene–Eocene sequence recovered at Site 527 appears complete and consists of nannofossil oozes and chalks and a clay layer. However, only a portion of the Paleocene/Eocene Thermal Maximum (PETM), including a 70-cm-thick clay layer, was recovered at Site 527 (Thomas and Shackleton, 1996; Thomas et al., 1999). A continuous Cretaceous/Paleogene (K/P) boundary was also recovered at Site 527. The basal Parvularugoglobigerina eugubina Zone in the Tertiary is well represented (25 cm), and faunas are well preserved. The sediments immediately above basement are of late Maastrichtian age. Site 527 was rotary cored and, as a consequence, recovery was poor (25%–75%) and much of the core suffered from severe drilling disturbance, particularly the unlithified Neogene and Paleogene oozes.
Our main objective for this site was the recovery of undisturbed sediments recording critical intervals in the early Cenozoic, specifically the K/P boundary and subsequent recovery of biota following the mass extinction, the PETM, and the period of global cooling and growth of polar ice caps across the Eocene/Oligocene (E/O) boundary into the earliest Oligocene (early Oligocene Glacial Maximum). We planned to recover 100% of the sedimentary section in multiple holes to establish a cyclostratigraphy and develop an astronomically tuned timescale. We aimed to fully document events across the critical intervals as well as short-lived events such as the mid-Paleocene biotic event (PBE) and episodes of climate fluctuation during the early Eocene Climatic Optimum. Site 1262 forms the deep anchor of the Leg 208 depth transect and is located close to the calcite compensation depth (CCD) in the present ocean, making the site most suitable to document fluctuations in the depth of the CCD.
We chose a location where the Neogene section is thin (~100 m) to facilitate recovery of the entire Paleogene section using the advanced piston corer (APC) rather than the extended core barrel. To this end, Site 1262 was positioned in a perched basin filled with ~230 m of sediments (common depth point 2775 on line GeoB 01-035) (Figs. F1, F2). Seismic profiles revealed two distinct packages of reflectors in the basin, a thin upper package (0–100 ms two-way traveltime [TWT] below seafloor) with a series of closely spaced sharp reflectors and a thicker lower package of weaker reflectors than in the upper package (100–280 ms TWT below seafloor) (Fig. F3). Based on Site 527, the upper package was interpreted as a condensed interval of Neogene calcareous oozes and clays and the lower package is interpreted as upper Maastrichtian to lower Eocene calcareous oozes and chalks. Two prominent reflectors dissect the lower package. The upper reflector (140 ms TWT below seafloor) was interpreted to represent the Paleocene/Eocene (P/E) boundary, whereas the deeper reflector (220 ms TWT below seafloor) was interpreted to represent the K/P boundary contact. Using an average velocity of 1.8 m/ms, the depths of these target reflectors were estimated to be 114 and 181 mbsf, respectively.
As anticipated, coring at Site 1262 yielded sediments deposited just above or below the CCD over most of the Cenozoic, and the APC system produced much better recovery and less distorted core than that obtained with the rotary coring system during the drilling of Site 527 (see "Site 1262" in "Site Summaries" in the "Leg 208 Summary" chapter). The upper Maastrichtian and Paleocene–lower Eocene sections are moderately expanded, and both the P/E and K/P boundaries were recovered by APC drilling in multiple holes at ~127 and ~195 mbsf, respectively, with no obvious coring disturbance. Both critical intervals appear to be stratigraphically complete, and both exhibit distinct lithologic cycles and thus are suitable for high-resolution studies.
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