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SITE SUMMARIES (continued)

Site 1267

Latitude: 28°5.88'S

Longitude: 1°42.66'E

Water depth: 4355 m

Maximum depth of penetration: 329.0 mbsf

Oldest formation: late Maastrichtian

Time on site: 5.3 days (0940 hr on 21 April–1648 hr on 26 April)

Site 1267 (proposed Site WALV-11B) is located on the lower northwestern flank of Walvis Ridge, just to the southwest of DSDP Site 527 (Figs. F29, F30). At 4.35 km, it is the second deepest site of the Leg 208 depth transect. Site 1267 is above the level of the present-day lysocline and CCD, which in this sector of the eastern Atlantic Ocean are below 4.8 and 5.0 km, respectively. Close proximity to the CCD appears to be maintained for much of the Cenozoic, as the rate of local subsidence has more or less kept pace with the long-term deepening of the CCD. As a result, Site 1267 is well situated to record major changes in regional carbon chemistry and/or circulation. Site 1267 was drilled with the objective of recovering sections suitable for detailing changes in bottom water chemistry and circulation at abyssal depths during several of the key paleoceanographic events of the Paleogene including the Eocene–Oligocene transition, the PETM, and the K/P boundary extinction. Initial results indicate that this objective was achieved.

Two holes offset ~20 m from each other were cored at Site 1267 using the APC and XCB coring systems. A 329-m-thick section of upper Maastrichtian to Pleistocene nannofossil ooze and clay was recovered. Hole 1267A was drilled from the mudline to 312 mbsf. Hole 1267B was cored from the mudline to 329 mbsf. Nominal recovery exceeded 99% in both holes. Using MS and color reflectance data, cores from the two holes were correlated by depth shifting and representative intervals were spliced together to create a single stratigraphic section with a total length of 368 mcd. At least five small recovery gaps remain in the interval from 267 to 368 mcd.

The Site 1267 lithologic units are nearly identical to those identified at Site 1262 (4.76 km water depth) but thicker and with slightly higher average carbonate contents (Fig. F31). Three lithologic units and five subunits were recognized. Unit I (0–102.3 mcd) consists of upper Miocene to Pleistocene nannofossil ooze and foraminifer-bearing nannofossil ooze. Unit II (102.3–157.8 mcd) is divided into three distinct subunits based on the relative abundance of clay. Subunits IIA (102.3–124 mcd) and IIC (143–157.8 mcd) are upper Oligocene to upper Miocene and middle to upper Eocene clay layers separated by a lower Oligocene nannofossil clay interval. Unit III (157.8–368 mcd) consists of upper Maastrichtian to middle Eocene clayey nannofossil ooze and chalk.

Biostratigraphic results show the section to be stratigraphically complete, at shipboard resolution, in the Pleistocene to uppermost Miocene and in the lower Eocene through upper Maastrichtian intervals (including the P/E and K/P boundaries), with sedimentation rates typically ranging 5–15 m/m.y. (Fig. F32). Two condensed intervals (sedimentation rates <1.5 m/m.y.) span the lowermost upper Miocene through lower Oligocene (~10.4–30.0 Ma; 108–124 mcd) and a large part of the upper and middle Eocene (34.0–42.3 Ma; 146–151 mcd), respectively.

As at Site 1262, sharp transitions between carbonate- and clay-rich facies at Site 1267 are an expression of the long-term deepening of the CCD and related changes in ocean carbon chemistry and/or circulation. The carbonate-rich facies include the Pleistocene, Pliocene, lower Oligocene, Paleocene and lower–middle Eocene, and Maastrichtian intervals. The clay-rich facies include the Miocene and middle to upper Eocene sections, as well as several discrete layers at the P/E and K/P boundaries. Preliminary age assignments indicate that each of the major facies changes at Site 1267 corresponds to a previously documented shift in the level of the CCD. The Pliocene and Pleistocene sedimentation rates of up to 26 m/m.y. are consistent with moderate rates of carbonate dissolution in this part of the Atlantic Ocean but with noticeably less dissolution than that at Site 1262, which is ~400 m deeper. The facies transition between lithologic Units II and I reflects on a regional deepening of the CCD during the late Miocene and earliest Pliocene, as has also been recorded in other cores in the abyssal Atlantic Ocean. Similarly, the carbonate-rich lower Oligocene interval (lithologic Subunit IIB) implies a deep CCD, whereas the underlying upper Eocene clay (lithologic Subunit IIC) implies a shallow CCD. The contact between these two units is sharp, indicating that the CCD descent occurred rapidly. The transition back into clay-rich facies in the mid-Oligocene does not imply a shoaling CCD but, rather, local deepening of the seafloor via subsidence.

The other clay-rich layers are relatively thin but pronounced as they are imbedded within relatively carbonate rich units. They include the P/E boundary (base at 231.53 mcd) that is present within a thick and uniform sequence of upper Paleocene and lower Eocene foraminifer nannofossil ooze. The benthic foraminiferal extinction event, including the uppermost appearance of Stensioeina beccariiformis, occurs just below the base of this layer at 231.53–231.62 mcd. This is followed by a shift in nannofossil abundance from Fasciculithus to Zygrhablithus between 230.3 and 230.8 mcd. Planktonic foraminifers are heavily dissolved in the clay layer with only extremely rare specimens of Acarinina soldadoensis, Acarinina coalingensis, Acarinina "chascanona," and Morozovella subbotinae. The basal color contact is relatively sharp, although MS data show a more gradual, steplike increase over the lower 20 cm. The upper contact, although gradational, is relatively sharp compared to P/E boundary sections recovered at shallower water depths. In essence, the overall pattern is consistent with other pelagic records and is inferred to result from seafloor carbonate dissolution because of the input of methane-derived CO2. Overlying the clay layer is a sequence of nannofossil ooze, which is slightly richer in carbonate than the unit immediately underlying the clay layer.

The K/P boundary was recovered at 320.4 mcd. The basal contact of this layer is sharp, both in color and in MS. This grades upward into clay nannofossil ooze over several meters. The lowest Danian biozones, the P and P1a zones, are ~0.2 and 0.8 m thick, respectively. Preservation of foraminifers and calcareous nannofossils is not as good as that observed at Site 1262. Many of the "dwarfed" foraminifer specimens are dissolved and slightly overgrown. The post-extinction flora is dominated by Thoracosphaera spp. Key marker species C. primus and C. tenuis first appear at 314.8 and 319.3 mcd, respectively. The boundary is present in the upper third of a reversed zone, Chron C29r, although postcruise analysis of discrete samples is required to confirm the chron boundaries.

Bedding cycles as expressed in the MS, color reflectance, and other high-resolution core logging data are common at Site 1267. The lower Eocene and upper Paleocene cores, in particular, are characterized by pronounced decimeter- to meter-scale bedding cycles. The shorter cycles have a frequency close to that of the orbital precession, whereas the longer oscillations have frequencies similar to the 100- and 400-k.y. eccentricity cycles. The bedding cycles are even more pronounced in the Maastrichtian with power again mostly concentrated in the precession and eccentricity bands. Above the K/P boundary, the power shifts primarily into the 100-k.y. eccentricity band. This appears to be an artifact of a reduction in accumulation rates, primarily in the carbonate component. As previously recognized in most pelagic K/P boundary sequences, carbonate accumulation rates do not recover until much later in the Cenozoic.

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