Water depth: 2505 m
Maximum depth of penetration: 282.8 mbsf
Oldest formation: early Oligocene
Time on site: 2.9 days (1310 hr on 5 April1140 hr on 8 April)
Site 1264 (proposed Site WALV-8A) is located at a water depth of 2505 m at the crest of a northsouth trending segment of Walvis Ridge in the uppermost segment of the Leg 208 Walvis Ridge depth transect (Figs. F16, F20). At 2.5 km depth, the site is well 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. As a result, Site 1264 is uniquely situated to record major changes in regional and/or global ocean carbon chemistry, ocean circulation, and the thermal evolution of the regional surface waters. Site 1264 was drilled as part of a two-site approach to the shallow water depth end-member of the Walvis Ridge transect. With a relatively expanded Oligocene to Neogene sediment sequence, Site 1264 was drilled with the objective to recover sections suitable for detailing changes in intermediate bottom water chemistry and circulation during key paleoceanographic events such as the OligoceneMiocene transition, the MCO, and the late PliocenePleistocene cooling in association with accelerated ice growth in the Arctic. Initial results indicate that this objective was achieved.
We recovered a ~273-m-thick sequence of lower Oligocene to Pleistocene nannofossil ooze at Site 1264. Three holes, offset ~20 m from each other, were cored by using the APC coring system. Hole 1264A was started few meters below the mudline and was terminated at 280.7 mbsf. Hole 1264B was cored from the mudline to 282.8 mbsf. One core was taken in Hole 1264C to confirm the mudline and recover the topmost sediments. A total of 566.5 m was cored and 563.8 m of sediment were recovered (average nominal recovery = 99.5%). Using color reflectance and MS core logging data, cores from Holes 1264A and 1264B were correlated by depth-shifting to create a mcd scale. Representative intervals were spliced together to create a single, nearly complete stratigraphic section for Site 1264.
The Site 1264 sediment sequence is divided into two lithologic units, with the lower unit divided into two subunits (Fig. F21). Unit I (029.4 mcd) consists of middle PliocenePleistocene nannofossil foraminifer ooze, foraminifer nannofossil ooze, and foraminifer-bearing nannofossil ooze. Unit II (29.4316.5 mcd) is divided into two subunits. Subunit IIA (29.4117.0 mcd) consists of white upper Miocene to middle Pliocene nannofossil ooze and foraminifer-bearing nannofossil ooze. Subunit IIB (117.0316.5 mcd) includes brown lower Oligocene to upper Miocene nannofossil ooze and foraminifer-bearing nannofossil ooze. Unit II sediments contain volcanic ashes and abundant oxides. Interstitial waters show high concentrations of iron in Subunit IIA, whereas Subunit IIB interstitial waters include high levels of manganese ions. Color reflectance and MS records from the recovered sequence at Site 1264 show centimeter- to meter-scale bedding cycles throughout. Centimeter-scale light bluish gray bands in Subunit IIB may represent orbital or even suborbital cycles.
Biostratigraphic results show that a nearly complete Neogene and upper Oligocene section is present, although a hiatus representing ~0.6 m.y. occurs in the upper Miocene (Fig. F22). The middle Miocene interval is condensed relative to the other parts of the record. In general, calcareous microfossils are reasonably well preserved at this site, although preservation deteriorates in the lower part of the record. Oligocene benthic foraminifers reveal downslope transport and reworking at Site 1264. Because of a pervasive overprint, only a few paleomagnetic reversals could be recognized. Sedimentation rates range from 5 to 10 m/m.y. in the Oligocene to middle Miocene, with the highest rates in the lower Miocene. Sedimentation rates are highly variable in the upper Miocene and Pliocene, ranging from 10 to 30 m/m.y.
Next Section | Table of Contents