SITE SUMMARIES
Latitude: 27°11.15´S
Longitude: 1°34.62´E
Water depth: 4755 m
Maximum depth of penetration: 213 meters below seafloor (mbsf)
Oldest sediments recovered: upper Maastrichtian
Time on site: 4.69 days (1300 hr on 24 March–0530 hr on 29 March)
Site 1262 (proposed Site WALV-12A) is located at the northwestern end of the Walvis Ridge drilling transect and represents the deep end-member of the depth transect (Figs. F12, F13). At 4.75 km depth, Site 1262 is close to 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 have been 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 the deep end-member of the Walvis Ridge transect, Site 1262 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.
Three holes (Table T1), offset ~20 m from each other, were cored at Site 1262 using the APC. A 213-m-thick section of upper Maastrichtian to Pleistocene nannofossil ooze and clay was recovered. Hole 1262A was started 6 m below the mudline and prematurely terminated at 150 mbsf because of a severed core barrel. Hole 1262B was cored from the mudline to 210 mbsf, and Hole 1262C was cored from 90 to 213 mbsf. Nominal recovery exceeded 100% in all three holes. Using MS data, cores from the three holes were correlated by depth shifting and representative intervals were spliced together to create a single stratigraphic section with a total length of 236 meters composite depth (mcd).
Three lithostratigraphic units and five subunits were identified (Fig. F14). Unit I (0–46 mcd) consists of upper Miocene to Pleistocene nannofossil ooze and foraminifer-bearing nannofossil ooze with sedimentation rates up to 10 m/m.y. Unit II (46–90 mcd) is divided into three distinct subunits based on the relative abundance of clay. Subunits IIA (46–68 mcd) and IIC (79–90 mcd) are upper Oligocene to upper Miocene and middle to upper Eocene clay units separated by a lower Oligocene nannofossil ooze interval, Subunit IIB (68–79 mcd). Unit III (90–236 mcd) consists of upper Maastrichtian to middle Eocene clayey nannofossil ooze and nannofossil ooze. Biostratigraphic results show the section to be stratigraphically complete in the Pleistocene and in the upper Paleocene–lower Eocene, with sedimentation rates up to 12 m/m.y. The middle to upper Eocene is highly condensed. Calcareous microfossils are generally well preserved at this site, particularly in the lower Eocene and upper Paleocene.
Sharp transitions between carbonate- and clay-rich facies at Site 1262 are an expression of a rapidly shifting CCD and related changes in ocean carbon chemistry and/or circulation. The carbonate-rich facies include the Pleistocene, Pliocene, lower Oligocene, Paleocene, lower–middle Eocene, and Maastrichtian. 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 1262 corresponds to a previously documented shift in the level of the CCD. The Pliocene and Pleistocene sedimentation rates of up to 10 m/m.y. are consistent with moderate rates of carbonate dissolution in this part of the Atlantic Ocean (Fig. F15). Dissolution seems to have occurred primarily during the Pleistocene glacial maxima, when the lower boundary of NADW shoaled and allowed more corrosive AABW to cross over into the Angola Basin through mid-ocean-ridge fracture zones. The facies transition between lithostratigraphic Units II and I reflects a regional deepening of the CCD during the late Miocene and earliest Pliocene. Regional deepening of the CCD indicates that the Angola Basin would have been filled primarily with more corrosive AABW prior to the late Miocene, and the CCD would have shoaled. Similarly, the carbonate-rich lower Oligocene interval (lithostratigraphic Subunit IIB) implies a deep CCD, whereas the underlying upper Eocene clay (lithostratigraphic Subunit IIC) implies a shallow CCD. The contact between these two units is sharp, indicating that the CCD descent occurred rapidly, possibly in the span of two obliquity cycles as suggested by observations of Pacific cores recovered during Leg 199. The transition back into clay-rich facies in the mid-Oligocene implies a shoaling CCD.
The most prominent clay layer at Site 1262 is a ~40-cm-thick unit at the P/E boundary (base at 140.04 mcd) that is embedded within a thick and uniform sequence of upper Paleocene and lower Eocene foraminiferal nannofossil ooze. The benthic foraminiferal extinction event occurs just below the base of this layer at 140.18 mcd, and a major shift in nannofossil abundances from abundant Fasciculithus to more abundant Zygrhablithus is observed just above the benthic extinction event (BEE). The basal color contact is relatively sharp, although MS data indicate a more gradual, steplike increase in clay content over the lower 20 cm, with at least two brief reversals. The upper contact, although gradational, is relatively sharp compared to P/E boundary sections recovered at shallower water depths. Still, 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 noticeably richer in carbonate than the unit immediately underlying the clay layer. This is an important feature of this boundary sequence, as it confirms another prediction of the hydrate dissociation model (e.g., an overcompensation in global carbonate deposition driven by weathering feedbacks). In theory, such a feedback would be a natural response to rapid input of a large mass (2000 Gt) of carbon dioxide.
Another anomalous clay layer is present at the K/P boundary at 216.58 mcd. The basal contact of this layer is sharp, both in color and in MS. This clay layer gradually grades upward into clayey nannofossil ooze over several meters. The lowest Danian biozones are well represented, if not expanded, in this section. The P
and P1a Zones are 0.4 and 1.0 m thick, respectively. Preservation of foraminifers and calcareous nannofossils is excellent, particularly in the clay-rich layers above the boundary. Many of the "dwarfed" foraminiferal specimens exhibit "glassy" texture and should be particularly useful for geochemical and textural studies. The postextinction flora is dominated by Thoracosphaera spp. Key marker species Cruciplacolithus primus and Cruciplacolithus tenuis first appear at 214.5 and 213.8 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. The combination of orbitally paced bedding cycles, stratigraphic continuity, and excellent fossil preservation will permit further refinement of key biostratigraphic datums, as well as testing of models concerning the rate of ecosystem recovery following mass extinction.
Pervasive bedding cycles are expressed in the MS, color reflectance, and other high-resolution core logging data from Site 1262. The lower Eocene and upper Paleocene cores, in particular, are characterized by pronounced decimeter- to meter-scale bedding cycles. The variance is concentrated in three frequency bands. 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. Assuming pacing by precession, the total number of high-frequency cycles in the upper Paleocene and lower Eocene would suggest that the sequence is stratigraphically continuous. 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 into the 100-k.y. eccentricity band. This phenomenon results from a 75% 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. The presence of these orbitally paced cycles in stratigraphically complete sections provides a unique opportunity to astronomically calibrate the duration of Paleocene and lower Eocene chrons.
Latitude 28°31.98´S
Longitude: 02°46.77´E
Water depth: 2717 m
Maximum depth of penetration: 346 mbsf
Oldest sediments recovered: upper Paleocene
Time on site: 6.79 days (1515 hr on 29 March–1015 hr on 5 April)
Site 1263 (proposed Site WALV-8E) is located along the northwestern flank of Walvis Ridge just a few hundred meters beneath the summit (Figs. F16, F17). At 2.72 km water depth, this site represents the shallow end-member of the Leg 208 depth transect. Situated well above the level of the CCD throughout the Cenozoic, Site 1263 was expected to yield a stratigraphically continuous and expanded sequence of Paleogene pelagic nannofossil ooze. The primary objective was to recover sedimentary sections with sufficient resolution to detail orbital-scale changes in bottom water chemistry and circulation at shallow bathyal depths during several of the key paleoceanographic events of the Paleogene, including the Eocene–Oligocene transition, the EECO, and the PETM. Ideally, this requires 100% recovery of the sedimentary section with minimal coring disturbance, a requirement that is best met by using APC coring. To this end, the site was positioned along a slope just beneath the ridge crest, where the Neogene is thin and the Paleogene target intervals are at subbottom depths of <300 m.
Four holes (Table T1), offset ~20 m from each other, were cored at Site 1263 using the APC and XCB to recover a 346-m-thick section of upper Paleocene to Pleistocene nannofossil ooze and chalk. Hole 1263A was cored with the APC from the mudline to 284 mbsf and with the XCB to 346 mbsf. Hole 1263B was cored with the APC from 46 to 262 mbsf and with the XCB to 339 mbsf. Hole 1263C was cored with the APC from 90 to 119 mbsf and from 203 to 286 mbsf and with the XCB to 291 mbsf. Hole 1263D was cored with the APC from 272 to 287 mbsf. Nominal recovery averaged ~100% with the APC and ~60% with the XCB. Total nominal recovery for the site was 91%. Using MS data, cores from the four holes were aligned by depth shifting and representative intervals were spliced to create a continuous stratigraphic section for the Eocene and uppermost Paleocene, extending from 48 to 340 mcd. The sections above and below were not completely recovered. Cores in those intervals were depth shifted, assuming a constant growth rate of 18% in the composite section. The total length of the composite is 401 mcd.
The sediments recovered at Site 1263 are predominantly composed of calcareous nannofossil ooze and chalk with relatively little downhole variability (Fig. F18). Calcium carbonate contents are typically 90–95 wt% (except for the P/E boundary interval). As a result, only one lithostratigraphic unit and three subunits were recognized. Subunit IA (0–99.1 mcd) is upper Eocene to Pleistocene foraminifer-bearing nannofossil ooze and nannofossil ooze. The Pliocene–Pleistocene interval (0–26 mcd) has sedimentation rates of 1–6 m/m.y. The upper Oligocene to upper Miocene section (26–48 mcd) is condensed, shows evidence of extensive winnowing as well as reworking and downslope transport (slumps and turbidites), and possibly contains one or more unconformities. The upper Eocene to lower Oligocene section (48–99 mcd) appears to be complete, although reworking is indicated by calcareous microfossils. Subunit IB (99.1–318.0 mcd) is nannofossil ooze, clay-bearing nannofossil ooze, and chalky nannofossil ooze with occasional layers of volcanic ash and disseminated chert or chert stringers, most of which were easily penetrated by the APC. Eocene Subunit IB has sedimentation rates of 5–15 m/m.y. (Fig. F19). The Paleocene to lowermost Eocene Subunit IC (318.0–400.7 mcd) is composed of nannofossil ooze and chalky nannofossil ooze. Several chert horizons are present in the upper Paleocene section. The P/E boundary interval is represented by a ~20-cm-thick "clay" layer at 335.7 mcd. The basal contact is sharp, with MS rising rapidly and carbonate content decreasing from ~90 to <1 wt% over the first 5 cm of the transition. The upper contact is gradational, with carbonate content increasing to >90 wt% over ~100 cm. Sedimentation rates in Subunit IC are generally 10–20 m/m.y. and reach 30 m/m.y. near the top of the subunit in the lowermost Eocene.
The P/E boundary clay layer proved to be an exceptionally challenging target to recover at this site. At the level of the clay layer in Hole 1263A (285 mbsf), the APC took only a partial stroke but still penetrated into the top of the layer, 40 cm of which was captured in the core catcher. Switching to the XCB system in the next core, we were able to recover another 50 cm of the clay layer. However, the contact with the underlying Paleocene ooze, which was softer, appeared unconformable. In Hole 1263B, we elected to use the XCB system to penetrate the boundary layer. This time, ~30 cm of the upper portion of the clay unit lodged in the core catcher, apparently as the core was being cut. As a result, the remaining portion of the clay layer and uppermost Paleocene were washed away. In Hole 1263C, we again elected to use the APC, this time backing off a few meters to allow the core barrel to attain maximum velocity before striking the critical sediment interval. Although the stroke was only partial, the core barrel penetrated the entire clay layer plus 50 cm of the underlying Paleocene ooze. Because this represented the only copy of the entire P/E clay layer at this site, we elected to drill a fourth hole. In Hole 1263D, we applied the same strategy as in the previous hole, firing the APC from a point 2 m above the bottom of the hole. This time the core barrel penetrated just the upper 30 cm of the clay layer. The second APC attempt, again fired from 2 m above the bottom of the hole, penetrated the remaining 50 cm of the clay layer as well as 150 cm of the upper Paleocene. As a result, the basal contact was recovered intact, providing the second complete copy of the P/E boundary for this site.
The moderate sedimentation rates and generally high carbonate content of the Site 1263 sediments are consistent with the relatively shallow depth of the site. During the Paleogene, the site remained well above the lysocline depth (<2 km). This is evident from the presence of carbonate-rich upper Eocene and Oligocene sections, which are largely represented by condensed clay units in deeper segments of the ridge and surrounding seafloor. The lone exception is the 1-m-thick P/E boundary interval at 335 mcd, which is present within a thick and uniform sequence of upper Paleocene and lower Eocene foraminiferal nannofossil ooze. The benthic foraminiferal extinction event occurs just below the base of this layer at 335.6 to 335.7 mcd. This is just below a major shift in nannofossil abundances from abundant Fasciculithus to abundant Zygrhablithus. The overall pattern of the P/E boundary interval is consistent with other pelagic records and is inferred to result from seafloor carbonate dissolution resulting from the input of methane-derived CO2 during the event. The fact that this site was at a paleodepth of 1400 m, ~2000 m shallower than Site 1262, attests to the scale of seafloor carbonate dissolution during this event.
The Site 1263 sediment record displays pervasive bedding cycles as expressed in the MS, color reflectance, and other high-resolution core logging data. The middle and lower Eocene, in particular, are characterized by pronounced decimeter- to meter-scale bedding cycles. The variance is concentrated in three frequency bands. The shorter cycles have a frequency close to that of the orbital precession, whereas the longer oscillations have a frequency similar to the 100- and 400-k.y. eccentricity cycles. Both the frequency and amplitude of the bedding cycles are similar to those observed at Site 1262 and should permit high-resolution correlation of units.
Latitude: 28°31.95´S
Longitude: 2°50.73´E
Water depth: 2505 m
Maximum depth of penetration: 283 mbsf
Oldest sediments recovered: lower Oligocene
Time on site: 2.9 days (1310 hr on 5 April–1140 hr on 8 April)
Site 1264 (proposed Site WALV-8A) is located at a water depth of 2505 m at the crest of a north-south–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 Oligocene–Miocene transition, the MCO, and the late Pliocene–Pleistocene 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 (Table T1), offset ~20 m from each other, were cored by using the APC. Hole 1264A was started a 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 from 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 was recovered (average nominal recovery = 99.5%) in three holes. 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 lithostratigraphic units, with the lower unit divided into two subunits (Fig. F21). Unit I (0–29.4 mcd) consists of middle Pliocene–Pleistocene nannofossil foraminiferal ooze, foraminiferal nannofossil ooze, and foraminifer-bearing nannofossil ooze. Unit II (29.4–316.5 mcd) is divided into two subunits. Subunit IIA (29.4–117.0 mcd) consists of white upper Miocene to middle Pliocene nannofossil ooze and foraminifer-bearing nannofossil ooze. Subunit IIB (117.0–316.5 mcd) includes brown lower Oligocene to upper Miocene nannofossil ooze and foraminifer-bearing nannofossil ooze. Unit II sediments contain volcanic ash and abundant oxides. Interstitial waters show high concentrations of iron in Subunit IIA, whereas Subunit IIB interstitial waters include high levels of manganese. 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.
Biostratigraphy shows that a nearly complete Neogene and upper Oligocene section is present, although an unconformity 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 poor data quality, 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.
Latitude 28°50.10´S
Longitude: 02°38.35´E
Water depth: 3060 m
Maximum depth of penetration: 321 mbsf
Oldest sediments recovered: upper Paleocene
Time on site: 6.9 days (1410 hr on 08 April–1130 hr on 15 April)
Site 1265 (proposed Site WALV-9B) is located along the northwestern flank of Walvis Ridge just a few hundred meters beneath the summit (Figs. F16, F23). At 3.08 km water depth, this site represents the shallow middepth site of the Leg 208 depth transect. Situated above the level of the CCD throughout the Cenozoic, Site 1265 was expected to yield a stratigraphically continuous and expanded sequence of upper Paleocene and lower Eocene pelagic nannofossil ooze. The primary objective was to recover sedimentary sections with sufficient resolution to characterize high-frequency changes in bottom water chemistry and circulation at shallow bathyal depths during several of the key climatic events of the Paleogene including the Eocene–Oligocene transition, the EECO, and the PETM. Ideally, this requires complete recovery of the sedimentary section with minimal coring disturbance, a requirement that is best met by using the APC. To this end, the site was located in a broad channel at the base of a slope extending down from the ridge crest. Because the Neogene is relatively condensed here, the key Paleogene target intervals are at subbottom depths of <300 mbsf.
Four holes (Table T1), offset ~20–30 m from each other, were cored at Site 1265 using the APC and XCB to recover a 321-m-thick section of upper Paleocene to Pleistocene nannofossil ooze and chalk. Hole 1265A was cored with the APC from the mudline to 286 mbsf and with the XCB to 321 mbsf. Hole 1265B was cored with the APC from the mudline to 252 mbsf, where mechanical problems prevented further penetration and required the recovery of the drill string. Hole 1265C was cored with the APC from 185 to 204 mbsf, where the same problem as in Hole 1265B occurred, and the drill string had to be recovered again. Hole 1265D was cored with the XCB from 248 to 270 mbsf and by the APC to 275 mbsf to recover the P/E boundary. Total nominal core recovery for the site was 95%. Using MS and color reflectance (red/blue) data, cores from the four holes were aligned by depth shifting and representative intervals were spliced to create a nearly continuous stratigraphic section for the uppermost Paleocene to Pleistocene, extending from 0 to 316 mcd. Two small (<1 m) gaps exist in the lower Eocene. Cores from the upper Paleocene, where recovery was low, were depth shifted by extrapolating a constant growth rate of 14% from the correlated interval. The total length of the composite section is 359 mcd.
The sediment sequence recovered at Site 1265 has been divided into two lithostratigraphic units and several subunits (Fig. F24). Unit I (0–55.8 mcd) is composed of upper Miocene to Pleistocene foraminifer-bearing nannofossil ooze and nannofossil ooze. Unit II (55.8–359.1 mcd) is composed of upper Paleocene to middle Miocene nannofossil ooze with rare intervals of foraminifer-bearing nannofossil ooze and clay. Unit II is further subdivided into three subunits. Subunit IIA (55.8–192.7 mcd) consists of lower Oligocene to upper Miocene nannofossil ooze and foraminifer-bearing nannofossil ooze. Subunit IIB (192.7–248.5 mcd) is lower to upper Eocene nannofossil ooze, with occasional intervals of foraminifer-bearing nannofossil ooze. The contact between Subunits IIA and IIB coincides with the E/O boundary interval and is marked by a step increase in MS and a step decrease in sediment lightness. Subunit IIC (248.5–359.1 mcd) is a Paleocene to lower Eocene nannofossil ooze and foraminifer-bearing nannofossil ooze.
The P/E boundary clay layer was recovered with mixed success. In Hole 1265A, the entire clay layer was recovered intact in Section 208-1265A-29H-7 (315.86 mcd), the last full-stroke APC of the hole. In Hole 1265B, the APC became stuck in the core barrel at 251.7 mbsf (~288.7 mcd), just ~30 m above the target interval. In Hole 1265C, during the attempt to spot core the lower Eocene and upper Paleocene sediment, the core barrel again became stuck, this time at 204 mbsf (~229.7 mcd). After several XCB cores were taken in Hole 1265D, we returned to APC to core the boundary interval. A partial stroke (4.8 m) penetrated the top of the clay layer and recovered 50 cm in the core catcher. A second APC, fired from 2 m above the bottom of the hole, advanced <1 m and recovered an additional 10 cm of the clay layer.
Based on biostratigraphy, the sequence appears to be relatively complete over the upper Paleocene and lower Eocene, upper Oligocene and lower Miocene, and upper Pliocene. The middle Eocene is condensed, and unconformities spanning ~7 and ~3 m.y., respectively, are present at the lower/middle and middle/upper Eocene boundaries (Fig. F25). An unconformity spanning ~2–3 m.y. is present at the Miocene/Pliocene boundary. Sedimentation rates range from 10 to 25 m/m.y. in the upper Paleocene and lower Eocene, from 4 to 12 m/m.y. in the upper Eocene to middle Miocene, and from 8 to 14 m/m.y. in the Pliocene–Pleistocene. Downslope reworking of microfossils is common in the middle Eocene through Pliocene sequences.
A number of "bioevents" are recorded at Site 1265 that are also recorded at the other Leg 208 Sites. These include an early Miocene bolivinid abundance acme at 85–87 mcd, an event recorded elsewhere in the Atlantic and Indian Oceans. Several discrete Braarudosphaera layers are present in the upper Oligocene between 154 and 161 mcd. These layers, which are prominent throughout the South Atlantic Ocean, particularly at sites along the margins, are recorded at precisely the same stratigraphic level at each of the Leg 208 sites.
The moderate sedimentation rates and generally high carbonate content of the Site 1265 sediments are consistent with the relatively shallow depth of the site. During the Paleogene, the site apparently remained above the lysocline depth with the exception of several brief periods in the latest Paleocene and early Eocene, including the P/E boundary. The latter is marked by an abrupt contact between upper Paleocene nannofossil ooze and lower Eocene dusky red, zeolite- and nannofossil-bearing clay that grades upcore into nannofossil ooze. The minimum carbonate concentration at this "intermediate" depth site is ~30 wt%, whereas minimum values near 0 wt% characterize the deeper and shallower Sites 1262 and 1263, respectively. Either carbonate was bioturbated into the first centimeters above the contact at Site 1265 or the earliest Eocene is not represented at Site 1265. Moreover, the P/E boundary interval is marked by a sharp increase in MS and a decrease in sediment lightness. The benthic foraminiferal extinction event occurs just below the base of this layer at 315.81–315.86 mcd. This slightly precedes a shift in nannofossils from abundant Fasciculithus to abundant Zygrhablithus.
Site 1265 sediments record pervasive bedding cycles as expressed in the MS, color reflectance, and other high-resolution core logging data. The lower Eocene, in particular, is characterized by pronounced decimeter- to meter-scale bedding cycles. The variance is concentrated in three frequency bands. The shorter cycles have a frequency close to that of the orbital precession, whereas the longer oscillations have a frequency close to the 100- and 400-k.y. eccentricity cycles. Both the frequency and amplitude of the bedding cycles are similar to those observed at Sites 1262 and 1263, which should permit the high-resolution correlation of units.
Latitude: 28°32.55´S
Longitude: 2°20.61´E
Water depth: 3798 m
Maximum depth of penetration: 334 mbsf
Oldest sediments recovered: upper Paleocene
Time on site: 5.6 days (1405 hr on 15 April–0445 hr on 21 April)
Site 1266 (proposed Site WALV-10F) is located along the northwestern flank of Walvis Ridge (Figs. F16, F26). At 3.8 km water depth, this site represents one of the middepth sites of the Leg 208 depth transect. Situated near the level of the CCD throughout the Cenozoic, Site 1266 was expected to yield a stratigraphically continuous and expanded sequence of upper Paleocene and lower Eocene pelagic nannofossil ooze. The primary objective was to recover sedimentary sections with sufficient resolution to characterize high-frequency changes in bottom water chemistry and circulation at shallow bathyal depths during several of the key climatic events of the Paleogene, including the Eocene–Oligocene transition, the EECO, and the PETM. Ideally, this requires recovery of the complete sedimentary section with minimal coring disturbance, a requirement that is best met with the APC. To this end, the site was located in a broad channel at the base of a slope extending down from the ridge crest. Because the Neogene is relatively condensed here, the key Paleogene target intervals are at subbottom depths of <300 mbsf.
Three holes (Table T1), offset ~20–30 m from each other, were cored at Site 1266 using the APC and the XCB to recover a 334.2-m-thick section of upper Paleocene to Pleistocene nannofossil ooze and chalk. Hole 1266A was cored with the APC to 217.1 mbsf and with the XCB to 298.6 mbsf. Hole 1266B was cored with the APC from the mudline to 7.6 mbsf. The hole was then drilled ahead to 220 mbsf without coring to save time, and the remainder of the hole (220–321 mbsf) was cored with the XCB. Hole 1266C was washed down to 62 mbsf and cored with the APC from 62 to 192 mbsf. From 192 to 245 mbsf the hole was washed again, and a single XCB core was taken from 245 to 254.5 mbsf, followed by three APC cores from 254.5 to 282.7 mbsf, which recovered the P/E critical boundary interval. Finally, the hole was completed with the XCB to 334.2 mbsf. Total nominal core recovery for the site was 98%.
Using MS and chromaticity data, cores from the three holes were aligned by depth shifting. A splice of representative intervals was created for the uppermost Paleocene to lowermost Eocene, the interval that contains the P/E boundary. As a result of the strategic decision not to double core the Pliocene–Pleistocene and upper Eocene and because of poor overlap between cores from Holes 1266A and 1266C in the Oligocene to Miocene interval, recovery of a complete section was not achieved in those intervals and cores from the Pleistocene down to lowermost Eocene were depth shifted, assuming a constant mcd growth rate of 15%.
The sediment sequence recovered at Site 1266 has been divided into three lithostratigraphic units (Fig. F27). Unit I (0–76.8 mcd) is composed of uppermost Miocene to Pleistocene foraminifer-bearing nannofossil ooze and nannofossil ooze. The unit contains frequent turbidites marked by distinctive light brown layers of coarse-grained foraminiferal ooze that have sharp bases and gradational tops. Unit II (76.7 to 214.7 mcd) is composed of Oligocene to uppermost Miocene clay-bearing nannofossil ooze and nannofossil ooze and clay. Unit II contains clay layers formed during periods of severe carbonate dissolution and inclined and folded layers indicative of synsedimentary slumping. Unit III includes upper Paleocene to Oligocene clay-bearing nannofossil ooze, nannofossil ooze, nannofossil chalk, and nannofossil clay. The chalky intervals are in the lower part of Unit III, mainly below the P/E boundary. Volcanic ash is a minor component throughout the sequence.
As at Sites 1263 and 1265, recovery of the P/E boundary clay layer met with mixed success. The XCB recovered only a partial clay layer in Hole 1266A (Core 208-1266A-31X), presumably because the cutting shoe rotation tends to grind away sediment at the interface of stiff clay and soft calcareous ooze. Therefore, the APC was used in the subsequent two holes. In Hole 1265B, the APC core catcher got stuck in the clay layer (Section 208-1266B-6H-CC). In Hole 1265C, the APC achieved a full stroke and recovered the entire clay layer in Section 208-1266C-17H-3.
The calcareous microfossils generally show moderate preservation. All microfossil groups indicate extensive reworking throughout the section except for the interval surrounding the P/E boundary. Despite all the reworked specimens, two unconformities were recognized, one with a duration of ~1.2 m.y. in the upper Miocene and the second one spanning ~37 to ~47 Ma, which represents a large part of the middle Eocene. Sedimentation rates range from 6 to 24 m/m.y. in the upper Paleocene to lower Eocene, <4 m/m.y. in the middle Eocene, and from 4 to 8 m/m.y. in the upper Eocene to Pleistocene, not including the upper Miocene unconformity (Fig. F28).
At the approximate middepth of the Leg 208 transect, Site 1266 is critical for constraining the timing of shifts in ocean carbonate chemistry. The moderate sedimentation rates and generally high carbonate content of the upper Paleocene–lower Eocene sediments are consistent with the results from Sites 1262 and 1267. During the Paleogene, the site apparently remained above the lysocline depth with the exception of at least two brief periods. The first reddish clay-rich layer is present in the lower Eocene at ~293 mcd (carbonate content = ~50 wt%). This clay layer falls in Zone NP11 and has now been identified in each of the lower Eocene sequences recovered on Walvis Ridge. This ~10-cm-thick layer clearly represents a regional bedding horizon and exhibits several lithologic features characteristic of the P/E boundary layer. The second prominent clay layer is the P/E boundary clay at 306.8 mcd. The P/E boundary is marked by an abrupt contact between upper Paleocene nannofossil ooze and lower Eocene dusky red zeolite- and nannofossil-bearing clay that grades upward into nannofossil ooze. The carbonate content is ~0 wt% at this "intermediate" depth site. Moreover, the P/E boundary interval is marked by sharp increases in MS and a decrease in sediment lightness. The BEE occurs just below the base of the clay layer (306.8 mcd). A major shift in nannofossil abundances, from abundant Fasciculithus to abundant Zygrhablithus, occurs just above the P/E.
The Site 1266 sediment record displays pervasive bedding cycles as expressed in the MS, color reflectance, and other high-resolution core logging data. The entire Site 1266 sequence shows cycles with different wavelengths. The Miocene sequence exhibits light gray to brown foraminifer-bearing nannofossil ooze that alternates with medium brown foraminifer-bearing nannofossil ooze on a meter scale. The lightness record shows cycles on a decimeter to meter scale. The lower Eocene, in particular, is characterized by pronounced decimeter- to meter-scale bedding cycles. The variance is concentrated in three frequency bands. The shorter cycles have a frequency close to that of the orbital precession, whereas the longer oscillations have a frequency close to the 100- and 400-k.y. eccentricity cycles. Both the frequency and amplitude of the bedding cycles are similar to those observed at Sites 1262, 1263, and 1265 and should permit the high-resolution correlation of units.
Latitude: 28°5.88´S
Longitude: 1°42.66´E
Water depth: 4355 m
Maximum depth of penetration: 329 mbsf
Oldest sediments recovered: upper 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 (Table T1), offset ~20 m from each other, were cored at Site 1267 using the APC and XCB. 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 lithostratigraphic 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 lithostratigraphic 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 Subunit IIB, a lower Oligocene nannofossil ooze and clayey nannofossil ooze interval. Unit III (157.8–368 mcd), subdivided into two subunits, consists of upper Maastrichtian to middle Eocene clayey nannofossil ooze and chalk and nannofossil clay.
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, lower–middle Eocene, and Maastrichtian intervals. The clay-rich facies include the Miocene and middle to upper Eocene sections, as well as 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 lithostratigraphic Units II and I reflects a regional deepening of the CCD during the late Miocene and earliest Pliocene. Similarly, the carbonate-rich lower Oligocene interval (lithostratigraphic Subunit IIB) implies a deep CCD, whereas the underlying upper Eocene clay (lithostratigraphic 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 implies a shoaling CCD.
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 foraminiferal nannofossil ooze. The BEE, 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 assemblage from abundant Fasciculithus to abundant 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. Two other prominent clay layers, which we label the X and Y layers, occur in the lower Eocene at Site 1267.
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" foraminiferal specimens are dissolved and slightly overgrown. The postextinction 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, sediment lightness, 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. As previously recognized in most pelagic K/P boundary sequences, carbonate accumulation rates do not recover until much later in the Paleocene.
