Next Section | Table of Contents


Proposed Sites WALV-8A, WALV-8B, and WALV-8C

A suite of three proposed sites, WALV-8A through WALV-8C (2530–2557 m water depth) has been positioned in the vicinity of DSDP Site 525 (Figs. F12, F13, F14; Table T1). This area represents the shallowest segment of the planned Walvis Ridge drilling transect. Total sediment thickness at these sites ranges from 460 to 490 ms two-way traveltime (TWT) (multichannel profile GeoB01-031), and the basal sediments are likely Campanian (Fig. F5). At Site 525 a major unconformity was encountered across the E/O boundary. We believe that sequences to the northeast of Site 525, along seismic reflection line GeoB01-031, may offer a more complete Paleogene sequence. The new seismic lines show a series of reflectors (Me, E1, and K/T) that can be traced from Site 525 to WALV-8A, WALV-8B, and Walv-8C and indicate the E/O unconformity (E1) to fade out laterally away from Site 525 (Figs. F12, F13). The E/O unconformity at Site 525 is seen in seismic line GeoB01-031 as a zone of hard and truncated reflectors. This zone is not seen at proposed Sites WALV-8A through WALV-8C. The next prominent reflector is the Cretaceous/Tertiary (K/T) boundary (500–570 ms TWT at Site 525), just above the basement reflectors. Correlating reflectors from Site 525 to the Sites WALV-8A through WALV-8C suggests the Paleogene sequence is most complete at Sites WALV-8A and WALV-8B. Total sediment thickness at these two locations is estimated to be 620 and 530 ms TWT. The E/O and P/E boundaries are shallowest at Site WALV-8C, <280 and 370 ms TWT, compared to 400 and 480 ms TWT at Site WALV-8A. Subbottom depths of the target reflectors at proposed Site WALV-8A are considerably deeper than is desirable for our planned work. Therefore, proposed Site WALV-8B is the primary site, and Sites WALV-8A and WALV-8C serve as alternates.

Proposed Sites WALV-9A and WALV-9B

Proposed Sites WALV-9A and WALV-9B (2979–3083 m water depth) are located in an area proximal to DSDP Site 529 in the upper segment of the planned Walvis Ridge drilling transect (Fig. F14). A total of 417 m of sediment was recovered at Site 529 by rotary drilling (Fig. F5). The sequence, which was poorly recovered, ranged from Pleistocene to late Maastrichtian in age. Based on Site 529, the EOGM, EECO, and PETM target intervals are expected at 189–208, 246–265, and 265–274.5 meters below seafloor (mbsf). Slumps were reported at this site in the upper Paleocene (293.5–312.5 mbsf), in the Oligocene–Miocene NN1 Zone (75–122.5 mbsf), and in the lower Pleistocene.

Site WALV-9A has been positioned on seismic lines GeoB01-055 and GeoB01-048, immediately northwest of DSDP Site 529 at a water depth of 2979 m (i.e., 66 m shallower than Site 529). The site is located on a topographic high that is underlain by a package of expanded sediment sequences. Seismic profile GeoB01-055 clearly shows a southward thinning of acoustic units and the presence of sediment slumps between 22:30 and 00:15 (i.e., immediately south of Site WALV-9A). An erosional channel is seen immediately northeast of the site on crossing line GeoB01-048, and a progressive thinning of acoustic units is seen to the southwest. Site WALV-9A therefore appears ideally located for obtaining expanded sediment sections in an area that remained unaffected by local erosion. Proposed Site WALV-9B is located along line GeoB01-048 (shotpoint 3854). It is located in an area where the Neogene sediment has been eroded and where the Paleogene is more accessible. As such, proposed Site WALV-9B has a higher priority for drilling., but approval for drilling by the Pollution Prevention and Safety Panel (PPSP) is still pending at the time of production of this prospectus.

Proposed Sites WALV-10A, WALV-10B, WALV-10C, and WALV-10D

These proposed sites (3719–3961 m water depth) are in the vicinity of DSDP Site 528 in the central segment of the Walvis Ridge drilling transect. A total of 474 m of Pleistocene through upper Maastrichtian sediment was retrieved at Site 528 (Fig. F14). The Paleogene was rotary drilled throughout with an average recovery rate of 60%. We suspect that the P/E boundary was lost in a core gap. Based on the Site 528 stratigraphy, our target intervals are at 217–236 mbsf (Eocene–Oligocene transition), 293–312 mbsf (EECO), and 312–321 mbsf (PETM). No hiatuses, slumps, or other sedimentary disturbances are reported for these intervals. We have tentatively labeled several prominent reflectors (Me, P-E, and K/T), which can be traced across all sites.

Positioning of sites was based on line GeoB01-059 and crossing lines GeoB01-062, GeoB01-064, and BeoB01-066. Site WALV-10A is a reoccupation of DSDP Site 528, with the goal of retrieving a more complete sediment sequence than was possible using rotary core barrel (RCB) drilling that was employed at the DSDP site. The site is at an isolated topographic high that is bounded by erosional channels in the southwest and northeast. Proposed Sites WALV-10B through WALV-10C are located along line GeoB01-059, on a gently northwest-dipping slope that shows parallel subbottom reflectors indicating undisturbed acoustic units. Total sediment thickness at these sites varies between 460 and 490 ms TWT (Table T1). At the deepest proposed Site WALV-10D, part of the Neogene is missing (due to slumping?), making it a more attractive target for accessing the Paleogene.

Proposed Sites WALV-11A, WALV-11B, WALV-11C, and WALV-11D

This is part of the deep segment of the Walvis Ridge drilling transect, in 4313–4526 m water depth, around the location of DSDP Site 527 (Fig. F15). The sediment column at Site 527 consists of a 360-m-thick Pleistocene to middle Maastrichtian sequence. A single but major regional unconformity spans the middle Miocene to the lower Oligocene and is responsible for a pronounced reflector (O-M unconformity) that is recognized in all profiles. A second prominent reflector marks the K/T boundary. From the Site 527 stratigraphic record we expect the EOGM, EECO, and PETM target intervals to be at 113.5–132.5, 180–189.5, and 189.5–199 mbsf. We have selected four possible locations where these reflectors can be recognized.

Proposed Site WALV-11B, the primary site, is located to the southwest of DSDP Site 527 and should yield a Paleocene–Eocene interval similar to, or more expanded than, that at Site 527. Along seismic line GeoB01-039, a series of undulating, diverting, and truncated reflectors is seen at 100 ms TWT at Site 527, around the subbottom depth where the middle Miocene to early Oligocene hiatus has been reported. Offsetting the drill site to the southwest where this acoustic pattern is not present appears desirable. Total sediment thickness at Site WALV-11B is 360 ms. Also along this line to the northeast of Site 527 is Site WALV-11C, with a total sediment thickness of 340 ms TWT (Table T1). Proposed Site WALV-11A is essentially a reoccupation of DSDP Site 527 on seismic line GeoB01-039. The intention is to retrieve a more complete sediment sequence than was possible using hydraulic piston corer drilling that was employed at the DSDP site. Site WALV-11D is positioned at the northern end of the sedimentary wedge that forms the slope along which the Walvis Ridge drilling transect is located. Total sediment thickness at Site WALV-11D is 300 ms TWT. Subbottom reflectors shoal at the site because of a progressive northwestward thinning of the uppermost acoustic units at the northern end of the wedge. From comparing acoustic units with those that were drilled at Site 527 it appears reasonable to infer that Paleogene sequences are near the sediment surface at proposed Site WALV-11D. The site appears to be unaffected by sediment slumping, which is indicated to the southeast along seismic line GeoB01-038 (14:30 to >18:00) and may offer a suitable alternate should slumping be a problem at Site WALV-11B.

Proposed Sites WALV-12A, WALV-12B, and WALV-12C

Proposed Sites WALV-12A through WALV-12C (4726–4768 m water depth) are designated to be the deep end-member of the drilling transect. Site WALV-12A is located on line GeoB01-035 in a perched basin that is filled with ~280 ms TWT of sediment. Sites WALV-12B (shotpoint 3349) and WALV-12C along line GeoB01-036 are located on a sedimentary ridge and a southeast-dipping slope (Fig. F16). Sediment thickness at these sites is 240 and 300 ms TWT. Here, identification of reflectors is tenuous given the lack of previous drilling in this area. Nonetheless, we expect the Neogene to be mostly clay and condensed. In contrast, the Paleogene should be relatively carbonate rich. One prominent reflector is most likely the K/T boundary contact. This deep site will be critical for establishing a possible overdeepening of the CCD following the PETM as the ocean carbon balance was restored through weathering feedbacks and carbonate deposition.

Proposed Site WALV-13B

Proposed Site WALV-13B (3768 m water depth) is an alternate site located northeast of the main Walvis Ridge transect area, half-way between Frio Ridge in the northeast and the transect at the central Walvis Ridge. Time permitting, this site will be targeted for an expanded Paleogene sequence. Site WALV-13B is located on line GeoB01-029b, common depth point 2890, on the flank of a narrow valley incision. It appears conceivable that the incision was cut into the sediment cover by a sediment slide that went down the narrow valley immediately southwest of the incision. As such, the Neogene cover may be thin or absent here. Total sediment thickness at the flank of the incision is 480 ms TWT. The K/T boundary is estimated to lie at 316 mbsf.

Next Section | Table of Contents