Site summaries (continued)

Proposed Site PEAT-4C (late Eocene and Eocene/Oligocene boundary)

Primary for Expedition 320, alternate for Expedition 321
07°59.999’N, 131°58.396’W (WGS-84)
Water depth (m):
4809 (6.412 s TWT)
Target drilling depth (mbsf):
268 then tag basement
Approved maximum penetration (mbsf):
300 (approved by TAMU safety panel based on EPSP June 2006 recommendation)
Survey coverage
(track map; seismic profile):
Roger Revelle (2 April 2006; 6 kt):
• Simrad EM-120 multibeam system
• Knudsen 320B subbottom profiler
• Dual 150 c.i. GI seismic sources
• Scripps 48-channel Geometrics GeoEel
Piston core: 11.25 m (RR0603-08JC)
Primary seismic line: PEAT-4 Line 1
Crossline: PEAT-4 Line 6 (Figs. F20, F21, F22) (see also report to the EPSP panel, available at
Site PEAT-4C targets events bracketing the Eocene–Oligocene transition, specifically to recover latest Eocene carbonate-bearing sediments prior to deepening of the CCD that occurred during this greenhouse-to-icehouse transition.
The site is located on late middle Eocene crust (~38 Ma). The Eocene–Oligocene transition experienced the most dramatic deepening of the Pacific CCD during the Paleogene, which has now been shown to coincide with a rapid stepwise increase in benthic oxygen stable isotope ratios, interpreted to reflect growth of the Antarctic ice sheet.
Site PEAT-4C will be instrumental in obtaining a carbonate-bearing record in the late Eocene through the Eocene–Oligocene transition.
Drilling program:
• Holes A, B, and C: APC with core orientation to refusal; then XCB to basement; logging in Hole A
• Hole A: APC/XCB to basement
• Holes B and C: wash to 100 m; APC/XCB to basement
Downhole measurement program:
• Wireline logging: triple-combo, FMS-sonic, possibly check shot
• Temperature measurements: 3 APCT-3, 2 DVTP
Nature of rock anticipated:
Clay, radiolarian ooze, nannofossil ooze/chalk, possibility of chert strings and thin diatom layers, hydrothermically altered ridge basalt