Site summaries (continued)

Proposed Site PEAT-7C (early to middle Miocene Equator)

Primary for Expedition 321, alternate for Expedition 320
03°50.009’N, 123°12.352’W (WGS-84)
Water depth (m):
4491 (5.988 s TWT)
Target drilling depth (mbsf):
452 then tag basement
Approved maximum penetration (mbsf):
480 (approved by TAMU safety panel based on EPSP June 2006 recommendation)
Survey coverage
(track map; seismic profile):
Roger Revelle (25 March 2006):
• Simrad EM-120 multibeam system
• Knudsen 320B subbottom profiler
• Dual 150 c.i. GI seismic sources
• Scripps 48-channel Geometrics GeoEel
Piston core: 14.09 m (RR0603-05JC)
Primary seismic line: PEAT-7 Line 4
Crossline: PEAT-7 Line 10 (Figs. F30, F31, F32) (see also report to the EPSP panel, available at
Site PEAT-7C, on 24 Ma crust, focuses on early and middle Miocene paleoceanographic events. The latest Oligocene–middle Miocene appears to have been relatively warm, comparable to the latest Eocene. However, variability in the isotopic record of the early–middle Miocene compared to that of the Eocene may indicate more variability in climate and global ice volume. The climatic "optimum" at ~15 Ma is just before development of major ice sheets on Antarctica and a marked increase in ice-rafted debris in circum-Antarctic sediments. The early Miocene also marks a major evolutionary change from relatively static Oligocene planktonic biota; in the equatorial Pacific abundant diatoms imply a major change in carbon cycling as well. In conjunction with Sites PEAT-5C, 6C, and 8C, it is designed to provide a latitudinal transect for early Miocene age slices, as well as a limited depth transect.
Drilling program:
• Holes A, B, and C: APC with core orientation to refusal; XCB to basement.; logging in Hole A
• Hole A: APC/XCB to basement
• Holes B and C: wash to 200 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/nannofossil ooze, nannofossil ooze/chalk, possibility of thin diatom layers, hydrothermically altered ridge basalt; low possibility of chert strings