Site summaries (continued)

Proposed Site LOUI-1B (Seamount 26.5°S - Detroit equivalent)

Priority: Alternate site
Position: 26°28.66′S, 174°43.46′W
Water depth (m): 1840
Target drilling depth (mbsf): ~400 (50 m sediment, ≥350 m basement)
Approved maximum penetration (mbsf): 420 (350 m basement, additional basement penetration needs to be reviewed by the operator during drilling operations)
Survey coverage: • AMAT02RR (Fig. AF1)
• Line AMAT 26.5-2 (CDP 7201) (Fig. AF2)
• Line AMAT 26.5-3 (CDP 8162) (Fig. AF3)
Objective: (see text for details) 1. Core thin sediment cover and igneous basement until enough igneous units suitable to acquire accurate paleolatitudes and 40Ar/39Ar ages are recovered.
2. Study the geochemical evolution of this guyot.
Drilling, coring, and downhole measurement program: • RCB coring to TD
• FFF deployment and two bit changes (2 reentries)
• Wireline logging (triple combo, FMS-sonic, magnetometer, and UBI).
Anticipated lithology (mbsf): • 0–10: pelagic ooze
• 10–50: lithified limestones, volcaniclastics, and minor lava flows(?)
• >50: basalt (~75 m.y. old)
Site characterization: The 26.5°S guyot shows <1° of tilting (in contrast to the older Osbourn Seamount to the north that approaches the Kermadec Trench) and has a simple (deeper) summit with less evidence of posterosional volcanism that contrarily characterizes the more southern 26.6°S guyot. Site LOUI-1B is also characterized by a thinner section (~40 m) of supposed volcaniclastics (which thicken toward the margins). Sidescan and 3.5 kHz data indicate this site is covered with 5–10 m of pelagic sediment or winnowed sand. Nonetheless, this drill site is a bit too central (and near a possible posterosional cone) to be ideal. A better drill target would be 1–2 km farther south along line 26.5-2 (proposed primary Site LOUI-1C), which is nearer the seamount margin and in the middle of a large low-reflectivity sediment patch.