Site summaries

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

Priority: Primary site
Position: 26°29.60′S, 174°43.75′W
Water depth (m): 1950
Target drilling depth (mbsf): ~405 (55 m sediment, ≥350 m basement)
Approved maximum penetration (mbsf): Approval pending (420 m requested)
Survey coverage: • AMAT02RR (Fig. AF1)
• Line AMAT 26.5-2 (CDP 7270) (Fig. AF2)
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): • 0–15: pelagic ooze
• 15–55: lithified limestones, volcaniclastics, and minor lava flows(?)
• >55: 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-1C 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 5–15 m of pelagic sediment or winnowed sand. Although it is not located at a crossing point of two seismic lines, Site LOUI-1C is proposed as a primary drill site because it is placed farther away from a possible posterosional cone (in contrast to Site LOUI-1B). Site LOUI-1C is located ~1.8 km south of Site LOUI-1B on seismic Line 26.5-2, which is nearer the seamount margin and in the middle of a large low-reflectivity sediment patch.