Site summaries (continued)

Proposed Site LOUI-7A (Seamount 32.3°S [Burton Seamount] - Suiko equivalent)

Priority: Alternate site
Position: 32°12.99′S, 171°52.84′W
Water depth (m): 1550
Target drilling depth (mbsf): ~470 (120 m sediment; ≥350 m basement)
Approved maximum penetration (mbsf): 470 (350 m basement; additional basement penetration must be reviewed by the operator during drilling operations)
Survey coverage: • AMAT02RR (Fig. AF16)
• Line AMAT 32.33-1 (CDP 36334) (Fig. AF17)
• Line AMAT 32.33-2 (CDP 36827) (Fig. AF18)
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 (two reentries).
• Wireline logging (triple combo, FMS-sonic, and magnetometer).
Anticipated lithology (mbsf): • 0–10: pelagic ooze
• 10–120: lithified limestones, volcaniclastics, and minor lava flows(?)
• >120: basalt (~64 m.y. old)
Site characterization: This alternate drilling site is located on a small guyot ~1.4° north of proposed primary Site LOUI-2B on the 33.7°S guyot, which gives this site an interpolated age of ~64–65 Ma, older than the Suiko Seamount (61 Ma) in the Emperor Seamount Trail. Three other seamounts also have crossing seismic lines; however, the 32.3°S guyot has the thinnest sequence of volcaniclastics. The estimated pelagic cap is ~10 m thick, with an intercalated sequence of volcaniclastics and lava flows estimated to be at least 70–110 m thick (0.055–0.060 s two-way traveltime at 2.5–3.5 km/s in volcaniclastic sediment). This guyot has a reflective summit (possibly due to a manganese pavement) and some small-scale roughness (5–20 m high peaks) that may be posterosional in origin or an erosional remnant (close-spaced small guyots like these can be submerged quickly before planation is complete, particularly if they end up in the flexural moat of the next-youngest volcano to load the lithosphere). Accordingly, a better drill target is 1–2 km to the southwest along seismic Line 32.33-2 (e.g., alternate Site LOUI-7B), which is farther away from some of these minor posterosional peaks or erosional remnants.