Site Summaries (continued) | Table of Contents

SITE SUMMARIES (continued)

Site: SEPAC-9A

Priority: 1 (Note - SEPAC-10A is an alternate to Site SEPAC-9A)
Position: 39°53.28´S, 75°53.28´W
Water Depth: 4087 m
Sediment Thickness: 470 m
Target Drilling Depth: 470 mbsf
Approved Maximum Penetration: 500 mbsf
Seismic Coverage: Primary Line: 970308 (Revelle), Line CBA-3A-3, 0657z, SP686
Crossing Line: 970308 (Revelle), Line CBA-3A-1, 0100z, SP1288

Trackline map | Seismic Line 1 | Seismic Line 3 | Bathymetry map

Objectives: The objectives at Site SEPAC-9A are to provide a continuous sedimentary sequence to:

1. Assess variations in the character of Antarctic Circumpolar Deep Water (CDW), which enters the Chile Basin from the south as bottom water over Neogene time, including responses to opening of Drake Passage.

2. Assess variations in the southernmost reaches of the northward flowing Humboldt Current, based on planktonic fauna and flora, including responses of the southern subtropical South Pacific to opening of Drake Passage.

3. Assess biostratigraphic and paleomagnetic stratigraphies in the southeast Pacific, for comparison to similar data in the subtropical and tropical regions.

4. Date basal sediments. SEPAC-9A is between Valdivia and Mocha Fracture Zones. Crustal age here is not well characterized, but is probably older than 19 Ma and younger than 29 Ma.

Drilling Program: Triple APC to refusal. Tensor orientation on APC cores. Single XCB to basement or refusal (expected penetration ~470 mbsf).

Logging and Downhole: Triple combo, third-party Lamont MGT, FMS/sonic, GHMT

Nature of Rock Anticipated: Upper section is expected to be fossiliferous pelagic-to hemipelagic clay. Some distal turbidites may be present. Based on sediment thickness and presumed basement age, the average Neogene sediment accumulation rate is near 20 m/m.y. Rates are likely higher in the Pleistocene and lower in older intervals when the site was far to the west of South America. Lower section is likely to contain more carbonates, gradually lithifying with greater meters below seafloor depth. Basement is likely oceanic basalt.

Site Summaries (continued) | Table of Contents