Part II

Primary Site (ODP Site 757)
Site 757 is located at 17°01.458'S, 88°10.899'E (Deep Sea Drilling Project [DSDP] Site 253 is located at 24°52.65'S, 87°21.97'E). The area near Site 757 was surveyed in August 1986 as part of the Robert Conrad Cruise 2707 (RC 2707). Tracks and examples of seismic profiles are presented in Figures 10, 11, and 12. The thickness of sediments is about 370 m. Because drilling conditions in this area were excellent, it is likely that basement penetration of 150-200 m can be achieved. This should be sufficient for installation of the GOBO. The hole must be cased down to basement with a reentry cone attached at the top, and the basement section of the hole cored.

Alternate Site (ODP Site 756)
Site 756 is located at 27°21.30'S, 87°35.85'E. This site was surveyed in September 1986 as part of the Robert Conrad Cruise 2708 (RC 2708). Site survey information is in the Leg 121 Initial Reports volume (Shipboard Scientific Party, 1989a, 1989b). Conrad and JOIDES Resolution tracks and seismic reflection profiles are also available for this site (Figs. 13, 14). At this site, sediment thickness is 139 m. The issue of basement penetration is largely dependent on the nature of the rocks and the need to avoid hydrothermal circulation. To facilitate the future installation of a GOBO, it is necessary to penetrate 200 m into basement.


The logging program at Site 757 is designed to measure physical properties, anisotropy, and borehole character in the basement basalts. It is likely that core recovery will be less than 100% and therefore log data will be a critical tool in providing a continuous profile of the cored interval. Standard tool strings, including the triple combo and formation microscanner (FMS)/sonic will be run following the completion of coring. The triple combo will be comprised of the natural gamma, density, porosity, and dual induction sondes. The digital array sonic tool (SDT) will be run with the FMS. If desired, the SDT may be configured to operate in cement bond log mode for casing cement evaluation.

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