The Leg 182 drilling strategy must be developed with the knowledge that although ODP has great experience with drilling deep-water pelagic carbonates, it is difficult to predict drilling conditions in the cool-water carbonates at the shallower sites. Accordingly, operational considerations may dictate that significant changes to drilling strategies are necessary on site. In particular, although easily drilled nanno-foram and foram-nanno oozes are expected to dominate the upper sequences at each site, there is the possibility that thin bioclastic grainstone horizons and/or thin chert horizons may complicate drilling at the shallowest sites. In addition, the order in which sites are drilled will need to be flexible to accommodate operational restrictions dependent on sea state for the sites in less than 650 m water depth (Sites GAB-05B, GAB-06B, GAB-07A, GAB-08A, and GAB 09A). This will be particularly important for the sites located in less than 300 m water depth (Sites GAB-06B and GAB-09A), where calm conditions will be imperative. The Leg 182 operational plan is summerized in Table 1.
Triple coring with the advanced hydraulic piston corer (APC), extended core barrel corer (XCB), and rotary core barrel corer (RCB) will be carried out at the four high-resolution paleoceanography and sea-level sites (Sites GAB-01C, GAB-02B, GAB-06B, and GAB-13B), which comprise the shelf-to-basin transect (water depth range of 332-4465 m). After the cores and downhole logs have been tied to the extensive seismic data in the area, these sites will provide the fundamental basis for regional stratigraphic and lithologic characterization. Lithologies intersected at all these sites should pass from carbonate oozes in the upper part of the holes down into more indurated calcareous siliciclastic sediments at the base. The 500- to 600-m high-resolution records of Plio-Pleistocene sea-level fluctuations within carbonate oozes targeted at Sites GAB-07A, GAB-08A, and GAB 09A should be achievable with double APC and XCB drilling, with triple APC at Site GAB-09A providing additional resolution.
The sites predominantly targeting cool-water carbonate facies objectives (Sites GAB-03B, GAB 04B, and GAB-05B) should be drilled using double APC and XCB, with the deeper (Cretaceous) parts of Site GAB-04B possibly requiring RCB, and the siliciclastic sequence in the deeper part of Site GAB-05B certainly requiring RCB.
Direct seismic ties connecting the dry oil exploration well Jerboa-1 (Fig. 1) to all sites-except Site GAB-01C and GAB-13B-demonstrate that there is negligible likelihood of encountering hydrocarbons, and vitrinite reflectance data show that most or all of the sedimentary succession underlying these shallower sites is thermally immature. Water depths at Sites GAB-01C (3884 m) and GAB-13B (4465 m) are too great for any significant safety risks.
To 182 Logging Plan
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