172 Scientific Prospectus


Logging is planned at Holes BBOR-4B and BR-1 (each ~350 m in depth). The primary objectives of Leg 172 will depend on good core recovery of material for stable isotope measurements, as well as other paleoclimate proxies. Downhole logging can help achieve the primary goals of this proposal by ensuring that full stratigraphic coverage is achieved through the integration of core and log measurements.Where core recovery is incomplete or core disturbance is high, usually in XCB cored sections, downhole logs will provide continuously sampled physical properties that can serve as proxies for paleoclimatic indicators.

Geophysical logs (sonic, porosity, density, natural gamma, resistivity, and Formation MicroScanner [FMS]) will characterize the sediment. Resistivity, FMS, and sonic logs can provide in situ data on the gas hydrate present in the sediments. FMS images can provide very high resolution (2.5 mm) characterization of sedimentary structures, which are particularly difficult to obtain in XCB cores. In addition, these images show grain-size changes that aid in interpreting sedimentary processes in drift deposits, help orient XCB cores for magnetic studies, and provide a record of resistivity (although not in absolute values) for cyclicity studies. The planned dedicated logging holes are likely to provide a stable borehole and, thus, good quality logs.

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