LOGGING PLAN
All sites should be logged with standard logging tool strings (triple-combo, formation microscanner [FMS]/sonic), together with deployment of the well seismic tool (WST) and geological high-sensitivity magnetometer tool (GHMT) at selected sites. The geophysical logs (triple-combo) will be important for evaluating the lithostratigraphic response of cool-water carbonates to sea-level and climatic fluctuations. The fine-scale characteristics of the bedding, including pore spaces, bioturbation, fractures, and stylolites, may be imaged through FMS.
Integrated interpretation of FMS and geophysical logs should provide a good complement to cores in describing the lithostratigraphy. Diagenesis in carbonates usually is well expressed through changes in porosity and chemical precipitation of soluble elements (such as uranium), leading to large changes in log properties seen on sonic, resistivity, density, and neutron gamma-ray logs. Thus, the diagenetic changes in the carbonate sediments, another key objective of the leg, may be evaluated through the petrophysical response measured in the wireline logs. Magnetostratigraphic characterization at selected deeper penetration sites using the GHMT string should also contribute to the sedimentary/stratigraphic objectives and intersite correlation.
Interstitial fluid characterization from cores will be the primary tool for the fluid-flow objectives, with logging data being of secondary importance. However, the assessment of fracture networks and basic fluid properties using sonic and resistivity logs, together with FMS images should provide an important contribution to this leg objective.
A detailed correlation between cores and logs and the extensive suite of high-quality seismic reflection data, including the closely spaced site survey grids and regional 2-D lines, will be critical for understanding the 3-D architecture of the Cenozoic sequences and for compiling a detailed sequence stratigraphy. Accordingly, check-shot (WST) surveys, at 30- to 50-m spacing, should also be run at all sites-except Site GAB-08A (where data from adjacent Sites GAB-07A and GAB-09A will be applicable).