LOGGING PLANUnder the primary operations plan, logging will be carried out at each of the five sites with penetration of 300 mbsf (Table 1). Three tool strings will be run at the logged sites: the triple combination (triple combo) (resistivity, density, porosity, and natural gamma logs); the Formation MicroScanner (FMS)/sonic (resistivity image, acoustic velocity, and natural gamma logs); and the geologic magnetic tool (GHMT) (magnetic field, susceptibility, and natural gamma logs). In addition, the third-party Lamont multisensor gamma tool (MGT) with about four times the vertical resolution of standard natural gamma tools will also be deployed on the triple combo string.
Coring seeks to answer questions about rapid and tectonic-scale climate changes and their link to regional oceanographic currents and Southern Hemisphere wind patterns. The expected changes will drive lithologic variability in both the biogenic components as well as the amount and type of terrigenous material that can be well documented by standard logging techniques. The density, porosity, and resistivity logs will provide continuous records of climate related changes in sediment lithology (e.g., percent CaCO3) where core recovery may not be 100%. With higher resolution, the FMS and MGT will provide continuous records of lithologic variability and terrigenous input on orbital to suborbital timescales. The FMS also allows imaging of fine-scale bedding in poorly recovered intervals.
The recovery of continuous sediment sections is a critical component to the success of the leg. Recent paleoceanographic legs with similar high-resolution goals have demonstrated the importance of core-log integration in developing a reliable composite section. The core-log integration program Sagan will be used to correlate downhole natural gamma ray, density, and magnetic susceptibility logs to their counterpart core measurements to provide more precise depth matching of cored sections and real-time assessment of the accuracy of the shipboard splice.
For more detailed information on any particular tool or its application, please see the Borehole Research Group (BRG) website at http://www.ldeo.columbia.edu/BRG/.
Shipboard Laboratory Operations | Table of Contents