162 Preliminary Report


Our strategy at most sites was to core three holes to refusal using the Advanced Hydraulic Piston Corer (APC) followed by the Extended Core Barrel (XCB). On the deepest holes the Rotary Core Barrel (RCB) was used. This approach allowed the retrieval of continuous sedimentary records without gaps due to core breaks or drilling disturbance. At every site, interhole comparison of magnetic susceptibility, GRAPE bulk density, natural gamma radiation, and spectral reflectance data permitted the development of continuous composite sequences. Furthermore, as these data were collected and compared in real time, we were able to adjust the coring strategy at each hole to provide maximum recovery of intervals that fell at core breaks in the first or second holes.

Triple APC coring was also necessary to exceed normal ODP sampling density guidelines, and thus to permit ultra-high-resolution paleoceanographic studies. At some sites, a 5-cm sample interval will give a temporal resolution of about 300 years. Likewise, triple APC coring provides enough material to generate continuous U-channel sequences with which to study century- to millennial-scale variability in the intensity of the Earth's geomagnetic field, as well as other magnetic properties of the sediments.

We began coring on the Feni Drift (FD in Fig. 5), located on the southeast flank of the Rockall Plateau, at Sites 980 and 981. We gained time at this site despite APC recovery that was significantly deeper than projected in the prospectus. Using this extra time in addition to time gained by an early departure from Leith, we chose also to deepen the next site by about 100 m more than was called for in the prospectus. As a result, Site 982 on the Rockall Plateau was drilled by APC and XCB to refusal at a depth of ~610 mbsf. Departing Site 982, still with significant time savings, we steamed to a second priority, alternate site that was on our cruise track: Site 983 on the Gardar Drift (Fig. 4). We spent about two days recovering three APC holes to approximately 250 mbsf. After coring Site 983, we moved to the nearby Bjorn Drift (Site 984) where we completed our proposed drilling objectives.

After moving north of Iceland, we cored two additional APC holes at Site 907 (907B and 907C) visited previously on Leg 151 (Hole 907A). Following Site 907, we would have proceeded to EGM-4, but for heavy ice cover in that region. As we needed to remain near Iceland to wait for resupplies (i.e., core liners), we elected to drill our second alternate Iceland Plateau site (Site 985). As soon as possible, we proceeded north to Site 986 on the Svalbard Margin. As we were finishing operations at this site, it was apparent that the proposed sites on the Yermak Plateau (including contingency sites) were well within the area of sea ice and hence could not be cored. We thus proceeded to our last target on the East Greenland Margin, Site 987 (EGM-4).

Four holes cored deeper than 400 m were logged on Leg 162, Sites 982, 984, 986 and 987. We typically chose to run the Formation MicroScanner (FMS), the Geological High-Sensitivity Magnetic Tool (GHMT-A), and the Geochemical Logging Tool (GLT) after the Quad Combo. These tools were run in order to measure in situ properties characteristic of the lithology such as bedding structures, downhole magnetic susceptibility, and major element abundances, as well as magnetic polarity sequence. The downhole logs are particularly useful in intervals where shipboard measurements were not possible due to a lack of recovery or coring disturbance, and proved to be extremely interesting when combined with discrete physical properties, pore-water chemistry measurements (e.g., see "Site 982" section of "Results" this report), and seismic stratigraphy. With these data we have also been able to develop synthetic seismograms in order to link more directly the cored sequences to the seismic sequences of the region, an objective that was particularly important on the Svalbard and East Greenland Margins. Likewise, the logging data will allow us to scale the recovered and typically expanded sedimentary sections back to their true subsurface depths.

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