The physical properties measurements made on both discrete samples (porosity and bulk density) and the MST (magnetic susceptibility and GRA density) for Palmer Deep Sites 1098 and 1099 are described. Three boreholes are studied, Hole 1098C and a single section joined from the geographically close boreholes 1099A and 1099B.
Cross-correlation of bulk density and GRA density has enabled validation of the GRA measurements, from which a high-resolution porosity curve has been derived for both analyzed sections. Four distinct petrophysical groups were observed for each borehole from a simple visual examination of magnetic susceptibility crossplotted with GRA density.
Plotting the variation in petrophysical group, magnetic susceptibility, GRA density, and the derived high-resolution porosity vs. depth for both sites revealed that each borehole could be zoned into a number of distinct petrophysical units based on the dominant petrophysical group(s), along with the magnitude and variance of the other properties. These petrophysical zones provide a much greater subdivision of the sedimentary sequence than was possible from the shipboard core descriptions.
Whereas some of the observed zoned unit boundaries coincide with recognized lithologic boundaries, most do not, and clearly there are boundaries within the sedimentary sequence that are not apparent from a visual description of the core. The petrophysical classifications draw attention to the alteration of magnetic susceptibility levels in the upper 25 m of both sections. The porosity data add to the evidence that this variation may be due to climate-induced changes in biogenic sedimentation rates, as suggested by Leventer et al. (1996), while also adding another mechanism for the susceptibility signal variations. The data also suggest that the diamict at Site 1099 is petrographically graded with water-lain sediments, suggesting that the diamict may also be water lain. This argument is backed up for the diamict at Site 1099 by high porosities, whereas the diamict at the base of Hole 1098C is closer to terrestrially lain diamict porosities. Finally, evidence is given for the overprinting of the physical properties of nonturbidite materials by turbidites, as well as evidence that the turbidites may only rework shallow sediments from near the seabed surface.
The results show, generally, the usefulness of cross-correlation for determining variations in the materials examined that are invisible to the eye, particularly in delimiting units in bioturbated material, using a methodology can be used during the short time periods available during Ocean Drilling Program (ODP) legs.