Measuring the cored sediments every 2 to 4 cm on the MST provided us with the highest temporal resolution data set collected during Leg 177. Physical properties are a function of sediment composition, structure, and porosity. Moreover, they are a tool for hole-to-hole correlations and comparisons among sites. Glacial-interglacial fluctuations in sediment composition were observed in GRA bulk density. High values in sediments at the northern sites are consistent with overall high carbonate contents, particularly in interglacial intervals. High percentages of biogenic opal (high porosity) result in a decrease of sediment bulk density during interglacials at the southern Sites 1093 and 1094. The opposite is observed in the alternating glacial deposits that have higher terrigenous percentages. At Site 1094, magnetic susceptibility and NGR show high signal amplitudes, but with different character. The shape of magnetic susceptibility is rectangular, whereas NGR displays an asymmetric, sawtooth pattern with highest intensities toward the end of glacial periods (Fig. 10). This indicates that both signals contain different information regarding terrigenous sediment components. Signal cyclicities are strongly developed in the Pleistocene sequences at Sites 1089, 1091, 1093, and 1094, and also in the continuous early Miocene to late Eocene sequence at Site 1090. These cyclic variations in lithologic parameters may permit the development of orbitally tuned age models in conjunction with biomagneto- and stable-isotope stratigraphies.
Diffuse spectral reflectance measurements obtained from the SCAT and the Minolta CM 2002 photospectrometer contributed greatly to the overall success of the leg, providing high resolution lithostratigraphic records in real time. These data provided important stratigraphic constraints for hole-to-hole correlation during the generation of shipboard spliced composite sections. At Sites 1088, 1089, and 1092, interglacial carbonate-bearing sediments were easily discernible from darker, diatom-rich glacial sediments. The spectral reflectance signals were especially important for correlation of the biosiliceous oozes at Sites 1091, 1093, and 1094, where magnetic susceptibility signals dropped below measurable values during interglacials. Records of reflectance also proved extremely useful as geochronologic tools during Leg 177. In conjunction with biostratigraphic and magnetostratigraphic datums, preliminary estimates of MISs were inferred on the basis of sediment brightness (Fig. 16).
Some of the oldest sediments thus far measured for diffuse spectral reflectance were recovered in the Miocene to Eocene sequences from Sites 1088, 1090, and 1092. The continuous lower Miocene to upper Eocene sequence at Site 1090 is noteworthy for the high-amplitude SCAT signal in the APC cores that span from early Miocene to Oligocene time, as well as in the deeper XCB sequence from which the cores were measured with the CM-2002 photospectrometer (Fig. 17). Leg 177 spectral reflectance records hold great potential for development of high-resolution age models and proxy estimation of sediment mineralogy.
To 177 Summary - Pore-Water Geochemistry
To 177 Table of Contents