CONTRIBUTIONS IN THIS VOLUME

Wei (Chap. 5, this volume) presents new nannofossil data from all three sites. Data from Sites 1071 and 1072 do not result in any change in the estimated ages of interpreted sequence boundaries. This is due to the rarity of fossils at these shelf sites and to the very significant regional offlap that results in large hiatuses. At Site 1073, the first appearance of Emiliania huxleyi at 120 mbsf marks the base of Zone CN15 (260 ka), slightly lower than specified in the Leg 174A Initial Reports volume. E. huxleyi increases abruptly in abundance around 70 mbsf at the base of the E. huxleyi acme zone (~85 ka). The recognition of Helicosphaera sellii in Sample 174A-1073A-57X-4, 54-55 cm, below the interpreted location of surface pp4(s) at 519.8 mbsf, suggests an age for that surface of <1.3 Ma. However, the presence of Calcidiscus macintyrei in Section 174A-1073A-57X-6 indicates an age >1.6 Ma. Since surface pp4(s) is known to be older than 1.4 Ma at the shelf sites, it is likely that the stratigraphically highest occurrence of Helicosphaera sellii is only an apparent top beneath the interpreted sequence boundary where it has been traced to the upper slope. In that case, surface pp4(s) is best dated as 1.6-1.4 Ma.

Savrda and Krawinkel (Chap. 3, this volume) provide a comprehensive summary of Pleistocene ichnofabrics at Site 1073, data that underpin the article by Savrda et al. (2001b). Thoroughly bioturbated intervals dominate the section and exhibit variable fabrics. Some are monochromatic and homogeneous; others are characterized by homogeneous background fabrics overprinted by diffuse burrow mottles.

Krawinkel (Chap. 6, this volume) summarizes the heavy mineral content of sandy intervals at each site. The bulk of the samples analyzed were obtained from shelf sites because sediments at slope Site 1073 are predominantly fine grained. Eight distinct mineral associations are recognized. In the interval overlying surface pp3(s), amphiboles and pyroxenes dominate, with generally high but variable proportions of garnet and low proportions of zircon, tourmaline, and rutile (ZTR). Below surface pp3(s) but above surface pp4(s), the proportions of ZTR increase at the expense of the other minerals in the overlying assemblage. Between surfaces pp4(s) and m0.5(s), heavy mineral assemblages are highly variable, with a distinct downsection decrease in the proportion of ZTR and an increase in the proportion of amphiboles and pyroxenes.

Hoyanagi and Omura (Chap. 4, this volume) report on the results of grain-size analysis. They provide a series of histograms for Sites 1071 and 1073 and plots of average grain size as a function of depth for all three sites. These data elaborate on the qualitative shipboard descriptions of cores.

Claypool et al. (Chap. 1, this volume) focus on microbially mediated redox diagenetic processes. Oxidation of organic matter results in dissolved CO₂ with about the same ¹³C value as the starting organic matter. Subsequent reduction of CO₂ to form CH₄ leads to significant ¹³C depletion in the CH₄ and to ¹³C enrichment of the residual CO₂ in pore water samples. These processes are well displayed in data from Sites 1071, 1072, and 1073. The ¹³C values for CO₂ from shelf Sites 1071 and 1072 vary downsection but are in the range of -12 to -27 (with respect to the PDB standard). At slope Site 1073, ¹³C values for CH₄ are highly depleted (-62 to -84); corresponding ¹³C values for CO₂ tend to be positive (<9.9), with negative values restricted mainly to the upper 20 mbsf.

Malone and Martin (Chap. 2, this volume) provide isotopic data (¹⁸O, D, and ⁸⁷Sr/⁸⁶Sr) for interstitial water samples from all three sites. Two well-developed Cl^- and ¹⁸O minima are observed at Site 1071, at the approximate level of upper Pleistocene surface pp3(s) and close to upper Miocene surface m0.5(s). Similar minima are observed also at Site 1072 near surface pp3(s), but samples were not recovered at that site from the level of surface m0.5(s). The authors suggest that the observed freshening may indicate relict water. However, no obvious freshening is observed at the level of the intervening sequence boundary pp4(s). At Site 1073 on the continental slope, both ¹⁸O and D values decrease downward to a depth of ~300 mbsf (by ~2 for ¹⁸O and by ~12 for D), below which they change little to a depth of >600 mbsf.