Detailed lithologic descriptions of the materials used are presented in Shipboard Scientific Party (2001b, 2001d, 2001e, 2001f). For processing and counting techniques of individual fossil groups see the overview in Shipboard Scientific Party (2001a). The stratigraphic positions of planktonic foraminiferal, radiolarian, and dinocyst bioevents in these age models are based on analyses of all core catcher samples (resolution ~9 m) or selected core catcher samples for palynology, whereas calcareous nannofossil stratigraphy is derived from analyses of two samples per section (resolution ~75 cm) for the Quaternary, and at least one sample per section (resolution ~1.5 m) for the Miocene. Diatom stratigraphy is based on analyses of all core catcher samples for the Neogene and Quaternary sections and of two to three samples per section (resolution ~50–75 cm) for the Paleogene intervals.
All depths are presented in meters below seafloor (mbsf) and are taken from the JANUS database (www-odp.tamu.edu/database). Correlation of datums observed in overlapping holes allowed refinement of the depth error (in meters) for those datums. Offsets in mbsf between overlapping holes for a particular site are not considered significant at this resolution, except for that between Holes 1171C and 1171D, where the offset is >3 m. Therefore, except for Site 1171, where depths for Hole 1171D are adjusted to correlate with overlapping parts of Hole 1171C, all age-depth data are presented "by hole" for a particular site. Refer to Shipboard Scientific Party (2001b, 2001d, 2001e, 2001f) for information on hole depth offsets and meters composite depth (mcd). Median depths (in mbsf) within the depth error of an event datum are used for simplicity, except where an obvious succession of events calls for otherwise. We acknowledge that by this methodology the FO events may be forced too shallow and the LO events too deep; therefore, depth errors for biostratigraphic datums are noted in Tables T1–T4. In some cases, due to the relatively low resolution of most of the biotic data, it is difficult to distinguish hiatus(es) from condensed sections. Further work is helping to refine these ambiguous intervals.
Amount of core disturbance including flow-in is noted and taken into account in these age models (Figs. F2–F13). In intervals where core disturbance is greatest (e.g., Cores 189-1170A-7H to 14H) and the resulting biostratigraphy is too chaotic to declare an unequivocal solution, we present the most likely scenario by (1) using the most robust and consistent datums (across Leg 189 sites and the Southern Ocean in general) and (2) loosely comparing the resulting sedimentation rate with those from nearby sites in the Southern Ocean that have established age models (e.g., isotopic or biostratigraphic). In such uncertain intervals we also present an alternative age model. Although isotopic work (for example) may help refine some uncertainties, the time frame of highly disturbed intervals may prove difficult to improve any further than is presented here. The geochronological timescale and epochal boundary definitions described in Berggren et al. (1995a, 1995b) are used throughout this report.