In all samples recovered at Leg 189 Sites 1168, 1170, 1171, and 1172, calcareous nannofossils were abundant and generally well preserved. Using the Gartner (1977) Pleistocene zonation scheme, a biostratigraphic analysis of these four sites was performed. A hiatus was observed at Sites 1168 and 1172 that eliminates the Helicosphaera sellii Zone, a time interval of ~0.3 m.y. Similar hiatuses were noted at DSDP Site 282 off the Tasman subcontinent (Edwards and Perch-Nielsen, 1975), ODP Site 1127 on the Great Australian Bight (Ladner, 2002), ODP Site 1088 in the South Atlantic Ocean (Flores and Marino, 2002), and ODP Site 1165 in Prydz Bay, Antarctica (Fontanesi and Villa, 2002). This hiatus has been attributed to a major lowering of sea level (Brunner et al., 2002), which is supported by its manifestation at shallower Leg 189 sites.
The presence of Discoaster brouweri only at Site 1172 suggests that surface waters were warmer there than at Sites 1168, 1170, and 1171 in the late Pliocene. Greater species diversity at Sites 1168 and 1172 than at Sites 1170 and 1171 also suggests the presence of a paleo-STF across the area during the Pleistocene. Similar sedimentation patterns were observed at all Leg 189 sites, with Site 1168 having the lowest average sedimentation rate throughout the Pleistocene. Sedimentation was uniform across the Pliocene/Pleistocene boundary, with a hiatus (Sites 1168 and 1172) or slower LSR (Sites 1170 and 1171) noted from ~1.26 to 1.59 Ma and then fairly uniform sedimentation to the top of the core.
The nannofossil biostratigraphy reported here agrees well with the biomagneto-benthic oxygen isotope, and light reflectance stratigraphy reported by Stickley et al. (this volume). The disagreement with BOI datums in Hole 1170A may have been caused by the disturbed nature of the cores through that interval (Fig. F3). The discrepancy with the magnetostratigraphy in Hole 1172A needs further examination, as does the puzzling apparent diachroneity of the LO of R. asanoi.