The biostratigraphic record at both Sites 1143 and 1146 is apparently continuous and clearly resolved in the sediments examined for this study. One exception to the complete delimitation of this record was the FO of Globoturborotalita nepenthes at Site 1146. Though strict definitions were applied for this species and its ancestor, Globoturborotalita druryi, its sporadic record and stratigraphic overlap with Globorotalia fohsi s.l. necessitated combining Zones N13 and N14. This overlap has been found elsewhere. A similar transposition of G. nepenthes and G. fohsi s.l. datums was observed at Deep Sea Drilling Project (DSDP) Sites 563 and 608 (see the discussion by Berggren et al., 1995). A second exception may lie at Site 1143, between 10.49 and 8.58 Ma. In this interval the planktonic foraminiferal and calcareous nannofossil datums appear to cluster and may represent a diastem.
At both sites the planktonic foraminiferal biostratigraphic record agrees well with the corresponding calcareous nannofossil record. Of particular note are the rapid changes in sedimentation rates observed between 10.49 and 5.54 Ma (Fig. F3) at Site 1143. These changes in sedimentation do not correspond to a change in lithologic units or shipboard geochemistry. Site 1146 does exhibit a lithologic change that corresponds well to a significant change in sedimentation rates at ~15.1 Ma as determined by this study. However, the shipboard geochemical record shows no corresponding change in trend. Mass accumulation rates at Site 1146 are sharply higher in the interval from 16.4 to 15.1 Ma and may be the result of lowered sea level or greater fluvial input. Both sites have a second interval of elevated mass accumulation rates from 8.58 to 6.4 Ma, which may be due to the onset of the East Asian monsoon.
The planktonic foraminiferal species observed in this study also provide several continuous, well-represented evolutionary lineages. For example, the following complete lineages were present in the sediments studied at both sites: the Globorotalia merotumida-Globorotalia plesiotumida-Globoratlia tumida plexus; the Globorotalia archeomenardii-Globorotalia praemenardii-Globorotalia menardii plexus; the Globorotalia peripheroronda-Globorotalia peripheroacuta-Globorotalia praefohsi-Globorotalia fohsi plexus; and the Globigerinoides bisphericus-Praeorbulina spp.-Orbulina spp. plexus. These lineages offer a rich opportunity to examine in detail the complex evolution of the species that compose them.