(Table T1) Fossil, magnetic reversal, and additional datums of ODP Leg 189 sites

The aim of this study is to assess the viability of age models based on shipboard and postcruise bio- and magnetostratigraphic datums, as of August 2002, using independently derived control points. The control points are based on matching between-site trends in stable isotope records, carbonate content, and weight percent sand. Site 1170 on the western South Tasman Rise has a good record of magnetic reversals, which suggests a hiatus prior to ~30 Ma (early Oligocene) relating to the Marshall Paraconformity, followed by strongly reduced sedimentation in the late Oligocene. Preservation of the Mi-1 event at this site is evidence for continued sedimentation across the Oligocene/Miocene boundary. Correlation of the Mi-1a event to the record at Site 1090 on the Agulhas Ridge confirms the usefulness of the magnetostratigraphic record at this site. However, the timing of the Mi-1 event at Site 1170 appears different from that at Site 1090, but is constrained by four magnetic reversals. At Site 1171 additional control points are consistent with biostratigraphic datums. Site 1172 is marked by the lowest sedimentation rates of all sites. Additional control points before 22 Ma are more consistent with the biostratigraphy than with the magnetostratigraphy. At Site 1168 we suggest that the magnetic reversal record MR1 provides the best match with the biostratigraphy and additional control points, as well as changes in the biogenic and lithogenic composition of the sedimentary record. The late Eocene/early Oligocene Marshall Paraconformity (base = ~33 Ma at the type location) is evident at Sites 1170-1172, and low sedimentation rates occur at the two eastern sites (1171 and 1172) in the early Oligocene. A change in sedimentation just after the early-late Oligocene transition appears to reduce rates at Site 1170 and strongly affect the biogenic composition of sediments at Site 1168, which is less exposed to the flow of the Antarctic Circumpolar Current. The Oligocene-Miocene transition finally is marked by reduced sedimentation at Sites 1170-1172, but a relatively stronger decrease is noticeable at Site 1168. Above this boundary sedimentation rates are identical at Sites 1168 and 1170 above 21.5 Ma and at Sites 1171 and 1172 above 17 Ma.本研究旨在评估截至2002年8月，基于船上及航后获取的生物地层与磁地层基准面构建年代模型的可行性，所用控制点均通过匹配不同站位的稳定同位素记录、碳酸盐含量与砂粒重量百分比的区域变化趋势独立推导得到。南塔斯曼海岭西侧的1170站位保存有完好的磁反转记录，表明约30 Ma（早渐新世）之前存在与马歇尔假整合（Marshall Paraconformity）相关的沉积间断，随后在晚渐新世出现沉积速率显著降低的现象。该站位保存的Mi-1事件记录，证明其在渐新世/中新世界线前后仍有持续沉积。将Mi-1a事件与厄加勒斯海岭1090站位的记录进行对比，证实了该站位磁地层记录的实用性。不过，1170站位的Mi-1事件出现时间与1090站位存在差异，但可通过四次磁反转进行约束。1171站位的额外控制点与生物地层基准面的结果一致。1172站位为所有站位中沉积速率最低的站位。22 Ma之前的额外控制点与生物地层结果的匹配度高于与磁地层结果的匹配度。在1168站位，我们认为磁反转记录MR1与生物地层及额外控制点的匹配效果最佳，同时该记录也与沉积物的生物成因与陆源组分变化相吻合。 始新世晚期/渐新世早期的马歇尔假整合（模式产地的底界约为33 Ma）在1170-1172站位均有显现，而东侧的1171和1172站位在早渐新世时期沉积速率较低。早-晚渐新世过渡期后的沉积速率变化，似乎导致1170站位的沉积速率降低，并强烈影响了1168站位沉积物的生物成因组分——该站位受南极绕极流（Antarctic Circumpolar Current）的影响较弱。渐新世-中新世界线最终以1170-1172站位的沉积速率降低为标志，但1168站位的沉积速率下降幅度相对更大。在该界线上方，1168与1170站位在21.5 Ma以来的沉积速率一致，1171与1172站位则在17 Ma以来的沉积速率保持一致。