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.
1Pfuhl, H.A., and McCave, I.N., 2003. Integrated age models for the early Oligocene-early Miocene, Sites 1168 and 1170-1172. In Exon, N.F., Kennett, J.P., and Malone, M.J. (Eds.), Proc. ODP, Sci. Results, 189 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/189_SR/108/108.htm>. [Cited YYYY-MM-DD]
2Max Planck Institute for Biogeochemistry, Hans Knöll Strasse 10, 07745 Jena, Germany. hapfuhl@yahoo.com
3University of Cambridge, Department of Earth Sciences, Downing Street, Cambridge CB2 3EQ, United Kingdom.
Initial receipt: 2 December 2002
Acceptance: 9 July 2003
Web publication:
12 November 2003
Ms 189SR-108