7. Pleistocene Deep-Sea Sediment in ODP Hole 1149A, Nadezhda Basin: Sources, Alteration, and Age Controls (0-800 ka)¹

Michael Urbat² and Thomas Pletsch³

ABSTRACT

We employed several approaches to refine age estimates for the late Pleistocene sedimentary section recovered from Ocean Drilling Program Hole 1149A, which is located in the abyssal plain of the Nadezhda Basin in the northwest Pacific Ocean. Our study is based on a combination of paleo- and rock magnetic as well as geochemical-mineralogic X-ray fluorescence and X-ray diffraction data measured on 300 pairs of samples. These were taken at high resolution (1 sample per 3-5 k.y.) from the uppermost 32 m in Hole 1149A, which covers the Brunhes Chron and extends into the Matuyama Chron. This section provides an expanded record of eolian dust (supplied from the Asian continent), of changing volcanic ash input, and of siliceous plankton accumulation, with recurrent diagenetic intervals in a deep-sea environment. We used normative calculations on the basis of Al and Cr contents to discriminate between the major groups of components (terrigenous, volcanogenic, biogenic, and diagenetic) in combination with our magnetic results. The magnetic signal in Hole 1149A is driven dominantly by the varying inputs of eolian dispersed ash and terrigenous dust. A glacial-interglacial influence on the record is established by a correlation of the CaO record from Hole 1149A to the SPECMAP ¹⁸O composite curve. Despite the generally excellent paleomagnetic properties of the sediment, there is no record of polarity events during the Brunhes Chron to allow construction of further age tie points nor is the record suitable for relative paleointensity stratigraphy. Several intervals are characterized by dramatic changes in rock magnetic parameters and adjacent enrichments in diagenetic minerals. These intervals correspond to paleoredox boundaries, where suboxic conditions promoted the destruction of the primary magnetic signal and the precipitation of rhodochrosite (MnCO₃).

¹Urbat, M., and Pletsch, T., 2003. Pleistocene deep-sea sediment in ODP Hole 1149A, Nadezhda Basin: sources, alteration, and age controls (0-800 ka). In Ludden, J.N., Plank, T., and Escutia, C. (Eds.), Proc. ODP, Sci. Results, 185 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/185_SR/012/012.htm>. [Cited YYYY-MM-DD]

²Department of Geology, University of Cologne, Zülpicherstrasse 49a, 50674 Köln, Germany. m.urbat@uni-koeln.de

³Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Stilleweg 2, 30655 Hannover, Germany.

Initial receipt: 16 January 2002
Acceptance: 5 February 2003
Web publication: 29 September 2003
Ms 185SR-012