Strontium Isotope Stratigraphy of Cretaceous Sediments at Sites 1183 and 1186, Ontong Java Plateau

Abstract

Strontium isotope stratigraphy of the Cretaceous sections recovered in Holes 1183A and 1186A generally matches trends expected from the seawater Sr isotope curve. Combined with biostratigraphic data, the 87Sr/86Sr measurements provide a good chronostratigraphic framework for these holes. In the mid-Cretaceous where the seawater Sr isotopic curve changes direction several times, biostratigraphy removes ambiguity in interpreting 87Sr/86Sr values. Furthermore, 87Sr/86Sr values refine the interpretation of several mid-Cretaceous unconformities suggested by nannofossil biostratigraphy. For the Campanian–Maastrichtian sediments in both holes, ages predicted from Sr isotope stratigraphy are as much as 2.5 m.y. younger than those from nannofossil stratigraphy. This offset likely results from differences in the way that ages are calibrated to nannofossil datums and the seawater Sr isotopic curve. Numerous Sr isotope values are high for their stratigraphic position, suggesting incorporation of excess 87Sr presumably derived from terrigenous clays. Other Sr isotope values suggest minor errors in the estimated ages of nannofossil datums. 1Bralower, T.J., Fullagar, P.D., McCay, T.A., MacLeod, K.G., Bergen, J., and Zapata, E., 2004. Strontium isotope stratigraphy of Cretaceous sediments at Sites 1183 and 1186, Ontong Java Plateau. In Fitton, J.G., Mahoney, J.J., Wallace, P.J., and Saunders, A.D. (Eds.), Proc. ODP, Sci. Results, 192, 1–19 [Online]. Available from World Wide Web: . [Cited YYYYMM-DD] 2Department of Geosciences, Pennsylvania State University, 503 Deike Building, University Park PA 16802, USA. bralower@geosc.psu.edu 3Department of Geological Sciences, University of North Carolina, Campus Box 3315, Mitchell Hall, Room 107, Chapel Hill NC 27599-3315, USA. 4Department of Geological Sciences, University of Missouri, 101 Geology Building, Columbia MO 65211-1380, USA. 5British Petroleum, 501 Westlake Park Boulevard, Houston TX 77079, USA. 6Department of Geology, Faculty of Engineering, Universidad Central de Venezuela, Caracas, Venezuela. Initial receipt: 29 April 2003 Acceptance: 13 January 2004 Web publication: 17 March 2004 Ms 192SR-106 T.J. BRALOWER, ET AL. STRONTIUM ISOTOPE STRATIGRAPHY 2