4. Data Report: Carbon and Oxygen Isotope Geochemistry along a Subducting Pelagic Section Offshore Costa Rica (ODP Legs 170 and 205)¹

Michael Strasser,² Helmut Weissert,² and Stefano M. Bernasconi²

ABSTRACT

In this data report we present results from stable isotope measurements (¹³C and ¹⁸O) on bulk sediment at several sites located on a transect along a subduction margin offshore Costa Rica (Ocean Drilling Program Sites 1039, 1040, and 1253). Comparison of stable isotope compositions (¹³C and ¹⁸O) of the pelagic carbonates Subunit U3C between the reference sites (Site 1039 and 1253) and the underthrust section (Site 1040) reveals similar ¹³C values and minor differences in ¹⁸O values within four specific intervals. Isotope stratigraphy was then used to further constrain the shipboard age models based on bio- and magnetostratigraphy. The resulting age models are in agreement with those derived from biostratigraphy and confirm that the sedimentation rate of the lower Subunit 3C is roughly constant on the order of 50 m/m.y. This is in contrast with the postulated very high sedimentation rates at ~12.7 Ma and lower sedimentation rates (~18 m/m.y.) in the lower part of the section between 16 and 13 Ma, as suggested by shipboard magnetostratigraphic datums.

¹Strasser, M., Weissert, H., and Bernasconi, S.M., 2006. Data report: Carbon and oxygen isotope geochemistry along a subducting pelagic section offshore Costa Rica (ODP Legs 170 and 205). In Morris, J.D., Villinger, H.W., and Klaus, A. (Eds.), Proc. ODP, Sci. Results, 205 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/205_SR/205/205.htm>. [Cited YYYY-MM-DD]

²Geological Institute, ETH Zurich, Universitaetsstrasse 16, CHN H71, CH-8092 Zurich, Switzerland. Correspondence author: strasser@erdw.ethz.ch

Initial receipt: 28 February 2005
Acceptance: 22 November 2005
Web publication: 3 April 2006
Ms 205SR-205