Geological Society of America

249 Stratigraphy (Posters)

Wednesday, 12 October 2011
9:00 AM - 6:00 PM
Hall C

STRONTIUM ISOTOPE STRATIGRAPHY FROM THE LATE PERMIAN TO EARLY TRIASSIC OF ZAL, IRAN

Paper number: 249-20
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Alexa R.C. Sedlacek Presenting Author
The Ohio State University, Columbus, OH
Matthew R. Saltzman
The Ohio State University, Columbus, OH
Thomas J. Algeo
University of Cincinnati, Cincinnati, OH
Micha Horacek
Lehr- und Forschungszentrum Francisco Josephinum, Wieselburg, N/A
Kenneth Foland
The Ohio State University, Columbus, OH
J.S. Linder
The Ohio State University, Columbus, OH
Amanda L. Howard
The University of Colorado, Boulder, CO
Christopher Sedlak
The Ohio State University, Columbus, OH
Andrew P. Walters
University of Arizona, Tuscon, AZ

Abstract

Late Permian to Early Triassic marine precipitates record an increase in seawater ⁸⁷Sr/⁸⁶Sr from approximately 0.707 to 0.708. Because Sr has a long residence time in the oceans, seawater values are homogenous and changes occur synchronously. This long residence time also ensures that changes in ⁸⁷Sr/⁸⁶Sr occur at a lower frequency than δ¹³C, which can make strontium isotope stratigraphy useful as an independent correlation tool during periods of increased volatility in the carbon cycle, such as the Early Triassic. Well-preserved brachiopod calcite and conodont apatite have been used to create a global composite seawater curve. However, because sample material is often in limited supply, most strontium isotope studies of Permian-Triassic strata show low resolution sampling of single sections or composites of multiple sections.

Here we present ⁸⁷Sr/⁸⁶Sr of bulk carbonate samples from the Permian-Early Triassic Zal section in Iran. This section was deposited along the Neotethyan margin and underwent relatively continuous deposition from the late Permian through Early Triassic. The resulting thick carbonate sequence enables high resolution sampling. The strata were biostratigraphically constrained and the samples were analyzed for δ¹³C_carbin a previous study. The resulting ⁸⁷Sr/⁸⁶Sr values produce a well defined curve increasing from approximately 0.7071 below the Permian-Triassic boundary to 0.7081 in the Spathian, and the data are consistent with the reported values of other biostratigraphically constrained sections. Sr concentrations of over 1000 ppm in many samples also increase confidence that these are relatively unaltered Permian-Triassic seawater ⁸⁷Sr/⁸⁶Sr values. Because of increased volatility in the carbon cycle during the Early Triassic, Sr isotope stratigraphy may be useful in correlating carbon isotope excursions between sections. The rise in ⁸⁷Sr/⁸⁶Sr in the Early Triassic is consistent with an increase in continental weathering caused in part by higher temperatures coupled with a loss of vegetative cover. Of particular note in the Zal section, a change in the rate of ⁸⁷Sr/⁸⁶Sr rise at the base of the Olenekian may be due to decreased sedimentation rates or needs to be confirmed in other sections in which sedimentation rates are better constrained.