COUPLED C AND SR ISOTOPE STRATIGRAPHY OF THE EARLY TRIASSIC OF ZAL, IRAN: A RECORD OF INCREASED WEATHERING

The Early Triassic was a period of environmental perturbations that slowed biologic recovery from the late Permian mass extinction. The Early Triassic carbon isotope record shows rapid fluctuations, and positive carbon isotope excursions are potentially the result of enhanced continental weathering due to episodes of volcanism and warming. One proxy for weathering is the ⁸⁷Sr/⁸⁶Sr of marine carbonate. We present a ⁸⁷Sr/⁸⁶Sr record from a single latest Permian-Early Triassic succession near Zal, Iran that is highly internally coherent, providing a high resolution Sr-isotope curve for this interval. The strata were biostratigraphically constrained and samples were analyzed for δ¹³C in a previous study. At the Zal section, ⁸⁷Sr/⁸⁶Sr increases from approximately 0.7071 below the Permian-Triassic boundary to 0.7081 in the Spathian, consistent with the reported values of other biostratigraphically constrained sections. At the base of the Dienerian, an increase in the rate of ⁸⁷Sr/⁸⁶Sr rise occurs concurrently with the onset of a positive δ¹³C excursion. This elevated rate continues until the Dienerian-Smithian boundary, where δ¹³C reaches a maximum. The increase in the rate of rise in ⁸⁷Sr/⁸⁶Sr in the Dienerian is consistent with previous studies showing evidence of increased bedrock weathering. Elevated weathering rates increased the nutrient flux into the oceans, which enhanced primary productivity and organic carbon burial rates. This study provides the first coupled ⁸⁷Sr/⁸⁶Sr and δ¹³C isotope records, providing a test of the hypothesis that increased continental weathering contributed to enhanced burial of organic matter during positive carbon isotope excursions.