Toward High Resolution Isotope Stratigraphy: Permian 87Sr/86Sr and δ13C Stratigraphy from Limestones In China and Nevada

Marine carbonate samples have been collected from the central Pequop Mountains, Nevada and the Tieqiao section, Laibin, China. The collected interval starts in the Gzhelian Stage of the Pennsylvanian and extends through the Wuchiapingian Stage of the Permian. These samples have been analyzed for carbon (δ¹³C) and strontium (⁸⁷Sr/⁸⁶Sr) isotopes as well as detailed biostratigraphy based on both foraminifers and conodonts. Both localities are characterized by continuous exposures of marine limestone each over a kilometer thick.

Two sections were sampled from the Pequop Mountains, Nevada; 1) Ninemile Canyon from the Gzhelian Stage of the Pennsylvanian through the Sakmarian Stage of the Permian and 2) Rockland Ridge from the Sakmarian Stage through the Artinskian Stage. Ninemile Canyon has yielded δ¹³C_carb values starting around 0‰ and culminating in a positive isotope excursion reaching almost +5‰. This carbon isotope excursion has not previously been documented and likely coincides with the biotic change that occurs across the Sakmarian boundary. The ⁸⁷Sr/⁸⁶Sr data shows a decreasing trend starting at 0.70825 in the Gzhelian and reaching low values in the Sakmarian of 0.70779. Rockland Ridge is still being analyzed.

The Tieqiao section in Laibin, China begins in the Artinskian Stage of the Permian and continues through the Wuchiapingian Stage. The ⁸⁷Sr/⁸⁶Sr values start at approximately 0.70773 and continue the decreasing trend seen in the Central Pequop sections reaching an inflection point in the Roadian where the trend changes to more positive values. Integration of all of these geochemical trends with age constraints achieved by refined biostratigraphy will provide a high-resolution isotope stratigraphy for global correlation.