Permian 87Sr/86Sr chemostratigraphy from carbonate sequences in South China

Abstract

A continuous strontium isotope profile with high-resolution sampling is desirable to calibrate multiple global events, realize temporal correlation among different continents, and understand tectonic history of the Permian Period. In this paper, we analyzed 90 micritic limestone samples from South China and 7 samples from Iran, with the aim to gain new 87Sr/86Sr data and obtain a curve of Sr isotopes for the Permian. The concentrations of Mg, Fe, Mn, and Sr are used to discriminate possible diagenesis of the samples. A comparison of those 87Sr/86Sr values between South China and southern Urals confirms that Sr-isotope proxy has the potential to be used for time calibration and correlation in regions where biostratigraphic or radiometric markers are not available. The 87Sr/86Sr curve obtained in this study shows a trend comparable with the LOcally WEighted Scatterplot Smoothing (LOWESS) regression curve from the previous studies. A continuous decline trend from the latest Carboniferous to late Guadalupian was shown, and the lowest 87Sr/86Sr values in the late Capitanian was constrained within the interval from the conodont Jinogondolella shannoni/J. altudaensis to J. xuanhanensis zones. It is followed by an increasing trend to more radiogenic values in the Lopingian with a minor fluctuation in the early Wuchiapingian. We consider that mid-ocean ridge spreading and increasing continental weathering during the transition from convergence to the breakup of Pangea as the dominant factors driving the changes of the seawater Sr isotope ratios.