Late Guadalupian to Lopingian (Permian) carbon and strontium isotopic chemostratigraphy in the Abadeh section, central Iran

The Abadeh section, well-exposed in the Hambast Valley in central Iran, has long been one of the most extensively studied sections because of its continuous carbonate-dominated strata from Lower Permian to Lower Triassic. However, biostratigraphy and correlation with the equivalent sequences in other regions remain controversial. In this paper both carbon isotope excursion (delta C-13(carb)) and strontium isotope ratio (Sr-87/Sr-86) based on bulk carbonate samples have been measured to serve as chemostratigraphical proxies to estimate the three different chronostratigraphical boundaries in the Lopingian at the Abadeh section, including the Permian-Triassic Event (PTEB), the Guadalupian-Lopingian (GLB), and the Wuchiapingian-Changhsingian boundaries (WCB). These three boundaries are important for understanding the marine biological evolution around this critical interval. Based on the delta C-13 excursions, the rising trend of Sr-87/Sr-86 and the value around 0.7073, and the occurrence of microbialite beds, the Permian-Triassic event boundary (=Bed 25 at the Meishan section) is suggested at -0.5 m below the base of the main microbialite bed. The GLB is suggested at -46.5 m based on the position of the minor delta C-13(carb) negative depletion, coupled with the values between 0.7069 and 0.7070 of Sr-87/Sr-86 and its beginning point of the rising trend, which is above the lowest value 0.7068 of Sr-87/Sr-86 ratio in the Paleozoic. The relationship between section thickness and their high-resolution depositional age (projecting age) is interpolated for the whole Lopingian using locally weighted regression scatter plot smoother (LOWESS) of strontium isotopic ratio. Based on the negative delta C-13 excursion and the value 0.7072 of Sr-87/Sr-86 ratio, the WCB is estimated at I m above the lithologic boundary between Unit 6 and Unit 7, much lower than the boundary defined by previous conodont biostratigraphy, but similar to other index fossils. This boundary is projected as ca. 254.6 Ma in Sr-87/Sr-86-age projecting model and is close to zircon U/Pb dating age from South China. (C) 2012 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.