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

• Published in: Gondwana research 2013-07, Vol.24 (1), p.222-232
• Main Authors: Liu, Xin-chun, Wang, Wei, Shen, Shu-zhong, Gorgij, Mohammad Nabi, Ye, Fa-cheng, Zhang, Yi-chun, Furuyama, Seishiro, Kano, Akihiro, Chen, Xiao-zheng
• Format: Article
• Language: English
• Subjects: 87Sr/86Sr ratio; Abadeh; Guadalupian–Lopingian boundary; Iran; Permian–Triassic event boundary; Wuchiapingian–Changhsingian boundary; δ13C
• ISSN: 1342-937X; 1878-0571
• DOI: 10.1016/j.gr.2012.10.012

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 (δ13Ccarb) and strontium isotope ratio (87Sr/86Sr) 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 δ13C excursions, the rising trend of 87Sr/86Sr 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 −0.5m below the base of the main microbialite bed. The GLB is suggested at −46.5m based on the position of the minor δ13Ccarb negative depletion, coupled with the values between 0.7069 and 0.7070 of 87Sr/86Sr and its beginning point of the rising trend, which is above the lowest value 0.7068 of 87Sr/86Sr 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 δ13C excursion and the value 0.7072 of 87Sr/86Sr ratio, the WCB is estimated at 1m 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. 254.6Ma in 87Sr/86Sr-age projecting model and is close to zircon U/Pb dating age from South China. [Display omitted] ► A new approach for chemostratigraphy of δ13C vs 87Sr/86Sr to applied 3 boundaries of the Lopingian in Abadeh section, Iran. ► δ13C defined the locations of boundaries under secular dating constrain supported by 87Sr/86Sr. ► Bioevents and δ13C have been projected with high resolution age constrains.