Analysis of the environmental conditions in Upper Permian deposits of NW Iran based on redox-sensitive trace metals

Authors

1 Assist. Prof., Dept., of Geology, Faculty of Sciences, Lorestan University, Khorramabad, Iran

2 Ph. D. (graduated), Dept., of Geology, Faculty of Sciences, Lorestan University, Khorramabad, Iran

Abstract

The lack of oxygen is considered as one of the main causes of mass extinction before Permian-Triassic boundary (ca. 251.9 million years ago). In this study redox conditions of Upper Permian shales of the Ali Bashi and Zal sections in SW Iran have been evaluated using redox-sensitive trace elements in order to examine the geochemical status of the seawater during Late Permian as well as before and after extinction horizon. According to V/Cr and V/(V +Ni) ratios the redox conditions throughout Upper Permian successions in both sections change from oxic/dysoxic to suboxic and in uppermost Changhsingian Aras Member which is located immediately after extinction horizon the increase of these for-mentioned rations are evident. The Mo/U authigenic ratios in both sections demonstrate their lower values than Mo/U molar ratio of seawater ( ~7.5-7.9) and MoEF and UEF covariate plots show the position of samples of two study sections in oxic/dysoxic to suboxic zones. Considering the obtained results, although there is evidence of low oxygen conditions in some parts of the Upper Permian deposits, the lack of oxygen and anoxic condition did not happen in extinction horizon and even in the Aras Member there was a suboxic status. Therefore, other mechanisms should be investigated for the low faunal diversity of the Upper portion of the Upper Permian deposits of the Ali Bashi and Zal sections.

Keywords