Establishment of oceanic conditions based on original mineralogy in end-Permian time using uranium log, central Persian Gulf

The original mineralogy of carbonate- evaporite series of Kangan and Dalan formations in central Persian Gulf area has been determined in this study. Uranium and strontium elemental concentrations were determined in the samples of two wells using inductively coupled plasma tool. The concentrations of these two elements show the same variations in the studied formations. Comparison of these elements with uranium wire line data showed the same trend. As both uranium and strontium preferentially enrich in aragonite other than calcite, they can be used for determination of the original mineralogy of carbonate deposits. The results showed that in the end-Permian time, there was an aragonite sea stage that was favorable of life for carbonate secreting organisms. After that, an equilibrium condition was dominated with simultaneous precipitation of aragonite and calcite. At the end-Permian time just below the Permian-Triassic boundary, there was an acidic condition that was hostile to life. Comparing this period with other sections withcomplete end-Permian record showed that there is a gap in these sediments. Using carbon- hydrogen- uranium and oxygen system, anoxic conditions determined at the later stage. These results show that combination of acidic and anoxic conditions made a serious problem for life at the end-Permian time in central Persian Gulf area at the time of deposition.