Cyclostratigraphy of the Lower Triassic Kangan Formation in the Salman gas field, eastern Persian Gulf, Iran

Abstract

Cyclostratigraphy plays a pivotal role in detecting and reporting Milankovitch cycles in sedimentary successions which allows for creating an independent astronomical time scale and estimates of sediment accumulation rates. In this study, cyclostratigraphic analysis of petrophysical logs from Lower Triassic Kangan Formation was performed in two wells of the Salman gas field, eastern part of the Persian Gulf, Iran. The results of power spectral analysis in the two studied wells reveal the main spectral peaks at wavelengths of long-eccentricity, short-eccentricity, obliquity, and precession cycles. Based on the orbital tuning using the long-eccentricity cycles, a floating astronomical time scale was established, according to which the depositional duration of Kangan Formation was estimated to be 1.6 ± 0.1 Myr. As well as, the duration of the Induan Stage of the Early Triassic Epoch in this study is estimated to be at least 1.6 Myr. Also, by integrating cyclostratigraphic analysis, results of the statistical methods of sedimentation rate evaluation, i.e., evolutionary correlation coefficient (COCO), it was estimated that the sedimentation rates of Kangan Formation in the two studied wells of Salman gas field increased from ~8 cm/kyr in the bottom to about 12–18 cm/kyr in the upper part, which were linked with the delayed life recovery in Early Triassic. We also observed an enhanced sedimentary noise (ESN) interval in eCOCO maps of the K1 member (upper part of Kangan Formation) at two studied wells, which were linked with the global sea-level fall in the late Griesbachian substage of the Early Triassic. The results of this study show that cyclostratigraphy has made an effective contribution towards analyzing sea-level change and estimating sediment accumulation rates and depositional duration of the Kangan Formation.