عنوان مقاله [English]
نویسندگان [English]چکیده [English]
According to facies analysis and sedimentological data integrated with statistical analysis, five microfacies (MF) and two lithofacies (LF) are identified in the Sargelu Formation (Middle Jurassic), exposed in the Lurestan sub-basin. The facies associations indicate the presence of three sunenvironments including the basin / shelf, slope and middle shelf facies belts with pelagic/hemipelagic sedimentation, periodically influenced by depositions of turbidites and tempestites. The sequence of identified sedimentary facies shows that among the main factors controlling the facies character, two factors of oxygen content and intra-basinal flows are the most important ones affecting the deposits of the Sargelu Formation. Statistical investigation on the distribution of size and skewness of Posidonia-containing microfacies, especially Posidonia Wackestone – Packstone (MF-G) also confirms that the Sargelu Formation deposited in a low-energy basin–outer shelf setting and high energy slope and middle shelf facies belts. The widespread occurrence of intervals containing Posidonia species was linked to nutrient supply and oxygen supply by marine currents. Differences in the Posidonia distribution pattern in the Wackestone – Packstone microfacies (MF-G) led to the decomposition of this microfacies into four subfacies (MF-G1, MF-G2, MF-G3, MF-G4), which differ in the patterns of statistical skewness and the position of sub-facies along the depositional profile. In this regard, the left-skewed distribution points toward the slope, whereas the right-skewed distribution points to the middle shelf, and the bimodal-skewed distribution indicates the outer basin/shelf subenvironment.