Lithofacies and Sedimentary Environments of Aghajari Formation in Dehsheikh Mountain, West of Shiraz, Iran

Aghajari Formation, known as Upper Fars Group, is developed throughout the Folded Zagros Zone and has a thickness of 2966 m in its type section in SW of Iran and 1473 m in the study area, located 20 km west of Shiraz. Aghajari Formation, in this area, consists of three major facies associations. These are "fine", "medium" and "coarse" grained terrigenous sediments, usually interpreted as channel deposits. Fine member deposits, mainly siltstone and mudstone, are the most abundant facies at lower part of Aghajari Formation. These deposits belong to inter-channel areas which receive sediment during floods. Medium member deposits consist a variety of Lithofacies: sharp-sided sandstone beds, cross-bedded sandstones, trough cross-bedded sandstones, cross-laminated sandstones, parallel-laminated sandstones and lateral accretion (epsilon) crossbedding. These features reflect the episodic and decelerating nature of the responsible flows. Coarse member deposits consist of micro-and macro-conglomerates. Micro-conglomerates generally occur as thin beds, only a few clasts thick and interbedded with sandstones and mudstones. Macro-conglomerates, with tightly packed clast supported frameworks, are the main facies that commonly grade through stratified pebbly sandstones into variously bedded sandstones. Bed thicknesses together with clasts sizes, vary from bottom to the top and usually increase upward. In lower parts of the sequence (small scale), bed thickness and clast size vary randomly; the conglomerates are commonly separated by fines, but in many cases these are scarce. In upper parts of the sequence (large scale), coarsening upward trends occur at the scale of tens of meters, recognized on the basis of maximum clast size. These conglomerates are interpreted as channel lags. The clasts of the conglomerates are extra-formational and derived from the erosion of neibouring or farther uplands. Upward coarsening in units of a few meters thick is attributed to the gradual reactivation of a channel after an interval of temporary abandonment in the braided complex. At the larger scale, the grain-size changes may be accompanied by changes in the relative abundance of constituent facies. Changes at this scale are commonly attributed to tectonic causes. There are also three minor facies associations. These are "gypsum", "marl" and "algal limestone", interpreted as playa lake and shallow lake sediments.