This research is focused on the Upper Jurassic (Oxfordian-Kimmeridgian) carbonates in Jajarm area, north-northeast Iran. These deposits have very good and wide exposure in this area. Five stratigraphic sections that are studied in Jajarm area is shown in Fig.1. Upper Jurassic sediments have transitionally overlain by Middle Jurassic deep water carbonates and unconformable underlain with fluvial siliciclastic deposits of Early Cretaceous. Thickness increases to the west part of study area and ranges from about 300 to 700m. These deposits mostly consist of gray to light gray and pink to red calicilutite to calcarenite and calcirudite with big ammonites, pelecypods, gastropods and brachiopods in coarser rocks. Interbedded fine and coarse crystalline dolomite are also present. Since Upper Jurassic carbonate rocks (Mozduran Formation) in Kopet-Dagh Basin (NE Iran) are a major gas reservoir, the objective of this study is comparison of lithofacies and depositional history of these formations. Based on five measured stratigraphic sections, field observations, detailed petrographic considerations on more than 500 thin sections, microfacies are analyzed and depositional environment are interpreted. Microfacies petrographically are mainly consist of skeletal grains such as bivalve, foraminifer, gastropod, brachiopod, echinoderm, bryozoan, coral and non- skeletal carbonate grains such as ooid, intraclast and peloid. Mudstone, dolomudstone, pelloid wackestone/packstone, pelloid ooid grainstone and bioclast wackestone/packstone are the most important microfacies that mainly deposited in intertidal-subtidal subenvironment in a carbonate platform (Flugel, 2004, Hips and Haas, 2009). The lacking reef constructers in the shallow water microfacies of study area and decreasing carbonate production led to ramp development. Transitional relation between microfacies in study area is supported carbonate sedimentation in a carbonate ramp (e.g. Brachert et al, 2001). Present of various bioclasts in these sediments also show all subenvironments are connected together. Foraminiferal and pelloid wackestone/packstones are deposited in lagoon environmrnt, ooid grainstone are formed in high energy conditions (Cadjenovic et al, 2008, Hofmann and Keller, 2006), bioclast

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