Sedimentary environment, sequence stratigraphy, diagenesis and geochemistry of the carbonate Ruteh Formation in north of Mahabad section

Abstract The Ruteh Formation is the second sedimentary cycle in Alborz basin. The petrography and laboratory studies of these deposits led to the identification of 15 microfacies which were deposited in seven sub-environments including supratidal, intertidal, lagoon, shoal, open marine, middle ramp, and outer ramp. Since there were no turbidity deposits, the lack of marginal reef belt and the gradual changes of facies, it turned out that these sediments were deposited in a homoclinal carbonate ramp. The study of relative sea level changes was done according to vertical distribution of facies and their stacking patterns. These studies lead to identification of four depositional sequences. The petrography data and geochemical analyzes were used in order to identify the diagenetic processes and geochemical changes. The recognized diagenesis processes include micritization, cementation, compaction, stylolitization, silicification, ferrugenation and neomorphysm. These diagenetic processes took place in three diagenetic environments: marine-phreatic, meteoric-phreatic and burial. Geochemical analyzes confirms that the carbonate sediments of Ruteh Formation were originally composed of aragonite, which was eventually recrystallized to calcite during diagenesis. Plotting Sr/Ca versus Mn diagram approved that sediments was subjected to a meteoric diagenesis in a semi-closed to open diagenetic system. The results of this research can be used to provide a sedimentary model for these deposits which completes the palaeogeographical data for the Tethys Ocean. Introduction The geological observations indicating a coherent Iranian-Gondwanaland continental landmass during the Late Precambrian to Permian are consistent with palaeomagnetic data (Berberian and King 1980). Palaeomagnetic evidences from the Upper Precambrian rocks and iron ores of Bafq area in central Iran (Becker et al. 1973), the Lower Paleozoic rocks of kuh-e-Gahkom and Surmeh of the Zagros (Burek and Furst 1975), the Cambrian purple sandstone of the salt range of Pakistan (McElhiny 1970), the Upper Devonian–Lower Carboniferous of the Alborz Mountain in north Iran (Geiroud Formation; Wensink et al. 1978) and from the Upper Precambrian, Ordovician and Permian rocks of central Iran (Soffel et al. 1975; Soffel and Forster 1977) show similar geomagnetic poles with those of Afro-Arabia. These data and the widespread similarity of Paleozoic sedimentary succession indicate that during the Late Precambrian and Pa