Facies analysis and sedimentary environment of mixed carbonate-siliciclastic deposits of Shirgesht Formation in Kalmard Block, Centeral Iran

Field Study and petrography of Shirgesht Formation (Ordovician)، in Kuh-e Asheghan and Kuh-e Rahdar sections، located in Kalmard block in Central Iranian Zone، led to identification of 4 carbonate microfacies associations and 7 siliciclastic petrofacies. These facies associations in conjunction with trace fossils، such as cruziana and skholithos ichnofacies، as well as the results of calcimetry، XRD analysis and SEM images from fine grained samples (shales)، show that these strata have been deposited in barrier island-lagoon depositional system. The trends of interpretated sea level curve، from bottom to the top of the two studied sections، represent relative falling stage in sea level. Moreover، this study shows the effect of regional and local mechanisms in deposition، such as movement of Kalmard basement fault that effected the spatial and temporal variations in sediment supply.