Lithostratigraphy and Microfacies Analysis of Upper Triassic Deposits in the Southern parts of Lut Block, Central Iran Microcontinent

In order to conformity of the sedimentary environment and biological faunal assemblage of Late Triassic deposits in the Central Iran subcontinent, stratigraphical section in the Lut block was selected. Shahdad section in the mentioned block with a thickness of 340 meters is mostly composed of shale, sandstone and limestone. According to the identified index microfossils, 10 interval biozones ( Triasina hantkeni, Trochammina almtalensis, Ophtalmidium exiguum, Agathammina oustroalpina, Duostomina alta, Planiinvoluta regularis, Ammodiscus parapriscus, Pilamminella falsofriedli, Glomospirella minima, Tetrataxis inflata, Interval Zone) were recognized in the Upper Triassic deposits. Based on the identified biozones, the geological age of the studied sequences, considered as Late Norian- Earlist Lias which is equivalent to the Howz-e- Khan and Qhadir members of the Nayband Formation in central Iran. Distribution of scattered coral reefs and absence of turbidite sediments indicate a relatively gentle and uniform homoclinal shallow carbonate platform. Also diversity of foraminifera in this basin show the normal conditions of the initial environment in terms of water circulation, salinity and oxygen levels. In general, the facies of the sedimentary basin of the Upper Triassic deposits in the region are formed from the lagoon or near the coast to the shallow area of the coastline with high to medium energy and to the open sea area in the range of marginal reefs.