Biostratigraphy, biofacies and CAI of the late Devonian deposits in Kale-Sardar section, North-east Tabas, based on conodont fauna

Kale-Sardar section, is located at the vicinity of Niaz village, 15 kilometers east of Tabas town. This section consists of 80 m thick and from Late Devonian deposits as known as Shishtu formation that upper part of this section has cut by a fault by Frasnian’s deposits. The entire studied thickness is subdivided into 12 lithostratigraphic units and in order to study of conodont elements, 27 species and subspecies belonging to 7 genera were recognized, that due to these revealed conodont elements, Shishtu formation’s age in the studied section spans from Eifelian to late Frasnian. The Frasnian-Famennian bio event in studied section is located between two intervals linguiformis Zone and Lower to Middle triangularis zones which is located at the top of the dark Frasnian shales and at the base of the thin limestones of the Famennian layer. The microfacies determined in studied section are subdivided into siliciclastic-carbonate and carbonate facies, which were deposited from the shore to the deep part of the marine environment. Gradual changes in facies within stratigraphical sequence, sedimentological hiatus due to sudden change in sedimentary environment’s slope, absence of reef facies (related to Wilson’s 5th facies zone) and presence of discontinuous bioclastic barrier (existence of semi-enclosed lagoon), convey that studied sediments were deposited in a homoclinal carbonate ramp.