Biostratigraphy and depositional environment of Miocene deposits in the Haft Cheshmeh section, north of Nourabad, Sanandaj - Sirjan Zone

Considering that detail paleontological and sedimentological studies have not been carried out on the northern Nourabad area, this study is based on measured stratigraphic section of the Haft- Cheshme to evaluate and analyize the parameters such as biostratigraphy and sedimentary environments of Miocene deposits, inorder to gain the new information about the geology of the area. In this study, large benthic foraminifers used to identify the biozones and determine the age of these deposits. On the other hand, in order to obtain new information on the formation of these deposits, the study of sedimentary environment was also discussed. For detail study of these deposits, sampling were done at 1 meter interval. A total of 100 samples were collected from a thickness of 127 meters. The sedimentary facies are named based on Flugel (2010) classification. Also, in the designation of carbonate facies, Dunham (1962) and Ambry and Klovan (1971) have been used for the classification of carbonate facies. The lower boundary of Miocene deposits in this section is sharp with Mc unit of ophiolitic complex and the upper boundary is erosional. Based on the studies of the larger benthic foraminifera assemblages, 18 genera and 20 species were identified which represent the Borelis melocurdica- B. melo melo assemblage zone and suggest a Burdigalian age. Also based on the field observations, petrographic studies and textural characteristics as well as the abundance and distribution of foraminiferal fauna and other components, 14 carbonate microfacies have been identified. These carbonate microfacies were deposited in 5 facies belts including lower slope facies, upper slope facies, margin facies, platform-margin sand shoals and lagoon. The existence of coral barrier reefs, intraclasts, aggregate grains and the sudden facies changes and also the absence of vast areas of intertidal flat represent that this sequence deposited on a rimmed carbonate platform.  Also based on the petrographic studies of Bouma Ta and Tb divisions and the existence of the sedimentary structures such as Bouma Ta division (re-deposited carbonates, calciturbidites), the studied section has been deposited on a rimmed carbonate shelf.