Lithostratigraphy and microbiostratigraphy of the Neogene deposits (the Mishan and Aghajari formations) in the Northeast of Bandar Abbas

The tectonic, morphology, geodynamic, stratigraphic architecture, and paleontological characteristics of the Zagros structural zone have studied by many researchers. However, we aimed to focus on the lithostratigraphy and microbiostratigraphy of the Neogene deposits, exposed in the Northeast of the Bandar Abbas. The studied area positioned at the south domain of the Kurgu Anticline, 65 Km north of the Bandarabbas. The Khurgu Anticline is the last outcropped anticline in the southeast of the Folded Zagros subzone. The studied area has never been studied before for microbiostratigraphical and lithostratigraphical characteristics. The studied successions include Mishan and Aghajari formations, which are outcropped in a syncline-anticline system.

The measured section of 2465 m thick consists of hard limestone, sandstone strata and loose marl, marly limestone, siltstone, non-solidified sandstone, and mudstone deposits. A systematic sampling process resulted in the collection of 324 loose and 54 hard samples. The loose and hard samples have processed for micropaleontological studies. The loose samples soaked in Sodium Sulfate solution and frizzed to disaggregating and washed over 2, 4 and 0.063 mm sieves. The faunal content of dried samples is handpicked and photographed by a Phenom Pro-X Desktop Scanning Electron Microscope connected to a 5MP camera. Several thin sections have prepared from hard samples and studied by a binocular microscope.

The lithostratigraphy of the section comprises limestone (Guri Member) and marly limestone at the base, marl and siltstone with marly limestone in the lower part, mudstone and marl in the middle parts and an alternation of sandstone and siltstone layers in the upper part. The sedimentary environment of the studied succession is marine in the basal and middle parts but in the upper part seems to be a marginal marine environment, influenced by coastal activities. The micropaleontology investigations resulted in the identification of 28 species of benthic, mainly deep benthic taxa, and 19 species of planktonic foraminifera. Based on the distribution of the identified taxa and the planktonic foraminifer’s biozonations (Bou Dagher-Fadel, 2013; Wade et al. 2011; Postuma, 1971; Blow, 1969; Bolli, 1966) and the ranges of the benthic foraminifera (Kender et al., 2008) the studied strata have deposited continually from the Early Miocene to the Pleistocene. The boundary between Mishan and Aghajari formations appears as gradual. The basal part of the Aghajari Formation is deposited in a marine environment.

The studied succession includes the deposits of the Mishan and Aghajari formations and comprises limestone, marly limestone, siltstone, sandstone, and mudstone strata. The basal and the middle parts of the section were deposited in a marine environment and the upper part was deposited in coastal and continental environments. The micropaleontological studies, based on the planktonic foraminifera, resulted in the identification of seven biozones and indicates that this succession deposited from the Lower Miocene to Pleistocene continuously. The sedimentary environment changes are gentle and no sedimentation disruptions had occurred.