Biostratigraphy, facies analysis and sequence stratigraphy of the Sachun Formation (Interior Fars, Zagros, SW of Iran)
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ORIGINAL ARTICLE
Biostratigraphy, facies analysis and sequence stratigraphy of the Sachun Formation (Interior Fars, Zagros, SW of Iran) Kamal Karimi1 · Massih Afghah1 · Seyyed Hossein Ghetmiri1 · Mohammad Bahrami2 Accepted: 28 September 2020 © The Author(s) 2020
Abstract Two sections of the Maastrichtian–Lower Eocene Sachun Formation, crossing Interior Fars zone, Zagros basin in SW Iran, were selected. To biostratigraphy, facies analysis, paleoenvironment and sequence stratigraphy, foraminifers and lithofacies were studied. Three foraminifer assemblage zones were observed in the studied areas. According to stratigraphic distribution of the identified foraminifers, the Sachun Formation is assigned to Upper Cretaceous (Maastrichtian)—Lower Eocene (Ypersian) age. The sedimentation of the Sachun Formation was controlled by the sea-level fluctuation. According to the sedimentary records, Sachun Formation has been deposited in a tectonically unstable basin. Microscopic investigation confirms the presence of seven microfacies, which can be grouped into four depositional environments: tidal flat, lagoon, shoal, and open marine. A carbonate shallow shelf is suggested for the depositional environment of the Sachun Formation, with the depth of sedimentary basin of the Sachun Formation decreasing from the study area to the south of Fars zone. Sachun Formation facies have been deposited in a shallow depositional basin characterized by permanent sea level changes. The vertical distribution of the investigated lithofacies supports two third-order cyclic sequences in the Sachun Formation, based on shallowing upward patterns in the determined lithofacies. Keywords Sachun Formation · Zagros basin · Biostratigraphy · Sedimentary environment · Sequence stratigraphy
Introduction The Upper Cretaceous–Paleogene is a period of the Earth history in which the close interaction between global climate changes and biological evolution can be clearly recognized (Pujalte et al. 2009). Meanwhile, the Sachun Formation was deposited in Zagros basin. The type section of the Sachun Formation was measured by James and Wynd (1965) in Fars Province (SW of Iran). This rock unit was first investigated by Perri and Player (1962). In its type section, Sachun Formation was divided into three members based on its lithological aspect (Motiei 1993, 1995; Shabafrooz et al. 2013) overlying uncomfortably the Upper Cretaceous mega sequence (Alavi 2004). The Sachun Formation is assigned to the late Maastrichtian to late Eocene mega sequence as * Massih Afghah [email protected] 1
Department of Geology, Shiraz Branch, Islamic Azad University, Shiraz, Iran
Payame Noor University Faculty of Science Center of Shiraz, Fars, Iran
2
the lowest unit, and is restricted to the northeastern internal part of the Zagros fold-thrust belt (James and Wynd 1965; Motiei 1995). The lithology of Sachun Formation is different in other areas of Zagros basin (Nairn and Alsharhanand 1997). On the other hand, the Sachun Formation in north of Fars province is mostly compos
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