Biostratigraphy and paleoecology of the Oligo-Miocene Asmari Formation in the Izeh zone (Zagros Basin, SW Iran)

Abstract

RESUMEN ABSTRACTIn this study, biostratigraphy and paleoecology of the Asmari Formation have been investigated. The study area is located in the Izeh zone, Zagros Basin. Four outcrop sections (Halayjan, Kuh Shur, Kuh-e Bad and Gharibi Ha) have been sampled. Based on distribution of the larger benthic and planktonic foraminifera, five assemblage zones have been recognized. Assemblages 1 and 2 indicate Chattian; assemblage 3 is restricted to Aquitanian and assemblages 4 and 5 suggest Burdigalian. During the Chattian, the carbonate deposits of the Asmari Formation are mostly composed of coralline red algae and large and flat benthic foraminifera. The common components of the Aquitanian are abundant imperforate foraminifera and Favreina asmaricus. The Burdigalian is characterized by coral, coralline algae, and perforate and imperforate foraminifera. During the Burdigalian toward the SE of study area (Gharibi Ha section), the shallow water deposits are abruptly overlain by pelagic limestone. It is interpreted as the result of a regional tilting that started in the upper part of the Burdigalian. The biotic associations suggest that carbonate sedimentation occurred in tropical to subtropical waters under oligotrophic to mesotrophic conditions. The carbonate grain associations in the Asmari Formation suggest heterozoan association. According to paleoecological parameters (such as: nutrient, depth, light and salinity) in the study area, the Asmari Formation belongs to nannofor-foralgal to foramol association which were deposited in slightly hyper to normal saline environment. In the euphotic zone, abundant imperforate foraminifera are present. Basinward, lens shaped rotalids developed in mesophotic conditions, and large lepidocyclinid-nummulitids characterize the sediments of the deeper oligophotic zone.Keywords: Asmari Formation, Oligocene-Miocene, biostratigraphy, paleoecology, larger benthic foraminifera, Zagros Basin.

Benthic foraminiferal biostratigraphy of the Oligocene Sequence of the Asmari Formation in the Interior Fars Sub-Zone, Zagros Belt, SW Iran

“…The sample numbers of the thin sections are indicated in the stratigraphic column of the Asmari Formation (Figure 2). Higher-level classification of the benthic foraminifera follows Loeblich & Tappan (1987), but identification of specific taxa is based on the works of Hakimzadeh & Seyrafian (2008), Amirshahkarami (2013), Kakemem et al (2016), Habibi (2016aHabibi ( , b, 2018, Taheri et al (2017), andBover-Arnal (2018). The benthic foraminiferal biozones proposed herein are defined according to Allahkarampour Dill et al (2020).…”

“…The age of the formation ranges from Oligocene to Early Miocene (Rupelian to Burdigalian: Wynd, 1965;Adams & Bourgeois, 1967;Ehrenberg et al, 2007;Laursen et al, 2009;Van Buchem et al, 2010;Kakemem et al, 2016;Allahkarampour Dill et al, 2020). Lithologically, the Asmari For mation consists mainly of limestones (argillaceous limestones, dolomitic limestones, pure limestones) with subordinate sandstones and evaporite deposits (James &Wynd, 1965;Motiei, 1993;Aghanabati, 2011;Roozpeykar & Maghfouri Moghaddam, 2016;Taheri et al, 2017). The limestones of the Asmari Formation were deposited in a carbonate platform, whereas the sandstones were deposited in the offshore marine zone, distal deltaic subtidal settings and coastal plain to terrestrial paleoenvironments (Van Buchem et al, 2010;Roozpeykar & Maghfouri Moghaddam, 2016).…”

Biostratigraphy, microfacies and reservoir quality of the Oligocene Qom Formation (Kharzan section, Northwest of Ardestan, Central Iran)

“…Num mu lites and lepidocyclinid in dex spe cies are com mon in the Oligocene Qom For ma tion and its equiv a lent in the Zagros Ba sin, the Asmari For ma tion, and have been used for biozonation (Mohammadi and Ameri, 2015). In a few sec tions, Num mu lites spe cies have been found alone in Rupelian, or lower Rupelian, strata whereas lepidocyclinids alone have been found in Chattian strata or Aquitanian for ma tions (e.g., Bozorgnia and Kalantari, 1965;Kalantari, 1976;Amirshahkarami et al, 2007;Ehrenberg et al, 2007;Laursen et al, 2009;Amirshahkarami et al, 2010;Van Buchem et al, 2010;Yazdi-Moghadam, 2011;Mohammadi et al, 2013Karavan et al, 2014;Mohammadi and Ameri, 2015;Taheri et al, 2017;Basso et al, 2019;Akbar-Baskalayeh et al, 2020;Allahkarampour Dill et al, 2018;Mohammadi, 2022). In Iran, Biozone No.57, the Num mu lites intermedius-Num mu lites vascus as sem blage zone, was first pro posed as an in dex for the Oligocene by Wynd (1965), who de scribed the prop er ties and biostratigraphic fea tures of Oligocene-Mio cene strata in the Asmari For ma tion in the south-west of Iran.…”

Microfacies correlation, analysis and palaeoecological reconstruction of Rupelian–Aquitanian succession in the central part of Lorestan Province, Northwestern Iran

“…At its type section, this formation consists of 314 m of limestones, dolomitic limestones and argillaceous limestones (Motiei, 1994), which the Gachsaran Formation overlies during the middle Miocene. In recent decades, extensive studies have mainly been conducted on the biostratigraphic criteria, determination of age, sedimentary and facies analyses of the Asmari Formation (e.g., Ehrenberg et al, 2007;Laursen et al, 2009;Mossadegh et al, 2009;Rahmani et al, 2009;Seyrafian et al, 2011;Shabafrooz et al, 2015;Taheri et al, 2017;van Buchem et al, 2010;Vaziri-Moghaddam et al, 2006, 2010. Among these, Laursen et al (2009) and van Buchem et al (2010) introduced new zonation based on faunal associations calibrated by strontium isotopes for the Asmari Formation.…”