Sequence stratigraphy and depositional environment of the Oligocene deposits at Firozabad section, southwest of Iran based on microfacies analysis (original) (raw)
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Acta Geologica Sinica ‐ English Edition, 2018
The Oligocene–Miocene carbonate record of the Zagros Mountains, known as the Asmari Formation, constitutes an important hydrocarbon reservoir in southern Iran. This marine carbonate succession, which developed under tropical conditions, is explored in terms of larger foraminiferal biostratigraphy, facies analysis and sequence stratigraphy in a new section at Papoon cropping out in the western Fars sub‐basin, in the south‐east of the Zagros belt. Facies analysis shows evidence of re‐working and transport of skeletal components throughout the depositional system, interpreted here as a carbonate ramp. The foraminifera‐based biozones identified include the Globigerina–Turborotalia cerroazulensis–Hantkenina Zone and Nummulites vascus–Nummulites fichteli Zone, both of Rupelian age, the Archaias asmaricus–Archaias hensoni–Miogypsinoides complanatus Zone of Chattian age and the ‘Indeterminate’ Zone of Aquitanian age. The vertical sedimentary evolution of the formation exhibits a progressive...
2019
In this study, four well-exposed outcrops of the Asmari Fm in the southeastern part of the Izeh Zone of the Zagros Mountains were measured and sampled. In this region, the Asmari Fm is Oligocene to Early Miocene in age as determined by large benthic foraminifera. Based on depositional geometries, biogenic contents and lateral and vertical variations of facies, three depositional models are proposed to illustrate the evolution of the Asmari carbonate platform. During the Chattian, large benthic foraminifera and coral-coralline red algae were dominant, while through the Early Miocene time interval (Aquitanian-Burdigalian), non-skeletal components along with porcelaneous foraminifera were the most conspicuous elements. These deposits formed a carbonate ramp in the Chattian and a low angle carbonate-ramp during the Early Miocene. Five major 3rd-order depositional sequences have been identified based on stratal stacking patterns and facies relationships. These depositional sequences show...
Depositional environment and sequence stratigraphy of the Oligo-Miocene Asmari Formation in SW Iran
Facies, 2006
The Asmari Formation, a thick carbonate succession of the Oligo-Miocene in Zagros Mountains (southwest Iran), has been studied to determine its microfacies, paleoenvironments and sedimentary sequences. Detailed petrographic analysis of the deposits led to the recognition of 10 microfacies types. In addition, five major depositional environments were identified in the Asmari Formation. These include tidal flat, shelf lagoon, shoal, slope and basin environmental settings and are interpreted as a carbonate platform developed in an open shelf situation but without effective barriers separating the platform from the open ocean. The Asmari carbonate succession consists of four, thick shallowing-upward sequences (third-order cycles). No major hiatuses were recognized between these cycles. Therefore, the contacts are interpreted as SB2 sequence boundary types. The Pabdeh Formation, the deeper marine facies equivalent of the Asmari Limestone is interpreted to be deposited in an outer slope-basin environment. The microfacies of the Pabdeh Formation shows similarities to the Asmari Formation.
The Oligocene-Miocene Asmari Formation is a thick sequence of shallow water carbonates of the Zagros Basin. Khaviz Anticline outcrop [near Behbahan city/Iran] was studied in this research in order to interpret the facies, depositional environment and sequence stratigraphy of the Asmari Formation succession. In this study, twelve different microfacies types have been recognized, which can be grouped into five (micro) facies associations: peritidal, lagoon, shoal, semi restricted marine and open marine. The Asmari Formation represents sedimentation on a carbonate ramp. According to the fauna data, the Asmari Formation is Oligocene (Rupelian/Chattian) to Early Mi-ocene (Burdigalian) in age at the study area. Eight third-order depositional sequences are identified on the basis of deepening and shallowing patterns in the microfacies. The depositional sequences 0 and 1 (Rupelian-Chattian), 2, 3 and 4 (Chattian) were referred to the lower while sequences 5 and 6 (Aquitanian) were referred to the middle and sequence 7 (Burdigalian) was referred to the upper Asmari Formation. The relative sea-level curve of the Asmari basin and its matching with the global sea-level curves documented that Global eustatic phenomena affected this basin.
Revista Brasileira De Paleontologia, 2022
The Paleogene carbonate deposits of Pabdeh and Jahrum formations are widespread in the northwest of the Shahrekord region (Dashte Zari area) in the High Zagros Mountains of Iran and record lateral and upward transition from open marine into shallow water environment within the Zagros foreland basin. The Pabdeh Formation shows a succession of open marine pelagic and hemipelagic limestone, argillaceous limestone, and argillaceous chert. It consists of planktonic wackestone, pellet-planktonic wackestone, mudstone with planktonic foraminifera, and radiolarian siliceous wackestone. The planktonic foraminifera are assigned to the Late Paleocene to Late Eocene, and correspond to subtropical to tropical Zones P4b-E15. Only one planktonic biozone (Zone E12), which corresponds to the high level stand of the Bartonian climate optimum (MECO) was not recognized in likely response to a tectonic event.The Jahrum Formation is represented by bioclast-bearing limestone and calcarenite. It consists of benthic foraminiferal wackestone, benthic foraminiferal-red algal packstone, and bioclast-intraclast packstone deposited in a shallow platform environment. The Jahrum Formation is inter-fingered in the upper part of the Pabdeh Formation and finally overlies it conformably during the Bartonian-Priabonian. Shallowing and offlap relationships record basin shrinking, while repeated interfingering signals moderate tectonic subsidence. Both formations are disconformably covered by the Late Oligocene-Miocene Asmari Formation.
Revista mexicana de …, 2010
The Asmari Formation deposited in the Zagros foreland basin during the Oligocene-Miocene. Four different measured sections were studied in this area in order to interpret the facies, depositional environment and sequence stratigraphy of the Asmari Formation. In this study, thirteen different microfacies types have been recognized, which can be grouped into six depositional environments: tidal flat, restricted lagoon, open lagoon, shoal, slope and basin. The Asmari Formation represents sedimentation on a carbonate ramp. Four third-order sequences are identified, on the basis of deepening and shallowing patterns in the microfacies and the distribution of the Oligocene-Miocene foraminifers. The depositional sequences 1, 2 and 3 were observed in Dehluran and Kabirkuh-Darrehshahr areas, and are synchronous with a period of either erosion or non-deposition represented by unconformities in Mamulan and Sepid Dasht areas.
Carbonates and Evaporites, 2007
This study investigates the depositional environment and sequence stratigraphy of the Asmari Formation (Oligoeene-Miocene) in Gaehsaran Area. The formation is carbonate sequence, which is laid down in the southern side edge Neotethys Ocean (Zagros area). The Asmari Formation represents sedimentation on a carbonate ramp. Seven major microfacies and three subfacies are recognized which include: MF-I) planktonic foraminifer wackestone-packstone, MF-2) nummulitic-bioclastic-corallinacean wackestonepackstone, MF-3) bioclastic grainstone. MF-4) ooid-grainstone, MF-5) bioclastic-miliolid-borelisid, MF-6) miliolid-intraclast-bioclast and MF-7) carbonate mudstones (laminated mudstone, fossiliferous mudstone and algal mudstones).
Acta Geologica Sinica - English Edition, 2021
Two stratigraphic sections (Arjooieh and Firoozabad) of the Mymand anticline located in the Interior Fars sub-basin of the Zagros mountains were measured and sampled in order to document sedimentological characteristics, microfacies types, and paleo-seagrasses indicators of the Oligocene succession (Asmari Fm.). Planktonic and benthic foraminifera and coralline red algae are the principal fossils from these strata. Foraminifera are represented by the following families: Soritidae, Peneroplidae, Austrotrillinidae, Alveolinidae, Planorbulinidae, Discorbidae, Lepidocyclinidae, Amphisteginidae, Rotaliidae, Nummulitidae, and Globigerinidae. Nine microfacies types were recognized, namely planktonic foraminiferal-peloidal packstone (MF1), bioclast nummulitid/Nerorotalia/Amphistegina packstone-grainstone-rudstonefloatstone(MF2), Neorotalia-echinoid coralline red algae packstone-grainstone (MF3), coral boundstone (MF4), coral/coralline red algae rudstone-floatstone-packstone-grainstone (MF5), diverse imperforate foraminifera bioclast packstone-grainstone (MF6), pelloid wackestonepackstone-grainstone (MF7), fenestrated mudstone and microbial mats (MF8), and anhydrite (MF9). MF1 indicates on outer ramp, MFs 2-4 represent middle ramp, and MFs 5-9 are interpreted as inner ramp environment. Paleo-seagrass indicators are consisting of foraminifera, hooked and tabular forms of coralline red algae, and corals. They were determined in MFs 5 and 6 reflecting the presence of vegetated environments within the middle-inner ramp setting. The Mymand anticline was dominated by the outer ramp environment at the start of the Rupelian. Middle to inner ramp environments prevailed during the Rupelian. The Chattian was correspond to the spread of inner ramp setting over the Mymand anticline.
Arabian Journal of Geosciences, 2015
This study deals with foraminiferal biostratigraphy and paleoecological interpretations for the Late Paleocene to the Early Oligocene carbonate sequence in the Zagros Basin, the Hajiabad Area, SW Iran. This sequence could be divided into three parts, basal fossil-less strata have related to Sachun Formation base on their stratigraphical position, the middle part involves dolomitic to dolomitic limestone of Jahrum Formation, and the upper part consists of the Lower Asmari Formation. In general, the bulk of the section consists of marine deposits, and it is possible to divide them in to several parts base on benthic foraminiferal biozones. The Late Paleocene to the Early Eocene (the Lower Jahrum Formation) has been distinguished by the Miscellanea, Kathina, Alveolina, Fallotella, Lokhartia, Orbitolites, and small rotalids Assemblage Zone. The Middle Eocene (the Middle Jahrum Formation) has been characterized by the Somalina Total Range Zone and the Nummulites-Alveolina Assemblage Zone. The Late Eocene (the Upper Jahrum Formation) has been distinguished by the Chapmanina, Pllatispira, Baccullogypsinoides Assemblage zone, and the outcrop of the Asmari Formation belongs to the Early Oligocene Base on the Nummulites vascus, Nummulites fichteli Assemblage Zone. Clustering content benthic foraminifera in the studied section base on their morphology, coiling, feeding habits, and habitats lead to identification of 15 distinct assemblages with similar ecological niches. Paleoecological reconstructions base on benthic foraminiferal communities indicate that five major ecological habitats include tidal flat and shore, restricted shelf, nonrestricted shelf, oligotrophic shelf, and open marine.
Open Journal of Geology, 2015
The Asmari Formation is a thick carbonate sequence of the Oligocene-Miocene in the Zagros Basin, southwest of Iran. This formation is located in Bandar Abbas and Coastal Fars regions on the following two sections: Anguro anticline (west-northwest of Bandar Abbas) and Gavbast anticline (southwest of Lar County). The Asmari Formation has diameters of 68 and 26 m in the Anguro and Gavbast sections, respectively. This formation is composed of limestone, dolomitic limestone and an altered form of marl. Based on the results of petrographic analyses, 7 facies were identified in the Anguro and Gavbast sections in the study region. The facies were deposited on the following 3 belts: tidal flat . According to evidence such as the gradual change of microfacies, the lack of main reef barriers, and the lack of slumping and sliding features, the Asmari Formation was formed in a marine environment of carbonate homoclinal ramp type. This environment is composed of the following two subenvironments: the inner ramp and the middle ramp. The comparison of the facies identified in the Anguro and Gavbast sections indicates that Gavbast section is mainly composed of lagoon facies. Moreover, the Anguro section demonstrates more facies diversity than Gavbast section.