Facies Analysis and Depositional Environment of the Sarvak Formation (Cenomanian) in the Zagros Basin (SW of Iran (original) (raw)
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Open Journal of Geology, 2016
The Sarvak Formation is the second major oil-bearing reservoir in the south and south west of Iran. The Middle Cretaceous Sarvak formation in the Zagros Mountains (Zagros Basin) is mainly composed of carbonate sequences. Based on facies studied, thirteen microfacies were recognized in the studied area, which were categorized in the three facies groups: including inner ramp, mid ramp and outer ramp. Evidences such as the gradual changes in the facies (basin slope), the absence of extensive uninterrupted barrier reef, the lack of calciturbidite and gravity sediments as well as the high proportion of grain-supported indicated that the Sarvak Formation was deposited in the ramp like depositional system, particularly on an inner ramp setting. Inner ramp facies group is the principal setting and subdivided to tidal flat, restricted and unrestricted lagoon as well as shoal sub-environments.
Carbonates and Evaporites, 2021
The Sarvak Formation is a thick carbonate sequence of Cenomanian age that has been deposited in a foreland basin across the Zagros Basin. Sarvak Formation is the main petroleum reservoir rock in the Zagros Basin. To study the foraminiferal paleoecology in the Sarvak Formation, the section was selected in the east of Shiraz (Khane Kat section) and 66 samples with a total thickness of 140 m were prepared. Then, these thin sections were studied precisely based on the lithostratigraphy, microfacies, geochemical stratigraphy (chemical XRF analysis), and paleoecology. Besides, the biozones were identified and geochemical changes of elements in each biozone were investigated. Totally, three biozones were identified in which the hyaline tests were abundant in biozone-1 and porcelaneous tests were accumulated in biozones-2 and-3. Based on the study of the foraminifera dispersion pattern, the age of the Sarvak Formation in Khane Kat section was determined as Cenomanian. The results indicated that the various environmental factors affected the test type, test size and the quantitative expansion of the test in the sedimentary basin. Geochemical, microfacies and paleoecology data indicated that the most appropriate and inappropriate condition of life was belonged to wackestone and mudstone facies, respectively. Increase in the ratio of benthic to pelagic (B/P ratios) throughout the section and the enhancement of microfossils with agglutinated tests represented the shallowness of the sedimentary basin and retrogradation of the sedimentary basin from the open marine to the Subtidal and intertidal.
Geopersia, 2011
The Asmari Formation was deposited in the foreland basin of southwest Iran (Zagros Basin). Carbonate sequences of the Asmari Formation consist mainly of large benthic foraminifera along with other skeletal and non-skeletal components. Three assemblage zones have been recognized by distribution of these large foraminifera in the study area that indicate Oligocene age (Rupelian-Chattian). Absence of turbidite deposits, reefal belt and gradual facies changes indicate that the Asmari Formation was deposited in a carbonate ramp environment. Based on analysis of large benthic foraminiferal assemblages and microfacies features nine different microfacies have been recognized, which can be grouped into three depositional environments: inner, middle and outer ramp. Based on the microfacies analysis and sequence stratigraphic studies, two third-order sequences in Firozabad section were identified.
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.
Himalayan Geology
The Fahliyan and Gadvan formationsof Lower Cretaceous age (Neocomian-Early Aptian) exposed on Kuh-e-Surmeh section were studied in order to evaluate microfacies, depositional environment and sequence stratigraphy. Petrographic study led to recognition of 18 microfacies deposited in five subenvironment : pelagic, hemipelagic, middle shelf, inner shelf, coastal plain. Sequence stratigraphy assessment of these deposits revealed three depositional sequence of third order of which the two lower ones belong to the Fahliyan Formation and the third one related to the Gadvan Formation. Except for the lower boundary of the sequence, the other boundaries are type 2
Iranian Journal of Earth Sciences, 2018
In the present research Kuh-e Siah Section in the Northeast of Shiraz in the Interior Fars, was investigated to study microfacies, sequence stratigraphy, facies analysis and sedimentary environment of Fahliyan Formation. Generally, 345 meters of these sediments were studied by investigating 240 thin sections. In this study, the indicator microfacies were accurately identified which include Mudstone, Wackestone, Packstone and Grainstone. Besides, skeletal and non-skeletal grains of these microfacies are Intraclast, Bioclast, Exteraclast and Peloid. According to lithostratigraphic study, underneath limit of Fahliyan Formation with the Surmeh Formation and its upper contact with Gadvan Formation were in the gradual form (SB2) and included (TST-LST-Early HST-Late HST) system tracts. In general, there were two second-degree sequences in this section., According to the analysis of the sedimentary environment, the The lowermost of the Fahliyan Formaion is comprised of the Inner shelf depos...
In the present study the Pabdeh Formation (late Paleocene-early Oligocene) was investigated in the Zagros Basin (W Iran). The main goal of this research was elucidating the depositional environments of this formation. This research was performed based on field observations and measurements, thin section petrography, trace fossil studies and OM (TOC % and kerogen type) measurements, from which seven microfacies assemblages were recognized. The Pabdeh Formation comprises alternation of thin to thick limestones and dark to light gray shale beds, rich in planktonic microfauna. These facies are interpreted as pelagic facies in the Zagros Basin and consist of mudstone (md), wackestone (wk), packstone (pk) and shale beds. Based on systematic study of the ichnofossil content of these facies, five ichnogenera grouped in two separate assemblages were recognized. The first assemblage present a relatively high ichnodiversity (Arenicolites, Chondrites, Planolites and Neonerites) and occurs in md-wk-pk facies. This assemblage represents the Cruziana ichnofacies, formed in relatively moderate-energy conditions. The second assemblage with lower ichnodiversity (Zoophycos and Chondrites) is found in shale, wk, md and pk beds and represents the Zoophycos ichnofacies which were formed in low energy and deeper conditions. Vertical stacking of these facies suggest a shallowing-up ward trend with these facies deposited in a distally steepend carbonate ramp, where the depositional settings evolved from an outer ramp with pelagic and turbidite facies (Microfacies 4B and 4C) and reducing condition to oxygen depleted waters (TOC> 2.5%; kerogens type , and less amount ) that gradually changed into a middle ramp where marine currents (e.g. turbidity currents) had an important impact on sediment reworking and resedimentation.
In this study a stratigraphy section of Asmari Formation is selected from Bavan Mountain-in Fars province,Iran-and 401.5 meter of this Formation's sediment is studied in total. Its index microfacies are carefully determined through studying of 152 thinsections. This research shows that the index microfacies in the studied sections are Mudstone, Wackestone, Packstone, Grainstone and the amount of microfacies elements such as bioclast,pellet,extraclast and intraclast are varied in different parts of the studied section and totally the amount of bioclast in the section is more than other elements. quantitative study of the microfacies of the Asmari Formation Bavan Section in northwest Shiraz. Researcher. 2011: 3 (10): 36 -40] (ISSN: 1553-9865). http://www.sciencepub.net/researcher.
Carbonates and Evaporites
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 basi...
Journal of …, 2009
Sarvak Formation, a thick carbonate succession with the age of Middle Cretaceous, is one of the most significant hydrocarbon reservoirs in the Zagros basin. The Tang-e Solak section of the Sarvak Formation in the Bangestan anticline with a total thickness of about 850 m has been studied, in order to determinate its microfacies types, depositional setting model and depositional sequences. Detailed textural and petrographic analysis led to the identification of 11 microfacies that arranged in three facies associations: inner ramp, mid-ramp, outer ramp and basin. Examination of vertical and lateral facies changes indicated these sediments were deposited in a carbonate ramp depositional system. Frequency analysis of facies indicated outer ramp and basin facies associations are the most frequent facies. Sea level fluctuations during in deposition of Sarvak successions led to formation of two depositional sequences. These depositional sequences are composed of transgressive systems tract and highstand systems tract. The highstand systems tract can be separated into Early HST and Late HST. Stacking pattern in Early HST part is aggradational and in Late HST is progradational.