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Researches in Earth Sciences (20088299) (3)pp. 15-44
Introduction Fossil vertebrates were first reported from Iran by Priem (1908), who reported on the fossil fishes from the Pabdeh Formation east of Ilam, in southwestern Iran. At the time, Priem (1908) considered these deposits to be Lower Cretaceous, but they are now known to be Eocene (Afsari et al. 2014). Several decades later, fish material from the same deposits was studied by Arambourg (1967), who had attributed the beds to the Oligocene. Since those studies, additional fish from the Pabdeh Formation have been described or revised (e.g. Haghipour and Brants 1971; Jafarian et al. 1999; Afsari et al. 2014; Davesne 2017) including members of the Scombridae, Carangidae, and Labridae. These support the revised Eocene age of the sediments. Recently, Mirzaei et al. (2016) reported a Pycnodontiform (a Neopterygian bony fish) tooth plate from the Albian–Cenomanian Sarvak Formation at Lorestan, southwest Iran. To our knowledge, this is the only Cretaceous vertebrate fossil from Iran, excluding the material we report here. The objectives of this paper are to describe and interpret the vertebrate-bearing horizons of the Dariyan Formation in order to determine the age of the vertebrate-bearing beds and to provide a preliminary report on the vertebrate assemblage present in this locality.Materials and MethodThe Sivand Section is located 80 km northeast of Shiraz, on the eastern flank of the Sivand Anticline at E 52° 51´ 27.70´´ and N 30° 4´ 54.88´´. The Fahlian, Gadvan, Dariyan, Kazhdumi, and Sarvak formations are exposed in this area. The thickness of the Dariyan Formation in the Sivand Section locality is about 287 ms. Dariyan Formation is mainly composed of cherty limestone, radiolaria-bearing limestones, Hedbergella-bearing marls, and thin-bedded micritic limestone layers. Vertebrates and ammonites occur mainly in the lower part of the Dariyan Formation. Among the bioclasts, fragments of bivalves, gastropods, and ammonites, Orbitalina foraminifera, and marine vertebrate debris can be observed. A section of sixty-five meters of the lower deposits of the Dariyan Formation was measured in detail in this region.Result and Discussion The samples, mainly slabs of micritic limestone with vertebrate fossils were collected, wrapped, packed and safely transferred to the Department of Geology lab., at University of Isfahan. Extra samples were systematically obtained from the special horizons for thin sections also a few washing samples in order to determine the precise age of the fossil bearing horizons of the Lower Dariyan Formation. Slabs of the vertebrate fossils were cleaned by special pneumatic air pen tool, photographed and studied in details for anatomical characteristics. Based on the succession of microfossil assemblages (Choffatella decipiens Range Zone, Radiolaria flood Range Zone, Globiogerinelloides blowi Range Zone, Mesorbitolina parva Range Zone), we propose that the Sivand fossiliferous deposits are Early Aptian (Bedoulian) through early Late Aptian (Early Gargasian) in age. Fossil vertebrates are preserved in the lower part of the formation.ConclusionsLaboratorial studies, Microscopic characteristics and the thin sections led to discrimination of five orders of fish fossils (Aspidorhynchiformes, Clupeiformes, Ichthyectiformes, Pycnodontioformes, and Semionotiformes) and a marine turtle fossil of genus Toxochelys, accompanied with 9 genera and 14 species of foraminifera were identified that represents early Aptian (Bedoulian) to the beginning of late Aptian (Early Gargasian) ages for the studied parts of the Dariyan Formation in Sivand section. The Sivand locality preserves the first known Early Cretaceous assemblage of marine vertebrates from southwestern Asia. The obtained samples of marine vertebrates also introduced from other regions of the world, including North America, Europe, Australia, Africa, China and Lebanon. The preservation of a diverse assemblage of fossil vertebrates, makes the Sivand locality of special significance for understanding the diversity of vertebrates in lower Cretaceous of South Asia.
Researches in Earth Sciences (20088299) (1)pp. 221-243
In order to understand the dolomitization processes in the eastern margin of the foreland Zagros sedimentary basin, the dolomites of Shahbazan Formation in the outcrop, located 6 kilometers north-west of Semirom, were studied by petrography and geochemistry. The Shahbazan Formation with a thickness of 74 m conformably overlaid on the terrigenous rocks of the Kashkan Formation and was covered disconformably by carbonate rocks of the Asmari Formation. Based on field evidence, petrography (including polarizing microscopes and SEM) and geochemistry of major, minor and rare earth elements (REE), four types of dolomites have been identified in the Shahbazan Formation. The results of this research indicate that the formation of very fine to fine crystalline dolomite occurred in tidal flat and other dolomites have been formed in shallow to intermediate deep burial diagenetic environments by moderately saline marine fluids (mean Na 363 ppm), via seepage reflux of evaporate seawater into the Shahbazan Formation platform.The similar distribution of the trace element versus Mg and REE pattern in the three dolomite types indicate that the Shahbazan dolomites formed a single diagenetic fluid with similar origin. The difference between the dolomite crystals size indicate variable water-rock interaction, temperature and depth of burial.
Researches in Earth Sciences (20088299) (2)pp. 29-52
Systematic investigation of vertebrate bearing horizons of Pabdeh Formation in Kuhrang area (Pole-Naal-Eshkanan, Kuhanak, Omid-Abad and Qanbar-Sini) leading to indentification of 8 families of Teleostis which includes: Fistularidae, Photichthyidae, Gempylidae, Myctophidae, Sternoptychidae, Gonostomatide, Clupeidae and Acanthuridae. Future to the fishes assemblages within the studied fauna 3 species of shrimp fossils were discriminated (Eopabdehus babaheydariensis, Eogordonella iranianiensis, Parsacus eocenicus). Based on the collected benthic and planctonic forminifers from the acid washing residues the Middle Eocene age can be assigned to the studied intervals.
Bagherpour, B. ,
Faghih, A. ,
Vaziri moghaddam, H. ,
Mehrabi, H. ,
Zare, M. ,
Immenhauser, A. Sedimentary Geology (00370738) 486
Basement highs and adjacent basins are significant structural elements controlling regional facies architecture. Overprinted by fluctuating sea-levels, the correlation of facies units from the crest into the flank environments is often challenging. Here, a case example of an upper Turonian–lower Campanian palaeohigh on the northeastern margin of the Arabian Plate is presented. Two stratigraphic sections (Jarhum and Qazi, respectively) compare the depositional dichotomy between crest and flank. The palaeohigh Jahrum section documents a deepening upward succession that includes brackish carbonates at the base, followed by shallow–marine carbonates, and culminates in basinal deposits. The sedimentary record of Santonian deposits in the Qazi section (flank) comprises stratigraphically thick calciturbidites, calcidebrites, slump folding, clinoforms, and channel-fill deposits, which conformably overlie deep-water deposits. This case study provides insights into processes that are rarely documented in the Tethyan realm. Data shown here exemplify the interaction between regional uplift (related to tectonic inversion) and eustatic sea–level changes. The regional correlation of the facies architecture highlights important lateral variations in facies and stratigraphic thickness controlled by bathymetry and seafloor inclination related to the geometry of the palaeohigh. We suggest that the redeposited carbonates described here are characteristic of tectonically active intervals along slope settings. Furthermore, we demonstrate that sustained carbonate production on unrimmed, distally steepened ramps supports the deposition of calciclastics. The data presented are crucial for understanding redeposition processes in Cretaceous carbonate systems along the Arabian margin and beyond. © 2025 The Author(s)
Rajabi A. ,
Mahmoodi P. ,
Alfonso P. ,
Canet C. ,
Andrew C. ,
Azhdari S. ,
Rezaei S. ,
Alaminia, Z. ,
Tamarzadeh S. ,
Yarmohammadi A. ,
Khan Mohammadi G. ,
Saeidi R. ,
Sattari, E. ,
Bahrami, A. ,
Vaziri moghaddam, H. ,
Taheri a., A. Minerals (2075163X) (7)pp. 1-25
Iran hosts more than 350 Precambrian to Cenozoic sediment-hosted Zn-Pb±Ba and barite-sulfide deposits, including shale-hosted massive sulfide (SHMS, also called SEDEX) and Irish-type and Mississippi Valley-type (MVT) mineralization, and barite is a common mineral in these deposits. In the SHMS deposits, barite is typically found as fine-grained disseminations in thin laminae. In these deposits, the sulfide laminae often occur as diagenetic replacements and as bands containing authigenic and diagenetic barite and pyrite framboids. In the Irish-type Zn-Pb-Ba and stratabound barite-sulfide deposits, barite exhibits various textures, including fine-grained disseminated barite, banded zebra textures, veins, and massive barite lenses. In some of the giant Irish-type deposits, as well as in the stratabound barite-sulfide mineralization, the main stratabound sulfide ore is developed within a barite envelope and is characterized by the replacement of barite and pyrite by chalcopyrite, galena, and sphalerite. In the MVT deposits, the formation of barite is often related to dolomitization, and sulfide mineralization involves the replacement of the dolomitized carbonate rocks, as well as associated barite. Fluid inclusion studies on the Irish-type deposits indicate that the temperatures and salinities of the sulfide-forming fluids are higher compared to those of the barite-forming fluids. Fluid inclusion analyses of coarse-grained barites from Irish and MVT deposits reveal their hydrothermal origin. The δ3⁴S values of sulfide minerals (pyrite, sphalerite, and galena) in Irish-type deposits exhibit a broad range of low values (mostly −28 to +5‰), primarily revealing a process of bacterial sulfate reduction (BSR). However, the textures (replacement, colloform, and banded) and more positive sulfur isotope values (+1 to +36‰) in the SHMS Zn-Pb deposits suggest that bacterial sulfate reduction (BSR) plays a less significant role. We suggest that thermochemical sulfate reduction (TSR) connected to the direct replacement of barite plays a more relevant role in providing sulfur for the sulfide mineralization in the SHMS, barite-sulfide, and MVT deposits. Based on the textual evidence, sulfur isotopic data, and fluid inclusion studies, barite has been identified as a key controller for the subsequent Zn-Pb mineralization by providing a suitable host and significant sulfur contribution in the sediment-hosted Zn-Pb and stratabound barite-sulfide deposits. This implies that diagenetic barite might be a precursor to all types of sediment-hosted Zn-Pb mineralization. © 2024 by the authors.
Boletin de la Sociedad Geologica Mexicana (14053322) 76(1)
The 1st order mass extinction at the Devonian/Carboniferous transition, known as the Hangenberg Crisis, is characterized by major transgressive/regressive cycles which led to widespread ocean anoxia during the Hangenberg Black Shale Event, as well as to a global major sea-level fall and the worldwide deposition of regressive Hangenberg Sandstone equivalents. The Devonian/Carboniferous transition at the Tuye-Darvar section in the eastern Alborz Range is studied in terms of conodont biostratigraphy, litho-, microfacies and sequence stratigraphy. In order to examine the biostratigraphical framework, forty conodont samples were systematically taken from the studied interval. Thirty-two conodont species belonging to ten genera led to the discrimination of twelve conodont zones, ranging from the Pseudopolygnathus granulosus Zone to the Scaliognathus anchoralis-Doliognathus latus Zone. Due to facies, the conodont record also exhibits some hiatuses. Field observations and sedimentological and microfacies studies led to the identification of thirteen facies types from sub-tidal environments to the fully marine environments, including seven microfacies types. The sediments deposited in a mixed carbonate-siliciclastic platform, revealed four third-order sequences. The Hangenberg Black Shale is not recorded in the Tuye-Darvar section as a result of depositional facies. In comparison with other studied Devonian/Carboniferous Boundary (DCB) sections of the central and northern Iran, the Tuye-Davar section suggests a tectonic position, which is most likely placed on a separate tectonic block. © (2024), (Boletin de la Sociedad Geologica Mexicana). All rights reserved.
Journal of African Earth Sciences (1464343X) 216
The Upper Cretaceous Gurpi Formation represents a pelagic interval composed of shale and marly limestone rich in planktonic foraminifera. This study focuses on the analysis of planktonic foraminifera from the Gurpi Formation in the Zard-Shehneh Anticline section in southwestern Iran. The formation is of significant importance in parts of the Zagros foreland basin, as it acts as both a cap rock and a source rock. The presence of the Cretaceous/Paleogene (K/Pg) boundary at the upper boundary of this formation further emphasizes the significance of studying it. Therefore, the study of its biozonation and bioevents is crucial. Through the recovery of planktonic foraminifera from 125 samples in thin sections and washed residues, 30 genera, 88 species, and 10 biozones were identified for the Gurpi Formation, as well as 7 genera, 12 species, and one biozone for the base of the overlying Pabdeh Formation. In addition, high accuracy was achieved in the placement of bioevents, including: 1) the occurrence of Globotruncana linneiana at the base of the Gurpi Formation, indicating the Santonian age; 2) the highest occurrences of Dicarinella asymetrica and most species of marginotruncanids, marking the Santonian/Campanian boundary; 3) the earlier occurrence of Globotruncana aegyptiaca; 4) the occurrence of the Campanian/Maastrichtian boundary in the lower part of Gansserina gansseri Zone; 5) the occurrences of five abundance events including: V. eggeri in the upper half of the Dicarinella asymetrica Zone, benthic foraminifera in the middle to upper half of the Radotruncana calcarata Zone, G. linneiana, G. lapparenti, and G. esnehensis in the lower part of Globotruncana falsostuarti Zone, G. esnehensis in the upper part of Globotruncana falsostuarti Zone, and G. gansseri at the end of the Pseudoguembelina hariaensis Zone; and 6) the disappearance of most keeled planktonic foraminifera species during the late Maastrichtian, starting from the middle parts of the Abathomphalus mayaroensis Zone. In this study, the K/Pg boundary, which is considered the upper boundary of the Gurpi Formation, exhibits unconformity and condensation. The high-resolution biozonation and bioevents framework not only allows for accurate dating of the Gurpi Formation in the Zard-Shehneh section, but also enhances the ability to precisely correlate sedimentary sequences and paleoenvironmental intervals at regional or global scales in future studies. © 2024 Elsevier Ltd
Annales Societatis Geologorum Poloniae (02089068) 94(1)pp. 61-82
This research attempted to determine the depositional sequences of the Qom Formation in the Urumieh-Dokhtar arc (Ghamsar section) and Esfahan-Sirjan fore-arc (Abadeh section) sub-basins in Iran, using microfacies and microtaphofacies analyses. The authors also investigated connections between the Qom Basin and the Zagros and Paratethys basins during the Oligocene. In this regard a total of eight microfacies, two terrigenous facies, and five microtaphofacies were identified on the basis of 269 samples from the Ghamsar section and 93 samples from the Abadeh section. The studied microfacies, terrigenous facies, and microtaphofacies were deposited on a homoclinal carbonate ramp. This carbonate platform can be divided into inner, middle and outer ramp environments. On the basis of the distribution of microfacies and sequence stratigraphy studies, five third-order depositional sequences and one incomplete depositional sequence were identified in the Ghamsar section and three third-order depositional sequences in the Abadeh section. According to the distribution of microtaphofacies and palaeobathymetric studies based on Amphistegina, the energy, and depth of the Qom sea in the Ghamsar section were greater than those evidenced in the Abadeh section. The results of local fault activity in the different sub-basins of the studied sections indicate a lesser effect of global sea-level changes in the Paratethys basin. On the basis of the formation of depositional sequences in these sub-basins; and differences in the number of depositional sequences; intense local fault activity is indicated during the Chattian Age (especially in the Urumieh-Dokhtar arc sub-basin). Regional sea-level fluctuations of the south Tethyan Seaway and the Paratethys Basin controlled sea-level changes in the Chattian Age. The depositional basins of the Tethyan seaway (southern Tethyan seaway, Paratethys Basin and Qom Basin) probably were related during the Burdigalian to Langhian and the early Serravallian. The results show that, the effect of sea-level changes of the Zagros Sea on the formation of depositional sequences in the Esfahan-Sirjan fore-arc sub-basin was significant. © 2024, Polish Geological Society. All rights reserved.
Acta Geologica Sinica (English Edition) (17556724) 97(4)pp. 1038-1057
The Late Devonian–early Carboniferous deposits of the Anarak section in northeastern Isfahan, Central Iran, evaluated based on conodont biostratigraphy, sedimentary environment and sequence stratigraphy. According to the field observations, five lithological units were identified. Investigating the conodont fauna of the Late Devonian–Carboniferous (Mississippian–Pennsylvanian) deposits of Bahram, Shishtu, and Qaleh (Sardar 1) formations in Anarak section led to the identification of 67 species of 18 conodont genera, and accordingly 22 conodont biozones were differentiated. The correlation of sea-level change curves, regarding to the conodont biofacies with the global sea-level curve, demonstrates the relative correlation in the mentioned times due to the shallow condition of the central Iran basin compared to the European and American basins. The microfacies analysis led to the identification of 12 microfacies related to the open sea, bioclastic barrier, lagoon and tidal flat sub-sedimentary environments in a homoclinal carbonate ramp environment. Based on sequence stratigraphy studies, three 3rd order sequences were identified. The first sequence, which is of the Late Devonian (upper part of the Bahram Formation, 32.5 m), the second sequence (12.5 m) is the Late Devonian (uppermost part of the Bahram Formation), and the third sequence (68 m) is the early Carboniferous (the Shishtu I Formation). © 2023 Geological Society of China.
Cretaceous Research (1095998X) 141
A new larger benthic foraminifera of the family Orbitolinidae Martin is described as Tarburiconus simplex gen. et sp. nov. from the upper Maastrichtian Tarbur Formation of southwest Iran (Zagros Zone). Differences of Tarburiconus gen. nov. to the Paleocene Fallotella Mangin and the Lower-Upper Cretaceous Paracoskinolina Moullade are discussed. Tarburiconus gen. nov. represents further evidence for an upper Maastrichtian diversification of larger benthic foraminifera, e.g. agglutinated conical taxa, before their extinction at the K-Pg boundary. Tarburiconus gen. nov. is another genus of the Orbitolinidae known only from the Upper Cretaceous Global Community Maturation Cycle (between CT and K-Pg boundaries). © 2022 Elsevier Ltd
Researches in Earth Sciences (20088299) 13(3)pp. 1-25
Introduction Close to the DCB, Hangenberg Event have occurred, due to rising global temperatures, evidence of sea level rise, eutrophic conditions, anoxic conditions, rising carbon burial, formation of the Hangenberg Black Shale, and depletion of shallow and especially deep marine fauna in deposits (De Vleeschouwer et al, 2013). The Jeirud Formation in its type section (consists of sandstone, brachiopod-bearing dark shales, and phosphate horizons) diconformably covers the Mila Formation, and is continously underlain by the Mobarak Formation (Bozorgnia, 1973). Materials and methods The Tuye-Darvar section location The Tuye-Darvar section is located Eastern Alborz Zone, adjacent to Darvar village (southwest of Damghan city) with base of the section: 36° 01' 27.31" N, 53° 53' 17.33" E; top of the section:36° 01' 19.32" N, 53° 53' 33.03" E. Method of study After detailed field studies, 44 rock samples were collected to study the conodont fauna based on standard methods (Jeppson and Anehus, 1995). After sediment dissolution, washing and hand picking under binocular microscope, stub preparation and gluing conodonts on aluminum base, determining the color alternation index of conodonts with the help of standard tables, preparing SEM photos, naming and identifying conodonts and their biozones was performed based on global refrences (Sandberg et al, 1978; Ziegler et al, 1990; Hartenfels, 2011; Corradini et al, 2016; Spalletta et al, 2017). Results and discussion Lithostratigraphy Jeirud Formation: The thickness of the Jeirud Formation in this section is 166 m, and includes the lower siliciclastic part with a thickness of 84 m and consists of 3 Lithostratigraphy units (included sandstone, conglomerate and shale) and the upper carbonate-siliciclastic part with a thickness of 82 m and consists of 3 Lithostratigraphy units (included sandstone, dolomites, microconglomerate, shale and limestone). Mobarak Formation: The Mobarak Formation disconformably covers the Jeirud Formation, with thickness 81.5 m thickness and underlies the vermiculite limestones of the Elika Formation (Triassic) through a fault surface. Based on the lithological characteristics, three stratigraphic units can be distinguished in this interval (including dark limestone and shale). Conodont biostratigraphy Study on the conodonts in the mentioned section led to the discrimination 32 species within 10 genera: Bispathodus, Branmehla, Clydagnathus, Gnathodus, Polygnathus, Pseudopolygnathus, Palmatolepis, Protognathodus, Scaphygnathus, Siphonodella According to the age range of conodont species, 12 conodont zonation were identified, of which 9 biozones belong to the Late Devonian (Late Famennian) and 3 biozones belong to the Early Carboniferous (Mississippian). The Late Devonian biozones included: 1. Pseudopolygnathus granulosus Zone, 2. Polygnathus styriacus Zone, 3. Palmatolepis gracilis manca Zone, 4. Palmatolepis gracilis expansa Zone, 5. Bispathodus aculeatus aculeatus Zone, 6. Bispathodus costatus Zone, 7. Bispathodus ultimus Zone, 8. Siphonodella praesulcata Zone to ckI Zone, 9. Protognathodus kockeli Zone And the Late Carboniferous included: 10. Siphonodella sulcata Zone – L. Siphonodella crenulata Zone, 11. Siphonodella isosticha-U. Siphonodella crenulata Zone – Gnathodus typicus Zone, 12. Scalignathus anchoralis-Doliognathus latus Zone Sea level changes and the paleoenvironment of the Tuye-Darvar section With combination of the 2 biofacies models to the Late Devonian deposits according to Sandberg and Dreseen (1984) studies and to the Early Carboniferous deposits according to Sandberg and Gutschick (1984) studies, conodont biofacies in the studied section was studied in the Late Devonian and the Early Carboniferous, that according to that, dominant biofacies in Late Devonian included (Polygnathid, Pseudopolygnathid, Bispathodid and Bispathodid-polygnathid) and dominant biofacies in the Early Carboniferous included (Bispathodid-polygnathid, Polygnathid, Pseudopolygnathid, Gnathodid and Gnathodid- pseudopolygnathid). Conclusion The lithostratigraphy study of the Tuye-Darvar section in Eastern Alborz Zone due to identified 9 lithostratigraphy unit belong to Jeirud Formation with the Late Devonian period and the Mobarak Formation with the Early Carboniferous period. 32 number of species within 10 genera were recognize, that base on this, 12 biozones in the Late Devonian and Early Carboniferous were separated. With study of biofacieces, in the Late Devonian and the Early Carboniferous, that according to that, dominant biofacies in Late Devonian included (Polygnathid, Pseudopolygnathid, Bispathodid and Bispathodid-polygnathid) and dominant biofacies in the Early Carboniferous included (Bispathodid-polygnathid, Polygnathid, Pseudopolygnathid, Gnathodid and Gnathodid- pseudopolygnathid). © 2021, Shahid Beheshti University. All rights reserved.
Acta Geologica Sinica (English Edition) (17556724) 96(1)pp. 147-166
Shallow carbonate deposits (Tarbur Formation) were formed in the Zagros foreland basin with dynamic tectonics during the Maastrichtian age. From the viewpoint of reconstruction of depositional conditions in these deposits, studies of biostratigraphy, microfacies, microtaphofacies, and sequence stratigraphy were performed in a single area at Tang-e Shabi Khoon, northwest of Zagros. Based on the identification of two assemblage zones consisting of benthic foraminifera in these strata, the formation was deposited during the middle to late Maastrichtian. The number of cycles in test size and type of coiling in Loftusia decreased from the study area toward the northwest of the Neotethys basin. The input of clastic sediments affected the distribution of Loftusia and rudists in the study area. Nine microfacies, six microtaphofacies, and one terrigenous facies (shale) were identified based on the sedimentary features. These deposits of the middle-late Maastrichtian were deposited on a homoclinal carbonate ramp. The platform can be divided into restricted and semi-restricted lagoon, shoal, and open marine environments. In the study area, the deposits of the Tarbur Formation were deposited during four third-order depositional sequences. Local fault activities affected the formation of depositional sequences in the study area. © 2021 Geological Society of China
Journal of African Earth Sciences (1464343X) 181
In this study, based on a multidisciplinary approach (biostratigraphy, cyclostratigraphy, and facies analysis), the Asmari carbonate successions were evaluated across two platform-to-basins transects including Parsi (Pr), Karanj (Kr), and Paranj (Prj) oil fields. In the biostratigraphy part, key large benthic foraminifera was used; which determined the Asmari carbonate Formation to the Chattian-Burdigalian in age. Facies analysis led to identifying eight microfacies (MF.1–8) arranged from basinal deep-water setting (MF.1) to lagoonal shallow-water to tidal zone (MF.8). In cyclostratigraphy, a total of seven positive breaks and five negative breaks related to 12 wells were recognized by cyclolog software, to identify and correlate coeval depositional packages across oil fields. These key breaks were calibrated with biostratigraphy dating and traced across studied oil fields. Finally, based on the combination of all extracted data, three carbonate platforms were distinguished evolved through the Chattian- Burdigalian. Chattian carbonate platform is composed of a high variety of carbonate producing (Stages I, II, and III), representing a fore-Stepping stacking pattern. Aquitanian Carbonate Platform is a soft-grained carbonate ramp with a low-angle gradient comprising two different Stages: IV and V. The Burdigalian platform (Stage VI) is composed of meters to decimetre–scale limestone (MF.6) rich in Borelis melo, discorbis, and small rotalids highlighting a shallow-water lagoon and has a uniform set throughout the study area. © 2021 Elsevier Ltd
Journal of African Earth Sciences (1464343X) 183
A Cretaceous/Paleogene (K/Pg) boundary interval in the north flank of Alborz Mountains (Aboksar section), northern Iran, has been studied to investigate the biological and geochemical variations of this event in the eastern Tethys. Abathomphalus mayaroensis at the late Maastrichtian, Pα (Parvularugoglobigerina eugubina), P1a (Parasubbotina pseudobulloides) and P1b (Subbotina triloculinoides) at the early Danian are the recognized planktic foraminiferal biozones and subzones in the studied area. The Plummerita hantkeninoides subzone at the uppermost Maastrichtian and P0 Biozone at the base of Danian were not defined in the studied section. This proposes a short-term hiatus and sedimentary discontinuity at the base of Paleocene and probably uppermost Maastrichtian, which most likely caused by winnowing of sediments after a cooling phase and development of bottom current in the Albors Basin. The K–Pg transition in the Aboksar section is characterized by a bloom in the Guembelitria cretacea, evolution of first Danian species (Pv. eugubina, Pv. longiapertura), δ13C negative shift (about 0.5‰), and a gentle Ir anomaly (0.1 ppb). Planktic foraminifera were diverse and abundant during the late Maastrichtian of studied section in a warm (relatively lower δ18O contents) and well stratified environment. Bloom of the opportunist species, G. cretacea, and decrease of planktic foraminiferal abundance and diversity at the base of Paleocene interval propose an abnormal stressful environment in this time probably after the asteroid impact and its following temperature decline. The appearance of more complete species with more specialized shells and larger sizes, such as Globoconusa daubjergensis, Parasubbotina pseudobulloides, Eoglobigerina eobulloides and Subbotina triloculinoides in the P1a and P1b subzones and return of carbon isotope diagram into the pre-boundary values testify an environmental recovery and optimization of ecosystem conditions. © 2021
International Journal Of Earth Sciences (14373254) 110(1)pp. 305-330
The uppermost Albian–Turonian interval has been studied in the south of the Izeh Zone (SW Iran) to investigate the depositional history of the Sarvak Formation in this area. This interval in the Middle East is characterized by the presence of very large shallow water carbonate platforms, surrounding the intra-shelf basins. The expansion of up to 90% hemipelagic strata throughout the studied outcrop proposes that it has been deposited in an intra-shelf basin. Three Cenomanian and one Turonian depositional sequences were distinguished in the studied interval based on the alternation of three microfacies associations including oligosteginid-dominated, oligosteginid-free, and platform-top microfacies. The biostratigraphical calibration by means of the planktic foraminifera indicates that these sequences can be well correlated on a global scale. The simultaneous influence of eustatic, tectonic, and environmental factors on the depositional sequences in the Lar Anticline section makes it difficult to identify the dominance of one over the others. The ability to correlate the sequence boundaries in the studied section with the global events suggests the effect of eustasy on the deposition of this interval. However, the tectonic control by the creation of a paleo-depression, subsidence (during the TST of Sequence 3), and uplift (at the Cenomanian/Turonian boundary (SB4) and mid-Turonian (SB5)) overprinted the eustatic factor. The influx of clay and the black shale formation during OAE2 conditions are the environmental factors that cannot be ignored in the deposition of sequence 1 and sequence 3, respectively. © 2021, Geologische Vereinigung e.V. (GV).
Palaeobiodiversity and Palaeoenvironments (18671608) 101(3)pp. 781-802
A relatively complete conodont record from Famennian to the Mississippian/Pennsylvanian boundary was investigated in the Anarak section, Central Iran. The studied interval belongs to the Bahram, Shishtu, Ghaleh and Absheni formations. The Famennian part of the section (Bahram Formation) ranges from the Palmatolepis triangularis Zone into the Bispathodus ultimus Zone. Not all conodont zones could be defined due to the lack of indicative species. Furthermore, it seems likely that a hiatus occurs around the Devonian/Carboniferous (D/C) boundary (most probably from the Siphonodella praesulcata to the ?Siphonodella sulcata–early Siphonodella crenulata conodont zones) based on the lack of stratigraphically important conodonts as well as on sedimentological criteria. The lack of representative siphonodellids and protognathodids at the base of the Mississippian prevents detailed stratigraphic position of the D/C boundary. Lower Carboniferous (Mississippian) rocks are characterized by red nodular limestone which is unique in comparison with other studied sections of the same age in Central Iran. Within the studied section, we could define the Mississippian/Pennsylvanian boundary. The mid-Carboniferous boundary was defined by the occurrence of Declinognathus noduliferus s.l. Conodont biofacies changes (Mississippian genera Gnathodus and Lochriea have been replaced by Pennsylvanian genera Declinognathus and Idiognathodus) are recognized in this section as well. © 2021, The Author(s).
Marine Micropaleontology (03778398) 162
This study examines the morphological changes of the Loftusia genus from the Zagros Belt of southern Iran using quantitative data. Eight Tarbur Formation outcrops were investigated in the High Zagros and the Lurestan sub zones. The observed Loftusia species are of mid Maastrichtian age in the High Zagros and the mid to late Maastrichtian age in the Lurestan and Murak areas, and they are often observed in deposits of the lagoon environments with high nutrient conditions. Two (Tang-e Shabi Khoon area) and four (Murak area) cycles were recognized based on the morphological parameter changes of Loftusia species. The correlation of the number of cycles of Loftusia species between the Zagros basin and the different areas of the Neotethys basin indicates that Loftusia species sizes change in time. The obtained data shows that the number of the sedimentary cycles (alternating shale and limestone layers) in the High Zagros zone is more different than the Lurestan zone. The High Zagros zone comprises rich terrigenous shale with higher nutrient flux in comparision to the Lurestan zone and other areas of the Neotethys basins. The number of cycles decreased from the southeast toward the northwest of the Neotethys basin. It is thought changes in Loftusia species in the Zagros basin are related to nutrient input during the Maastrichtian age and were independent of evolutionary trends. The genus Loftusia disappeared in the High Zagros zone at the end of the late Maastrichtian. The subsidence of the basin is associated with the Dena and High Zagros Faults. Due to the activities of those faults, the Tabur Formation was not deposited in the High Zagros zone areas. The genus Loftusia appeared in the southeast region of the Arabian plate during the early Maastrichtian, and migrated to the northwest of the Neotethys during the Maastrichtian. © 2020 Elsevier B.V.
Marine and Petroleum Geology (02648172) 129
New high-resolution biostratigraphy and facies analyses indicate that a Coniacian-Santonian homoclinal carbonate ramp (Ilam Fm.) developed on the subaerially exposed mid-Turonian surface at the top of Sarvak Fm. in Fars zone of the Zagros Basin (northeastern margin of the Arabian Plate). Spatial facies distribution, sequence stratigraphy, and lateral variation in the thickness of Ilam Fm., as well as extend of erosion of the underlying Sarvak Fm. suggest that a combination of regional tectonic activities and global sea-level changes controlled the development of this succession. A major tectonic configuration in the Zagros belt including several basement faults subdivide the belt into different blocks with distinctive sedimentary records. Reactivation of these preexisting basement faults during Late Cretaceous provided a horst and graben geometry due to the closure of Neo-Tethys. Three of our studied sections are located on an upthrown block, bounded between Kazerun and Karebas basement faults, include inner and mid-ramp deposits. These sections represent an eastward deepening trend which correspond to eastward tilting of this fault block. The easternmost section is located in the eastern neighboring downthrown block, bounded between Karebas and Bastak faults, and includes outer ramp and basin deposits confirming a significant paleo-bathymetrical contrast between the two blocks. Furthermore, eastward thickening of the Ilam Fm. independently confirms the increase of accommodation space, as a result of deeper depositional condition, toward center of the Fars zone. Absence of subaerial exposure features at top of the Sarvak Fm. in the downthrown block shows that the global sea-level fall and regional tectonic regime also controlled the extend of unconformity underlying the Coniacian-Santonian platform deposits (Ilam Fm.). © 2021 Elsevier Ltd
Revue de Micropaleontologie (00351598) 66
Developing a more precise time framework in any hydrocarbon-bearing basin is potentially of great value to geologists and reservoir modelers for better understanding the hydrocarbon reservoir zonation, and identifying unconformities. In the Asmari Formation, which is the most important Oligocene–Miocene carbonate reservoirs in Iran, broad time zonation is generally used based on larger benthic foraminifera (LBF). In this study, the biostratigraphic zonation of the Asmari intra-shelf basin is re-evaluated based on the spatial and temporal distribution of LBF (i.e., different species of Nummulites, Eulepidina, Archaias, Spiroclypeus, Miogypsinoides, Miogypsina, and Borelis) as well as Sr isotope datasets. This research proposes a new zonation to improve time resolution in the Oligocene and explains the effects of environmental factors on some index fossils and the limited range of some key fauna. The newly proposed zonation consists of one biofacies and nine biozones occurring throughout the Rupelian to Burdigalian allowing differentiating Oligo-Miocene stages, and tuning the chronostratigraphic framework of the Oligocene–Miocene deposits. Moreover, based on this new biozonation, regional-scale palaeogeographical maps of the Asmari intra-shelf basin during Rupelian-Burdigalian were officially established. © 2020 Elsevier Masson SAS
Zeitschrift der Deutschen Gesellschaft fur Geowissenschaften (18601804) 171(4)pp. 503-519
One outcrop of the Qom Formation was measured for age determination and interpretation of palaeoenvironmen-tal conditions based on benthic foraminifera and the vertical distribution of microfacies and microtaphofacies in the Bijegan area of Iran. The study area is located about 20 km northeast of Delijan. There the Qom Formation is 162 m thick and dominantly contains thin, medium, thick bedded, and massive limestone. The formation overlies the Lower Red Formation in the Bijegan area. The upper boundary of the Qom Formation is formed by unconformably overlying recent alluvial sedi-ments. Three assemblage zones were identified. Assemblage zone 1 indicates a Rupelian age while assemblage zones 2 and 3 were deposited during the Chattian. The correlation between the curve of seawater depth changes and the distribution curve of microtaphofacies in the study area is indicative of a high energy environment (under the effect of the fair-weather wave base [FWWB] or storm wave base [SWB]) throughout the Rupelian-Chattian. Salinities are interpreted to have oscil-lated between normal marine (30–40 psu) and hypersaline (>50 psu) during deposition. The trophic conditions were mainly mesotrophic to oligotrophic. Euphotic conditions prevailed during the Rupelian and Chattian. In the Bijegan area, the Qom Formation formed in euphotic to meso-oligophotic conditions. Lagoonal and open marine environments characterise the lower section of the studied sequence (Rupelian and lower Chattian stages) and open marine conditions were dominant in the upper section of the study sequence (upper Chattian stage). Correlation of the study area with five other Rupelian-Chattian outcrops shows high sedimentation rate in the Qohrud area during the Rupelian and in the Mashhad Ardehal area during the Chattian. Throughout the Oligocene, the activity of local faults presumably affected sedimentation rates, sedimentary environments, and sea-level change in the Qohrud, Vidoje, Naragh, Bijegan, Mashhad Ardehal and Neizar areas. © 2020 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany.
Marine and Petroleum Geology (02648172) 116
Mud-dominated facies distribution of Barremian–Turonian succession in the northeastern Arabian Plate in the central Persian Gulf represents a shallow ramp platform. On the basis of petrographical studies, core analysis data and gamma ray logs, this succession has been studied for facies analysis, defining depositional environment, sequence stratigraphy and reservoir properties. A total of 6 microfacies and 3 petrofacies types are recognized in this succession. Lagoonal environment was dominated during the deposition of Dariyan, Kazhdumi and Sarvak formations. The lagoon rapidly changed to a sand shoal by falling sea-level and increasing energy level of the depositional environment. Sequence stratigraphy of Barremian–Turonian succession shows that mud-dominated facies have been deposited in TSTs and grain dominated facies in HSTs of the sequences. Although grain-dominated facies like packstone to grainstone and algal floatstone were spread during the HSTs of sequences, the changes in the texture and size of the grains had a negligible effect on reservoir quality. During this period (Barremian–Turonian), two major sea-level falls caused considerable environmental changes such as platform emergence, incised valley fills and clastic sediments influx into the carbonate platform. Meteoric diagenesis during the falling sea-level had a major effect on the reservoir properties of the reservoirs, under the sequence boundaries. Grains, matrix and micrite dissolution and subsequent selective blocky and equant calcite cementation, strongly modified the primary reservoir properties. Local dolomitization also enhance the porosity and permeability of the samples. While large pores have been filled by cements, microporosities remained unfilled until the late stages of diagenesis and burial. © 2020 Elsevier Ltd
Micropaleontology (00262803) 66(5)pp. 419-423
The large-sized agglutinated benthic foraminifera Loftusia Brady is a typical constituent of the shallow-water carbonates of the (upper) Maastrichtian Tarbur Formation, SW Iran (Zagros Zone). Different bio- and lithoclasts from the ambient depositional environment can be observed incorporated into the wall and other skeletal elements. These can include various small-sized benthic foraminifera belonging to different groups, but very rarely have planktonic forms have been observed inside the tests. The inclusion of a single specimen of an “Eocene planktonic foraminifera” observed within one of the type-specimens of Loftusia persica Brady (the type species of Loftusia) from Iran was reported in a recent paper by BouDagher-Fadel and Price (2009). The authors concluded that Loftusia persica represents an Eocene Lazarus taxon. Our conclusion (supported by abundant specimens from the Tarbur Formation of Iran) is that this single specimen is undiagnostic. Instead, Loftusia persica and the genus Loftusia are considered as Maastrichtian marker taxa that became finally extinct at the end Cretaceous. © 2020 Micropaleontology Press. All rights reserved.
Gondwana Research (1342937X) 83pp. 1-15
Cenomanian/Turonian boundary (upper Sarvak Formation) benthic foraminiferal assemblages were analyzed to reconstruct oxygen level, primary productivity, and water turbulence in the Izeh Zone, Zagros Basin. The interplay between environmental perturbations during the Oceanic Anoxic Event 2 (OAE2) and regional tectonic activities in the Zagros Basin resulted in formation of various benthic foraminiferal assemblages in the study section. The OAE2 interval at the region of study starts with extinction of rotaliporids at the onset of δ13C positive excursion (peak “a”), which is associated with population of infaunal benthic foraminifera (especially Bolivina alata). The following interval at the onset of Whiteinella archaeocretacea Biozone is characterized by the total absence of benthic taxa and dominance of planoheterohelicids (“Heterohelix shift”) in the black shale strata, indicating expansion of oxygen minimum zone and unhospitable conditions for both benthic and planktic foraminifera. The upper part of OAE2 interval (including δ13C peaks “b” and “c”) coincides with harbinger of Neo-Tethys closure in the Arabian Plate, causing a compressional tectonic regime, and creation of uplifted terrains in the basin. The relative sea level started to locally fall in this succession, which was accompanied by a better ventilation of seafloor, lower TOC contents, and reappearance of benthic foraminifera. © 2020 International Association for Gondwana Research
Salehi, M.A. ,
Bahrami, A. ,
Moharrami, S. ,
Vaziri moghaddam, H. ,
Pakzad, H.R. ,
Shakeri, B. Journal of African Earth Sciences (1464343X) 171
The predominantly warm greenhouse climate and high global sea level during the Middle–Late Devonian resulted in fully marine conditions along the northern Gondwana margin, including the Iranian Plate. Over three-hundred meter-thick fossiliferous Middle-to Late Devonian carbonate deposits of the Bahram Formation in the Anarak region (western Central Iran) are composed of dark grey limestone, dolostone, and interbedded shale. Seventeen microfacies have been distinguished, which correspond to four depositional sub-environments, i.e., tidal flat, lagoon, shoal, and open marine. The Middle–Late Devonian carbonate deposits were deposited on a homoclinal carbonate ramp. Seven third-order depositional sequences are identified, apparently controlled by relative sea level change. Carbon and oxygen stable isotopes, and major and trace elements of micritic carbonate samples document details about the geochemical, palaeoenvironmental, and diagenetic processes; they also indicate that the carbonates underwent meteoric diagenesis within a semi-closed diagenetic system. The low concentrations of trace elements indicative of euxinic conditions, including Mo, Cr, V, and As, suggest well-oxygenated depositional environment. Carbon isotope values show a meaningful relationship to major sequence-stratigraphic key surfaces, with more negative values occurring at the sequence boundaries and positive values corresponding to maximum flooding surfaces. © 2020 Elsevier Ltd
Acta Geologica Sinica (English Edition) (17556724) 94(5)pp. 1339-1363
In this study, the Maastrichtian-Danian boundary was measured and sampled in two stratigraphic sections, the north and south flanks of the Dehnow anticline in Coastal Fars, Southern Iran. This boundary was also investigated in the drilled exploratory well-1 in the same region. The lithology of the Maastrichtian-Danian deposits consists of glauconitic, phosphatic argillaceous limestones and marlstones. 30 genera and 77 species of planktonic foraminifera have been determined. The recognized biozones are the Gansserina gansseri Interval Zone, and the Contusotruncana contusa Interval Zone, which indicates latest Campanian to middle Maastrichtian age for the upper part of the Gurpi Formation. In addition, the Eoglobigerina edita (P1) Partial Range Zone, Praemurica uncinata (P2) Lowest Occurrence Zone, Morozovella angulata (P3) Lowest Occurrence Zone and Globanomalina psudomenardii (P4) Taxon Range Zone represent a Danian to Thanetian age for the lower part of the Pabdeh Formation. From the absence of the Abathomphalus mayaroensis Interval Zone, Pseudoguembelina hariaensis Interval Zone, Pseudotextularia elegans Interval Zone, Plummerita hantkeninoides Interval Zone, Guembelitria cretacea (P0) Partial Range Zone and Parvularugoglobigerina eugubina (Pα) Total Range Zone, it can be deduced that there is a paraconformity across the Maastrichtian–Danian boundary in the studied area, this hiatus encompassing the late Maastrichtian and the earliest Danian. Danian deposits from the study area contain reworked glauconitized macrofossils, planktonic and benthic foraminifera of the Cretaceous. The obtained surface gamma-ray spectrometry logs resemble the exploratory well-1 gamma-ray wireline log. © 2020 Geological Society of China
Russian Geology and Geophysics (10687971) 60(12)pp. 1368-1384
This research attempted to reconstruct the sedimentary environment and depositional sequences of the Qom Formation in Central Iran, using biofacies and taphofacies analyses. The Qom Formation in the Andabad area (3º48'12.6″ N, 47º59'28″ E) is 220 m in thickness. The thickness of the Qom Formation in the Nowbaran area (35º05'22.5″ N, 49º41'00″ E) was found to be 458 m. In both areas, the formation consists mainly of shale and limestone. The lower boundary between the Qom and Lower Red Formations is unconformable in both areas. In the Nowbaran area, the Qom Formation is covered by recent alluvial sediments. In the Andabad area, the Qom Formation is unconformably overlain by the Upper Red Formation. A total of 122 limestone and 15 shale rock samples were collected from the Andabad area, and 94 limestone and 24 shale rock samples were collected from the Nowbaran area. Analysis of the collected samples resulted in the recognition of nine biofacies, one terrigenous facies, and five taphofacies within the Qom Formation in both areas. Based on the vertical distributions of biofacies, the Qom Formation is deposited on an open shelf carbonate platform. This carbonate platform can be divided into three subenvironments: inner shelf (restricted and semirestricted lagoon), middle shelf, and outer shelf. Two third-order and one incomplete depositional sequences were identified in the Nowbaran area, but in the Andabad area, three third-order and one incomplete depositional sequences were distinguished. © 2019, V.S. Sobolev IGM, Siberian Branch of the RAS.
Palaeobiodiversity and Palaeoenvironments (18671608) 99(3)pp. 477-494
The Middle to Upper Devonian Kuh-e-Bande-Abdol-Hossein section in eastern Central Iran is an overall shallow marine, nearshore to open marine facies setting that contains a highly variable conodont record generally characterised by an Icriodid-Polygnathid biofacies. The lithology and the palaeoenvironmental setting is similar to other localities in Central Iran and exhibits numerous hiatuses. A continuous biostratigraphic record could not be established, but the section preserves the Givetian/Frasnian boundary. Based on the conodont record, major gaps also occur in the Famennian which confirms earlier results reported from other sections of similar palaeoenvironments in Central Iran. © 2019, Senckenberg Gesellschaft für Naturforschung and Springer-Verlag GmbH Germany, part of Springer Nature.
Sedimentary Geology (00370738) 390pp. 31-44
This study focuses on the facies associations and depositional sequences of a Cenomanian/Turonian (C/T) outcrop, spanning the upper part of the Sarvak Formation in the Izeh zone, Zagros basin, Iran. The significant variations in sedimentary facies of the studied succession suggest an evolution from a late Cenomanian open-shelf to an early Turonian ramp system. This change is believed to be response of transition in the tectonic regime of Arabian plate from a passive to an active margin during the late Cretaceous. Two partial and one complete third-order depositional sequences and also several fourth-order sequences and small-scale cycles were recognized in the studied section. The global correlation of the third-order sequences suggests that they were eustatically-driven. However, local tectonic activities overprint the eustatic signature from the latest Cenomanian. The association of transgressions with cooling and regressions with warming during the fourth-order sequences support the aquifer-eustasy model as a controlling factor for the sea-level fluctuations under C/T supergreenhouse conditions. © 2019 Elsevier B.V.
Carbonates and Evaporites (08912556) 34(4)pp. 1293-1306
Qom Formation (Oligo-Miocene marine deposits of Middle Iran) in the southwestern Kashan was studied to determine its microfacies and depositional environments. Outcrops of the Qom Formation in the study area with 410 m, consist mainly of limestone, sandy limestone, shale and marl. Study section is unconformably underlain by the Eocene volcanic rocks and overlain by alluvium. Biogenic components of the Qom Formation comprise mainly of larger benthic foraminifera, coralline red algae and corals. Based on the presence of Nummulites spp. (Nummulites fichteli, Nummulites vascus, Nummulites cf. vascus, Nummulites sp.) throughout the study section, the Qom Formation is considered to be Rupelian in age. Microfacies analysis and field investigations on the study section led to recognition of six carbonate microfacies and two marl and shale facies. Two major depositional environments were identified in the study area including lagoon and open marine. Based on the recognized microfacies and field investigations, deposition of the Qom Formation in Barzok area took place on a carbonate ramp; besides, most of the carbonate parts of the study section are deposited in the open-marine settings. The high abundance of larger benthic foraminifera, coralline red algae and corals indicates that deposition took place in the tropical warm waters. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.
Palaeogeography, Palaeoclimatology, Palaeoecology (00310182) 533
The Cenomanian/Turonian (C/T) boundary interval, spanning the upper part of the Sarvak Formation in the Zagros Basin (Izeh Zone), has been studied to determine the timing and the possible cause of biotic turnovers, coinciding with the intense environmental perturbations during the Oceanic Anoxic Event 2 (OAE2). The upper Cenomanian strata in the study section, composed of light-colour marlstone/organic-rich marlstone and shale bedding couplets, record fluctuations in microfossil assemblages and organic carbon contents. We suggest that the organic-poor layers, characterized by high abundance of radiolarians, were deposited during cold periods under surface water eutrophication (upwelling) and ventilated seafloor. In contrast, water column stratification during warm periods enhanced organic matter preservation and allowed deposition of organic-rich strata. Continued stratification and also increased runoff and primary productivity during warm intervals of OAE2 led to expansion of oxygen minimum zone (OMZ), which may have caused extinctions of deep followed by intermediate water planktic foraminifera. Such conditions may have led to significant decreases in the abundance and diversity of planktic foraminifera and dominance of the biserial genus Planoheterohelix (“Heterohelix” shift event). The δ13C curve in the study interval reveals the diagnostic features of global C/T boundary carbon isotope record, including three positive peaks (A, B and C) within the Whiteinella archaeocretacea Biozone. These carbon isotope features and the most important bioevents in the study section are stratigraphically listed below: 1- Highest occurrences (HOs) of Th. greenhornensis and Th. deeckei, 2- HO of R. cushmani and δ13C peak A, 3- HO of “G”. bentonensis, 4- Onset of “Heterohelix” shift event, 5- δ13C peak B, 6- δ13C peak C, 7- Filament event, 8- Lowest occurrence (LO) of H. helvetica, and 9- Holywell event. © 2019 Elsevier B.V.
Carbonates and Evaporites (08912556) 33(3)pp. 489-507
To interpret the biofacies, depositional model, and sequence stratigraphy of the Asmari Formation in Western Interior Fars sub-zone, one stratigraphic section with 407 m was studied in Sefidar anticline. The studied area is located in Simply Folded Zagros Zone. The Asmari Formation in the studied section is Rupelian–Chattian (Oligocene) in age. The distribution of the Oligocene larger benthic foraminifera indicates that shallow marine carbonates of the Asmari Formation at the studied area deposited in the photic zone and oligo-mesotrophic conditions in tropical-to-subtropical waters. In this study, nine different microfacies were recognized, which are formed in lagoon, shoal, and open-marine sub-environments corresponding to inner and middle ramps. The lower parts of the Asmari Formation are dominated by lagoonal microfacies; in the middle parts, the open-marine microfacies are prevailed; and the upper parts are mainly deposited in lagoonal settings. Three third-order sequences were identified based on the deepening and shallowing patterns in microfacies and foraminifera distributions. © 2017, Springer-Verlag GmbH Germany.
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749) 288(1)pp. 87-105
The Pir-Sabz Section of the Asmari Formation is located in the Interior Fars province, Zagros Basin (Iran). The Asmari Formation at the study area is 312 m in thickness and formed by massive bedded limestone. According to the identified index microfossils, three Oligocene assemblage biozones were recorded: 1) Globigerina spp., 2) Lepidocyclina – Operculina – Ditrupa, and 3) Archaias asmaricus – Archaias hensoni. Twelve facies types were recognized according to their texture, occurrence and abundance of foraminifera, scleractinian corals and other skeletal grains: F1 Bioclastic planktonic foraminiferal wackestone–packstone, F2 Bioclastic planktonic foraminiferal echinoid packstone, F3 Bioclastic Operculina packstone, F4 Bioclastic Lepidocyclinidae packstone–rudstone, F5 Bioclastic coralline algal Lepidocyclinidae packstone–rudstone, F6 Bioclastic Lepidocyclinidae – Nummulitidae wackestone–packstone–grainstone, F7 Bioclastic Lepidocyclinidae – Neorotalia – coral packstone–rudstone, F8 Coral boundstone, F9 Bioclastic porcellaneous foraminifera – coral packstone, F10 Bioclastic coralline algal bryozoan wackestone–packstone, F11 Bioclastic benthic foraminifera (perforate and imperforate) wackestone–packstone, and F12 Bioclastic benthic foraminifera (imperforate) wackestone–packstone. From the base to the top of the section the facies types indicate: F1 aphotic zone and outer shelf; F2 aphotic to oligophotic zones on the outer and middle shelf (distal); F3 and F4 oligophotic zone and distal middle shelf; F5, F6 and F7 mesophotic zone situated on the middle shelf (proximal); F8, F9, F10 and F11 euphotic zone and inner shelf (open marine), F12 euphotic zone and inner shelf (slightly restricted). The Pir-Sabz coral fauna has a clear Mediterranean affinity and is represented by at least six different scleractinian species which formed a non-reefal coral community on the proximal middle-shelf. © 2018 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany.
Journal of African Earth Sciences (1464343X) 140pp. 94-113
The Upper Cretaceous sediments in the Moghan area, NW Iran, contain diverse planktonic and benthic foraminifera, with a total of 33 genera and 53 species (17 genera and 38 species of planktonic foraminifera and 16 genera and 15 species from benthic foraminifera), which led to the identification of six biozones spanning the middle Campanian to late Maastrichtian. A detailed paleontological study and biostratigraphic zonation of these sequences has been carried out in four surface sections. This study shows that there are two different facies in the Moghan area, based on the faunal content. A deep open marine condition exists in the Molok, Selenchai and Nasirkandi sections. In these sections, Upper Cretaceous sequences have diverse planktonic foraminiferal species including the Globotruncana ventricosa (middle to late Campanian), Globotruncanella havanensis (late Campanian), Globotruncana aegyptiaca (latest Campanian), Gansserina gansseri (latest Campanian to early Maastrichtian), Contusotruncana contusa- Racemiguembelina fructicosa (early to late Maastrichtian) and Abathomphalus mayaroensis (late Maastrichtian) zones. This deep open marine setting grades laterally into shallower marine condition dominated by large benthic foraminifera such as Orbitoides media, Orbitoides gruenbachensis, Orbitoides cf. apiculata, Lepidorbitoides minor, Pseudosiderolites sp., Siderolites praecalcitrapoides, Siderolites aff. calcitrapoides and Siderolites calcitrapoides. This facies is mainly recorded in the Hovay section. A detailed biostratigraphic zonation scheme is presented for the studied sections and correlated with the results of other studies in the Tethyan realm. This is the first biozonation scheme for Upper Cretaceous sequences of the Moghan area that can be used as a basis for ongoing studies in this area and other parts of Tethys basin. © 2018 Elsevier Ltd
Marine and Petroleum Geology (02648172) 92pp. 437-461
This study is based on seven outcrops along a regional transect in the central subdivision of the Zagros Foreland Basin. This NE-SW trending transect extends for 140 km and covers the northern margin of the Asmari intra-shelf basin in dip direction (from proximal to distal). Results of facies analysis led to the recognition of eight facies associations (Planktonic Wkt, Nummulitic Eu F/R, Alg LR Pkt, Coralgal F-R/Bdt, LR LPBF P-G, Epy.R PBF P-G, Dol M, and TRGS) along the depositional dip direction. They are dominated by large and flat rotalids (e.g., Nummulites, Lepidocyclina and Spiroclypeus), coral and coralline red algae (e.g., build-up features), porcellaneous benthic foraminifera (e.g., Archaias, Peneroplis, and Borelis), and fossiliferous lime-mud. Spatial and temporal distribution of these facies associations conform five platform types with different depositional profiles: a) a Nummulites-bearing mixed terrigenous/carbonate distally steepened ramp, lower Rupelian, b) a Nummulitidae-Lepidocyclina bearing carbonate distally steepened ramp, upper Rupelian-lower Chattian, c) a Coral bearing flat-topped open shelf, middle-upper Chattian, d) an Aquitanian homoclinal ramp, and e) a very shallow-water Burdigalian carbonate shelf. Amongst these platform types, the Late Rupelian-Early Chattian carbonate ramp additionally consists of three successive phases and the Middle-Late Chattian flatted top open shelf was developed in two phases. The changes in platform type resulted from changes in the carbonate producing biotas, sediment redistribution processes and significant impact of relative sea level changes. © 2017 Elsevier Ltd
Kalanat, B. ,
Mahmudy-gharaie, M.H. ,
Vahidinia, M. ,
Vaziri moghaddam, H. ,
Kano, A. ,
Kumon, F. Cretaceous Research (1095998X) 86pp. 261-275
A Cenomanian/Turonian boundary succession in the northeastern Tethyan realm, Kopet-Dagh Basin in NE Iran, was studied to examine the effects of biological productivity, atmospheric CO2 concentration, and sea water temperature on the benthic foraminiferal assemblages. Our δ13Ccarb and δ13Corg chemostratigraphy of the Gharesu section reveals three positive peaks that can be correlated with carbon isotope peaks in the CTB reference sections (Eastbourne, England; Pont d'Issole, France; Rock Canyon, USA). Two intervals of suspected high sea surface temperature were distinguished according to pCO2 maxima (Δ13C; difference between δ13Ccarb and δ13Corg), low δ18O values, and high TOC bearing deposits. These intervals are followed by falling pCO2 and cooling caused by enhanced burial of organic matter into the sediments. Patterns of changes in the benthic foraminiferal assemblages are correlated with these climatic changes. Warm intervals are characterized by low diversity of benthic foraminifera, dominance of agglutinated forms, and high abundance of infaunal morphogroups or opportunistic epifauna due to intensified weathering, high primary productivity, and oxygen deficiency in the bottom water. The cold intervals coincide with higher diversity of benthic foraminifera and dominance of calcareous benthic taxa. © 2017
Journal of African Earth Sciences (1464343X) 134pp. 33-47
In order to evaluate Oceanic Anoxic Event 2 (OAE2) at the Cenomanian-Turonian boundary and its effects on benthic foraminifera, the Taherabad stratigraphic section in the east of Kopet-Dagh basin was studied for pattern of changes in benthic foraminiferal communities. Total Organic Carbon (TOC) concentration at the Taherabad section shows that black shale was not deposited in this succession but TOC increases up to 0.68 wt% in the three intervals of Rotalipora cushmani, Whiteinella archaeocretacea and Helvetoglobotruncana helvetica Zones. Also, Total Nitrogen (TN) values were measured in our study succession. High TOC/TN ratios (up to 18) occur in the intervals of TOC enrichment. Foraminiferal assemblages, TOC, TOC/TN and Detrital Index (DI, an index for detrital input) changes in the study section allowed us to divided study section into 4 intervals. Interval A and C are associated with low abundance and diversity of benthic assemblages coeval with lack of planktic foraminifera. Benthic assemblages are strongly dominated by shallow and deep infaunal agglutinated foraminifera including Lagenammina, Saccammina, Reophax and Tritaxia. The foraminiferal composition associated with higher TOC, TOC/TN and DI suggest an influx of fresh water to the basin in the warm-wet periods, which diminished hospitable conditions for planktic foraminifera and probably enhanced land-derived organic matter and/or primary productivity. The hyposaline cap led to development of salinity-stratified water and induce bottom water oxygen depletion. By contrast, the assemblages found in the interval B and D are more diverse and contain high abundance of planktic and calcareous benthic foraminifera. Common benthic taxa in these parts are praebuliminids, lenticulinids, gavelinellids and Valvulineria. These assemblages associated with lower TOC, TOC/TN and DI indicate decreased detrital input and more normal marine condition resulted in improved ventilation of sea-floor, which is favorable for planktic and benthic taxa. © 2017 Elsevier Ltd
Boletin de la Sociedad Geologica Mexicana (14053322) 69(1)pp. 59-85
In 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.
Geopersia (22287817) 7(1)pp. 1-9
The Cenomanian-Turonian Gharesu section in the east of Koppeh-Dagh basin have been investigated to determine the relationship between palaeoenvironmental perturbations and nitrogen cycling across OAE2. This succession is composed of 43 m shale and marl interbedded with glauconitic sandstone and lies between Aitamir-Abderaz formations boundary. The nitrogen isotope values fluctuate between 0‰ to +3‰ and TOC/TN ratios range from 3.5 to 20.5 in this section. The TOC/TN exhibits high ratios in the organic-rich sediments which were deposited in a low-oxygen environment because nitrogen-rich organic matter was preferably degraded in this condition. The d15N values are also low in the organic-rich sediments which indicate a nitrogen fixation process as a consequence of greenhouse climate, enhanced productivity and expanded oxygen minimum zone during OAE2.
Early Aptian Lithocodium–Bacinella floatstone facies from the central Persian Gulf were a response of the Dariyan platform to a global disturbance. Carbon- and strontium-isotope data combined with facies analysis for the Late Barremian–Early Aptian Dariyan Formation record the timing of OAE1a and provide evidence for a causal relationship between OAE1a and Lithocodium–Bacinella occurrence. Carbon isotope stratigraphy allows the correlation of OAE1a-related segments in the Dariyan carbonates with other Tethyan shallow-water platform and pelagic reference sections. Strontium-isotope stratigraphy provides a numerical age of 124.3 ± 0.1 to 124.8 ± 0.1 Ma for OAE1a, indicating earliest Aptian, in the central Persian Gulf. Correlation of carbon isotope stratigraphy and Lithocodium–Bacinella-bearing facies shows that the Dariyan L–B occurrence post-dated OAE1a. The delay in the development of the Dariyan L–B facies is ascribed to the physiographic setting and a set of regional parameters including nutrient levels, alkalinity, and tolerance of dominant carbonate producers to OAE1a. Lithocodium–Bacinella floatstone facies of the Dariyan Formation is characterized by patchy-cloudy to columnar and oncoidal morphotypes. These growth patterns reflect the environmental conditions of probable high sedimentation rate, low alkalinity, low trophic level, and high oxygenation. Lithocodium–Bacinella facies and associated foraminifera and algae suggest peritidal to lagoonal (inner ramp) conditions for the upper Dariyan interval. © 2016, Springer-Verlag Berlin Heidelberg.
Journal of Petroleum Geology (17475457) 39(3)pp. 269-286
The late Aptian disconformity at the top of the carbonate-dominated Dariyan Formation is a regional-scale surface recognised throughout SW Iran and adjacent areas to the south. This study investigates the disconformity using wireline logs, petrographic analyses, SEM observations, and CL and stable isotope data from an oilfield offshore SW Iran. The top-Dariyan surface in the studied field is characterised by erosional incisions and clastic-filled fissures which, together with secondary porosity in the underlying carbonates, uranium enrichment and meteoric infill cements, are interpreted as subaerial exposure-related features. The clastic-filled fissures were identified from gamma-ray logs in horizontal wells, and infill material is composed of argillaceous carbonates, clays, quartz and iron-bearing minerals. The correlation of GR logs in 19 vertical wells resulted in the recognition of erosional incisions (up to about 16 m deep) on the top-Dariyan surface, together with thickening of siliciclastic sediments in the overlying basal part of the Kazhdumi Formation. Back-filled sediments in erosional incisions may form potential exploration targets. Secondary porosity in the uppermost 20 m of the Dariyan Formation was created by meteoric processes during subaerial exposure. Cathodoluminescence microscopy of diagenetic cements, carbon and oxygen isotope data and elemental analyses were used to reconstruct the diagenetic history of the carbonates in the Upper Dariyan interval. © 2016 The Authors. Journal of Petroleum Geology © 2016 Scientific Press Ltd.
Geologica Acta (16965728) 14(4)pp. 363-384
Upper Cretaceous mixed carbonate-siliciclastic sequences are among the most important targets for hydrocarbon exploration in the Moghan area, located in the eastern Para-Tethys Basin. Despite of their significance, little is known about their facies characteristics and depositional environments. Detailed facies analysis and paleoenvironmental reconstruction of these sequences have been carried out in eight surface sections. Accordingly, four siliciclastic facies, eight carbonate facies and one volcanic facies have been recognized. Detailed facies descriptions and interpretations, together with the results of facies frequency analysis, standard facies models and Upper Cretaceous depositional models of Para-Tethys Basin, have been integrated and a non-rimmed carbonate platform is presented. This platform was affected by siliciclastic influx, in the form of coastal fan delta and submarine fans in the shallow- to deep-marine parts, respectively. This model is interpreted to be shallower in the central and northeastern parts of the Moghan area. Toward the southeast and southwest, this shallow platform turns into deep marine settings along steep slopes without remarkable marginal barriers. © M. Omidvar, A. Safari, H. Vaziri-Moghaddam, H. Ghalavand, 2016 CC BY-SA.
Geologica Carpathica (13368052) 67(5)pp. 451-462
Two Late Cenomanian-Early Turonian (C-T) intervals of the eastern part of the Kopet-Dagh basin, NE Iran have been investigated to evaluate the response of planktonic foraminifera to the geological event OAE2. The Gharesu and Taherabad sections with the thicknesses of 30 m and 22.5 m are composed of shale and marl interbedded with glauconitic sandstone. Three biozones Rotalipora cushmani, Whiteinella archaeocretacea and Helvetoglobotruncana helvetica were recognized based on study of planktonic foraminifera, in these sections. We observed the patterns of planktonic foraminiferal assemblage changes around the C-T boundary and divided this succession into several successive intervals. This study confirms that OAE2 was a long term event. A gradual perturbation in the study successions starts in the interval 1 with low abundance and diversity of planktonic foraminifera. An enhanced oxygen minimum zone (OMZ) occurs in the interval 3 which coincides with a temporary absence of planktonic foraminifera and sedimentation of framboidal pyrite. High diversity of planktonic foraminifera and appearance of new genera in the interval 5 indicate return of normal conditions to the basin. A significant short-term sea surface temperature cooling is also indicated by planktonic foraminiferal turnover and carbonate contents in the interval 2 which is comparable with other parts of the Tethys Ocean, Boreal sea and Atlantic region. © 2016 Geologica Carpathica.
Arabian Journal of Geosciences (discontinued) (18667538) 8(10)pp. 8373-8384
A Cenomanian-Turonian interval in the Mozduran pass section, eastern part of Kopet-Dagh basin (NE of Iran), was measured and studied in order to interpret the biostratigraphy and paleoecology (based on distribution of planktonic foraminifera). This section consists of 52.5-m light and gray marl and coincides with the Aitamir and Abderaz formation boundary. Based on study of 47 samples, 11 planktonic foraminifera genera and 27 species were encountered, and the following zones have been defined: Rotalipora cushmani Total Range Zone and three zones of Helvetoglobotruncana helvetica, Dicarinella primitiva-Marginotruncana sigali, and Dicarinella concavata as condenced zones. This study shows that the sediment record is incomplete in the section. This unconformity is just after a drowning succession, places in the Late Cenomanian-Early Turonian Whiteinella archaeocretacea Zone, and interpreted as a drowning unconformity. A paleoenvironmental model has been formulated to explain the successive paleocommunity changes during this drowning of the platform. We attribute the drowning of some parts of the platform to the occurrence of the Cenomanian-Turonian oceanic anoxic event. The impingement of anoxic waters over the platform could produce the drastic reduction of the carbonate producing observed in the stratigraphic section and therefore a reduction in carbonate accumulation rates. Subsidence and the Late Cenomanian-Early Turonian sea level rise were then able to drown the platform. © 2015, Saudi Society for Geosciences.
Facies (01729179) 61(1)pp. 1-32
In the easternmost part of the main Izeh Zone of the Zagros Mountains, Iran, the Asmari carbonate platform system of Oligo-Miocene age is superbly exposed in three-dimensional outcrops displaying a variety of carbonate facies associated with well-preserved depositional geometries. The main biogenic components of the Asmari Formation are large benthic foraminifera, corals, coralline algae, and planktonic foraminifera. The Asmari carbonate platform system, based on dating by large benthic foraminifera, biogenic components, and depositional geometries, is divided into four distinct intervals of carbonate platform growth. This depositional system during the Rupelian and Rupelian/earliest Chattian was a carbonate ramp. During the Chattian, the system was dominated by coral buildups, and later, porcellaneous benthic foraminifera and coralline algae were prominent during late Chattian- early Miocene time. Six major depositional sequences are distinguished, with an overall systematic progradationfrom NE to SW. These progradations are evidenced in the Rupelian and lower Chattian by major changes in facies and stratal architectures, whereas such complex geometries are not observed in the upper Chattian and lower Miocene carbonates, since only platform-top facies are exposed and there are no outcrops of the platform margin. Comparison of the proposed depositional sequences with those reported in the Dezful Embayment and adjacent areas suggests a correlation with the global sea-level curve. © Springer-Verlag Berlin Heidelberg 2014.
Shabafrooz, R. ,
Mahboubi, A. ,
Vaziri moghaddam, H. ,
Moussavi-harami, R. ,
Ghabeishavi a., A. ,
Al-aasm, I.S. Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749) 276(1)pp. 121-146
A high-resolution well data in the Gachsaran and Bibi-Hakimeh oilfields and outcrops from nearby Mish Anticline, in the SE Dezful Embayment and the Izeh Zone of the Zagros Basin were used in this study to investigate facies and depositional settings of the Asmari Formation (Oligo- Miocene). The main skeletal constituents in the Asmari Formation include large benthic foraminifera, red algae, coral and planktonic foraminifera. Six foraminiferal assemblages have been distinguished and their palaeoenvironmental settings were suggested based on their position along the depositional profile as well as in comparison with published work. Six main facies have been distinguished, representing a shallowing upward cycles, including planktonic foraminifera dominated-facies, nummulitidae-lepidocyclinids facies, Nummulites facies, coral-coralline red algal facies, small benthic foraminifera facies and mudstone facies. Facies changes during the Rupelian- to Early Miocene are generally associated with carbonate ramp models. These including a number of distinct phases, namely: a Nummulites-dominated ramp with minor corals during the Rupelian, a nummulitidae and lepidocyclinids-dominated ramp during the Rupelian/Chattian, a coral- to algal-dominated ramp during the most of the Chattian and a dolomitized low angle benthic foraminifera-dominated ramp during Early Miocene. © 2015 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.
Acta Geologica Sinica (English Edition) (17556724) 88(6)pp. 1681-1695
A rich assemblage of planktonic foraminifera has been studied from an outcrop of the Gurpi Formation, the hydrocarbon source rock in the southwest Iran, Deh Dasht area (Kuh-e Siah anticline). Based on the distribution of the planktonic foraminifera, eight biozones have been recognized that included: Dicarinella concavata Interval Zone (Earliest Santonian), Dicarinella asymetrica Total Range Zone (Santonian to Earliest Campanian), Globotruncanita elevata Partial Range Zone (Early Campanian), Globotruncana ventricosa Interval Zone (Middle to Late Campanian), Radotruncana calcarata Total Range Zone (Late Campanian), Globotruncanella havanensis Partial Range Zone (Late Campanian), Globotruncana aegyptiaca Interval Zone (Late to latest Campanian), Gansserina gansseri Interval Zone (Latest Campanian to Early Maastrichtian). These biozones indicates that the Gurpi Formation deposited during the Early Santonian- Early Maastrichtian. These biozones are compared to the most standard biozones defined in Tethysian domain. Based on distribution of morphotype groups of planktonic foraminifera, planktonic to benthic ratio (P/B) and content of carbonate, nine third-order sequences are recognized. © 2014 Geological Society of China.
Mohammadi, E. ,
Hasanzadeh-dastgerdi, M. ,
Ghaedi, M. ,
Dehghan, R. ,
Safari, A. ,
Vaziri moghaddam, H. ,
Baizidi, C. ,
Vaziri, M. ,
Sfidari, E. Carbonates and Evaporites (08912556) 28(3)pp. 321-345
The aim of this research is to shed light on the distribution of Rupelian (Early Oligocene) and evaporate deposits as evidences for timing and trending of opening and closure of the Tethyan Seaway. To accomplish these goals, four sets of data were scrutinized: (1) two stratigraphic sections (Ghohroud and Vidoja) of the Qom Formation in the southern and southwestern Kashan (to determine the age of their lower deposits), (2) results of the study of more than 100 stratigraphic sections of the Qom Formation, (3) Geological maps of Iran Sheets and (4) more than 30 geological maps of different parts of Iran. Consideration of four sets of data led to the following conclusions. Deposition of the Qom Formation (with Rupelian-Burdigalian range) took place in three NW-SE-trending basins: Sanandaj-Sirjan (fore-arc basin), Urumieh-Dokhtar magmatic arc (intra-arc basin) and Central Iran (back-arc basin). Marine conditions in the low latitudes of these three basins started in the Rupelian. Rupelian deposits are vastly distributed in the intra-arc and fore-arc basins but in the back-arc basin Rupelian deposits are deposited only in a few places in close proximity of the magmatic arc. It is remarkable that mostly all of the intra-arc Rupelian deposits-bearing sections are underlain by Eocene volcanic rocks. Latitudinally, the Rupelian deposits of the Qom Formatiom are deposited below 34 2′N, the Chattian deposits continue to 35 N, but above 35 N the Qom Formation is deposited during the Miocene, based on previous age dating; therefore, transgression of the Tethyan Seaway on the Iranian Plate started from the southeast and continued northwestward gradually. The last true Nummulites spp. became extinct at the top of Late Rupelian and all of the in situ Nummulites-bearing layers of the Qom Formation are Rupelian in age. According to the presence of Nummulites spp. (Nummulites fichteli, Nummulites vascus, Nummulites sp.), the lower 185 m of the Ghohroud section and whole deposits of the Vidoja section are attributed to the Rupelian. Evaporate deposits of the Qom Formation are deposited in a rather small area of Central Iran back-arc basin and are deposited totally in the Early Miocene (Aquitanian-Burdigalian). This indicates that due to the compressive tectonic regime in the Central Iran back-arc basin, the gates to the open ocean became restricted in the Early Miocene gradually. During the Aquitanain and Burdigalian, restricted marine conditions prevailed and episodic precipitation of evaporate deposits occurred. In the Qom area near the depocentre of the Qom basin, evaporates were precipitated episodically. Deposition of evaporate deposits took place along the concave side of an assumptive curved line crossing from SE of Anarak, Nain, Navab Anticline (SE of Kashan), Shourab (SE of Qom), immediate S, SW and W of Qom, N of Howz Soltan Lake, SW of Tehran, SW, W and SE of Varamin, NE of Garmsar and NW, N and NE of Semnan. Distribution of the Qom Formation, evaporate deposits and Rupelian deposits are illustrated on new maps shown herein as figures. © 2012 Springer-Verlag Berlin Heidelberg.
Iranian Journal of Science and Technology, Transaction A: Science (10286276) 36(1)pp. 51-60
Biofacies and palaeoecology of the limestone of the Jahrum Formation in the Lar area in the southwest of Iran (Zagros Basin) is addressed in this paper. Our detailed analysis of biofacies and palaeoecology shows that the Jahrum Formation in the studied area were deposited in a carbonate open shelf dominated by heterozoan and, subordinately, photozoan skeletal assemblages. Based on analysis of larger benthic foraminiferal assemblages and biofacies features, two major depositional environments are identified. These include inner shelf and middle shelf environments. The inner shelf facies is characterized by wackestone-packstone, dominated by various taxa of imperforate foraminifera. The middle shelf is represented by wackestone-packstone with a diverse assemblage of larger foraminifera with perforate wall. The distribution of the larger benthic foraminifera indicates that shallow marine carbonate sediments of the Jahrum Formation at the studied areas have been deposited in the photic zone of tropical to subtropical oceans.
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749) 263(1)pp. 1-16
Paleontological and biostratigraphical studies on a carbonate platform succession from southwestern Iran documented a high diversity of shallow-water benthic foraminifera during the Oligocene-Miocene. Larger foraminifera are the main means for stratigraphie zonation of the As-mari Formation. The distributions of larger benthic foraminifera in two outcrop sections (Khaviz and Bangestan Anticlines) in the central part of the Zagros Fold-and-Thrust Belt (Iran) are used to determine the age of the Asmari Formation in this area. Four assemblage zones are recognized by distribution of larger benthic foraminifera in the study areas. Assemblage zone 1 is Rupelian-Chat-tian in age and occurs in the lower part of the Asmari Formation. Assemblage zone 2 suggests a Chattian age. Assemblage zone 3 indicates an Aquitanian age and Assemblages zone 4 is restricted to the Burdigalian. Assemblage zones 1 (Rupelian-Chattian) and 2 (Chattian age) were not recognized in the Asmari Formation of the Bangestan Anticline section. The Oligocène shallow carbonate part of the Asmari Formation has been replaced by the basinal marl of the Pabdeh Formation in the Bang-estan Anticline. This suggests that the Bangestan Anticline section was situated in a basinal position during the Oligocene. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung Stuttgart Germany.
Historical Biology (08912963) 24(1)pp. 91-100
In the Central Iran Basin, the mixed carbonate-siliciclastic deposits of the C member of the Qom Formation were deposited on a carbonate platform which is dominated by rhodalgal associations occurring in tropical-subtropical environment. The biogenic rhodalgal association is dominated by bryozoa, coralline red algae, bivalves and echinoids together with smaller amounts of photo-dependent biota including large benthic foraminifera and corals. The abundance of heterozoan association and the bloom of suspension-feeding organisms are the result of an increase in nutrient availability which has profound controlling effect on the biotic system. The low occurrence of symbiont-bearing benthic foraminifera and coral, typical of stable, oligotrophic condition, represents their low tolerance to unstable, nutrient-rich environment. In the investigated Oligocene-Miocene shallow marine carbonate succession, 10 different microfacies were distinguished through depositional texture and biotic components. The rock sequences investigated are referred to an open shelf carbonate platform in which the depositional environments range from outer shelf to inner shelf conditions. © 2012 Copyright Taylor and Francis Group, LLC.
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749) 263(2)pp. 167-184
The distribution of carbonate grain associations in the Asmari Formation (Dill Anticline, Dezful Embayment of the Zagros Basin was examined. The Asmari Formation was deposited in a subtropical environment in an oligophotic to euphotic zone. The setting was a carbonate ramp with oligotrophic to mesotrophic conditions as indicated by the association of large benthic foraminifera (Heterostegina, Spiroclypeus, Amphistegina, Neorotalia, Miogypsinoides, Borelis, Archaias, Pen-eroplis and Dendritina) with coral debris during Chattian to Early Aquitanian and Burdigalian times. The carbonate grain associations within the Asmari Formation indicate: 1. that the lower part of the Asmari Formation (Early Chattian) was deposited in normal saline waters (middle ramp), and 2. that the middle and upper parts of the Asmari Formation (Middle Chattian-Burdigalian) experienced higher to hyper-saline waters (semi-to restricted lagoon environments of inner ramp). The diversity of large benthic foraminifera, the rarity of coral debris and the absence of green algae in the Dill Anticline area indicate a minimum surface water temperature of < 20 °C Based on the faunal as-sociations, the nannofor (aphotic zone-outer shelf and also foralgal (oligophotic to rarity mesophotic-middle shelf)) associations reflect a deeper water environment relative to the Asmari Formation in Khuzestan and the Coastal Fars provinces. Foramol associations (euphotic zone-inner shelf) are asso-ciated with the shallow part of the Asmari Formation and the coeval Champeh Member of the Gach-saran Formation into the Interior Fars province during the Oligocene (Rupelian-Early Chattian). Fo-ramol associations embraced the carbonate platform from the Late Chattian until the Early Miocene. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung Stuttgart Germany.
Carnets de Geologie (17652553) pp. 173-181
The limnic ostracode Frambocythere tumiensis zagrosensis subsp. nov. (Limnocytheridae, Timiriaseviinae), has been found for the first time in Iran. The strata containing this species are in the lower part of the Tarbur Formation in the interior Fars of the Zagros Mountains. The Late Maastrichtian age is indicated by rudists, larger foraminifers (Omphalocyclus macroporus, Loftusia spp.) and plank-tonic foraminifers(Contusotruncana contusa-Racemiguembelina fructicosa Zone) present in the upper part of the Tarbur Formation. The Maastrichtian age is confirmed by the occurrence in the same strata of the charophytes Platychara shanii, Peckichara cristellata and Stephanochara cf. producta. The genus Frambocythere COLIN, 1980, was until now known mostly from the Upper Maastrichtian to Middle Eoce-ne of southern Europe, India and China, as well as the Albian of the Democratic Republic of Congo. The presence of Frambocythere gr. tumiensis in Iran is therefore a newly recognized link between southern Europe and the Far East (China).
Carbonates and Evaporites (08912556) 26(2)pp. 167-180
In this research, biostratigraphy and paleoecological implications related to the carbonates of the Asmari Formation located at the Naura anticline, Interior Fars of the Zagros Basin Iran, are discussed. The Asmari Formation at the study area is Rupelian-Chattian in age. Age was determined by the occurrence of 22 genera and 41 species which led to identification of four faunal assemblages: (1, Globigerina-Tuborotalia cerroazulensis- Hantkenina; 2, Nummulites vascus-Nummulites fichteli; 3, Lepidocyclina-Operculina-Ditrupa; 4, Archaias asmaricus- Archaias hensoni-Miogypsinoides complanatus). Based on faunal associations and biofacies analysis with emphasize on large benthic foraminifera and coralline red algae communities, the following paleo-ecological factors are defined for deposition of the Asmari Formation at the study area: water salinity of 34 to more than 50 psu, depth zones of 0-35 m of inner and middle part of proximal open shelf, 35-150 m of middle open shelf and more than 200 m of outer open shelf, water temperature of 18-25°C in a tropical to sub-tropical environments, oligophotic to near mesotrophic conditions and grain association communities of foralgal and rhodalgal. © Springer-Verlag 2011.
Historical Biology (08912963) 23(2-3)pp. 145-153
The Maastrichtian shallow-water carbonate platform (Tarbur Formation) is described from outcrop in southwest Iran. It is characterised by eight microfacies types, which are dominated by larger foraminifera, rudist debris and dasycladacean algae. They are grouped into four distinct depositional settings: tidal flat, lagoon, barrier and open marine. The depositional settings include stromatolitic boundstone of tidal flat, peloidal dasycladacean miliolids wackestone and peloid bioclastic imperforate foraminifera wackestone of restricted lagoon, Omphalocyclus miliolids bioclast packstone-grainstone and miliolids intraclast bioclast packstone-grainstone of open lagoon, rudist bioclast grainstone of inner-platform shoals and rudist bioclast floatstone-rudstone and bioclastic wackestone of open-marine environments. The facies and faunal characters are typical of a ramp-like open shelf. The lack of reef-constructing organisms resulted in a gently dipping ramp morphology for the margin and slope. On the basis of facies analysis, three depositional sequences (third order) are defined. © 2011 Taylor & Francis.
Carbonates and Evaporites (08912556) 26(3)pp. 255-271
Qom Formation (Oligo-Miocene marine deposits, Central Iran) in the South of Kashan, was studied in order to determine its microfacies and depositional environment. Thirteen microfacies (MF A-M) were distinguished based on petrography, sedimentological features, components distribution and present fauna. According to recognized microfacies and absence of gravity deposits, real and continuous reef, barrier and storm structures, carbonate platform of the Qom Formation in South of Kashan developed on an open shelf without effective barriers separating it from the sea. The cooccurrences of miliolids and planktonic foraminifera in planktonic microfacies is the reliable evidences for absence of any reefal, oolitic and bioclastic barriers in depositional environment, and deposition of the study section on an open shelf, as in the absence of barrier, currents removed miliolids to deeper parts of sea (basin). Three major depositional environments were identified in the Oligo-Miocene succession in the study section, on the basis of the distribution of the foraminifera and vertical facies relationships. They include inner shelf, middle shelf and proximal outer shelf. Inner shelf includes MF A-G and characterized by abundant imperforate foraminifera. Middle shelf comprises MF H-J and characterized by association of larger benthic foraminifera with hyaline wall. Proximal outer shelf includes MF K-M and characterized by the presence of planktonic foraminifera and absence of larger benthic foraminifera, as well as abundance of lightindependent, heterotroph organisms. © Springer-Verlag 2011.
Facies (01729179) 57(3)pp. 431-446
The Asmari Formation is a thick carbonate succession of the Oligo-Miocene in Zagros Mountains (southwest Iran). In order to interpret the facies and depositional environment of the Asmari Formation, three measured sections were studied in Fars area for microfacies analyses. There, 12 microfacies types are distinguished based on their depositional textures, petrographic analysis, and fauna. Thus, three major depositional environments were identified in the Asmari Formation including open-marine, reef/shoal, and lagoon. These depositional environments correspond to inner, middle, and outer ramp. © 2010 Springer-Verlag.
Iranian Journal of Science and Technology, Transaction A: Science (10286276) 34(3)pp. 257-266
This research is focused on facies distribution, palaeoecology and palaeoenvironment of the Guri Member of the Mishan Formation in Kuh-e Shur and Kuh-e Kurdeh sections at the Lar area, Fars province. The Guri Member is composed of limestone, marly limestone and marl and the thickness at Kuh-e Shur and Kuh-e Kurdeh is about 72 and 110 meters, respectively. Based on petrographical studies of 120 thin sections, 8 microfacies have been identified that are deposited in open shelf environment (inner and middle shelf). Palaeolatitudinal reconstructions based on skeletal grains suggests that carbonate sedimentation of Guri Member took place in tropical waters under oligotrophic conditions, a typical environment for photozoan assemblages. These biotic assemblages of the Guri Member belong to foralgal association and may be broadly defined as comprising heterozoan assemblages. An important factor controlling the spread of heterozoan assemblages during the Early Miocene in the study areas seem to be related to the palaeoecology and evolution of zooxanthellate corals. © Shiraz University.
Journal of Asian Earth Sciences (18785786) 37(3)pp. 275-285
The Sarvak Formation (Albian to Turonian in age) of the Zagros basin is a thick sequence of shallow-water carbonates. This work focuses on the microfacies and sedimentary environment of the margin of the Cenomanian intrashelf basin. In the study area (southwest of Iran), the Sarvak Formation is subdivided into 12 microfacies that are distinguished by petrographic analysis on the basis of their depositional textures and fauna. In addition, four major depositional environments were identified in the Sarvak Formation. These include shelf lagoon, platform margin, slope and basin environmental settings, which are interpreted as a carbonate shelf without an effective barrier separating the platform from the open ocean. © 2009 Elsevier Ltd. All rights reserved.
Revista Mexicana de Ciencias Geologicas (10268774) 27(1)pp. 56-71
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 (08912556) 25(2)pp. 145-160
The Asmari Formation is exposed at the Dill anticline in the Dezful Embayment of the Zagros foreland basin with 206 m thickness comprising thin, medium and thick to massive bedded carbonates. The Asmari Formation is Late Oligocene (Chattian)-Early Miocene (Burdigalian) in age at the study area. Ten facies characterizing upward gradual shallowing trend of an open marine (MF 1-3), shoal (MF 4), semi-restricted and restricted lagoon (MF 5-9) and near-shore lagoon (MF 10) depositional environments were identified. Based on environmental interpretations, a homoclinal ramp consisting of inner and middle parts prevails. MF 4-10 were characterized by the occurrence of large and small porcelaneous benthic foraminifera representing a shallow-water setting of an inner ramp influenced by wave and tide processes. MF 1-MF 3 with large and small hyaline benthic foraminifera represent a deeper fair water wave base of a middle ramp setting. Three-third-order depositional sequences were recognized. Sequence 1 mostly consists of an open marine to the lower part and is followed by semi to restricted lagoon facies. Sequences 2 and 3 are characterized by semi to restricted lagoon facies. Moreover, the relative sea-level change curves correlate with the global sea-level change curves. © Springer-Verlag 2010.
Historical Biology (08912963) 21(3-4)pp. 215-227
Platform carbonate sediments of Oligocene-Miocene age (Asmari Formation) in the Zagros Basin (SW Iran) have been investigated in order to determine their paleoecology and depositional environment. The Zagros Basin is the result of the opening and closure of the Neo-Tethys Ocean along the northeastern border of the Arabian Plate. The thick sedimentary sequences of the Zagros Basin contain rocks ranging in age from Cambrian to recent. The geological evidence suggests that the region was part of a passive continental margin, which subsequently underwent rifting in the Permo-Trias and collision in the Late Tertiary. The Asmari carbonate system was dominated by foraminifera and corallinacean assemblage. Based on the distribution of the larger foraminifera, four assemblage zones have been recognised. Facies analysis allowed the recognition of nine microfacies types that are grouped into three depositional environments that correspond to the inner, middle and outer shelf. The biota assemblage of the Asmari Formation suggests that carbonate sedimentation took place in tropical waters and oligotrophic to slightly mesotrophic conditions. Our detailed analysis of microfacies and paleoecology shows that the Asmari Formation deposited on a carbonate open shelf dominated by heterozoan and, subordinately, photozoan skeletal assemblage. © 2009 Taylor & Francis.
Historical Biology (08912963) 21(1-2)pp. 17-31
Paleontological and biostratigraphical studies on carbonate platform succession from southwest Iran documented a great diversity of shallow-water benthic foraminifera during the Oligocene-Miocene. Larger foraminifera are the main means for the stratigraphic zonation of carbonate sediments. The distributions of larger benthic foraminifera in two outcrop sections (Abolhayat and Lali) in the Zagros Basin, Iran, are used to determine the age of the Asmari Formation. Four assemblage zones have been recognized by distribution of the larger benthic foraminifera in the study areas. Assemblage 3 (Aquitanian age) and 4 (Burdigalian age) have not been recognized in the Abolhayat section (Fars area), due to sea-level fall. The end Chattian sea-level fall restricted marine deposition in the Abolhayat section and Asmari Formation replaced laterally by the Gachsaran Formation. This suggests that the Miocene part of the formation as recognized in the Lali section (Khuzestan area) of the Zagros foreland basin is not present in the Abolhayat outcrop. The distribution of the Oligocene larger benthic foraminifera indicates that shallow marine carbonate sediments of the Asmari Formation at the study areas have been deposited in the photic zone of tropical to subtropical oceans. Based on analysis of larger benthic foraminiferal assemblages and microfacies features, three major depositional environments are identified. These include inner shelf, middle shelf and outer shelf. The inner shelf facies is characterized by wackestone-packstone, dominated by various taxa of imperforate foraminifera. The middle shelf is represented by packstone-grainstone to floatstone with a diverse assemblage of larger foraminifera with perforate wall. Basinwards is dominated by argillaceous wackestone characterized by planktonic foraminifera and large and flat nummulitidae and lepidocyclinidae. Planktonic foraminifera wackestone is the dominant facies in the outer shelf. © 2009 Taylor & Francis.
Facies (01729179) 55(2)pp. 243-257
This study is focused on the sedimentary environments, facies distribution, and sequence stratigraphy of the Coniacian-Santonian sediments of the Bangestan Palaeo-high in the Bangestan Anticline (Zagros, Iran). These sediments are subdivided into nine microfacies types belonging to various sedimentary environments, ranging from continental lacustrine to very shallow and relatively deep-water (hemipelagic to pelagic) marine environments. The lower boundary of the studied sections is characterised by an unconformity. The lacustrine and very shallow marine sediments at the base of the studied sections are interpreted as a lowstand system tract. The establishment of an open shelf carbonate platform took place during the transgressive system tract. The maximum flooding zone of the Early Santonian is an important surface because it extends from the distal to the proximal part of the depositional environment. © Springer-Verlag 2008.
Historical Biology (08912963) 20(3)pp. 191-201
The Jahrum Formation was deposited in the foreland basin in southwest Iran (Zagros Basin). The Zagros mountain belt of Iran, a part of the Alpine-Himalayan system, extends from the NW Iranian border through to SW Iran, up to the strait of Hormuz. The various facies of the Jahrum Formation were deposited in four main genetically related depositional environments, including: tidal flat, lagoon, shoal and open marine. These are represented by 14 microfacies. The Jahrum Formation represents sedimentation on a carbonate ramp. Tidal flat facies are represented by fenestral fabric, stromatolitic boundstone and thin-bedded planes. Carbonate deposition in a shallow marine lagoon was characterised by wacke-packstone, dominated by various taxa of imperforate foraminifer. The shoals are made up of medium- to coarse-grained skeletal and peloidal grainstone. This facies was deposited predominantly in an active high energy wave and current regime, and grades basinward into middle ramps facies are represented by wackestones-packstones with a diverse assemblage of echinoderm and large benthic foraminifers with perforate wall. Outer ramp facies consist of alternating marl and limestones rich in pelagic foraminifera. There is no evidence for resedimentation processes in this facies belt. The sequence stratigraphy study has led to recognition of three third-order depositional sequences.
Journal of Applied Sciences (discontinued) (18125654) 8(8)pp. 1426-1434
The main objectives of this research were to identify the geometry and structure of the Qom-Zefreh fault and to determine the extent of its effects on stratigraphy and facies changes. The identification of movement mechanism of major faults in basement, extent and time of their activities are important effects for evaluation of paleogeography of the Iran plateau. In the Orumieh-Dokhtar volcanic band, there are nearly parallel faults to the Zagros Zone. These faults were formed during closure of the Neothetys and collision of the Arabic plate with crust of Iran. The Qom-Zefreh fault is one of these faults, which is known as havitig four different trend faults. The result indicates that, this fault is not divided in four segments with different trends but the major trend is of Central section, which is the Kashan segment with AZ140 trend and other segments are just related faults. Thus the name of the Kashan fault is recommended for this fault. The mechanism of the Kashan fault is dextral transpression and other related faults in the region are in good correlation with fractures in a dextral transpression system. The stratigraphic studies conducted on the present formations show the effect of fault movements in Upper Cretaceous sedimentary basin. Lack of noticeable changes in Lower Cretaceous sediments and before that indicates that the fault system activity has been started from the Upper Cretaceous. Thus, based upon these results, the effect of the Neothetys sea closure in this region could be considered at least from the Upper Cretaceous. © 2008 Asian Network for Scientific Information.
Historical Biology (08912963) 19(2)pp. 173-183
The Asmari Formation is a thick carbonate succession of the Oligo-Miocene in southwest Iran (Zagros Basin). The Zagros Basin was a continental margin attached to the eastern edge of Africa throughout the Phanerozoic. The foraminiferal limestone from the Asmari Formation has been studied to determine its microfacies, paleoenvironments and sedimentary sequences. Based on analysis of larger benthic foraminiferal assemblages and microfacies features three major depositional environments are identified. These include open marine, barrier and lagoon-lower intertidal. These three are represented by eleven microfacies. A carbonate ramp platform is suggested for the depositional environment of the Asmari Formation. The inner ramp facies are characterized by wackestone-packstone, dominated by various taxa of imperforate foraminifera. The middle ramp facies represented by packstone-grainstone to floatstone with a diverse assemblage of larger hyaline foraminifera. The outer ramp is dominated by argillaceous wackestone, characterized by planktonic foraminifera and larger hyaline foraminifera. Two third-order sequences are identified based on deepening and shallowing patterns in microfacies, staking patterns and the distribution of Oligocene-Miocene foraminifers.
Journal of Asian Earth Sciences (18785786) 29(5-6)pp. 947-959
The Oligocene-Miocene Asmari Formation of the Zagros Basin is a thick sequence of shallow water carbonate. In the study area, it is subdivided into 14 microfacies that are distinguished on the basis of their depositional textures, petrographic analysis and fauna. Based on the paleoecology and lithology, four distinct depositional settings can be recognized: tidal flat, lagoon, barrier, and open marine. The Asmari Formation represents sedimentation on a carbonate ramp. In the inner ramp, the most abundant lithofacies are medium grained wackestone-packstone with imperforated foraminifera. The middle ramp is represented by packstone-grainstone to floatstone with a diverse assemblage of larger foraminifera with perforate wall, red algae, bryozoa, and echinoids. The outer ramp is dominated by argillaceous wackestone characterized by planktonic foraminifera and large and flat nummulitidae and lepidocyclinidae. Three third-order depositional sequences are recognized from deepening and shallowing trends in the depositional facies, changes in cycle stacking patterns, and sequence boundary features. © 2006 Elsevier Ltd. All rights reserved.
Facies (01729179) 52(1)pp. 41-51
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. © Springer-Verlag 2005.
Carbonates and Evaporites (08912556) 20(2)pp. 131-137
An analysis of microfacies features and of larger benthic foraminiferal assemblages which include imperforate and perforate, was used to define microfacies types. The predominant microfacies are; 1) Rudist, orbitoidae wackestone packstone; 2) Rudist packstone; 3) Bioclast grainstone; 4) Orbitoidae, miliolids, bioclast wackestone packstone; 5) Dicyclina, miliolids, bioclast wackestone packstone; 6) Miliolids mudstone; 7) Peloidal, bioclast wackestone packstone; 8) Bioclast, ostracoda packstone grainstone. Three major depositional environments are identified in the Tarbur Formation on the basis of grain types, physical and biogenic sedimentary structures and vertical facies relationships. These include shallow subtidal (shelf lagoon), sand shoal and open marine. Tarbur Formation sediments were deposited on a ramp carbonate platform. Four depositional sequences were also recognized in the Tarbur Formation. TST sediments dominated by hyaline foraminifera and HST sediments dominated by various taxa of imperforate foraminifera. The assemblages of perforate and imperforate foraminifera and microfacies are used for interpretation of palaeoenvironment features of the Tarbur Formation.
