Facies analysis and depositional environments of the Oligocene–Miocene Asmari Formation, Zagros Basin, Iran

The Asmari Formation(a giant hydrocarbon reservoir)is a thick carbonate sequence of the Oligocenee Miocene in the Zagros Basin,southwest of Iran.This formation is exposed at Tang-e-Lendeh in the Fars interior zone with a thickness of 190 m comprising medium and thick to massive bedded carbonates.The age of the Asmari Formation in the study area is the late Oligocene(Chattian)eearly Miocene(Burdigalian).Ten microfacies are defned,characterizing a gradual shallowing upward trend;the related environments are as follows:open marine(MF 8e10),restricted lagoon(MF 6e7),shoal(MF 3e5),lagoon(MF 2),and tidal fat(MF 1).Based on the environmental interpretations,a homoclinal ramp consisting of inner and middle parts prevails.MF 3e7 are characterized by the occurrence of large and small porcelaneous benthic foraminifera representing a shallow-water setting of an inner ramp,infuenced by wave and tidal processes.MF 8e10,with large particles of coral and algae,represent a deeper fair weather wave base of a middle ramp setting.     

Biostratigraphy of the Garau Formation (Berriasian?–lower Cenomanian) in central part of Lurestan zone,northwest of Zagros,Iran

Deposition of organic rich black shales and dark gray argillaceous limestones in the Berriasian–Turonian interval has been documented in many parts of the world. Northwest of Zagros, Iran (Lurestan zone), thin bedded black shales and marls, dark gray argillaceous limestones and fissile limestone layers, having bitumen, of the Garau Formation are deposited. For biostratigraphic studies two stratigraphic sections including one surface section (Kuzaran) and one subsurface section (Naft well) were selected, respectively. In this study, 61 foraminiferal species belonging to 17 genera have been identified, and 12 biozones were recognized. Based on fossils distribution and biozones identification, the age of the Garau Formation is Berriasian?–early Cenomanian. In addition, the micropalaeontological study demonstrated a variety of widespread morphological changes in planktonic foraminifera assemblages (e.g., the elongation of the final chambers, appearance of twin chambers in the last whorl). These changes coincide with deposition of argillaceous limestones and marls rich in organic matter, indicating oceanic anoxic events. On this basis, three oceanic anoxic events such as OAE1a, OAE1b and OAE1d were recognized in Naft well section and two (OAE1b and OAE1d) in Kuzaran section.     

Larger Foraminiferal Biostratigraphy and Facies Analysis of the Oligocene–Miocene Asmari Formation in the Western Fars Sub-basin, Zagros Mountains, Iran

The Oligocene–Miocene carbonate record of the Zagros Mountains, known as the Asmari Formation, constitutes an important hydrocarbon reservoir in southern Iran. This marine carbonate succession, which developed under tropical conditions, is explored in terms of larger foraminiferal biostratigraphy, facies analysis and sequence stratigraphy in a new section at Papoon cropping out in the western Fars sub-basin, in the south-east of the Zagros belt. Facies analysis shows evidence of re-working and transport of skeletal components throughout the depositional system, interpreted here as a carbonate ramp. The foraminifera-based biozones identified include the Globigerina–Turborotalia cerroazulensis–Hantkenina Zone and Nummulites vascus–Nummulites fichteli Zone, both of Rupelian age, the Archaias asmaricus–Archaias hensoni–Miogypsinoides complanatus Zone of Chattian age and the ‘Indeterminate’ Zone of Aquitanian age. The vertical sedimentary evolution of the formation exhibits a progressive shallowing of the facies belts and thus the succession is interpreted as a high-rank low-order regressive systems tract. This long-lasting Rupelian–Aquitanian regressive event is in accordance with accepted global long-term eustatic curves. Accordingly, long-term eustatic trends would have been a factor controlling accommodation during the deposition of the Asmari Formation studied in the western Fars sub-basin.     

Petrography and geochemistry of Paleocene–Eocene limestones in the Ching-dar syncline, eastern Iran

The Ching-dar syncline is located to the west of the city of Birjand, in the east of han. The ca. 500 m thick studied section at the eastern flank of the syncline contains a sequence of almost continuous shallow- marine limestones that exhibit no major sedimentary breaks or evidence for volcanic activity. Skeletal grains consist of large benthic foraminifera and green algae whereas non-skeletal grains are mostly peloids and intraclasts. They were deposited on a shallow-marine carbonate ramp. The limestones have undergone extensive diagenetic processes with varying intensities, the most important of which are micritization, cementation, compaction （chemical and mechanical）, internal filling and stylolitization. Chemical analysis of the limestone samples revealed high calcium and low magnesium content. Major and minor element values were used to determine the original carbonate mineralogy of these lime- stones. Petrographic evidence and elemental values indicate that calcite was the original carbonate mineral in the limestones of the Ching-dar syncline. The elemental composition of the Ching-dar car- bonates also demonstrates that they have stabilized in a meteoric phreatic environment. Variation of Sr/ Ca vs. Mn values suggests that diagenetic alteration occurred in an open geochemical system.     

The distribution of calcareous nannofossils in the late Santonian–Late Maastrichtian deposits in the southwest of Iran (Khuzestan Province)

The first data on the distribution of calcareous nannofossils in the Behbehan section, the Kuh-e-Rish, are considered. According to the distribution of nannofossils, the Upper Cretaceous deposits of the section are subdivided into nine biostratigraphic zones. CC17 (Calculites obscurus zone) indicate the Late Santonian. Biozones CC18 (Aspidolithus parcus zone), CC19 (Calculites ovalis zone), CC20 (Ceratolithoides aculeus zone), CC21 (Quadrum sissinghii zone), and CC22 (Quadrum trifidum zone) represent the Campanian. Biozone CC23 (Tranolithus phacelosus zone) indicate the Late Campanian–Early Maastrichtian. Biozones CC24 (Reinhardtites levis zone) and CC25 (Arkhangelskiella cymbiformis zone) suggest the Middle and Late Maastrichtian, respectively. In the late Late Maastrichtian, due to decreasing in water depth at the study area, Nephrolithus frequens zone (CC26) defined in Tethysian domain was not recognized. The boundary between Gurpi–Pabdeh Formations represented a non-depositional period from the late Late Maastrichtian to the end of Early Paleocene. Also, it seems that predominant conditions of the sedimentary environment of Neotethys basin with the presence of index species calcareous nannofossils specified, which itself indicates that the warm climate and high depth of the basin in Late Santonian to Late Maastrichtian, in low latitudes has been prevalent.     

Petrography,geochemistry, and U–Pb geochronology of pegmatites and aplites associated with the Alvand intrusive complex in the Hamedan region,Sanandaj–Sirjan zone,Zagros orogen (Iran)

International Journal of Earth Sciences - The Alvand intrusive complex in the Hamedan area in Iran is in the Sanandaj–Sirjan zone of the Zagros orogen. It consists of a wide range of plutonic...     

Kink-band Kinematic Analysis and its Implications for Late-stage Deformation in the Internal Parts of the Zagros Collision (Sanandaj–Sirjan Zone) in West Iran

In the internal parts of the Zagros collision zone, several deformation phases have been superimposed. The early deformation phase caused the development of a penetrative foliation. The late-stage deformation phase was preferentially accommodated within shear zones and caused the generation of shear bands, implying a non-coaxial component of deformation, the end of this stage deformation was marked by the development of kink-bands. In the vicinity of Zagros suture zone, the kink angle increased from 40° to 60°, and the kink-bands was converted to chevron folds. In this region, the external (α) and internal (β) angular ratio is α/β ≠ 1 and kink angle increased, and deformation occurred with 10% to 30% volume loss. Farther from the suture zone in the east, α/β = 1; and total volume was constant or increased by 5% to 10%. Kink-bands kinematic analysis in the study area revealed this structures were sensitive to deformation conditions and components such that, with decreasing distance to the Zagros suture zone, shearing and rotation increased, a high kinematic vorticity dominated, and volume loss occurred during deformation.     

Biostratigraphy,sequence stratigraphy,and paleoecology of the Lower–Middle Miocene of Northern Bandar Abbas,Southeast Zagros basin in south of Iran

The Guri Member is a limestone interval at the base of the calcareous marls of the Mishan Formation. It is the youngest hydrocarbon reservoir of the southeast part of the Zagros sedimentary basin. This Member overlaid siliciclastic rocks of Razak Formation and is overlain by green and gray marls of the Mishan Formation. In order to consider the paleoecology and paleoenvironments of the Lower–Middle Miocene (Guri Member), we have studied biostratigraphy and sequence stratigraphy of the Guri Member based on foraminifer and microfacies in two stratigraphic sections including Dorahi–Homag and Chahestan. A total of 33 genera and 56 species of benthic and planktonic foraminifera were identified in two studied stratigraphic sections. Benthic and planktonic foraminifera demonstrate Aquitanian to Langhian age (Early–Middle Miocene) for this Member at the study area. Studied interval has deposited in four facies association including supratidal, lagoon, coral reef, and open sea on a carbonate ramp. Carbonate rocks of the Guri Member have precipitated in two and three depositional sequences at Chahestan and Dorahi–Homag sections, respectively. Sedimentation of marine carbonates of the Guri Member on siliciclastic deposits reflects a major transgression of sea level at Lower to Middle Miocene that led to creating a new sea in the Zagros basin at that age. Increasing siliciclastic influx along with a sea level fall finally caused burying of the carbonate ramp. Except for the beginning of sedimentation of carbonate at the base of both stratigraphic sections (depositional sequence 1), most of the system tracts are not matched to global sea level curve that reflect local effects of the basin. Distribution of foraminifera suggests precipitation in tropical to subtropical in mesotrophic to oligotrophic and eutrophic to oligotrophic conditions. Based on large benthic foraminifera (porcelaneous large benthic foraminifera and hyaline larger benthic foraminifera), water temperature average was determined between 25 and 30 °C that was confirmed by analyzing oxygen and carbon stable isotopes. Finally, we have utilized achieved data to reconstruction and modeling of paleoecology, paleoenvironments, and sea level changes in the southeast part of the Zagros basin.     

Stratigraphy and ammonite fauna of the upper Shemshak Formation (Toarcian–Aalenian) at Tazareh,eastern Alborz,Iran

With a thickness of 3900 m, the Tazareh section is one of the thickest developments of the Shemshak Formation in the Alborz range. It overlies with sharp and disconformable contact the limestones and dolomites of the Lower–Middle Triassic Elikah Formation and is topped, again with a disconformable contact, by the marls and limestones of the Middle Jurassic Dalichai Formation. The nearly exclusively siliciclastic succession represents a range of environments, from fluvial channels, flood plains, swamps and lake systems to storm-dominated shelf, and a comparatively deep marine and partly dysoxic basin. The segment of the section between 2300 and 3500 m is exclusively marine and contains a moderately diverse ammonite fauna, ranging from the Middle Toarcian to the Upper Aalenian. The ammonite fauna comprises 21 taxa, among them the new genus Shahrudites with two new species, Shahrudites asseretoi and S. stoecklini from the Middle Aalenian Bradfordensis Zone. The other ammonites from the Shemshak Formation at Tazareh (as elsewhere in North and Central Iran) are exclusively Tethyan in character and closely related to faunas from western and central Europe. An ammonite-based correlation of Toarcian–Aalenian successions of the eastern Alborz with time-equivalent strata of the Lut Block, part of the Central-East Iranian Microcontinent (ca. 500 km to the south), suggests a strong influence of synsedimentary tectonics during the deposition of the upper Shemshak Formation.     

Sequence stratigraphy of Aqra Formation (Late Upper Campanian–Maastrichtian) in Geli Zanta corge,Northern Iraq

The Aqra Formation represents a succession that was deposited over most of Northern Iraq and adjacent regions. In north Iraq, in the core of NW–SE trending Aqra anticline, a 438-m-thick section of the Aqra Formation crops out at Geli Zanta corge. The base of the Aqra Formation is not exposed here. The upper contact is unconformably overlain by Paleocene–Lower Eocene formations (Kolosh and Khurmala formations). A hundred and one samples were collected from the section and used for biostratigraphic and microfacies analysis. According to the occurrence of larger Foraminifera (Orbitoides media and Orbitoides apiculata) and planktonic Foraminifera (Abathomphalus mayaroensis), Late Upper Campanian–Maastrichtian age was determined for Aqra Formation. Fifteen facies were distinguishable throughout the formation, representing tidal flat (supratidal), restricted marine shelf (lagoon) and shelf margin rudist reef, and its related debris. These environments were used to interpret three depositional sequences which correlate with those of Aruma Formation (KSA), Simsima Formation (UAE) in Arabian Plate, and with Iraqi formation sequences. Three maximum flooding surfaces were recognized as MFS 175, MFS 180, and MFS 190.     

Facies Analysis and Sequence Stratigraphy of the Qal’eh Dokhtar Formation (Middle–Upper Jurassic) in the West of Boshrouyeh, East Central Iran

The study area is located in the east Tabas Block in Central Iran. Facies analysis of the Qal’eh Dokhtar Formation (middle Callovian to late Oxfordian) was carried out on two stratigraphic sections and applied to depositional environment and sequence stratigraphy interpretation. This formation conformably overlies and underlies the marly-silty Baghamshah and the calcareous Esfandiar formations, respectively. Lateral and vertical facies changes documents low- to high energy environments, including tidal-flat, beach to intertidal, lagoon, barrier, and open-marine. According to these facies associations and absence of resedimentation deposits a depositional model of a mixed carbonate–siliciclastic ramp was proposed for the Qal’eh Dokhtar Formation. Seven third-order depositional sequences were identified in each two measured stratigraphic sections. Transgressive systems tracts (TSTs) show deepening upward trends, i.e. shallow water beach to intertidal and lagoonal facies, while highstand systems tracts (HST) show shallowing upward trends in which deep water facies are overlain by shallow water facies. All sequence boundaries (except at the base of the stratigraphic column) are of the no erosional (SB2) types. We conclude eustatic rather than tectonic factors played a dominant role in controlling carbonate depositional environments in the study area.     

U–Pb dating of detrital zircon grains in the Paleocene Stumpata Formation,Tethyan Himalaya,Zanskar, India

The sediments deposited on the northern margin of Greater India during the Paleocene allow the timing of collision with the Spontang Ophiolite, the oceanic Kohistan–Dras Arc and Eurasia to be constrained. U–Pb dating of detrital zircon grains from the Danian (61–65 Ma) Stumpata Formation shows a provenance that is typical of the Tethyan Himalaya, but with a significant population of grains from 129 ± 7 Ma also accounting for ∼15% of the total, similar to the synchronous Jidula Formation of south central Tibet. Derivation of these grains from north of the Indus Suture can be ruled out, precluding India’s collision with either Eurasia or the Kohistan–Dras before 61 Ma. Despite the immediate superposition of the Spontang Ophiolite, there are no grains in the Stumpata Formation consistent with erosion from this unit. Either Spontang obduction is younger than previously proposed, or the ophiolite remained submerged and/or uneroded until into the Eocene. The Mesozoic grains correlate well with the timing of ∼130 Ma volcanism in central Tibet, suggesting that this phase of activity is linked to extension across the whole margin of northern India linked to the separation of India from Australia and Antarctica at that time. Mesozoic zircons in younger sedimentary rocks in Tibet suggest a rapid change in provenance, with strong erosion from within or north of the suture zone starting in the Early Eocene following collision. We find no evidence for strongly diachronous collision from central Tibet to the western Himalaya.     

Provenance, Tectonic Setting and Geochemistry of Ahwaz Sandstone Member (Asmari Formation, Oligo-Miocene), Marun Oilfield, Zagros Basin, SW Iran

The Asmari Formation deposited in the Zagros foreland basin during the OligoceneMiocene. Lithologically, the Asmari Formation consists of limestone, dolomitic limestone, dolomite, argillaceous limestone, some anhydrite(Kalhur Member) and sandstones(Ahwaz Member). This study is based on the analysis of core samples from four subsurface sections(wells Mn-68, Mn-281, Mn-292 and Mn-312) in the Marun Oilfield in the Dezful embayment subzone in order to infer their provenance and tectonic setting of the Ahwaz Sandstone Member. Petrographical data reveal that the Ahwaz Sandstone comprises 97.5% quartz, 1.6% feldspar, and 0.9% rock fragments and all samples are classified as quartz arenites. The provenance and tectonic setting of the Ahwaz Sandstone have been assessed using integrated petrographic and geochemical studies. Petrographic analysis reveals that mono- and poly-crystalline quartz grains from metamorphic and igneous rocks of a craton interior setting were the dominant sources. Chemically, major and trace element concentrations in the rocks of the Ahwaz Sandstone indicate deposition in a passive continental margin setting. As indicated by the CIW′ index(chemical index of weathering) of the Ahwaz Sandstone(average value of 82) their source area underwent "intense" recycling but "moderate to high" degree of chemical weathering. The petrography and geochemistry results are consistent with a tropical, humid climate and low-relief highlands.     

Hydrocarbon migration in the Zagros Basin,offshore Iran,for understanding the fluid flow in the Oligocene–Miocene carbonate reservoirs

Kuh-e Mond Field is a conventional heavy oil resource in the Zagros foreland Basin, Iran, produced from the fractured carbonates partially filled by dolomite, calcite, and anhydrite cement. Vitrinite reflectance data from carbonate reservoir suggest low-maturation levels corresponding to paleotemperatures as low as 50 °C. The observed maturation level (< 0.5% Rmax) does not exceed values for simple burial maturation based on the estimated burial history. Oil inclusions within fracture-filled calcite and dolomite cement indicate the key role of these fractures in oil migration.The fluid inclusion temperature profiles constructed from the available data revealed the occurrence of petroleum in dolomite, calcite, and anhydrite and characterize the distinct variations in the homogenization temperatures (T_h). Fluid inclusions in syntectonic calcite veins homogenize between 22 °C and 90 °C, showing a salinity decrease from 22 to 18 eq. wt.% NaCl. Fluid inclusions in anhydrite homogenize at < 50 °C, showing that the pore fluids became warmer and more saline during burial. The T_h range in the calcite-dolomite cement depicts a change in water composition; therefore, we infer these cements precipitated from petroleum-derived fluids. The microthermometry data on the petroleum fluid inclusions suggest that the reservoir was filled with heavy black oils and high-salinity waters and indicate that undersaturated oil was present in a hydrostatically pressured reservoir.The T_h data do not support vertical migration of hot fluids througout the section, but extensive lateral fluid migration, most likely, drove tectonically dewatering in the south or west of the pool.     

Evolution of radiolarians in the late Albian–Campanian

The dynamics of radiolarian evolution in the late Albian–Campanian is analyzed, and several stages are recognized. The first stage (late Albian–middle Cenomanian), related to the MCE regional anoxic event, showed low evolutionary tempos and hence lacked structural change in radiolarian communities. The second stage (late Cenomanian–early Turonian), corresponding to ОАЕ 2, which was a global anoxic event, is characterized by a decrease in the number of genera, while many genera showed increased diversification of species composition. At this stage, a considerable number of genera became extinct and appeared, suggesting an increased rate of the radiolarian evolution. The third stage (middle Turonian–early Coniacian), including the beginning of ОАЕ 3, is characterized by a stabilized number of genera. The fourth stage (late Coniacian–Santonian) completely encompasses ОАЕ 3 except for its very beginning. At this stage, the radiolarian communities underwent a significant structural change, while their rate of evolution increased considerably. Nevertheless, during the ОАЕ 3 stage, a distinct trend toward a decrease in generic diversity continued from the late Cenomanian to the middle Turonian. The fifth stage (Campanian) is characterized by quite significant changes in the assemblage composition, while the trend toward a gradual decrease in the number of genera steadily continued. At this stage, which coincided with a considerable cooling, twice as many genera became extinct as during ОАЕ 2. The analysis of the dynamics of radiolarian evolution showed that the anoxic MCE, ОАЕ 2, and ОАЕ 3 events did not result in degradation of radiolarian assemblages. This suggests that this group has significant stratigraphic potential. In general, the evolution of radiolarians in the Late Cretaceous was gradual. By the end of the Campanian, nearly half of the generic diversity was composed of genera which appeared at the beginning of the Cretaceous and earlier.     

Chondrichthyans from the Menuha Formation (Late Cretaceous: Santonian–Early Campanian) of the Makhtesh Ramon region,southern Israel

Exposures of the Menuha Formation (Santonian–Early Campanian, Mount Scopus Group) in the Makhtesh Ramon region of the southern Negev have produced numerous chondrichthyan teeth. The isolated teeth represent at least ten different species: Cretalamna appendiculata, Cretoxyrhina mantelli, Squalicorax falcatus?, S. kaupi, Scapanorhynchus rapax, S. raphiodon?, Carcharias samhammeri, Carcharias cf. C. holmdelensis?, and two other fish (Hadrodus priscus and a pycnodont). This assemblage has important implications for Late Cretaceous chondrichthyan palaeobiogeography. The majority of teeth were contained within a glauconite-rich, yellow-brown, soft chalk that included oysters (Pycnodonte vesicularis?), trace fossils (Planolites, Thalassinoides, and Chondrites), phosphatic peloids, and foraminiferans (globigerinids). The teeth were collected mainly through surface-sampling and sieving. The Menuha Formation probably represents a temperate to subtropical, shallow, open-shelf environment deposited during the formation of the Ramon anticline. Reworked conglomeratic chalks in the western section represent marginal facies derived from this structural uplift. With little to no published material describing the chondrichthyan fauna of the Menuha Formation, these data improve interpretations of its palaeoenvironment. Interpretation of the palaeoenvironment of the formation is important for understanding the larger stratigraphic/tectonic framework of the Ramon monocline region of southern Israel.     

Sedimentary Micro-facies and Macro Heterogeneity of Reservoir Beds in the Third Member of the Qingshankou Formation,Qian'an Area,Songliao Basin

An analysis of drill cores and well logs shows that the main micro-facies of the third member sand bodies of the Qingshankou Formation in Qian'an are subaqueous distributary channel facies, sheet sand facies and subaqueous fan facies(olistostrome).Maps showing the distribution of these micro-facies together with inter-channel bay and prodelta mocro-facies are presented for different time-slices(lower,middle and upper parts of the Qingshankou Formation).These maps reveal the instability and change of sediment transport in the Baokang sedimentary system during the depositional period.Sediment transport was from the west in the early stage,from the south in the middle stage and from the northwest in the late stage.Values of thickness,porosity and permeability of the sand bodies in the third member of the Qingshankou Formation show that they have low to medium porosity and low permeability,and are characterized by serious reservoir heterogeneity.The joints between micro-facies and subaqueous fan micro-facies are characterized by the highest heterogeneity, the sheet sand and distal sand bar subfacies come next,and the heterogeneity of the subaqueous distributary channel sand bodies is relatively weak.     

Biostratigraphy,Microfacies, Sedimentary Environments and Sequence Stratigraphy of the Late Devonian–Carboniferous Deposits at the Anarak Section,Central Iran

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 ...