Kopet-Dagh Basin Research Articles

The impact of fractures and planar structures on the quality of the Upper Jurassic Mozduran reservoir, Kopet Dagh basin (Northeast Iran)

In this study, based on stereographic projections, two sets of planar structures were identified in the Mozduran reservoir, a prolific reservoir in Northeast Iran. The first set includes shallow structures, consisting of stylolites, solution seams, dense veins, and bedding planes. These structures were created by both sedimentary and diagenetic processes and do not have much effect on reservoir quality. The second set includes structures are related to deformation, and these have a substantial impact on increasing the reservoir quality. To investigate the relationships between the types of fractures and their respective influences on reservoir quality, the production logging tool (PLT) gas production rate data was utilized. This analysis revealed that in fractured zones 2 and 4 of Mozduran reservoir, where fractures and flat structures have increased the quality of the reservoir, the PLT gas production rate also increases. Conversely, in areas where filled fractures and diagenetic processes have negatively affected reservoir quality, the PLT gas production rate decreases. This pattern indicates the contrasting impact of planar features on reservoir quality. Moreover, a higher frequency of fractures corresponds to a higher permeability in the Mozduran reservoir of Well #B, whereas a lower frequency of fractures corresponds to lower permeability in that reservoir in Well #A. These relationships confirm the positive influence of fractures on the Mozduran reservoir quality. The study results reveal that deformation variables in the examined reservoir have greater impacts on its quality than the sedimentary and diagenetic porosity/permeability components, but those impacts can have both positive and negative consequences.

Earliest upper Barremian (Lower Cretaceous) record of bivalve Pinna (Pinnidae) from the Kopet-Dagh Basin, northeastern Iran and its possible predators

The bivalves Pinna sp. cf. cretacea (Schlotheim, 1813) and Pinna cretacea cretacea (Schlotheim, 1813) are systematically described for the first time from the ammonite-constrained upper Barremian (Lower Cretaceous) strata of the Kopet-Dagh Basin, northeastern Iran. This is also, the first record of the Family Pinnidae from the Kopet-Dagh Basin. The specimens were collected from the basal part of the Sarcheshmeh Formation, exposed in the Bojnurd city, North Khorasan province. Additionally, this study includes observations on predation scars (such as scalloped, embayed, and cleft scars), and encrustations by orbitolinids on the Pinna samples. Insights into the contemporary paleoenvironment, characterized by quiet and shallow waters with a soft, muddy substrate, are also discussed.

Upper Cambrian–Lower Ordovician conodonts from the southern margin of the Kopet-Dagh Basin, Saluk Mountains, Iran

A detailed Furongian to Tremadocian conodont biostratigraphy is established from the Saluk Mountains located in southern Kopet-Dagh, northeast Iran. Thirty species assigned to 17 genera were recovered from decimetre-scale limestone beds in a fine-grained siliciclastic succession, deposited in an intraplate rift system. The following biozones are established for the region, in ascending order: Proconodontus muelleri, Eoconodontus, Cordylodus intermedius, Cordylodus lindstromi, Cordylodus angulatus, Paltodus deltifer and Acodus triangularis interval zone. This low-to medium-richness conodont fauna comprises cosmopolitan euconodont species of Proconodontus, Eoconodontus, Cordylodus, Teridontus nakamurai, Semiacontiodus nogamii and a few long- ranging proto- and paraconodont species, which inhabited a narrow marine basin flanked by landmasses and formed by active rifting. It lacks shallow water tropical taxa and probably belongs to the Cold Domain of the Shallow Sea Realm. The occurrence of conodonts of the Paltodus deltifer Biozone in the uppermost part of the Qyzlar Formation in the Ghelli section suggests that the major episode of flood basalt volcanism in south Kopet-Dagh commenced in the late Tremadocian. Hadi Jahangir [Jahangir.hadi@nigpas.ac.cn] and Guanzhou Yan [gzyan@nigpas.ac.cn], State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, PR China.

Morphogenesis of Balkhania balkhanica Mamontova, 1966 (benthic foraminifera) from Lower Cretaceous successions along the northern Tethyan margin (NE and Central Iran): Time and environmental control

Among large benthic foraminifera, Balkhania genus is one of the most valuable taxon that has been used to better constrain the biostratigraphy of the Lower Cretaceous successions along the Tethyan carbonate platforms. The species Balkhania balkhanica is considered as biostratigraphical index for the Barremian-Aptian interval. This study is focused on the B. balkhanica-bearing intervals of the Tirgan and Taft formations from two sections, deposited on the carbonate platform of the Iranian Tethyan margin (Kopet-Dagh Basin, NE Iran and Yazd Block, Central Iran). The age of the studied sections has already been determined in previous works. In present research, morphology and stratigraphical and ecological distribution of the recorded specimens are interpreted. According to the morphological changes, two morphotypes of B. Balkhanica have been introduced. Small-size morphotype is recorded in the Upper Valanginian to Upper Hauterivian interval of the Tirgan Formation. The Upper Barremian to Lower Aptian successions are mostly associated with larger sized specimens having a coarse quartz agglutinated wall, and named arenaceous morphotype. Their wall is in contrast to the Turkmenistan type specimens having a calcite microgranular-agglutinated wall. Inherent evolutionary factor suggests an evolutionary trend of this species from smaller to larger sized specimens during the Late Valanginian to Early Aptian. A preliminary study of the depositional environment also indicates an environmental control for this type of morphological variation. It suggests that the small-size morphotype mostly occurred in an under-stress shallow-water environment, while the larger size morphotype was associated with deeper and more stable outer-shelf environments.

Post-depositional history of the lower Palaeocene interval using petrographic, CL and geochemical data in the East Tethys: Kopet-Dagh Basin, northeast Iran

AbstractThis study investigates the Danian siliciclastic successions in the East Tethys in the Kopet-Dagh Basin, NE Iran, which are composed of conglomerates, sandstones, shales and mudstones. The studied interval includes significant changes in sedimentary environments from alluvial to fluvial systems. The Danian siliciclastic formation is sandwiched between two marine carbonate sequences. The effects of the late Palaeocene sea transgression can be traced back to the precipitation of several types of carbonate cement in the studied siliciclastic formation. Several diagenetic features have been identified in the studied successions. The most observed features comprise physical and chemical compaction, cementation, alteration, dissolution, fractures and fillings. Some of the mentioned diagenetic processes, such as cementation, may be seen in a range of diagenetic environments and phases, such as early meteoric, low depth and deep burial, and late meteoric after the tectonic uplifting. The calcite cements considered in this study have been subdivided into four types. Some of the calcite cements, such as the rim, gravity pendant and meniscus, are classified as type one. They have formed around the rock grains and show no luminescence. The blocky and poikilotopic types have been grouped in type two. They are deposited between grains and exhibit dark luminescence. Type three cement consists of some of the blocky and poikilotopic cements that have formed amid grains and present a bright luminescence. Finally, type four comprises filled fractures which display a dark luminescence (blocky cement). Geochemical data revealed that the categorized cement types were precipitated in three diagenetic environments: early meteoric; burial; and late meteoric after the uplifting. The meteoric diagenetic environment is subdivided into vadose and phreatic meteoric. The burial diagenetic environment is subdivided into shallow burial and deeper burial. The qualitative petrographic method contributed to the initial recognition of the diagenetic features. The semi-quantitative cathodoluminescence method, the quantitative major and trace elements, and oxygen and carbon stable isotope analysis were utilized to evaluate the exact diagenetic processes and environments. Finally, the diagenetic sequence was reconstructed and depicted as diagenetic models and a paragenesis sequence. The data of this study can lay the foundation for future studies on the siliciclastic diagenesis in the studied basin.

Petrology and mineralogy of Middle Jurassic siliciclastic rocks of the Kopet-Dagh rift basin, NE Iran: A comparison with the Binalud intramontane basin

The Middle Jurassic Kashafrud Formation of the Kopet-Dagh Basin is a succession of fluvial to turbiditic siliciclastic rocks deposited in a rift basin that was initiated in the Late Bajocian and was filled with conglomerates, sandstones, and mudstones. The sandstones are mainly lithic arkoses and feldspathic litharenites. The sandstones of the Kashafrud Formation contain evidence of numerous diagenetic processes, including compaction and fracturing, cementation, dissolution, and formation of authigenic minerals. For evaluation of the thermal history and diagenetic processes, and the formation of clay minerals, a burial temperature range for the Kashafrud Formation of more than 100 °C has been assumed. Geochemical results point to felsic, mafic, and metamorphic rocks, as well as to Proterozoic recycled sandstones as source rocks. The chemical index of alteration and plagioclase index of alteration indicate a humid to semi-arid climate at the time of sedimentation. Based on petrographic and geochemical data, the main tectonic sources for the sediments of the post-orogenic Middle Jurassic Kashafrud Rift Basin were a recycled orogen and passive margin. The Early Jurassic to early Middle Jurassic Binalud Intramontane Basin, situated at the northern margin of the Binalud Mountains and formed during a late phase of the Early Cimmerian Orogenic Event, was also filled with sediments derived from the Cimmerian mountain belt. The two basins represent different tectonic settings, but both are connected to the closure of the Palaeo-Tethys, reflecting similar source rocks and similar climatic conditions.

Palynostratigraphy and paleoenvironments of the upper Turonian–lower Campanian Abderaz Formation in the east of Kopet-Dagh Basin (NE Iran)

The palynology and palynofacies of the Abderaz Formation have been studied to interpret the paleoenvironments and sea-level changes in the Upper Cretaceous deposits of the Kopet-Dagh Basin. This formation in the Kalat-e-Naderi region (Gharesu section) is composed of 462 m of gray to cream shales, marlstone layers and three chalky limestone units. Seven dinoflagellate cyst (dinocysts) and four planktonic foraminiferal biozones have been identified in the studied succession, which suggest a late Turonian–early Campanian age for this interval. Four different depositional environments have been recognized in the studied section based on the relative proportion of organic matter (terrestrial organic matter, marine palynomorphs and amorphous organic matter). High abundance of marine palynomorphs in most samples indicates the predominance of an oxygenated distal shelf environment in the upper Turonian–lower Campanian interval. Seven third-order depositional sequences are proposed for the Abderaz Formation. A good correlation of sequence boundaries with the global sea-level fall events suggests that eustasy played an important role during the deposition of the Abderaz Formation.

From Gondwana rifting to Alpine orogeny: Detrital zircon geochronologic and provenance signals from the Kopet Dagh Basin (NE Iran)

The Kopet Dagh mountains in NE Iran exhibit a 7-km-thick continuous sedimentary sequence recording detritus from exposed surrounding terranes from the last 175 Ma. This work presents a multi-disciplinary geochronologic and provenance analysis in an attempt to identify and date major geologic events along the northern segment of the Tethys and reconstruct the regional tectonic history from Gondwana-related rifting until the Alpine orogeny. Sandstone framework, heavy mineral analysis, U-Pb dating of detrital zircons, and Hf-isotope ratio measurements on dated zircons from Triassic to Paleocene sandstones indicate three main tectonic events that include Early Silurian intracontinental rifting (opening of Paleo-Tethys), Early Carboniferous rifting of a back-arc basin (Aghdarband Complex), and Late Triassic collisional to post-collisional magmatism (Paleo-Tethys collision). Mineralogical and age peak considerations indicate that detritus was supplied from the south into the extensional Kopet Dagh Basin during Middle Jurassic, while Cretaceous to Paleocene sandstones show signs of increasing recycling.

The oxic Coniacian-Santonian interval in the Kopet-Dagh Basin (NE Iran): Carbon isotope and benthic-planktic foraminiferal assemblages at the time of the last Cretaceous OAE

A middle Coniacian-middle Santonian interval has been studied in the Kopet-Dagh Basin (NE Iran) to reconstruct the paleoenvironmental conditions in the eastern part of Tethyan realm at the time of the last Cretaceous Oceanic Anoxic Event (OAE3). This succession is composed of a chalky limestone unit, sandwiched by light gray calcareous mudstone and marlstone beds. The δ 13 C curve indicates several minor positive shifts up to 1‰ in the studied section that is correlative to other carbon isotope curves from the Tethys and Boreal realms. A prominent upward increase of P/B ratio in the studied section suggests a relative sea-level rise toward the Santonian. Lithology (low carbonate contents) and faunal contents (high %benthic and higher infaunal benthic foraminifera) reveal that the lower part of the studied section was deposited in a neritic environment influenced by continental-derived nutrients and mesotrophic to eutrophic conditions. Enhanced carbonate contents, higher diversity of benthic foraminifera and dominance of epifaunal taxa suggest more oligotrophic conditions and/or higher oxygen concentrations in the interval equivalent with a δ 13 C positive shift, caused by a transgression phase at this time. The overlying deposits are characterized by the maximum flooding surface and the highstand phase. The stratification of water column and more oxygen consumption in this interval resulted in higher abundance of infaunal benthic foraminifera and decline of carbonate production in a bathyal environment. • Coniacian/Santonian boundary interval was deposited under oxic conditions in the E Tethys. • No black shales or anoxia mark this inferred OAE3 interval. • Sea-level fluctuations control foraminiferal assemblages in this study. • The δ 13 C curve reveals the diagnostic features of global Co/Sa boundary record.

Biostratigraphy and geometry of the Lower Cretaceous Tirgan and Taft formations from NE and Central Iran (Northern Tethyan margin): Critical discussion of recently published comments

Biostratigraphy of the Tirgan and Taft formations (Lower Cretaceous successions) from the Kopet-Dagh Basin (NE Iran) and Yazd Block (Central Iran) has been described using the benthic foraminifera and colomiellids, which calibrated with the stable isotope records. They have demonstrated that ages at the base and top of the formations are diachrone, and these successions start in the Berriasian? or the lower Valanginian and end in the upper Aptian or the Albian. Evidence for this diachrony in ages has been provided by geometry of the Tirgan and Taft formations, showing explicit onlap patterns for the deposits. Furthermore, comments have been recently published on some benthic foraminifera and age models of the Tirgan and Taft formations by Schlagintweit (2021). Here, we explain about accuracy of the palaeontology of these species and demonstrate that discussion on the age models is wrongly addressed.

The trace fossil Gyrolithes lorcaensis from the Lower Cretaceous of the Kopet-Dagh Basin, NE Iran

The helical, vertical trace fossil Gyrolithes lorcaensis is described from marine to marginal-marine deposits of the Lower Cretaceous of the Sarcheshmeh Formation near the city Kalat-e-Naderi in the Kopet-Dagh Basin. This is the first report of Gyrolithes from Iran and thus expands the geographic range of this trace fossil. G. lorcaensis is characterized by its unique morphometric parameters, a small burrow size and whorl radius, which distinguishes it as the smallest Gyrolithes ichnospecies. The most likely producers of the Iranian Gyrolithes were crustacean decapods, which is supported by the paleoenvironment (shallow and warm water ramp) in which it is found. The function of the spiral structure in the described Gyrolithes of the Sarcheshmeh Formation can be explained as a permanent dwelling structure with the main purpose of farming bacteria via increasing the surface area of the burrow margin that allows more microbial activities. The small burrow dimensions may reflect reduced burrower body size in response to the dysoxic to anoxic conditions suggested by sedimentological evidence.

Paleogene Molluscan Communities in the Kopet-Dagh Basin, NE Iran

Paleogene Molluscan Communities in the Kopet-Dagh Basin, NE Iran

Palynofacies and Palaeoenvironment of the Sanganeh Formation, East and the Center of the Kopet-Dagh Basin

Palynofacies and Palaeoenvironment of the Sanganeh Formation, East and the Center of the Kopet-Dagh Basin

Environmental significance of trace fossil assemblages in a tide‒wave-dominated shallow-marine carbonate system (Lower Cretaceous), northern Neo-Tethys margin, Kopet-Dagh Basin, Iran

Environmental significance of trace fossil assemblages in a tide‒wave-dominated shallow-marine carbonate system (Lower Cretaceous), northern Neo-Tethys margin, Kopet-Dagh Basin, Iran

Turonian-Maastrichtian biostratigraphy and isotope stratigraphy of the Kopet-Dagh Basin deposits, northeastern Neo-Tethys, Iran

Planktonic foraminiferal biostratigraphy and isotope stratigraphy analyses of Turonian-Maastrichtian deposits have been carried out in the western part of the Kopet-Dagh Basin. The identification of the planktonic foraminiferal assemblages has led to the recognition of twelve Upper Cretaceous zones (Helvetoglobotruncana helvetica Zone to the Contusotruncana contusa-Abathomphalus mayaroensis zone) from the Tethyan realm. The obtained stable carbon isotope profile correlates with other reference curves, revealing many Late Cretaceous events including the Hitchwood, Navigation, Light Point, East Cliff, White Fall, Late Campanian Event (LCE), Campanian-Maastrichtian Boundary Event (CMBE), Middle Maastrichtian Event (MME) and KPg Events (KPgE). The Turonian-Maastrichtian deposits of the studied area represent severe changes in sedimentation rate and several hiatuses and condensed intervals, which mostly coincide with lithological boundaries. The data indicate a general shallowing -upwards in association with the Late Cretaceous tectonics of the Kopet-Dagh Basin. The reconstruction of the age model allows a discussion of the results in terms of changes in palaeoenvironmental conditions (eutrophic vs. oligotrophic).

Diagenetic history of Cretaceous sandstones of the Neyzar Formation, Kopet-Dagh Basin, NE Iran: a case study of albitization

Diagenetic history of Cretaceous sandstones of the Neyzar Formation, Kopet-Dagh Basin, NE Iran: a case study of albitization

Late Paleocene-Middle Eocene Planktonic and Small Benthic Foraminiferal Fauna from the Type Section of Khangiran Formation, Kopet-Dagh Basin (NE Iran), Southernmost Peri-Tethys

Late Paleocene-Middle Eocene Planktonic and Small Benthic Foraminiferal Fauna from the Type Section of Khangiran Formation, Kopet-Dagh Basin (NE Iran), Southernmost Peri-Tethys

FIRST RECORD OF CALCAREOUS GREEN ALGAE (DASYCLADALES, HALIMEDACEAE) FROM THE PALEOCENE CHEHEL KAMAN FORMATION OF NORTH-EASTERN IRAN (KOPET-DAGH BASIN)

The micropalaeontological inventory of the shallow-water carbonates of the Paleocene Chehel-Kaman Formation cropping out in the Kopet-Dagh Basin of north-eastern Iran is poorly known. New sampling has evidenced for the first time the occurrence of layers with abundant calcareous green algae including Dasycladales and Halimedaceae. The following dasycladalean taxa have been observed: Jodotella veslensis Morellet & Morellet, Cymopolia cf. mayaense Johnson & Kaska, Neomeris plagnensis Deloffre, Thyrsoporella-Trinocladus, Uteria aff. merienda (Elliott) and Acicularia div. sp. The studied section is devoid of larger benthic foraminifera and can be referred to the middle-upper Paleocene (SBZ 2-4) due to the presence of Rahaghia khorassanica (Rahaghi). Some of the dasycladalean taxa are herein reported for the first time not only from Iran but also the Central Neotethyan realm.

Gastropods in love: a fossilized mating behavior of coupling ampullinids in the Paleocene of Kopet-Dagh Basin, NE Iran

Gastropods in love: a fossilized mating behavior of coupling ampullinids in the Paleocene of Kopet-Dagh Basin, NE Iran

Glauconite within Albian-Cenomanian Aitamir Formation, Kopet-Dagh Basin, northeastern Iran: origin and implications of cretaceous seawater

An integrated petrographical, geochemical, and mineralogical investigation reveals the wide variation in the mineral chemical composition of glauconites within the Albian-Cenomanian Aitamir Formation. Bounded between a black shale (Sanganeh Formation) below and chalky limestone (Abderaz Formation) above the Aitamir Formation represents an inner shelf deposit. Glauconite may occur either as pellets or as altered zones within feldspar and mica. Poor sorting and deeply penetrative crack indicate the authigenic nature of glauconite pellets. The contents of Fe2O3, MgO, Al2O3, and SiO2 of glauconites vary widely while the K2O exhibits a limited spread indicating the evolved nature of the glauconite. The glauconite matures at a fixed and high value of K2O with variable Fe2O3 (total) supporting the replacement origin. The X-ray diffraction study reveals a negligible interstratification within glauconites. The micro-textural study attests to the highly evolved nature of the glauconite. The shallow marine glauconite within the Albian-Cenomanian Aitamir Formation formed under sub-oxic, shallow depositional setting during the middle Cretaceous global warming phase within the Tethyan domain.