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Cyclic successions are one of the most important types of deposits in the carbonate platform of the Mississippian (Tournaisian-Viséan) in Gondwanan and Laurussian margins. The importance of climatically induced events impact on the amplitudes and frequencies of sea-level fluctuations in Mississippian of Iran is significant because the beginning, extent, duration, and significance of periods of climatically induced events in northern margin of Gondwana are not well recognized. A high-resolution sequence architecture in integration with paleoenvironmental reconstruction and foraminiferal biozonation from the Tournaisian-early Visean carbonate successions of the Mobarak Formation in Alborz basin along depositional strike (E-W- a distance of c. 340 km) suggests a mosaic-like pattern of deposition and compartmentalization of the depositional settings (homocline ramp to distally steepened ramp). According to the recognized facies, the stacking pattern of high-frequency cycles across the platform, and major accommodation events recognized on the correlated Fischer plots, six 3rd-order sequences (DS1–DS6) were identified. Detailed analysis on high-frequency cycles representing a highly variable number of shallowing-upward cycles, types, thicknesses, and facies heterogeneity along depositional strike. A combination of the episodic tectonic events along faults interacting with autocyclic processes, and inherited topographic irregularities are suggested as the driving mechanism for the cycle development. Six stages of Mobarak carbonate platform evolution based on understand the interplay of autocyclic and allocyclic controls are recognized in a hierarchical 3rd-order sequence stratigraphic framework and a chronological order: (1) early Hastarian corresponds to post-glacial transgressive episode with progressive backstepping of facies belts of early TST of DS1 throughout the region; (2) middle to late Hastarian corresponds to a major transgressional phase of DS1 following global temperature rise superimposed on different subsidence/uplift rates with the deformation of the platform along depositional strike; (3) Hastarian–Ivorian boundary corresponds to TST of DS2 with facies heterogeneity along depositional strike related to continuation of different subsidence/uplift rates. The absence of any systematic changes in the amplitude and period of cyclicity or lowstand deposits and subaerial surfaces during this phase shows the lack of influence of mid-Tournaisian glaciation and concurrent eustatic regression in northern margin of Gondwana. (4) early to middle Ivorian coincides with the RST of DS2 and TST of DS3 showing by remarkable topographic irregularities in the basin physiography and change in the position of the depocenter axis from a E–W trend to the center; (5) late Ivorian-early Moliniacian coincides with the RST of DS3 and DS4 showing by the Late Tournaisian thermal period and eustatic rise superimposed on uplift and subaerial exposure of the western part and subsidence in the central and eastern parts of the basin; (6) Moliniacian coincides with DS5-DS6 sequences showing by change from fault-related topography to major tilted fault-block topography accompanied by eustatic sea-level fall caused indirectly by the Viséan and Serpukhovian glaciations phases. • Analyze along-strike variations in stratigraphic architectural style of the Tournaisian-Viséan successions. • Synthesis of autocyclic and allocyclic controls on changes in accommodation space along depositional strike. • Access a framework for tectonic and climatically induced event histories in the northeastern margin of Gondwana. • The importance of climatically induced events impact on the amplitudes and frequencies of sea-level fluctuations. • Results are useful for correlation to Tournaisian-Viséan strata in other parts of Gondwana. [ABSTRACT FROM AUTHOR]

Abstract An updated lithostratigraphy of the Carboniferous to Early Permian succession, exposed in the southeastern Sanandaj-Sirjan Block is presented. The succession includes the unnamed Mississippian strata, the Asad Abad Formation (new) and the Vazhnan Formation (revised). The unnamed Mississippian strata, are disconformably covered by the Asad Abad Formaition. The Asad Abad Formation (late Serpukhovian-Moscovian), is disconformably overlain by the Vazhnan Formation. The late Gzhelian-Asselian Vazhnan Formation is disconformably covered by the late Early–Middle Permian Surmaq Formation at the type and reference sections. According to facies and stratal patterns, continuity, lithology, sedimentary structures, and skeletal composition, most of the Early Carboniferous sediments were deposited on broad, low-gradient ramps during periods of relative tectonic stability and regional subsidence. In contrast, during much of the Middle Carboniferous to Early Permian, southeast and northwest parts of the Sanandaj-Sirjan Block were dominated by siliciclastic influx, whereas the central part of this basin was dominated by ramp type platforms and sediment gravity flow deposits. The mosaic-like pattern of deposition observed in stages of platform evolution during Middle Carboniferous to Early Permian suggests a compartmentalization of the depositional settings that could be linked to considerable differential subsidence of fault movements. [ABSTRACT FROM AUTHOR]

Abstract The lower Cambrian Lalun Formation of the Tabas Block, Central Iran, allows to generate a sequence stratigraphic model which characterises the sedimentary evolution and improves palaeoenvironmental interpretation of sedimentary successions along the northern margin of the Prototethys. This formation provides a key for understanding processes that took place during the late early Cambrian in Iran and is the best representative for the complex mosaic of mixed siliciclastic-carbonate systems which illustrate the development and evolution of fluvial and tide-dominated estuarine systems adjacent to an open coast during this interval in the region. Detailed facies analysis allows to differentiate five vertically-stacked groups of facies associations (fluvial facies associations; estuarine facies association; open coast tidal flat facies association; carbonate ramp facies association; and delta facies association) in the uppermost interval of the Lalun Formation. The conceptual depositional models for the siliciclastic-carbonate successions of the Lalun Formation are summarised in a sequence stratigraphic framework, including three third-order depositional sequences (braided fluvial systems; incised-valley fill; and carbonate ramp and tide-influenced delta systems). The data suggest that the Central Iranian Microcontinent broke up during latest Neoproterozoic–early Cambrian times, resulting in the Proto-/Palaeotethys rifting, with considerable differential subsidence recognizable from the reactivation of faults in the early Cambrian which led to new syn-rift successions. The mosaic pattern of deposition observed among the studied sections suggests a compartmentalization of the depositional setting as a result of the interplay between tectonics, sediment supply, and eustasy. Abrupt lateral changes in facies and thickness within the sequences depositional sequences suggest that deposition was controlled by repeated tectonic downdrop and uplift as a consequence of local syndepositional, extensional fault movements. Tectonic activities in the studied region controlled sedimentation and accommodation as well as the position of depocentres within the basin, and the stratal geometries within the sequences. However, the stratigraphic architectural style of the depositional sequences and the asymmetrical trend of the transgressive and regressive second-order sequences imply that the deposition of the late early Cambrian successions is at least partly a result of eustatic sea level changes and cannot be linked exclusively to differential subsidence due to fault movements. Our study indicates that stratigraphic relationship between carbonate and siliciclastic facies in the depositional sequences was also controlled by subsidence/uplift in the hinterland and the areas of siliciclastic input rather than climatic changes. The late early Cambrian depositional environments evolved from braided rivers and an incised valley system (lowstand) to transgressive incised-valley-fill successions which are capped by transgressive open coast tidal flat and carbonate open marine facies. Depositional history of the formation terminated with a regression that ceased with progradation of tide-influenced delta systems. The stratigraphic evolution described in this study documents an eustatic sea-level fall interposed between the top of the Lalun Formation and the base of transgressive tidal bars of the overlying Fasham Formation reflecting the complex (sub-)globally recognizable regressive–transgressive event at the lower–middle Cambrian boundary interval, which led to the establishment of an extensive middle–late Cambrian carbonate platform in present-day northern and central Iran. Highlights • Stratigraphic analyses of the early Cambrian Lalun Formation has been conducted. • Synthesis of tectonic and eustatic controls on stratigraphic architecture. • The depositional models were proposed based on sequence stratigraphic framework. • Results are useful for correlation to Cambrian strata in other parts of Gondwana. [ABSTRACT FROM AUTHOR]

The siliciclastic Gadvan Formation from Abadan Plain, southwestern Iran, is highly bioturbated and allows relationships between changes in ichnocoenoses within a depositional system to be documented and placed in a high-resolution sequence stratigraphic framework. Relying on the sedimentary and ichnological characteristics, the siliciclastic succession is divided into two facies associations: a wave-dominated offshore-shoreface complex and a tide-river influenced delta. The first includes facies that have been deposited in shelf-offshore, upper offshore, lower shoreface and upper/middle shoreface environments, the latter includes facies that have been deposited in prodelta and delta front. Integrated ichnologic and sedimentologic studies of the Gadvan Formation, allow distinction between prodelta and delta front and open marine deposits. With the identification of maximum flooding and ravinement surfaces as bounding surfaces of the stratal units, detailed analysis on systematic changes in the stacking pattern (cycle thickness, cycle type, and facies proportion) are made. Eight ichnocoenoses could be differentiated in the studied sections. The positions of the ichnocoenoses within genetically related stratal units (genetically related ichnocoenoses), indicate three large-scale cycles (DS1 to DS3, from oldest to youngest). The cyclical nature of the Gadvan Formation is attributed to low-amplitude eustasy in greenhouse conditions formed under interaction of eustatic high-frequency cycles and longer term tectonically driven sea-level variations during the long-term transgressive sea-level trend of the early Cretaceous. Stratigraphic architectural style of sequences DS1 to DS3 (which includes scarce evidence of lowstand deposits, partial or total truncation of the HST, and predominance of thick transgressive deposits), is remarkably similar to long-term transgressive sea-level trend of the Early Cretaceous across the Arabian Plate. This study suggests a more relatively seaward position of the siliciclastic successions of the Gadvan Formation of Abadan Plain than the Mesopotamian Basin (upper Zubair Formation equivalent in western Iraq and Kuwait), which would be concordant with the prevailing view of an easterly prograding coastline across the Arabian Plate. This study reveals important sedimentological and ichnological features and permits the development of predictive models for the paleoenvironmental and sequence stratigraphical significance of trace fossil assemblages that can be readily compared or translated to analogous depositional systems worldwide. The ichnological analysis is based on cores and can be especially applied to evaluate the applicability of current ichnological models to the study of Cretaceous reservoirs of western Iraq, Kuwait and western Saudi Arabia. [ABSTRACT FROM AUTHOR]

The palaeoenvironmental significance of trace fossil assemblages in the flysch deposits of the Upper Cretaceous of the Sistan ocean – the Sefidabeh basin in the Sistan Suture Zone SSZ in Eastern Iran – has been assessed for the first time. The Sefidabeh basin of turbidite origin consists of 10 sedimentary facies, which can be grouped into 3 facies associations (FA) representing submarine channel-related facies associations (FA1), lobe-related facies associations (FA2), distal fan-basin floor facies associations of a deep-water turbidite system (FA3). Thirty three ichnogenera, with many ichnospecies, have been identified in this deep sea succession: Alcyonidiopsis , Arthrophycus , Asterostoma , Belorhaphe , Bergaueria , Cardioichnus , Chondrites , Cosmorhaphe , Desmograpton , Gyrophyllites , Halopoa , Helminthopsis , Helminthorhaphe , Laevicyclus , Lophoctenium , Mammilichnis , Megagrapton , Multina , Nereites , Ophiomorpha , Palaeophycus , Planolites , Phycodes , Phycosiphon , Paleodictyon , Rutichnus , Scolicia , ?Strobilorhaphe , Taenidium , Teichichnus , Thalassinoides , Zoophycos and Urohelminthoida . Their distribution is clearly linked with lithofacies and depositional palaeoenvironments. Changes in trace fossil assemblages and ichnocoenoses follow different environments of the turbidity system of the submarine channel to fan system of the Sefidabeh basin and are associated with variations in environmental controlling factors. Environmental controlling factors including hydrodynamic regime, oxygen level, organic content and sedimentation rates. Ten ichnocoenoses were recognized in the facies associations of the deep-sea fan system of this study. Taking into consideration the diversity, bioturbation level, and colonization order of bioturbated beds and the obvious deepening of the deep-sea depositional system from inner to outer parts of the succession, ichnocoenoses can express a bathymetric trend from shallower to deeper parts, and from higher-to-lower hydrodynamic condition of deep-sea fan systems of the Sefidabeh basin. This study reveals important sedimentological and ichnological features of turbiditic systems in deep sea settings of Iran and permits the development of predictive models for the palaeoenvironmental significance of trace fossil assemblages that can be readily translated to analogous depositional systems in the surface/subsurface. [ABSTRACT FROM AUTHOR]

The trace fossil assemblages from the Upper Cretaceous Neyzar Formation are described for the first time from Kopet-Dagh, Iran, enhancing the record of this fossil group in the Cretaceous of the Middle East. Thirty-one ichnogenera have been identified in open marine successions: Agrichnium , Asteriacites , Asterosoma , Bergaueria , Chondrites , Cylindrichnus , Halopoa , Helminthopsis , Gordia , Gyrochorte , Laevicyclus , Lockeia , Megagrapton , Nereites , Neonereites , Ophioichnus , Ophiomorpha , Palaeophycus , Phycodes , Phycosiphon , Planolites , Protovirgularia , Rhizocorallium , Rosselia , Scolicia , Sinusichnus , Skolithos , Spongeliomorpha , Taenidium , Teichichnus , and Thalassinoides. The Neyzar Formation accumulated on a gently dipping shelf dominated by storm- and fair weather-wave processes and includes shelf, lower offshore, upper offshore, lower shoreface-proximal offshore, middle-upper shoreface and foreshore deposits. Identification and interpretation of ichnological signatures and the spatial arrangement of sedimentary structures in the successions are used to further refine sedimentary interpretations of parameters such as wave energy, substrate properties, the nature of the available food supply, variability in sedimentation rates and proximal–distal trends of the wave-dominated shoreface–offshore complex. The prevalent palaeoceanographic situation during the deposition of the studied successions was ideal for tropical storms, thus promoting tempestite deposition and the occurrence of a tropical and subtropical trace fossil suite. According to this study, increasing mobility and infaunality with more complex trace systems or sophisticated feeding strategies, climax population strategies and the high diversity, associated with rapid increase in the abundance and depth of infaunal structures, indicate a major reorganization of the shallow-marine benthic communities that occurred in response to the Mesozoic marine revolution. [ABSTRACT FROM AUTHOR]

Changes in stacking patterns of facies, stratal architecture and shoreline trajectory along depositional strike are mainly dependent on along-strike differences in factors such as physical processes (rivers, waves, tides), tectonics, eustatic changes, sediment supply, and local physiography. The lower-upper Ordovician successions (Lashkerak Formation) deposited in a Peri-Gondwana shallow continental shelf have been interpreted using the sequence stratigraphic concepts. This approach allowed to highlight main differences along-strike in the co-existing depositional systems (coastal plains, estuaries, deltas, and shoreline to shelf systems) in the Alborz basin along the northern edge of Gondwana. On the basis of sedimentary and ichnological characteristics, the siliciclastic successions are divided into four facies associations: (i) Wave-dominated estuarine, (ii) Wave-dominated shoreface-offshore complex, (iii) Mixed fluvial (F)- and wave (W)-influenced delta (Fw and Wf), and (iv) Tide-dominated, fluvial-influenced delta (Tf). Six third-order depositional sequences (DS1-DS6) were recognized, each of them are bounded by unconformities and pronounced shifts in the facies. Along depositional strike (NE/SW- a distance of c. 150 km), significant intrabasinal changes in sediment supply produced evident lateral changes in the shoreline trajectory and stratal architecture, of the DS1-DS3 (Tremadocian-Floian), may be attributed to differences in physical processes (rivers, waves, tides activity) and topographic irregularities derive probably by different rates of subsidence in the basin. During the deposition of the DS1-DS3, a significant along-strike differences in the composition of ichnological suites and the lifestyle of benthonic organisms, dependent on the relative supremacy of wave, storm, river, and tidal processes. Sedimentary supply and processes are the main controlling factors for the stratigraphic architecture rather than the tectonic activity between Tremadocian and Floian. While during the Darriwilian-Katian interval (DS4-DS6), the tectonic activity predominates with the beginning of extensional phases related to the rifting in the Alborz basin causing the activation of syn-depositional normal faults and the development of block-faulted craton-ward margin. Typically, differential subsidence due to extensional tectonic activity causes the uplift of tectonic blocks west of the Alborz Basin into the emerging areas, on one hand, and simultaneous deepening-upward stacking patterns (i.e., increased subsidence rates) in the hanging-wall depocenters of east of the Alborz Basin, on the other hand. This outcrop-based study suggests that the identification of genetically related depositional units in a larger paleogeographic context is fundamental for understanding along-strike variability in controlling mechanisms of the spatial distribution and stratigraphic architecture of coexisting and linked depositional systems. • Analyze along-strike variations in stratigraphic architecture of the Ordovician successions. • Synthesis of autocyclic and allocyclic controls on changes in accommodation space along depositional strike. • Interpreting along-strike variability in controlling mechanisms of stratigraphic architecture. • Unravelling the palaeogeography of continental shelf of the Prototethys margin along the northern edge of Gondwana. • Results are useful for correlation to Ordovician strata in other parts of Gondwana. [ABSTRACT FROM AUTHOR]

The stratigraphic architecture, changes of depositional systems in lateral and vertical extent, and 3D-stacking pattern of second- and third-order sequences of the Cambrian successions on the northern Gondwanan margin indicates a distinct sea-level fall in the Alborz Zone and Central Iran corresponding with global sea-level fluctuations. The peak of the sea-level fluctuations is located at the boundary between the Lalun Formation and the base of the overlying Mila Group. A vertical trend from gradual sea-level rise during the Cambrian Series 2 (recorded as thick transgressive deposits of the Lalun Formation) to transgressive valley-fill system at the base of the Fasham Formation and overlying highstand subtidal carbonates (carbonate platform of the Deh-Sufiyan Formation) can be observed. This trend is paralleled by a change from mixgrounds with metazoan body fossils to microbial matgrounds and microbial boundstones (thrombolites and stromatolites). The general increase in vagile bilaterian metazoans led to a distinct proliferation in ichnofossils in the Lalun Formation indicating a considerable increase in progressive ecospace utilization and tiering complexity. These are associated with biodiffusion, sediment reworking and bioirrigation so that matgrounds were disrupted and mixed layer substrates developed. A proliferation of microbes took place at the base of the Mila Group, which is regarded as a reaction to unfavourable environmental conditions and considerable challenges for metazoans. Consequently, a dramatic degradation of marine bottom communities followed the major eustatic sea-level fall at the Cambrian Series 2–Miaolingian boundary interval and led to the decrease in ichnodiversity, bioturbation intensity, depth of bioturbation and burrow size at the base of the Mila Group. The amount of biogenic mixing significantly decreased, and eventually sedimentary mixed layers disappeared. • Facies and sequence stratigraphic analyses of the Cambrian Series 2–Miaolingian boundary interval. • The impact of the eustatic sea-level fall on mixground and matground ecosystems. • The trace-fossil record of organism–matground interactions by changes in environmental conditions. • Document trend of change from mixgrounds to matgrounds and microbial boundstones. • Results are useful for correlation to Cambrian strata in other parts of Gondwana. [ABSTRACT FROM AUTHOR]

The Lower Carboniferous Mobarak Formation in the east of Central and Eastern Alborz Mountains, northern Iran, is deposited on a distally steepened carbonate ramp. Detailed facies analysis allowed to differentiate seven facies associations, includes deep marine basinal (FA1), toe-of-slope/outer ramp (FA2), ramp/slope (FA3), shallow open marine (FA4), bioclastic bars or shoal (FA5), lagoon (FA6) and intertidal flat (FA7). The trace-fossil suites of the studied successions are shown for the first time. Twenty eight ichnogenera were identified, i.e. Arenicolites, Asterosoma, Bergaueria, Chondrites, Cochlichnus, Diplocraterion, Halopoa, Helminthopsis, Helminthorhaphe ? , Helminthoidichnites, Gordia, Gyrochorte, Lockeia, Mammilichnis, Megagrapton, Nereites ? , Palaeophycus, Phycodes, Phycosiphon, Planolites, Protovirgularia, Rhizocorallium, Rosselia, Sinusichnus, Skolithos, Taenidium, Thalassinoides, and Zoophycos. The seven facies associations deposited in a wide range of physico-chemical conditions, show distinct proximal to distal trends. As a result of oxygen-depleted depositional conditions, only the tracemakers of Zoophycos survived in deep marine slopes, which were close to turbiditic sedimentation zones. The development of a benthic community under the stable condition and a long-term colonization window were documented by highly diverse suites of the Cruziana ichnofacies. Under a stressed environment (after tempestite deposition), the Skolithos ichnofacies displayed a low diversity of opportunistic ichnocommunity suite. The mixed Skolithos – Cruziana ichnofacies occur in the middle to distal lower inner ramp. The identification of the archetypal ichnofacies may document broad changes of environmental parameters such as variability in sedimentation rates, energy level, salinity, substrate properties/consistency, nature of nutrient supply and dissolved oxygen content. Relationships among different modes of ethology of tracemakers and sedimentary structures in the studied successions are used to clarify sedimentary conditions. • The Lower Carboniferous Mobarak Formation in the east Central and Eastern Alborz Mountains, is deposited on a distally steepened carbonate ramp. • Detailed facies analysis allowed to differentiate seven facies associations, including FA1 to FA7. • The trace-fossil suites of the studied successions are shown for the first time. • The ichnofacies in the Mobarak Formation including. [ABSTRACT FROM AUTHOR]

The Albian–Turonian Sarvak Formation is the second most important reservoir of Iran. In this study, an integrated field-scale reservoir zonation is applied to the Sarvak reservoir in one oil field of the Dezful Embayment, SW Iran to understand the distribution of speed, barrier, and baffle zones. The geologic controls of depositional and post-depositional factors on the suggested reservoir zonation are also discussed here. Based on the results, the studied reservoir is composed of seven zones with different reservoir qualities. The best reservoir zones show considerable amount of dissolution pores, and are developed beneath regional-scale paleo-exposure surfaces that are also recognizable in coeval strata on the Arabian Plate. These surfaces represent recurring subaerial exposure episodes during the development of the Sarvak Formation through which meteoric diagenesis highly affected the rock record leading to the development of paleo-karst profiles with noticeable dissolution pores in the strata beneath the paleo-exposure surfaces. However, the long-lasting emergence time of the mid-Turonian exposure (mT-ES; the interface between the Sarvak Formation and overlying Ilam Formation) caused the over-maturation of the related paleo-karst profile and the deterioration of the created reservoir quality. The results of this study reveal the effects of regional-scale geologic controls on the reservoir characteristics of the Sarvak Formation and may be also applicable to the reservoir characterization of other time-equivalent strata in the Arabian Plate. • Diagenesis acted as the superior control on reservoir quality of the Sarvak Fm. • Seven reservoir zones are recognized in the Sarvak Formation. • Best reservoir zones are beneath some regional unconformity surfaces. • Subaerial exposures led to the development of secondary dissolution pores. • Emergence duration determines the reservoir quality of subaerially exposed strata. [ABSTRACT FROM AUTHOR]