Yazd Block Research Articles

Stratigraphy, depositional environments and provenance of the Shemshak Group (Upper Triassic–lower Middle Jurassic) on the northern Tabas Block; evidence for the emergent Cimmerian ridge in Central Iran

The Upper Triassic to lower Middle Jurassic Shemshak Group of the Central-East-Iranian-Microcontinent is important for understanding Mesozoic geodynamics of the Middle East during and in the aftermath of the collision of the Cimmerian microplates with Eurasia, resulting in the massive burial of organic matter and the formation of significant coal reserves. The present study thus aims to elucidate the stratigraphic patterns, lithofacies inventory, depositional environments and geodynamic significance of the Shemshak Group in the Halvan area of the Kalmard sub-block of the northern Tabas Block where the succession is most completely developed. Lithostratigraphic studies through detailed logging resulted in a differentiation of the siliciclastic Upper Triassic Nayband and Lower Jurassic Ab-e-Haji formations, bounded at their bases by the Eo- and Main Cimmerian unconformities, respectively, and the mixed carbonate-siliciclastic Badamu Formation (upper Lower to lower Middle Jurassic). The lithofacies analysis and stacking patterns of siliciclastic strata indicate deposition in a variety of environments ranging from (proximal to distal) coastal and delta plains to delta front and prodelta settings for the Nayband and Ab-e-Haji formations. Detailed litho- and microfacies studies of the Badamu Formation revealed inner to middle parts of a mixed carbonate-siliciclastic ramp system. Careful petrographic studies indicate that sandstones of the succession are generally lithic-rich (ranging from phyllarenite to sedarenite) and, up-section, grade into quartz-rich sublitharenite, providing important information for sedimentary provenance analysis. The sandstones rich in metamorphic- and sedimentary lithic fragments indicate a proximal source on the western Yazd Block as well as rocks exposed on the Kalmad sub-block itself. The integrated studies also led to the recognition of the Eo- and Main Cimmerian orogenic phases, characterized by rapid uplift and/or subsidence phases. Late Triassic and Early Jurassic deposition took place in a back-arc extensional basin characterized by normal faulting. During the Toarcian–Aalenian, the reduced input of clastic material due to source-area denudation and/or a major transgression resulted in the development of the mixed carbonate-siliciclastic system of the lower Badamu Formation in the western part of the northern Tabas Block. This ramp system developed into an attached, ocean-facing carbonate platform with a prograding margin of ooid shoals.

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.

Morphotectonic Analysis of Sub-Basins along the North Termination of Anar Fault, Yazd Block, Iran

Morphotectonic Analysis of Sub-Basins along the North Termination of Anar Fault, Yazd Block, Iran

Coral fauna across the Cretaceous–Paleogene boundary at Zagros and Sistan Suture zones and Yazd Block of Iran

From the upper Maastrichtian (Tarbur Fm.) and Paleocene of Iran, 20 species of scleractinian corals belonging to 17 genera and 14 families, and one species of the octocoral Heliopora are newly recorded. Furthermore, coral species previously described from the upper Maastrichtian Tarbur Fm. and the Paleocene are revised and included in the evaluation, resulting in a total of 37 species from 28 genera belonging to 20 families (including 3 subfamilies) for the Iranian K/Pg-boundary time period. The majority of the taxa (21 out of 37 = 57%) crossed the K/Pg-boundary. The genera Acropora and Stylocoeniella are recorded from strata older than the Paleogene (upper Maastrichtian) for the first time; for Lobopsammia it is the first report from strata older than the Eocene (Selandian‒Thanetian). The vast majority of the coral taxa occurring in both the upper Maastrichtian (Tarbur Fm.) and the Paleocene of Iran have been reported from a variety of both reefal and non-reefal paleoenvironments. On the species level, a slight majority of the corals from the upper Maastrichtian (Tarbur Fm.) are endemic (14 out of 27 species = 52%). In contrast, the vast majority of the Paleocene Iranian corals are cosmopolitan to subcosmopolitan; only 4 taxa are endemic during the Paleocene. While the upper Maastrichtian coral fauna of Iran shows greatest affinities to contemporaneous assemblages of Europe and the Caribbean, the Paleocene coral fauna is most closely related to contemporaneous coral associations of central Asia, Europe, and North America.

Depositional and thermal history of a continental, coal-bearing Middle Jurassic succession from Iran: Hojedk Formation, northern Tabas Block

AbstractDuring the early Bajocian, a conspicuous coal-bearing siliciclastic succession was deposited in the northern Tabas Bock, which is important for understanding the regional geodynamics of the Central-East Iranian Microcontinent (CEIM) as well as for the Jurassic coal genesis in this part of Laurasia. Sedimentary facies analysis in a well-exposed section of the lower Bajocian Hojedk Formation (Kalshaneh area, northern Tabas Block) led to the recognition of ten characteristic sedimentary facies and three facies associations, representing channels with point bars and floodplains of a Bajocian meandering river system. Modal analysis indicates that the mature quartz arenites and quartzo-lithic sandstones of the Hojedk Formation originated from the erosion and recycling of older, supracrustal sedimentary rocks on the Yazd Block to the west. The coal petrography and maturity show an advanced maturation stage, whereas the great thickness of these continental strata points to a pronounced extension-related subsidence in the northern Tabas Block. The rapid rate of differential subsidence can be explained by accelerated normal block-faulting in the back-arc extensional basin of the CEIM, facing the Neotethys to the south. Compared to the thick Jurassic, the post-Jurassic strata are relatively thin and played a limited role in the thermal history of the coal in the northern Tabas Block. A relatively high geothermal gradient in the tectonically highly mobile area of the northern Tabas Block and/or heating by regionally widespread Palaeogene intrusions were most probably the key drivers of the thermal maturation of the Middle Jurassic coals.

A record of Late Cambrian–Early Ordovician arc magmatism in Yazd block, Central Iran

A record of Late Cambrian–Early Ordovician arc magmatism in Yazd block, Central Iran

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.

Biostratigraphy of Baghamshah Formation based on calcareous nannofossils in the Southwest Tabas, Iran

The Tabas Block is part of the Central Iran microcontinent, located between the Lut Block in the East and the Yazd Block in the West. The Baghamshah Formation is the second lithostratigraphic unit from the sedimentary cycle of the Magu Group and the Baghamshah Subgroup in the Jurassic of Tabas Block. This formation is conformably underlaid with the grey pisoidal limestones of the Parvadeh Formation and overlaid with the Pectinid limestones of the Kamar-e-Mehdi Formation (Esfandiar Subgroup). In this research, the biostratigraphy of the Baghamshah Formation in the Rizu and Kamar-e-Mehdi sections, based on calcareous nannofossils, is examined. The thickness of the Baghamshah Formation in the Rizu section is 270 m (mostly including marl and green shales with intercalation of limestones and calcareous sandstones), and in the Kamar-e- Mehdi section is 236 m (composed of gypsiferous marly shales, marl, marly shales and alternation of marl-shale with limestones and calcareous sandstones). According to the taxonomic studies in the Rizu section, 52 species belong to 24 genera, and in the Kamar-e-Mehdi section, 45 species belong to 23 genera of calcareous nannofossils. Based on index calcareous nannofossils, the CC1, CC2, CC3, and CC4 biozones established by Sissinghh in both sections were determined. It is mentioned that CC5 biozone only occur in Kamar-e-Mehdi section. According to the identified biozones, the suggested age of the Baghamshah Formation is early Berriasian–early Hauterivian in the Rizu section, and early Berriasian–late Hauterivian in the Kamar-e-Mehdi section. Keywords: biostratigraphy, Baghamshah, calcareous nannofossils,Tabas, Iran.

Ordovician crustal thickening and syn-collisional magmatism of Iran: Gondwanan basement along the north of the Yazd Block (Central Iran)

ABSTRACT This study investigates relicts of some granitic Gondwanan basement unexpectedly outcropping in the northwest of Central-East Iranian Microcontinent (CEIM) and incorporated into an ophiolitic mélange. Based on petrographical (e.g. high modal content of muscovite (~10 vol.%), absence of hornblende, inherited zircons (>541 Ma)), geochemical (peraluminous and calc-alkaline S-type affinity, high silica, high ‘light rare earth element (LREE)/heavy rare earth element (HREE)’ ratios, negative Nb and Ti anomalies), and geochronological (magmatic zircon age ~448 Ma) results, it is an Ordovician anatectic granite formed from a sedimentary source during crustal thickening in a syn-collisional setting. It shows some signatures of metamorphic deformation (cataclastic fabric, quartz bulging recrystallization, and foliation) likely developed in the Devonian (~410 Ma). The U-Pb zircon ages from this granite are analogous to the other Ordovician collision-related magmatic events in the CEIM (Chahak to Airekan, Balvard). Our results confirm that Cadomian subduction and closure of the Proto-Tethys Ocean to the north of the Gondwana supercontinent resulted in crustal thickening during Ordovician collision-related magmatism and Devonian-Carboniferous regional metamorphism in the CEIM.

An exploratory model for sediment-hosted lead and zinc deposits by using the fractal method in Yazd block- Central Iran

Structure processes have a significant role in forming sediment-hosted lead and zinc deposits. On other words, they are formed in an individual pattern located in the related rift basins. So, the first-order, the second-order, and the third-order basins have been created. Faults operate as the conduct of ore-bearing fluid and the bounding-the second-order basins. By starting rifting, hydrothermal fluid enters a sedimentary basin and as a result of the extending faults, it creates convection cells confined by faults. Therefore, structural processes are the main control factor for these deposits. Also, factors controlling the mineralization are recognized by spatial analysis methods. In this study, to identify controlling factors and present an exploratory pattern for sediment-hosted Pb-Zn deposits in the southern part of the Yazd Block, the fractal (Box- counting) method has been used. This method was utilized to estimate the distance of sub-basins which are the host of sediment-hosted Pb and Zn mineralization for the first time. The results of this method depicted three different populations representing three factors controlling the mineralization in the studied area. These results were consistent with the basin structure which has been formed from three sub-basins. Therefore, three populations obtained from the fractal analysis showed the dimensions of three sub-basins in the studied area. The distance between mineral deposits in the third-order basin obtained about 8 Km while it is about 31 Km for the second-order basins. So, three second-order basins were recognized in which the distance between sub-basin numbers 1 and 2 is about 30 Km while it is about 60 Km between sub-basin numbers 2 and 3. Based on this exploratory model, there could be another second-order basin between sub-basin numbers 2 and 3. According to reports and literature, no other deposit has been discovered between them until now. So, based on the suggested model, there is a possibility of other deposits occurring between sub-basins numbers 2 and 3.

Early Cambrian highly fractionated granite, Central Iran: Evidence for drifting of northern Gondwana and the evolution of the Proto-Tethys Ocean

The Zarin granitic body is located in the eastern part of the Yazd Block in the Central Iran microcontinent. The granite has variable granular to mylonitic textures. New zircon U-Pb dating shows that the granitic rocks crystallized at 535–530 Ma. The pluton has high SiO2 abundances (72.1–77.5 wt%), K2O (4.4–6.3 wt%) and low MgO (0.2–0.7 wt%) contents, as well as high K2O/Na2O (1.10–1.97) and A/CNK (molar ratio of Al2O3/(CaO + Na2O + K2O)) 0.9–1.1 ratios, and is dominantly peraluminous. The granite is enriched in light rare earth elements (LREEs) relative to heavy REEs (HREEs), has negative Eu anomalies, and is extremely depleted in Nb, Ba, P, Ta and Ti. It is also characterized by variable but commonly high 87Sr/86Sr(i) (0.7018–0.7093) and negative εNd(i) values of −1.1 to −2.6. The geochemical features indicate that the rocks are highly fractionated I-type granite and have undergone extensive fractional crystallization of hornblende, biotite and feldspar. Results are consistent with melting of an evolved lower crust source during the subduction of the Proto-Tethys Ocean. The emplacement of the Zarin granite is contemporaneous with the extension of a Cadomian continental arc on the north side of Gondwana, that rifted away to create the Rheic Ocean to its south. Cadomian basement rocks in Iran are interpreted as an important link between western and eastern sectors of the Late Proterozoic-Early Paleozoic orogenic belts along the northern side of Gondwana, and the histories of the Rheic, Iapetus and Proto-Tethyan oceans

Paleoenvironment and paleobiogeography of Lower Cretaceous carbonate successions of the northern Tethyan margin: Examples from Northeastern and Central Iran

Lower Cretaceous carbonate successions outcrop extensively along the northern Tethyan margin in the Kopet-Dagh (NE Iran) and Yazd Block (Central Iran). These carbonate units are not well constraint in terms of stratigraphic, sedimentological, geochemical, and paleobiogeographic view point. To improve our knowledge, a detailed multidisciplinary study has been presented on two roughly coeval stratigraphic units in the two different areas, and correlated with other tethyan carbonates. The two stratigraphic units (Taft and Tirgan formations) have been deposited along a carbonate shelf with microfacies associations ranging from the outer-shelf to the inner-shelf settings. Diachrony in ages at the base and top of the stratigraphic units suggests the long-term subsidence effects during the Early Cretaceous, followed by a Cimmerian phase of epi-orogenesis, and also the remnant paleoreliefs. New biostratigraphic data coupled with stable isotope δ13C records shows that the onset of carbonate production started much earlier than previously thought (Valanginian rather than Barremian). Our results also permit us to correlate the lower Aptian stratigraphic units with the OAE1a. The worldwide distribution of index microfossils including benthic foraminifera and colomiellids reported on paleobiogeographic reconstructions. They have been used to define paleobiogeographic provinces for the Valanginian, Hauterivian and Aptian intervals and show predominant basin connections. Significantly, the allochem content of the lithostratigraphic units and their phosphorus accumulation show phases of important heterozoan to photozoan carbonate production, which are recorded in other localities of the Tethyan realm as the consequence of global paleoceanographic changes.

A summary of the Jurassic System in North and East-Central Iran

The rocks of the Jurassic System in North and Central Iran are represented by very thick sedimentary successions reflecting the deposition during two tectono-stratigraphic megacycles, bounded by three important unconformities. The older (Early to early Middle Jurassic) cycle starts, after the Late Triassic closure of the Palaeotethys and the collision of the Iran Plate with the southern margin of Eurasia (Turan Plate), with an abrupt uplift of the Cimmerian Mountains around the Triassic–Jurassic boundary (Main-Cimmerian Event) and is terminated by the Mid-Cimmerian Tectonic Event in the mid-Bajocian. The predominantly siliciclastic sediments of this tectono-stratigraphic cycle are accommodated in the Ab-e-Haji Subgroup of the (upper) Shemshak Group. The Ab-e-Haji Subgroup consists of thick and widespread, partly coal-bearing siliciclastic strata and also records some important marine ingressions, especially in the Toarcian and Aalenian. The younger tectono-stratigraphic cycle starts with an extensive marine transgression in the Late Bajocian and ends around the Jurassic-Cretaceous boundary with the Late Cimmerian Tectonic Event. In the aftermath of the Mid-Cimmerian Tectonic Event, the Iran Plate was dissected into several structural units, the geological histories of which differed and so did their facies patterns. Thus, in North Iran two main sedimentary areas developed, namely the Alborz and Koppeh Dagh basins, which show moderate diffe-rences in lithology and thicknesses. However, the differentiation is much more pronounced on the Central-East Iranian Microcontinent, which comprises three N–S-oriented and independent structural units, i.e., from east to west the Lut, Tabas and Yazd blocks. During the Jurassic Period, the sea mostly covered the Tabas and Lut blocks, whereas the Yazd Block remained largely emergent. The lithologically diverse and numerous formations of the area are combined in the Magu and Bidou groups. Early to Early Middle Jurassic ammonite fau-nas of North and Central Iran are palaeobiogeographically closely related to Northwest European (Subboreal) ammonite faunas, allowing a similar biozonation. Concurrent with the Late Bajocian transgression, there is an abrupt change in faunal composition and the Middle and Late Jurassic ammonite faunas of North and Central Iran are much more similar to those of epicontinental seas bordering the nort-hern margin of the western Tethys and occupy an intermediate position between the Mediterranean and the Submediterranean Province. The results of the studies on ammonoid palaeobiogeography are in line with Early Jurassic palaeogeographic reconstructions that place the Iran Plate at fairly high palaeo-latitudes of about 45°N, followed by a rapid southward shift throughout the Middle and Late Jurassic to a position of about 30°N.

Stratigraphic distribution of shallow-water benthic foraminifera from the Lower Cretaceous Taft formation, Central Iran (Yazd Block), with evidence for the importance of hiatuses

In this contribution, two stratigraphic sections are described through the Lower Cretaceous shallow-water platform sediments (Taft formation) from the northern Tethys, which are located in the Yazd Block, Central Iran. Benthic foraminifera are used to propose a biostratigraphy for these successions. They are grouped around several assemblage zones, and several genera and species are reported from the Yazd Block basin for the first time (e.g., Arenobulimina cochleata, A. meltae, Belorusiella sp., Bolivinopsis cf. labeosa, Decussoloculina barbui, Martinotiella jucunda, Myncinabulgarica, Novalesiacornucopia, Sabaudiabriacensis,Simplorbitolina manasi). Their presence can provide a better understanding for the paleogeographic reconstruction of the Tethyan seaways. Furthermore, they represent candidates as potential index fossils in the Lower Cretaceous stratigraphy of the Yazd Block. The new biostratigraphic data allow to date the Lower Cretaceous successions between the probable Valanginian and the late Aptian. Based on the absence of early Barremian indicators and also late Aptian markers, two hiatuses are recognized through the Taft formation. This formation also displays a diachrony in ages at its base and top, which suggests the effect of long-term subsidence in the Yazd Block during the Early Cretaceous, following the Cimmerian phase of orogeny.

Palaeoenvironment, sequence stratigraphy and palaeogeography of the Lower Cretaceous deposits of Mehdi Abad, Yazd Block, Central Iran

Four Lower Cretaceous sections in the southern Yazd Block were measured and studied to interpret the palaeoenvironments, synsedimentary tectonics, and sequence stratigraphy. The Early Cretaceous sedimentary record of this block, consisting of the Sangestan, Taft, Abkuh, and Darreh Zanjir formations, was mainly influenced by synsedimentary tectonic activities in a tectonically unstable basin. Field observations and laboratory studies were used to identify lithofacies and microfacies, based on which six depositional environments were identified: upper coastal plain (alluvial fans), shore, tidal flat, lagoon, shoal, and open marine. A carbonate-siliciclastic shallow platform including an alluvial-coastal plain and an inner platform is suggested for the depositional environment of the Sangestan Formation. The depth of the overall shallow sedimentary basin of Sangestan Formation increases from west to east and deposition was controlled by long- term sea-level changes. A carbonate platform consisting of inner and outer parts, including tidal flat, lagoon, open marine belts, is suggested for the depositional environment of the Taft and Abkuh formations, while the Darreh Zanjir Formation accumulated in a deep basin. The predominant facies demonstrate an overall transgression-regression cycle (the 2rd order cycle) during the depositional time of these formations in the southern Yazd Block.

Campanellula herishtensis n. sp. (Foraminifera; Orbitolinidae?) from the upper Aptian (Lower Gargasian) of Central Iran

The new orbitolinid foraminifer Campanellula herishtensis n. sp. is described from the upper Aptian (Gargasian) of the Yazd Block, Central Iran. Campanellula herishtensis n. sp. occurs within a small interval of the Herisht section near Ardakan, displaying more or less uniform microfacies types (foraminiferal wackestones/packstones). The Iranian form differs from Campanellula capuensis De Castro (upper Hauterivian – lower Barremian of Italy, and Algeria), the only species described of the genus so far, in size and morphology (shape, apical angle). The generic assignment of the new taxon is discussed including also the genus Orbitolinopsis Henson. The suprageneric placement of Campanellula within the Orbitolinidae according to current classifications (but contrasting the original description) still remains doubtful.

A Cathaysian rugose coral fauna from the upper Carboniferous of central Iran

AbstractTwelve rugose coral species belonging to seven genera are described and discussed based on 70 thin sections of 32 specimens collected from the Anarak section, northeast of Nain, Esfahan Province, Yazd Block, central Iran. These species include two new colonial rugose coral species,Antheria fedorowskiiandAntheria robusta, and five previously named species of colonial rugose corals,Antheria lanceolataandStreptophyllidium scitulum, and solitary rugose corals,Arctophyllum jiangsiense,Caninophyllumcf.somtaiense, andPseudotimania delicata. Five species are left in open nomenclature:Antheriasp.,Arctophyllumsp.,Caninophyllumsp.,Nephelophyllumsp., andYakovleviellasp. These Iranian corals are associated with the fusulinidsRauserites(several species) andUltradaixina bosbytauensis, indicating a latest Carboniferous age (Gzhelian age). All the described genera and named species belong to the families Aulophyllidae, Bothrophyllidae, Cyathopsidae, and Kepingophyllidae, among which the family Kepingophyllidae has been previously documented only from China and Indochina. They are typical representatives of the Cathaysian rugose fauna, which was widely developed around the South China and Indochina blocks near the paleoequator and was absent from the Gondwanan and Cimmerian continents in high latitudes during the Late Pennsylvanian. Hence, the occurrence of the Cathaysian fauna from central Iran in the latest Carboniferous suggests that it may have had a close biogeographical connection with China and Indochina, which further implies its latitudinal position intermediate between the Gondwanan continent and South China and Indochina blocks during this time.UUID:http://zoobank.org/5257d2bb-1346-4dee-8f3e-f4b1b33ba5a9

A magmatic record of Neoproterozoic to Paleozoic convergence between Gondwana and Laurasia in the northwest margin of the Central-East Iranian Microcontinent

This paper presents petrographic and U-Pb LA-ICP-MS isotopic data of a single peraluminous intrusion (alkali-feldspar granite of Airekan) with partial gneissic foliation on the north western margin of the Yazd Block in the west of the Central-East Iranian Microcontinent (CEIM) to discuss the evolution of this terrain. This intrusion typically suggests a continental collision orogenesis along the northern frontier of Gondwana in the CEIM. The U-Pb dating of zircons indicates that Airekan granite has a distinctive inherited magmatic component at ∼518.2 ± 4.9 Ma but zircons with 892, 679, 614 and 554 Ma ages. These zircons were likely to be ultimately sourced from neighboring Neoproterozoic – Cambrian leucogranite terrains, similar to the other localities in the northern margin of Gondwana, along the Alpine-Himalayan belt from Europe, Turkey, NE Iran, CEIM, Pakistan, India to southern Tibet. The zircons and overgrowths around the inherited components with igneous morphology indicate a plutonism at Lower Ordovician (∼483 ± 2.9 Ma). Petrographic features and morphology of zircon crystals indicate that partial resetting of the U-Pb system in zircons have occurred at ∼382.6 ± 3.2 Ma in Devonian, during the Paleo-Tethys evolutions in Khur region (Anarak-Jandaq terrane) in the southern active margin of Laurasia.

A Late Cretaceous epeiric carbonate platform: the Haftoman Formation of Central Iran

An integrated study of the litho-, bio-, and microfacies of several sections has greatly improved the knowledge on the stratigraphy and depositional setting of the Coniacian to Campanian Haftoman Formation in the Khur area of the northern Yazd Block, Central Iran. Generally, the Haftoman Formation rests on a major tectonic unconformity and commences with a basal conglomerate followed by up to 900 m of shallow-water carbonates with local red sandstone intercalations. Five different depositional environments (from distal to proximal) characterize the facies associations (FA) of the Haftoman Formation: silty, spiculitic wackestone (proximal basin, FA I), bio-/intraclastic wacke-, pack-, and grainstone (marginal shoals, FA II), bioclastic rud-/float-/boundstone (outer platform, FA III), silty mud-/wackestone (lagoonal inner platform, FA IV), and sandstone/sandy limestone (areas close to the mouth of ephemeral streams, FA V). The litho-, micro-, and biofacies of the Haftoman Formation are typical for an epeiric carbonate platform characterized by an arid climate and lagoonal circulation, resulting in nutrient-poor waters, warm temperatures, and high salinities. The Haftoman Platform was attached to an emergent arid hinterland formed by the Anarak Metamorphic Complex to the west and southwest of the study area. Unconformity-bounded depositional units indicate sea-level changes that may correspond to 400-kyr high-frequency sequences but further studies are needed to fully exploit the potential of sequence stratigraphy for regional and inter-regional correlation of the Haftoman Formation.

A tectono-stratigraphic record of an extensional basin: the Lower Jurassic Ab-Haji Formation of east-central Iran

The Lower Jurassic Ab-Haji Formation consists of siliciclastic strata which are widespread and superbly exposed across the Tabas and Lut blocks of east-central Iran. The formation records the geodynamic history of central Iran during the Early Jurassic in the aftermath of the main Cimmerian event (near the Triassic–Jurassic boundary) through its sedimentary facies and stratigraphic architecture and allows palaeogeographic and palaeoenvironmental reconstructions. We measured and studied three well-exposed outcrop sections and identified lithofacies and facies associations (fluvial plain, delta plain, delta front, prodelta, and shallow-marine siliciclastic shelf). The integration of all geological, stratigraphic, and sedimentological data shows a west-to-east continental-to-marine gradient within the Ab-Haji Formation. Based on thickness variations, lateral facies changes, palaeocurrent patterns, and changes in the nature of the basal contact of the Ab-Haji Formation on the Tabas and Lut blocks, we locate the fault-bounded Yazd Block in the west and the Shotori Swell at the eastern edge of the Tabas Block as provenance regions. The pattern of thickness variations, rapid east–west facies changes, and provenance is best explained by a tectonic model invoking large tilted fault blocks in an extensional basin. The basal unit shows distinct increase in grain size at the base of the Ab-Haji Formation, similar to the Shemshak Group of the Alborz Mountains (the base of the Alasht Formation) and the non-marine time-equivalent succession of the Binalud Mountains of northeastern Iran. This grain size pattern may have been caused by rapid source area uplift due to slab break-off of the subducted Iran plate in the course of the Cimmerian collision in east-central Iran.