Tethyan Domain Research Articles

Hydrocarbon migration and accumulation in the large Samandepe Gas Field in the chardzhou step-fault zone, Amu Darya Basin, northeastern Turkmenistan: A response to the tectonic evolution of the northern margin of the tethys

The mechanism of large-scale hydrocarbon accumulation in the Tethys domain has long been of interest to petroleum geologists. Located in the northern margin of the Tethys, the Amu Darya Basin (ADB) is well known for its large, indeed giant, gas fields. However, there has been surprisingly little research on the mechanisms of hydrocarbon accumulation in the basin. This paper investigates the accumulation history of the Samandepe Gas Field, a large condensate gas field in the Chardzhou step-fault zone in the northeastern ADB. Trap evolution in the basin is analyzed, the oil and gas sources and hydrocarbon charging periods are determined, and the process of hydrocarbon migration and accumulation explored to establish the relationship between hydrocarbon accumulation and the tectonic evolution of the Tethys. Geophysical logging, organic geochemistry, fluid inclusion analysis, basin modeling are used for analysis. The results show that hydrocarbon accumulation in the Samandepe Gas Field occurred in two stages. First, a lithological ‘large trap’ formed in a barrier reef belt in the Late Cretaceous Santonian, before the present anticline structure of the gas field formed. This trap was filled with oil generated in Upper Jurassic marine source rocks, forming a lithological paleo-oil reservoir. In the second stage, at the end of the Paleogene, the large trap was reformed as structural traps with reef-shoal reservoirs. Natural gas generated from coal-measure source rocks in Middle and Lower Jurassic strata migrated along basement faults, filling the traps. Excess natural gas displaced the oil, some of which dissolved in the gas, forming ‘gas washing’-type secondary condensate oil and creating a structural condensate oil-bearing field. The inherited paleo-uplift in the step-fault zone is crucial to large-scale hydrocarbon accumulation in the ADB.

Cimmerian metamorphism and post Mid-Cimmerian exhumation in Central Iran: Insights from in-situ Rb/Sr and U/Pb dating

The pre-Alpine evolution of the Tethyan domains between Gondwana and Laurasia, and in particular that of the Cimmerian continental blocks, remains poorly constrained. Central Iran is a key area to constrain the closure of the Paleotethys and the collision of Laurasia with the Cimmerian blocks drifted from Gondwana. The present study provides a combined metamorphic and geochronologic approach focused on two areas of Central Iran: the Kashmar-Kerman Tectonic Zone (KKTZ) and the Jandaq area, whose tectonometamorphic units are affected low- to middle-pressure high-temperature metamorphism. We performed in-situ texturally constrained U/Pb dating on titanite and Rb/Sr dating on mica to quantify the timing and intensity of burial and exhumation of these metamorphic rocks. Results show that metamorphism in the central and eastern KKTZ (7–9 kbar; ∼700 °C) is synchronous or slightly postdates the Cimmerian orogeny (∼190-180 Ma) and relates to the collision following the Paleotethys closure, whereas metamorphism in the Jandaq complex (12–13 kbar; ∼450 °C) relates to the Paleotethys subduction. Based on paleogeographic reconstructions, the KKTZ lied hundreds of kilometers south of the Paleotethys suture zone. As such, we propose that metamorphism along the KKTZ results from the closure and shortening of a rheologically weak domain located outboard of the main suture. In-situ Rb/Sr dating of biotite yields precise and accurate cooling ages (±2-5 Ma) ranging from 170 to 140 Ma. These cooling ages document the exhumation of these terranes from the Mid-Cimmerian event onward (∼170 Ma), coeval with the widespread extension distributed across Iran and thought to reflect upper plate extension above the Neotethyan subduction system.

Diverse P‐T‐t Paths Reveal High‐Grade Metamorphosed Forearc Complexes in NW China

AbstractSubduction zones provide important constraints on reconstruction of tectonic configurations and convergent geodynamics. The timing and evolution of the subduction zones at the interaction between the Paleo‐Asian and Tethyan Oceans remain ambiguous, casting significant uncertainty on the reconstructions of proto‐Asia and subduction dynamics. Here, we report new petrologic and geochronologic data of a high‐grade metamorphic complex in the Dunhuang area, NW China, together with thermodynamic modeling, geothermobarometry, and second ion mass spectrometry U‐Pb chronology to reveal the complex metamorphic structure and history of the Paleozoic subduction‐exhumation channel at the intersection of the Paleo‐Asian and Tethyan domains. The subduction zone contains a diverse collection of eclogite, high‐pressure (HP) granulites, amphibolites, and metasedimentary rocks with a broad spectrum of P‐T‐t paths, which were buried and exhumed at different depths at ∼463–411 Ma. Our first dating of the oldest (∼463 Ma) HP granulite extends the orogenic period earlier to the Middle Ordovician. The uneven change in subduction gradients from ∼18°C/km to ∼10°C/km illustrates the thermal evolution of the subduction zone from infancy to maturity. A dramatic drop of the gradient at ∼420 Ma suggests a potential short‐term switch of the subduction dynamics from “hot” to “cool,” possibly due to plate geometry reorganization in response to slab roll‐back. Our data demonstrate that the Dunhuang Complex was chaotically mixed and juxtaposed at different levels in the subduction‐exhumation channel. The southward younging and increase in depth of the HP metamorphism indicate that the Dunhuang Complex was formed by north‐dipping subduction of the Proto‐Tethyan Ocean from the Early Paleozoic.

Morphology and paleobiology of the Late Cretaceous large-sized sharkCretodus crassidens(Dixon, 1850) (Neoselachii; Lamniformes)

AbstractThe definition of the Cretaceous shark genusCretodusSokolov, 1965 is primarily based on isolated teeth. This genus includes five species. Among these,Cretodus houghtonorumShimada and Everhart, 2019 is the only species based on a partially preserved skeleton. Here, the taxonomic attribution of a virtually complete skeleton ofCretodusfrom the Turonian of northeastern Italy is discussed, together with a few specimens from the Turonian of England. One of the latter is investigated through micropaleontological analysis to determine its stratigraphic position. The material is referred toCretodus crassidens(Dixon, 1850), the diagnosis of which is emended herein. The dentition is tentatively reconstructed, exhibiting strong similarities with congeneric species, although it differs in having strong vertical folds on the main cusp labial face, a mesiodistally broad tooth aspect, weak and well-spaced ‘costulae’ at crown base, and a different dental formula in the number of parasymphyseal and lateral rows. Some tooth malformations are interpreted as feeding-related or senile characters. The Italian specimen suggests thatCretodus crassidenshad a wide and laterally expanded mouth and head, a stout body, and attained a gigantic size.Cretodus crassidenswas a moderate-speed swimming shark ecologically like the extant tiger sharkGaleocerdo cuvier(Péron and Lesueur in Lesueur, 1822). The age estimate from vertebral-band counting suggests that the Italian individual was at least 23 years old and the growth model indicates a longevity of 64 years and a maximum attainable total length of 9–11 m.Cretodus crassidensoccurs both in Boreal and Tethyan domains, implying a broad paleobiogeographic distribution and a preference toward offshore settings.

The Proto- and Palaeo-Tethys tectonic evolution in Southeastern Tibetan Plateau: Constraints from detrital zircon dating of metasedimentary rocks from the Diancang Shan complex

ABSTRACT Metamorphic rocks from the Diancang Shan (DCS) complex along the Ailao Shan-Red River belt between the South China plate and Simao-Indochina block are studied in this contribution to constrain the Proto- to Palaeo-Tethys tectonic evolution of the eastern Tethys domain. LA-ICP-MS zircon U-Pb geochronological dating is conducted in this study on the metasedimentary rocks (garnet-biotite-plagioclase gneisses, biotite-quartz schists and phyllonites) from different stratigraphical horizons (Proterozoic and Triassic) of the DCS complex. The analyses yielded three major age peaks at ca. 248 Ma, ca. 441 Ma, ca. 1000–900 Ma and one subordinate age peak at ca. 828 Ma. The youngest ages for the samples help to constrain the maximum ages of deposition of the complex at Early Carboniferous and Late Triassic, respectively. The existence of the diagnostic age peak at ca. 440 Ma and the euhedral-subhedral morphology of the detrital zircons in the Palaeozoic and Mesozoic strata may indicate that there were early Palaeozoic magmatic activities along the eastern margin of the Simao-Indochina block. At the meantime, the age peak at ca. 440 Ma was never reported in the early Palaeozoic strata from the western margin of the South China plate, which supports the existence of an early Palaeozoic rift zone, i.e., the Proto-Tethys Jinsha Jiang-Ailao Shan-Song Ma rift zone, being consistent with geochemical discriminations. Furthermore, we conclude, from the significant difference between detrital zircon age data of Silurian to Devonian sedimentary rocks from the Simao-Indochina block and South China plate, the opening of the Palaeo-Tethys ocean since Early Carboniferous, the absence of evidence for the Palaeozoic orogeny, and the successive sedimentation from the Cambrian to Triassic along the western margin of the South China plate, that the Proto-Tethys rifting and subsequent Palaeo-Tethys ocean evolution along the Jinsha Jiang-Ailao Shan-Song Ma zone formed actually a complete ‘Wilson Cycle’ from early Palaeozoic to the Late Triassic.

Granitic Magmatism in Eastern Tethys Domain (Western China) and their Geodynamic Implications

AbstractWestern China locates in the eastern section of the Tethys domain, granitic rocks in this region with variable formation ages and geochemistry record key information about the crust‐mantle structure and thermal evolution during the convergent process of Tethys. In this study, we focus on some crucial granitic magmatism in the western Yangtze, Qinling orogen, and western Sanjiang tectonic belt, where magma sequence in the convergent orogenic belt can provide important information about the crust‐mantle structure, thermal condition and melting regime that related to the evolution processes from Pre‐ to Neo‐Tethys. At first, we show some features of Pre‐Tethyan magmatism, such as Neoproterozoic magmatism (ca. 870–740 Ma) in the western margin of the Yangtze Block were induced by the assembly and breakup of the Rodinia supercontinent. The complication of voluminous Neoproterozoic igneous rocks indicated that the western Yangtze Block underwent the thermodynamic evolution from hot mantle‐cold crust stage (ca. 870–850 Ma) to hot mantle and crust stage (ca. 850–740 Ma). The Neoproterozoic mantle sources beneath the western Yangtze Block were progressively metasomatized by subduction‐related compositions from slab fluids (initial at ca. 870 Ma), sediment melts (initial at ca. 850 Ma), to oceanic slab melts (initial at ca. 825–820 Ma) during the persistent subduction process. Secondly, the early Paleozoic magmatism can be well related to three distinctive stages (variable interaction of mantle‐crust to crustal melting to variable sources) from an Andeans‐type continental margin to collision to extension in response to the evolution of Proto‐Tethys and final assembly of Gondwana continent. Thirdly, the Paleo‐Tethys magmatism, Triassic granites in the Qinling orogenic display identical formation ages and Lu‐Hf isotopic compositions with the related mafic enclaves, indicate a coeval melting event of lower continental crust and mantle lithosphere in the Triassic convergent process and a continued hot mantle and crust thermal condition through the interaction of subducted continental crust and upwelling asthenosphere. Finally, the Meso‐ and Neo‐Tethyan magmatism: Early Cretaceous magmatism in the Tengchong Block are well responding to the subduction and closure of Bangong‐Nujiang Meso‐Tethys, recycled sediments metasomatized mantle by subduction since 130 Ma and subsequently upwelling asthenosphere since ca. 122 Ma that causes melting of heterogeneous continental crust until the final convergence, this process well recorded the changing thermal condition from hot mantle‐cold crust to hot mantle and crust; The Late Cretaceous to Early Cenozoic magmatism well recorded the processes from Neo‐Tethyan ocean slab flat subduction, steep subduction, to initial collision of India‐Asia, it resulted in a series of continental arc magmatism with enriched mantle to crustal materials at Late Cretaceous, increasing depleted and/or juvenile materials at the beginning of early Cenozoic, and increasing evolved crustal materials in the final stage, implying a continued hot mantle and crust condition during that time. Then we can better understand the magmatic processes and variable melting from the mantle to crust during the evolution of Tethys, from Pre‐, Paleo‐, Meso‐, to Neo‐, both they show notably intensive interaction of crust‐mantle and extensive melting of the heterogeneous continent during the final closure of Tethys and convergence of blocks, and thermal perturbation by a dynamic process in the depth could be the first mechanism to control the thermal condition of mantle and crust and associated composition of magmatism.

Stratification and productivity in the Western Tethys (NW Algeria) during early Toarcian

Profound environmental changes punctuated the Early Jurassic period, as recorded by marked carbon and oxygen isotope anomalies and major biotic crises. The response of low-latitude regions of Northern Gondwana to such intense changes is not documented as well as that of other Tethys areas. We present new calcareous nannofossil assemblages from three sections located in NW Algeria, in the Sahara and Tlemcen Basins, respectively. New stable carbon and nitrogen isotope data are provided from the Tlemcen Basin to reconstruct local environmental conditions in the wider context of a Toarcian greenhouse climate. We first established a solid chemo- and biostratigraphic framework by integrating stable carbon isotope data and calcareous nannofossil events. Calcareous nannofossil assemblages show common trends in the two basins, such as the occurrence in high proportions of the deep-dweller species Mitrolithus jansae , likely indicating stratification of the water column with a deep nutricline. This taxon dominated the assemblage during the negative carbon isotope excursion (CIE) interval, often used to delineate the base of the Toarcian anoxic event (T-OAE). Such a nannofossil record is unique in the Western Tethys domain, as M. jansae is known to drastically decrease in abundance during the T-OAE until its disappearance in the aftermath of the event. The NW Algeria nannofossil record indicates prolonged thermal stratification of water-masses, finally triggering hyper-oligotrophy and low productivity in shallow waters during the Toarcian CIE. Such peculiar conditions are likely related to the combined effects of a warm and arid climate dominating along the northern Gondwana margin and the presence of a strong clockwise gyre over the epicontinental shelf, which brought warm equatorial waters from the Tethys Ocean to the NW Algeria shelf. • The NW Algeria nannofossil record suggests prolonged thermal stratification of water-masses. • Hyper-oligotrophy and low productivity in shallow-waters occurred during the Toarcian Event. • Such conditions are likely related to the effects of a warm and arid climate of the Northern Gondwana.

The Eocene carbonate platform of the central-western Malaguides (Internal Betic Zone, S Spain) and its meaning for the Cenozoic paleogeography of the westermost Tethys

The Eocene Peñicas (Almería) and Harania (Málaga) stratigraphic sections from the Malaguide Complex (Betic Cordillera, South Spain) belonging to the Mesomediterranean Microplate from the westernmost Tethys (about-35°N and 0° to 5°E according to the Eocene coordinates) have been studied. The Eocene sections cover the Cuisian to middle Lutetian deposits, which show several lithofacies representing shallow marine platform realms. Based on the fossiliferous assemblage, texture and fabrics, eight microfacies related to inner to outer ramp settings were defined. In the inner ramp of the Harania section abundant colonial corals have been recognized. The Eocene deposits are arranged into a transgressive succession composed by three minor transgressive-regressive sedimentary cycles. The Eocene fossiliferous assemblage shows a mixture of photozoan (Larger Bentic Foraminifera –LBF–, green and red calcareous algae and corals) and heterotrophic (mollusks, echinoids, bryozoans, small benthic and planktic foraminifers) elements, suggesting euphotic to mesophotic conditions in oligo-mesotrophic marine warm-waters at low-middle latitudes. This assemblage indicates a transition from photozoan to heterozoan carbonates and in particular a shift towards outer marine ramp settings. During the Early Eocene, the widespread distribution of LBF leads in the Tethyan domains to disappearance or extreme reduction of coral constructions. Nevertheless, abundant corals associated to inner ramp realms have been observed in the Harania stratigraphic section indicating that corals could continue to develop in the westernmost Tethys at the transition to the Atlantic Ocean, in contrast with respect to other Tethyan sectors. Therefore, the Ypresian-Lutetian time-span is a transitional period for the global temperature during which corals locally survived only where optimal ecologic conditions occurred, preferably in marginal contexts, as it seems to have happened in the studied area. • Westernmost Tethys (about-30° N and 0° to 5°E according to the Eocene coordinates) • Cuisian to Middle Lutetian deposits • Shallow marine platform realms • Photozoan elements (LBF, green and red calcareous algae and corals) • Abundant corals associated to inner ramp realms

The Anisian continental-marine transition in Sardinia (Italy): state of the art, new palynological data and regional chronostratigraphic correlation

The scarce evidence of paleontological records between the upper Permian and the Anisian (Middle Triassic) of Western Europe could reflect (1) large stratigraphic gaps in the continental successions and/or (2) the persistence of disturbed conditions after the Permian–Triassic Boundary extinction event and the succession of ecological crises that occurred during the Early Triassic. In this context, the study of palynological associations, integrated with the stratigraphical and sedimentological data, plays a key role in dating and correlating the successions of the Western European domain and improves our understanding of environmental and paleoclimatic conditions. In some cases, pre-Anisian paleontological evidence is lacking, as in Sardinia (Italy), where a long gap encompasses the middle Permian (pars) to late Lower Triassic successions. Although fragmented and disseminated, the continental Lower-Middle Triassic sedimentary successions (Buntsandstein) of Sardinia have proved crucial to our understanding of the evolution of the southern edge of the Paleo-Europe and the different timings of the Tethys transgression (Muschelkalk facies) in some of these areas. Various paleogeographic reconstructions were attempted in previous works, without providing any consensus on the precise position of Sardinia and its surrounding seaways in the Western Tethys domain during this time interval. At present, the configuration and distribution of the subsiding and emerging landmasses and the temporal development of the transgressions of the Western Tethys during the Middle Triassic remain unclear. This work focuses on the stratigraphical, sedimentological and palynological aspects of three Middle Triassic continental-marine sedimentary successions in Sardinia, with particular attention to the analysis of the palynological associations sampled there, and it also provides a detailed review of all previous palynological publications on the Sardinian Anisian. The studied successions are: Su Passu Malu section (Campumari, SW Sardinia), Arcu is Fronestas section and Escalaplano section (Escalaplano, Central Sardinia). These sections were also correlated to other significant sections in the SW (Scivu Is Arenas) and NW (Nurra) parts of the island.

First record of fossil fish (Enchodontoidei, Actinopterygii) in the Struganik quarry in Western Serbia

This paper presents the first Upper Cretaceous remains of fish in Serbia, discovered near the village of Struganik. This is also the first described find of Mesozoic fish in Serbia. A stone slab with visible contours of an almost complete fish, with a total body length of about 20 cm, was excavated from the Struganik quarry. Most bones are preserved as imprints. The number of vertebrae, the shape and position of the cranial bones, the type of teeth, and the position of the first dorsal fin all indicate that the studied specimen belongs to the genus Enchodus known from several Upper Cretaceous localities in the Tethys domain.

Faunal composition and paleoenvironmental reconstruction of a Middle–Late Triassic boundary assemblage in the Pyrenean basin (Catalonia, NE Spain)

AbstractThe Ladinian–Carnian transition in the Tethys domain was accompanied by an important environmental change representing a milestone in the climate evolution of the Triassic. However, estimations on paleodiversity composition and paleoenvironmental conditions across this interval are scarce in marine settings due to the lack of fossil-bearing successions. In this work, a refined paleontological and sedimentological study has allowed us to better characterize a well-preserved marine ?Ladinian–Carnian carbonate succession in the South Central Pyrenees (Odèn site, Catalonia, NE Spain). Vertebrate faunas include numerous actinopterygian specimens, forming an assemblage composed of at least four taxa: Peltopleurus cf. P. nuptialis Lombardo, 1999, Saurichthys sp., Colobodus giganteus (Beltan, 1972), and an indeterminate halecomorph. Specimens belonging to the genus Peltopleurus are dominant; the long-snouted Saurichthys, the halecomorph, and the large-bodied Colobodus giganteus are less abundant. Tetrapod remains are scarcely present and are assigned to sauropterygians. Invertebrate faunas include bivalves (Pseudocorbula gregaria [Münster in Goldfuss, 1838]) and brachiopods (Lingula sp.). The fossil assemblage was recovered from organic-rich laminated silty mudstone layers. Sedimentological and textural analyses suggest that fossil biotas were deposited below the fair-weather wave base in shallow subtidal coastal settings. These environments were sporadically sourced by silt/clay. The age of the Odèn site, on the basis of the recovered fauna, is assigned to the ?late Ladinian–middle Carnian (Middle–Late Triassic), which is in agreement with previously published ages based on palynomorph data.The refined integration of paleontological, sedimentological, and biostratigraphic data from the Odèn site and other vertebrate-bearing localities in the Tethys domain can help better constrain the paleoenvironmental conditions and paleogeographical configuration impacting ecosystem diversity during the late Ladinian–Carnian interval.

Tectonic evolution and multi–episodic metallogenesis of the Sanjiang Paleo-Tethys multi-arc-basin-terrane system, SW Tibetan Plateau

The Sanjiang Tethys region in SW China lies in the tectonic junction of the Tethys domain, and represents a key precious/base metal province in China. Based on a compilation of studies from the past decades on the formation, evolution, and metallogenesis of the tectonic units in the region, we proposed a multi-arc-basin-terrane (MABT) structural framework for the Paleo-Tethys Sanjiang region. Convergence between South China and Indochina-Pu'er blocks had led to the accretion of many island arcs and micro-continental terranes, which is different from the traditionally direct convergence between two continents. Such prolonged terrane accretion process likely formed the various metallogenetic belts that contain diverse deposit types and mineral assemblages. In this contribution, we divided the Sanjiang region into ten metallogenetic belts, according to their characteristic lithologic assemblages, structures, and interpreted tectonic settings . Subsequently, we discussed the regional tectonic-metallogenic evolution of these ten ore belts and propose their metallogenetic models. This study reveals a genetic link between the MABT system and the regional metallogenesis, which is important for future mineral exploration in this region.

The Plenus Cold Event Record in the Abyssal DSDP Site 367 (Cape Verde, Central Atlantic): Environmental Perturbations and Impacts on the Nitrogen Cycle

The Oceanic Anoxic Event 2, at the Cenomanian-Turonian boundary (∼93.9 Ma), was an episode of widespread burial of organic matter in marine sediments, underlined by a positive carbon-isotope (δ13C) excursion observed worldwide. Within this episode of O2-depleted conditions, a short interval of cooling, termed as the Plenus Cold Event, has been recorded in many sites and sections in the northern hemisphere (Tethyan domain, Western Interior Seaway, proto-North Atlantic Ocean). But, its record and its impact on the biogeochemical cycles of carbon and nitrogen in the southern part of Central Atlantic Ocean has not been explored yet. Here, we present a detailed geochemical study of the Deep Sea Drilling Project site 367 (Cape Verde) based on a compilation of previous and new data of carbon and nitrogen isotope signals as well as trace element concentrations. The aim of this study is to better constrain the evolution of oxygenation in the water column and the associated changes in nitrogen cycle before and during the Oceanic Anoxic Event 2 in order to understand the paleoceanographic and environmental consequences of the Plenus Cold Event at one of the deepest site of the Central Atlantic Ocean. Our new dataset improves the resolution of the δ13C curve for this site, and we propose a new chemo-stratigraphic frame of the carbon excursion allowing for a better identification of the short-term negative carbon isotope excursion associated to the Plenus Cold Event. The detailed evolution of redox-sensitive proxies (Mo, U, V, Fe, Cu, Ni enrichments and Corg/Ptotal) and isotopic signals (δ13Corg and δ15Ntotal) evidence that this deep site was impacted by this cooling event. While anoxic conditions prevailed in bottom waters before and during the onset of the Oceanic Anoxic Event 2 characterized by euxinic NH4+-rich water column, this cooling event was accompanied by reoxygenation of the water column, which had affected the behavior of the redox-sensitive elements and caused changes in nitrogen biogeochemical cycling.

Exceptionally preserved calcified sponge assemblagesin Upper Jurassic carbonates of the eastern Getic Carbonate Platform (Southern Carpathians, Romania)

A rich poriferan assemblage was identified within the easternmost part of the Getic Carbonate Platform of Romania (Grădiștei Gorges). The excellent preservation state of most poriferans here led to the discovery of a new species (Neuropora gigantea Pleș & Schlagintweit, n. sp.) and to the identification of previously unknown diagnostic features in some species (Sarsteinia babai Schlagintweit & Gawlick, 2006 emend., Neuropora lusitanica Termier, 1985, Sphaeractinia steinmanni Canavari, 1893). Calciagglutispongia yabei Reitner, 1992, Sarsteinia babai and Sphaeractinia steinmanni are reported for the first time from the Upper Jurassic carbonates of the Getic Carbonate Platform. The sedimentary input fluctuations and the nutrient competition had an important role in understanding the morphological adaptations of the analysed species. The existing palaeoecological and palaeoenvironmental conditions generated different distribution patterns towards the reef profile and also preferential adaptations to a specific Tethyan domain. As opposed to the poriferan assemblages from the northern Tethyan shelves, these organisms formed sponge-coral-microencruster boundstones at the margins and fore-reefal zones of isolated carbonate platforms within the intra-Tethyan realm. The importance of calcified sponges in reef-zonation is highlighted by the establishment of a general zonation model. Three zones can be distinguished: 1) Cladocoropsis-Milleporidium zone (back-reef area); 2) Bauneia-Chaetetopsis-Parastromatopora zone (central reef area); and 3) Sphaeractinia/Ellipsactinia-Neuropora zone for the fore-reef area. In the absence of a true reef framework these calcified sponges developed typical morphologies, environmental adaptations and partnerships with other biotic groups which strongly influenced the carbonate production throughout the intra-Tethyan domain.

Characterization of Cenomanian-Turonian oxic facies in Tunisia: sequence stratigraphy and correlation of recorded bioevents

On the southwestern Tethyan Margin of Tunisia, the well-known anoxic black shale facies of the Cenomanian-Turonian transition contrasts with oxic fossiliferous carbonates, first characterized here as lateral equivalents. In terms of sequence stratigraphy, the analysis of four wisely sampled sections in Central and Southern Tunisia led to interpret these deposits as a transgressive interval (TST). This interval spans the Whiteinella archaeocretacea Zone of foraminifera and is capped with a glauconite-rich highly bioturbated maximum flooding surface (MFS). In the reference section of Oued Bahloul and the Kalaat Senan area of North-Central Tunisia, these deposits overlay a Shelf Margin Wedge made of conglomeratic and bioclastic limestones. In South-Central and Southern Tunisia, the TST is characterized by the onset of oxic facies relaying laminated carbonates with local emergence surfaces. The analysis of both oxic and anoxic facies from the Cenomanian-Turonian transition allows identifying five successive bioevent markers, known elsewhere within the Tethyan domain: the extinction of the foraminifera genus Rotalipora (or Thomasinella), the Heterohelix shift, the Whiteinella proliferation, the filament event, and the appearance of Helvetotruncana helvetica. Among these bioevents, the Heterohelix shift coincides with the transgressive surface, while the filament event announces the maximal flooding surface. These Cenomanian-Turonian transition bioevents are of a particular relevance for regional and long-distance high-resolution correlations.

Eocene to Oligocene nannofossils stratigraphy and environmental conditions in Izeh Province, Zagros Basin, East Tethys

Data obtained from the calcareous nannofossils, distributed in the upper part of the Pabdeh Formation (Priabonian–Rupelian) and the lower part of the Asmari Formation (Chattian) in the Bid-Zard section, were used to investigate the Eocene to Oligocene palaeoenvironmental conditions in the southwest of Izeh, southwestern Iran (eastern Tethys). The upper part of the Pabdeh Formation was composed of shale, thin-bedded pelagic limestone and dolostone, which is disconformably overlain by the Asmari Formation. For the first time, 29 species of calcareous nannofossils belonging to 13 genera were identified in the studied section. The calcareous nannofossils in the upper part of the Pabdeh Formation indicate the Isthmolithus recurvus Zone/Sphenolithus pseudoradians Zone (combined zone), Ericsonia subdisticha Zone, Helicosphaera reticulata Zone and Sphenolithus praedistentus Zone, from the Priabonian to the Rupelian. The Sphenolithus ciperoensis Zone of the Chattian was identified in the lower part of the Asmari Formation. Calcareous nannofossil stratigraphy across the upper Eocene–Oligocene interval also reveals a disconformity at the Rupelian/Chattian transition due to a bio-event. Shallowing of the basin and environmental changes in this part of the Tethyan domain could have led to the lithostratigraphic and biostratigraphic changes. In fact, during the late Eocene to late Oligocene, marine phytoplankton was sensitive to climate changes such as decreasing temperature, as well as possibly to a nutrient increase and changes in basin depth.

Nannoplankton and 13C and 13O stable isotope stratigraphy record of the mid Cretaceous sequences, Zagros Basin (western Iran)

Deposition of black shales and dark argillaceous limestones across the Cenomanian to Turonian interval has been recorded in many parts of the world. In this regard, a stratigraphic section in the Iran's hydrocarbon field in the Kermanshah region in the Zagros Basin has been studied in detail to reconstruct palaeoceanographic conditions under a reliable biostratigraphic framework. Biostratigraphy based on calcareous nannofossils integrated with high resolution carbonate and oxygen stable isotope analyses were carried out on the Cenomanian-early Turonian interval of the upper part of Garau Formation. In this formation, 24 species of calcareous nannofossils were identified in the pelagic marine deposits. Our study allowed the definition of nannoplankton bio zones from the upper part of Eiffellithus turriseiffelii Zone to the lower part of Quadrum gartneri Zone in the mid Cretaceous. This research first recorded the upper part of the Garau Formation at site and it is consistent with the previous bio zones identified in the Tethyan domain in the region. The middle Cretaceous events of calcareous nannofossils proposed here correlate with the isotope global profile for the early Cenomanian-earliest Turonian interval and with those, reported for the southeastern France and south England reference curves, represented by the positive Cenomanian to Turonian δ13C excursion. Thus, the sequences of dark argillaceous limestone rich in organic matter in Kermanshah region can be considered as a continuation of the global trend in the Tethyan domain, where the Cenomanian-Turonian Oceanic Anoxic Event constrained to about 91.5 ± 8.6 millions of years, occurred in an anoxic pelagic sedimentary environment correlates with both, global and local sea-level rises, represented in this study by the characterization of the nannoflora assemblage reflected in a variety of widespread paleoenvironmental changes that coincides with significant shifts in the stable carbon and oxygen isotope signature.

Middle Jurassic evolution of a northern Tethyan carbonate ramp (Alborz Mountains, Iran)

Here, we provide a detailed facies and depositional record from a NE-SW-directed, 250-km-long transect across a distally steepened, Middle Jurassic carbonate ramp in the northern Tethyan realm (Iran). Among the six main facies types described, two stand out because of their beyond-regional significance: (i) Middle Callovian microbial and microbial-skeletal mounds embedded in muddy intermound sediment and (ii) Upper Callovian conglomeratic debris-flow deposits truncating the mound unit. The mound features described here did not evolve into reefal structures and evidence for a framestone structure is lacking. They occur as low-relief, mud-dominated domical structures (a few metres wide). The development of the Middle Callovian mounds is perhaps best linked to a period of minimum sedimentation rates and sufficient accommodation space resulting from a long-term gradual sea-level rise commencing in the Late Bajocian. With respect to the Upper Callovian conglomeratic deposits overlying the mound interval, the absence of sedimentary structures such as grading, the nature of the sub-angular or rounded clasts and the very poor sorting are indicative of a catastrophic debris flow origin. Based on data compiled here, the conglomeratic deposits likely formed due to relative sea-level fall inducing the reworking of mound facies by the lowered wave base and currents, and basinward transport of reworked material to the distal outer ramp. Our findings are compared with coeval deposits from the western Tethyan domain and placed into a process-oriented context. The described northern Tethyan Late Bajocian to Middle Callovian deepening-upward trend, followed by relative sea-level fall in the Late Callovian near the Middle-Late Jurassic transition, is in agreement with observations from other coeval Tethyan basins/platforms. Data shown here have wider relevance for workers concerned with the Jurassic evolution of the Tethyan Ocean in general and shed light on the intricate relation of changes in accommodation space and ramp architecture.

New insights on the age of the Mengyejing Formation in the Simao Basin, SE Tethyan domain and its geological implications

Knowledge on the origin and mechanism of the large potash formation in the southeast Tethyan tectonic domain are still under debate, one of which mainly due to the controversial ages of the potash-bearing strata. Here we present a detailed detrital zircon U-Pb geochronologic-magnetostratigraphic study of the potash-bearing Mengyejing (MYJ) Formation (Fm) from the Simao Basin. 948 paleomagnetic cores and 4 detrital zircon U-Pb samples were collected from a 932-m thick Jiangcheng section. Thermal demagnetization isolated 857 primary characteristic remnant magnetization (ChRM) directions, indicated by positive reversals and fold tests and petrologic examinations. Seven normal and seven reversed polarity zones were identified and correlated well with chrons C27r to C34n of the geomagnetic polarity timescale (GPTS2012), yielding the first known age sequence of >112 to ∼63 Ma for the MYJ Fm. The ages for the potash bearing strata in the Simao commenced ∼20 Ma earlier than those in the adjacent Khorat basins, opposite to the traditional viewpoint that the former would rather correspond to the middle and lower parts of the latter. Given the paleogeographic reconstruction of likely a pan-Simao-Khorat basin during the Cretaceous, ∼85 Ma would be another important potential period for future potash exploration in the Simao Basin.

Evolution of magma oxidation states and volatile components in the Cenozoic porphyry ore systems in the western Turkey, Tethyan domain: Constraints from the compositions of zircon and apatite

特提斯成矿域中段的土耳其西部集中产出了与俯冲、碰撞-后碰撞、伸展动力学背景有关的斑岩型铜、钼、金矿床。前人已完成了针对这些斑岩型矿床构造背景的大量研究工作，但对于区内不同构造背景下斑岩型矿床的成矿岩浆源区性质、成矿元素-挥发分含量和成矿物质演化关系尚未有系统研究。而这些研究将对认识中特提斯构造域晚白垩世以来在新特提斯洋俯冲、欧亚板块-Tauride-Anatolide板块碰撞和伸展过程中斑岩矿床形成时地壳厚度、壳幔相互作用方式及成矿物质演化过程具有重要意义。本研究选择土耳其西段三个斑岩成矿带（Tavsanli带、Biga半岛成矿带和Afyon-Konya带）内五个斑岩型矿床的成矿岩体与同期侵入岩-火山岩，开展锆石微量元素和磷灰石主量元素研究，限定碰撞与伸展环境下斑岩型矿床成矿岩浆的形成温度、氧逸度条件及其与岩浆形成时地壳厚度的关系，利用磷灰石F-Cl-S含量组成揭示熔体挥发分和硫元素的物质组成，进而约束新特提斯洋俯冲-碰撞-伸展过程中斑岩系统的深部物质演化规律。研究结果表明，土耳其西部新生代斑岩型矿床成矿岩浆锆石大部分落于高水含量-高氧逸度区间，具有相似的稀土元素标准化配分曲线。从始新世到中新世，锆石氧逸度Ce4+/Ce3+比值呈现出先降低（斑岩型Cu-Mo矿到斑岩型Mo矿）后升高（斑岩型Mo-Cu矿到斑岩Au矿）的趋势，且相对于斑岩型Mo矿和Mo-Cu矿，斑岩型Au矿和Cu-Mo矿成矿岩体的锆石形成时具有相对较高的氧逸度。绝大部分斑岩型矿床成矿岩体的锆石EuN/EuN*位于0.4~0.7之间，但斑岩型Mo矿和斑岩型Mo-Cu矿床的锆石具有相对较低的EuN/EuN*比值，可能是由于在结晶时熔体受斜长石结晶影响较大。锆石微量元素显示（Yb/Gd和Hf/Y-Th/U）锆石组成大部分受岩浆房中角闪石±榍石±磷灰石分离结晶控制。根据锆石Ti温度计估算土耳其西部斑岩型矿床成矿岩体及其相关岩体的形成温度在650~900℃之间，结晶温度从斑岩型Au矿、斑岩型Cu-Mo/Mo-Cu矿至斑岩型Mo矿呈现递减趋势。对于熔体的挥发分与硫含量组成，始新世-渐新世斑岩型Cu-Mo与Mo矿床成矿岩浆相对具有高F和低Cl组成，中新世伸展环境形成的斑岩型Mo-Cu矿和斑岩型Au矿床成矿岩浆Cl含量普遍较高。与成矿岩体同期的暗色包体或基性岩脉中磷灰石计算获得的熔体硫含量均大于侵入体对应熔体的硫含量，且具有不均一的含量组成，表明基性岩浆注入可能为岩浆房提供硫。结合区域动力学和地壳厚度估算，本文认为触发土耳其西部新生代斑岩矿床形成的动力学机制是：在新特提斯洋向北单向汇聚的背景下，北部始新世-渐新世斑岩矿床受控于碰撞后俯冲的新特提斯洋板片（Vardar洋）后撤-回转-断离过程；南部中新世斑岩矿床的形成则受控于爱琴海板片俯冲控制的地壳伸展-减薄过程。北侧Izmir-Ankara-Erzincan缝合带附近的Tavsanli与Biga半岛斑岩成矿带始新世-渐新世斑岩型矿床的形成与熔融-同化-储存-均一过程（MASH）有关，深部地壳热区过程（DCHZ）与中新世Afyon-Konya带斑岩型矿床的形成有关。