Eastern Tethys Research Articles

Paleoclimate and sea level response to orbital forcing in the Middle Triassic of the eastern Tethys

The Middle Triassic is thought to have had a greenhouse paleoclimate with a few short humid phases. However, the timing of these humid events, and the extent to which orbital forcing influenced the evolution of climate, are unclear. Here, a cyclostratigraphic analysis has been carried out based on the integrated study of magnetic susceptibility, elemental chemistry and lithofacies from two shallow-marine carbonate platform sections in Guizhou, South China. Combined, these sections (Pohong and Yongyue) span the late Anisian to early Carnian. Spectral analyses of magnetic susceptibility, Fe/Al and P through the studied sections show significant cycles of ~85-m, ~7-m and ~ 4-m. Based on independent age constraints and sedimentation rate modelling, these cycles are interpreted as orbital cycles that reflect 405-kyr long-eccentricity, ~33-kyr obliquity, and ~ 20-kyr precession forcing, respectively. Tuning of the records to the stable 405-kyr long-eccentricity parameter in each section yields a tuned astronomical time scale spanning ~7.4 ± 0.2 Myr, which covers from ca. 244.4 to 237.0 Ma and includes the entire Ladinian Stage. Magnetic susceptibility and Fe/Al data from the studied sections show intervals with relatively high values in the middle-late Anisian (ca. 244.0 to 242.6 Ma), and the latest Anisian to early Ladinian (ca. 241.8 to 240.9 Ma). These geochemical changes, combined with lithological changes, indicate enhanced terrigenous flux caused by the acceleration of hydrological circulation under a warmer and more humid climate. In addition, P data records two sharp falls that appear broadly coeval with the previously postulated late Ladinian ecological crisis. Our new astrochronology also reveals that ~1.2-Myr obliquity amplitude modulation cycles are expressed in the Middle Triassic. The regional sea level changes inferred from sequence stratigraphy and sedimentary noise modelling can be correlated with Tethyan and global sea level change. This work demonstrates the utility and power of sedimentary noise modelling in shallow marine environments for inferring past sea level dynamics. It also furthers constrains the timing of putative Middle Triassic climatic and ecological events.

Paleoclimate evolution and aridification mechanism of the eastern Tethys during the Callovian–Oxfordian: evidence from geochemical records of the Qiangtang Basin, Tibetan Plateau

Paleoclimate evolution and aridification mechanism of the eastern Tethys during the Callovian–Oxfordian: evidence from geochemical records of the Qiangtang Basin, Tibetan Plateau

Palynostratigraphy of the Upper Jurassic to Lower Cretaceous strata, Upper Indus Basin, Pakistan: implication for Jurassic/Cretaceous boundary and paleoclimate in the Eastern Tethys

This paper investigates the much-debated Jurassic/Cretaceous (J/K) boundary as well as the Early Cretaceous climate using palynomorphs of the Chichali Formation, Upper Indus Basin, North Pakistan. Based on the palynostratigraphy, two dinoflagellates and one spore/pollen assemblage are recorded, suggesting a Kimmeridgian to Valanginian age for the sediments of the Chichali Formation. The palynostratigraphic results further suggest that the Tithonian to Berriasian strata are truncated along the J/K boundary. The warm and humid conditions are supported by the consistent dominance of ferns corresponding to the Schizaeaceae and the intermittent appearance of herbs from Gleicheniaceae. Such climatic conditions are further supported by the consistent presence of evergreen trees with a broad leave of Cyatheaceae and Matoniaceae. The warm and humid conditions are also supported by conifers of the Araucariaceae in association with Cycadaceae. Such conditions during the Valanginian are further supported by the switch from the Bajocian–Oxfordian shallow carbonates of the Samana Suk Formation to the Kimmeridgian–Valanginain clastics of the Chichali Formation. Hence, the expansion of warm and humid tropical flora to the middle latitude (∼40°S) during the Valanginain hints strongly for global warming instead of previously suggested global cooling. KEY POINTS: Palynostratigraphic investigation shows Kimmeridgian to Valanginian age for the Chichali Formation, Upper Indus Basin, Pakistan. The J/K boundary is marked by an unconformity along which the Tithonian to Berriasian time record is missing. The reconstruction of paleovegatation indicates warm humid climate during the Valanginian instead of previously reported global cooling.

Geology and geochemistry-based metallogenic exploration model for the eastern Tethys Himalayan metallogenic belt, Tibet

The Tethyan Himalaya is the fourth metallogenic belt discovered to date within the Tibetan Plateau and contains chromite, gold and Sb–polymetallic mineralization. The belt records a series of complex tectonic–magmatic events that include the break-up, subduction, collision, detachment, and obduction of the Eastern Gondwana continent, all of which generated ideal conditions for ore formation. However, this area remains under-explored, with only limited knowledge of the deposit types present in this area and their relationship to tectonic and magmatic events. This has hampered mineral exploration in the region. This study uses previous research and mineral exploration in this region, combined with knowledge of mineralization in adjacent regions, to suggest the presence of three main deposit types (ophiolitic chromite, orogenic Au, and hydrothermal vein Sb–polymetallic deposits), and highlights the potential for this area to host as yet undiscovered island arc-type porphyry Cu–Au and leucogranite-related Sn–(Be) mineralization. This study summaries the relationship between the tectonic evolution and magmatism within the region and the mineralization, establishing a temporal and spatial framework for mineralization within the eastern Tethys Himalayan metallogenic belt.Improved knowledge of the geochemical signatures of mineralization, obtained using compositional data analysis (CoDA) combined with geological information, enabled the identification of nine compositional balances, including the presence of sedimentary units, accretionary wedge structures, leucogranites, mafic–ultramafic rocks, chromite mineralization, Au mineralization, and Sb–polymetallic mineralization. This study establishes a predictive mineral exploration model for the eastern Tethys Himalayan metallogenic belt and combines this model with geological and geochemical data to identify areas for future exploration. These targets include a 50-km-long ophiolitic belt in the Nedong area that is highly prospective for chromite mineralization; a positive Au–Cu–Mo geochemical anomaly in the Qonggyai–Qusum area that is prospective for orogenic Au mineralization; and positive Au–Cu–Mo geochemical anomalies in the Nianzha, Sangri, and Gyaca areas that are prospective for exploration for Xiongcun-type island arc-associated porphyry Cu–Au mineralization, as well as deep-seated extensions to known Sb–polymetallic mineralization and the inner and outer contacts of the Lhozhag and Cuonadong leucogranite, all of which are prospective for exploration for Sn–(Be) mineralization.

Evolution of the upper Paleocene-lower Eocene larger benthic foraminifera in the Eastern Tethys, Hormak area, north of Zahedan

Evolution of the upper Paleocene-lower Eocene larger benthic foraminifera in the Eastern Tethys, Hormak area, north of Zahedan

Decoupled δ13Ccarb and δ13Corg records at Triassic–Jurassic boundary interval in eastern Tethys: Environmental implications for spatially different global response

Although δ13C data (either δ13Ccarb or δ13Corg) of many Triassic–Jurassic (T-J) sections have been acquired, paired δ13Ccarb and δ13Corg from continuous T-J carbonate sections, especially in eastern Tethys, have been scarcely reported. This study presents paired and decoupled δ13Ccarb and δ13Corg data from a continuous T-J carbonate section in Wadi Naqab. The T-J Wadi Naqab carbonate section, located in United Arab Emirates, Middle East, represents tropical and shallow marine sedimentation in eastern Tethys. At the T-J boundary interval, an initial carbon isotope excursion (CIE) is observed with different magnitude of isotope excursion and timing in δ13Ccarb and δ13Corg, while subsequently a positive CIE is only distinct in δ13Ccarb. Based on petrological, carbon isotope, Rock-Eval and elemental analyses, the δ13Ccarb is thought to record marine inorganic carbon, and the δ13Corg to record terrigenous organic carbon. Therefore, the paired δ13Ccarb and δ13Corg herein potentially document simultaneous changes in T-J atmospheric and marine settings of eastern Tethys. Their decoupled behavior may likely be caused by different changes or evolution of carbon pool between marine and atmospheric settings. The initial CIE present in both δ13Ccarb and δ13Corg may indicate influence of isotopically light carbon release related to CAMP activity in both atmospheric and marine settings. The following positive CIE only in δ13Ccarb suggests relatively steady carbon isotope composition in atmosphere, but enhanced burial of isotopically light carbon in marine settings. Furthermore, the T-J carbonates in the studied section were possibly deposited in normal and oxic shallow marine conditions. Global correlation based on the Wadi Naqab section and other T-J sections suggests spatially different T-J environmental parameters: in eastern Tethys and western Panthalassa, oxic condition, lacking organic-rich sediment, weaker ocean acidification and less influence of isotopically light carbon are more prevalent; in western Tethys and eastern Panthalassa, oxygen-depleted condition, black shales, stronger acidification and heavier influence of isotopically light carbon are more prevalent. These differences may be related to spatial distance from the CAMP or to different paleogeography.

Middle Eocene carbonate platforms of the westernmost Tethys

A study of the paleoenvironmental evolution of the middle Eocene platforms recognized in the westernmost Tethys has been carried out in the well-exposed middle Eocene succession from Sierra Espuña-Mula basin (Betic Cordillera, S Spain). Eight microfacies (Mf1 to Mf8) have been recognized, based mainly on fossil assemblages (principally larger benthic foraminifera), and rock texture and fabric. The fossiliferous assemblage can be assigned to the ‘subtropical’ heterozoan association or to the low-latitude ‘foralgal facies’, which are dominated by non-framework building, light-dependent biota such as perforate larger benthic foraminifera, coralline algae, and sometimes green algae and solitary corals. Larger benthic foraminifer assemblages, corresponding from euphotic to oligophotic conditions and the large surface showed, suggest a progressive marine ramp under essentially oligotrophic conditions. Eventually, supply of detrital sediments from the continent and/or upwelling currents increases the nutrients of marine waters. Comparison with other Tethyan sectors allows stating that coral-reef buildups (z-corals) were widespread on shallow platforms of the central and eastern Tethys Ocean, but these were neither of great dimensions nor dominant because of the much more dominant presence of larger benthic foraminifera. Moreover, these coral constructions were completely absents in the westernmost Tethys. The dominance of larger benthic foraminifera and the absence of z-corals in the westernmost Tethys are explained by particular paleogeographic features due to the occurrence of a narrow and deep oceanic branch (i.e., the Maghrebian Flysch Basin) connecting the Tethys with the Atlantic Ocean. The various issues regarding the morphological characters and evolution of larger benthic foraminifera in the study area, such as sizes of tests, specific diversity and/or intraspecific variability, number of appearances and last occurrences during the middle Eocene are analyzed and compared with those appearing in other Tethyan sectors. In addition, the early to late Bartonian boundary is recognized in the study area as critical for the biological change as in other shallow-marine environments along the Tethys margins.

Marine late Triassic-Jurassic carbon-isotope excursion and biological extinction records: New evidence from the Qiangtang Basin, Eastern Tethys: Comment and reply

Abstract This is a comment on the Triassic and Jurassic boundary from the Qiangtang region, northern Tibet, reported by Hu et al., 2020, as there is no convincing evidence to support the identification of the boundary in the section, either by stratigraphy or by fossils presented in the paper.

Early Paleozoic Arc Magmatism and Accretionary Orogenesis in the Indochina Block, Southeast Asia

AbstractSoutheast Asia plays a key role in the evolution of the eastern Tethys, which is characterized by accretion and amalgamation of numerous terranes since early Paleozoic. In the present study...

Precambrian crustal evolution of the Tethyan Yunnan, Southwest China: Records in detrital zircons from Paleozoic sedimentary rocks of the Baoshan block

The Baoshan Block in western Yunnan is one of the major micro-continents in the eastern Tethyan orogenic belt, but its provenance and crustal evolution remain enigmatic. Sedimentary rocks prior to an amalgamation of continental blocks recorded key information about crustal evolution and the origin of terranes and can provide vital data for understanding orogenic processes. Here, we present U–Pb ages and Hf isotopic data on detrital zircon and Nd isotopic data on whole rock for Paleozoic sedimentary rocks from the Baoshan Block to constrain their provenance and tectonic history. Crystallization ages of detrital zircon grains illustrate that the magmatic activities of the source areas occurred at ~2.5 Ga, ~1.9 Ga, and ~1.0–0.5 Ga, with a major peak occurring around 0.95 Ga. Several old zircon grains from >3.0 Ga up to ~3.8–3.7 Ga were observed. Zircon Hf isotopic data from one sample suggest that the major crustal growth occurred at ~2.1 Ga. Cambrian to Carboniferous sedimentary rocks showed similar Nd isotopic features with two–stage Nd model ages of approximately 2.1 Ga. The age distribution patterns and isotopic data suggest that detritus material in the Paleozoic sedimentary rocks was mainly derived from continental terrane similar to the Indian craton, implying that the Baoshan Block was likely adjacent to Northwest India before the collision of the Baoshan and Simao blocks. No significant inputs of the juvenile crust were documented in the Nd–Hf isotopic data, appearing to be incompatible with a magmatic arc setting for the Baoshan Block during the Paleozoic. This block might have been situated at the interior of Gondwana before rifting and drifting northwards to the Eurasia continent.

Oceanic water redox conditions of the region between Tethys and Panthalassa during the late early Triassic

Fossil evidence of a complex food-chain in the marine ecosystem after the end-Permian mass extinction (EPME) event has been reported from the Osawa Formation, which consists of upper Olenekian (Spathian) shallow marine, mudstone-dominant strata in the South Kitakami Belt in Northeast Japan. This sedimentary sequence offers an important material that records the paleoenvironment of the oceanic region between the eastern Tethys and Panthalassa. This paper reports detailed records of the oceanic environment from two sections of the Osawa Formation focusing on the redox condition. Parallel, undisturbed laminae suggesting limited benthic activity are prominent in the middle to upper parts of the Osawa Formation, while disturbance of laminae by burrows occurs in the lower and uppermost parts, suggesting active benthic activity in an oxygen-rich depositional environment. The amount of pyrites (euhedral pyrite, pyrite framboids, and pyrite polyframboids) increases in the well-laminated mudstones. A relatively broad size distribution of pyrite framboids indicates that these mudstones were deposited under dysoxic conditions and suggest that the water column was not sulfidic. Redox-sensitive elements such as Mn, V, and U show values close to the average values of the upper continental crust throughout the Osawa Formation. Mo is moderately enriched in the well-laminated and pyrite-abundant mudstone horizons although the degree of enrichment is lower than known examples of modern sulfidic basins. These data suggest that the condition of the bottom water in this oceanic region during the Spathian varied between oxic and dysoxic (weakly oxygenated) and was never sulfidic. Such an oceanic environment characterized by mildly reducing bottom water and oxic water column appears to have been the settings for the recovery and establishment of the Early Triassic marine ecosystem characterized by diverse nektonic motile animals and limited diversity of benthic, in-motile animals.

Tracing Argoland in eastern Tethys and implications for India-Asia convergence

AbstractIncremental accretion of continental fragments from East Gondwana to Eurasia resulted in the growth of Asia and rise of the Tibetan Plateau, yet its detailed evolution remains uncertain. Argoland, a continental fragment that rifted from NW Australia during the Late Jurassic, played a key role in the initial opening of the Indian Ocean and the evolution of eastern Tethys. However, its present identity remains elusive, with East Java-West Sulawesi currently assumed to be the most likely option. To constrain the missing Argoland and its role in India-Asia convergence, we report new detrital zircon data from Sulawesi, Indonesia, and West Burma, Myanmar, and synthesize literature results from relevant regions in Southeast Asia, which (>15,000) reveal age profiles of West Sulawesi, the central Sulawesi metamorphic belt, and southeast Borneo comparable to that of Bird's Head, New Guinea, whereas age patterns of West Burma and East/West Java are similar to those of NW Australia. Notably, the most dominant age populations in NW Australia are rarely detected in Sulawesi and Borneo. These observations, combined with previous geological records and recent paleomagnetic data, suggest that West Burma is the mysterious Argoland, opposing the currently favored East Java-West Sulawesi model, with East Java and West Sulawesi probably having originated from NW Australia and Bird's Head, respectively. We estimate an average northward motion of ∼6–8 cm/yr for West Burma, which split from NW Australia to approach the equator during ca. 155–95 Ma, shedding new light on the reconstruction and breakup of northern East Gondwana, progressive building of Southeast Asia, and India-Asia convergence.

First record of non-mineralized cephalopod jaws and arm hooks from the latest Cretaceous of Eurytania, Greece

Due to the lower fossilization potential of chitin, non-mineralized cephalopod jaws and arm hooks are much more rarely preserved as fossils than the calcitic lower jaws of ammonites or the calcitized jaw apparatuses of nautilids. Here, we report such non-mineralized fossil jaws and arm hooks from pelagic marly limestones of continental Greece. Two of the specimens lie on the same slab and are assigned to the Ammonitina; they represent upper jaws of the aptychus type, which is corroborated by finds of aptychi. Additionally, one intermediate type and one anaptychus type are documented here. The morphology of all ammonite jaws suggest a desmoceratoid affinity. The other jaws are identified as coleoid jaws. They share the overall U-shape and proportions of the outer and inner lamellae with Jurassic lower jaws of Trachyteuthis (Teudopseina). We also document the first belemnoid arm hooks from the Tethyan Maastrichtian. The fossils described here document the presence of a typical Mesozoic cephalopod assemblage until the end of the Cretaceous in the eastern Tethys.

Sedimentological attributes of the Middle Jurassic peloids-dominated carbonates of eastern Tethys, lesser Himalayas, Pakistan

The carbonate factories of the tropical to sub-tropical regions characterize a number of facies, attributable to biological and oceanographic variables. For this purpose, the Middle Jurassic carbonate rock unit (Samana Suk Formation) of the Upper Indus Basin of Pakistan was studied to understand the various Tethyan platform attributes. Four sections from Hazara area were chosen which were also compared with a section from the Nizampur Basin. The resultant microfacies were placed in their paleoenvironmental settings to reveal the facies distribution and geometry of the platform. The platform represents a gently dipping ramp, dominated by peloidal–bioclastic–ooidal grainstones and peloidal lime mudstones. The allochems and fauna show some contrasting signatures regarding paleoclimate. These microfacies infer about existence of a relatively extended tropical climatic belt in the paleo Tethys during the Middle Jurassic. The notable presence of planktonic lime mudstone facies corresponds with global marine transgression, occurring in the middle of rock unit. The nature of ooids and types of fauna of sub-tropics to tropics advocate an extended warm climatic zone in comparison with today. The dominance of gently dipping inner-ramp shoals accompanied by lagoons to steep dipping outer-ramp planktonic lime mudstones restricted the development of least encountered middle-ramp facies. The ramp platform was struck by waves and tides of different strengths including low-middle amplitude storms and the overall absence of evaporites and primary dolostones designate a humid region as manifested by euryhaline conditions. The study has drawn paleoenvironmental and palaeoceanographic similarities with sections in Tanzania, western India, NW Iran, NW Afghanistan and Western Australia. The oceanic parameters compare with present day Trucial Coast of Persian Gulf, reflecting an almost similar nature of paleoceanography in the paleo Tethys.

Latest Permian Peltasperm Plant From Southwest China and Its Paleoenvironmental Implications

A monospecific flora containing a peltasperm species, Germaropteris martinsii, is discovered from the uppermost Permian Kayitou Formation of Southwest China. The epidermal characteristics of G. martinsii from the South China Block are described for the first time on the basis of charcoalified specimens. The plant is characterised by small, leathery foliage with prominent papillate epidermal cells and slightly sunken stomata. The stomatal apertures are covered by the long papillae of the surrounding subsidiary cells. The specific epidermal traits suggest that G. martinsii is a highly environmentally tolerant taxon that probably formed monospecific communities during the dramatic degradation of the peat-forming rainforest ecosystems. The frequent appearance of charcoalified leaves in the flora demonstrates that intense wildfires were prevalent at the time. The appearance and reflectance value (1.33%) of these charcoalified leaves reveal that they were formed at temperatures of 450–500°C during brief surface fires. Our study indicates that the terrestrial ecosystems may have been frequently subjected to desiccation and was vulnerable to the spread of fires as a result of the end-Permian biotic crisis in the tropics of the eastern Tethys region.

Late Cretaceous changes in oceanic currents and sediment sources in the eastern Tethys: insights from Nd isotopes and clay mineralogy

The Late Cretaceous is marked by geodynamical changes including Africa-Eurasia convergence that resulted in the narrowing of the Tethys Ocean and in ophiolite obduction along the southern margin of the various continental blocks in eastern Tethys. Geochemical and mineralogical analyses were performed on the Shahneshin section (Zagros Basin - eastern Tethys), to explore the consequences of this evolution on oceanic circulation, and to estimate the role of ophiolite weathering that can impact climate through atmospheric CO2 drawdown. [Ni] and [Cr] sharply increase in the uppermost Campanian – Maastrichtian interval and are not coeval with an increase in the Nd isotope composition (ɛNd) of the detrital fraction of the sediments. This is interpreted as reflecting weathering of the mantellic, ultramafic part of the ophiolite sequence at that time, implying that ophiolites were exposed on the continents as soon as the Coniacian in the vicinity of the Zagros Basin. Hence their weathering could have contributed to the Late Cretaceous climatic cooling. Clay mineralogy reveals an alternation of kaolinite-rich humid periods (Coniacian/Santonian and late early Campanian to latest Campanian) and kaolinite-depleted arid periods (early Campanian and the latest Campanian to late Maastrichtian). The ɛNd(t) of bathyal waters (carbonate leached fraction) appears quite radiogenic, in the range of -3.4 to -5.2 ɛ-units, about 2 to 4 ɛ-units higher than the detrital fraction. Changes in the ɛNd(t) of detrital material delivered to the Zagros Basin appear to control the ɛNd(t) of the local bottom waters from the Coniacian to the middle Campanian. By contrast, decoupling of detrital ɛNd(t) from that of the local bottom waters from the middle Campanian to the Maastrichtian points to increasing fluxes of westward flowing Pacific radiogenic water masses into the eastern Tethys at that time. These results support an intensification of the Tethyan Circumglobal Current, likely related to the narrowing of the Tethyan seaway.

Discovery of the Paleocene-Eocene Thermal Maximum in shallow-marine sediments of the Xigaze forearc basin, Tibet: A record of enhanced extreme precipitation and siliciclastic sediment flux

The Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) was one of the major global deep-time hyperthermal events of the past. Studies of shallow-marine PETM records are crucial to understand the continental hydrological response to current global warming. This study presents the first detailed documentation of the PETM in the Xigaze forearc basin located along the northern active continental margin of the eastern Tethys Ocean, and illustrates the associated environmental and hydrological changes. Based on carbon-isotope stratigraphy, foraminiferal biostratigraphy, and zircon UPb chronostratigraphy, the PETM event was identified within a siliciclastic unit in the largely calcareous Jialazi Formation. Foraminiferal assemblages of Shallow Benthic Zone 4 are present below the siliciclastic unit, but are replaced by Shallow Benthic Zone 6 assemblages above the siliciclastic unit. High-resolution microfacies analysis indicates that the pre-PETM deposits consist of carbonate-ramp sediments followed by a sudden change to syn-PETM siliciclastic rocks, followed in turn by renewed post-PETM carbonate-ramp deposition. The siliciclastic supply increased notably during the PETM, as indicated by the thickness of both sandstone and shale intervals, resulting in a temporary demise of the carbonate ramp. Provenance analysis does not indicate any major change in the source areas of terrigenous detritus through the early Paleogene. Increasing siliciclastic supply is thus chiefly ascribed to the intensification of seasonal precipitation and consequently increased hydrological circulation in the Gangdese arc during the PETM event.

A late Jurassic carbon-isotope record from the Qiangtang Basin (Tibet), eastern Tethys, and its palaeoceanographic implications

An Upper Jurassic succession of deep-marine limestones, marls and claystones preserved in the Ambo section of the Qiangtang Basin (Tibet) contains information concerning the response of the eastern Tethys Ocean to multiple carbon cycle perturbations and to palaeoceanographic changes. Three positive δ 13 C excursions (P-CIE 1–3), dated as latest Callovian, middle Oxfordian and early Late Kimmeridgian, respectively, are observed in our section and related to high organic carbon burial episodes; they are correlatable with profiles from the Atlantic, western Tethys and western Paleo-Pacific regions. A significant decrease in δ 13 C values in our section in late Oxfordian to early Kimmeridgian times is attributed to the onset of upwelling of 13 C-depleted watermasses caused by the opening of new seaways during the progressive collapse of Pangaea. A fourth positive δ 13 C excursions (P-CIE 4), dated as Late Kimmeridgian-Early Tithonian, is unlikely to be due to accelerated burial of organic carbon, but may be associated with the establishment of a stable low-latitude thermohaline circulation that replaced the upwelling zones. Due to the oceanic changes linked to the breakup of Pangaea, incursions of cold Arctic waters and associated changes in water mass density triggered a collapse in thermohaline circulation in the Tethys Ocean during the middle Early Tithonian (ca. ~151–150 Ma). As a consequence, an upwelling cold bottom current was formed, triggering global cooling and a significant reduction in the δ 13 C values. This study is the first to show continuous carbon isotope profiles for the eastern Tethys Ocean, and provides an inter-regional correlation and new paleoceanographic information. • The first high-resolution carbon isotope record of the Upper Jurassic from the Tibet, eastern Tethys. • Remarkable P-CIEs during the earliest Tithonian are associated with the major reorganization of Tethys oceanography. • A collapse in thermohaline circulation likely occurred in the middle Early Tithonian.

Geochronology and geochemistry of the Tongjige granodiorites in the Jinshajiang suture zone, SW China: Constraints on petrogenesis and tectonic evolution of the Palaeo‐Tethys Ocean

The Jinshajiang suture zone (JSZ) is one of the most significant tectonic zones in the eastern Tethys area. A large number of plutons are regarded as the result of tectono‐magmatic activities associated with the evolution of the Palaeo‐Tethys Ocean. The Tongjige pluton in the central part of JSZ can indicate the magmatism and its geodynamic evolution. The Tongjige pluton (225.6 Ma) consists mainly of granodiorite with abundant coeval mafic microgranular enclaves (MMEs) (226.1 Ma). The host granodiorite is calc‐alkaline and typical I‐type, with SiO2 contents ranging from 65.75 to 66.91 wt%. The MMEs have relatively high MgO (4.00–4.07 wt%) and Fe2O3T (9.27–9.40 wt%) abundances and low SiO2 (53.59–53.87 wt%). Both MMEs and host granodiorites are characterized by the enrichment of light rare earth elements and depletion of heavy rare earth elements. They are also negative in Eu and enriched in Th and U, which are consistent with the trace element characteristics of typical island‐arc magmatite. The zircon Hf(t) values (−3.48 to −0.31) are negative, with the model ages of 1.3–1.2 Ga. These petrographic and geochemical characteristics indicated that the Tongjige pluton was derived from the melting of an ancient lower crust and underwent the process of mafic‐felsic magmatic mixing in the post‐collision background. The Triassic granitoids in the JSZ show a temporal–spatial relationship with the subduction zone, which constrain the evolution of the Palaeo‐Tethys Ocean. The mixing mechanism of the Tongjige pluton is associated with the break‐off of a subducted slab, which triggered subsequent upwelling of asthenosphere beneath accreted arc fragments and induced underplate of lithospheric mantle‐derived magmas and mixed with the lower crust‐derived felsic magma. In general, the Late Triassic pluton recorded significant crustal growth and continental development, marking the final stage of subduction‐related magmatism in the JSZ region, after which the region entered into a stage of post‐collision evolution.

Cisuralian and Guadalupian global paleobiogeography of fusulinids in response to tectonics, ocean circulation and climate change

During the Permian, major icehouse-greenhouse climate shifts and tectonic reconfiguration had important biogeographic implications, especially for climate-sensitive organisms such as fusulinids. Here we present multivariate methods on a global fusulinid species dataset including 1546 species from 58 localities in the Early (Asselian, Sakmarian, Artinskian and Kungurian) and Middle (Roadian, Wordian and Capitanian) Permian. Our results show that fusulinid global provincialism was high in the Asselian, Sakmarian, and Artinskian, driven by the development of multiple fusulinid bioregions in and near the Tethys Ocean. During the Asselian, Uralian sites and nearby regions of western Tethys were distinct from eastern Tethys, while stations in Arctic Russia and Norway formed a separate Boreal bioregion. Tectonic closure of the oceanic gateway in the southern Urals resulted in progressive isolation of the Uralian and Boreal bioregions during the Sakmarian and Artinskian and their ultimate disappearance by the Kungurian. Climate warming likely was the most important control on the Sakmarian formation of the distinct peri-Gondwana bioregion, because its development coincided with deglaciation following the Late Paleozoic Ice Age but preceded the separation of the Cimmerian terranes from northern margin of Gondwana. On the other hand, northward movement of the Cimmerian blocks following Artinskian-Kungurian rifting ultimately led to the merger of the peri-Gondwanan bioregion with tropical Tethyan faunas, resulting in lower provincialism in the Guadalupian and minimal faunal differentiation across Tethys. In contrast, faunal similarity between Tethys and eastern Panthalassa (the McCloud region and southwestern United States) was higher in the Asselian-Artinskian but decreased in the Kungurian and Middle Permian, perhaps as the result of sluggish ocean circulation following the warming episode of Late Paleozoic deglaciation.