Eastern Tethys Research Articles

Late Triassic sedimentary records in the northern Tethyan Himalaya: Tectonic link with Greater India

The Upper Triassic flysch sediments (Nieru Formation and Langjiexue Group) exposed in the Eastern Tethyan Himalayan Sequence are crucial for unraveling the controversial paleogeography and paleotectonics of the Himalayan orogen. This work reports new detrital zircon U-Pb ages and whole-rock geochemical data for clastic rocks from flysch strata in the Shannan area. The mineral modal composition data suggest that these units were mainly sourced from recycled orogen provenances. The chemical compositions of the sandstones in the strata are similar to the chemical composition of upper continental crust. These rocks have relatively low Chemical Index of Alteration values (with an average of 62) and Index of Compositional Variability values (0.69), indicating that they experienced weak weathering and were mainly derived from a mature source. The geochemical compositions of the Upper Triassic strata are similar to those of graywackes from continental island arcs and are indicative of an acidic-intermediate igneous source. Furthermore, hornblende and feldspar experienced decomposition in the provenance, and the sediment became enriched in zircon and monazite during sediment transport. The detrital zircons in the strata feature two main age peaks at 225–275 Ma and 500–600 Ma, nearly continuous Paleoproterozoic to Neoproterozoic ages, and a broad inconspicuous cluster in the Tonian–Stenian (800–1200 Ma). The detrital zircons from the Upper Triassic sandstones in the study area lack peaks at 300–325 Ma (characteristic of the Lhasa block) and 1150–1200 Ma (characteristic of the Lhasa and West Australia blocks). Therefore, neither the Lhasa block nor the West Australia blocks likely acted as the main provenance of the Upper Triassic strata. Newly discovered Permian–Triassic basalt and mafic dikes in the Himalayas could have provided the 225–275 Ma detrital zircons. Therefore, Indian and Himalayan units were the main provenances of the flysch strata. The Tethyan Himalaya was part of the northern passive margin and was not an exotic terrane separated from India during the Permian to Early Cretaceous. This evidence suggests that the Neo-Tethyan ocean opened prior to the Late Triassic and that the Upper Triassic deposits were derived from continental crustal fragments adjacent to the northern passive continental margin of Greater India.

Petrogenesis and tectonic implications of ∼130 Ma diabase dikes in the western Tethyan Himalaya (western Tibet)

Early Cretaceous mafic dikes are widely exposed in the eastern Tethyan Himalaya. However, coeval mafic rocks are limited in the western Tethyan Himalaya. We report the major and trace elements and zircon U–Pb ages of the newly discovered diabase dikes in the Zhongba area in the western Tethyan Himalaya. The ICP-MS zircon U–Pb analyses from one representative diabase dike yields a crystallization age of 129.8±1.3Ma (MSWD=6.7). These mafic dikes are characterized by high concentrations of TiO2 (2.81–3.27%), Fe2O3T (10.79–12.14%), and MgO (5.11–6.71%). The chondrite-normalized diagram indicates the enrichment of LREE and the depletion of HREE. The primitive mantle-normalized trace element patterns do not display negative anomalies of Nb, Ta, and Ti. These characteristics imply an OIB affinity. Trace element modelling (Sm/Yb vs. Sm) suggests that the dikes originated from an enriched mantle source region, composed primarily of garnet and spinel (spinel<garnet), with a low degree of partial melting (4–8%). Comparing with coeval OIB-affinity mafic rocks from the areas of Gyangze, Kangma, Cona, and Laguila, we propose that the Cretaceous mafic rocks were generated in an extensional setting along a passive continental margin and were derived from similar magma sources with some crustal contamination in the case of the Zhongba intrusives. Because of the similar geochemical characteristics, ages and tectonic settings, of the Zhongba diabase rocks and other volcanic rocks from the Kerguelen LIP, we suggest that the Zhongba diabase rocks are likely also part of the Kerguelen LIP.

Microfacies analysis of larger benthic foraminifera-dominated Middle Eocene carbonates: a palaeoenvironmental case study from Meghalaya, N-E India (Eastern Tethys)

Larger benthic foraminifera (LBF) show significant abundance and diversity in the Palaeogene carbonate sediments of Meghalaya, N-E India, but have previously received less attention from the palaeoenvironmental perspective. LBF are important contributors to recent as well as fossil shallow marine, tropical carbonate settings. They find wide application in biostratigraphy and palaeoenvironmental reconstructions. The larger foraminiferal turnover (LFT) during the Palaeocene-Eocene transition is very important with respect to their evolution in several parts of the world including the Eastern Tethys. The present microfacies analysis documents the status of LBF in the Middle Eocene sediments from the Prang Formation of the Sylhet Limestone Group in Meghalaya, N-E India. Five major facies types (MFTs)—miliolid grainstone-packstones, alveolinid-rotaliid grainstone-packstones, nummulitid-alveolinid grainstone-packstones, coralline algal-nummulitid packstone-wackestones and coralline algal wackestones have been recorded in the current study. Evaluation of the palaeoenvironmental parameters aids in understanding the seascape of this Eastern Tethyan domain. It is suggested that an oligotrophic nutrient regime supported the rapid evolution and dominance of the LBF. Most notable is the prolific augmentation in Alveolina and Nummulites populations. High surface water temperatures during the Late Palaeocene-Early Eocene global warming episode possibly persisted to a certain level during the Middle Eocene and continued to favour the larger foraminifera as the major carbonate producers instead of the vulnerable corals.

Multiple Mesozoic porphyry-skarn Cu (Mo–W) systems in Yidun Terrane, east Tethys: Constraints from zircon U–Pb and molybdenite Re–Os geochronology

Porphyry Cu±Mo±Au deposits typically formed in volcanoplutonic arcs above subduction zones. However, there is increasing evidence for the occurrence of porphyry deposits related to magmas generated after the underplating arc has ceased. Post-subduction lithospheric thickening, lithospheric extension, or mantle lithosphere delamination could trigger the remelting of subduction-modified arc lithosphere and lead to the formation of post-subduction porphyry deposits. The NNW-trending Yidun Terrane, located in the eastern Tethys, experienced subduction of Garze–Litang oceanic plate (a branch of the Paleotethys) in the Late Triassic and witnessed two mineralization events respectively associated with the ca. 215Ma arc-related intermediate–felsic porphyries and the 88–79Ma mildly-alkaline granitic porphyries. It is, therefore, an ideal place to investigate the genetic linkage between the subduction-related porphyry deposits and post-subduction porphyry deposits. Our new in situ zircon U–Pb dating of the two granitic intrusions (biotite granite, 213.4±0.9Ma; monzogranite porphyry, 86.0±0.4Ma) in the Xiuwacu district, the molybdenite Re–Os age (84.7±0.6Ma) of the mineralization, and previously published geochronological data, together show the spatially overlapping distribution of the multiple Mesozoic porphyry systems in the Late Triassic Yidun arc system. Furthermore, the arc-like elemental signatures and the mixed Sr–Nd–Hf isotopic signatures of the Late Cretaceous ore-related porphyries (i.e., originating from a mixed components between the ∼215Ma juvenile arc crust and the Mesoproterozoic mafic lower crust) indicate a genetic linkage between the Late Triassic and Late Cretaceous porphyry systems. This suggests that the remelting of underplated arc-related mafic rocks formed during the subduction of the Garze–Litang Ocean could be responsible for the mixing between the mantle-derived components and the Mesoproterozoic lower crustal materials, when post-subduction transtension occurred in the Late Cretaceous. The formation of the Late Cretaceous porphyry–skarn Cu–Mo–W deposits could most likely be related to the remelting of Late Triassic residual sulfide-bearing Cu-rich cumulates in the subduction-modified lower crust that triggered by the Late Cretaceous transtension.

Early Jurassic tectonism occurred within the Basu metamorphic complex, eastern central Tibet: Implications for an archipelago-accretion orogenic model

The Basu metamorphic complex, surrounded by ophiolitic melanges and intruded by a large volume of undeformed granitoid rocks along the eastern segment of the Bangong-Nujiang suture, holds one of the keys to understanding the pre-Cenozoic tectonic evolution of central Tibet. Zircon U-Pb dating of rocks from the Basu metamorphic complex reveals that meta-igneous rocks yield Early Paleozoic crystallization ages of 500–492Ma and an Early Jurassic metamorphic age of ~173Ma, and that undeformed granitoid rocks yield crystallization ages of approximately 186–174Ma. Whole rock geochemical and zircon Lu-Hf isotopic data indicate that the undeformed granitoid rocks originated mainly from partial melting of ancient crustal sources, which may reflect a collisional orogenic setting. 40Ar/39Ar dating of biotite from a sillimanite-garnet-biotite paragneiss shows cooling to 300±50°C at ~165Ma. These data indicate significant Early Jurassic tectonism, during which most of the Basu metamorphic complex was formed. Furthermore, the age data resemble those of the Amdo metamorphic complex located approximately 500km to the west along the Bangong-Nujiang suture. Together, these complexes may represent a “destroyed or unrecognized” block, i.e., the Amdo-Tongka block, which may be the eastern extension of the South Qiangtang terrane. Based on the tectonic outlines of the multiple ophiolitic zones and magmatic belts, we suggest a new archipelago-accretion model that attributes the Early Jurassic tectonism to an arc-continent/micro-continent collision. This model further enables the reconstruction of the eastern Tethyan Ocean and the orogenic processes of central Tibet during the Mesozoic.

Palaeogeographic variation in the Permian–Triassic boundary microbialites: A discussion of microbial and ocean processes after the end-Permian mass extinction

Shallow marine carbonate sediments that formed after the end-Permian mass extinction are rich in a thin (maximum ca. 15 m) deposit of microbialites. Microbial communities that constructed the microbialites have geographic variability of composition, broadly divisible into two groups: 1) eastern Tethys sites are calcimicrobe-dominated (appearing as thrombolites in the field), with rare occurrence of sediment-constructed microbialites and uncommon cements either within microbial structure or as inorganic precipitates, 2) other Tethys sites are sediment-dominated structures forming stromatolites and thrombolites, composed of micrites and cements, with some inorganic precipitates. These other Tethys locations include western and central Tethys sites but their palaeogeographic positions depend on the accuracy of continental reconstructions, of which there are several opinions. In contrast to geographic variation of microbialites, the conodont Hindeodus parvus, which appeared after the extinction and defines the base of the Triassic, is widespread, indicating easy lateral migration throughout Tethys. Conodont animals were active nekton, although being small animals were presumably at least partly carried by water currents, implying active Tethyan surface water circulation after the extinction event. Post-extinction ammonoid taxa, presumed active swimmers, show poor evidence of a wide distribution in the Griesbachian beds immediately after the extinction, but are more cosmopolitan higher up, in the Dienerian strata in Tethys. Other shelly fossils also have poorly defined distributions after the extinction, but ostracods show some wider distribution suggesting migration was possible after the extinction. Therefore there is a contrast between the geographic differences of microbialites and some shelly fossils.Determining the cause of geographic variation of post-extinction microbialites is problematic and may include one or more of the following possibilities: 1) because calcifying microbial organisms that create calcimicrobes were benthic, they may have lacked planktonic stages that would have allowed migration, 2) eastern Tethyan seas were possibly more saturated with respect to calcium carbonates and microbes, so microbes there were possibly more able to calcify, 3) significant reduction of Tethyan ocean circulation, perhaps by large-scale upwelling disrupting ocean surface circulation, may have limited lateral migration of benthic microbial communities but did not prevent migration of other organisms, and 4) microbes may have been subject to local environmental controls, the mechanisms of which have not yet been recognized in the facies. The difficulty of distinguishing between these possibilities (and maybe others not identified) demonstrates that there is a lot still to learn about the post-extinction microbialites and their controls.

Paleogene Nummulitid biostratigraphy of the Kohat and Potwar Basins in north-western Pakistan with implications for the timing of the closure of eastern Tethys and uplift of the western Himalayas

The Paleogene larger benthic foraminifera (LBF) of the Kohat and Potwar basins, Pakistan are very useful in dating shallow marine sediments and cessation of marine sedimentation that provides constraint for crucial information on the initial age of India-Asia collision. We record important Paleogene LBF species in multiple sections of the two basins. We performed the biometric analysis of the nummulitid species useful for taxonomic purposes. We recognize six Larger Benthic Foraminiferal Zone (BFZ Zone 1-6) in the Kohat Basin. Among these Zones the first three (BFZ Zone 1-3) occur also in the Potwar Basin and the adjoining Trans Indus Ranges (TIR). The correlation of BFZ 1-6 Zones with the previous local and regional LBF biostratigraphic schemes in the Eastern Tethys (Pakistan-India) and Western Tethys (European Basins) resulted in recognition of useful index taxa for developing a regional stratigraphic framework during Paleogene. In the BFZ 1 Zone, The last occurrence (LO) of Miscellanea miscella and first occurrence (FO) of Assilina dandotica in the BFZ 2 Zone mark the Late Paleocene (Late Thenetian) Early Eocene (Lower Illerdiuan1) Boundary. The co-occurrence of A. pustulosa, Al. vredenburgi, Al. globula and Al. pasticillata in the BFZ 2 Zone characterizes the Early Eocene (Lower IlIerdian 1-Middle Illerdian 1) sediments. The synchronous FO of N. atacicus and N. globulus is an excellent global biostratigraphic marker of the Early Eocene (Middle Illerdian 1 Middle Illerdian 2) Boundary and the FO of O. complanatus is a useful biostratigraphic marker for the Early Eocene (Lower Cuisian 2-Middle Cuisian) Boundary in the BFZ 3 Zone. Mammalian bones found at the base of Koldana Formation in the Kohat Basin represent Early Eocene (Upper Cuisian), which is in agreement with the LBF biostratigraphy of the underlying Middle Cuisian strata. The FO of A. exponens in the BFZ 4 Zone record the Middle Eocene (Middle Lutetian 1) sediments while FO of N. beaumonti in the BFZ 5 Zone marks the Middle Lutetian 1Middle Lutetian 2 Boundary. The FO of A. cancellata in the BFZ 6 Zone marks Middle Lutetian 2Upper Lutetian Boundary. The implications of our LBF study are that cessation of marine sedimentation in both Pakistani basins occurred in Early Eocene (Middle Cuisian ≈BFZ 3) around 50-49.5 Ma. Notably, marine conditions returned in the Kohat Basin in Middle Eocene (Middle Lutetian 1 ≈ BFZ 4) due to an eustatic sea level rise. The final cessation of marine sedimentation, causing closure of the Eastern Tethys seaway in the Kohat Basin occurred in Middle Eocene (Upper Lutetian ≈BFZ 6) around 41.2 Ma, probably a result of some form of post-collisional stress.

A new site with Oligocene terrestrial mammals and an Oligocene selachian fauna from Minqar Tibaghbagh, the Western Desert of Egypt

A new fossil site at Minqar Tibaghbagh, east of Siwa, in the Egyptian Western Desert is described. This represents the first place in Egypt outside the Fayum Depression yielding Paleogene, terrestrial mammals. Initial studies indicate the presence of palaeomastodonts, hyracoids, and anthracotheres, presumably early Oligocene in age. As only surface prospecting has been performed, more taxa will almost certainly be discovered in future investigations here and probably also elsewhere in the surroundings. A comparison is made with the most important contemporaneous sites in Libya and Egypt that yield terrestrial mammal remains. The selachian fauna from a higher level in the section confirms the Paleogene age of the subjacent strata. It is compared with selachians faunas from the early Oligocene Eastern Tethys Ocean at other places (the Fayum Depression in Egypt, and sites in Oman and Pakistan), and differs from these sites in being fully marine. Contrary to earlier studies, the open marine mudstones of the Daba’a Formation at Minqar Tibaghbagh are overlain by Paleogene marine sediments of most probably early Oligocene age and not early Miocene marine sediments as previously reported. These strata represent not only a new site with great potential for future finds, but also allows for biostratigraphic correlation.

COMPARATIVE ANALYSIS OF THE COMPOSITION OF THE TERRESTRIAL FAUNA AND FLORA OF THE TETHYS DESERT-STEPPE REGION OF PALEARARTICS, BIOGEOGRAPHIC BOUNDARIES OF THE CAUCASUS. MESSAGE 1. TERRESTRIAL FAUNA

Aim. The aim is to conduct a comparative analysis of the composition of the terrestrial fauna of the Tethys desert-steppe region of the Palearctic. Materials and methods. The work was based on the materials collected in different republics and regions of the Caucasus and the south of the European part of Russia during 50 years (from 1961 to 2016) which are kept in various domestic and foreign institutions. Catalogs on the studied model groups were also used to conduct the research. In making the dendrograms, a cluster analysis based on the Jaccard coefficient was used. Results. A detailed analysis was carried out by model groups of the animals of the Eastern and Western Thethys complexes of the desert-steppe region of the Palearctic. Comparative analysis has shown that a significant number of species and genera of the discussed territories is characterized by an exceptionally high ratio of endemic species and superspecies taxa. Indicators of endemism in model groups fluctuate depending on the population's ability to resettle. High endemism of faunas of darkling beetles, ground beetles, click beetles and land snails in the Eastern Tethys complex was noted. Conclusion. The Caucasus (in a new interpretation) is characterized by a high percentage of endemism for the studied model groups. A large number of the common Tethys genera and species in all model groups attests to their fundamental role in the overall composition of the biota against the background of powerful autochthonous centers of species-formation and, most importantly, the formation and functioning of the Palaearctic desert-steppe belt as the Tethys ocean reduced.

Late Jurassic to Cretaceous evolution of the eastern Tethyan Hawasina Basin (Oman Mountains)

AbstractRemnants of a Mesozoic continental margin can be studied today in the nappe pile of the Oman Mountains. Successions of the Arabian carbonate platform and the adjacent deep Hawasina Basin are preserved in the nappe pile and in the foothills of this Mountain range. The Jurassic–Cretaceous sediment successions of the Hawasina Basin (Sumeini and Hamrat Duru Group) are focus of this study. These basinal archives contain information on the response of an eastern Tethyan equatorial ocean system to multiple perturbations of the carbon cycle and of climate during the Cretaceous. Turbiditic continental slope and basinal successions formed near the Calcite Compensation Depth are difficult to date with biostratigraphy and sequence stratigraphy. The available stratigraphic framework for the Hawasina successions was not sufficient for tracing palaeoceanography through the time window of interest in this study. Therefore, existing sequence stratigraphy and biostratigraphy are complemented by additional biostratigraphic data and with a newly established carbon and strontium isotope chemostratigraphy. The Hawasina Basin was affected by sea‐level variations, by changes in oceanography and also by regional tectonics. A first major modification of oceanography occurred at the end of the Jurassic when pelagic Maiolica‐type sediments were accumulated in the deep basin and on adjacent submarine highs (Lower Member of Huwar and Sid'r formations). Pelagic to hemipelagic conditions existed until the Valanginian, marked by a major carbon isotope excursion. Pelagic sediments were replaced afterwards by a succession of fine to coarse‐grained turbidites of Hauterivian to Aptian age. The transition into the mid‐Cretaceous is marked by a sudden shift to fine‐grained siliceous or chert deposits, at a time when sediments enriched in organic carbon were accumulated in the western Tethys and Atlantic Oceans. The continental slope as well as the Hawasina Basin seemed to have been well‐ventilated during Early and mid‐Cretaceous time. Siliceous limestones and chert are indicators of well‐mixed and nutrient‐rich surface water, while the absence of black shales suggests young and oxygenated deep water with a possible source on the vast Arabian platform. These peculiar oceanographic conditions were most pronounced during the onset of the extreme greenhouse episodes of the Oceanic Anoxic Event 1a.

Shallow-water carbonate responses to the Paleocene–Eocene thermal maximum in the Tethyan Himalaya (southern Tibet): Tectonic and climatic implications

This study presents a detailed stratigraphic record of the Paleocene–Eocene Thermal Maximum (PETM) in the Gamba area of the Tethyan Himalaya, a carbonate-platform succession originally deposited along the southern margin of the eastern Tethys Ocean. The Paleocene-Eocene boundary interval is marked by a negative carbon isotope excursion at the boundary between members 3 and 4 of the Zongpu Formation. The succession is erosionally truncated at this surface, which is overlain by an intraformational carbonate conglomerate, and only the upper part of the PETM interval is preserved. Foraminiferal assemblages of Shallow Benthic Zone 4 are present below the conglomerate bed, but are replaced by assemblages of Shallow Benthic Zone 6 above the conglomerate. Depositional facies also change across this surface; below the disconformity, floatstones and packstones containing nummulitid forams record progressive transgression in an open-marine environment, whereas restricted or lagoonal inner-ramp deposits containing Alveolina and Orbitolites are typical above the disconformity. The prominent negative excursion observed in the δ13C of whole-rock carbonate (−1.0‰ at Zongpu, −2.4‰ at Zengbudong) and organic matter (−24.7‰, at Zengbudong) is correlated to the characteristic PETM carbon isotope excursion. This major negative excursion in shallow-marine carbonates may have partly resulted from syndepositional alteration of organic matter. The erosional unconformity can be constrained to the lower PETM interval (between 56 and 55.5Ma), and is identifiable throughout the Tethyan Himalaya. This widespread disconformity is attributable to tectonic uplift associated with the southward migration of an orogenic wave, originated 3±1Ma earlier in the middle Paleocene at the first site of India-Asia continent-continent collision. A possible eustatic component of the pre-PETM sea-level fall, which resulted in the excavation of incised valleys filled during the subsequent sea-level rise when the conglomerate bed was deposited, remains to be assessed.

A NEW PRIABONIANHETEROSTEGINAFROM THE EASTERN TETHYS (SULAIMAN FOLD BELT, WEST PAKISTAN): IMPLICATIONS FOR THE DEVELOPMENT OF EASTERN TETHYAN HETEROSTEGINES AND THEIR PALEOBIOGEOGRAPHY

The stratigraphic utility of Eocene Heterostegina in the Western Tethys prompts an interest in the Eastern Tethyan domain, where virtually no information exists on this group. The classic Eocene sections, Zinda Pir and Rakhi Nala, in West Pakistan offer a unique opportunity to fill this information gap. The genus here is confined only to the upper part of the Drazinda Formation (‘ Pellatispira beds’ of the obsolete Kirthar series) associated with Pellatispira , Silvestriella , reticulate Nummulites , rare orthophragminids and other less significant larger benthic foraminifera. Heterostegina specimens are characterised by notably small, nearly flat to flat tests with fine granulation over the test surface, a small proloculus and tight early spirals. The early operculinid chambers, few in number, are followed by the heterosteginid stage consisting of rectangular chamberlets, developed only in the median part of the test, but not in alar prolongations. The latter are remarkably wide and extend to the umbilical part of the test. A combination of these features permits their differentiation from the Western Tethyan and Pacific Eocene Heterostegina , also demonstrated morphometrically, and a new species, H. indusensis n. sp., is erected. Our data favor the polyphyletic origin for the Eocene heterostegines in the Tethys and do not support a previous hypothesis that the genus was confined to the high-latitutes in Priabonian times.

Multiple Phases of Mafic Magmatism in Gyangze‐Kangma Area: Implications for the Tectonic Evolution of Eastern Tethyan Himalaya

Multiple Phases of Mafic Magmatism in Gyangze‐Kangma Area: Implications for the Tectonic Evolution of Eastern Tethyan Himalaya

Early Jurassic carbon-isotope excursion in the Qiangtang Basin (Tibet), the eastern Tethys: Implications for the Toarcian Oceanic anoxic event

The Early Jurassic was characterized by a global disturbance of the carbon cycle known as the Toarcian oceanic anoxic event (T-OAE). This event is recorded by a large negative carbon-isotope excursion (CIE) in marine carbonates and marine organic matter, as well as fossil wood. Here, we present new high-resolution carbonate (δ13Ccarb) and organic (δ13Corg) carbon-isotope records and total organic content from the Bilong Co section in the Qiangtang Basin, the eastern Tethys. This section is high in organic carbon, and black shale facies are also identified. The Bilong Co section shows heavy δ13Corg values compared to other reported marine organic carbon-isotope values for the T-OAE. This is explained by variable mixing of terrestrial and marine organic matter. Compared to European sections, the magnitude of the negative CIE in the Bilong Co section is slightly different, which could be explained by different local paleoenvironmental conditions and strata missing. Although these, the carbon-isotope profile from the Bilong Co area displays a similar trend to those in contemporaneous strata in the western Tethyan and Boreal realms of NW Europe, which is characterized by a distinct negative excursion in the Early Toarcian. Our new data from the Bilong Co section in N Tibet provide the first high-resolution record of the Early Toarcian Oceanic Anoxic Event in the eastern Tethys.

Sedimentary patterns and palaeoceanography of the Albian Marne a Fucoidi Formation (Central Italy) revealed by high‐resolution geochemical and nannofossil data

AbstractThe pelagic Marne a Fucoidi Formation from the Umbria–Marche Basin (Central Italy) is one of the best‐preserved deep‐marine archives of the Aptian–Albian. Frequent changes in lithology, from black to green and red marlstones and limestones, record fluctuating oceanographic and climatic conditions during the deposition of these sediments. Here, the lithological changes in the Albian of the Marne a Fucoidi Formation are studied with unprecedented resolution using X‐ray fluorescence core scanning measurements of major and minor element abundances, as well as statistical analyses of calcareous nannofossil indices. The results obtained with these two independent methodologies are in good agreement and allow for improving the understanding of the peculiar palaeoceanographic conditions of the western Tethys during the Albian. Black shale–marlstone couplets were driven by orbitally forced changes in physical oceanography, resulting in oxygen‐depleted bottom water at times of decreased mixing of shallow water masses. On the other hand, red marlstones represent episodes of enhanced oxygenation at the bottom, probably due to the influence of deep waters from the eastern Tethys. Overall, the Marne a Fucoidi Formation is the expression of highly variable oceanographic conditions related to an unstable Albian circulation mode.

Middle Triassic radiolarians from the Southeastern Pamirs (Republic of Tajikistan)

Triassic radiolarians were studied from a limestone/chert succession of the Dzhangisu and Boztere formations, Southeastern Pamirs, Republic of Tajikistan. The middle part of the Dzhangisu Formation is characterized by a Late Anisian assemblage with Eptingium nakasekoi Kozur and Mostler, Archaeospongoprunum bispinosum Kozur and Mostler, A. mesotriassicum mesotriassicum Kozur and Mostler, Paroertlispongus multispinosus Kozur and Mostler, P. rarispinosus Kozur and Mostler and Hozmadia rotunda (Nakaseko and Nishimura) that belongs either to the upper part of the Tetraspinocyrtis laevis Zone or to the Spongosilicarmiger transitus Zone (Kozur, 2003). The lowermost part of the Boztere Formation is characterized by a Late Ladinian assemblage with Muelleritortis cochleata (Nakaseko and Nishimura), M. expansa (Kozur and Mostler), Spongoserrula rarauana Dumitrica that corresponds to the M. cochleata Zone. Pamirian localities have a transitional position between the Western Tethys (Alpine–Mediterranean region) and the Eastern Tethys–Pacific junction (Southern China and Thailand). The assemblages are Tethyan in affinity.

The earliest record of the genus Lariosaurus from the early middle Anisian (Middle Triassic) of the Germanic Basin

ABSTRACTA new skull representing the oldest record of the genus Lariosaurus in the Germanic Basin is described. The small-sized skull originates from the early middle Anisian (Bithynian) of the Winterswijkse Steengroeve (Winterswijk, The Netherlands) and is assigned to L. vosseveldensis, sp. nov. Supplementation of a recently established phylogeny with L. vosseveldensis, sp. nov., recovered it within Lariosaurus as the sister taxon to Nothosaurus winkelhorsti and L. buzzii. The generic assignment of N. juvenilis, N. youngi, and N. winkelhorsti to Nothosaurus must be reevaluated to reestablish support for a monophyletic Lariosaurus, and only a definitive resolution of the polytomy including Germanosaurus could recover a monophyletic Nothosauridae. The Winterswijk locality has previously yielded a rich and diverse marine reptile fauna, including an endemic basal placodont. The nearly contemporaneous occurrence of L. vosseveldensis, sp. nov., and L. hongguoensis from the middle Anisian (Pelsonian) of China indicates a very rapid dispersal of the group, but does not resolve the origin of Sauropterygia (eastern Tethyan faunal province vs. western Tethyan faunal province).http://zoobank.org/urn:lsid:zoobank.org:pub:9FAFC2A0-77CE-476F-938A-7858EDA61FBACitation for this article: Klein, N., D. F. A. E. Voeten, A. Haarhuis, and R. Bleeker. 2016. The earliest record of the genus Lariosaurus from the early middle Anisian (Middle Triassic) of the Germanic Basin. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1163712.

Climate warming, euxinia and carbon isotope perturbations during the Carnian (Triassic) Crisis in South China

Abstract The Carnian Humid Episode (CHE), also known as the Carnian Pluvial Event, and associated biotic changes are major enigmas of the Mesozoic record in western Tethys. We show that the CHE also occurred in eastern Tethys (South China), suggestive of a much more widespread and probably global climate perturbation. Oxygen isotope records from conodont apatite indicate a double-pulse warming event. The CHE coincided with an initial warming of 4 °C. This was followed by a transient cooling period and then a prolonged ∼7 °C warming in the later Carnian (Tuvalian 2). Carbon isotope perturbations associated with the CHE of western Tethys occurred contemporaneously in South China, and mark the start of a prolonged period of carbon cycle instability that persisted until the late Carnian. The dry-wet transition during the CHE coincides with the negative carbon isotope excursion and the temperature rise, pointing to an intensification of hydrologic cycle activities due to climatic warming. While carbonate platform shutdown in western Tethys is associated with an influx of siliciclastic sediment, the eastern Tethyan carbonate platforms are overlain by deep-water anoxic facies. The transition from oxygenated to euxinic facies was via a condensed, manganiferous carbonate (MnO content up to 15.1 wt%), that records an intense Mn shuttle operating in the basin. Significant siliciclastic influx in South China only occurred after the CHE climatic changes and was probably due to foreland basin development at the onset of the Indosinian Orogeny. The mid-Carnian biotic crisis thus coincided with several phenomena associated with major extinction events: a carbonate production crisis, climate warming, δ 13 C oscillations, marine anoxia, biotic turnover and flood basalt eruptions (of the Wrangellia Large Igneous Province).

Bathonian–Callovian (Middle Jurassic) ammonites from northwestern Qiangtang Block, Tibet, and the revised age of the Suowa Formation

The age of the Suowa Formation, the latest Jurassic marine deposit in the Qiangtang Block, is important not only because of its great hydrocarbon potential, but also because it defines the termination of the Jurassic ocean in the area. New ammonite evidence from the upper part of the Suowa Formation in the northwestern Qiangtang region allows us to revise the age of the formation previously regarded as late Jurassic due to the absence of time-diagnostic fossils. Newly collected ammonites include Gracilisphinctes suprapanatinus (Arkell), Oxycerites orbis (Giebel), Macrocephalites (Macrocephalites) madagascariensis Lemoine, Macrocephalites compressus (Quenstedt), Nothocephalites semilaevis (Waagen) [M], Nothocephalites asaphus Spath [m], Eucycloceras cf. cogginbrowni Spath, Choffatia (Subgrossouvria) recuperoi (Gemmellaro) and Choffatia cf. sakutala Spath. Correlation with the biostratigraphical framework based on ammonites from Kachchh, western India, places the age of the Suowa Formation as Middle Bathonian to Early Middle Callovian. An unconformity and depositional break between the Suowa Formation and the overlying Lower Cretaceous Xueshan Formation is proposed. Characteristic ammonite-taxa of Kachchh appearing in the northwestern Qiangtang area document significant dispersal from the Indo-Malgach Province to the northern margin of eastern Tethys region for the first time.

A correlation between the Large Igneous Provinces and mass extinctions: constraint on the end-Guadalupian mass extinction and the Emeishan LIP in South China, eastern Tethys

ABSTRACTWell-documented outcrops around the Emeishan Large Igneous Province (ELIP) in South China, eastern Tethys, encompassing the end-Guadalupian mass extinction have been investigated. Correlatable sections recording the event exhibit very similar lithological characters, positive-then-negative C isotope excursions and massive biotic demise. Detailed analyses of the fossil record and carbon isotopic variations were carried out on the Guadalupian–Wuchiapingian Boundary sections over the inner, middle, outer zones of the ELIP and its margin. Due to a pronounced decrease in marine habitat area and the environmental and ecological change over this part of the Tethys, the biota crisis records show the loss of numerous tropical invertebrate taxa, and exhibit fewer genera and smaller testing sizes and low productivity. The biota crisis was a sustainable and gradual reduction in diversity over the Capitanian. The associated carbon isotopic data reveal unusually high δ13C(carb) values before the late Capitanian, representing higher primary productivity (or buried rate) and more 13C-enriched CO2 released by hydrothermal carbonate breakdown from the upper crust into the sediments at that time. Subsequently, an accelerated negative excursion across the boundary and the gradual excursion with low carbon isotope amplitude favours an increased influx of light 12C sourced by the volcanism around the eastern Tethys. The very similar time–space relation between the biota crisis and the Emeishan volcanism confirms that volcanic eruptions may have triggered the biota crisis event in South China. Intensive volcanism could result in detrimental environmental and ecological stresses, habitat loss, organic material splitting, or the emission of light carbon and thermal fluid (or aerosol), implying that the losses of the shallow-marine invertebrates either occurred geologically instantaneously or in a series of closely spaced crises coinciding with the initial phase of ELIP formation. These findings in South China may reveal the causal relation between mass extinctions and LIPs in a global context.