Late Jurassic Early Research Articles

Tectonic Evolution of Tuvinian Trough (Northern Part of Central Asian Orogenic Belt): Synthesis of Geological Data and Results of Feldspar Ar‒Ar Dating

The Tuvinian rift trough, located in the northern part of the Central Asian orogenic belt (CAOB), was formed in the Early Devonian on late Proterozoic (?)‒Early Paleozoic terranes as a result of the activity of the Altai-Sayan mantle plume. The sedimentary record from the middle Paleozoic to the middle Mesozoic, preserved in the Tuvinian trough, and the middle Paleozoic igneous complexes confined to the structures of the trough, reflect the stages of evolution of the Earth’s crust in the Tuva segment, that necessary for understanding the history of the geological development of the CAOB as a whole. Dating of accessory and rock-forming minerals from igneous rocks using low-temperature geochronology methods allows us to obtain additional information about post-magmatic processes and thereby update the model of tectonic evolution of the region. In this study, we have reconstructed the stages of tectonic development of the Tuvinian trough in the northern part of the CAOB based on the analysis of geological data and new Ar‒Ar dating data on feldspars from mafic intrusions. As a result of this study, the chronology of the previously known stages of post-magmatic processes manifested in the Tuvinian trough was clarified, and new stages were identified according to the tectonic evolution of the CAOB. Ar‒Ar dating of feldspars carried out on eight samples showed four age groups: (i) Late Devonian, (ii) middle Carboniferous, (iii) early Permian and (iv) Early Jurassic. Late Devonian (~377 and 375 Ma) ages record an impulse of mafic magmatism, widely manifested in the northern segments of the CAOB (~380‒365 Ma). Middle Carboniferous (~320 and 319 Ma) dates may be associated with the closure of the Ob-Zaisan branch of the Paleo-Asian ocean as a result of the Kazakhstan-Siberian collision. Early Permian (~290–279 Ma) ages are consistent with the formation of late Carboniferous–Early Permian (~305–275 Ma) large igneous provinces in connection with rifting processes in the northern segments of the CAOB. Finally, a single Early Jurassic (~188 Ma) age marks tectonic reorganization of the CAOB in Late Triassic‒Early Jurassic in response to (i) closure of the Paleotethys ocean with subsequent collision of the Cimmerian blocks and the southern margin of the Eurasian continent and/or (ii) activity of the Mongolian mantle plume.

New Chinese Jurassic damsel-dragonflies of the families Paragonophlebiidae, Selenothemistidae and Isophlebiidae (Odonata, Epiproctophora) from the Jurassic Ordos Basin of NW China

The Jurassic damsel-dragonfly family Paragonophlebiidae was till now monogeneric, with the sole genus Paragonophlebia and the two species P. inexpectata and P. patriciae, from the Middle Jurassic of Central Asia. Here we describe the new genus and species Sinagonophlebia yananensis Nel and Huang, from the Middle Jurassic of China, and we attribute the late Triassic and early Jurassic Diastatommites liassina (Strickland, 1840) from UK to the same family. We restore it in the genus Diastatommites Tillyard, 1925. We also describe the selenothemistid Yananthemis zaoyuanensis Nel and Huang, nov. gen., nov. sp., plus an isophlebiid gen. et sp. indet. from the same outcrop. These three damsel-dragonflies increase our knowledge on the already impressive diversity of the Odonata from the Mesozoic of China.

Influence of climate and marine transgression on Mesozoic–Cenozoic diagenesis of clastic rocks in the Tabei Uplift, Tarim Basin, China

The Mesozoic–Cenozoic clastic rocks in the Tabei Uplift form one of the most hydrocarbon-rich zones in the Tarim Basin of China. Understanding how diagenesis has affected the petrophysical properties of the sandstone is crucial for developing regional exploration strategies. Although most studies have investigated the physical conditions during sedimentation and chemical processes during diagenesis, the hydrochemical environment during sedimentation and subsequent diagenesis has received little attention. This study employed petrographic observations, paleo-geothermal reconstructions, and paleoenvironmental analysis to constrain the regional climatic conditions, hydrochemical environment of deposition, and diagenetic features of clastic rocks in the Tabei Uplift. The sandstone at depths of 3500–6000 m is located mainly in the A phase of the middle diagenetic stage, and exhibits three types of diagenesis. Triassic–Jurassic sandstones are dominated by silica, kaolinite, and chlorite cements, Cretaceous sandstones by mainly carbonate cements, and Paleogene sandstones by carbonate and evaporite cements. These diagenetic stages correspond to paleoclimatic changes during the earliest Late Jurassic and the maximum marine transgressions of the Proto-Tethys during the Paleogene, thereby highlighting the influence of climatic change and transgressions on the water conditions during deposition and the type of diagenesis.

Genesis of the Ulaan silver-lead–zinc deposit in Northeast Mongolia: Constraints from S and Pb isotopes, together with U-Pb and Rb-Sr geochronology

The Ulaan silver-lead–zinc deposit (hereinafter referred to as the Ulaan deposit) is identified as the largest silver-lead–zinc polymetallic deposit in Mongolia, with proved reserves including 2,240 tons of silver (Ag; average grade: 49 g/t), 440,000 tons of lead (Pb; average grade: 1.13 %), and 810,000 tons of zinc (Zn; average grade: 2.07 %). However, the genesis of this deposit remains unclear. The Ag-Pb-Zn ore bodies in the deposit, occurring as cylinders in shape within the Middle-Late Jurassic rhyolites, are governed by a concealed breccia pipe. The ore minerals include galena, sphalerite, and pyrite, followed by chalcopyrite, hematite, stibnite, and siderite. The primary alterations of the surrounding rocks include silicification, chloritization, kaolinization, argillization, carbonatization, and skarnization. The Rb-Sr dating of sulfide minerals and associated vein minerals in the ores yielded isochron ages varying in a range of 146 ± 3 Ma (n = 6, MSWD=1.3), suggesting mineralization during the Late Jurassic. The δ34S values of sulfide minerals in the ores range from 1.6 ‰ to 4.3 ‰, suggesting that the sulfur originated primarily from magmas or deep sources. The isotopic compositions of coexisting sphalerite-galena minerals in the deposit revealed mineralization temperature estimates ranging between 331 °C and 449 °C, indicating a medium- to high-temperature ore-forming conditions. The sulfide minerals exhibit 208Pb/204Pb ratios ranging from 38.138 to 38.301, 207Pb/204Pb ratios from 15.543 to 15.594, and 206Pb/204Pb ratios from 18.318 to 18.354, suggesting that ore-forming metals, represented by Pb, also originated primarily from mantle source. The zircon U-Pb dating of rhyolites in the ore-hosting strata and ore-controlling breccia pipes yielded ages of 160.6 ± 1.7 Ma (n = 24, MSWD=0.68) and 161.6 ± 1.6 Ma (n = 30, MSWD=0.89), respectively, indicating volcanic eruptions during the early Late Jurassic. These ore-hosting rhyolites exhibit characteristics of A-type rhyolites, suggesting that they were formed in an intracontinental extensional environment. These rhyolites share similar rare earth element (REE) distribution patterns with fluorite formed in the main mineralization stage, suggesting a genetic link between the mineralization and magmatic processes. This study proposes that the Ulaan deposit was a hydrothermal deposit formed in an extensional environment following the closure of the Mongol-Okhotsk Ocean, with ore-forming metals and hydrothermal fluids associated with volcanic rocks or magmatic-hydrothermal processes.

New Age Constraints of the Bilong Co Oil Shale in the Qiangtang Basin, Northern Tibet: Evidence from In Situ U–Pb Dating and Palaeontology

The Bilong Co oil shale is one of the most significant source rocks in the Mesozoic Qiangtang Basin (Northern Tibet); however, its absolute chronology remains controversial. In this study, in situ carbonate U–Pb isotope dating analysis was carried out for the first time. Detailed field geological investigations yielded some age-diagnostic ammonites, enabling a re-evaluation of the stratigraphic age of the Bilong Co oil shale. A total of 61 spots of U–Pb isotope dating from the middle part of the Bilong Co oil shale section suggests an average age of 181 ± 13 Ma. Elemental geochemistry and diagenetic analysis indicate that the proposed age represents the early deposition of the calcite, and the oil shale was deposited during the Early Jurassic time. This estimated age is further supported by the newly discovered ammonite assemblage of Hildoceratidae–Tiltoniceras sp. at the top part of the oil shale section, which confirms the deposition of the oil shale during the Toarcian age of the late Early Jurassic. Consequently, the Bilong Co oil shale can be assigned to the Quse Formation, which is attributed to the Lower Jurassic rather than the Middle Jurassic. The re-assessment of the stratigraphic age of the Bilong Co oil shale is of great significance for regional evaluation and exploration activities of hydrocarbon source rock layers in the Qiangtang Basin as well as for global stratigraphic correlation of the late Early Jurassic Toarcian oceanic anoxic event.

Dolomitization of the Lower Part of the Sargelu Formation, Northeastern Iraq

The prominent characteristic of the lower part of the Sargelu Formation of the Middle Jurassic is the occurrence of destructive dolomitization. This dolomitized unit, cropped out in the high folded and Imbricated zones in Northern Iraq, is situated in the Gotnia Basin and has been distinctly identified and are documented in previous studies. Dolomite crystals are euhedral in shape; hence, they are classified as saccharoidal dolomite, resulting in the elimination of all biocontent and the destruction of the original rock fabrics. Despite the abundance of intercrystalline pores in this unit and their role in the quality of reservoirs in the oil fields, the origin or mechanism of dolomitization is not well understood yet. The aim of this investigation is to find out a suitable model for the dolomitization and to propose possible mechanisms that led to the dolomitization. At the top of the Lower Jurassic Sehkaniyan Formation, an extensive mass of destructive dolomitization has also occurred. The dolomitic unit of the Sargelu Formation, which extends for hundred kilometers constantly. Stratigraphic correlation reveals that the Sargelu Formation is juxtaposed with different successions, such as the Alan and Sehkaniyan formations, that show evidence about peritidal and sabkha environments, where the dolomitization units were associated with solution collapse breccia and microbial stromatolite. This study proposes that the reflux and burial dolomitization models for the lower part of the Sargelu Formation by comparing the paleoenvironmental conditions of the late Lower Jurassic and early Middle Jurassic in the Gotnia basin with a modern analogue model.

New stratigraphic and palaeontological data from carbonates related to the Vourinos–Pindos ophiolite emplacement: implications for the provenance of the ophiolites (Hellenides)

Microfacies analysis and conodont dating on carbonates associated with the Vourinos–Pindos ophiolite emplacement on the Pelagonian unit in northern Greece, combined with structural analysis, enhance our understanding of the palaeogeography and geotectonic evolution of the Hellenides. We focus on a dismembered Triassic Hallstatt Limestone succession incorporated as blocks in the Middle–Late Jurassic Avdella ophiolitic mélange, which is identical to a Triassic succession in the western Pindos (Hallstatt–Pindos succession). Initially, the Hallstatt–Pindos succession was deposited on the outer shelf along the eastern Pelagonian margin and later incorporated into the mélange during west-directed obduction processes. During the Middle to early Late Jurassic, ophiolites were obducted on the eastern Pelagonian margin, resulting in a nappe stack in front of the ophiolites in the lower plate position. Newly formed trench-like basins in front of the advancing nappe stack became filled with sedimentary mélanges, consisting of ophiolitic material mixed with blocks from the Hallstatt–Pindos succession, deposited in an outer shelf position. Subsequently, the Pindos ophiolites overthrust their foreland basin, forming a typical ophiolitic mélange (Avdella mélange). Consequently, the Triassic–Middle Jurassic Hallstatt–Pindos succession represents a far-travelled Middle–Late Jurassic nappe derived from east of the Pelagonian unit, which was bulldozed westward in front of the west-directed obducting Neotethys ophiolites. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

Substrate control in track registration and preservation: insights across the Triassic–Jurassic boundary in southern Africa

Tracks registration is influenced by the dynamic interplay between the pedal anatomy of the trackmaker, its behaviour, and the substrate conditions it interacts with. Differences in substrate conditions, especially those linked to grain size and moisture content, often result in the most dramatic variations in track morphology. In the upper Stormberg Group, main Karoo Basin of southern Africa, diverse trace fossils, primarily comprising Late Triassic–Early Jurassic dinosaur tracks, are preserved. Numerous studies have extensively documented individual ichnosites, investigating variations between sites over time, with recent studies suggesting that track abundance and anatomical fidelity increase up-stratigraphy. Despite the well-established link between substrate and track morphology, past studies have not specifically focused on substrate conditions, often emphasizing macro-sedimentary features instead. Here, we examine the micro-sedimentary features of track-bearing units in the upper Stormberg Group using petrographic techniques to better understand the palaeosubstrate and its effect on fossil track registration and preservation. The analysis revealed that very fine-grained sandstones and substrates modified by microbial activity tend to preserve tracks with greater abundance and/or higher anatomical fidelity. Furthermore, the prevalence of very fine-grained and microbially modified strata, and their associated track trends increases in younger stratigraphic units. Across the Triassic – Jurassic boundary in southern Africa, a boom in dinosaur track abundances is observed and credited to the proliferation of dinosaur populations during the Early Jurassic. Our findings, however, suggest that the observed local increase in track abundance (and anatomical fidelity) up-stratigraphy may be linked to substrate composition differences, which were ultimately controlled by large-scale changes in the palaeoenvironment from high-energy meandering fluvial to lower-energy aeolian-lacustrine settings in the Late Triassic and Early Jurassic, respectively. These findings have implications for global macroevolutionary patterns, palaeo-geographical reconstructions, and biostratigraphic correlations in the early Mesozoic.

Sedimentary infill of Early-Middle Jurassic in the southeastern Tarim Basin and its constraints on the evolution of the Altyn Tagh Fault in the Northeast Tibet Plateau

The Altyn Tagh Fault (ATF) is the boundary between the Tarim Basin and the Tibetan Plateau, which is crucial for the tectonic evolution and uplift of the Tibetan Plateau. However, the Mesozoic tectonic evolution of the ATF remains controversial. This study reconstructed the Early-Middle Jurassic palaeogeographic pattern of the southeast depression of the Tarim Basin (SDTB) and revealed potential source-sink relationships between the SDTB and its adjacent mountains to constrain the Mesozoic tectonic evolution of the ATF based on sedimentology and provenance analyses. The results indicated that the SDTB was infilled with alluvial fan facies during the Early Jurassic and the late Early Jurassic, giving rise to the braided-river delta to lacustrine facies. During the Middle Jurassic, the lacustrine basin expanded with the wide development of lacustrine facies, and the lacustrine basin contracted and was primarily infilled with braided delta facies in the late Middle Jurassic. The Jurassic sedimentary center, the SDTB situated in front of the Altyn Tagh Mountain and East Kunlun Mountain, played a crucial role in the development of three types of hydrocarbon source rocks: charcoal mudstone, coal beds, and dark mudstone. Combined with seismic reflection data interpretations, the Early Jurassic the STDB is a rift basin that underwent a rift-depression transition in the late Early Jurassic, solidifying the characteristics of the depression basin in the Middle Jurassic. The extensional environment in the SDTB resulted from the tectonic effects of slab break-off following the closure of the Tethys Ocean and the spreading of the distal stress field of the Bangonghu–Nujiang Ocean. The analyses of gravel component and heavy mineral indicated that the Jurassic source of the basin was traced back to the ancestral Altyn Mountains, the East Kunlun Mountains, and the internal palaeo-uplift of the basin, which demonstrated that the SDTB and Western Qaidam Basin (WQB) shared a common lacustrine basin during the Jurassic, suggesting that the ATF did not initiate strike-slip movements during this period. This study significantly enhanced our understanding of the Mesozoic tectonic evolution in Northwest China, providing valuable insights into exploring Mesozoic oil-bearing basins in the northern Tibetan Plateau. Furthermore, it served as a useful reference for constraining the timing of the initial slip of similar plate boundary strike-slip faults.

The rise of macropredatory pliosaurids near the Early-Middle Jurassic transition

The emergence of gigantic pliosaurid plesiosaurs reshaped the trophic structure of Mesozoic marine ecosystems, and established an ~ 80 million-year (Ma) dynasty of macropredatory marine reptiles. However, the timescale of their ‘defining’ trait evolution is incompletely understood because the fossil record of gigantic pliosaurids is scarce prior to the late-Middle Jurassic (Callovian), ~ 165.3 Ma. Here, we pinpoint the appearance of large body size and robust dentitions to early-Middle Jurassic (Bajocian) pliosaurids from northeastern France and Switzerland. These specimens include a new genus that sheds light on the nascent diversification of macropredatory pliosaurids occurring shortly after the Early-Middle Jurassic transition, around ~ 171 Ma. Furthermore, our multivariate assessment of dental character states shows that the first gigantic pliosaurids occupied different morphospace from coeval large-bodied rhomaleosaurid plesiosaurs, which were dominant in the Early Jurassic but declined during the mid-Jurassic, possibly facilitating the radiation and subsequent ecomorph acme of pliosaurids. Finally, we posit that while the emergence of macropredatory pliosaurids was apparently coordinated with regional faunal turnover in the epeiric basins of Europe, it paralleled a globally protracted extinction of other higher trophic-level marine reptiles that was not completed until after the earliest-Late Jurassic, ~ 161.5 Ma.

Finding the world’s oldest mammals: sieving, dialectical materialism, and squabbles

Abstract Mammals (or properly, mammaliaforms) originated in the Late Triassic and the first 50 Myr of their evolution through Late Triassic and Early Jurassic are best documented by rich faunas from numerous localities around Bristol in south-west England and in South Wales. The mode of preservation of the fossils, in sediment washed into karst features such as caves, is unusual but has led to a demand for specialized processing methods to extract the exquisitely preserved tiny teeth and bones from huge volumes of sediment. This rich documentation of the oldest mammals has made them especially important for mammalian palaeobiology on a global scale. The first specimens were found in the 1860s, and collection and study has been sporadic, with especially fruitful times in the 1860s, and then from 1938–1979. Throughout, the field collecting, processing, and interpretation of the fossils has been fraught, with heated debates between leading protagonists during the second half of the past century. Here, we track the substantial contributions made by Charles Moore, Walter Kühne, Rex Parrington, Kenneth Kermack, Pamela Robinson, and others, using published sources, unpublished letters and notebooks, and interviews, to establish some of the facts about the most heated public disputes.

The First Record of a Representative of the Toarcian–Early Aalenian Belemnites in Kimberlites of the Obnazhennaya Pipe (Northeastern Siberian Platform)

A rostrum fragment of a representative of the Toarcian–Early Aalenian (the latest Early Jurassic–the earliest Middle Jurassic) belemnites Arcobelus cf. krimholzi (Sachs, 1970) was found for the first time in kimberlites of the Obnazhennaya pipe of the Kuoika kimberlite field (northeastern Siberian Platform, Olenek Uplift). It was shown that the belemnite records previously known here and dated to the Late Jurassic or Early Cretaceous may be of Bajocian–Bathonian (Middle Jurassic) age. The stage of kimberlite magmatism of 177 ± 1.5 Ma, recently established in the northeastern part of the Siberian craton according to U–Pb geochronological data, falls on the time of the existence of belemnites of the genus Arcobelus. The estimated Late Bajocian–Early Bathonian age of the representative of the genus Pachyteuthis, previously found in kimberlites of the Obnazhennaya pipe, is consistent with the 40Ar/39Ar age (167 Ma), as well as with the age based on some paleomagnetic data (168 ± 11 Ma) reported for the pipe. Taking into consideration the new data on belemnites, the internal part of the shelf should be extended to the territory of the Kuoika kimberlite field in the paleogeographic schemes of the northeastern part of the Siberian Platform during the Toarcian–Early Bathonian.

Geological and chronostratigraphic overview of the Upper Triassic and Jurassic successions of the Junggar Basin, NW China

Abstract The vast, widely exposed terrestrial (lacustrine to fluvial) Upper Triassic–Jurassic (except Tithonian) successions of the Junggar Basin not only record most of the stratigraphic boundaries of the Upper Triassic and Jurassic, including the Triassic–Jurassic boundary and the Hettangian–Sinemurian, Sinemurian–Pliensbachian, Pliensbachian–Toarcian, Lower–Middle Jurassic, Middle–Upper Jurassic and Oxfordian–Kimmeridgian boundaries, but also record a range of geological, organic, palaeogeographic and palaeoclimatic events known to have happened globally in the Late Triassic and Jurassic. The Triassic–Jurassic boundary is placed in the stratigraphic interval of the first occurrence of Retitriletes austroclavatidites and Callialasporites dampieri and the last occurrence of Lunatisporites rhaeticus . The end-Triassic mass extinction is characterized by the disappearance of most of the sporomorph and macro-plant taxa. The end-Triassic mass extinction occurred before the first occurrence of the sporomorph Cerebropollenites thiergartii , and ended after its appearance when life began to revive. The Junggar Basin was situated at a high latitude during the Late Triassic–Early Jurassic Pliensbachian ‘hothouse’ and ‘greenhouse’ periods. The Late Triassic–Mid Jurassic Bajocian was humid and warm, and rich in coal swamps, except the Toarcian, which yields little coal because it was relatively warmer and drier. It became arid from the early Late Jurassic Oxfordian.

Geochronology, Eruption Sequence and Geochemistry of Mid–Late Jurassic Volcanics South of Manzhouli: Petrogenesis and Implications for Mesozoic Tectonic Regime Transformation

AbstractTo the south of Manzhouli, Hulunbuir, Inner Mongolia, experienced a tectonic regime transformation from compression to extension in the mid‐Mesozoic. Based on systematic research of the volcanics, petrology, volcanic facies, chronology and geochemistry of rocks in the Buridun area, two stages of volcanics are identified. The first stage named the trachyte series was formed in the late Middle Jurassic (167–163 Ma), its eruption rhythm is pyroxene trachyandesite–trachyandesite–trachyte, and its origin rock is basic volcanics from thickened lower crust, with a tectonic setting in the collision orogeny after the closure of the Mongolia Okhotsk Ocean (MOO). The second stage is a bimodal volcanic rock, formed in the early Late Jurassic (163–160 Ma). The eruption rhythm of basic volcanics in this stage is basaltic andesite–basalt–olivine basalt, which comes from the metasomatized lithospheric mantle, the acidic volcanics of which being characterized by the eruption rhythm of sedimentary‐explosive‐overflow facies, which came from the partial melting of newly formed lower crust, and this shows the characteristics of A‐type granite; the tectonic setting is extension of the lithosphere after collision and closure of the MOO. The changes in the formation age and tectonic setting of the two stages of volcanics demonstrate that the transition time from the compressive system to the extensional system south of Manzhouli is about 163 Ma.

Paleozoic and Mesozoic magmatism in the Gaodi porphyry Mo-Cu deposit: Implications for the evolution of the Mongol-Okhotsk Ocean in the northern Great Xing'an Range, NE China

The newly discovered "460 Gaodi porphyry Mo–Cu deposit" (with Re-Os age of 179.6 ± 3.6 Ma) is located 30 km west of Hanjiayuanzi town in the northern Great Xing’an Range (GXR), NE China. The intrusive rocks in the deposit area can be classified into four periods: (1) Early Ordovician, which includes a high-K calc-alkaline monzodiorite (480 Ma) indicating significant crustal contamination, and a “syntectic” I-type granodiorite (479 Ma) with low Mg# values (34–38) and εHf(t) values (−4.4 to +0.9) show mixing of mantle-crust derived materials, which is related to post-orogenic event between the Ergun and Xing’an blocks; (2) Late Triassic, which includes an adakitic granodiorite porphyry (220 Ma) related to partial melting of the lower part of a thickened crust (C-type adakitic) with low Na2O/K2O ratio (1.27–1.49), Cr and Ni contents, with εHf(t) values of −0.7 to +3.3; (3) early Early Jurassic, which includes a differentiated I-type monzogranite (198 Ma) and syenogranite (196 Ma) with negative Eu anomaly (0.06–0.74), low Mg# (9–37) and high Rb/Sr (0.84–5.07). The εHf(t) values of them are −3.3 to 1.8 and −3.0 to +2.3, respectively, indicating the same source areas originated from partial melting of juvenile lower crust; (4) late Early Jurassic, which includes an ore-related C-type adakitic granite porphyry (182 Ma) with relative low Mg# (36–38), and low Na2O/K2O (0.65–0.81), strongly peraluminous quartz porphyry (181 Ma) with highly differentiated characteristics, and post-collisional gabbroic diorite (180 Ma). The ore-related granite porphyry yields εHf(t) values ranging from −4.1 to −0.4, suggesting partial melting of juvenile lower crust. The 460 Gaodi deposit formed in a late-collisional setting related to the Mongol-Okhotsk Ocean system. A post-collisional stage about 182 to 163 Ma immediately following the main collision is proposed.

Paleogeographic and tectonic evolution of Mesozoic Qiangtang basins (Tibet)

Reconstructing the Mesozoic paleotectonic and paleogeographic evolution of marine Qiangtang basins is essential for understanding the evolution of diverse Tethyan oceanic seaways and pre-Cenozoic mountain building in the Tibetan Plateau, with significant implications for hydrocarbon exploration. The geological knowledge of these basins is, however, largely incomplete. Here we illustrate new geological mapping, stratigraphic, structural, sedimentological, and provenance data collected along a >40-km-long, well exposed cross-section of the Biluoco fold-thrust belt in South Qiangtang, together with a compilation of regional data from the Qiangtang, Amdo, and Hoh-Xil terranes. We also provide refined biostratigraphy and chronostratigraphy of the exposed successions in the Biluoco type area. Newly achieved information indicates that the North Qiangtang and South Qiangtang basins evolved independently during the Mesozoic. The South Qiangtang basin started to subside by the Late Triassic and closed by the Late Jurassic. In contrast, sedimentation in the North Qiangtang basin commenced in the latest Early Jurassic and ended in the latest Jurassic. The Qiangtang basins received sediments from volcanic rocks exposed in the central Qiangtang and Hoh-Xil terranes since the Late Triassic, whereas Paleozoic strata in the Central Qiangtang mountain range were the primary source of detritus for the North Qiangtang basin in the early Middle Jurassic and for South Qiangtang basin in the Late Triassic and Middle Jurassic. Middle to Late Triassic volcanism and convergence associated with the closure of Paleo-Tethys within the Hoh-Xil and central Qiangtang terranes resulted in the topographic uplift of the central and northern Qiangtang regions. The Jurassic development of Qiangtang basins and their final inversion were controlled by the dynamics of the northward-subducting Bangong-Nujiang oceanic slab, microcontinent accretion to South Qiangtang, and Lhasa/Qiangtang collision.

Late Triassic (Late Early to Early Middle Norian) and Late Triassic or Early Jurassic Radiolarians from Limestone in the Tha Sao Area, Kanchanaburi Province, Western Thailand: Low-Latitude Fauna in the Eastern Tethys

Moderately-preserved Late Triassic (late early to early middle Norian) and Late Triassic or Early Jurassic radiolarians have been identified from two sections of limestone and dolomitic limestone, respectively in the Tha Sao area, Kanchanaburi Province in western Thailand. Previously these limestones have been assigned as the Permian because of the similarity of lithology without any fossil evidence. Section 1 is a succession of about 18 m in thickness, consisting of calcareous mudstone, micritic limestone, and dolomitic limestone, in ascending order. Section 2 is about 30 m in thickness and consisting of dolomitic limestone. Middle micritic limestone of about 10 m thick of Section 1 yielded diversified radiolarians. Dolomitic limestone of Section 2 yielded rare radiolarians from two levels. We identified radiolarians from five levels of micritic limestone and two levels of dolomitic limestone and totally identified 53 species belonging to 39 genera including two species of which generic position is uncertain and one new species Colum tekini Sashida and Ito sp. nov. At the Late Triassic time, the Tethys Ocean between Sibumasu and Indochina blocks almost closed due to the collision of these two continental blocks. Upper Triassic radiolarian-bearing limestones have been deposited in the eastern to western Tethyan areas within 35° of both hemispheres. The present radiolarian fauna is representative of low latitude Tethyan fauna. The faunal similarity between the eastern and western Tethys indicates the uniformity of the establishment of the low latitude fauna by the Late Triassic.

The early evolution of the Neotethys in the eastern Mediterranean area: implication of new evidence from the Levant basin and margin

Analysis and re-evaluation of recently obtained data from seismic reflection surveys and deep offshore and onland boreholes from the continental margin of Israel and the adjacent Levant basin, combined with pre-existing data, provide significant new insight into their early, Triassic to Middle Jurassic, development. Thick Middle Jurassic and older sediments in the Levant basin next to Israel cover a substantial relief of a pre-existing thin crust that was shaped in the Middle Triassic or earlier times. In the Levant margin near the present-day coastal area and further onshore the early development of the basin was accompanied by two major deformation phases, in the Triassic and in the Middle Jurassic, separated by a period (much of the Late Triassic and Early Jurassic) in which deformation and subsidence slowed down considerably or ceased. In contrast, in the Mt Carmel area conspicuous faulting and magmatism took place in the Late Triassic (older history unknown); that is, during the period of tectonic quiescence farther south, implying significantly different evolution of this and the more southern parts of the margin. Few Triassic igneous rocks are known onshore Israel, but widespread Late Triassic submarine volcanic rocks, associated with deep-marine sediments, were documented in the remnants of the northern extension of the Levant basin in the present-day area of Turkey and Cyprus, which probably represent the same regional tectonic phase. Renewed subsidence of the Levant margin and adjacent lands since the late part of the Early Jurassic was associated with renewed faulting along the Levant margin and in the adjacent lands, involving significant changes in the deformation pattern. A Middle Jurassic continental slope, >1 km high from top to base, developed along the Levant margin and deep-water conditions in the adjacent basin were established. This configuration is expected to have existed also in earlier times, in association with the formation of the basin's thin crust next to the much thicker crust beneath the bordering continental area, but evidence for the earlier depositional history is limited by the lack of deep seismic and well data. In view of the extensive evidence presented here, a Cretaceous age for the formation of the Levant basin and margin that was recently suggested appears to be unlikely.

Petrogenesis of Early Mesozoic volcanic rocks in southeastern NE China: Geochemical and Sr–Nd–Pb–O isotopic evidences

This paper reports a study of whole-rock geochemical, Sr–Nd–Pb isotopic compositions and zircon UPb ages and O isotopic compositions of Late Triassic to Early Jurassic volcanic rocks of the Yanbian–Dongning area, northeastern China. The obtained data are used to constrain the petrogenesis of these rocks and to provide new insights into the timing of transition from the Paleo-Asian to the Paleo-Pacific tectonic regime. The studied Late Triassic to Early Jurassic volcanic rocks can be divided into two periods: Late Triassic–early Early Jurassic (212–198 Ma) and late Early Jurassic (ca. 181 Ma). The former rocks display high SiO2 and total alkalis contents, high Ga/Al ratios, depleted SrNd and highly radiogenic Pb isotopic signatures, and low zircon δ18O values. The former rocks have a genetic relationship with coeval intrusions, and their primitive melt was derived from juvenile crustal materials and underwent subsequent differentiation and assimilation of low-δ18O rocks. In contrast, the latter rocks have SiO2 contents of 49.00–63.30 wt%, are classified as calc-alkaline, and display arc-type trace-element features. Their geochemical and Sr–Nd–Pb–O isotopic compositions imply derivation from the partial melting of depleted mantle wedge metasomatized by oceanic slab-derived fluid and sediment melt. Combining these new results with published data, the Late Triassic–early Early Jurassic volcanic rocks are inferred to have formed in a rift-like extensional setting, whereas the late Early Jurassic volcanic rocks were generated in a subduction-related setting. The transition from the Paleo-Asian to the Paleo-Pacific tectonic regime occurred during the Early Jurassic.

A new model for the segmentation, propagation and linkage of the Tan-Lu fault zone, East Asia

• The Tan-Lu Fault formed by coalescence of two kinematically independent segments. • The northern and southern Tan-Lu faults exhibit contrasting displacement profiles. • The northern and southern Tan-Lu faults propagated in opposite directions. • Southward indentation of the Siberian craton initiated the northern Tan-Lu Fault. • The northern and southern Tan-Lu faults linked in the early Late Jurassic. The Tan-Lu fault zone (TLF) is a major strike-slip fault with a long and complex history in East Asia, whose evolution provides a new perspective on the formation of large-scale faults (>1000 km long). Fault displacement analysis, geological mapping and U-Pb LA-ICP-MS dating have been performed to understand the evolution of the TLF. Along-strike displacement variation reveals that the TLF consists of two kinematically independent segments, the northern and southern TLF, with opposite long-term propagation directions. Structural and geochronological studies in the eastern Yanshan belt, located around the linkage area of the southern and northern TLF, indicates that NNE-trending sinistral strike-slip faults initiated at 167-164 Ma and were reactivated at 124-121 Ma. Structural analysis suggests that these early NNE-trending strike-slip faults transferred sinistral motion along the northern TLF into southward thrusting along the Yanshan belt, representing the Middle Jurassic southern termination of the northern TLF. Our studies suggest that the through-going TLF formed when the younger southward-propagating northern TLF merged with the older northward-propagating southern TLF in the Late Jurassic. A new model is thus proposed for the Mesozoic evolution of the TLF. The initiation and southward propagation of the northern TLF is interpreted to have resulted from the southward indentation of the Siberian craton into the amalgamated Central Asian Orogenic Belt and North China block. The divergent mega-splays of the northern TLF likely resulted from westward-younging formation during the clockwise rotation of northeast Asia. Coalescence of two genetically unrelated faults could be an alternative mode for large-scale fault formation.