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The India-Asia collision is an outstanding smoking gun in the study of continental collision dynamics. How and when the continental collision occurred remains a long-standing controversy. Here we present two new paleomagnetic data sets from rocks deposited on the distal part of the Indian passive margin, which indicate that the Tethyan Himalaya terrane was situated at a paleolatitude of ∼19.4°S at ∼75 Ma and moved rapidly northward to reach a paleolatitude of ∼13.7°N at ∼61 Ma. This implies that the Tethyan Himalaya terrane rifted from India after ∼75 Ma, generating the North India Sea. We document a new two-stage continental collision, first at ∼61 Ma between the Lhasa and Tethyan Himalaya terranes, and subsequently at ∼53−48 Ma between the Tethyan Himalaya terrane and India, diachronously closing the North India Sea from west to east. Our scenario matches the history of India-Asia convergence rates and reconciles multiple lines of geologic evidence for the collision. [ABSTRACT FROM AUTHOR]

Mesozoic oceanic anoxic events were characterized by relatively low seawater sulphate concentrations ([SO42−$$ {{\mathrm{SO}}_4}^{2-} $$]), which likely regulated the development and evolution of these major palaeoceanographic phenomena. However, there is little reliable sedimentary evidence for low [SO42−$$ {{\mathrm{SO}}_4}^{2-} $$] in ancient marine waters and understanding of how such a seawater chemistry potentially impacted oceanic anoxic events is limited. This study presents an integrated sedimentological, mineralogical and geochemical investigation of the mineral siderite hosted in dark grey shale and sideritic concretions of Early Aptian (coeval with Oceanic Anoxic Event 1a) from the Tibetan Himalaya. Siderite is present throughout the section and possesses similar morphological characteristics whether in dark grey shale or concretions. Siderite can be present as disseminated and rhombic crystals formed during early diagenesis, or minor spherical crystals formed during late diagenesis. The evidence from redox elements, middle rare‐earth element bulge patterns and extremely low carbon‐isotope values of the sideritic concretions indicates that the iron carbonate was formed in the Fe‐reduction zones by the process of dissimilatory iron reduction. This process would have required conditions of low [SO42−$$ {{\mathrm{SO}}_4}^{2-} $$], reducing environment, abundant iron and high alkalinity. Additionally, the coexistence of siderite and pyrite may indicate that dissimilatory iron reduction occurred close to the microbial sulphate reduction zone, with seawater [SO42−$$ {{\mathrm{SO}}_4}^{2-} $$] hovering around the tipping point at which pyrite could form once seawater sulphate increased. Such an increase during Oceanic Anoxic Event 1a could have resulted from basalt–seawater interaction and associated enhanced continental weathering, and/or hydrothermal activity. This study's observations support the previous hypothesis that low [SO42−$$ {{\mathrm{SO}}_4}^{2-} $$] for Oceanic Anoxic Event 1a was probably caused by massive gypsum burial in the proto‐South Atlantic. Subsequently, enhanced sulphate input could have promoted microbial sulphate reduction and accompanying oxidation of organic matter, which likely further enhanced nutrient recycling, increased primary productivity and organic‐carbon burial, leading to more oxygen consumption and expansion of oxygen minimum zones, as reconstructed for many oceanic anoxic events. [ABSTRACT FROM AUTHOR]

The Neoproterozoic Jiangnan orogen plays an important role in the study of the Precambrian tectonic evolution of South China. The tectonic nature of the Neoproterozoic sedimentary basins is still controversial, due to poor understanding of the sedimentary sequences and the lack of geochronological data. Here, we present sedimentological, provenance and geochronological data from the Heshangzhen Group in the eastern Jiangnan orogen. Sedimentological analysis shows that the Luojiamen Formation was deposited in a submarine fan, and the overlying Hongchicun Formation was deposited in front of a fan delta. The youngest detrital zircons constrain the lower Luojiamen and Hongchicun formations with ages of 827.3 ± 8.4 Ma and 825 ± 12 Ma, respectively. The sandstones of the Luojiamen Formation are characterized by a large number of intermediate to felsic volcanic grains, suggesting a volcanic arc source. In contrast, quartz and sedimentary lithic grains increase in the Hongchicun Formation, showing a new input from a collisional orogenic source. Detrital zircon from six sandstone samples in the Luojiamen and Hongchicun formations yield similar age spectra of 930–820 Ma with a peak at ca. 845–860 Ma, with one main cluster at 930–820 Ma. Detrital zircons of 930–845 Ma show a positive value of ∊Hf (t) (+2.4 to +11, mean +7.6), which is similar to the volcanic arc of the nearby Shuangxiwu Group. There are a minor group of zircons with U‐Pb ages ranging from 820 Ma to 845 Ma from the middle part of the Luojiamen Formation and Hongchicun Formation, with ∊Hf (t) values between –20 to +2.4, which are consistent with the characteristics of the Shuangqiaoshan Group. within light of the bidirectional paleocurrents in the Luojiamen Formation, it is speculated that the zircons of 820–845 Ma were recycled from the Shuangqiaoshan Group, which is derived from a continental arc to the northwest. Our data suggests that the Luojiamen Formation was formed in an inter‐arc basin, while the Hongchicun Formation was formed in an accretionary wedge‐top basin. When juxtaposed with the conglomeratic characteristics at the bottom of the Luojiamen Formation, it is believed that the unconformity represented by the 'Shen Gong Movement' reflects the rapid erosion and accumulation process of island arc volcanic material. The disconformity between the Luojiamen and Hongchicun formations is the imprint of transition from inter‐arc basin to accretionary wedge‐top basin, which represents the collision between the Shuangxiwu arc and the Yangtze Plate. [ABSTRACT FROM AUTHOR]

Abstract The Mesozoic trench deposits in the Bangong-Nujiang suture zone in central Tibet can provide critical information for reconstructing the paleotectonic evolution of the Bangong-Nujiang Ocean and constraining the timing of the Lhasa-Qiangtang initial collision. In this paper, the Gamulong Formation, which is well exposed in the Dong Co area, western Bangong-Nujiang suture, central Tibet, was studied. The sedimentological analysis shows that the Gamulong Formation was deposited in a submarine fan environment. The youngest detrital zircon age and fossils from limestone pebbles within the Gamulong Formation combine to determine a Middle Jurassic age. The pebbles in the conglomerate are dominated by limestones and sandstones, which is consistent with the sandstone petrology showing limestone and sandstone fragments as the main framework components. Detrital zircon U-Pb ages from the sandstones yield age populations of 164–178 Ma, 200–500 Ma, 700–1000 Ma, 1700–2100 Ma and ~2500 Ma. The corresponding zircon ε Hf (t) values are distributed between −23.5 and +11.1. These zircon features are similar to those from the Qiangtang terrane. Accordingly, the provenance results imply that the Gamulong Formation was recycled from the accretionary complex (Mugagangri Group mélange) in the Bangong-Nujiang suture zone and the forearc basin deposits (Lower-Middle Jurassic Sewa/Shaqiaomu/Jiebuqu formations) in the southern Qiangtang subterrane. The Gamulong Formation is characterized by sedimentary recycling in the trench, likely in response to a tectonic event (possibly the continental collision). Together with the previous studies, this work on the occurrence of the Gamulong Formation indicates that the Lhasa-Qiangtang initial collision could have occurred in Middle Jurassic time (~166 Ma). Graphical abstract Unlabelled Image Highlights • Discovery of the Middle Jurassic trench deposits in the Bangong-Nujiang suture zone • Featuring the sedimentary recycling from the Bangong-Nujiang suture zone and southern Qiangtang subterrane • Implications for Lhasa-Qiangtang initial collision at Middle Jurassic [ABSTRACT FROM AUTHOR]

Located between the Bangong-Nujiang suture zone and the Qiangtang Block in central Tibet, the Najiangco area (~5 km to the north of Nima-Selinco) contains an Upper Jurassic-Lower Cretaceous sedimentary succession deposited during a period of marine regression. The youngest marine sedimentary unit in the Najiangco area is the Upper Jurassic Shamuluo Formation, which consists of sandstone, limestone, siltstone, and shale. Sedimentary facies analysis shows that tidal flat and subtidal lagoonal facies characterized the northern margin of the basin, while delta front and prodelta facies dominated the middle part, and carbonate shoal and patch reef facies prevailed along the southern margin. Provenance analysis, including petrographic modal analysis of sandstones and U-Pb dating of detrital zircons, shows that a recycled orogen in the central Qiangtang to the north of Najiangco area was the source of the sandstones in the Shamuluo Formation. Biostratigraphy and U-Pb zircon dating of a porphyritic granitoid dike (151 ± 2 Ma) indicate that the Shamuluo Formation was deposited during the Late Jurassic (Oxfordian to Kimmeridgian). During Middle Jurassic time, the southern Qiangtang Basin was dominated by shallow-marine environments. Later, during the Late Jurassic (Oxfordian to Kimmeridgian), the shallow-marine facies retreated to the southern margin of the basin. Combined with regional paleogeographic data from central Tibet, two stages of southward retreat of the Qiangtang remnant sea, and three stages of topographic uplift of the Qiangtang Block can be recognized during late Middle Jurassic to Early Cretaceous time. [ABSTRACT FROM AUTHOR]

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. • North and South Qiangtang terranes hosted independent Mesozoic basins. • Field mapping and refined stratigraphy of Qiangtang basins are presented. • Mesozoic paleogeographic evolution of Qiangtang basins is reconstructed. • Main sediment sources were Hoh-Xil, central Qiangtang, and active arc volcanoes. • Jurassic Qiangtang basins evolved via subduction of ocean and microcontinent. [ABSTRACT FROM AUTHOR]

Tropical rimmed platforms represent a much more efficient protection from coastal erosion than carbonate ramps. Understanding the controlling factors of platform geometry is therefore crucial to predict the fate of rimmed platforms under global-warming conditions. Here, we present detailed biostratigraphic, sedimentological, geochemical, and high-resolution carbon-isotope analyses of mid-Cretaceous (Albian-Cenomanian) carbonate rocks well exposed in the Khormoj section located in the Zagros Mountains of southern Iran. Sixteen microfacies were identified, allowing us to define the superposition of different platform geometries, a carbonate ramp in the Albian and a rimmed platform in the Cenomanian. Biostratigraphic and carbon-isotope analyses allowed us to identify the OAE1b, OAE1d, and Middle Cenomanian events in the Khormoj section. The paleodepth changes documented by carbonate microfacies testify to two transgressive events that can be correlated with long-term eustatic curves during the ramp stage. The Albian ramp was formed by orbitolinids under high siliciclastic input whereas the Cenomanian rimmed platform was built by rudists during clear water conditions. These two carbonate factories have drastic different carbonate sedimentation modes. The orbitolinid factory is characterized by a low carbonate production rate and fine carbonate grains resulting in ramp geometry, whereas the rudist factory is characterized by a high carbonate production rate and coarse carbonate grains leading to a rimmed platform geometry. • Transition from ramp to rimmed platform is recognized in SW Iran • Platform geometries are controlled siliciclastic input [ABSTRACT FROM AUTHOR]

The history of convergence between the India and the Asia plates, and of their subsequent collision which triggered the Himalayan orogeny is recorded in the Yarlung Zangbo suture zone. Exposed along the southern side of the suture, turbidites of the the Jiachala Formation fed largely from the Gangdese arc have long been considered as post-collisional foreland-basin deposits based on the reported occurrence of Paleocene-early Eocene dinoflagellate cysts and pollen assemblages. Because magmatic activity in the Gangdese arc continued through the Late Cretaceous and Paleogene, this scenario is incompatible with U-Pb ages of detrital zircons invariably older than the latest Cretaceous. To solve this conundrum, we carried out detailed stratigraphic, sedimentological, paleontological, and provenance analyses in the Gyangze and Sajia areas of southern Tibet, China. The Jiachala Formation consists of submarine fan deposits that lie in fault contact with the Zongzhuo Formation. Sandstone petrography together with U-Pb ages and Hf isotope ratios of detrital zircons indicate provenance from the Gangdese arc and central Lhasa terrane. Well preserved pollen or dinoflagellate cysts microfossils were not found in spite of careful research, and the youngest age obtained from zircon grain was ∼84 Ma. Based on sedimentary facies, provenance analysis and tectonic position, we suggest that the Jiachala Formation was deposited during the Late Cretaceous (∼88-84 Ma) in the trench formed along the southern edge of Asia during subduction of Neo-Tethyan oceanic lithosphere. [ABSTRACT FROM AUTHOR]

During Late Cretaceous to Eocene times, a vast epicontinental sea existed in the western Tarim Basin of China, and its appearance, evolution, and demise played an important role in the paleogeographic and paleoclimatic history of central Asia. Sea-level changes in the Tarim Sea and its controlling factors have been poorly studied so far. Here we present a detailed stratigraphic and sedimentological analysis of six Upper Cretaceous to Eocene stratigraphic sections in the southwestern Tarim Basin. Seventeen lithofacies types were identified overall, based on which changes of paleowater-depth were reconstructed. Between the mid-Cretaceous (Cenomanian) and the late Eocene (Priabonian), the Tarim Sea experienced five transgressive-regressive cycles. Deposition took place in middle-ramp to inner-ramp settings during transgressions, and in coastal-plain, lacustrine, and braided-river environments during regressions. The sea retreated but did not withdraw completely during Late Cretaceous to early Paleocene regressive stages, whereas seaways disappeared completely from the studied area during late Paleocene to Eocene regressions. The Tarim Basin lay on a stable craton in the Late Cretaceous, when paleowater-depth was chiefly controlled by eustatic change. Tectonic subsidence started to increase at middle Paleocene time, simultaneously with the Selandian dry event in the Tarim Basin, when a thick gypsum unit was deposited during incipient development of a foreland basin. Such a middle Paleocene onset of tectonic activity, also indicated by discrepancies between the regional paleowater-depth curve and the global sea-level curve and by penecontemporaneous uplift of the West Kunlun range in northeastern Pamir, were most likely a far-field effect of the onset of the India-Asia continental collision to the south. [ABSTRACT FROM AUTHOR]

The Lower Cretaceous sedimentary strata in the Lhasa Terrane record the palaeogeographic and tectonic history of the Tibetan Plateau prior to the India-Asia collision. The Lower Cretaceous strata in the Coqen Basin of the northern Lhasa subterrane include the Duoni and Langshan Formations. The Duoni Formation is composed of conglomerates, sandstones, siltstones and mudstones in the south deposited in a fluvial environment and quartzose-lithic sandstones, siltstones and mudstones in the north deposited in a shelf-coastal environment. The overlying Langshan Formation is characterized by abundant Orbitolina - and rudist-bearing wackestones and packstones, which were deposited on a low-energy carbonate ramp. The Langshan Formation in the Coqen Basin was deposited between ~ 119–115 Ma and ~ 98 Ma based on its large benthic foraminiferal assemblages. Age constraints based on the interbedded tuff and conformably overlying Langshan Formation indicate that the Duoni Formation was deposited between ~ 123 and 115 Ma. Sandstone detrital modal compositions further indicate that the Duoni Formation was primarily derived from magmatic arc and recycled orogen sources. Detrital zircons from the Duoni Formation yield a primary age population of 160–110 Ma (peaking at ~ 130 Ma), with negative ε Hf ( t ) values (− 18.7 to − 2.7), and additional age ranges of 550–500, 1200–900, and 1600–1500 Ma, thereby indicating that the Zenong volcanic rocks and Palaeozoic sedimentary bedrocks in the northern Lhasa subterrane are the most likely sources. The palaeogeography of the northern Lhasa subterrane can be approximately described in two stages. During the Aptian (~ 123–115 Ma), with the eruption of the Zenong volcanic rocks, the Duoni Formation accumulated in fluvial and shelf-coastal environments and was sourced from the Zenong volcanic rocks and basement rocks from the southern region of the northern Lhasa subterrane. The enhanced magmatic activities in the northern Lhasa subterrane may have influenced the Duoni Formation deposition. During the Late Aptian-Early Cenomanian (~ 115–98 Ma), a north-south transgression occurred, causing the majority of the northern Lhasa region to be dominated by shallow-marine limestones of the Langshan Formation. [ABSTRACT FROM AUTHOR]

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 δ 13 C 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 55.5 Ma), 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 ± 1 Ma 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. [ABSTRACT FROM AUTHOR]

We performed a detailed study of the stratigraphic transition of Oceanic Anoxic Event 1a (OAE1a) to oceanic red bed 1 (ORB1) from the classic Gorgo a Cerbara section in the Umbria region of central Italy. We focused on a 25.5-m-thick stratigraphic succession, from which we analyzed 305 samples for total organic carbon (TOC), CaCO 3 , magnetic susceptibility, diffuse reflectance spectrophotometry and the stable carbon and oxygen isotopic composition of both bulk samples and organic matter. In the Gorgo a Cerbara section, the Selli Level of OAE1a (∼1.81 m thick) consists of laminated to bioturbated dark gray to black mudstones and shales with medium to dark gray radiolarian-rich silty to sandy layers and a maximum TOC content of 20.22%. The carbon isotopic values show a negative excursion (C3 stage, ∼0.14 m) at the base of the Selli Level, followed by a stepwise positive excursion (C4–C6 stages, ∼1.67 m) in the upper part of the Selli Level. The transition from OAE1a to ORB1 (∼3.19 m thick) is characterized by bioturbated greenish gray cherty limestones and marly limestones with subordinate marls, corresponding to stable carbon isotopic C7 stage and lasts for ∼0.75 Ma. The ORB1 interval (∼13.15 m) consists of reddish marly claystones, dark-red marlstones, red marly limestones and red calcareous shales which indicate a highly oxic environment. Our results reveal a stepwise transition from a predominantly mesotrophic and dysoxic to anoxic environment at the time that the OAE1a black shales were deposited to an oligotrophic and oxic environment during the transitional interval and finally to highly oxic conditions during the ORB1 interval. The nannoconid crisis occurs at the top of the C2 stage, just 0.34 m below the negative excursion in δ 13 C isotopic values. The massive CaCO 3 dissolution phase occurs 0.25 m above the negative excursion; it persisted for 0.85 Ma and probably resulted from excess CO 2 , ocean acidification, and carbonate compensation depth (CCD) shoaling. Deposition of massive black shales occurs at the base of the C6 stage and lasted for 0.4 Ma. [ABSTRACT FROM AUTHOR]