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The Emeishan large igneous province (LIP), southwestern China and northern Vietnam, is thought to have been a potential driver for the biotic crises and paleoclimate changes around the Guadalupian-Lopingian boundary (GLB; Permian), but the lack of high-precision radiometric dates to constrain the duration and eruption rates of the volcanism has limited the assessment of their relationship. We present new chemical abrasion–isotope dilution–isotope ratio mass spectrometry U-Pb zircon geochronology of three samples from the lowermost and uppermost parts of the volcanic succession in the central portion of the Emeishan LIP. The results demonstrate that Emeishan volcanism began by 260.55 ± 0.07 Ma and persisted until at least 257.22 ± 0.37 Ma. Combined with a previously published age of 259.1 ± 0.5 Ma for silicic ignimbrites, we estimate that ~85% of Emeishan LIP volume erupted within 1.45 ± 0.50 m.y. Our new results confirm that the Emeishan volcanism began slightly prior to the initiation of the associated mass extinction event and was contemporaneous with the associated warming interval. The new data support the hypothesis that the Emeishan LIP likely triggered the biotic crises and paleoclimate changes around the GLB.

Salinity variation in ancient epicontinental seas has long been challenging to reconstruct. We determined salinity variation in the Late Pennsylvanian North American Midcontinent Sea based on normalized boron concentrations (B/Ga) and isotopic compositions (δ11B) of bulk shale. We analyzed the Stark Shale Member of the Missourian Stage Dennis Limestone cyclothem in the Charleston core (CC) from the Illinois Basin (eastward, more proximal) and the Iowa Riverton core (IRC) from the Midcontinent Shelf (westward, more distal). Both cores exhibited the same pattern of secular variation, with lower B/Ga and δ11B values at their base and top, recording less saline conditions during lower sea-level stands, and higher values in their middle part, recording more saline conditions at highstands—a pattern that conforms to conventional sequence stratigraphic and glacio-eustatic interpretations of Midcontinent cyclothems. At equivalent stratigraphic levels, B/Ga and δ11B values are systematically lower at CC relative to IRC, reflecting the generally lower salinity conditions of the Illinois Basin relative to the Midcontinent shelf, which is consistent with greater freshwater influence from the east due to heavy river runoff into the Appalachian foreland basin. Our findings serve to demonstrate the utility of paired B concentration and isotope data for paleosalinity analysis of deep-time shale formations.

The Lower Carboniferous Jiujialu Formation bauxite deposits of northern Guizhou Province, China, are a Kazakhstan subtype of karst bauxite deposits. The provenance of the Jiujialu Formation has long been debated, with uncertainty about the formation of the bauxite deposits. Here we report new geochemical data that indicate the affinity between the Lower-Middle Ordovician clastic rocks and argillaceous dolostones and the overlying Carboniferous bauxite deposits, all of which are characterized by high Al2O3, K2O, and ΣREE contents, flat post-Archean Australian shale (PAAS)-normalized REE patterns, and uniform immobile element ratios (TiO2/Al2O3, Nb/TiO2, and Zr/TiO2). Their similar detrital zircon age distributions further indicate the link between the bauxite deposits and the clastic rocks and argillaceous dolostones. Zircon age spectra of clastic rocks of the Lower Silurian Hanchiatien Formation in northern Guizhou match those of the bauxite deposits, with a maximum age peak at ∼980 Ma and other secondary age peaks, suggesting these clastic rocks may represent the provenance of the bauxite deposits. The youngest detrital zircons (∼445 Ma) occur only in the bauxite deposits and are probably sourced from K-bentonite beds of the Ordovician-Silurian transition. Our analyses indicate that the source materials of the bauxite deposits in the Jiujialu Formation are of mixed provenance: Lower-Middle Ordovician aluminosilicate rocks and argillaceous dolostones of the underlying strata, and Lower Silurian clastic rocks and K-bentonite from adjacent areas. A comparison of Early Carboniferous bauxitic provenances in northern and central Guizhou indicates that paleotopography was the major factor controlling the provenance of these bauxite deposits.

Silicic volcanic rocks generally constitute a minor, but key product to track the magmatic evolution in mafic rock dominated large igneous provinces (LIPs). However, for their generally late-stage nature of the silicic volcanic rocks they have a poor preservation potential due to extensive post-eruption erosion. We track the eroded volcanic rocks from the ∼260 Ma Emeishan LIP by analyzing the provenance of the LIP-derived sedimentary rocks. Sandstones from a cored succession of the Late Permian Longtan Formation in the northern Youjiang Basin are rich in volcanic rock fragments, and associated mudstones have low Al2O3/TiO2 ratios. Detrital zircon grains from the Longtan Formation display typical unimodal U–Pb age spectra with a prominent peak at ca. 260 Ma. These detrital zircons show an overall geochemical affinity akin to those crystallized from within-plate/anorogenic magmas. Such petrological and geochemical characteristics are consistent with a dominant source from the Emeishan volcanic rocks. Through the sampled succession, zircon grains of ∼260 Ma from the lower Longtan Formation generally display lower U/Yb (most

New age data for the Baoban Complex, South China establishes that it lay outboard of western Laurentia in the early Mesoproterozoic but was not part of the Cathaysia Block, with which it is traditional linked, until the mid-Paleozoic. Our geochronology data for detrital zircon and authigenic monazite grains from metasedimentary rocks indicate accumulation between ca. 1.55 Ga and 1.45 Ga for the Gezhencun succession of the Baoban Complex and ca. 1.45 Ga and 1.30 Ga for the Ewenling succession. The former unit is dominated by detrital zircon populations between 1900 Ma and 1500 Ma with two peaks at 1780 Ma and 1580 Ma. The Ewenling succession has detrital zircon peaks at 1720 Ma and 1450 Ma. Newly discovered gneissic granites were emplaced at 1550 Ma and intruded by 1450 Ma leucogranite dykes that are coeval with 1460–1430 Ma bimodal magmatism. The whole Baoban Complex was metamorphosed over the range of 1.3–0.9 Ga based on ages of authigenic zircon and monazite. Depositional ages of metasedimentary rocks are coeval with successions of the Belt-Purcell Basin, western Laurentia. Detrital zircon from the two regions have similar age populations and Lu-Hf compositions, and display a synchronous provenance shift at ca. 1.45 Ga. Basement lithologies on Hainan Island range in age from ca. 1.55–1.43 Ga and underwent metamorphism during 1.3–0.9 Ga. This is younger than basement rocks on the mainland of the Cathaysia Block in South China, suggesting the two regions are spatially unrelated at this time and hence the Mesoproterozoic record of the island cannot constrain the location of the Cathaysia Block in the Nuna and Rodinia supercontinents.

In South China, the Datangpo Formation was deposited during the Cryogenian interglacial stage between the Sturtian and Marinoan glaciations. The variations in paleoocean chemistry recorded in the Datangpo Formation are important to understand the formation of Mn ore as well as the early evolution of animals, which are not well constrained. Based on lithological observation and multi-geochemical proxies (iron speciation, Mo, U, V, Mn, Al and pyrite sulfur isotope) from drill core ZK43-6 from southeastern Chongqing, South China, the results indicate an anoxic (mostly euxinic) water condition for the lower black shales of the Datangpo Formation, which can be further divided into four intervals (I, II, III, IV). Among of them, very high Mn content and manganese metallogenesis is related to the suboxic Interval II between two euxinic depositions (Interval I and Interval III). Thus, our new findings suggest that the general euxinic condition at the basal Datangpo Formation is interrupted by a suboxic deposition (Interval II) where the manganese deposits formed. An updated model is proposed to shed light on the evolution in redox conditions of the Datangpo Formation as a function of sea-level and terrigenous input, and the genesis of “Datangpo-type” manganese in light of the temporal seawater redox conditions and microbial activity.

Phosphorite of the Ediacaran Doushantuo Formation accumulated in the central Guizhou province during the Neoproterozoic-Cambrian Phosphogenic Event, producing the first true phosphorite giant in Earth history. Deposition is interpreted to have occurred on a wave-dominated epeiric platform along the northern margin of the Qianzhong Uplift. Lithofacies stacking patterns and two paleokarst surfaces record phosphogenesis through at least two sea-level cycles. As in younger Phanerozoic epeiric sea phosphorites, the delivery of upwelled phosphorus is interpreted to have stimulated phosphogenesis in a range of shallow-water environments. Ten phosphatic and associated lithofacies are recognized in the Doushantuo Formation. Wavy and horizontal laminated pristine facies were the locus of phosphogenesis and reflect the authigenic precipitation of francolite in accumulating fine sediment. Granular, cross-stratified phosphorite is interpreted to have been produced through storm-wave winnowing of pristine facies and the subsequent transport, redeposition, and concentration of phosphatic peloids into economic beds. Beds with the highest concentration of phosphorus formed in shallow, wave-agitated environments around paleo-topographic highs. Paragenetic analysis suggests that secondary meteoric processes further enriched the phosphorus content (>35 wt%) of these granular beds during sea-level lowstands. Such aerially extensive, upwelling-related phosphorite contrasts Paleoproterozoic and Neoproterozoic phosphatic deposits. Throughout much the Proterozoic francolite precipitation was restricted to shallow-water, photosynthetic oxygen oases where redox sensitive phosphogenic processes were focused in the sediment. The Doushantuo Formation is interpreted to record the oxygenation of the water column and concomitant expansion of phosphogenic environments during the Neoproterozoic Oxygenation Event. This progressive ventilation of the deep ocean forever changed the biogeochemical cycling of phosphorus in the marine realm and set the stage for the deposition of phosphorite giants that punctuate the Phanerozoic stratigraphic record.

The Datangpo Formation manganese deposits (DFMnD) in South China formed during the interglacial stage between the Sturtian and Marinoan glaciations of the Cryogenian period. These black shale-hosted deposits are composed of massive Mn-carbonates with microscopic laminae/laminations and cherty veins. To date, it has been thought that the DFMnD formed through inorganic processes, which were controlled by redox changes in the post-Sturtian Nanhua Rift Basin, South China. However, in this study, systematic petrographic, mineralogical, and geochemical analyses indicate a microbially mediated origin of the Mn ore deposits. Mineralized microbial woven micro-textures (observed at the μm scale) and microbial fossils are common in the laminated Mn-carbonate ores. We infer that microbial enzyme activity formed poorly crystallized Mn oxide/hydroxides and carbonaceous material, which transformed to rhodochrosite, kutnohorite, ankerite/dolomite, framboidal pyrite, and apatite via diagenesis. Some micro-scale quartz and K-feldspar may be detrital but most appears to have formed during diagenesis or through hydrothermal activity. A micro-mineralogical profile determined by 2500 spectra via high-resolution in situ micro-Raman spectroscopy also revealed cyclic laminations of Ca-rhodochrosite as microbialite (ankerite/dolomite) and quartz, indicating a mineralized biomat system. Ca-rhodochrosite transformed to kutnohorite under elevated temperatures, as indicated by the maturation level of organic matter (determined via Raman spectroscopy). Alternating micro-laminae denote cyclic changes in microbial groups (Mn- and Fe-oxidizing microbes versus cyanobacteria) during the formation of the Mn ore deposits. Our proposed model for the microbially mediated metallogenesis of Mn-carbonate deposits begins with enzymatic multi-copper oxidase processes associated with autotrophic microbial activity under obligatory oxic conditions, which results in the precipitation of Mn bio-oxides. Following their burial in organic-rich sediments, the Mn(IV) oxides and hydroxides are reduced, producing soluble Mn(II) via processes mediated by heterotrophic microbes under suboxic conditions, which in turn form the Mn-carbonates. This microbial metallogenesis model for the Cryogenian DFMnD in South China is similar to that proposed for the Jurassic Urkut Mn deposit in Hungary, indicating that a two-step microbially mediated process of Mn ore formation might be common throughout geological history.

The 87Sr/86Sr minimum of the Capitanian seawater is one of the most significant features in the Phanerozoic seawater 87Sr/86Sr history. In order to assess possible contribution of the Emeishan large igneous provinces (LIPs) to strontium isotope evolution of the Capitanian seawater, 87Sr/86Sr ratios were measured from the Capitanian limestones which are locally interlayered with the Emeishan basalts. The limestones underlying the Emeishan basalts have high 87Sr/86Sr ratios (0.7070–0.7074). However, extremely low 87Sr/86Sr ratios (0.7068–0.7070) were identified in the late Capitanian Jinogondolella prexuanhanensis–J. xuanhanensis zones, which correspond to the eruption time of the Emeishan LIP. The temporal coincidence of these two phenomena supports the idea of a potential linkage between Capitanian 87Sr/86Sr minimum and eruption of this igneous province. The strong submarine hydrothermal activity and erosion of the Emeishan LIP could have released large amounts of non-radiogenic Sr to the oceans and play an important role in strontium isotope evolution of the seawater.

The late Paleozoic Era was an interval of major tectonic and climatic changes, including formation of the supercontinent Pangea and the ~60-Myr-long Late Paleozoic Ice Age (LPIA). Although bauxite formation declined globally from the Carboniferous to the Permian in conjunction with global cooling, it was an interval of widespread bauxite formation in China. In South China, (1) the Jiujialu Formation bauxite deposits in central and northern Guizhou (Zunyi area) are of early-middle Visean age; (2) the Dazhuyaun Formation bauxite deposits in northern Guizhou (Wuchuan–Zheng'an–Daozheng area) to southern Chongqing (Nanchuan area) and southeastern Guizhou (Fuquan–Kaili area) are of Late Pennsylvanian–Early Permian age; and (3) the Heshan Formation bauxite deposits in western Guangxi to Yunnan are of Middle–Late Permian age. In North China, the Benxi Formation bauxite deposits are of Late Mississippian–Middle Pennsylvanian age. The contrasting trends in bauxite metallogenesis between China and the rest of the world imply different climatic patterns in the eastern Tethys (high annual humidity with seasonal dryness) and Pangea (aridification). This hypothesis is further supported by differences in the chemical index of alteration, or CIA (>80 in the eastern Tethys vs. ~50 in western Pangea), and in paleotemperatures (mean annual temperature, or MAT = ~20 °C in the eastern Tethys vs. ~4 °C in western Pangea) determined from Permo-Carboniferous siliciclastic deposits. Permo-Carboniferous bauxite deposits in South China formed in coastal plain and coastal karstic depression environments, in which the position of the groundwater table was related to sea-level changes. During the late Paleozoic, high-frequency eustatic fluctuations caused by waxing and waning of Gondwana icesheets controlled sedimentation in these coastal depositional systems, leading to cyclic accumulation of coal and bauxite deposits and cycles of vadose- and phreatic-type bauxite formation. The results of the present study show that, during interglacial stages, lateritization resulted from high pCO2, high sea-level and groundwater-table elevations, low precipitation, and limited vegetation cover, whereas during glacial stages, bauxitization of these ferralitic weathering products was promoted by low pCO2, low sea-level and groundwater-table elevations, high precipitation, and more extensive vegetation cover. Thus, a unique combination of geographic, climatic, and eustatic factors accounted for widespread formation of bauxite in South China during the LPIA.

The Lower Carboniferous Jiujialu Formation bauxite deposits at Zunyi, northern Guizhou are distinguished by their great thickness (to 110 m) and cyclic alternation of bauxite ore and bauxitic claystone layers. These features are typical of the Kazakhstan subtype of karst bauxite deposits, although the genesis of this type of deposit is poorly understood. Here, we undertook a petrological, mineralogical, and geochemical study of the Zunyi deposit in drillcore ZK5600 to gain insights into its formation history. The Zunyi profile contains seven bauxite cycles, as recorded by petrological, mineralogical and geochemical features, indicating a multistage formation history. Each cycle is composed of a lower bauxitic claystone layer and an upper bauxite ore layer. The bauxite ore is characterized by high Al2O3, high Al-mineral (diaspore), and low SiO2 content. Positive Ce anomalies, high CIA values (>90), and strong depletion of major elements indicate that the bauxite ore formed through intense chemical weathering and leaching in a well-drained soil environment. The bauxitic claystone is characterized by relatively lower Al2O3 and higher SiO2 and clay mineral (mostly illite) content. This lithology exhibits both negative and positive Ce anomalies, moderate CIA values (70–80), and enrichment of some elements (e.g., Fe, K), indicating formation through moderate chemical weathering in a poorly drained soil environment. Secular variations in chemical weathering intensity and soil drainage conditions were linked to regional hydrologic changes. During the early Carboniferous, the Zunyi area was located in a karstified coastal upland setting, and its hydrologic system was affected by glacio-eustatic fluctuations. High groundwater table elevations during eustatic highstands led to formation of bauxitic claystone layers, whereas low groundwater table elevations during eustatic lowstands led to formation of bauxite ore layers.

Tracking climate change and its relationships with chemical weathering and massive volcanic activity in deep-time greatly improves our understanding of the Earth's climate system. The Permo-Carboniferous period is a critical time interval with million year-scale glacial-deglacial cycles and massive basaltic volcanism, such as the Skagerrak-Centered (also named Skagerrak or Jutland) large igneous province. To explore the volcanism-climate interactions in this period, we obtained high precision CA-TIMS U-Pb zircon ages for three tuffaceous layers from a cored upper Pennsylvanian-lower Permian marginal marine succession in southern North China. These ages calibrate the Permo-Carboniferous biostratigraphy between ∼301–296 Ma in North China. From this dated core succession, mudrock samples and their calculated weathering index values were screened to constrain the weathering trends for the source landscapes and demonstrate a rapid increase with a subsequent decrease in source chemical weathering intensity during the period of ∼299 to 296.5 Ma. These trends coincide with the southern Gondwana glacial records, low latitude temperature changes, relative sea-level variations, and shifts in atmospheric pCO2 that together document an earliest Permian climate warming-cooling perturbation with a temperature maximum at ∼298 Ma. This climate warming in the Permo-Carboniferous icehouse correlates with the emplacement of the Skagerrak-Centered large igneous province, which likely released voluminous CO2 that led to climate warming during the Permo-Carboniferous transition. The immediately following cooling could possibly result from the rapid post-eruptional weathering of the massive basaltic rocks of this province in tropical latitudes, which would have sequestered atmospheric CO2 and promoted return to cooler icehouse conditions. This study supports the assertation that massive basaltic volcanism could first cause rapid climate warming and then may have an overall net cooling effect as previously suggested for the Deccan Traps and the Central Atlantic Magmatic Province.

Weathering of basalt in tropical environments is sensitive to climate change and considered to play a significant role in regulating climate evolution. Though extensively studied on the modern Earth and hypothesized for the geological past, basalt weathering is difficult to directly track in geological archives. We here focus on the basaltic sediments derived from the Emeishan large igneous province (LIP) in South China and determined their organic carbon content and isotope, mineral and geochemical compositions. Based on the newly obtained high-precision zircon U-Pb age of 251.79 ± 0.12/0.13/0.36 Ma, we establish temporal variations of weathering intensity for the Emeishan LIP basaltic landscapes in the tropical latitudes through the Permo-Triassic rapid climate warming periods. Analysis of weathering trends indicates a significant decrease in weathering intensity across the Permo-Triassic transition. This decrease in intensity is anomalous considering its coincidence with the climate warming at the Permo-Triassic transition, which tends to elevate chemical weathering rate of basalts and produce sediments with high chemical weathering intensity. Combining these weathering trends with present-day basalt weathering-temperature relationship and reported paleo-temperatures, total erosion rate is quantitatively estimated to increase from 282 ± 43 t/km2/yr in the latest Permian to > 1618 ± 187 t/km2/yr in the Early Triassic. This massive erosion in the Early Triassic is plausibly related to amplified extreme precipitation associated with intensification of the hydrological cycle in the Early Triassic hothouse climate. This study underlines the weathering responses of tropical landscapes to rapid climate warming.

The Upper Triassic strata within the Nanzhao Basin are thought to have formed in response to the Qinling Indosinian Orogeny. Thus, the provenance record of this succession can be used to trace the basin-mountain interactions by using petrology and zircon geochronology. The Upper Triassic sandstones of the Nanzhao Basin are composed of a moderate proportion of quartz along with a comparable volume of feldspar and lithic fragments and the compositions plot mainly within orogenic source areas. The detrital zircon age spectra of these strata display six prominent age peaks at 232 Ma, between 420 and 442 Ma, and at 750, 914, 1828, and 2452 Ma and are inferred to have been derived from the South Qinling Belt, North Qinling Belt, and southern North China Block. The sediments sourced from the South Qinling Belt are thought to have evolved from Triassic volcanic rocks to basement units indicating that an unroofing process occurred within this orogenic region. In contrast, the North Qinling Belt acted as a continuous source, while the southern North China Block evolved into an accessory source in the late stages of the basin evolution. It is apparent that the Nanzhao Basin received an influx of clastic detritus from both the southern and northern source areas indicating that this region was isolated within the North Qinling Belt. Thus, the Nanzhao Basin can be defined as a wedge top depozone of the southern North China foreland basin system. Tuff zircons with a single age peak at 225 Ma are thought to be related to a volcanic eruption that occurred towards the southern margin of the South Qinling Belt. This hypothesis implies the existence of subduction along the Mianlve Suture before the early Late Triassic, which is consistent with both oblique collision and unequal margin collisional models.

Whole-rock geochemistry and zircon trace element, U Pb and Hf isotopic data for Upper Permian volcanic ash at Shangsi show a significant change in source from the Emeishan Large Igneous Province (LIP) to a convergent plate margin magmatic arc. The lower stratigraphic samples display high Al2O3/TiO2 ratios, strong negative Eu anomalies, and no depletion in high field strength elements. Zircons with ages of ca. 260 Ma from these ashes have a geochemical affinity to within-plate-type magmas and with felsic ignimbrites from the uppermost part of the Emeishan volcanic succession at Binchuan. These features, combined with relatively high eHf(t) values and low Th/Nb ratios in the zircons, imply a late-stage felsic volcanic origin related to Emeishan LIP. The upper stratigraphic samples at Shangsi display significant depletion in Nb and Ti; zircons separated from these volcanic ashes are chemically similar to those from arc-related/orogenic rocks, indicative of a magmatic arc source. Combined with published high-precision CA-TIMS data for these volcanic ash layers, the Emeishan volcanism can be constrained to between ca. 260–257.8 Ma. The age of Emeishan volcanism is consistent with the Wuchiapingian climate cooling event, supporting a potential linkage between these two phenomena.

The last glaciation during the late Paleozoic ice age commenced at around the Guadalupian–Lopingian (G–L) boundary and is synchronous with the emplacement of the Emeishan large igneous province. Using CA-TIMS zircon U–Pb dating, we obtained an age of 259.51 ± 0.21 Ma for the uppermost tuff from the Puan volcanic sequence in the eastern Emeishan large igneous province, constraining the timing of Emeishan volcanism and providing another candidate age for the G–L boundary. In addition, we determined an age of 259.69 ± 0.72 Ma for a basal claystone in the immediately overlying Longtan Formation from a drill core section in southwest South China. These ages, along with source weathering trends of mudstones from the lower Longtan Formation, and compiled paleotemperature records, indicate an earliest Wuchiapingian cooling coinciding with the onset of the last Permian glaciation. This global cooling is associated with positive shifts in both organic and carbonate carbon isotopic records and likely a decrease in atmospheric pCO2. A hypothesised causal linkage is proposed in which the rapid post-eruptive basaltic weathering of the Emeishan province in an equatorial humid belt may accelerate the atmospheric CO2 consumption and lead to climate cooling. Our work supports the long-term climate cooling effects of large igneous provinces.

The Kungurian (late Cisuralian) is associated with elevated atmospheric p CO 2 levels and numerous substantial changes in the ocean and terrestrial systems, but carbon cycle perturbations through this time interval are poorly understood. Here, three well-dated organic carbon isotope (δ 13 C org ) curves from South China, paired with their respective carbonate carbon isotope (δ 13 C carb ) data published before, are presented for the first time. Their comparison demonstrates that a prominent, rapid, and synchronous negative excursion in δ 13 C org and δ 13 C carb occurred in the early Kungurian (the herein proposed KCIE event dated to ca. 277.9–277.4 Ma). A comparable shift is observed in other deeper-water marine sections in South China and two terrestrial sections in North China and eastern Australia. Based on carbon mass-balance calculations and a review of concurrent geological records, we propose that the KCIE event was driven by an intensive volcanism of a large igneous province in northern Gondwana, dissociation of voluminous methane hydrates induced by this volcanism, and the ensuing worldwide conflagrations. Predicted elevated production of greenhouse gases involved would have warmed the Earth and further resulted in ocean stagnation, anoxia, and acidification, all of which are in conformity with the documented sedimentological, geochemical, and palaeontological data. This major anomaly in the carbon cycle in the late Cisuralian is considered here to play a key role to promote the transition of the Earth to a greenhouse mode.

The closure of Mianlue Ocean lead to the collisional assembly between the North China Block (NCB) and the South China Block (SCB). But the timing of initial continental collision remains unclear, with the proposed ages ranging from the Late Permian to the Late Triassic. This study presents stratigraphic, sedimentological, tectonic subsidence, and provenance data from the Triassic strata in the Zigui and Dangyang basins lying along the eastern Qinling Orogenic Belt. These data document a tectonic transition in the central northern-SCB, and locally provide constraints on the timing of initial SCB–NCB collision. The Lower Triassic Daye Formation was deposited in a marginal basin to slope environment, and consists of mudrocks containing detrital zircons with major age peaks at ca. 1900 and 850 Ma. The overlying Lower Triassic Jialingjiang Formation comprises a shallowing carbonate sequence, with intercalated evaporites at the top of the formation. It contains mudrocks that are rich in detrital zircons with of ca. 270‐–245 Ma. The mixed carbonate and siliciclastic sequences of the Middle–Upper Triassic Badong Formation records tectonic uplift at its base, and contains detrital zircons with U Pb age peaks at ca. 2500, 1850, 920–800, 450 and 350–220 Ma. Combined with petrographical observations and tectonic subsidence calculation, these detrital zircon U Pb ages record a significant provenance change from recycled material derived from the SCB to newly generated detrital material from the NCB. This provenance change records the initial SCB–NCB collision in the eastern Qinling Orogenic Belt during the Early Triassic.

Manganese deposits in the Early Carboniferous Baping Formation of central Guangxi, South China were formed in the Youjiang Basin on the southern passive margin of the South China Block. Hosted in the Second Member of the Baping Formation, the manganese ore layers were interbedded by thin-middle manganese carbonate and silicified carbonate. Previous studies provide limited information about this manganese deposit, and the sedimentary characteristics of ores and the metallogenic mechanism are not clear. In this study, integrated analyses of petrology, mineralogy, geochemistry, and carbon isotope reveal microbial metallogenesis in the Early Carboniferous manganese deposit of central Guangxi for the first time. Oncoid-bearing massive Mn carbonate and laminated Mn ore contain evidence of disseminated mineralized microbial biosignatures in millimeter scale. An in situ mineralogical study based on CL, FTIR, SEM-EDS and Raman spectroscopy has identified the syngenetic and diagenetic Mn and Fe systems during the formation of the manganese deposit. Both were formed by biomats and precipitated micro-laminae of microbiogenic minerals such as Mn-calcite, rhodochrosite, kutnohorite, and apatite. The metallogenic model of the manganese deposit in the Baping Formation can be divided into two main stages: (1) Sediment accumulation stage, where enzymatic Mn(II) oxidation controlled the accumulation of Mn oxides within the cyanobacterial organic and carbonate network, thus enriching the manganese; (2) Diagenetic stage, where Mn-metasomatism of microbial carbonate and the reaction between syngenetic manganese oxides and the organic matter led to the precipitation of proto-ore (Ca-rhodochrosite). A positive δ13C value (+1.53‰) within the Mn carbonate sample and negative δ13C values (−7.15‰ to −3.64‰) in Mn ore samples indicate the participation of organic carbon in the alkalinity source of Mn-bearing carbonates. The presence of kutnohorite and of Mn-sulfide minerals indicates a transitional zone between suboxic and anoxic conditions. Anatase represents the diagenetic mineral of Fe-biomat. After release of elements in the decomposed cells and EPS, a series of accessory minerals (feldspar, apatite, pyrite, etc.) formed.

Economically important manganese deposits are hosted in the Middle Permian Maokou Formation of Zunyi, northern Guizhou, South China. During the Middle Permian, the intense rifting related to the initial stage of the Emeishan Large Igneous Province (ELIP) led to the development of carbonate platforms and inter-platform troughs. The manganese deposits occur in the transitional zone between carbonate platforms and troughs. Previous studies emphasized that the hydrothermal activities at the bottom of the trough basin controlled the formation of manganese deposits. In this study, new sedimentary, mineralogical, and stable isotope evidence are acquired from this manganese deposit, indicating that the microbially-mediated metallogenic mechanism also made an important contribution for the Middle Permian manganese deposition. The metallogenesis of this manganese deposit is highly like the combination of hydrothermal and microbial processes. Manganese ores in Zunyi are manganese carbonate, showing massive and clastic structures, no macroscopic nor microscopic lamination are found, samples are coarse-grained, diagenetically recrystallized with abundant mineralized microbial and microfossil biosignatures. FTIR, EPMA, and Raman analyses recognize micrometer-scale cyclic mineralogical assembly and help reconstruct the proposed new model of microbial manganese metallogenesis. Hydrothermal activity in the basin provided dissolved Mn 2+ ions into the anoxic basal watermass. In the syngenetic stage, microbial systems could be subdivided into three categories: (1) cyanobacterial system, (2) Mn-biomat system and (3) Fe-biomat system. Cyanobacterial activity led to the precipitation of calcite, and it could be partially affected by Mn-metasomatism and transformed to Mn-bearing calcite. Mn-oxidizing microbes led to the precipitation of manganese bio-oxide (δ-MnO2) near the redoxcline of the basin. Fe-biomat system was responsible for the precipitation of Fe-oxides (hematite) and Fe-hydroxides (ferrihydrite and lepidocrocite). After burial, manganese oxides reacted with the organic matter in the sediments through the microbially-mediated processes during the early diagenesis and the Mn-metasomatism of the cyanobacterial carbonate jointly contributed to formation of early diagenetic manganese carbonate ore. The redox fluctuations between oxic/suboxic and anoxic zones led to the re-oxidation process and resulted in cyclic marcasite. Anatase cycles observed in samples were interpreted as the diagenetic product of Fe-biomat system.

The delayed diversification of early animals until the middle Ediacaran Period, despite their likely origin in the Cryogenian Period or earlier, has been attributed to low levels of dissolved O2 in global seawater. To provide more robust constraints on the extent of global-ocean oxygenation during the mid-Cryogenian Period, we analyzed paired U (δ238U) and Mo (δ98Mo) isotope compositions of organic-rich shale in the basal Datangpo Formation from two separate drillcores in South China. This unit yielded an average δ238U of −0.39 ± 0.23‰ (2SD; relative to standard CRM145), which is significantly lower than the average δ238U (+0.02 ± 0.12‰) of euxinic sediments of the modern restricted Black Sea and well below a modeled δ238U of +0.2‰ for modern unrestricted euxinic facies (e.g., Saanich Inlet). The U/Al ratios of our samples indicate that ~ 40% of U was derived from detrital materials (δ238Udetrital = ~−0.3‰), suggesting that the δ238U of authigenic U is even lower than the measured bulk-sample values. Taking into consideration the 0.4–0.8‰ enrichment of 238U in euxinic sediments relative to seawater, the δ238U values of the Datangpo shales correspond to contemporaneous seawater δ238U of −1.20‰ to −0.73‰. Owing to mass balance considerations, these low seawater δ238U values are indicative of widespread development of anoxia in the Cryogenian interglacial ocean (~658–654 Ma). These shales yield mostly low δ98Mo values (+0.56 ± 0.46‰), although the youngest samples have values as high as +1.21 ± 0.23‰ (relative to NIST SRM 3134 = +0.25‰), all of which are significantly lower than modern seawater δ98Mo (+2.34 ± 0.10‰). The Datangpo shales either directly record the global seawater δ98Mo signature or provide a minimum estimate thereof (in the event of local influences). The consistently low δ98Mo values of the Datangpo shales thus confirm widespread anoxia in the Cryogenian interglacial ocean. These findings based on paired δ238U-δ98Mo analyses thus provide key information regarding global-ocean redox conditions during the interval immediately preceding the rise of macroscopic and morphologically complex animals

Terrigenous clastic sediments are generated by the integration of the Earth surface processes and their deep-time counterparts provide a valuable archive for regional/global climatic, geographic and landscape evolution. It is thus important to read and interpret these deep-time sedimentary records, especially for reconstructing continent climate. Previous studies on the Early Permian sequences from the North China document a dominant control of source chemical weathering on mudstone compositions and its linkage with continent climate conditions. Based on the weathering geochemical data of these mudstones, element mobility during weathering can be ordered as Ca > Na ≥ Mg > Sr > K ≥ Ba > Rb. The weathering regime in the source area is inferred to be supply-limited according to the estimated continent physical erosion rate and regional tectonic evolution, sedimentation in North China. Further exploration of palaeoclimate implication is presented in terms of variation of high-to-low latitudinal temperature gradient across the Early Permian glacial to post-glacial climate transition.

The Qin-Fang Trough, South China, trends northeast-southwest, orthogonal to the adjoining southern margin of the craton. The Devonian strata within the trough are unconformable on late Neoproterozoic units of the Yunkai Massif, indicating that strata within the trough are autochthonous. U-Pb ages and Hf isotope compositions of detrital zircons from the Silurian to Devonian succession are consistent with derivation from the massif. In comparisons of our data with those from equivalent units in the Ailaoshan Belt and Hainan Island, detrital zircons from the Silurian strata show similar age distributions and Hf isotope compositions, indicating that the three areas shared a common source and were adjacent to each other during the Silurian. In contrast, the age distributions of detrital zircons preserved in Devonian strata in the Qin-Fang area are different from those of equivalent units in the Ailaoshan Belt. This, along with the absence of Devonian strata on Hainan Island, suggests that the Qin-Fang ...

The Kungurian ocean-climate system has received little attention, but a new compilation of geochemical and paleoclimatic proxies suggest more complex climate dynamics during the Late Paleozoic icehouse–greenhouse transition than previously considered. Here, integrated carbon isotope stratigraphical, sedimentological, and geochemical data across two Early–Middle Permian successions in the Youjiang Basin, South China, is presented. These proxies indicate widespread anoxia below or near the water-sediment interface in South China during the Kungurian. High primary productivity, high sedimentation rate, and a relative sea-level rise are here proposed as being responsible for this process in the late Kungurian, but cannot account for the remaining anoxia at cycle boundaries. We put forward a hypothesis that divergent climate trends between the tropics and Gondwana might have played an important role in ocean stagnation and prevailing O2-deficient conditions in and probably outside South China during the Kungurian. The termination of anoxia in this region during the latest Kungurian is attributed to an intensification of oceanic circulation, a rise in atmospheric pO2 concentrations, a sea-level drop, depressed primary productivity, and low sedimentation rates. This study calls for further high-resolution sedimentological and geochemical investigations on the paleotropics outside South China, in order to elucidate the icehouse-greenhouse transition at the global scale.

The Pennsylvanian to lower Permian succession at Madiyi, South China, represents a nearshore mixed siliciclastic-carbonate system characterized by cyclic sedimentation patterns along a depth gradient from continental siliciclastics to marine open platform carbonates. Various palaeokarst features related to subaerial exposure are widely distributed. Additionally, pedogenesis was pervasive. The identification of twenty-eight sedimentary cycles grouped into five sequences allows the reconstruction of a relative sea-level curve. The cycles represent higher frequency changes superimposed on the long-term evolution. After the initial transgression, the sea level remained relatively low in the late Bashkirian to early Moscovian. Then, it rose stepwise until a major drop occurred in the late Moscovian. Afterwards, the sea level rose again, but marine sedimentation ceased during at least the early Kasimovian. The area was flooded in the late Kasimovian, and the sea level rose until a late Gzhelian sea-level drop. The subsequent marine sequence contains uppermost Gzhelian to upper Asselian deposits, which are capped by lower Permian continental facies associated with a major regional regression. Shallow to deeper marine sedimentary settings recorded high-frequency sea-level changes throughout South China during the late Bashkirian to Asselian. The main transgression–regression cycles are clearly associated with different depositional settings during several time intervals. Furthermore, the good correlations among South China, Ukraine, and the U.S. Mid-continent are rooted in the impact of Gondwanan glaciations on the global sedimentation patterns. However, not all changes at Madiyi are the result of glacio-eustatic sea-level fluctuations; some are related to the local subsidence history and the rise of the Xuefeng Uplift.

Sturtian cap carbonate deposits, previously unknown in South China, are documented in this study from the base of the Datangpo Formation in the Nanhua Basin (Guizhou Province). The age of these deposits is constrained by an LA-ICP-MS U-Pb zircon age of 662.7 ± 6.2 Ma from the overlying Mn-shale layer, which is approximately coeval with the termination of the Sturtian glaciation globally. The newly discovered cap carbonates are composed of massive, laminated, pisolitic, and sandy dolomites, and formed subtidally on the summits of horsts within the Nanhua Basin. Two δ13Ccarb profiles (from the JJS-1 and ZK01 sections) show positive shifts of 4–5‰ from the base to the top of the cap carbonates with a ∼2‰ offset between the profiles. These features suggest both a large global perturbation as well as local influences on carbonate carbon isotopes during the Sturtian deglaciation, which is consistent with aspects of both the Snowball Earth and gas hydrate destabilization hypotheses for the origin of cap carbonates. The newly discovered cap carbonates are inferred to be correlative with rhodochrosite (Mn-carbonate)-bearing deposits of the basal Datangpo Formation in adjacent grabens of the Nanhua Basin. This correlation is based on (1) the equivalent stratigraphic positions of the cap carbonates and Mn-deposits, both of which are found at the base of the Datangpo Formation, and (2) consistent U-Pb dates of 667–663 Ma for tuff layers interbedded with these deposits at two locales. The Mn-deposits show significantly higher TOC content (1–3% vs

Little attention has been focused on the stratigraphical imprints of the Late Paleozoic Ice Age on the equatorial eastern Paleo-Tethys. An integrated study of biostratigraphy, microfacies, and stable carbon isotope stratigraphy was carried out on Pennsylvanian–middle Guadalupian carbonates of the Gongchuan section in the Bama Platform, South China. It records seven cooling and two warming pulses in the pre-Kungurian interval, comparing with ice-proximal stratigraphical records and far-field indirect proxies in lower latitudes. A Kungurian negative δ 13 C excursion (from + 4.4‰ at the base of the Kungurian to + 1.6‰) recorded only in the subequatorial belt is documented here. It is followed by a global positive δ 13 C trend reaching + 5.3‰ near the Cisuralian–Guadalupian boundary. Seven third-order shallowing–upward cycles are reported for the first time from the Kungurian succession. The duration of each cycle is estimated to ca. 1 myr. These cycles are interpreted as being of glacioeustatic origin and mainly driven by long-period modulations of obliquity (~ 1.2 myr) under major p CO 2 decreasing condition. This interpretation is supported by recent climate–ice sheet modeling and Cenozoic glaciation studies, which argue that astronomical forcing will be amplified by large-magnitude perturbations in the carbon cycle, when only localized ice-centers persist. Our results emphasize the need for integration of sedimentological and paleoclimatological proxies in elucidating the dynamics of the deglacial phases of the Late Paleozoic Ice Age.

This work was supported by the National Natural Science Foundation of China (Grant No. 41772106 and 41472086) and by the Australian Research Council (Grant FL160100168). Mid-Neoproterozoic magmatic rocks from the southeastern part of the Nanhua Basin constrain the tectonic setting of the basin. Data from rhyolitic tuffs of the Louqian Formation that overlie the Cathaysia Block in southeastern South China indicate accumulation of the unit at ca. 770 Ma, and provide an upper age limit on collisional assembly of the Yangtze and Cathaysia blocks. The zircons within the tuffs display largely positive εHf(t) (−3.66 to +13.94) and juvenile TDM (Hf) values (1.74–0.90 Ga), which indicate involvement of Neoproterozoic to late Paleoproterozoic crustal materials in their generation. Geochemically, the tuffs are peraluminous and characterized by both A-type and arc affinities with high SiO2, Ga, accentuated negative Eu anomalies, strong depletion in high field strength elements and high zircon saturation temperatures (TZr), which are comparable to contemporaneous (800–750 Ma) felsic rocks from the northwestern of the Nanhua Basin. These characteristics suggest the Nanhua Basin lay inboard of a convergent plate margin arc. This arc is represented by 860–730 Ma magmatism along the western and northern margin of the South China Craton (Panxi-Hannan Belt), with the Nanhua Basin occupying an upper plate, back arc setting. Postprint

Three major late Neoproterozoic global cryochrons mark the coldest climate state in Earth history, with glaciers covering most, if not all, continents. However, the terrestrial paleosurface temperature differential between cryochron and nonglacial interlude is unknown. Time-equivalent Cryogenian and Ediacaran sedimentary successions from South China and Oman show multiple negative excursions of the corrected values of their chemical index of alteration (CIAcorr). These excursions reflect climate cooling and correlate with the Sturtian, Marinoan and Gaskiers cryochrons. Based on the τNa-MAT transfer function (sodium chemical depletion index-mean annual temperature), we estimate the temperature differential between Cryogenian cryochron and nonglacial interlude reached 20 ± 5.4 ℃ at around 30° paleolatitude, and 12 ± 5.4 ℃ temperature difference between the Ediacaran cryochron and nonglacial interlude near the equator. The fluctuation of CIAcorr and MAT trends within individual cryochrons likely indicate cold-warm climate cycling during the Cryogenian cryochron.