Lower Yangtze Region Research Articles

A deep water shelly fauna from the uppermost Ordovician in northwestern Hunan, South China and its paleoecological implications

It is the first time to document the trilobite Mucronaspis ( Songxites ) wuningensis and the brachiopod Paromalomena - Aegiromenella Assemblage from the Xinkailing Bed (Hirnantian, uppermost Ordovician) in Taoyuan and Cili counties, northwestern Hunan Province. Synecological analysis shows that this is a deep water shelly fauna of South China during the Hirnantian. It lived on the upper Jiangnan Slope in northwestern Hunan, adjacent to the southeast margin of the Upper Yangtze Region, and belongs to the Hirnantia fauna with cool and deep water, and low diversity affinity, similar to its contemporary shelly faunas from the southern Shaanxi Slope adjacent to the north margin of the Upper Yangtze Region, the northern Chongqing depression (new name), and the Jiangxi-Anhui-Jiangsu gentle slope of the Lower Yangtze Region. Paleoecologically, it could be attributed to the BA 4–5 benthic regime (about 60–150 m deep, and deepest to 200 m), and was significantly different from the trilobite M . ( S .) mucronata and the typical Hirnantia fauna while the latters may have habited in BA 2–3 benthic regimes (about 5–60 m deep). A new paleogeographic distribution pattern of the Hirnantian shallow and deep water shelly faunas of South China is herein proposed for the first time. Assuming that the depositional rate was constant in northwestern Hunan during the end Ordovician, the duration of the Xinkailing Bed might be only 12 thousand years according to the thickness of the Wufeng Formation and the absolute age values of those relevant graptolitic biozones. Such a short time interval may indicate that the global environmental change during the crisis was much shorter than previously thought, and its influence on the deep water regime was significantly shorter than that on the shallow water regime.

Paleogeographic evolution of the Lower Yangtze region and the break of the “platform-slope-basin” pattern during the Late Ordovician

Wide distribution of the black shales and diversification of the graptolite fauna in South China during the Late Ordovician resulted from its unique paleogeographic pattern, which was significantly affected by the paleogeographic evolution of the Lower Yangtze region. In the study, 120 Upper Ordovician sections from the Lower Yangtze region were collected, and a unified biostratigraphic framework has been applied to these sections to establish a reliable stratigraphic subdivision and correlation. Under the unified time framework, we delineate the distribution area of each lithostratigraphic unit, outline the boundary between the sea and land, and reconstruct the paleogeographic pattern for each graptolite zone. The result indicates that, with the uplift and expansion of the ‘Jiangnan Oldland’ in the beginning of the late Katian, the oldland extended into the Yangtze Sea gradually from south to north, which finally separate the Jiangnan Slope and the Yangtze Platform. Consequently, the longstanding paleogeographic pattern of “platform-slope-basin” in South China was broken. The paleogeographic change led to sedimentary differentiation among the two sides of the ‘Jiangnan Oldland’ during the Late Ordovician. This event also led to the closure of the eastern exit of the Upper Yangtze Sea, and formed a semi-closed, limited and stagnant environment for the development of the organic-rich black shales during the Late Ordovician. The major controlling factors of these paleogeographic changes in the Lower Yangtze region were not consistent from the Katian to the Hirnantian. In the late Katian, the sedimentary differentiation between the east and west sides mostly resulted from regional tectonic movement - the Kwangsian Orogeny. However, during the Hirnantian, the whole Yangtze region became shallower, which was mostly influenced by the concentration of the Gondwana ice sheet and the consequent global sea level drop.

Development of a high-productivity and anoxic-euxinic condition during the late Guadalupian in the Lower Yangtze region: Implications for the mid-Capitanian extinction event

Widespread marine anoxia is considered one of the most important causes for the mid-Capitanian mass extinction. However, the mechanisms and subsequent sulfidic process for the mid-Capitanian mass extinction are still debated. Here, we focus on a comprehensive study including marine productivity and redox conditions of the Lower Yangtze area across the mid-Capitanian mass extinction based on multiple geochemical indicators. Our results show that the redox conditions and marine productivity have gone through three stages. The pre-extinction early-middle Capitanian is characterized by anoxic conditions with intermittent euxinic episodes and moderate-high productivity, whereas the middle Capitanian is dominated by stronger euxinic conditions and higher productivity. Subsequently, an oxic shallow water environment and low productivity are recognized by significant decreases in all of these geochemical indicators across the mid-Capitanian. The appearance and development of the anoxic-euxinic conditions was probably caused by high productivity related to enhanced upwelling, which led to the intensified heterotrophic respiration and subsequent oxygen-depletion of the water column. More sluggish oceanic circulation that resulted from the global warming associated with the eruption of the Emeishan Large Igneous Province and upward movement of the chemocline due to great regression also further exacerbated the euxinic conditions during the middle Capitanian. The development of these euxinic conditions may have played a major role in triggering the super-anoxic ocean and is also coincident with the mid-Capitanian biotic crisis, which suggests the possible causal link between them. With comprehensive analysis of profiles across the globe, sulfidic models showing that the sulfidic water first occurred in the deep water during the early-middle Capitanian and shoaled to shallow water in the middle-late Capitanian could be established, despite the fact that the temporally and spatially heterogeneous sulfidic processes in the late Guadalupian are still debated.

Important role of hornblende fractionation in generating the adakitic magmas in Tongling, Eastern China: evidence from amphibole megacryst and cumulate xenoliths and host gabbros

ABSTRACTTongling, in eastern China, is an area well-known for intra-plate adakites. Here, we present the mineral chemistry and zircon U–Pb ages for amphibole cumulate xenoliths, the mineral chemistry of amphibole megacrysts, and the whole–rock chemistry, zircon U–Pb age and Sr–Nd isotopic compositions of host gabbros from Tongling. Zircon U–Pb dating yields a crystallization age of 120.6 ± 1.2 Ma (MSWD = 4.2) for the host gabbros, which are characteristically depleted in high field strength elements (Nb, Ta, and Ti) and enriched in large ion lithophile elements (Ba and Sr), with εNd (t) of −3.00 to −4.52 and initial 87Sr/86Sr ratios of 0.7068–0.7072, suggesting an enriched mantle source. Parental melts, as estimated from average amphibole megacryst and cumulate compositions, have Mg# values of 26–33, are enriched in Ba, Th, U, and Nd, and depleted in Nb, Ta, Zr, Hf, and Ti, similar to 136 Ma mafic magmas in Tongling. Zircon U–Pb dating yields a crystallization age of 135.4 ± 1.0 Ma (MSWD = 1.6) for the amphibole cumulates. It is concluded that the Tongling adakitic rocks were formed by polybaric crystallization involving early high-pressure intracrustal fractional crystallization of cumulates comprising hornblende and clinopyroxene, and late low-pressure fractional crystallization of hornblende and plagioclase phenocrysts. The flat subduction of Pacific plate and its subsequent foundering during the Cretaceous may have triggered the generation of extensive adakitic magmas and lithospheric thinning in the Lower Yangtze Region.

Fracture development and fluid pathways in shales during granite intrusion

Shales generally act as barriers to subsurface fluid flow due to their low permeability. Magmatic intrusion can produce fractures in host rocks, but the relationship between fracture development and permeability changes in shales is still not clear. A 48m-wide granitic dike intruded into the Cambrian black shales at 131.8±1.5Ma in the Luocun section of the Lower Yangtze region (China). Shale samples from the Luocun section were collected to investigate the influence of granite intrusion on fracture parameters, density, porosity and permeability of shales. Based on the cross-cutting relationship, cements and characteristics of microfractures, three phases of fractures in the Luocun shales were recognized and related with the stress evolution. The widespread, narrow and straight shear fractures (Phase-I) reflect initial fracturing under compression around the intrusion. With continued magma intrusion, thermal reaction of organic matter produced CH4, CO2 and H2O, which joined with siliceous fluids from the granitic dike and increased pore fluid pressure in surrounding shales. High pore fluid pressure and thermal expansion counteracted the regional compression and caused wide, curving extension fractures (Phase-II) in shales near the dike. Meanwhile siliceous fluids transported carboniferous residues through the open pore space and fractures, sealed the fractures and silicified the shales. In the late cooling stage, pore fluid pressure and thermal contraction produced bedding-parallel, narrow extension fractures (Phase-III) in shales near the dike. The small shear displacement along Phase-II and Phase-III fractures implies that they originated as extension fractures and immediately reactivated as shear planes.The effective porosity of shale samples increases from ~0.5% at distance ≥12.95m to ~2% at 10.05m and ~4% at 0.5m from the granitic dike. Pressure dependence of plug permeability of shale samples follow an exponential equation. At 6.9MPa, plug permeability of the shales increases from 1.81×10−19m2 at 27.45m to 4.98×10−16m2 at 0.5m. Within ~37% of the dike width, the fracture density, effective porosity, plug permeability, as well as the equivalent vitrinite reflectance from our previous study, increase sharply with a decreasing distance from the dike, suggesting coincidence of a narrow contact aureole with the “permeability aureole” due to localized hydrofracturing and hydrothermal circulation. Because Phase-II and Phase-III fractures only occur within ~37% of the dike width and they were filled by microcrystalline quartz and carboniferous residues, they should be effective fluid pathways and allow fast escape of shale gas during granite intrusion.

A multi-proxy lacustrine record of last deglacial–early Holocene environmental variability in the lower Yangtze region from the Chaohu Lake Basin, eastern China

AbstractThe Rb, Sr, and Ti content, Rb/Sr ratio, grain size, magnetic susceptibility, and magnetic fabric in sediments of the BZK1 core were utilized to reconstruct the evolution of the climatic environment in the Chaohu Lake Basin between the last deglacial and the early Holocene. Multi-proxy analyses indicate that lacustrine sediments in Chaohu Lake clearly record the Bølling-Allerød interstadial, the Younger Dryas event and dry-cold climate events occurring between 10.7 cal ka BP and 10.5 cal ka BP. At approximately 15.6–14.8 cal ka BP, the waters became deeper and the climate turned cool. The climate subsequently shifted to a relatively humid period and the lake was largest from 14.8 to 12.8 cal ka BP. From 12.8 to 11.7 cal ka BP, the climate abruptly turned dry and cold and the lake shrank to its lowest level. During 11.7–10.7 cal ka BP, the climate became relatively humid but, from approximately 10.7 to 10.5 cal ka BP, suddenly reverted to a dry and cold state. These climatic change records suggest that lacustrine sediments from the Chaohu Lake Basin in the lower Yangtze region responded actively to global climate changes, comparable with the environmental records from stalagmites and other lacustrine sediments in the region.

Pore characteristics and controlling factors of the Lower Cambrian Hetang Formation shale in Northeast Jiangxi, China

To identify the microscopic pore characteristics and controlling factors of Hetang Formation Shale in the Lower Yangtze Region, the pore types, pore size distribution characteristics, and controlli...

Sandstone memory of a Late Paleozoic continental arc in southeast China (Lower Yangtze region)

Provenance analysis was carried out on Paleozoic siliciclastic rocks exposed in the South China Block (Lower Yangtze region, Chaohu and Nanjing areas) by sandstone petrography, U-Pb detrital-zircon geochronology, and zircon Hf isotopes. Sandstones of the Silurian Fentou Formation are feldspatho-quartzose with a few igneous and low-grade metamorphic rock fragments. Sandstones of the Devonian Wutong Formation are quartzose with a few quartz-rich metamorphic rock fragments. The Fentou and Wutong formations share similar detrital-zircon age spectra, with peaks mainly at 465−420 and 838−812 Ma. Zircons of Early Paleozoic age were with all likelihood derived from magmatic rocks associated with the Kwangsian orogeny, documented by a widespread unconformity across the South China Block. Neoproterozoic zircons were probably shed from Proterozoic basement of the Wuyi terrane in the Cathaysian block, interpreted to have been uplifted south of the Lower Yangtze region during the Kwangsian orogeny. The Permian Longtan Formation in Chaohu area and Nanjing area are litho-quartzose and feldspatho-quartzose, respectively, with dominant felsic and intermediate volcanic lithic fragments, indicating that detrital source areas did not change markedly after the Kwangsian orogeny. Zircon-age spectra from the Longtan Formation in the Chaohu area display a diagnostic peak at ~ 1866 Ma, indicating provenance from the Paleoproterozoic basement of the Wuyi terrane. Instead, detrital zircons in the Longtan Formation in the Nanjing area display peaks at ~ 445 and ~ 970 Ma, similar to those in the underlying Paleozoic sandstones. The Wuyi terrane in the Cathaysian block thus remained as a major source area for long, as supported by independent sedimentological and seismic evidence. The Longtan Formation in both Chaohu and Nanjing areas also contain detrital zircons with ages distributed continuously from 341 to 254 Ma and a major peak around 270 Ma, reflecting renewed intermediate and felsic magmatism in the source area. These zircons have e Hf( t ) ranging from −19.8 to +14.9, indicating melting of old crust and mixing with crustal magmas. Such a continuously magmatic source supplied sediments all across the South China Block from east to west. These and other lines of evidence including probability accumulation-curve analysis favor deposition in a convergent plate-tectonic setting. We suggest that source rocks were part of a continental arc developed along the southeast coast of China during the Late Paleozoic, shedding sediments to as far as north as the northern South China Block. According to previous studies, such continental arc would be related to the subduction of the paleo-Pacific plate. Magmatism generated at first by melting of old crust was mixed later on with felsic and intermediate magma newly generated during mantle upwelling and associated uplift. The continental arc remained as the main detrital source to the Lower Yangtze region and other parts of the South China Block until it was eventually denudated or buried by the Mesozoic times.

A Permian-Triassic boundary microbialite deposit from the eastern Yangtze Platform (Jiangxi Province, South China): Geobiologic features, ecosystem composition and redox conditions

A Permian-Triassic (P-Tr) boundary microbialite (PTB-microbialite) deposit occurs near Xiushui on the southern margin of the eastern Yangtze Platform, South China. This 2-m-thick microbialite overlies uppermost Permian bioclastic limestone with a 5-cm-thick oolite-like grainstone layer at the contact. This PTB-microbialite consists of lower thrombolite (1.5-m thick) and an upper dendrolite (0.5-m thick). The thrombolite interval is characterized by a clotted texture of reddish sparitic patches embedded in a gray micritic matrix, whereas the dendrolite texture consists of brownish sparitic patches embedded within a yellow micritic matrix. Abundant calcified microbes occur in both the thrombolite and the dendrolite, including 1) columnar and clustered fabrics, which are especially rich in the thrombolite, assigned as products of Gakhumella or related microorganisms and 2) microspheroids, 40–60μm in diameter, with different interior structures. These calcimicrobes are considered to have played an important role in constructing the Xiushui PTB-microbialite. The demise of the microbialite was likely due to a sea-level fall during the early Griesbachian (lowermost Triassic), which resulted in a lowering of the wave base thereby destroying the microbialite frameworks and facilitating the deposition of winnowed skeletal grainstone. Metazoan community structures within the microbialite changed sharply across the end-Permian extinction horizon, which is placed at a sharp negative shift in δ13Ccarb. Quantitative analyses show that the Xiushui microbialite community is similar to that of Chongyang and Cili microbialites. This is probably because all of these microbialites grew along the margins of the Lower Yangtze region during the P-Tr transition. However, unlike other PTB-microbialites, the Xiushui ecosystem contains fairly abundant metazoans, which are dominated by ostracods with minor occurrences of foraminifers, microgastropods and microconchids. Both the ostracod assemblage and the pyrite framboid analyses indicate an upper dysoxic zone to a well-oxygenated condition for the Xiushui microbialite. This implies that some PTB-microbialite ecosystems developed in conditions that were not always harsh; instead, some were hospitable for some metazoans to survive immediately after the end-Permian crisis. Considering that the redox conditions indicated by PTB-microbialites are quite variable, we infer that oxygen levels probably were not the crucial factor affecting the growth of the PTB-microbialites.

Quantitative Holocene climatic reconstructions for the lower Yangtze region of China

Quantitative proxy-based and high-resolution palaeoclimatic datasets are scarce for the lower reaches of the Yangtze River (LYR) basin. This region is in a transitional vegetation zone which is climatologically sensitive; and as a birthplace for prehistorical civilization in China, it is important to understand how palaeoclimatic dynamics played a role in affecting cultural development in the region. We present a pollen-based and regionally-averaged Holocene climatic twin-dataset for mean total annual precipitation (PANN) and mean annual temperature (TANN) covering the last 10,000 years for the LYR region. This is based on the technique of weighted averaging-partial least squares regression to establish robust calibration models for obtaining reliable climatic inferences. The pollen-based reconstructions generally show an early Holocene climatic optimum with both abundant monsoonal rainfall and warm thermal conditions, and a declining pattern of both PANN and TANN values in the middle to late Holocene. The main driving forces behind the Holocene climatic changes in the LYR area are likely summer solar insolation associated with tropical or subtropical macro-scale climatic circulations such as the Intertropical Convergence Zone (ITCZ), Western Pacific Subtropical High (WPSH), and El Nino/Southern Oscillation (ENSO). Regional multi-proxy comparisons indicate that the Holocene variations in precipitation and temperature for the LYR region display an in-phase relationship with other related proxy records from southern monsoonal China and the Indian monsoon-influenced regions, but are inconsistent with the Holocene moisture or temperature records from northern monsoonal China and the westerly-dominated region in northwestern China. Overall, our comprehensive palaeoclimatic dataset and models may be significant tools for understanding the Holocene Asian monsoonal evolution and for anticipating its future dynamics in eastern Asia.

Assessing the harvested area gap in China

Total crop production is a function of the harvested area and the yield. Many studies have investigated opportunities to increase production by closing the yield gap and by expanding cropland area. However, the potential to increase the harvested area by increasing the cropping frequency on existing cropland has remained largely unexplored. Our study suggests that the attainable harvested area gap (HAG) in China ranges from 13.5 to 36.3 million ha, depending on the selected water allocation scenario, relative to the current harvested area of 160.0 million ha. Spatially, South China and the Lower Yangtze region have the largest potential to increase harvested area, as these regions allow triple-cropping, have sufficient water available, and have a good irrigation infrastructure. The results imply that management factors are equally important for exploring the potential against the resource endowment: water allocation has a large impact on both the size and the spatial pattern of the attainable HAG. This indicates the necessity of further examining the spatial-temporal dynamics of HAG at national and regional scales, and its potential contribution to food security and sustainable agricultural development.

Pathways of Rice Diversification across Asia

The archaeology of rice has made important methodological advances over the past decade that have contributed new data on the domestication process, spread and ecology of cultivation. Growing evidence from spikelet bases indicates that non-shattering, domesticated forms evolved gradually in the Yangtze basin and that there were at least two distinct processes around the Middle Yangtze region pre-dating 6000 BC, and the in the Lower Yangtze region between 6000 and 4000 BC. Early rice cultivation in these areas was based on wet field ecologies, in contrast to rainfed rice that is indicated among the earliest systems in India. When rice first spread north it was not entirely suited to shorter temperate summer growth seasons, and we are able to infer from high levels of apparently green-harvested spikelets that genetic adaptations to temperate conditions evolved after 2000 BC. When rice first spread south, to mainland Southeast Asia, after 2500 BC, it was grown in rainfed, dry ecologies that were less labour-demanding and less-productive. More productive and intensive irrigated rice then redeveloped in Southeast Asia around 2000 years ago, supporting growing population densities and social complexity.

Phylogeography, Historical Demography, and Genetic Structure of the Rose Bitterling, Rhodeus ocellatus (Kner, 1866) (Cypriniformes: Acheilognathidae), in East Asia.

Yao-Feng Tsao, Wen-Wen Lin, Chia-Hao Chang, Takayoshi Ueda, Nian-Hong Jang-Liaw, Ya-Hui Zhao, and Hsiao-Wei Kao (2016) Rose bitterling, Rhodeus ocellatus, is a small cyprinid fish distributed in East Asia. To infer its phylogeography and genetic structure, specimens from Taiwan, China, and Japan were collected, and complete mitochondrial cytochrome b (cyt b) DNA sequences were amplified and sequenced. Phylogenetic analyses identified seven mitochondrial lineages (A-G). Among them, three lineages (A, B, and C) distributed in mainland China. Lineages D, E, and F distributed in Japan, Korea, and Taiwan, respectively. Lineage G distributed in both China and Japan. The results of the Bayesian Binary MCMC analysis (BBM) suggested that the most recent common ancestor of R. ocellatus was from Lower Yangtze region. Divergence times among lineages inferred by molecular clock ranged from 7.55 to 1.44 million years ago. We propose that topography and climate changes by uplift of the Tibetan Plateau in the Late Miocene-Pliocene and the glacial-interglacial cycles in the Pleistocene might account for population expansion and genetic differentiation. Divergence times among lineages A, B, and C in Yangtze River basin ranged from 7.55 to 2.27 million years ago that might result from changes of flow directions of rivers from westward to eastward driven by the uplift of the Tibetan Plateau. The glacial-interglacial cycles in the Pleistocene might further cause population expansion to the northward of lineage G at about 0.19 million years ago. Lineage D in Japan was dispersed from the mainland China before the opening of the Sea of Japan, and lineage F in Taiwan was dispersed from the mainland China through the land bridge in the Pleistocene. Because of the genetic differentiation is statistically significant among populations, protection of genetic diversity and distinctness of R. ocellatus should be considered in the future conservation management.

Pore system characteristics of the Permian transitional shale reservoir in the Lower Yangtze Region, China

The Permian shale, a set of transitional shale reservoir, is considered to be an important shale gas exploration target in the Lower Yangtze region. Due to little research conducted on the pore system characteristic and its controlling factors of the shale gas reservoir, SEM, FE-SEM, low-pressure N2 adsorption, and mercury intrusion tests were carried out on the Permian shales from the outcrop and HC well in the southern Anhui. The results show that the Permian shales mainly consist of organic matter, quartz, illite, calcite, and pyrite, of which pyrite occurs as framboids coexisting with organic matter and the organic matter is distributed in shales in stripped, interstitial, thin film and shell shapes. The basic pore types are inorganic mineral pore (intercrystalline pore, intergranular edge pore, intergranular pore, and interlayer pore in clay minerals) and the organic pore and microfracture, of which organic pore and microfracture are the dominating pore types. In shale, organic pores are not developed at all in some organic grains but are well developed in others, which may be related to the types of and maceral compositions of kerogen. Under tectonic stress, shale rocks could develop mylonitization phenomenon exhibiting organic grains well blend with clay minerals, and produce a mass of microfractures and nanopores between organic matter grains and clay minerals. Mercury intrusion tests show that the shale is mainly composed of micropore and transition pore with high porosity, good pore connectivity and high efficiency of mercury withdraw, while the shale that mainly dominated by mesopore and macropore has a low porosity, poor pore connectivity, and low efficiency of the mercury withdraw. The volume percentage of mesopore and marcopore is increasing with the increase of quartz, and that of micropore and transition pore has a decreased tendency along with the increase of soluble organic matter (S1). Organic matter is the main contributor to the specific surface area. However, clay minerals could significantly inhibit the numbers of the microscopic pore and specific surface area due to the clay minerals being mainly dominated by illite and chlorite.

Effect of magmatic hydrothermal on gas reservoir formation in Permian-Lower Triassic source rocks in Huangqiao Area, South China

The main source rocks for gas reservoirs in Huangqiao area of Lower Yangtze region in south China are Permian-Lower Triassic marine strata with high maturity, including carbonate and clastic rocks. A series of geochemical experiments have been carried out in order to reveal the forming mechanism of large gas reservoirs. Geochemical characteristics of crude oils show the source kitchen, which contributes to the large gas reservoir formation, has changed from kerogen cracking to oil cracking. Based on the results of geological evidences, abnormal distribution of vitrinite reflectance, and fluid inclusion characteristics, magmatic hydrothermal is believed to be existed in Huangqiao area. The magmatic hydrothermal changes the source kitchen in two ways. First, the source rock evolution is accelerated by thermal provided by magmatic hydrothermal. Second, it provides hydrogen in the water contained in magmatic hydrothermal to improve liquid hydrocarbons transforming into gases. Thus, the magmatic hydrothermal might considered to be an important factor forming large-scale gas reservoirs in South China.

U–Pb and Re–Os Geochronology of the Hucunnan Copper–Molybdenum Deposit in Anhui Province, Southeast China, and its Geological Implications

AbstractThe Middle–Lower Yangtze Region (MLYR) is one of the most important metallogenic belts in China that hosts numerous Cu–Fe–Au–S deposits. The Hucunnan deposit in the central part of MLYR is a newly discovered porphyry–skarn‐type copper–molybdenum deposit during recent drilling exploration. Laser ablation ICP–MS analysis carried out in this study yields U–Pb isotopic ages of 137.5 ± 1.2 Ma for the Cu–Mo bearing granodiorite rock and 125.0 ± 1.5 Ma for the Cu‐bearing quartz diorites. The Re–Os isotopic dating of seven molybdenite samples gave an isochron age of 139.5 ± 1.1 Ma, suggesting a syn‐magma mineralization of molybdenite in the Hucunnan deposit. Since porphyry‐type molybdenum deposits are rare in central MLYR, the discovery of the Hucunnan deposit suggests possible molybdenite mineralizations in the deep places of the Cu–Mo bearing granitoids. In addition, the U–Pb isotopic age of 125 Ma for the Cu‐bearing quartz diorites implies a new Cu mineralization period for the MLYR that was rarely reported by previous studies.

Heterogeneous volcanism across the Permian–Triassic Boundary in South China and implications for the Latest Permian Mass Extinction: New evidence from volcanic ash layers in the Lower Yangtze Region

Volcanism has been suggested to have occurred widely in South China across the Permian–Triassic boundary (PTB); this has important implications for understanding the cause of the Latest Permian Mass Extinction (LMPE). However, few volcanic deposits have been reported in the Lower Yangtze Region and the extent of volcanism is uncertain. Herein we report new discoveries of intensive volcanism in this region for the first time, as evidenced by multiple (n>20) and thick (3–5cm) claystones (volcanic ash layers, K-bentonite) found in three deep-water outcrops in Xuancheng city, southern Anhui Province. Detailed petrographic and geochemical analyses of the ash layers were conducted to understand their origin and implications for the cause of the LPME, including X-ray diffraction, scanning electronic microscopy, energy dispersive spectroscopy, and whole-rock geochemistry. The petrological and mineralogical results show that the claystones contain clastic minerals indicative of a volcanic origin, such as zircon, analcites, pentagonal dodecahedral pyrite, and micro-spherules. The whole-rock geochemical data of the claystones suggest that the source rock of the ash layers was intermediate–acidic rhyodacite. The claystones are different from previously known claystones in the Middle–Upper Yangtze regions, indicating the occurrence of chemically heterogeneous volcanism in South China at the PTB.

Distribution patterns and dynamics of phosphorus forms in the overlying water and sediment of Dongting Lake

Abstract Dongting Lake is a typical shallow lake in the lower Yangtze region and is the second largest freshwater lake in China. The distribution, speciation, and sediment release characteristics of phosphorus (P) were investigated by analyzing sediment and water samples collected during high and low flow periods. The average concentration (range) of total phosphorus (TP) in the water was 0.05 mg L − 1 (0.02 ~ 0.09 mg L − 1 ), while the value in sediment was 703 mg kg − 1 (466 ~ 869 mg kg − 1 ). The concentrations of TP and different P forms decreased as depth increased. Inorganic phosphorus was the dominant form of P, accounting for 72% of TP. The bioavailable P was a relatively large portion of TP, indicating a high risk of P release to overlying water. The Langmuir equation can well describe the P isotherm adsorption characteristics in sediment. The amount of P desorption from sediment tended to increase with increasing concentrations of adsorbed P.

Permian–Triassic boundary (PTB) in the Lower Yangtze Region, southeastern China: A new discovery of deep-water archive based on organic carbon isotopic and U–Pb geochronological studies

The Lower Yangtze Region of southeastern China is an important area for the study of Permian–Triassic Boundary (PTB). In this region many well-known PTB sections (e.g., Meishan) have been investigated widely and extensively; however, these sections are dominantly in shallow-water settings and data from deep-water areas are lacking. To fill the gap, we conducted a field survey recently and found a deep-water PTB section with relatively continuous deposition using integrated organic carbon isotopic and U–Pb geochronological studies. This well-exposed and fresh section is located at Niushan, Xuancheng city, Anhui Province, ~90km west of the well-known Meishan section, which is the PTB Global Boundary Stratotype Section and Point. The organic carbon isotope curve of the section contains three positive excursions (PCIEs) and two negative excursions (NCIEs), which can be well correlated with other PTB sections as well as with Wuchiapingian–Changhsingian Boundary (WCB) sections worldwide. They archive the original PTB and WCB signatures. Further U–Pb dating of magmatic zircons in volcanic ashes validates this new finding, i.e., the PTB interval between 252.49±0.76Ma and 251.74±0.77Ma. Carbon isotopes of PTB sections in South China reflect the regional paleogeography. The two NCIEs (NCIE-2 and NCIE-3) across the PTB transition are most likely caused by widespread large-scale volcanic activity. In contrast, the NCIE-1 near the WCB is possibly related to an increase in the productivity of organic matter as a result of transgression and a change in the organic matter type from terrigenous to marine.

Topographic architecture and drainage reorganization in Southeast China: Zircon U-Pb chronology and Hf isotope evidence from Taiwan

The uplift of Tibet Plateau and the marginal sea spreading have had important influence on the tectonic, landform and drainage system in East Asia, although the marginal sea spreading in shaping the topography and drainage reorganization in East Asia has been still controversial. Here we present U-Pb age and Hf isotopic composition of detrital zircon grains from Cenozoic sedimentary rocks in Taiwan to understand how the provenance and river systems evolved. Our data show that the U-Pb age spectra of detrital zircon grains in Paleogene sandstones are dominated by Yanshanian (180–67Ma) zircon grains and with subordinate or nil Proterozoic and Archean zircon grains. These results are in contrast to those in Miocene rocks that are dominated by the Indosinian (257–205Ma) zircon grains together with Yanshanian, Proterozoic and Archean population. The initial Hf isotope ratios [εHf(t)] of the zircon grains also display systematic change in Paleogene and Neogene strata. Our data demonstrate that the Hsuehshan Range and Western Foothills in Taiwan have the same sedimentary sources. The source region of Paleogene strata was mainly located at the coast in southeast China and migrated inland over time. The source might have reached the Lower Yangtze region during early Miocene. Although the mechanism of transport of sediments from the Lower Yangtze region to Taiwan is unclear, we speculate that the Minjiang River might have been larger in Early Miocene than the present and might have delivered inland material along the boundary of Yangtze and Cathaysia Blocks to Taiwan. These were then captured by the Yangtze River systems at some time after Late Miocene. This change corresponds to the time of the drainage reorganization in East Tibet, such as Yangtze River, and the regional subsidence resulting from the opening of marginal sea. The combined effects of Tibet uplift and opening of marginal sea might have shaped the topography and river system reorganization in East Tibet. The evolution of topography and drainage systems in southeast China seems to be mainly controlled by the opening of marginal sea.