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    Core value of the Chengjiang fauna: formation of the animal kingdom and the birth of basic human organs (English)
    SHU Degan, HAN Jian
    Earth Science Frontiers    2020, 27 (6): 382-412.   DOI: 10.13745/j.esf.sf.2020.10.28
    Abstract517)      PDF (25271KB)(135)      

    Well known for its abundant and extraordinary soft-tissue fossils, the Chengjiang fauna has witnessed the main phase of the Cambrian explosion and the first great congress of the ancestors of nearly all major phyla of animals on Earth. The large-scale survey and exploration of the fauna by Chinese paleontologists, partly in collaboration with international scientists, over the past 30 years can be broadly divided into three stages. In the first decade since 1984 (1984—1994), a large number of invertebrates, including basal animals and the protostomes of the early animal tree were discovered, but the subkingdom Deuterostomia was completely unknown. Then in the second decade (1995—2005), the great discoveries of various deuterostomes led to the construction of the basic framework of the Deuterostomia and then to the formation of the tripartite phylogenetic trees of early animals (TPTEA, including basal animals, protostomes and deuterostomes), for the first time. In the third decade (after 2005), the academic community began to think about the internal relationships between the formation of TPTEA and the multi-episode Cambrian explosion, leading to the new hypothesis of the three-episode Cambrian explosion. The Chengjiang fauna is important for deciphering the fauna structure, paleoecological environment, and so on. However, its core academic values mainly rest on two aspects. Firstly, The Chengjiang fauna, as the main phase witness of the Cambrian explosion, has created a nearly complete phylogenetic framework of the TPTEA on Earth for the first time. The three-phase radiation hypothesis reveals the essential connotation of the Cambrian explosion: a step-wise divergent evolution of animals, from basal to highly advanced groups, lasting about 40 million years. In the first phase, it gave birth to a bulk of basal animals (including some now extinct “animal” groups) in the latest Ediacaran, probably including some pioneer protostomes. The second phase took place in the first epoch of the Cambrian period (Terreneuvian), giving rise to the main invertebrate protostomes with a persistent prosperity of basal animals. The third phase proceeded in Cambrian Epoch 2 (represented by the Chengjiang fauna), which not only maintained the prosperity of basal animals and protostomes, but also, more importantly, gave birth to all the main phyla of the subkingdom Deuterostomia. Thus, the rudimental framework of the whole TPTEA has been shaped, with the termination of the major innovation events of the Cambrian explosion. Here, we discussed the evolutionary properties of Ediacaran biota, small shelly fossils and the Chengjiang fauna in the Cambrian explosion with emphasis on the biological properties of several important animal groups. The order Myllokunmingiida is the only known oldest vertebrate, while Yunnanozoon and Haikouella are neither vertebrates nor stem-group chordates but a special group of basal deuterostomes; Cheungkongella is a credible ancestor of the urochordate and it supports the classical hypothesis on the origin of the urochordates; and the gill slits were first invented in the members of the phylum Vetulicolia to provide key information on the origin of the deuterostomes. The second core value of the  Chengjiang fauna is of profound humanistic and philosophical significance: the discoveries of the ‘first gill openings’, ‘first brain’, ‘first vertebrae’ and ‘first heart’ provide the pivotal evidence for solving the unsolved mystery of the origin of the main basic human organs as described in Darwin’s “The Descent of Man”. In addition, the morphological and anatomical information of the Chengjiang fauna can provide important clues for a better understanding of most components of Ediacaran and Cambrian metazoans.

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    A new Early Cretaceous pterosaur from the Ordos region, Inner Mongolia
    JI Shu’an, ZHANG Lifu
    Earth Science Frontiers    2020, 27 (6): 365-370.   DOI: 10.13745/j.esf.sf.2020.6.14
    Abstract370)      PDF (4202KB)(233)      

    The western Ordos region in Inner Mongolia, including Hanggin Banner and Otog Banner, is one of the most important localities yielding the Early Cretaceous Psittacosaurus Fauna across northern China. No pterosaur material had been formally depicted until Ordosipterus planignathus was named and described in the early 2020. Here, we report a new partial pterosaur mandibular symphysis discovered at the Zhaoshao site in the Luohandong Formation in Otog Banner. Its mandibular symphysis is long and straight and bears a developed lateral ridge that divided the dentary lateral side into the upper and lower parts. Nearly round dentary alveoli of each side lie just above the lateral ridge along a straight line anteroposteriorly. The diameters of alveoli (22.5 mm) vary slightly from rostral to caudal. The distance between the adjacent alveoli is about half the diameter of either alveolus. The tooth density is 3 teeth per centimeter. This pterosaur could be assigned to the family Ctenochasmatidae, it represents a new taxon-Otogopterus haoae gen.et sp.nov. The generic name refers to the type locality (Otog Banner) of this pterosaur, and the species name is in honour of Prof. Hao Yichun, who made outstanding contributions on the Mesozoic paleontology and stratigraphy in China. This new fossil is the second definitive pterosaur kind in the Inner Mongolian Ordos region following Ordosipterus planignathus, further enriching the components of the Early Cretaceous vertebrate fauna in this region. This pterosaur is also the second ctenochasmatid taxon in the Ordos Basin, after Huanhepterus quingyangensis from eastern Gansu Province. The new finding enlarged the geographical distribution of ctenochasmatid pterosaurs in the Ordos Basin and revealed the Ordos Basin to be another important distribution area of Ctenochasmatidae in China.

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    Core value of the Chengjiang fauna: formation of the animal kingdom and the birth of basic human organs(English version of the full article is on pages 382412 of this issue.)
    SHU Degan, HAN Jian
    Earth Science Frontiers    2020, 27 (6): 1-27.   DOI: 10.13745/j.esf.sf.2020.6.15
    Abstract309)      PDF (15933KB)(318)      

    Well known for its abundant and extraordinary soft-tissue fossils, the Chengjiang fauna has witnessed the main phase of the Cambrian explosion and the first great congress of the ancestors of nearly all major phyla of animals on Earth. The large-scale survey and exploration of the fauna by Chinese paleontologists, partly in collaboration with international scientists, over the past 30 years can be broadly divided into three stages. In the first decade since 1984 (1984—1994), a large number of invertebrates, including basal animals and the protostomes of the early animal tree were discovered, but the subkingdom Deuterostomia was completely unknown. Then in the second decade (1995—2005), the great discoveries of various deuterostomes led to the construction of the basic framework of the Deuterostomia and then to the formation of the tripartite phylogenetic trees of early animals (TPTEA, including basal animals, protostomes and deuterostomes), for the first time. In the third decade (after 2005), the academic community began to think about the internal relationships between the formation of TPTEA and the multi-episode Cambrian explosion, leading to the new hypothesis of the three-episode Cambrian explosion. The Chengjiang fauna is important for deciphering the fauna structure, paleoecological environment, and so on. However, its core academic values mainly rest on two aspects. Firstly, The Chengjiang fauna, as the main phase witness of the Cambrian explosion, has created a nearly complete phylogenetic framework of the TPTEA on Earth for the first time. The three-phase radiation hypothesis reveals the essential connotation of the Cambrian explosion: a step-wise divergent evolution of animals, from basal to highly advanced groups, lasting about 40 million years. In the first phase, it gave birth to a bulk of basal animals (including some now extinct “animal” groups) in the latest Ediacaran, probably including some pioneer protostomes. The second phase took place in the first epoch of the Cambrian period (Terreneuvian), giving rise to the main invertebrate protostomes with a persistent prosperity of basal animals. The third phase proceeded in Cambrian Epoch 2 (represented by the Chengjiang fauna), which not only maintained the prosperity of basal animals and protostomes, but also, more importantly, gave birth to all the main phyla of the subkingdom Deuterostomia. Thus, the rudimental framework of the whole TPTEA has been shaped, with the termination of the major innovation events of the Cambrian explosion. Here, we discussed the evolutionary properties of Ediacaran biota, small shelly fossils and the Chengjiang fauna in the Cambrian explosion with emphasis on the biological properties of several important animal groups. The order Myllokunmingiida is the only known oldest vertebrate, while Yunnanozoon and Haikouella are neither vertebrates nor stem-group chordates but a special group of basal deuterostomes; Cheungkongella is a credible ancestor of the urochordate and it supports the classical hypothesis on the origin of the urochordates; and the gill slits were first invented in the members of the phylum Vetulicolia to provide key information on the origin of the deuterostomes. The second core value of the  Chengjiang fauna is of profound humanistic and philosophical significance: the discoveries of the ‘first gill openings’, ‘first brain’, ‘first vertebrae’ and ‘first heart’ provide the pivotal evidence for solving the unsolved mystery of the origin of the main basic human organs as described in Darwin’s “The Descent of Man”. In addition, the morphological and anatomical information of the Chengjiang fauna can provide important clues for a better understanding of most components of Ediacaran and Cambrian metazoans.

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    Comparison of biodiversity of the Early Cretaceous pterosaur faunas of China
    WANG Xiaolin, LI Yang, QIU Rui, JIANG Shunxing, ZHANG Xinjun, CHEN He, WANG Junxia, CHENG Xin
    Earth Science Frontiers    2020, 27 (6): 347-364.   DOI: 10.13745/j.esf.sf.2020.6.19
    Abstract182)      PDF (24877KB)(170)      

    A large number of continental basins in northeastern and northwestern China contain abundant vertebrate fossils in lacustrine deposits. Among them, the Wuerho Pterosaur Fauna from the Junggar Basin on the north side of the Tian Shan Mountains, the Hami Pterosaur Fauna from the Turpan-Hami Basin on the south side of the Tian Shan Mountains, and the Jehol Biota of western Liaoning, all bear rich pterosaur fossils. The former two faunas of northwestern China shared similar prosperous time and were both discovered in the Lower Cretaceous Tugulu Group. Pterosaur diversity of these two faunas is low but the faunas included abundant individuals. Fossils of the Wuerho Pterosaur Fauna, preserved mostly in the fine-sandstones and siltstones of the semi-deep lacustrine deposits, were relatively complete and formed by normal death. The fossils of the Hami Pterosaur Fauna were largely preserved in the tempestites of the event deposits of a shore-shallow lake. The disarticulated bones were complete after the short-distance transport by storms and a fast burial. By contrast, the pterosaurs of the Jehol Biota of northeastern China have high diversity as well as an association with fishes, amphibians, dinosaurs and other reptiles, and birdsand mammals, They were mainly preserved in the semi-deep to deep lacustrine shales. The skeletons are relatively complete, as a volcanic eruption caused massive death and fast burial (by volcanic ashes) creating a very different outlook from that of the two northwestern faunas. Based on the preliminary comparison of the pterosaur faunas from the south and north sides of the Tian Shan Mountains, we inter that the dominant pterosaurs on the north side, dsungaripterids, are distributed in the Junggar Basin and neighboring western Mongolia, that they have a distant relationship with the only known taxon, Hamipterus, from the faunas from the south side. Hence, we have proposed that the Tian Shan Mountains rose to a relatively high level in the Mesozoic, blocking the migration of the faunas from both sides of the mountains. In western Liaoning and its neighboring regions, the destruction of the North China Craton caused abundant volcanic eruptions, which created a highly diversified ecological environment with rapid replacements of creatures thus resulting in unique biodiversity in the Jehol Biota. However, the continental basins in northwestern China, which experienced no volcanic eruption, have low diversity but high abundancy of pterosaurs. Therefore, we proposed that the frequent and intense volcanic eruptions caused by the destruction of the North China Craton played an essential role in the varying diversity between the pterosaur faunas of northeastern and northwestern China.

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    Natural mineral photoelectric effect: non-classical mineral photosynthesis
    LU Anhuai, LI Yan, DING Hongrui, WANG Changqiu, XU Xiaoming, LIU Feifei, LIU Yuwei, ZHU Ying, LI Yanzhang
    Earth Science Frontiers    2020, 27 (5): 179-194.   DOI: 10.13745/j.esf.sf.2020.5.35
    Abstract159)      PDF (3267KB)(109)      

    Under the ever-existing solar irradiation, the organisms on Earth have evolved with a structurally sophisticated photosynthesis system. However, the inherent impact and response mechanism of solar illumination on the inorganic minerals widespread on the Earth surface has drawn little attention. We discovered for the first time the solar energy conversion system of the “mineral membrane”, which exerts potential oxygen production and carbon sequestration functions on the Earth surface. Our finding shed light on the photoelectric effect and non-classical photosynthesis of the natural semiconducting minerals. We carried out this research on the semiconducting property and photoelectron energy of the typical minerals in the “mineral membrane”. We further discussed the photoelectric effect, oxygen production and carbon sequestration functions of the ferromanganese oxides, as well as the corresponding geological records. We proposed that the sensitive and stable photon-to-electron conversion are performed by birnessite, goethite and hematite, which are semiconducting minerals commonly present in the natural “mineral membrane”. In addition, we put forward the non-classical mineral photosynthesis function as follows: the solar energy conversion system developed by inorganic minerals resembles the biological photosynthesis process regarding to oxygen evolving and carbon fixing; also, the “mineral membrane” may take part in the photocatalytic water-oxidation reaction and in the transformation of atmospheric CO2 into marine carbonate. Last but not least, minerals might as well have promoted the biologic photosynthesis system as the core complex in the Mn4CaO5 photosynthesis system evolved during water-oxidation process to form the structural analog birnessite. Therefore, it is fair to postulate that birnessite could play a role in the initiation of the photosynthesis system of cyanobacteria. On the other hand, minerals could weaken hydrogen bond strength and alter water property, thus to facilitate water oxidation and photosynthesis efficiencies, which would hopefully give further insights into the molecular mechanism of mineral participation in the biologic photosynthesis process.

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    Redescription of Eochondrosteus sinensis (Acipenseriformes, Actinopterygii) and its geological age
    LU Liwu, TAN Kai, WANG Xi
    Earth Science Frontiers    2020, 27 (6): 371-381.   DOI: 10.13745/j.esf.sf.2020.6.6
    Abstract136)      PDF (6392KB)(100)      

    Acipenseriformes are a group of early actinopterygian fish with an unfossified vertebral column, a smooth body without scales, or only with a few rows of bone scute. The group comprises of four families, two of them have living members. They are Acipenseridae and Polydontidae, which include the living fish Acipenser and Psephurus from Asia, Polydon from North America, and some fossil species such as the Early Cretaceous Protopsephurus and Late Cretaceous Paleopsephurus. The other two families are only fossil species, they are Chondrosteidae found in the Early Lias of Europe, and Peipiaosteidae from the Middle Jurassic-Early Cretaceous of Northeast Asia. Eochondrosteus sinensis Lu, Li et Yang, 2005, which does not belong to any of the aforementioned families, was preserved in 2005 as the oldest fossil acipenseriform fish. It was found in a black-grey silty shale previously identified as Late Permian in age, exposed 50 km west of Mazongshan Township, Gansu Province, Northwest China. Based on certain newly prepared specimens, this fish is redescribed herein. The revised diagnosis is as follows: small-sized acipenseriform fish; vertebral column unossified but with a row of basal dorsal and supraneural along its body; frontal (fr) rectangular in shape, nearly the size of the parietal (pa); posttemporal (pt) large, triangular in shape; dermosphenotic (dsp) small, connected with infraorbital (io); subopercular (sop) fan-shaped with an elongated anterior process, large in size, nearly double that of the opercular (op); more than two branchiostegal rays and one large size gular plate present; upper jaw (max) uprise in its middle part and a triangular premaxilla (pmx) with sharp teeth in its anterior ventral edge; dentary (den) long and slim, toothed in the anterior part; dorsal fin located behind pelvic fin, and caudal fin heterocercal, with both dorsal and ventral fulcra scales present; and fish body smooth and scaleless, with only a few rhombic scales present in the upper lobe of caudal fin. Eochondrosteus can be distinguished from other acipenseriform fish by the following composed characteristics: (1) a large subopercular, with an elongated anterior extension; (2) a premaxillary bone present and a toothed jaw; (3) a large gular bone; and (4) a smooth body, with scales present only in the upper lobe of caudal fin. A brief phylogenetic analysis was performed mainly based on the character matrix of Hilton and Forey with a few modifications, and a heuristic tree search was conducted using the TNT(V1.5) software. The parsimony cladograms obtained show that Eochondrosteus is on the root of the phylogenetic tree, as the sister group of all other acipenseriformes. The result suggests that it could be the most primitive acipenseriformes fish, although some bone characteristics of the fish skull still need to be added. The opinion on geological age from recent studies on non-mammalian fossil reptiles (trirachodontid Beishanodon youngi) and on fossil fish (Plesiofuro mingshuica and scanilepiform Beishanichthyes) from the ‘Beishan Hills’ of Gansu, is temporarily agreed here. All relevant studies suggest an Early Triassic age for the fossil-bearing beds. Therefore, the age of Eochondrosteus sinensis was changed from Late Permian, dated in 2005, to Early Triassic as those ‘Beishan Hills’ fossils are regarded as having the same stratigraphic horizon and even the same fossil locality as Eochondrosteus sinensis, according to the literature review and field investigation. Eochondrosteus sinensis remains as the oldest acipenseriform fish.

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    Earth Science Frontiers   
    Stable potassium isotope geochemistry and cosmochemistry
    WANG Kun, LI Weiqiang, LI Shilei
    Earth Science Frontiers    2020, 27 (3): 104-122.   DOI: 10.13745/j.esf.sf.2020.4.5
    Abstract134)      PDF (2507KB)(277)      

    The high-precision potassium (K) stable isotope system is one of the emerging non-traditional isotope systems enabled in recent years by the advance of Multi-Collector Inductively-Coupled-Plasma Mass-Spectrometry (MC-ICP-MS). Here we provide a brief overview on 1) the geochemical and cosmochemical properties of potassium and its major reservoirs, and the abundances of K on earth and in the rest of the Solar System; 2) the history of K isotope studies from 1922 to 2019; 3) the analytical methods of studying K isotopes including column chromatography and mass spectrometry (Thermal Ionization Mass Spectrometry-TIMS, Secondary Ion Mass Spectrometry-SIMS, and MC-ICP-MS); 4) the applications of K stable isotopes in low-temperature geochemistry and biogeochemistry, such as understanding processes of continental weathering, hydrothermal alteration, and reverse weathering; 5) the applications of K stable isotopes in high-temperature geochemistry, such as studying subduction dehydration/metamorphism, tracing subducted oceanic crustal materials and evaluating mantle heterogeneity; and 6) the applications of K stable isotopes on cosmochemistry, such as understanding solar nebular condensation, parent-body processing, planetary formation and magma ocean evolution.

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    Major challenges and development in Chinese sedimentological research on petroliferous basins
    ZHU Xiaomin, DONG Yanlei, LIU Chenglin, YE Lei, ZHANG Meizhou
    Earth Science Frontiers    2021, 28 (1): 1-11.   DOI: 10.13745/j.esf.sf.2020.5.1
    Abstract133)      PDF (1652KB)(234)      
    Sedimentological research is highly relevant to human survival and mineral resource exploration and exploitation. In this paper, we briefly analyzed the rearch hotspots in sedimentological researches both at home and abroad by examining the recent 200 years of research history. The International Association of Sedimentology has paid much attention to the IODP, deep-time climate and global sea level changes, source-to-sink system, carbonate sedimentary environment, mixed clastic-carbonate sedimentation, microbialite, shelf edge delta, gravity flow, fine-grained sedimentation, tectono-sedimentology, and volcanic and seismic sedimentology. While Chinese sedimentologists have focused on continental sedimentation, sedimentary models of continental basins, sedimentology of the South China Sea, sedimentary process of different types of basins in China, shallow and shelf edge deltas, source-to-sink systems of different sizes and geological ages, and carbonate deposits in small cratonic basins of southern China. Presently, the major global sedimentological research hotspots include continental sedimentology, onshore and shallow-water deposits, deep-water sedimentation and event deposits, carbonate sedimentation, sedimentary process and new methods. Future areas of sedimentological research development in China shall include theory of sedimentary dynamics of different petroliferous basins, regional characteristic continental sedimentology, multi-disciplinary approach, quantitative sedimentology, and new research methods. Sedimentology as a very important discipline of geology can guide more efficient hydrocarbon prospecting and exploration.

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    Natural mineral photoelectric effect: mineral non-classical photosynthesis
    LU Anhuai, LI Yan, DING Hongrui, WANG Changqiu, XU Xiaoming, LIU Feifei, LIU Yuw
    Earth Science Frontiers    2020, 27 (5): 300-.   DOI: 10.13745/j.esf.sf.2020.12.3
    Abstract121)      PDF (1024KB)(78)      
    Under the ever-present solar radiation, photosynthetic organisms on Earth evolved structurally-sophisticated photosynthetic systems. However, little attention has been paid to the inherent impact of sunlight illumination on the inorganic minerals widespread on the Earth surface. We discovered for the first time the solar energy conversion system of the “mineral coatings” on the Earth's surface ( aka “mineral membrane”), which exerts potential oxygen-production and carbon-sequestration functions on the Earth surface. Our finding shed a light on the photoelectric effect and non-classical photosynthesis involving natural semiconducting minerals. In this contribution, we studied the semiconducting property and photoelectron energy of typical minerals in the “mineral membrane”, focusing primarily on the photoelectric effect in and oxygen-production/carbon-sequestration function of ferromanganese oxides, as well as relevant geological records. We propose that birnessite, goethite and hematite, the semiconducting minerals commonly found in the “mineral membrane”, can perform sensitive and stable photon-to-electron conversion under solar radiation.  The non-classical mineral photosynthetic function we put forth is as follows: Solar energy utilization by inorganic minerals resembles photosynthesis in regarding to oxygen evolution and carbon fixing, and the “mineral membrane” may take part in both photocatalytic water-oxidation reaction and transformation of atmospheric CO 2 into marine carbonate. In addition, minerals might as well have promoted photosynthesis in photosynthetic organisms. During the water-oxidation reaction, the inorganic cluster Mn 4CaO 5 of photosystem II cycles through redox intermediates that are analogous to birnessite both in structure and component. Thus, it is fair to postulate that birnessites could play a role in the initiation of the photosynthesis in cyanobacteria, as minerals could weaken the hydrogen bond strength and alter water properties, thus facilitating water oxidation and photosynthesis. This observation offers further insights into the molecular mechanism of mineral participation in photosynthesis in photosynthetic organisms.
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    Earth Science Frontiers    2021, 28 (1): 0-0.  
    Abstract111)      PDF (3553KB)(132)      

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    The Late Ordovician fish-like animal from Xinjiang
    GUO Xianpu, WANG Shitao, GAI Zhikun, ZHAO Ziran, DING Xiaozhong, LI Tianfu
    Earth Science Frontiers    2020, 27 (6): 341-346.   DOI: 10.13745/j.esf.sf.2020.6.17
    Abstract109)      PDF (10956KB)(115)      

    This paper is the first to report the discovery of a well-preserved Ordovician fish-like animal fossil with a reliable shield armor structure. The vertebrate fossil was collected from purplish-red sandy-limestone outcrops of coast-shallow marine facies that are part of the Upper Ordovician Qarbake Formation in the Yijianfang section, Bachu county, Xinjiang. The new genus and species has been denoted Haoina elegantia Guo & Wang as per the system of binomial nomenclature, and a new family (Haoinaspididae) and order (Haoinaspidiformes) have also been described based on the unique biological features of this species. The new genus describes an ostraeoderm, while the Qarbake Formation can be constrained to the Sandbian stage based on the conodont fossil zone. The fossil of the new fish-like animal preserves its dorsal shield armor and shows that the dorsal shield on its head is covered with ridges composed of complex tumors on the derma. The ridges can be subdivided into four types: The orbit openings are situated at the dorsal-front edge of the head shield with wide and deep orbit hollows. The pineal area is located at either side of the orbits. And the well-developed sensory canal system in the armor of the head shield shows the tube system texture of corium and subcutaneous tissues. Based on comparisons with the vertebrate biogeographic regions of other fossils, we suggest the establishment of a new fish-like animal typified in a proto-Tethys Ordovician Haoniaspid-Bachuiaspid vertebrate biogeographic province. This fossil is the oldest fish-like animal with a reliable exoskeleton found in China or even in Asia.

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    Source-reservoir characteristics and coupling evaluations for the Lower Jurassic lacustrine shale gas reservoir in the Sichuan Basin
    HU Zongquan, WANG Ruyue, LIU Zhongbao, LIU Guangxiang, FENG Dongjun, YANG Zhenheng, WANG Pengwei
    Earth Science Frontiers    2021, 28 (1): 261-272.   DOI: 10.13745/j.esf.sf.2020.5.24
    Abstract108)      PDF (4973KB)(176)      
    Continental shale gas in the Sichuan Basin has good exploration prospects with obtainable industrial gas flow in the Lower Jurassic formation of the northeastern Sichuan Basin. Compared with marine shale, the characteristics of continental shale include rapid lithofacies variation, multiple types of lithofacies association (often interlayers), low total organic matter content (TOC), and complex source-reservoir relationship. Based on the idea of “source-reservoir coupling”, using macro-micro reservoir characterization methods, we analyzed and evaluated the source-reservoir characteristics and coupling relationship for the continental shale in the Da’anzhai Member of the Low Jurassic Ziliujing Formation. The results can be summarized into four main areas. (1) Lithofacies combinations. The Da'anzhai Member is a set of shallow to semi-deep lake deposits with dark shale and shell limestone interlayers of varying thickness. The main lithofacies combinations of 4 lithofacies and 3 thicknesses are mainly thin (< 1 m) interlayers of shell limestone between high TOC argillaceous shale, thin to medium-thin (< 3 m) interlayers of shell limestone between medium TOC argillaceous/silty shale, and medium-thick interlayers of shell limestone with a small amount of fine-silty sandstone between low-medium TOC silty shale. Shale is the source rock and main reservoir; shell limestone serves as secondary reservoir and interlayer; and tight sandstone with poor physical properties mainly functions as interlayer. (2) Source-reservoir characteristics. The thickness of shale in the northeastern Sichuan Basin is between 30-40 m, with TOC content generally between 1.0%-2.0%. Organic matter types are mainly types II2 and III. The shale reservoir space types are organic and inorganic pores and macro-micro fractures. The most developed pores are marginal and interparticle pores in clay minerals, followed by organic pores, while interconnected micro fractures are also well developed. In the shell limestone interlayers, the inter and intraparticle pores and micro fractures are the main types of reservoir space. (3) The macro source-reservoir configuration and micro source-storage coupling mechanism of continental shale strata in the Da’anzhai Member. Macroscopically, both TOC and porosity decreased with increasing carbonate content. The condition of source-reservoir coupling is better in shale than in interlayers, and the argillaceous shale is the best shale. Microscopically, there are a integrated source-reservoir coupling between organic matter and organic pore and a migration coupling within nm to μm distance between organic matter/inorganic pore and micro-fracture in shale strata; between shale and interlayer there is a migration coupling within mm to cm distance; and in the interlayer, migration coupling occurs within cm to m distance between organic matter (from the adjacent shale)/inorganic pore and micro-fracture. (4) Coupling evaluation. The corresponding source-reservoir coupling evaluation parameters are established for shale strata and interlayers, while coupling conditions are evaluated for two typical wells, and a preferred horizontal well’s target window has been suggested based on the evaluation results.
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    Alteration minerals in Martian surface rocks: a comparative study of Martian meteorites and in-situ exploration in the Gale crater
    FU Xiaohui,LING Zongcheng,ZHOU Qin,Bradley L. JOLLIFF,YIN Qingzhu,WANG Alian,LI Bo,WU Zhongchen,ZHANG Jiang
    Earth Science Frontiers    2020, 27 (4): 340-354.   DOI: 10.13745/j.esf.sf.2019.8.21
    Abstract107)      PDF (2847KB)(94)      

    Alteration minerals record the aqueous conditions and climate changes in Mars geological history. They are key to revealing the habitable environments on Mars, as well as the most signification objects of Mars exploration mission and Martian meteorite investigations. We present here detailed studies of alteration minerals in a Martian regolith breccia NWA7034, a Nakhlite meteorite MIL03346, and Sheepbed mudstone detected by Mars Curiosity rover. We compared the inventory of hydrous minerals in these rocks, and determined the formation mechanisms and conditions of smectite, Fe-oxides/hydroxides, and CaSO4 found in these rocks. We concluded that NWA7034, MIL03346, and Sheepbed mudstone were all altered during diagenesis or after lithification. However, the secondary alteration processes they experienced are distinct with each other. NWA7034 were mostly altered by oxidization and heating. For the meteorite MIL03346, secondary minerals are mostly present in veining within brittle fractures in the mafic minerals and mesostasis. This indicates the vein-filling alteration products result from hydrothermal fluid introduced by an impact event. Compared with two Martian meteorites, the Sheepbed mudstone in Gale crater is more altered with Chemical Index of Alteration (CIA) of 47 and 50. The original debris with basaltic mineral composition experienced at least two stages of secondary alterations: olivine altered to smectite and magnetite during diagenetic processes, and CaSO4 veins formation after lithification. This result suggests aqueous conditions in various geological setting are different, and chemical weathering under different climate conditions could produce diverse alteration mineral assemblages. This study summarized the secondary mineral found by Mars missions and in Martian meteorites and their possible origins. It could help understand the formation of secondary minerals and future data interpretation in the China Tianwen-1 Mars mission.

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    Earth Science Frontiers    2020, 27 (6): 0-0.  
    Abstract104)      PDF (384KB)(138)      
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    The mineral intelligence identification method based on deep learning algorithms
    GUO Yanjun, ZHOU Zhe, LIN Hexun, LIU Xiaohui, CHEN Danqiu, ZHU Jiaqi, WU Junqi
    Earth Science Frontiers    2020, 27 (5): 39-47.   DOI: 10.13745/j.esf.sf.2020.5.45
    Abstract98)      PDF (2272KB)(105)      

    Mineral classification plays an important role in many research fields. Intelligent mineral identification based on deep learning brings a new development direction to these fields, it can effectively save labor costs as well as reducing classification errors. The purpose of this paper is to study an accurate, efficient and versatile intelligent mineral identification method by deep learning. We trained and tested this method on five kinds of minerals: quartz, hornblende, biotite, garnet and olivine. We used the convolution neural network, commonly applies to image analysis, to establish the model and designed the model structure based on residual network (ResNet). In order to support deep learning, we collected microscopic imaging data sets of five kinds of minerals independently, and used them to train, verify and test the model. Besides, we also expanded the data sets for training through reasonable data augmentation. In terms of structural design of the convolutional neural network, we selected ResNets-18 as the framework and finally trained a successful mineral identification model achieving 89% accuracy in the test.

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    Microvertebrate remains from the Kuanti Formation of the Liujiachong Section in Qujing, Yunnan and their stratigraphic significance
    WANG Jianhua, ZHAO Wenjin, ZHU Min, LI Qiang, CAI Jiachen, ZHANG Na, PENG Lijian, LUO Yanchao
    Earth Science Frontiers    2020, 27 (6): 329-340.   DOI: 10.13745/j.esf.sf.2020.6.7
    Abstract96)      PDF (4534KB)(149)      

    The Kuanti Formation, with the discovery of the Xiaoxiang Vertebate Fauna in 2007, has become the focus of global research on early vertebrates. However, its stratigraphic subdivision, correlation and age, especially the subdivision and age of its lower part, remain contentious, despite many biostratigraphic attempts made since 1914. In recent years, we conducted a series of extensive geological investigations in the Kuanti Formation near the Xiaoxiang Reservoir in Qujing, Yunnan Province. Based on the recently obtained data from the Liujiachong Section (dominated by the lower part of the Kuanti Formation) and the preliminary study of the newly discovered microvertebrate remains, we documented the sequence of the Kuanti Formation of the Liujiachong Section, and further explored the geological age of the related strata. The Kuanti Formation of the Liujiachong Section can be subdivided into three members, in ascending order according to the main lithological changes: Member Ⅰ (Yuejiashan Member), Member Ⅱ (Chongjiawan Member), and Member Ⅲ (Cailian Member). The lower part of Member Ⅰ is characterized by light yellow and yellow-green gravelly silty mudstones and calcareous siltstones lacking any fossils, while the upper part is composed of dark grey and grey-black carbonaceous shales with rare Lingula sp. and bivalves. Member Ⅱ is dominated by grey-green and purple-red shales, intercalated with light grey thin-bedded or lenticular limestones or bioclastic limestones containing many invertebrate fossils (brachiopods and crinoid stems) and abundant microvertebrate remains. Member Ⅲ, partially exposed in the section, is composed of purple-red and grey-green silty and calcareous mudstones or marls intercalating with minor purple-red or yellow-green shales or siltstones containing brachiopods, fish, and stout tubular trace fossils. A thin layer of medium-thick-bedded fine sandstone is developed on the bottom of the member, which marks the boundary between Members Ⅲ and Ⅱ. The microvertebrate remains from several beds in Member Ⅱ show high diversity, including four early vertebrate groups: agnathans, placoderms, acanthodians, and osteichthyans. They are characterized by the Yangtze Fish Assemblage of the Xiaoxiang Vertebrate Fauna. The discovery of the acanthodians Nostolepis spp. in this section reveals the stratigraphic correlation and the precise geological age of the lower part of the Kuanti Formation. Based on the acanthodians from Member Ⅱ, coupled with previous palaeontological data, we suggest the age of Member Ⅱ to be late Gorstian Stage of the Ludlow, in the Silurian. The upper part of Member I, containing the placoderm ‘Wangolepis’, might be referred to as early Gorstian. However, the age of the lower part of Member I without fossils is uncertain, and the possibility of its base extending down to the Wenlock is not excluded. This study offers new palaeoichthyological evidence for the Silurian biostratigraphy of China and provides a new chronostratigraphic scheme in the study of early vertebrate evolution.

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    Stable chromium isotope geochemistry
    WANG Xiangli,WEI Wei
    Earth Science Frontiers    2020, 27 (3): 78-103.   DOI: 10.13745/j.esf.sf.2020.3.5
    Abstract90)      PDF (4639KB)(233)      

    With the advancement of multicollector mass spectrometry, the stable chromium isotopic system has been widely applied to solving environmental and geochemical problems. Chromium is a redox-sensitive element, and transformations between different oxidation states are accompanied by large isotopic fractionations. Therefore, chromium isotopes play important roles in investigating the redox conditions of modern and paleo-environments. Moreover, chromium is a moderately compatible and slightly siderophile element, and large isotope fractionation exists between different minerals. Thus, chromium isotopes can also be potentially applied to study mantle partial melting, magma differential crystallization, and planetary evolution. In this review, we covered the following topics: (1) an overview of chromium stable isotopic systematics; (2) analytical methods; (3) isotopic fractionation mechanisms; and (4) applications of stable chromium isotopes in high- and low-temperature geochemistry.

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    Comparison of the geochronological frameworks and preliminary study on key geological events during the Neoproterozoic Late Tonian period in the Hunan-Guizhou-Guangxi area
    ZHANG Jiawei,CHEN Jianshu,WU Tao,YE Taiping,CHEN Minghua,DAI Yaran,DENG Xiaojie,MU Jun
    Earth Science Frontiers    2020, 27 (4): 1-16.   DOI: 10.13745/j.esf.sf.2019.12.5
    Abstract84)      PDF (5016KB)(165)      

    The Neoproterozoic Late Tonian stratum (the Xiajiang Group and its time-equivalent stratum) is well exposed in the Hunan-Guizhou-Guangxi area. It is an important research subject for studying the evolution of the rift basin in South China after the collision between the Yangtze Craton and the Cathaysia Block. Here, we report the zircon U-Pb ages of the tuffs and tuffite in the upper part of the Qingshuijiang Formation and the bottom and middle parts of the Pinglue Formation in the Wanshan area, Tongren City, Guizhou Province to be 763.8±5.5 Ma (N=24, MSWD=0.29), 760.2±4.1 Ma (N=25, MSWD=0.39), and 759.1±3.9 Ma (N=26, MSWD=0.38), respectively. By compiling the area’s volcanic, volcanic-sedimentary and tuffeous rock ages, we further determined the deposition periods of the Xiajiang Group and its equivalence to be around 822-715 Ma. We propose that the basalt within the Sanmenjie Formation of the Danzhou Group in northern Guangxi formed in an extensional setting after the Wuling movement, as a result of maximum extension of the Hunan-Guizhou-Guangxi rift basin. A large amount of volcanic materials in the Qingshuijiang and Pinglue Formations are mainly sourced from the intermediate-acidic extrusive rocks (800-760 Ma) in the eastern section of the Jiangnan Orogen. Combined with regional stratigraphy, lithology and geochronology, we restore the Neoproterozoic Late Tonian evolutionary history of the Hunan-Guizhou-Guangxi basin and propose to establish the Xiajiang System.

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     Advances in chlorine isotope geochemistry
    ZHOU Qiushi,WANG Rui
    Earth Science Frontiers    2020, 27 (3): 42-67.   DOI: 10.13745/j.esf.sf.2020.5.56
    Abstract83)      PDF (4286KB)(222)      

     As the most representative and the most abundant halogen on the earth, chlorine has gained high attention due to its significant properties and remarkable distribution among reservoirs. Chlorines chalcophile and volatile (incompatible) nature are significant and affect its geochemical behavior and distribution. 35Cl and 37Cl are the two stable isotopes of chlorine, their isotope abundances are respectively 75.76% and 24.24%. The stable isotope composition is reported as δ37Cl. The commonest and the most traditional analytical method in modern chlorine isotope research is IRMS, it is highlighted by better precision compared to other analytical methods, though there are some defects such as the demand for a large sample mass and slow processing. Other analytical methods include TIMS, SIMS, LA-ICP-MS, their employment in Cl isotope analysis is still under development and not mature enough for geological application. A chlorine isotope standard commonly accepted by worldwide researchers is present and known as the Standard Mean Ocean Chloride (SMOC) proposed by Kaufmann. Its outstanding advantages include handy to collect, stable in analysis, and excellent in reproducibility. On the macroscale, the major reservoirs of chlorine on the earth can be divided into the mantle, continental crust, oceanic crust, and oceans. The mantle is undoubtedly a major reservoir due to its volume, yet we are still unable to acquire a clear result of the exact chlorine concentration constrained by our limited approaches to investigate it. The same situation applies to the Cl isotope composition of the mantle as well, in which all kinds of processes may bring about changes to Cl isotope composition. Continental crust can be further divided into sediments and its pore water, evaporites, and silicate lithosphere. Many low δ37Cl values were observed in pore water in previous research and were generally interpreted as the result of kinetic fractionation. Large variation of δ37Cl exists among evaporites depending on the different kinds of chloride species; although silicate lithosphere is light in chlorine contents, an observation is made suggesting the apatite Cl isotope composition varies as a function of the host rock lithology, which may be a good indicator of hydrothermal fluid activities. The oceanic crust can also be further divided into sediments and pore water, evaporite, and additionally altered oceanic crust (AOC). The altered hydrous minerals (amphibole, serpentine, etc.) are featured by a heavy δ37Cl value and may have something to do with the oxidation states of metal cations. The oceans are together a massive chlorine reservoir as well, the stability of their Cl isotope composition has already been approved by many studies. In addition to all the mentioned reservoirs, Cl isotope analysis is applied to extraterrestrial samples such as meteorites, lunar rocks, and atmosphere as well. Generally, the mechanisms of Cl fractionation can be divided into equilibrium fractionation and kinetic fractionation. Factors controlling equilibrium fractionation include the valence state of chlorine itself, the metal cation it bonds with, and the difference of chloride species in a solid-aqueous phase equilibrium system. Processes of kinetic fractionation include diffusion, ion filtration, and activities in the magma degassing system. Ever since the two stable isotopes of chlorine got discovered about 100 years ago, geochemical methods related to chlorine isotopes have been applied to all branches of geology. For example, chlorine isotopes can be used to trace the sources of formation water in hydrogeology, or contaminants in environmental geology; chlorine isotopes can also be used to track deposit formation in economic geology or interpret the evolution process of the earth in planetary geology. Attempts and explorations are continuously conducted using chlorine isotopes. However, constrained by our knowledge of the actual geological processes, there are still a bunch of frontier problems hindering the development of chlorine isotope research. For example, what is the key factor in early solar system processes determining the current chlorine content of the earth; what kind of evolution history caused the current volatile distribution in the earth; what is going on with respect of the volatile cycling; what is the flux process between the subducting plate and mantle and so on.

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