• Volume 90,Issue 3,2016 Table of Contents
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    • CONTENTS

      2016, 90(3):777.

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    • ORIGINAL ARTICLES

      2016, 90(3):777.

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    • A new pterodactyloid pterosaur from the Early Cretaceous of the western part of Liaoning Province, northeastern China

      2016, 90(3):777-782.

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      Abstract:Pangupterus liui gen. et sp. nov. from the Jiufotang Formation of Sihedang, Lingyuan City, Liaoning Province is erected based on a nearly complete lower jaw. It is characterized by having a total of 36 slender curved teeth with sharp tips, forming a distinct fish-grabbing mechanism; the teeth are well-spaced and are circular in section; the length ratio of the mandibular symphysis to the whole jaw is 20%; and the ratio of the tooth root width to tooth length is 12%. Toothed pterosaurs make up about 56.3% of the pterosaur assemblage from the Jiufotang Formation, which indicates that toothed forms played a key role in the ecosystem.

    • Distribution of Chancelloriids in a Middle Cambrian Carbonate Platform Deposit, Taebaek Group, Korea

      2016, 90(3):783-795.

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      Abstract:The onset of the Cambrian witnessed the diversification of “small shelly fossils (SSF)”, which affected carbonate depositional system. One of the problematic SSF, chancelloriids, are common components of the early to middle Cambrian carbonate and shale, and their contributions toward Cambrian carbonates are not yet fully understood. This study assesses distribution patterns of chancelloriid sclerites in the Cambrian Series 3 Daegi Formation based on microfacies analysis and discusses their sedimentologic implications. In the lower part of the formation, partially articulated chancelloriid sclerites occur mainly in bioclastic packstone and grainstone facies, with isolated sclerite rays in nodular packstone to grainstone facies. In the middle part of the formation, chancelloriid fragments occur only sporadically in bioclastic wackestone to packstone, bioclastic grainstone and oolitic packstone to grainstone facies, whereas boundstone facies are nearly devoid of their fragments. There are no chancelloriid fragments in the upper part of the formation, which consists of oolitic packstone to grainstone facies. Chancelloriids are interpreted to have primarily occupied platform margin shoal environments, shedding their sclerites to surrounding areas, and thus contributed as sediment producers. The distribution of Daegi chancelloriid sclerites is similar to other Cambrian examples, with the exception of common chancelloriids in Cambrian Series 2 reefs and their apparent near absence in the Daegi and other Cambrian Series 3 reefs. This disparity resulted from changes in the ecologic niche of chancelloriids after the end-Cambrian Series 2 reef crisis, coupled with an overall decline of chancelloriids in the middle Cambrian.

    • A New Species of Amsassia from the Ordovician of Korea and South China: Paleobiological and Paleogeographical Significance

      2016, 90(3):796-806.

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      Abstract:A new species of the probable calcareous alga Amsassia, A. koreanensis, is recognized from the Duwibong Formation (Middle Ordovician, Darriwilian) of the Taebaeksan Basin in mid-eastern Korea. This is the first report of the genus from the Korean Peninsula, expanding its geographical range to the eastern Sino-Korean Block. The new species also occurs in the Xiazhen Formation (Upper Ordovician, Katian) at Zhuzhai in the South China Block. Amsassia koreanensis is the smallest species of this modular genus, having a maximum module diameter of 0.28 mm. Module increase is by bipartite, tripartite and quadripartite types of longitudinal axial fission, but unlike other species of the genus, quadripartite fission is common. The types of fission are comparable to those in some Tetradiida (now Prismostylales, florideophycean rhodophyte algae), although the processes of fission are different. The distribution of A. koreanensis further strengthens the biogeographical connection between the Sino-Korean and South China blocks, suggesting that these two paleocontinents were located closer together during the Middle to Late Ordovician than previously speculated.

    • Distinctive Scleritome with Marginal Tubercles of a New Palaeoscolecid Worm from the Shipai Fauna (Cambrian Epoch 2) at Three Gorges, South China

      2016, 90(3):807-817.

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      Abstract:SEM analysis of trunk ornamentation on a compressed palaeoscolecid fossil from the Shipai fauna, Cambrian Series 2 and Stage 4 at Three Gorges, South China, allows a reassignment of the material to a new taxon, Sanxiascolex papillogyrus gen. et sp. nov. The preserved body is entirely annulated. Each annulus is ornamented by four rows of irregularly alternating plates and each plate bears numerous tubercles at the marginal region and a variable number (zero to six) of nodes at its central part. These features are unique among known palaeoscolecids. Comparative analyses with other compressed palaeoscolecid macrofossils and phosphatized material on the pattern of trunk ornamentation indicates that a detailed examination of the cuticle ornament weighs heavily in analyses of their taxonomic distinctions. A similar sclerite pattern to that of S. papillogyrus has been found in some phosphatized palaeoscolecid cuticle fragments as well as in isolated sclerites. The upper series of nodes and tubercles of these sclerites suggest an accretional mode of sclerite growth. The considerable variation in node number observed across the plates of S. papillogyrus demonstrates that phosphatic palaeoscolecid taxonomy based on?relatively?minor variations in?the number of sclerite nodes?should perhaps be reconsidered. As the origins of the phosphatized specimens are quite diverse, a large variety of isolated sclerites from the Early Palaeozoic may not reflect actual biodiversity.

    • Dimorphism of Bivalved Arthropod Branchiocaris? Yunnanensis from the Early Cambrian Chengjiang Biota, South China

      2016, 90(3):818-826.

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      Abstract:The bivalved arthropod Branchiocaris? yunnanensis Hou, 1987 is redescribed on the basis of new fossil material from the early Cambrian Chengjiang biota, South China. In total, 81 specimens have been examined. The carapace comprises two identical valves, each valve are sub-circular in outline, ranging from 24 mm to 58 mm in length, and from 15 mm to 46 mm in height. The dorsal margin is straight and bears two short cardinal spines. The valve surface is either smooth or ornamented with polygonal reticular structures, which may result from different preservation conditions. Two morphotypes have been recognized based on the presence or absence of a subdorsal swelling of the valve, which is convex dorsolaterally and extends beyond the dorsal margin when it appears. Statistic and ontogenetic analyses show both morphotypes grow isometrically and have the same growth trajectory. Therefore, the two morphotypes are interpreted as dimorphism within the same species. Our results are helpful for investigating the taxonomy and ontogeny of arthropod fossils and suggest that dimorphism might be fairly common in these early arthropods.

    • Cambrian Stem-group Cnidarians with a New Species from the Cambrian Series 3 of the Taebaeksan Basin, Korea

      2016, 90(3):827-837.

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      Abstract:Five species, Lipopora lissa Jell and Jell, 1976, Lipopora daseia Jell and Jell, 1976, Tretocylichne perplexa Engelbretsen, 1993 from Australia, Cambroctoconus orientalis Park, Woo, Lee, Lee, Lee, Han and Chough, 2011 from China, and Cambroctoconus kyrgyzstanicus Peel, 2014 from Kyrgyzstan, belonging to the Cambrian stem-group cnidarians have been documented in the fossil record. Cambroctoconus coreaensis sp. nov., interpreted here as a stem-group cnidarian, from the Seokgaejae section in the Daegi Formation, Taebaek Group (Cambrian Series 3), Taebaeksan Basin, central-eastern Korean Peninsula, has a slender cup-shaped skeleton. A cladistic analysis produced 21 most parsimonious trees, which invariably placed the six stem-group cnidarians below the crown-group, but their relationships within the stem-group are unresolved. Nine out of the 21 trees suggest a monophyletic relationship for the Cambrian stem-group cnidarians, whereas in six other trees a monophyly of Cambroctoconus and Tretocylichne appeared as the sister-group to the crown-group cnidarians with Lipopora at the most basal branch. This result may reflect the fact that crown-group cnidarians evolved in the Precambrian, and suggests that the diversity of stem-group cnidarians was a result of an independent radiation in the Cambrian.

    • Fossil Liverworts from the Lower Cretaceous Huolinhe Formation in Inner Mongolia, China

      2016, 90(3):838-846.

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      Abstract:A new genus and species, Rebouliothallus huolinhensis sp. nov., and two uncertain species, Ricciopsis sp. and Hepaticites sp., are described. The fossils were collected from the Lower Cretaceous Huolinhe Formation of Huolinhe Basin, northeastern China. The new genus Rebouliothallus was established in the Aytoniaceae family of Marchantiales. Rebouliothallus huolinhensis appears to be quite similar to species of the extant genus Reboulia Raddi. The species is characterized by the relatively large ventral scales. Ventral scales are large, imbricate and arranged in two rows on the ventral surface. Rhizoids are either pegged or smooth. Ricciopsis sp. is characterized by the rosette-forming thallus. Hepaticites sp. shows some similarities to liverworts. Of the forty-nine Early Cretaceous floras of China, only two floras, one from the Huolinhe basin, Inner Mongolia and the other from the Jixi Basin, Heilongjiang Province, contain fossil liverworts. The rare fossil liverwort records in the Early Cretaceous floras of China may be the result of taphonomic bias.

    • Early Cretaceous Tectonics and Evolution of the Tibetan Plateau

      2016, 90(3):847-857.

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      Abstract:Selected geological data on Early Cretaceous strata, structures, magmatic plutons and volcanic rocks from the Kunlun to Himalaya Mountains reveal a new view of the Early Cretaceous paleo-tectonics and the related geodynamic movement of the Tibetan Plateau. Two major paleo-oceans, the Mid-Tethys Ocean between the Qiangtang and Lhasa blocks, and the Neo-Tethys Ocean between the Lhasa and Himalayan blocks, existed in the Tibetan region in the Early Cretaceous. The Himalayan Marginal and South Lhasa Seas formed in the southern and northern margins of the Neo-Tethys Ocean, the Central Tibet Sea and the Qiangtang Marginal Sea formed in the southern and northern margins of the Mid-Tethys Ocean, respectively. An arm of the sea extended into the southwestern Tarim basin in the Early Cretaceous. Early Cretaceous intensive thrusting, magmatic emplacement and volcanic eruptions occurred in the central and northern Lhasa Block, while strike-slip formed along the Hoh-Xil and South Kunlun Faults in the northern Tibetan region. Early Cretaceous tectonics together with magmatic K2O geochemistry indicate an Early Cretaceous southward subduction of the Mid-Tethys Oceanic Plate along the Bangoin-Nujiang Suture which was thrust ~87 km southward during the Late Cretaceous-Early Cenozoic. No intensive thrust and magmatic emplacement occurred in the Early Cretaceous in the Himalayan and southern Lhasa Blocks, indicating that the spreading Neo-Tethys Oceanic Plate had not been subducted in the Early Cretaceous. To the north, terrestrial basins of red-beds formed in the Hoh-Xil, Kunlun, Qilian and the northeastern Tarim blocks in Early Cretaceous, and the Qiangtang Marginal Sea disappeared after the Qiangtang Block uplifted in the late Early Cretaceous.

    • Cenozoic Vertical-Axis Rotations of the Hoh Xil Basin, Central–Northern Tibet

      2016, 90(3):858-869.

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      Abstract:Understanding the Cenozoic vertical-axis rotation in the Tibetan Plateau is crucial for continental dynamic evolution. Paleomagnetic and rock magnetic investigations were carried out for the Oligocene and Miocene continental rocks of the Hoh Xil basin in order to better understand the tectonic rotations of central Tibet. The study area was located in the Tongtianhe area located in the southern part of the Hoh Xil basin and northern margin of the Tanggula thrust system in central-northern Tibet. A total of 160 independently oriented paleomagnetic samples were drilled from the Tongtianhe section for this study. The magnetic properties of magnetite and hematite have been recognized by measurements of magnetic susceptibility vs. temperature curves and unblocking temperatures. The mean directions of the Oligocene Yaxicuo Group in stratigraphic coordinates (Declination/Inclination = 354.9°/29.3°, k = 33.0, α95 = 13.5°, N =5 Sites) and of the Miocene Wudaoliang Group in stratigraphic coordinates (Declination/Inclination = 3.6°/36.4°, k = 161.0, α95 = 9.7°, N =3 Sites) pass reversal tests, indicating the primary nature of the characteristic magnetizations. Our results suggested that the sampled areas in the Tuotuohe depression of the Hoh Xil basin have undergone no paleomagnetically detectable rotations under single thrusting from the Tanggula thrust system. Our findings, together with constraints from other tectonic characteristics reported by previous paleomagnetic studies, suggest tectonic rotations in the Cuoredejia and Wudaoliang depressions of the Hoh Xil basin were affected by strike-slip faulting of the Fenghuo Shan-Nangqian thrust systems. A closer examination of geological data and different vertical-axis rotation magnitudes suggest the tectonic history of the Hoh Xil basin may be controlled by thrust and strike-slip faulting since the Eocene.

    • The Exhumation History of North Qaidam Thrust Belt Constrained by Apatite Fission Track Thermochronology: Implication for the Evolution of the Tibetan Plateau

      2016, 90(3):870-883.

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      Abstract:Determining the spatio-temporal distribution of the deformation tied to the India-Eurasian convergence and the impact of pre-existing weaknesses on the Cenozoic crustal deformation is significant for understanding how the convergence between India and Eurasia contributed to the development of the Tibetan Plateau. The exhumation history of the northeastern Tibetan Plateau was addressed in this research using a new apatite fission track (AFT) study in the North Qaidam thrust belt (NQTB). Three granite samples collected from the Qaidam Shan pluton in the north tied to the Qaidam Shan thrust, with AFT ages clustering in the Eocene to Miocene. The other thirteen samples obtained from the Luliang Shan and Yuka plutons in the south related to the Luliang Shan thrust and they have showed predominantly the Cretaceous AFT ages. Related thermal history modeling based on grain ages and track lengths indicates rapid cooling events during the Eocene-early Oligocene and since late Miocene within the Qaidam Shan, in contrast to those in the Cretaceous and since the Oligocene-Miocene in the Luliang Shan and Yuka region. The results, combined with published the Cretaceous thermochronological ages in the Qaidam Shan region, suggest that the NQTB had undergo rapid exhumation during the accretions along the southern Asian Andean-type margin prior to the India-Eurasian collision. The Cenozoic deformation initially took place in the North Qaidam thrust belt by the Eocene, which is consistent with the recent claim that the deformation of the northeastern Tibetan Plateau initiated in the Eocene as a response to continental collision between India and Eurasia. The immediate deformation responding to the collision is tentatively attributed to the pre-existing weaknesses of the lithosphere, and therefore the deformation of the northeastern Tibetan Plateau should be regarded as a boundary-condition-dependent process.

    • Magnetotelluric Constraints on the Occurrence of Lower Crustal Earthquakes in the Intra-plate Setting of Central Indian Tectonic Zone

      2016, 90(3):884-899.

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      Abstract:Lower crustal earthquake occurrence in the Central Indian Tectonic Zone (CITZ) of the Indian sub-continent was investigated using magnetotelluric (MT) data. MT models across the CITZ, including the new resistivity model across the 1938 Satpura lower crustal earthquake epicenter, show low resistive (<80 ?m) mid-lower crust and infer small volume (<1 vol%) of aqueous fluids existing in most part of lower crust. This in conjunction with xenoliths and other geophysical data supports a predominant brittle/semi-brittle lower crustal rheology. However, the local deep crustal zones with higher fluid content of 2.2%–6.5% which have been mapped imply high pore pressure conditions. The observation above and the significant strain rate in the region provide favorable conditions (strong/moderate rock strength, moderate temperature, high pore pressure and high strain rate) for brittle failure in the lower crust. It can be inferred that the fluid-rich pockets in the mid-lower crust might have catalyzed earthquake generation by acting as the source of local stress (fluid pressure), which together with the regional stress produced critical seismogenic stress conditions. Alternatively, fluids reduce the shear strength of the rocks to favor tectonic stress concentration that can be transferred to seismogenic faults to trigger earthquakes.

    • Platinum-group Mineral (PGM) and Base-metal Sulphide (BMS) Inclusions in Chromitites of the Zedang Ophiolite, Southern Tibet, China and their Petrogenetic Significance

      2016, 90(3):900-912.

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      Abstract:Voluminous platinum-group mineral (PGM) inclusions including erlichmanite (Os,Ru)S2, laurite (Ru,Os)S2, and irarsite (Ir,Os,Ru,Rh)AsS, as well as native osmium Os(Ir) and inclusions of base metal sulphides (BMS), including millerite (NiS), heazlewoodite (Ni3S2), covellite (CuS) and digenite (Cu3S2), accompanied by native iron, have been identified in chromitites of the Zedang ophiolite, Tibet. The PGMs occur as both inclusions in magnesiochromite grains and as small interstitial granules between them; most are less than 10 μm in size and vary in shape from euhedral to anhedral. They occur either as single or composite (biphase or polyphase) grains composed solely of PGM, or PGM associated with silicate grains. Os-, Ir-, and Ru-rich PGMs are the common species and Pt-, Pd-, and Rh-rich varieties have not been identified. Sulfur fugacity and temperature appear to be the main factors that controlled the PGE mineralogy during crystallization of the host chromitite in the upper mantle. If the activity of chalcogenides (such as S, and As) is low, PGE clusters will remain suspended in the silicate melt until they can coalesce to form alloys. Under appropriate conditions of ?S2 and ?O2, PGE alloys might react with the melt to form sulfides-sulfarsenides. Thus, we suggest that the Os, Ir and Ru metallic clusters and alloys in the Zedang chromitites crystallized first under high temperature and low ?S2, followed by crystallization of sulphides of the laurite-erlichmanite, solid-solution series as the magma cooled and ?S2 increased. The abundance of primary BMS in the chromitites suggests that ?S2 reached relatively high values during the final stages of magnesiochromite crystallization. The diversity of the PGE minerals, in combination with differences in the petrological characteristics of the magnesiochromites, suggest different degrees of partial melting, perhaps at different depths in the mantle. The estimated parental magma composition suggests formation in a suprasubduction zone environment, perhaps in a forearc.

    • Geology, Fluid Inclusion and Isotopic Study of the Neoproterozoic Suoi Thau Copper Deposit, Northwest Vietnam

      2016, 90(3):913-927.

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      Abstract:The Sin Quyen-Lung Po district is an important Cu metallogenic province in Vietnam, but there are few temporal and genetic constraints on deposits from this belt. Suoi Thau is one of the representative Cu deposits associated with granitic intrusion. The deposit consists of ore bodies in altered granite or along the contact zone between granite and Proterozoic meta-sedimentary rocks. The Cu-bearing intrusion is sub-alkaline I-type granite. It has a zircon U-Pb age of ~776 Ma, and has subduction-related geochemical signatures. Geochemical analysis reveals that the intrusion may be formed by melting of mafic lower crust in a subduction regime. Three stages of alteration and mineralization are identified in the Suoi Thau deposit, i.e., potassic alteration; silicification and Cu mineralization; and phyllic alteration. Two-phase aqueous fluid inclusions in quartz from silicification stage show wide ranges of homogenization temperatures (140–383°C) and salinities (4.18wt%–19.13wt%). The high temperature and high salinity natures of some inclusions are consistent with a magmatic derivation of the fluids, which is also supported by the H-O-S isotopes. Fluids in quartz have δD values of –41.9‰ to –68.8‰. The fluids in isotopic equilibrium with quartz have δ18O values ranging from 7.9‰ to 9.2‰. These values are just plotted in the compositional field of magmatic-hydrothermal fluids in the δDwater versus δ18Owater diagram. Sulfide minerals have relatively uniform δ34S values from 1.84‰ to 3.57‰, which is supportive of a magmatic derivation of sulfur. The fluid inclusions with relatively low temperatures and salinities most probably represent variably cooled magmatic-hydrothermal fluids. The magmatic derivation of fluids and the close spatial relationship between Cu ore bodies and intrusion suggest that the Cu mineralization most likely had a genetic association with granite. The Suoi Thau deposit, together with other deposits in the region, may define a Neoproterozoic subduction-related ore-forming belt.

    • Newly Discovered Native Gold and Bismuth in the Cihai Iron-Cobalt Deposit, Eastern Tianshan, Northwest China

      2016, 90(3):928-938.

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      Abstract:The Cihai iron-cobalt deposit is located in the southern part of the eastern Tianshan iron-polymetallic metallogenic belt. Anomalous native gold and bismuth have been newly identified in Cinan mining section of the Cihai deposit. Ore formation in the deposit can be divided into three stages based on geological and petrographical observations: (I) skarn, with the main mineral assemblage being garnet-pyroxene-magnetite; (II) retrograde alteration, forming the main iron ores and including massive magnetite, native gold, native bismuth, and cobalt-bearing minerals, with the main mineral assemblage being ilvaite-magnetite-native gold-native bismuth; and (III) quartz-calcite-sulfide assemblage that contains quartz, calcite, pyrrhotite, cobaltite, and safflorite. Native gold mainly coexists with native bismuth, and they are paragenetically related. The temperature of initial skarn formation was higher than 340°C, and then subsequently decreased to ~312°C and ~266°C. The temperature of the hydrothermal fluid during the iron ore depositional event was higher than the melting point of native bismuth (271°C), and native bismuth melt scavenged gold in the hydrothermal fluid, forming a Bi-Au melt. As the temperature decreased, the Bi-Au melt was decomposed into native gold and native bismuth. The native gold and native bismuth identified during this study can provide a scientific basis for prospecting and exploration for both gold- and bismuth-bearing deposits in the Cihai mining area. The gold mineralization in Cihai is a part of the Early Permian Cu-Ni-Au-Fe polymetallic ore-forming event, and its discovery has implications for the resource potential of other iron skarn deposits in the eastern Tianshan.

    • Hydrogen Incorporation in Crystalline Jadeite: Insight from First Principles Calculations

      2016, 90(3):939-945.

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      Abstract:Hydrogen incorporation is critical for explaining defect energies, structure parameters and other physical characteristics of minerals and understanding mantle dynamics. This work analyzed the hydrogen complex defects in jadeite by the plane-wave pseudo-potential method based on density functional theory, and optimized the atomic positions and lattice constants in all configurations (different defective systems). Incorporation mechanisms considered for hydrogen (H) in jadeite include: (1) hydrogen incorporating with the O2 site oxygen and coexisting with M2 vacancy; (2) one H atom combined with an Al atom replacing Si in tetrahedron; (3) 4H atoms directly replacing Si in tetrahedron and (4) 3H atoms replacing Al on the M1 site. The four incorporation mechanisms mentioned above form the corresponding VNa-Hi, AlSi-Hi, VSi-4Hi and VAl-3Hi point defects. The molecular dynamics simulation to the ideal, VNa-Hi, AlSi-Hi, VSi-4Hi and VAl-3Hi point defects under the P-T conditions of 900 K, 2 GPa, the VNa-Hi and AlSi-Hi point defects under different pressures at T = 900 K, and AlSi-Hi point defects under different temperatures at P = 3 GPa was performed to examine the preferential mode of hydrogen incorporation in jadeite by means of first-principles calculations. The calculations show that the averaged O–H bond-length in the hydrogen point defects system decreased in the order of AlSi-Hi, VNa-Hi, VSi-4Hi and VAl-3Hi. VNa-Hi complex defects result in a contraction of the jadeite volume and the presence of AlSi-Hi, VSi-4Hi and VAl-3Hi defects could increase the supercell volume, which is the most obvious in the VAl-3Hi defects. The energy of formation of AlSi-Hi and VAl-3Hi complex defects was much lower than that of other defect systems. The VAl-3Hi defects system has the lowest energy and the shortest O–H bond-length, suggesting that this system is the most favorable. The analytical results of vacancy formation energy, O–H bond-length, and the stability of the hydrogen defects in jadeite have suggested that the preferred hydration incorporation mode in jadeite is VAl-3Hi complex defect.

    • Regional Geochemistry and Fluid Flow in the Palaeogene Aquifers of the Gaoyou Subbasin in the Southern Part of North Jiangsu Basin, China

      2016, 90(3):946-955.

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      Abstract:Chemical analysis of groundwater in petroliferous basins can be an effective way to determine the regional hydrogeological regime and to evaluate the preservation conditions of hydrocarbons. This paper presents the hydrochemical distribution of both individual aquifers and different structural units within the Palaeogene strata of the Gaoyou subbasin in the North Jiangsu Basin, east China. The results show that the salinity of the Palaeogene aquifers in the Gaoyou subbasin displays a systematic increase from the central deep depression to the periphery areas, and shows a reverse trend as the burial depth increases. Salinity maps of individual aquifers suggest that formation water in the deep layers at the centre of the study area probably retains original features of fresh lake water. Geofluids near the central deep depression of the Gaoyou subbasin migrate vertically through the Zhenwu and Hanliu faults, while those of the northern slope belt mainly flow laterally through aquifers. Both low and high salinity formation water can be found in the hydrocarbon producing areas. The low salinity zones commonly affected by infiltrated meteoric water are unfavourable conditions for the preservation of trapped hydrocarbons.

    • Diagenesis of the Triassic Yanchang Formation Tight Sandstone Reservoir in the Xifeng–Ansai Area of Ordos Basin and its Porosity Evolution

      2016, 90(3):956-970.

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      Abstract:This work aims to reveal the evolution of the porosity in the Triassic Yanchang Formation tight sandstone reservoir of the Xifeng–Ansai area of Ordos Basin. Based on destructive diagenesis (compaction and cementation) and constructive diagenesis (dissolution) of sandstone reservoirs, this study analyzed the diagenesis characteristics of the tight sandstone reservoirs in this area, and discussed the relationship between sandstone diagenesis and porosity evolution in combination with present porosity profile characteristics of sandstone reservoir. The effect simulation principle was employed for the mathematical derivation and simulation of the evolution of porosity in the Yanchang Formation tight sandstone reservoirs. The result shows that compaction always occurs in tight sandstone reservoirs in the Yanchang Formation, and cementation occurs when the burial depth increases to a certain value and remains ever since. Dissolution occurs only at a certain stage of the evolution with window features. In the corresponding present porosity profile, diagenesis is characterized by segmentation. From the shallow to the deep, compaction, compaction, cementation and dissolution, compaction and cementation occur successively. Therefore, the evolution of sandstone porosity can be divided into normal compaction section, acidification and incremental porosity section, and normal compaction section after dissolution. The results show that the evolution of sandstone porosity can be decomposed into porosity reduction model and porosity increase model. The superposition of the two models at the same depth in the three stages or in the same geological time can constitute the evolution simulation of the total porosity in sandstone reservoirs. By simulating the evolution of sandstone reservoir porosity of the eighth member in Xifeng area and the sixth member in Ansai area, it shows that they are similar in the evolution process and trend. The difference is caused by the regional uplift or subsidence and burial depth.

    • Groundwater Recharge and Mixing in Arid and Semiarid Regions: Heihe River Basin, Northwest China

      2016, 90(3):971-987.

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      Abstract:A sound understanding of groundwater recharged from various sources occurring at different time scales is crucial for water management in arid and semi-arid river basins. Groundwater recharge sources and their geochemical evolution are investigated for the Heihe River Basin (HRB) in northwest China on the basis of a comprehensive compilation of geochemical and isotopic data. Geochemical mass-balance modeling indicates that mountain-block recharge accounts for a small fraction (generally less than 5%) of the shallow and deep groundwater sustaining the oasis, whereas infiltration of rivers and irrigation water contribute most of the groundwater recharge. Dedolomitization is the primary process responsible for the changes in groundwater chemical and carbon isotope compositions from the piedmont to the groundwater discharge zone, where the dedolomitization is very likely enhanced by modern agricultural activities affecting the shallow groundwater quality. Analysis of radioactive isotopes suggests that these primary recharge sources occur at two different time scales. Radiocarbon-derived groundwater age profiles indicate a recharge rate of approximately 12 mm/year, which probably occurred during 2000–7000 years B.P., corresponding to the mid-Holocene humid period. The recharge of young groundwater on the tritium-dated time scale is much higher, about 360 mm/year in the oasis region. Infiltration from irrigation canals and irrigation return flow are the primary contributors to the increased young groundwater recharge. This study suggests that groundwater chemistry in the HRB has been influenced by the complex interaction between natural and human-induced geochemical processes and that anthropogenic effects have played a more significant role in terms of both groundwater quantity and quality.

    • Experimental Study on the Mobility of Channelized Granular Mass Flow

      2016, 90(3):988-998.

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      Abstract:Granular mass flows (e.g., debris flows/avalanches) in landslide-prone areas are of great concern because they often cause catastrophic disasters as a result of their long run-out distances and large impact forces. To investigate the factors influencing granular mass flow mobility, experimental tests were conducted in a flume model. Granular materials consisting of homogeneous sand and non-homogeneous sandy soil were used for studying particle size effects. Run-out tests with variable flow masses, water contents, and sloping channel confinement parameters were conducted as well. The results indicated that granular mass flow mobility was significantly influenced by the initial water content; a critical water content corresponding to the smallest flow mobility exists for different granular materials. An increase in the total flow mass generally induced a reduction in the travel angle (an increase in flow mobility). Consistent with field observations, the travel angles for different granular materials decreased roughly in proportion to the logarithm of mass. The flume model tests illustrate that the measured travel angles increase as the proportion of fine particles increases. Interestingly, natural terrain possesses critical confinement characteristics for different granular mass flows.

    • Free-surface Simulations of Newtonian and Non-Newtonian Fluids with the Lattice Boltzmann Method

      2016, 90(3):999-1010.

      Abstract (649) HTML (0) PDF 12.68 M (1127) Comment (0) Favorites

      Abstract:This paper describes the application of a three-dimensional lattice Boltzmann method (LBM) to Newtonian and non-Newtonian (Bingham fluid in this work) flows with free surfaces. A mass tracking algorithm was incorporated to capture the free surface, whereas Papanastasiou’s modified model was used for Bingham fluids. The lattice Boltzmann method was first validated using two benchmarks: Newtonian flow through a square cross-section tube and Bingham flow through a circular cross-section tube. Afterward, the dam-break problem for the Newtonian fluid and the slump test for Bingham fluid were simulated to validate the free-surface-capturing algorithm. The numerical results were in good agreement with analytical results, as well as other simulations, thereby proving the validity and correctness of the current method. The proposed method is a promising substitute for time-consuming and costly physical experiments to solve problems encountered in geotechnical and geological engineering, such as the surge and debris flow induced by a landslide or earthquake.

    • Early Cretaceous Climate Changes Recorded in Magnetic Susceptibility and Color Index Variations of the Lower Liupanshan Group, Central China

      2016, 90(3):1011-1023.

      Abstract (743) HTML (0) PDF 14.75 M (1091) Comment (0) Favorites

      Abstract:This study carried out comprehensive analysis on sedimentology, magnetic susceptibility (χlf) and color data of the continental sediments of the Liupanshan Group in Central China so as to obtain climatic change information during the 129.14–122.98 Ma interval. Based on the results of the clf and of the redness (a*), the section can be divided into two segments: (1) 129.14–126.3 Ma, with the lowest clf values and strongly variable relatively high values of redness and (2) 126.3–122.98 Ma, with high clf values and relatively low redness. Analysis of the lithology and facies as well as the magnetic minerals and their contents points to a detrital origin of the magnetic minerals and this allow us to interpret the relationship between magnetic susceptibility variations and climate changes. Our study shows that the climate was significantly dry and hot during the whole studied interval although the interval between 126.3 Ma and 122.98 was a little bit cooler with increased humidity.

    • Reservoir Characteristics of Lacustrine Shale and Marine Shale: Examples from the Songliao Basin, Bohai Bay Basin and Qiannan Depression

      2016, 90(3):1024-1038.

      Abstract (1021) HTML (0) PDF 20.04 M (1299) Comment (0) Favorites

      Abstract:Lacustrine shale from the Qingshankou Formatin of Songliao basin and the Shahejie Formation of Bohai Bay basin, and marine shale from the lower Cambrian Jiumenchong Formation of Qiannan depression were analysed by using rock pyrolysis, TOC (total organic carbon), XRD (X-ray diffraction), SEM (scanning electron microscope), FE-SEM (field emission scanning electron microscope), high pressure mercury intrusion, and low pressure N2 and CO2 gas adsorption experiments, in aim to reveal their reservoir features. The results show that: (1) the width of micro-pores of all the studied samples mainly ranges from 0.45 to 0.7 nm indicated by CO2 isotherms, and the width of meso-pores is less than 10 nm, with type IV adsorption isotherms and type H2 hysteresis loop, indicative of “ink-bottle”-shaped pores. Good correlations exist among pore volume, surface area and averaged pore diameter, and a good positive correlation exists between micro-pore volume and TOC content; however, there is no obvious correlation between meso-pore volume and TOC content; (2) interparticle pores, pores among the edge of mineral grains and organic matter pores were all identified in marine and lacustrine shale, among which the interparticle pores may be influence by dissolution effect. Not all bitumen develops organic matter pore, and only high to over mature bitumen present pores. Now the description methods of micrometer scale pores developed in shale are very lack. Micro-fractures developed in Jiyang depression and dissolution interparticle pores developed in Songliao Basin should be the accumulation sites for shale oil in lacustrine shale, and can be as sweet spots.

    • NEWS AND HIGHLIGHTS

      2016, 90(3):1039.

      Abstract (525) HTML (0) PDF 0.00 Byte (0) Comment (0) Favorites

      Abstract:

    • China has Built a Mammoth Museum

      2016, 90(3):1039-1040.

      Abstract (536) HTML (0) PDF 5.36 M (846) Comment (0) Favorites

      Abstract:

    • Probing the Troodos Ophiolite: IGCP-649 Workshop and Field Excursion Held in Agros-Cyprus

      2016, 90(3):1041-1044.

      Abstract (593) HTML (0) PDF 3.76 M (1027) Comment (0) Favorites

      Abstract:

    • RESEARCH ADVANCES

      2016, 90(3):1045.

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      Abstract:

    • Xixiang Biota—Another Rare Scientific Window of the Cambrian Explosion

      2016, 90(3):1045-1046.

      Abstract (575) HTML (0) PDF 1.54 M (1060) Comment (0) Favorites

      Abstract:

    • Genesis of the Cenozoic Sodic Alkaline Basalt in the Xiahe–Tongren Area of the Northeastern Tibetan Plateau and its Continental Dynamic Implications

      2016, 90(3):1047-1048.

      Abstract (740) HTML (0) PDF 1.53 M (1078) Comment (0) Favorites

      Abstract:

    • Late Ordovician to Early Silurian Tectonic Events in the Himalayan Terrain

      2016, 90(3):1049-1050.

      Abstract (731) HTML (0) PDF 1.64 M (1036) Comment (0) Favorites

      Abstract:

    • The Mesozoic Basin-Mountain Coupling Process of the Southern East China Sea Shelf Basin and its Adjacent Land Area

      2016, 90(3):1051-1052.

      Abstract (701) HTML (0) PDF 1.74 M (1024) Comment (0) Favorites

      Abstract:

    • Ore-Forming Mechanism of the Asikaerte Granitic Pegmagtite Beryllium Deposit in Xinjiang, China

      2016, 90(3):1053-1054.

      Abstract (641) HTML (0) PDF 1.31 M (973) Comment (0) Favorites

      Abstract:

    • The Electrical Conductivity Structure of the Lanping–Simao Basin and its Implications for Mineralization

      2016, 90(3):1055-1056.

      Abstract (622) HTML (0) PDF 1.92 M (966) Comment (0) Favorites

      Abstract:

    • The Characteristics and Distribution Pattern of Seafloor Sinuous Pockmark Train in the Niger Delta Basin, West Africa

      2016, 90(3):1057-1058.

      Abstract (653) HTML (0) PDF 2.43 M (930) Comment (0) Favorites

      Abstract:

    • Source Rock and Cap Rock Controls on the Upper Ordovician Wufeng Formation–Lower Silurian Longmaxi Formation Shale Gas Accumulation in the Sichuan Basin and its Peripheral Areas

      2016, 90(3):1059-1060.

      Abstract (899) HTML (0) PDF 1.50 M (1018) Comment (0) Favorites

      Abstract:

    • Long-Term Geophysical Observations and Analysis of the World’s Deepest Borehole

      2016, 90(3):1061-1062.

      Abstract (584) HTML (0) PDF 2.06 M (945) Comment (0) Favorites

      Abstract:

    • Provenance of Detrital Magnetites from Quaternary Sediments in the Yichang Area and its Significance to the Birth of the Three Gorges, Yangtze River

      2016, 90(3):1063-1064.

      Abstract (805) HTML (0) PDF 3.89 M (876) Comment (0) Favorites

      Abstract:

Chief Editor:HOU Zengqian

Governing Body:China Association for Science and Technology

Organizer:Geological Society of China

start publication :1922

ISSN:ISSN 1000-9515

CN:CN 11-2001/P

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