Middle Permian radiolarians from Anmenkou, Chaohu, Northeastern Yangtze platform, China

The biostratigraphy of the Middle Permian Gufeng Formation in the northeastern Yangtze platform is examined based on radiolarians. This study is concentrated on the Anmenkou section in the Chaohu area of Anhui Province, China. The Gufeng Formation is divided into the Phosphate Nodule-bearing Mudstone Member (PNMM) and the Siliceous Rock Member (SRM) in ascending order. The former primarily consists of mudstone including abundant phosphate nodules, and the latter consists mainly of alternating beds of chert, siliceous mudstone and mudstone, with intercalations of porous chert. Ammonoids in the mudstone of the lower PNMM are Wordian. Chert, siliceous mudstone and mudstone of the SRM include abundant radiolarians with sponge spicule assemblages suggestive of the Wordian–Capitanian. Albaillellaria are predominant in the lower SRM, while Entactinaria and Spumellaria are predominant in the middle and upper SRM. These radiolarians correspond to three radiolarian assemblage zones: Pseudoalbaillella longtanensis – Pseudoalbaillella fusiformis , Follicucullus monacanthus , and Follicucullus scholasticus – Ruzhencevispongus uralicus . The assemblage of radiolarians and sponge spicule fauna suggests a depositional depth of 150–500 m. The radiolarian fauna of the Gufeng Formation is considered to be representative of the relatively shallow, tropical radiolarian fauna of the Middle Permian eastern Paleotethys.     

Geochemistry and mineralogy of the Late Permian coals from the Songzo Coalfield, Chongqing, southwestern China

Mineralogy and geochemistry of the four main workable coal seams (No.6, No.7, No.8, and No.11) of Late Permian age from the Songzao Coalfield, Chongqing, Southwest China, were examined using inductively coupled plasma-mass spectrometry (ICP-MS), X-ray fluorescence spectrometry (XRF), cold-vapor absorption spectrometry (CV-AAS), ion-selective electrode (ISE), scanning electron microscopy equipped with an energy-dispersive X-ray spectrometer (SEM-EDX), and X-ray diffraction analysis (XRD). The results showed that the main workable No.8 Coal that accounts for about 60% of the total coal reserves in the Songzao Coalfield was not enriched in hazardous trace elements. The No.11 Coal has high concentrations of alkaline elements, Be (9.14 μg/g), Sc (12.9 μg/g), Ti (9508 μg/g), Mn (397 μg/g), Co (23.7 μg/g), Cu (108 μg/g), Zn (123 μg/g), Ga (32 μg/g), Zr (1304 μg/g), Nb (169 μg/g), Hf (32.7 μg/g), Ta (11.4 μg/g), W (24.8 μg/g), Hg (0.28 μg/g), Pb (28.1 μg/g), Th (24.1 μg/g), and rare earth elements (509.62 μg/g). The concentration of Nb and Ta in the No. 11 Coal is higher than the industrial grade, and their potential utilization should be further studied. Besides pyrite, quartz, calcite, and clay minerals, trace minerals including chalcopyrite, marcasite, siderite, albite, mixed-layer clay minerals of illite and smectite, monazite, apatite, anatase, chlorite, and gypsum were found in the No.11 Coal. It should be noted that alabandite of hydrothermal origin and anatase occurring as cement were identified in coal. In addition, the clayey microbands derived from alkaline volcanic ashes were identified in the coal. The dominant compositions of these clayey microbands were mixed-layer clay minerals of illite and smectite, which were interlayered with organic bands. The modes of occurrence of alkaline volcanic ash bands indicate that the volcanic activities were characterized by the multiple eruptions, short time interval and small scale for each eruption during peat accumulation. The alkaline volcanic ashes were the dominant factors for the enrichment of alkaline elements, Nb, Ta, Zr, Hf, and rare earth elements, and the sulfide minerals are the main carriers of Ga, Cu, and Hg in the No. 11 Coal. Supported by the National Key Basic Research and Development Program (Grant No. 2006CB202201), the National Natural Science Foundation of China (Grant No. 40472083), and the Foundation for the Author of National Excellent Doctoral Dissertation of China (Grant No. 200448)     

Geochemistry and mineralogy of the Late Permian coals from the Songzao Coalfield, Chongqing, southwestern China

Mineralogy and geochemistry of the four main workable coal seams (No.6, No.7, No.8, and No.11) of Late Permian age from the Songzao Coalfield, Chongqing, Southwest China, were examined using in- ductively coupled plasma-mass spectrometry (ICP-MS), X-ray fluorescence spectrometry (XRF), cold-vapor absorption spectrometry (CV-AAS), ion-selective electrode (ISE), scanning electron mi- croscopy equipped with an energy-dispersive X-ray spectrometer (SEM-EDX), and X-ray diffraction analysis (XRD). The results showed that the main workable No.8 Coal that accounts for about 60% of the total coal reserves in the Songzao Coalfield was not enriched in hazardous trace elements. The No.11 Coal has high concentrations of alkaline elements, Be (9.14 μg/g), Sc (12.9 μg/g), Ti (9508 μg/g), Mn (397 μg/g), Co (23.7 μg/g), Cu (108 μg/g), Zn (123 μg/g), Ga (32 μg/g), Zr (1304 μg/g), Nb (169 μg/g), Hf (32.7 μg/g), Ta (11.4 μg/g), W (24.8 μg/g), Hg (0.28 μg/g), Pb (28.1 μg/g), Th (24.1 μg/g), and rare earth elements (509.62 μg/g). The concentration of Nb and Ta in the No. 11 Coal is higher than the industrial grade, and their potential utilization should be further studied. Besides pyrite, quartz, calcite, and clay minerals, trace minerals including chalcopyrite, marcasite, siderite, albite, mixed-layer clay minerals of illite and smectite, monazite, apatite, anatase, chlorite, and gypsum were found in the No.11 Coal. It should be noted that alabandite of hydrothermal origin and anatase occurring as cement were identi- fied in coal. In addition, the clayey microbands derived from alkaline volcanic ashes were identified in the coal. The dominant compositions of these clayey microbands were mixed-layer clay minerals of illite and smectite, which were interlayered with organic bands. The modes of occurrence of alkaline volcanic ash bands indicate that the volcanic activities were characterized by the multiple eruptions, short time interval and small scale for each eruption during peat accumulation. The alkaline volcanic ashes were the dominant factors for the enrichment of alkaline elements, Nb, Ta, Zr, Hf, and rare earth elements, and the sulfide minerals are the main carriers of Ga, Cu, and Hg in the No. 11 Coal.     

Evolutionary patterns of Productida (Brachiopoda) morphology during the Permian in South China

The evolutionary patterns of Productida (brachiopod) morphology throughout the Permian show that while the percentage proportion of Productida (brachiopod) with strongly concentric and radial ornamentation declined from the Cisuralian to the Guadalupian, and then increased towards the Changhsingian via Wuchiapingian, the percentage proportion of Productida (brachiopod) with fine concentric and radial ornamentation distinctly increased from the Cisuralian to the Guadalupian, slightly declined towards the Wuchiapingian, and then increased towards the Changhsingian. From the Cisuralian to the Changhsingian, the percentage proportion of brachiopods with spinose ornamentation shows a persistent declining trend. The shell size generally indicates a miniaturization trend at species level during the Wuchiapingian to Changhsingian (including the transitional bed). These evolutionary patterns of brachiopod ornamentation and size are possibly related to the anoxia, food shortage, sea-level fluctuation, and change of substrate in the Permian (including the Permian-Triassic transitional interval) in South China.     

Geochemistry and petrogenesis of Late Ladinian OIB-like basalts from Tabai,Yunnan Province,China

Major and trace elements analysis has been carried out on the Late Ladinian Tabai basalts from Yunnan Province with the aim of studying their petrogenesis. Their SiO2 contents range from 43.63 wt.% to 48.23 wt.%. The basalts belong to the weakly alkaline(average total alkalis Na2 O+K2O=3.59 wt.%), high-Ti(3.21 wt.% to 4.32 wt.%) magma series. The basalts are characterized by OIB-like trace elements patterns, which are enriched in large ion lithosphile elements(LILE) including Rb and Ba, and display negative K, Zr and Hf anomalies as shown on the spider diagrams. The Tabai basalts display light rare-earth elements(LREE) enrichment and are depleted in heavy rare-earth elements(HREE) on the REE pattern. Those dates indicate that the parental magma of the Tabai basalts was derived from low-degree(1%–5%) partial melting of garnet peridotite. The magma underwent olivine fractional crystallization and minor crustal contamination during their ascent. The Tabai basalts were related to a relaxation event which had triggered the Emeishan fossil plume head re-melting in the Middle Triassic.     

Late Changhsingian radiolarian biostratigraphy from Guangxi,South China and its correlation to conodonts

A well-preserved, abundant radiolarian fauna was obtained from three sections: the Dongpan, Liuqiao, and Paibi sections, in southern Guangxi, South China. Sixteen species belonging to Albaillella and Neoalbaillella, including seven undetermined species, are recognized. On the basis of stratigraphic distribution of these species, two radiolarian zones, the Albaillella triangularis Zone and the Albaillella yaoi Zone, are established. The correlation between radiolarian zones and conodont zones is suggested based on the discovery of coexisting conodonts. Albaillella triangularis and Albaillella yaoi zones correspond to Neogondolella postwangi and Neogondolella yini zones respectively.     

First evidence of Middle to Late Triassic radiolarians in the Garba mountains,South Sumatra,Indonesia

A Middle to Late Triassic (Ladinian–Carnian) radiolarian fauna was discovered in cherts of the Situlanglang Member of the Garba Formation, South Sumatra, which is generally regarded as of Late Jurassic–Early Cretaceous age. This fauna is characterized by the presence of Annulotriassocampe sulovensis, Triassocampe postdeweveri, Spongotortilispinus tortilis, Poulpus piabyx, Canoptum levis and others. This evidence possibly indicates that the deposition of the Situlanglang cherts took place after the collision of the Sibumasu and East Malaya blocks recorded in the Bentong–Raub Suture in Peninsular Malaysia in Late Permian–Early Triassic times. During the Middle–Late Triassic Sumatra and Peninsular Malaysia consisted of submarine horst and graben structures. It is possible that a submarine graben, the Tuhur basin, whose southern boundary was formerly undefined, extends into South Sumatra, to the area in which the Situlanglang cherts were deposited. The Situlanglang Member is proposed to be a rock unit stratigraphically contemporaneous with those of the Middle–Upper Triassic Kualu and Tuhur Formations in North and Central Sumatra.     

Late Cretaceous palynology and paleoclimate change:Evidence from the SK1(South) core,Songliao Basin,NE China

Cretaceous climate was warmer than today.The Songliao Basin contains one of the most important Late Cretaceous non-marine deposits in China for the research of the paleoenvironment and paleoclimate.This research is based on core samples from the SK1(S)borehole.The strata sampled are the upper part of the Quantou Formation to member 2 of the Nenjiang Formation,where spores,pollen,dinoflagellates,and other microfossils are abundantly preserved.Based on analysis of the spores and pollen fossils from the core samples,the following six fossil assemblage zones have been recognized in ascending order:The Cicatricosisporites-Cyathidites-Pinuspollenites,Schizaeoisporites-Cyathidites-Classopollis,Cyathidites-Schizaeoisporites,Schizaeoisporites-Cyathidites-Proteacidites,Proteacidites-Cyathidites-Dictyotriletes,and the Lythraites-Callistipollenites-Schizaeoisporites zones.The six fossil zones range from the late Cenomanian to early Campanian.The Late Cretaceous dinoflagellate cysts in the Songliao Basin are of high abundance and low diversity.Specific phytoplankton types reflect salinity changes of the Songliao Lake.Paleoecology of the dinoflagellates suggests that sediments of members 2 and 3 of the Yaojia Formation(K2y2+3)were deposited in a freshwater environment,whereas members 2 and 3 of the Qingshankou Formation(K2q2+3)and members 1 and 2 of the Nenjiang Formation(K2n1+2)were deposited in freshwater to brackish water environments.Combined with the paleoecology of dinoflagellates and the palynomorph biozones,valuable information of the paleoclimate was provided.The quantitative analyses of spores and pollen fossils,such as vegetation type,climate type,and humidity type,diversity and dominance,indicate a relatively sub-humid,mid-subtropical paleoclimate,with slight climatic fluctuation and/or temporal change.     

The geobiological formation process of the marine source rocks in the Middle Permian Chihsia Formation of South China

The Chihsia Formation is one of the four sets of regional marine hydrocarbon source rocks from South China.In the past two decades,detailed geochemical and sedimentological studies have been carried out to investigate its origination,which have demonstrated that the high primary productivity plays a primary role in the deposition of sediments enriched in the organic matter.However,the mechanism of this high productivity and the path of the deposition and burial of the organic matter have always been a mystery.Based on the previous studies on the Shangsi Section in Guangyuan City,Sichuan Province,we proposed that the development of the equatorial upwelling due to the sea level rise is responsible for the relatively high productivity in the Chihsia Formation.The sea waters with high nutrient were transported by the sub-surface currents along the equator.High organic carbon flux was deposited on the deeper shelf,and then decomposed by bacteria,leading to the occurrence of anaerobic respiration.The metabolism of the microorganisms consumed the dissolved oxygen in waters,which was in favor of the preservation of the organic matter.This suggested geobiological model integrating with paleoclimatology,paleoceanography and geomicrobiology will help us to understand the causes of this particular sedimentary sequence.     

Biostratigraphy constraining strontium isotopic stratigraphy and its application to the Lopingian(Late Permian)

The Lopingian is one of the fastest rising periods of seawater strontium isotopic ratios(87Sr/86Sr) in earth history, and its mechanisms and increasing rates of the 87Sr/86 Sr evolution were still disputed widely. These disputations among researchers were caused mainly by timeframe selection(sections' thickness or data of radiometric ages), and different stratigraphic boundaries and un-upmost dated ages. This paper examined published 87Sr/86 Sr data of the Lopingian, and projected them on timescales based on evolutionary and age constrained conodonts fossils. 87Sr/86 Sr evolution vs fossil constraining timescales was re-established in this period. This research suggests:(1) 87Sr/86 Sr excursion projects on fossil zones can truly support 87Sr/86 Sr evolutionary pattern in the period;(2) 87Sr/86 Sr evolution provides a new approach for stratigraphic research of marine carbonate sections in lieu of biostratigraphic data;(3) 87Sr/86 Sr stratigraphy works on marine carbonate sections of different sedimentation rates even between different basins;(4) the 87Sr/86 Sr data and its shift was dependent on samples materials and chemical treatment methods;(5) the increasing rate of marine water 87Sr/86 Sr in the Late Permian is suggested as 5.4×10?5/Ma or slightly lower;(6) sedimentation age and its 87Sr/86 Sr of the Lopingian marine carbonate suggested as: DPro=259?(RS? 0.70695)/5.4×10?5(Ma).     

Geochemistry and petrogenesis of rift-related volcanic rocks from South Kivu (Zaire)

Two volcanic zones (Bukavu and Kamituga) south of Lake Kivu (southeastern Zaire) are part of the western branch of the Eastern African rift. They were formed during three volcanic cycles, one pre-rift (70-7 Ma old) and the other two syn-rift (7.8-1.9 Ma old and 14,000 y.-sub-Recent, respectively), and evolved from quartz tholeiites of the pre-rift period to alkali basalts of the rift stage. The basaltic rocks, which strongly predominate, are compositionally similar to other rift-related basalts and also to oceanic-island rocks. Most of the basalts have undergone only limited fractional crystallization (5–10%) dominated by olivine and clinopyroxene. The distinct variations of incompatible elements even in rocks of very similar major-element composition imply that the basaltic rocks were derived from a heterogeneous source by variable degrees of melting. The inferred source composition closely resembles that of metasomatized peridotite xenoliths from alkali basalts.     

华南二叠系卡匹敦阶高分辨率浮点年代标尺

基于详细的生物地层学研究,以磁化率为古气候替代指标,对广西来宾铁桥剖面卡匹敦阶地层开展时间序列分析,建立高分辨率浮点年代标尺(FPTS).结果表明,磁化率记录了铁桥剖面中二叠世晚期沉积序列中的米兰科维奇旋回,卡匹敦阶上部磁化率突然增加与峨眉山玄武岩喷发和卡匹敦晚期全球性海退有关,这些事件导致同期沉积物中碎屑物质增加.铁桥剖面瓜德鲁普—乐平统界线附近磁化率和蓬莱滩剖面(乐平统底界GSSP)表现出一致的变化趋势,具可对比性.利用多窗谱法(MTM)和傅里叶变换(FT)从磁化率序列中识别出五个米兰科维奇周期:长偏心率周期(E2,405 ka)、短偏心率周期(E1,100 ka)、长地轴斜率周期(O2,44.1 ka)、长岁差周期(P2,20.95 ka)和短岁差周期(P1,17.7 ka).对比基于E2周期建立的磁性地层磁化率(MSS)带和标准参考带(SRZ),建立整个沉积序列的高分辨率(200 ka)FPTS,提出卡匹敦阶的时限为3.85 Ma(存在+0~0.28 Ma误差),整段沉积序列的平均沉积速率为2.91 cm·ka-1.同时计算出卡匹敦阶内部七个牙形石带的时限,从最短26.6 ka到最长2.3 Ma.另外,估算出峨眉山大火成岩省喷发启动时间为262.67 Ma,位于瓜德鲁普—乐平统界线之下1.42 Ma.     

Paleomagnetic results from Late Carboniferous to Early Permian rocks in the northern Qiangtang terrane,Tibet, China,and their tectonic implications

Results of a systematic paleomagnetic study are reported based on Late Carboniferous to Early Permian sedimentary rocks on the north slope of the Tanggula Mountains,in the northern Qiangtang terrane(NQT),Tibet,China.Data revealed that magnetic minerals in limestone samples from the Zarigen Formation(CP^z)are primarily composed of magnetite,while those in sandstone samples from the Nuoribagaribao Formation(Pnr)are dominated by hematite alone,or hematite and magnetite in combination.Progressive thermal,or alternating field,demagnetization allowed us to isolate a stable high temperature component(HTC)in 127 specimens from 16 sites which successfully passed the conglomerate test,consistent with primary remnance.The tilt-corrected mean direction for Late Carboniferous to Early Permian rocks in the northern Qiangtang terrane is D_s=30.2°,I_s=-40.9°,k_s=269.0,a_(95)=2.3°,N=16,which yields a corresponding paleomagnetic pole at 25.7°N,241.5°E(dp/dm=2.8°/1.7°),and a paleolatitude of 23.4°S.Our results,together with previously reported paleomagnetic data,indicate that:(1)the NQT in Tibet,China,was located at a low latitude in the southern hemisphere,and may have belonged to the northern margin of Gondwana during the Late Carboniferous to Early Permian;(2)the Paleo-Tethys Ocean was large during the Late Carboniferous to Early Permian,and(3)the NQT subsequently moved rapidly northwards,perhaps related to the fact that the Paleo-Tethys Ocean was rapidly contracting from the Late Permian to Late Triassic while the Bangong Lake-Nujiang Ocean,the northern branch of the Neo-Tethys Ocean,expanded rapidly during this time.     

New stylophorans (Echinodermata) from the upper Cambrian of Guangxi,South China

This paper describes for the first time the cornute stylophorans (Echinodermata) in China. The new material came from the Guole Formation of the Furongian (Late Cambrian) in the Guole area of Jingxi, Guangxi Province, South China. These new cornute specimens are preserved in situ and found along with well-preserved trilobites and brachiopods. One new species, Phyllocystis jingxiensis sp. nov., is proposed to accommodate these unusual materials. The new species is defined by the small, heart-shaped theca with the frame composed of ten narrow, smooth and thick marginal plates, three adoral plates and distinctive zygal and aulacophore. Both supracentrals and infracentrals are polygonal-outlined. The marginal plate M1' on the inferior face extends posteriorly to form zygal that possesses a broadened proximal end and the proximal portion joining with the conjunction between M4 and M5 on the inferior face. Aulacophore comprises ten segments at its proximal part and is conical at the middle part (named stylocone). Its distal portion is rather long and bears conspicuous ambulacrum grooves. Tectals are horizontally arranged on superior face and obliquely arranged on inferior face. Both cothurnopore and anal pyramid are vaguely seen on the right anterior corner and the extremity of theca's superior face.     

Community replacement sequences and paleoenvironmental changes in reef areas of South China from Late Permian to Early Triassic exemplified by Panlongdong section in northeastern Sichuan Basin

The well-known Permian Changhsingian calcisponge reef located at Panlongdong section,Xuanhan county,northeastern Sichuan Basin has attracted wide attention.Due to severe dolomitization and poor quality of the fossils,the P-T boundary in this section is difficult to determine.This study,for the first time,recognized six communities in the Upper Permian Changhsingian Changxing Formation through the Lower Triassic Induan Feixianguan Formation of the Panlongdong section.They are Bryozoan-Archaeolithoporella-calcisponge Community,Calcareous green algae-foraminifer-crinoid Community,Microgastropod-foraminifer Community,Ostracod-microgastropod-cystic microbe Community,Ostracod-small brachiopod Community,and Non-calcified cyanobacteria Community.By using community replacement and palaeoenvironmental analysis,for the first time,we set the P-T boundary of the Panlongdong section at the middle of the calcimicrobialite containing cystic microbes.The community replacement sequence in the Panlongdong section is similar to that in other contemporaneous sections in reef areas of South China,indicating universal palaeoenvironmental changes during the Permian-Triassic transition.The results show that:(1)Changhsingian calcisponge reefs in South China generally vanished before the mass extinction and may be related to the large regression in the Late Permian.(2)The Calcareous green algae-foraminifer-crinoid Community replaced reef community and continued till the mass extinction.The mass extinction was probably related to the global sea-level drop.(3)The first aftermath community was dominated by specialized microgastropods,followed by the microbes,and then by the specialized microgastropods and small brachiopods.The succession of the three communities reflected the change in environmental conditions from dysoxic to anoxic and again to dysoxic.(4)In the Early Triassic,the relict community in shallow sea had very low diversity and low abundance,and was dominated by crinoids,gastropods,and bivalves.     

南海北部大陆边缘盆地地热特征与油气富集

本文报道了莺歌海盆地、北部湾盆地共148个新测热导率数据,根据收集的钻井温度数据新增计算65个大地热流数据;结合前人研究成果绘制了南海北部大陆边缘沉积盆地的地温梯度图、大地热流分布图;系统归纳了南海北部大陆边缘油气勘探成果.结果表明,南海北部大陆边缘珠江口盆地、琼东南盆地、北部湾盆地、莺歌海盆地的平均热流值分别为68.7±11 mW/m2、71.1±13 mW/m2、65.7±8.9 mW/m2、74.7±10 mW/m2,属于典型的“热盆”.热流区域分布特征总体上受大地构造背景控制,随地壳厚度从北向南,由陆架到陆坡区逐渐减薄而增高,水热活动与岩浆活动等是引起局部高热流异常的原因.盆地地温场的差异控制和约束了油气分布富集规律,从研究区油气勘探成果中可以发现,该区域的气田多发育于高热流盆地（凹陷）,而中-低热流盆地（凹陷）则多孕育油田,油气田具有“北油南气”的分布特征.     

Evolution of strontium isotopic composition of sea-water from Late Permian to Early Triassic based on study of marine carbonates,Zhongliang Mountain,Chongqing,China

Collected from a Late Permian to Early Triassic sedimentary section in the Zhongliang Mountain of Chongqing, Southwest China, sixty marine carbonate samples were measured for the 87Sr/86Sr ratios, and corresponding evolution curve was constructed. The concentrations of SiO2, CaO, MgO, Mn and Sr are used to evaluate reservation of strontium isotopic composition for original seawater and the credi-bility of the dissolution method for sample preparation. The results show that most of the samples (except seven samples with the Mn/Sr ratios higher than 2) contain the original geochemistry signa-tures of ancient seawater. Compared to the published 87Sr/86Sr ratios from the Late Permian to Early Triassic, our database reported here is the largest and the curve constructed is the most complete. The strontium isotopic curve from Late Permian to Early Triassic is consistent globally and exhibits a gen-eral trend of steady increase during this period. The minimum of 87Sr/86Sr ratios (0.707011) occurs in the Late Permian (30 m in thickness below the Permian-Triassic boundary), and the maximum (0.708281), near the Early-Middle Triassic boundary. The lack of land plants and the rapid continental weathering result in the increase of 87Sr/86Sr ratios during the interval. The Permian-Triassic boundary in Zhongli-ang Mountain Section has been accepted internationally. The 87Sr/86Sr ratios of six samples near the boundary vary from 0.70714 to 0.70715 with an average of 0.70714, which is consistent with the value of 0.70715 (samples are from articulate brachiopod shells) from Korte et al. published in 2006 (within the error range in experiment). Accordingly, the strontium isotope composition in the Permian-Triassic boundary in this paper is of global significance. It can be confirmed that the 87Sr/86Sr ratios of the sea-water in the Permian-Triassic transition are in the range of 0.70714―0.70715.     

Discovery of a Late Permian Angara-Cathaysia mixed flora from Acheng of Heilongjiang,China, with discussions on the closure of the Paleoasian Ocean

This work documents a new flora from the Upper Permian Hongshan Formation of Acheng County, Heilongjiang Province, Northwest China. The flora consists of 20 species: Paracalamites sp., Pecopteris tangwangheensis Huang, Callipteris obese Huang, Callipteris shenshuensis Huang, C. tangwangheensis Huang, C. heilongjiangensis Huang, C. zeilleri Zalessky, C. sp., Comia yichunensis Huang, C. tenueaxis Huang, Iniopteris sibirica Zalessky, Supaia teiliensis Huang, Compsopteris tchirkovae Zalessky, C. cf. adzvensis Zalessky, Nilssonia sp. 1, Nil. sp. 2, Taeniopteris cf. densissima Halle, T. cf. nystraemii Halle, T. sp. and Noeggerathiopsis derzavinii Neub. It is dominated by Angara species but mixed with some typical Cathaysian elements. The age of the flora is assigned to late of the Late Permian according to the stratigraphic ranges of the known species and the comparisons of it with the similar floras. The new discovery indicates that the final collision between the North China Plate and Siberian Plate occurred in Late Permian along the Xar Moron River-Changchun-Yanji sutured zone, and the Paleoasian Ocean was finally closed at the end of the Permian.     

Mega-shoaling in carbonate platform of the Middle Triassic Leikoupo Formation,Sichuan Basin,southwest China

Shoaling is a common type of sedimentation in the evolution of carbonate platform,and commonly has poor continuity.This paper presents a newly discovered and rare type of shoaling,i.e.,mega-shoaling in nearly basin scale,which is developed in the Middle Triassic Leikoupo Formation of the Sichuan Basin,southwest China.During the Leikoupo time,the studied Sichuan Basin experienced hot and dry climate conditions and developed a carbonate platform within a restricted epicontinental sea.In B sub-layer of the Lei-1-1 sub-member of the Leikoupo Formation a series of grainstones of shoal facies accumulated throughout almost the entire basin,thereby generating features associated with basin-scale mega-shoaling.By detailed core examination and microscopic observation of thin sections,it is shown that the lithology of this set of grainstones is dominated by doloarenite(calcarenite)followed by oolitic dolomite(limestone).In addition,it contains three types of sedimentary sequences characterized by upward-coarsening and upward-shallowing as the followings:restricted lagoon to platform interior beach;restricted lagoon to platform interior beach and to platform flat;and tidal flat to peritidal beach.Subsequently,a multicyclic stratigraphic division and correlation revealed that this set of grainstones can be well traced and compared horizontally,and is generally isochronous.In addition,a template for logging facies,established based on core calibrations and logging data,was employed to analyze the 235 wells in the basin.The results demonstrate the shoal grainstones to be 10–40 m thick with a15×104km2continuous distribution area.These findings indicate that the carbonate platform developed mega-shoals within a short period of time.The genesis of such a mega-shoaling was investigated by focusing on various shoaling conditions,such as paleo-tectonics,paleo-geomorphology,paleo-climate,sea-level changes,and palaeo-hydrodynamics.A specific combination of independent geological factors creates beneficial geomorphologic conditions for the mega-shoaling including a quiescent paleo-tectonic environment,relatively flat paleo-geomorphology and evaporites filling up and leveling off.In addition,a stably settling carbonate platform underwent sea-level fluctuations through swift transgressions and protracted regressions,which is not only conducive to continuous,multicyclic and superimposed vertical development of grain beaches but also beneficial for the horizontal migration,coalescence and superimposition of individual grain beaches.As a consequence,large-scale and continuously-distributed grain beach sedimentation emerges and mega-shoals develop.     

Lithology, kinematics and geochronology related to Late Mesozoic basin-mountain evolution in the Nanxiong-Zhuguang area, South China

The Nanling Mountain is an important Mesozoic orogenic belt in the south of China, its E-W-trending granites and adjacent sedimentary basins form a dis-tinctive basin-mountain landform. The Nanxiong basin and the Zhuguang granite, both located in the northern Nanling belt, make up a typical basin-mountain sys-tem. Since the 1970s, a systematical research on gran-ites and their deposit ores was carried out, from that the two main viewpoints were proposed[1—5], including (1) the polyphase gr…