Sponge spicules in phosphorites of the Early Cambrian Gezhongwu Formation, Zhijin, Guizhou

Phosphorites occurring at the bottom of the Cambrian system contain abundant small shelly fossils, which are the product of the first episode of life explosion in the Cambrian. It was previously reported that the small shelly fossils are dominated by hyolithids, olivooids, zhijinitids, conodontomorphs, yubelichitids, camenitids and algae, with minor amounts of sponge fossils. Large amounts of sponge spicules, diverse in form, have been found for the first time in the Gezhongwu Formation phosphorites at Shixing, Zhijin County, Guizhou Province, of which such spicules as diaxon-triactins, diaxon-tetractins, pentaxon-pentactins and hexon-hexactins account for 30%. These spicules constitute the sponge clastic phosphorites made up of sponge clastics. Meanwhile, it is also expected that the radiation and diversity of sponge animals started as early as in the earliest Early Cambrian. Habit and burying environment of sponge animal are discussed in the paper.     

Isotopic evolution of the terminal Neoproterozoic and early Cambrian carbon cycle on the northern Yangtze Platform, South China

Profound geotectonic, climatic and biological changes occur during the terminal Neoproterozoic and its transition into the early Cambrian. These are reflected in temporal variations of the chemical and isotopic composition of seawater. We are studying a sequence of sedimentary rocks at the Shatan section, northern Yangtze Platform, Sichuan Province of China. This succession comprises, in ascending stratigraphic order, predominantly calcareous sediments of the Sinian upper Dengying Formation and black shales of the lower Cambrian Guojiaba Formation (time equivalent of Niutitang Fm.). Paleoenvironmental setting represents shallow-water shelf deposits. The objective of our study is to provide temporal records for the isotopic compositions of organic and carbonate carbon throughout this time interval. Organic carbon isotope values display a range between -35.8‰ and -30.1‰ with clear stratigraphic variations. Carbonate carbon isotope data vary between -3.5‰ and +0.5‰. These secular variations are interpreted to reflect perturbations of the global carbon cycle, specifically changes in the fractional burial of organic carbon. However, local conditions have further affected the isotopic signals.     

Paleoceangraphic significance of redox-sensitive metals of black shales in the basal Lower Cambrian Niutitang Formation in Guizhou Province, South China

TheLowerCambrianblackshalesequenceoccursinSouthChinaalonganarc parallellinearbeltex tendingmorethan 16 0 0km .Theseorganic richblackshalesformedinvariousmarineenvironmentsandtypicallycontainhigheramountsofmolybdenum ,nickel,vanadium ,andanumberofothereconomical lyimportantmetalsthandoanyothersedimentaryrocks[1,2 ] .Therefore ,thestudyoftheseblackshaleshasnotonlypaleoceangraphicimplicationbutalsoe conomicsignificance .Marinesedimentssuchasblackshalearecom plexmixturesofdetritalphasesandseawat…     

Pb-Pb isotope dating of black shales from the Lower Cambrian Niutitang Formation, Guizhou Province, South China

Withthedevelopmentofnewanalyticaltech niquesandstate of artinstruments ,isotopetracinganddatingmethodshavemadeconsiderableprogressinrecentyears .Inparticular ,variouskindsofradio genicisotopedatingmethodshavebeenappliedsuc cessfullyinigneousrocks.However,directdatingofsedimentaryrocksremainsundevelopedandcontro versial.Inmostcases ,researchersapplyU PbandK ArorAr Armethodstodatingvolcanicashesthatareinterbeddedwithinsedimentarystratainanattempttoobtaintheageofsedimentsindirectly[1] .Howev e…     

Vermicular fossils in the Early Cambrian Xidashan Formation in the Quruqtagh region of Xinjiang, China

Large amounts of vermicular fossils and a minor amount of sponge animal fossils have been found in the Early Cambrian Xidashan Formation in the region of Quruqtagh, Xinjiang. Vermicular fossils are generally more than 50 mm long and 0.3?1.4 mm wide; their wrinkled lamellae are microfine with 3?10 pieces within the length of every each millimeter. The fossils are considered to be Sabellidites cambriensis Sokolov (1965). The Xidashan Formation is the highest stratum in which Sabellidites occur, as has been so far reported.     

Redox condition during Ediacaran–Cambrian transition in the Lower Yangtze deep water basin,South China: constraints from iron speciation and δ~(13) Corg in the Diben section,Zhejiang

Cherts of the Piyuancun Formation and black mudstones of the Hetang Formation in Diben Town, Kaihua County, Zhejiang were deposited in a deep water basin of the Lower Yangtze area during the Ediacaran–Cambrian transition(E–C transition), offering an opportunity to reconstruct the ancient redox condition of the deep water basin. Total 53 samples were collected and analyzed for iron speciation, including pyrite iron(FePy), carbonate associated iron(FeCarb), iron oxide and hydroxide(FeOx),magnetite iron(FeMag) and total iron(FeT) as well as d13 Corgto gain a deeper understanding of specific redox condition during the period. The results show that(1) most samples have pyrite concentration \1 %, with the FePy/FeHR ratio ranging from \0.01 to 0.81(mostly \0.5), and the FeHR/FeT ratio between 0.39 and 0.93(mostly [0.5).(2) The E–C boundary in the Diben section occurred at the maximum negative excursion of organic carbon isotope within the Piyuancun Formation, which can be correlated with other sections by using d13 Corg. We thus concluded that the relatively high content of highly reactive iron and low content of pyrite iron in the Diben section indicate a minor occurrence of H2 S and a predominance of anoxic and ferruginous environment, which is similar to other reported sections such as the Longbizui and Yanwutan sections, western Hunan. In addition, oxygen concentration in sea water showed an increasing trend in the interval corresponding to the bottom and upper layer of the Hetang Formation as indicated by the FeHR/FeT ratio, which decreased from 0.7 to 0.38, however, it was not great enough to oxidize the whole deep water. Therefore, during the E–C transition deep water basin in South China was most likely an anoxic and ferruginous enrironment, which prevented metazoon from the evolution in the deep water basin. Our work offers an important reference to better understanding of the spatiotemporal occurrence and dynamic processes of the ‘‘Cambrian Explosion'.     

Discovery of a Miaohe-type Biota from the Neoproterozoic Doushantuo Formation in Jiangkou County, Guizhou Province, China

A megascopic algal fossil assemblage was first discovered by Ma Guogan and Chen Meng‘e in the black shales of the Neoproterozoic Doushantuo Formation in Miaohe Town, Zigui County, Hubei Province in 1978. Formal naming of the Miaohe Biota was proposed by Cheng Meng‘e and Xiao Zongzheng in 199112j, and eleven morphological genera have been previously described. including megascopic algae and putative metazoans .Ding et al. greatly expanded the scope of the Miaohe Biota to 9 phyla consisting of 140 genera, including microphytoplanctons, megascopic algae, metazoans, spongesand trace fossils. Xiao et al. further restudied this fossil assemblage, concluding that only about 18 distinct taxa could be recognized and that many Miaohe taxa are poorly defined or svnonvmous.     

Oxygen isotope geochemistry of phosphorite and dolomite and palaeo-ocean temperature estimation: A case study from the Neoproterozoic Doushantuo Formation, Guizhou Province,South China

The Neoproterozoic Doushantuo Formation at Weng'an in Guizhou Province of South China consists of phosphorites and dolomites.Three types of samples are recongnized for the phosphate-bearing rocks.In Type I samples, interstitial phosphates occur within the dolomite rocks, whereas in Type III samples, interstitial dolomites occur within the phosphorites; both of them may have diagenetic origin.The Type II samples are interbedded phosphorites and dolomites.Oxygen isotopic compositions of phosphate and coeval carbonate were analyzed.Phosphates of Type I and II samples show similar low δ18Ophos (SMOW) values of 10.9‰～12.1‰ and 10.7‰～12.8‰, respectively, whereas Type III phosphates show higher δ18Ophos (SMOW) values of 13.2‰～15.0‰.Dolomites from Type I and II samples have δ18Ocarb (PDB) and δ13Ccarb (PDB) values of -6.2‰～-3.4‰ and -2.2‰～-0.7‰, respectively, whereas interstitial dolomites from Type III samples show lower δ18Ocarb (PDB) and δ13Ccarb (PDB) values of -12.9‰～-8.6‰ and -4.4‰～-2.6‰.Petrology and oxygen isotope data suggest that diagenetic alteration may have partially affected the studied rocks, but the dolomites from Type I and phosphates from Type III samples represent the most pristine isotopic compositions of primary carbonates and phosphates precipitated from seawater.Calculations of palaeocean temperatures from the most 18O enriched dolomite and phosphate indicate a temperature range of 32.2 ℃ to 34.0 ℃ for the seawater of the Doushantuo Formation period.Ce anomaly also suggests more oxic conditions and possibly shallower water depth in the upper strata of the Doushantuo Formation at Weng'an, Guizhou Province.     

On the genetic classification and tectonic implications of the Early Yanshanian granitoids in the Nanling Range, South China

Early Yanshanian (Jurassic) granitoids are widespread in the Nanling Range of South China, and are associated with numerous non-ferrous and rare metal mineral deposits. These granitoids consist mainly of slightly peraluminous biotite monzogranites and K-feldspar granites that are closely associated in time and space with subordinate amphibole-bearing granites and muscoviteand garnet-bearing granites. In most previous studies, the biotite-bearing granites were classified as crustal transformation-type (corresponding to the S-type) granites which were interpreted to be derived from the regional Paleoproterozoic meta-sedimentary rocks. In this paper, we re-analyze the geochemical characteristics of a number of representative Early Yanshanian Nanling granitoids. There exists a clear negative correlation between SiO2 and P2O5 for the studied granitoids. The Early Yanshanian Nanling granitoid suites (including amphibole-bearing granodiorites→biotite monzogranites→K-feldspar granites→two-mica (muscovite) granites) are metaluminous to slightly peraluminous I-type or fractionated I-type granites. They were derived predominantly from Proterozoic igneous protoliths. The juvenile crust and/or newly mantle-derived materials might also have been involved in some of these granites. In addition, the Iand fractionated I-type granites are closely associated in time and space with minor amount of A-type felsic and mafic volcanic and intrusive rocks as well as alkaline rocks. All these rocks constitute a typical assemblage of anorogenic, intraplate magmatism, suggesting a dominant lithospheric extensional regime for the Nanling Range and neighboring region during the Early Yanshanian period.     

Discovery of sponge body fossils from the late Meishucunian (Cambrian) at Jinsha, Guizhou, south China

Here we report discovery of a sponge body fossil Triticispongia sp. from the base of lower Cambrian Niutitang Formation at Jinsha, Guizhou. Stratigraphically, the fossil horizon is located below Ni-Mo ore layer with the Niutitang Biota above, and is equivalent to the late Meishucunian. The species is global in shape with skeletons composed of stauractins and monaxons. Triticispongia sp. reported here may be the earliest sponge body fossils of Cambrian, which provides new information for understanding early evolution and radiation of sponge animals.     

δ~(13)C and water-use efficiency indicated by δ~(13)C of different plant functional groups on Changbai Mountains, Northeast China

Leaf δ13C of different plant functional groups (trees, shrubs and forbs; evergreen and deciduous; annual, biennial and perennial) were examined on the Changbai Mountains, China. Life form has a significant influence on plant δ13C, suggesting that leaf δ13C is also ideal for distinguishing functional groups species in temperate and frigid zones with high humidity. Additionally, the difference of water-use efficiency (WUE) is significant among different plant functional groups. δ13C and WUE are in the followi...     

Stable isotopic geochemistry of organic carbon and pyrite sulfur from the Early Cambrian black shales in Northwestern Hunan, China

The early Cambrian black shale sequence in Northwestern Hunan Province has been investigated for its stable isotopic geochemistry of organic carbon and pyrite sulfur. The relatively low δ 13C values of organic matter, -29.7‰～-34.2‰, are interpreted as caused by the high CO2 concentration in atmosphere/ocean and an anoxic depositional environment in early Cambrian. Variable, but significantly positive δ 34S values, 10.2‰～ 28.2‰, for sedimentary pyrite reveals bacterial sulfate reduction as the pyrite-forming process but under sulfate-limited conditions. A protected anoxic basin, which had very limited access to open ocean, and its sediments, where metabolizable organic matter was rich and bioturbation was absent, are supposed to be the sulfate-limited environments and might have existed in South China in the early Cambrian.     

Stratigraphic architecture of the Neoproterozoic glacial rocks in the “Xiang-Qian-Gui” region of the central Yangtze Block, South China

Recently ,theinterestinglowlatitudeandlowaltitudeSnowballEarthhypothesis[1,2 ] iswidelyreco gnized ,and greatlystimulatingthestudyoftheNeoproterozoicglaciations ,whichmaybecloselyre latedtothewell knownEarlyCambrianbio radiationevent.By 1980 ,theNeoproterozoicglaciationinSouthChinaisbelievedtobedividedintotwoglaciationsandoneinterglaciation[3～ 5] ,namely ,theearlyChang’anGlaciation ,lateNantuoGlaciationandFu luInterglaciation .However ,thereweredifferentwaysofcorrelation ,themostobvious…     

Speciation of the genus Arthricocephalus Bergeron, 1899 (Trilobita) from the late Early Cambrian and its stratigraphic significance

The genus Arthricocephalus Bergeron, 1899 is revised, and Halipanktos Balker & Peel, 1997 is suggested here as a senior synonym. The subgenus Arthricocephalus (Arthricocephalites) Chien & Lin in Lu et al. , 1974 is considered as a separate genus. Of the 20 previously assigned species of Arthricocephaius (Arthricocephalus) Bergeron, 1899, Arthricocephalus (Arthricocephalites) Chien & Lin in Lu et al. , 1974, Arthricocephalus (Euarthricocephalus) Ju, 1983 are lumped into eight species. The speciation trend of Arthricocephalus and Arthricocephalites is demonstrated based on their stratigraphic occurrences. It not only enhances the resolution of the biostatigraphic zonation in the uppermost Lower Cambrian, but also represents a potential candidate to define the Duyunian stage. The base of the stage is suggested at the first appearance datum (FAD) of Arthricocephalus chauveaui Bergeron, 1899 within the evolutionary lineage from Ar. jiangkouensis Yin in Yin & Li, 1978 to Ar. chauveaui in a global scale.     

Speciation of the genus Arthricocephalus Bergeron, 1899 (Trilobita) from the late Early Cambrian and its stratigraphic significance

The genus Arthricocephalus Bergeron, 1899 is revised, and Halipanktos Balker & Peel, 1997 is suggested here as a senior synonym. The subgenus Arthricocephalus (Arthricocephalites) Chien & Lin in Lu et al., 1974 is considered as a separate genus. Of the 20 previously assigned species of Arthricocephalus (Arthricocephalus) Bergeron, 1899, Arthricocephalus (Arthricocephalites) Chien & Lin in Lu et al., 1974, Arthricocephalus (Euarthricocephalus) Ju, 1983 are lumped into eight species. The speciation trend of Arthricocephalus and Arthricocephalites is demonstrated based on their stratigraphic occurrences. It not only enhances the resolution of the biostatigraphic zonation in the uppermost Lower Cambrian, but also represents a potential candidate to define the Duyunian stage. The base of the stage is suggested at the first appearance datum (FAD) of Arthricocephalus chauveaui Bergeron, 1899 within the evolutionary lineage from Ar. jiangkouensis Yin in Yin & Li,1978 to Ar. chauveaui in a global scale.     

Speciation of the genus Arthricocephalus Bergeron, 1899 (Trilobita) from the late Early Cambrian and its stratigraphic significance

The genus Arthricocephalus Bergeron, 1899 is revised, and Halipanktos Balker & Peel, 1997 is suggested here as a senior synonym. The subgenus Arthricocephalus (Arthricocephalites) Chien & Lin in Lu et al., 1974 is considered as a separate genus. Of the 20 previously assigned species of Arthricocephalus (Arthricocephalus) Bergeron, 1899, Arthricocephalus (Arthricocephalites) Chien & Lin in Lu et al., 1974, Arthricocephalus (Euarthricocephalus) Ju, 1983 are lumped into eight species. The speciation trend of Arthricocephalus and Arthricocephalites is demonstrated based on their stratigraphic occurrences. It not only enhances the resolution of the biostatigraphic zonation in the uppermost Lower Cambrian, but also represents a potential candidate to define the Duyunian stage. The base of the stage is suggested at the first appearance datum (FAD) of Arthricocephalus chauveaui Bergeron, 1899 within the evolutionary lineage from Ar. jiangkouensis Yin in Yin & Li,1978 to Ar. chauveaui in a global scale.     

Re-Os isotopes and PGE geochemistry of black shales and intercalated Ni-Mo polymetallic sulfide bed from the Lower Cambrian Niutitang Formation, South China

The paleo oceanenvironmentalchangeduringthePrecambrian Cambriantransitionisakeyissuere latedtothecausesforanexplosiveradiationofdiffer entmetazoanphyladuringtheEarlyCambrianera .Thechemicalandisotopiccompositionsofmarinesed iments (carbonates ,phosphorites ,siliceousrocks ,andblackshales)recordthechangingcompositionandphysicalconditionsoftheseawaterinwhichtheserocksaccumulated .Organiccarbon richblackshalesfrommarineenvironmentsarecommonlyenrichedinanumberoftraceelementssuchasNi,Mo ,V ,Co ,…     

Application of backflush and micro-flow techniques to the analysis of C_5—C_(13) hydrocarbons in crude oils and its geochemical significance

An Agilent 6890N GC equipped with both FID and Agilent 5975 MSD analyzer has been employed to analyze C5—C13 hydrocarbon fractions of crude oils. A technical combination of program temperature volatilizer injection, backflush and micro-flow controller afforded a fine separation of C5—C13 compounds on a PONA column with the heavy part of crude oils being cut off before entering the analytical column. Both GC-FID chromatogram and GC-MS mass chromatograms (MID and full scan) could be obtained at the same time. The retension time differences of nC6—nC13 alkanes between GC and TIC were in the range of 0.02—0.58 minutes. Totally 286 peaks have been assigned group compositions. Results on 8 typical oil samples from CNPC Key Laboratory Crude Oil Library showed that the characteristics of C6—C13 hydrocarbon group composition could be used in oil-oil correlation studies.