Carbon isotope chemostratigraphy has proved to be an efficient tool for refining the temporal correlation of ancient sedimentary successions. For the Ordovician period, numerous studies have been carried out over the last years, resulting in recognition of a series of distinct anomalies in the carbon isotope record. These ‘excursions’ form the basis for regional and global correlation of sedimentary packages that may be only a few metres thick or even less. Up to now, only one positive δ13C excursion has been formally named from this time interval, i.e., the Middle Darriwilian Isotope Carbon Excursion. Recently, Dr. WU Rongchang from Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences and colleagues from Lund university (Sweden) and University of Erlangen-Nürnberg (Germany) have carried out carbon isotope analysis of the Lower through Middle Ordovician cool-water carbonates of the Brunflo 2 core from near Brunflo in the J？mtland province of west-central Sweden. The studied succession is 41.55 m thick and includes, in ascending order, the Bj？rk？sholmen Formation, Latorp Limestone, T？yen Shale, and the Lanna, Holen,and Segerstad limestones. The result shows that two distinct positive δ13C excursions that can be used for intra- as well as inter-continental correlations. A positive excursion in the T？yen Shale probably correlates to the mid-late Floian and the Oepikodus evae Zone in Baltica and Precordillera, and the Reutterodus andinus Zone in North America. A continuous increase in δ13C values through the upper Holen Limestone and the preserved part of the overlying Segerstad Limestone is interpreted as the rising limb of the Middle Darriwilian Isotope Carbon Excursion (MDICE), an important tie-point for the global correlation of the J？mtland strata. This study is supported by the National Natural Science Foundation of China, the Swedish Research Council and Crafoord Foundation and the Deutsche Forschungsgemeinschaft.
Related information of this paper: Wu, R.C., Calner, M., Lehnert, O., Perterffy, O. & Joachimski, M.M., 2015. Lower–Middle Ordovician 13C chemostratigraphy of western Baltica (J？mtland, Sweden). Palaeoworld 24, 110–122. doi:10.1016/j.palwor.2015.01.003 Carbon isotope chemostratigraphy in the Brunflo 2 core from J？mtland, Sweden showing the levels of identified δ13C events: LTNICE (Late Tremadocian Negative Isotopic Carbon Excursion), LDNICE (Lower Darriwilian Negative Isotopic Carbon Excursion), and the rising limb of the MDICE (Middle Darriwilian Isotopic Carbon Excursion). There are many fluctuations in the Floian and Dapingian δ13C record; the assumed position of the BDNICE (Basal Dapingian Negative Isotopic Carbon Excursion) is placed in the lower Lanna Limestone where generally slightly lower values are observed.
The Tibet Plateau, which is the highest in the world, is relatively difficult to access; therefore, the stratigraphy and fossils in this area are poorly known although they are very important to interpret the palaeogeographical evolution of different tectonic blocks. Dr. YUAN Dongxun, Dr. ZHANG Yichun from the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences and their colleagues reported a new discovery of an abundant conodont fauna from the lowest part of the Xiala Formation in the central part of the Lhasa Block, Tibet. This conodont fauna includes three genera and four species (Mesogondolellaidahoensis, M. siciliensis, Vjalovognathusnicolli n. sp. and Hindeodus sp.). The conodont fauna indicates that the lowest part of the Xiala Formation is late Kungurian in age based on the presence of abundant Mesogondolellaidahoensis and the denticle characters of Vjalovognathu snicolli n. sp. The presence of the conodont genus Vjalovognathus, the associated small solitary corals and the absence of any fusulinids clearly suggest a cool-water condition in the lower part of the Xiala Formation. Thus, the Xiala Formation in the central Lhasa Block can be restricted to an age from late Kungurian to Wuchiapingian. This is in contrast to the warm-water faunas consisting of abundant fusulinids, compound and large solitary corals, and warm-water conodonts in the upper part of the Xiala Formation from late Guadalupian to Wuchiapingian in age. This dramatic faunal change suggests that either palaeoclimate had greatly changed from a cold condition to a warm condition after late Kungurian in the peri-Gondwanan region or the palaeogeographical position of the Lhasa Block had drifted northward into the warm-water regime from late Kungurian to Guadalupian. The new family Vjalovognathidae n. fam. and a new species (Vjalovognathusnicolli n. sp.) are proposed, based on abundant specimens from central Tibet.
Reference information of this paper: Yuan Dong-xun, Zhang Yi-chun, Shen Shu-zhong, Henderson, C.M., Zhang Yu-jie, Zhu Tong-xing, An Xian-yin, Feng Hong-zhen, 2015. Early Permian conodonts from the Xainza area, central Lhasa Block, Tibet and their palaeobiogeographical and palaeoclimatic implications.Journal of Systematic Palaeontology. DOI: 10.1080/14772019.2015.1052027. Generalized Permian succession in the Xianzaarea, ranges of fossils at the Mujiucuo section and their implication of palaeoclimatic changes Reconstruction showing the palaeogeographic distribution of Mesogondolellaidahoensis, M.siciliensis,Vjalovognathusshindyensis and V.nicolli. 1, Idaho; 2, West Texas; 3, Sicily; 4, Oman; 5, Pamir; 6, Shiquanhe, Tibet; 7, Xainza, Tibet; 8, Timor; 9, Canning Basin; 10, Carnarvon Basin; 11, Sverdrup Basin.
A Global Stratotype Section and Point, abbreviated GSSP, is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale. It is usually defined by the First Appearance Datum (FAD) of a certain taxon within a continuous evolutionary lineage of a fossil species at the stratotype section. For instance, the Permian-Triassic boundary (PTB) GSSP was defined by the FAD of the conodont Hindeodus parvus at the Meishan D Section, and it has been regarded as a unified standard to identify the PTB in the worldwide. However, with the great improvement of high precision radiometric dating technology and high-resoltuion chemostratigraphy, its accurancy and FAD at Meishan D Section is greatly challenged. Recently, Dr. YUAN Dong-xun and his colleagues from Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences established a high-resolution conodont succession from a carbonate facies of the Changhsingian Stage and across the PTB at the Daijiagou section, about 35 km north to Chongqing City, Southwest China. Based on the high-resolution biostratigraphical framework at Daijiagou, the end-Permian mass extinction was rapid and it began in the base of the Clarkina meishanensis Zone. Associated with the extinction, a negative excursion of d13Ccarb started in the middle part of Clarkina yini Zone with a progressive shift of 1.6‰ to the middle part of the Clarkina meishanensis, followed by a sharp shift of 3.51‰ from the Clarkina meishanensis Zone to the Hindeodus parvus Zone. This study also suggests that the Triassic index species Hindeodus parvus co-occurred with Hindeodus changxingensis and Clarkina zhejiangensis and directly overlies the Clarkina meishanensis Zone at the Daijiagou section. All these data from the Daijiagou section and some previous studies of other sections in Sichuan, Guizhou provinces and Chongqing City suggest that the first occurrences of Hindeodus parvus are slightly earlier than the sharp negative excursion of d13Ccarb and the FAD at the Meishan GSSP section. They consider that the slight difference of the end-Permian mass extinction, chemostratigraphy and conodont biostratigraphy at Daijiagou and its adjacent areas is most likely subject to different lithofacies, fossil preservation, and the constraint on the stratigraphic resolution rather than a different tempo of the end-Permian mass extinction in a global sense. The controversial results of biostratigraphy and chemostratigraphy between the sections investigated in the paper and the Meishan GSSP section also provide some important implications that accurate chronocorrelation requires the evaluation of multiple, varied stratigraphcal signals rather than relying solely on the FAD of the Triassic index species Hindeodus parvus for recognizing the Permian–Triassic boundary (PTB). Information of the paper: Yuan Dong-xun, Chen Jun, Zhang Yi-chun, Zheng Quan-feng, Shen Shu-zhong, 2015. Changhsingian conodont succession and the end-Permian mass extinction event at the Daijiagou section in Chongqing, Southwest China. Journal of Asian Earth Sciences, 105: 234-251. DOI: 10.1016/j.jseaes.2015.04.002. d13Ccarb profile from upper Changhsingian to lowest Triassic at the Daijiagou section and its correlation with other sections in South China. The grey bar shows the whole negative shift of d13Ccarb in different sections, which is associated with the end-Permian mass extinction. The four sections shown here suggest a general consistent pattern in d13Ccarb profile. However, it is quite clear that the sharp negative excursions of the three sections in Sichuan and Guizhou provinces are all in the middle part of the Hindeodus parvus Zone (A-C), but the same sharp excursion is in the Clarkina meishanensis Zone at the Meishan section (D). Red line shows the correlation based on the first occurrences of Hindeodus parvus; blue line indicates the correlation based on the most negative d13Ccarb excursions. End-Permian mass extinction pattern at the Daijiagou section in Chongqing City.
A synthetic comparison and correlation between the marine and terrestrial end-Permian extinctions. The end-Permian mass extinction reflects the most severe life crisis during the Phanerozoic and was associated with major global environmental changes. However, the consistency of the time and pattern of the terrestrial and marine extinctions remains controversial. In recently, Dr. ZHANG Hua and colleagues from Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences and MIT presented detailed analyses of the high-resolution biostratigraphical and geochemical data from terrestrial sections in South China. Their analyses show that the transitional Kayitou Formation actually recorded the process of terrestrial mass extinction as evidenced by the mass disappearance of the Gigantopteris megaflora in the lower part, the dramatic reduction in abundance of palynomorphs in the middle, and the last occurrences of plant remains and abundant charcoal fossils in the uppermost part. It is associated with a distinct negative shift of d13Corg, beginning in the middle part of the formation, which is correlative with that in the top of Bed 26 at the marine Meishan section. In addition, the Kayitou Formation is characterized by a distinct shift of lithofacies of fresh lake-swamp or river flat environment from olive/grey/black mudstone, siltstone, fine to coarse sandstone in the lower part to gradually increasing maroon rocks, to purely maroon mudrocks with poorly-sorted breccia, calcic palaeosols and calcareous nodules in the lowest part of the Dongchuan Formation, which indicates a dramatic collapse of soil system associated with rapid deforestation and climatic warming and drying. In the coastal area, the Kayitou Formation contains marine beds with the typical Permian-Triassic mixed faunas and floras which are correlative with the latest Changhsingian marine mixed fauna 1 at Meishan. The Kayitou Formation also recorded a distinct transgression that began in the latest Changhsingian. All above phenomena suggest that the Kayitou Formation is actually the witness of the terrestrial end-Permian mass extinction; and it is mostly or entirely of latest Changhsingian (Permian), rather than Triassic age. This research was published in Palaeogeography, Palaeoclimatology, Palaeoecology. It was supported by the National Natural Science Foundation of China. Related information of this paper: Zhang, H., Cao, C.Q., Liu, X.L., Mu, L., Zheng, Q.F., Liu, F., Xiang, L., Liu, L.J., and Shen, S.Z., 2015. The terrestrial end-Permian mass extinction in South China: Palaeogeography, Palaeoclimatology, Palaeoecology, http://dx.doi.org/10.1016/j.palaeo.2015.07.002
Sinotubulites is a late Ediacaran biomineralizing tubular fossil with a probable animal affinity. It was first reported from the late Ediacaran Dengying Formation in the Three Gorges area, Hubei Province, South China. Subsequently increased fossil localities—including USA, Mexico, and recently central Spain—indicate that it has a worldwide geographic range, thus playing a significant role in intercontinental stratigraphic subdivision and correlation of late Ediacaran successions. As such, Sinotubulites would be served as another potential index fossil other than the coeval index fossil Cloudina. The poor preservational resolution of Sinotubulites specimens significantly limited a full morphological reconstruction and taxonomic disparity on this important taxon. Nonetheless, three dimensionally preserved Sinotubulites through authigenic phosphatization from the late Ediacaran Dengying Formation in southern Shaanxi Province, South China allows a more detailed paleobiological investigation. Recently, CAI Yaoping, a postdoctoral fellow at Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences and his colleagues have documented a systematic study on Sinotubulites. The majority of previously published Sinotubulites species are considered as synonymous with the type species: S. baimatuoensis. Three new species—S. triangularis n. sp., S. pentacarinalis n. sp., and S. hexagonus n. sp.—are reported from the late Ediacaran Beiwan Member of the Dengying Formation in southern Shaanxi Province, South China. The three new species are similar to the type species in having nested, multilayered inner and outer tube walls. However, they are different in their polygonal cross sections and longitudinal ridges. S. baimatuoensis is more or less circular in cross section and lack longitudinal ridges on the outer tube wall, whereas S. triangularis, S. pentacarinalis, and S. hexagonus are respectively triangular, pentagonal, and hexagonal in cross section with three, five, and six longitudinal ridges on the exterior surface of the outer wall. The new material adds to the diversity of late Ediacaran biomineralizing animals. The triradial, pentaradial, and hexaradial tubes of S. triangularis, S. pentacarinalis, and S. hexagonus share some intriguing similarities in body symmetry with several early Cambrian tubular fossils, although these Cambrian tubes are not open at both ends. Still, it would be interesting to explore the tantalizing possibility of evolutionary continuity of triradial, pentaradial, and hexaradial tubular animals across the Precambrian–Cambrian boundary. Related information of this paper: Cai, Y., Xiao, S., Hua, H., Yuan, X., 2015. New material of the biomineralizing tubular fossil Sinotubulites from the late Ediacaran Dengying Formation, South China. Precambrian Research, 261(C), 12-24. Schematic diagram showing morphological reconstruction of the four species of Sinotubulites New species Sinotubulites triangularis showing triradial symmetry New species Sinotubulites pentacarinalis showing pentaradial symmetry
A paper entitled “Biostratinomic Analysis of Lycoptera Beds from the Early Cretaceous Yixian Formation, Western Liaoning, China” by Dr. PAN Yanhong et al. from Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences and their colleagues has been recently published in Palaeontology. Little is known about the palaeoenvironments of the Early Cretaceous lakes of western Liaoning. Uncertainties exist especially about the water depth, water temperatures and annual temperature fluctuations. Here, Dr. PAN et al. analyse the preservation of the most abundant fish of the lakes, the teleost Lycoptera, articulated skeletons of which occur in large concentrations suggestive of mass mortality. Taphonomic features such as degree of disarticulation, orientation patterns and displacement of skeletal elements reveal distinct preservational patterns. They suggest that the water temperature was low during winter and exhibited pronounced seasonal fluctuations. The depth of the lakes was not deep. Possible causes of the fish mortality are discussed, of which anoxia is favoured. This leads to a more refined palaeoenvironmental model for these palaeolakes, which harbour one of the most important Mesozoic Lagerst？tten. Related information of this paper: Yanhong Pan, Franz T. F Fürsich, Jiangyong Zhang, Yaqiong Wang, Xiaoting Zheng, 2015. Biostratinomic analysis of Lycoptera Beds from the Early Cretaceous Yixian Formation, Western Liaoning, China. Palaeontology, Vol 58, pp. 537-561. Examples of Lycoptera A B concentrations. A, monospecific concentration of Lycoptera davidi on slab 1, from Daxinfangzi village, deposited in IVPP. B, monospecific concentration of Lycoptera davidi on slab 2, from Daxinfangzi village, deposited in Tianyu Museum. C, monospecific concentration of Lycoptera muroii on slab 3, from Jinggangshan village, deposited in Tianyu Museum. All scale bars represent 5 cm. Model representing stages C and D mentioned in the text. A, during late autumn to early winter, upwelling toxic bottom waters caused mass mortality of a fish population. B, in winter, the fish carcasses sank to the anoxic lake floor, which favoured the high preservational fidelity of Lycoptera carcasses.
Devonian witnesses great increases of the land plant diversity and the plant type. All kinds of plants except angiosperms have fossil records in the Devonian. The main euphyllophyte lineages (i.e. ferns sensu lato, progymnosperms and gymnosperms) had evolved laminate leaves by the Late Devonian. The evolution of laminate leaves, however, remains unclear for early-diverging ferns, largely represented by fern-like plants. Recently, a cooperative study was carried out by Prof. XU Honghe from Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (CAS) and researchers from Peking University and Institute of Botany, CAS. The study presents a new fern-like taxon with pinnules, which provides new insights into the early evolution of laminate leaves in early-diverging ferns. In the study, a new fern-like taxon, Shougangia bella is described from the Upper Devonian (Famennian) Wutong Formation of Anhui and Jiangsu Provinces, South China and represents an early-diverging fern with highly derived features. Shougangia has a partially creeping stem with adventitious roots only on one side, upright primary and secondary branches arranged in helices, tertiary branches borne alternately or (sub)oppositely, laminate and usually lobed leaves with divergent veins, and complex fertile organs terminating tertiary branches and possessing multiple divisions and numerous terminal sporangia. Shougangia provides unequivocal fossil evidence for laminate leaves in early-diverging ferns. It suggests that fern-like plants, along with other euphyllophyte lineages, had independently evolved megaphylls by the Late Devonian, possibly in response to a significant decline in atmospheric CO2 concentration. Among fern-like plants, planate ultimate appendages are homologous with laminate pinnules, and in the evolution of megaphylls, fertile organs tend to become complex. The study was published as a cover paper in the recent issue of Annals of Botany. Related information of this paper: Wang D-M*, Xu H-H*, Xue J-Z, Wang Q, Liu L, 2015. Leaf evolution in early-diverging ferns: insights from a new fern-like plant from the Late Devonian of China. Annals of Botany, 115: 1133-1148. doi:10.1093/aob/mcv049 Part and counterpart specimens of the vegetative Shougangia The preparation processes and the reconstruction (right) of the fertile portion of Shougangia
Flat-pebble conglomerates (limestone breccias and conglomerates) (Fig. 1) are a common phenomenon in the Cambrian successions worldwide. They bear important geological implications that have attracted geologists for several decades. There are, however, still controversies on their origins, especially those of the breccias with abundant vertically orientated clasts. The Furongian (upper Cambrian) Chaomidian Formation of the North China Platform contains numerous levels of limestone breccias and conglomerates that provide an excellent example to look into their formative processes. These breccias and conglomerates have been the focus of study and discussion since the 1980s, but yet there is still no consensus with respect to their geneses. Recently, Van Loon and others argued that the vertically orientated clasts of the breccias developed by a number of simultaneous “fountains” on the paleo-seafloor; the “fountains” formed by upward-directed fluidized flows originated from the sediment underlying the brecciated limestones. In order to understand the formative processes of flat-pebble conglomerate, Dr. CHEN Jitao from Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences briefly overviewed and specifically discussed the hypothesis proposed by Van Loon et al. (2013). While the novel “fountain” hypothesis is not impossible, based on field evidences and theoretical considerations, however, it is most likely that the vertically orientated clasts resulted from their re-orientation by upward flow of thixotropically liquidized, uncemented argillaceous sediment that was interbedded with brecciated limestone fragments. Besides, the deformation processes most likely took place under shallow burial. Further investigations by experimental analysis and model simulation may help to delineate and clarify the formative processes of these unusual Cambrian breccias. In addition, CHEN Jitao was invited by Prof. Paul Myrow from Colorado College as a co-corresponding author, to carry out the researches on some unusual soft-sediment deformation structures found in Rocky Mountain, western Colorado, including slide scarps, thrusted beds, irregular blocks and internally deformed beds (Figs 2 and 3). These features represent parts of beds that detached, moved up onto and some distances across, the laterally adjacent undisturbed bed surfaces. Deformation of thin intervals of mud on the ocean floor by moving blocks rules out the possibility of storm-induced deformation, as the mud was not eroded by high shear stresses that would accompany the extremely large forces required to produce and move the blocks. Finally, internally deformed beds are characterized by large blocks, fitted fabrics of highly irregular fragments, and contorted lamination, which represent heterogeneous deformation, such as brecciation and liquefaction. The deformation structures were produced by earthquakes linked to the reactivation of Mesoproterozoic, crustal-scale shear zones in the central Rockies during the Late Cambrian. Analysis of the deformation structures indicates very large body forces, and calculated earthquake-generated ground motion velocities of ~1.6 m/s. These correspond to moment magnitudes of ~7.0 or more and a Mercalli Intensity of X+. These are the only known magnitude estimates of Phanerozoic (other than Quaternary) large-intensity earthquakes for the Rocky Mountain region, and they are as large as, or larger than, previous estimates of Proterozoic earthquakes along these major shear zones of the central Rockies. These studies were financially supported by the National Natural Science Foundation of China, and were recently published by Science China Earth Sciences and sedimentology. Related information of these papers: 1. Chen, J., 2015. Origin of the Furongian limestone breccias in the North China Platform. Science China Earth Sciences 58, 770–775. 2. Myrow, P.M.*, Chen, J.*, 2015. Estimates of large magnitude Late Cambrian earthquakes from seismogenic soft-sediment deformation structures: Central Rocky Mountains. Sedimentology 62, 621–644. Fig. 1. Various limestone breccias and conglomerates in the Furongian Chaomidian Formation of the North China Platform. (a)-(b) Limestone conglomerate with imbricated clasts, indicating they were reworked by currents. (c)-(d) Limestone breccia containing undulatory platy clasts and abundant vertically orientated clasts that were most likely formed by soft-sediment deformation of limestone-marlstone alternations. Fig. 2. Irregular blocks and relationships to underlying and overlying layers. (A) Two stacked blocks representing possible duplex structure. (B) An irregular block showing deep penetration into the underlying bed. (C) An irregular block with deformation of laterally adjacent grainstone and shale. (D) Close-up showing that some grainstone and shale beds were forced downward, and others forced upward (white arrows) during lateral movement of the block (yellow arrow). Fig. 3. Thrusted bed and irregular blocks. (A) Line drawing showing heterogeneous deformation of laterally adjacent sediment around an irregular block (center). (B) Large irregular block on a thick bed, which slid across the upper surface and inserted into the overlying strata. Hammer is about 30 cm long. (C) Irregular block with flat base and irregular top, showing heterogeneous deformation of laterally adjacent sediment. (D) Close-up showing brittle failure of thin grainstone beds and ptygmatically folded grainstone dikes in shale above pencil cap. Fig. 4. Schematic model for the formation of various deformation features in the Dotsero and Manitou formations. (A)–(E) Deformation at the sediment-water interface. (F)–(J) Deformation taking place under a thin layer of much-rich strata.
A paper entitled “Triassic-Jurassic climate in continental high-latitude Asia was dominated by obliquity-paced variations Junggar Basin, ürümqi, China” by Prof. SHA Jingeng from Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences and his colleagues has been recently published online in PNAS. Our understanding of Triassic and Early Jurassic high-latitude climate, biotic evolution, mass extinction, and geochronology is very poor in contrast to that of the contemporaneous tropics. This poor resolution impairs an elucidation of the basic patterns of Earth system function during the early Mesozoic. Besides, integral to the long-term chaotic behavior of the Solar System are the secular resonances of the planets, particularly for the inner Solar System. Analysis of the LITH proxy of environmental change shows that an astronomical signal in which obliquity is dominant can be extracted from lacustrine strata of the high-latitude (~60o N) Junggar Basin straddling the end-Triassic extinction and Triassic-Jurassic boundary. This is dramatically different from the climate precession-dominated continental tropics. In combination, the data are incompatible with published astronomical solutions for the Triassic-Jurassic in phase and amplitude, consistent with chaotic behavior of the Solar System whereas, at the same time, the Earth-Mars orbital resonance seems to have been in today’s two-to-one ratio of eccentricity to inclination, providing a constraint for the Earth-Mars orbital resonance for around 201 Ma. With the prospect of the acquisition of better temporally resolved records from deeper lake settings in the Junggar and other basins, the use of more directly climate-sensitive proxies, and additional exploration of the paleobiological context of the strata, it will be possible to test these findings, constraining the history of Solar System chaos, during this transitional time in Earth history. The research was financially supported by the National Basic Research Program of China, National Natural Science Foundation of China, Chinese Academy of Sciences, etc. Related information of this paper: Jingeng Sha, Paul E. Olsen, Yanhong Pan, Daoyi Xu, Yaqiong Wang, Xiaolin Zhang, Xiaogang Yao, and Vivi Vajda. Triassic-Jurassic climate in continental high-latitude Asia was dominated by obliquity-paced variations (Junggar Basin, ürümqi, China). PNAS. Doi:10.1073/pnas.1501137112. Paleogeographic position of the Junggar Basin (A), present position of the Junggar Basin (B), and map of the surficial geology of the ürümqi area (C). LITH Index data of Junggar Basin (C) and other correlative sections. Photograph of portion of the Haojiagou section including beds 45-53.
The Early Carboniferous was an important interval in geological history characterized by the transition from the greenhouse climate of the Devonian to the icehouse climate of the Carboniferous-Permain. The first glaciation of the Carboniferous-Permain Ice Age is thought to have occurred during the mid-Tournaisian based on glacial deposits, eustatic regression, and positive excursions in carbon (δ13Ccarb and δ13Corg), oxygen (δ18O), nitrogen (δ15N) and strontium (δ87Sr) isotopes. To date, it is still unclear about the process of carbon-nitrogen cycles and their relationships to contemporaneous changes in marine environments during the mid-Tournaisian. To better understand the process of carbon-nitrogen cycles and paleoenvironmental changes during this critical interval, a high-resolution study of the δ13Ccarb and δ15N records of the Tournaisian at two sections (Malanbian and Long'an) was undertaken by Dr. YAO Le and his colleagues from Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, China University of Geosciences, Wuhan, and so on. Their C-isotope profiles document a large positive excursion, herein termed the ‘mid-Tournaisian carbon isotope excursion’ (TICE), during the Siphonodella isosticha conodont Zone. The TICE event coincided with sedimentologic and oxygen-isotopic evidence of climatic cooling and glaciation during the mid-Tournaisian. It was probably triggered by an increase in organic carbon burial rates linked to changes in global-ocean circulation. The study sections also document a large positive shift in δ15N which is coincided with TICE and thus may have been linked to ocean-circulation changes that resulted in intensified upwelling and an increase in water-column denitrification. The continuation of the N-isotope shift over millions of years may have been linked to glacio-eustatic fall and a long-term shift in the locus of denitrification from continental-shelf sediments to continent-margin oxygen-minimum zones. The TICE event thus marks the onset of sustained continental glaciation during the Late Paleozoic Ice Age. The paper was published in Chemical Geology, and the research was financially supported by the National Natural Science Foundation of China and the Ministry of Science and Technology Foundation Project. Reference: Yao, L., Qie W.K., Luo, G.M., Liu, J.S., Algeo, T.G., Bai, X., Yang, B., Wang, X.D., 2015. The TICE event: Perturbation of carbon-nitrogen cycles during the mid-Tournaisian (Early Carboniferous) greenhouse-icehouse transition. Chemical Geology, 401: 1-14.
Lithologic column, conodont biozones, δ15N, δ13Ccarb, Corg/N and carbonate content at the Malanbian (a) and Long'an (b) sections Model for ocean-circulation control of δ15N variation during greenhouse climate scenario (a) and icehouse climate scenario (b) in the Tournaisian
