2015 Vol. 26, No. 2
Abundant microconchid worm tubes were extracted from the microbialites deposit near the Permian-Triassic boundary at the Zuodeng Section, Baise area, Guangxi Zhuang Autonomous Region, South China. These calcareous worm tubes were studied in both petrographic thin sections and isolated specimens using optical microscope and sensitive electronic microscope (SEM), respectively. They are categorized into two morphological types: helically coiled and planispirally coiled tubes, which are assignable toMicroconchus aberrans (
Various environmental changes were associated with the Permian-Triassic mass extinction at 252.2 Ma. Diverse unusual sediments and depositional phenomena have been uncovered as responses to environmental and biotic changes. Lithological and detailed conodont biostratigraphic correlations within six Permian-Triassic boundary sections in South China indicate rapid fluctuations in carbonate deposition. Four distinct depositional phases can be recognized: (1) normal carbonate deposition on the platform and slope during the latest Permian; (2) reduced carbonate deposition at the onset of the main extinction horizon; (3) expanded areas of carbonate deposition during the Hindeodus changxingsensis Zone to the H. parvus Zone; and (4) persistent mud-enriched carbonate deposition in the aftermath of the Permian-Triassic transition. Although availability of skeletal carbonate was significantly reduced during the mass extinction, the increase in carbonate deposition did not behave the same way. The rapid carbonate depositional changes, presented in this study, suggest that diverse environmental changes played key roles in the carbonate deposition of the Permian-Triassic mass extinction and onset of its aftermath. An overview of hypotheses to explain these changes implies enhanced terrestrial input, abnormal ocean circulation and various geobiological processes contributed to carbonate saturation fluctuations, as the sedimentary response to large volcanic eruptions.
Approximately 230 million years ago in the middle of the Carnian stage of the Upper Triassic, the sedimentary records in different regional basins display dramatic changes. Tropical carbonate platforms abruptly ended, and engorged river systems left widespread sand-rich layers across inland basins and coastal regions. This pulse lasted less than a million years in some basins, but constituted a permanent shift in others. Following this event, the Late Carnian has the earliest record of significant dinosaurs on land and the emergence of the calcareous nannoplankton in the oceans that now govern Earth's carbon cycle. This "most distinctive climate change within the Triassic" has been interpreted by some geoscientists as a global disruption of the Earth's land-ocean-biological system. The eruption of the Wrangellia large igneous province may have been the trigger for a sudden carbon-dioxide-induced warming and associated increased rainfall in some of these regions. Indeed, some workers have proposed that this "wet intermezzo" warming event is a useful analog to aid in predicting the effects of our future greenhouse on land ecosystems and ocean chemistry. However, the understanding of the onset, duration, global impacts and relatively rapid termination of this postulated warming pulse has been hindered by lack of a global dataset with inter-calibrated terrestrial and marine biostratigraphy, precise radio-isotopic ages, stable isotope records of temperature and the carbon system, and cycle-calibrated rates of regional and global change.
Abundant well-preserved tubular fossils of caddisfly (Insecta: Trichoptera) larval cases are reported from the Early Cretaceous Madongshan and Naijiahe formations of the Liupanshan Basin, Ningxia Province, western China. Most cases were mainly preserved in life position and densely packed in various layers. Individual cases in each layer tended to be same in size and were erect and parallel to one another and open at both ends. In a transverse section cut perpendicular to the long axis of the cases, individual case appears to form a rounded ring. Small cases are elliptic in a cross-section oblique to the long axis of the cases. Tube walls are nearly subparallel to one another in longitudinal section with both ends being open. The caudal end of the case slightly tapers and usually points downward. The cases were closely packed, almost touching with one another and lacking bifurcate or connecting structure. The overwhelming majority of cases were partially or fully filled with calcite. The case wall embraces a medium particle layer flanked by inner and outer organic layers. Individual particles are ovate in outline and comprise cryptocrystalline or ganic pellets. SEM imaging shows that those pellets are sub-cylindrical in outline and elliptic in cross section, and are made primarily of calcium carbonate. All features observed justify the assignment of the Liupanshan caddisfly cases to ichnogenusCoprindusia. The extinct insect Ningxiapsyche fangi was found in association with the Liupanshan caddisfly larval cases, and thus could be the candidate of the potential trace-maker.
The Quanji Group is composed of siliciclastics and carbonates and was deposited on a relatively stable block, in the northern margin of the Qaidam Basin, NW China. It is one of the research hotspots in the Qilian-Qinling-Kunlun tectonic zones. However, it has long been argued whether the upper Quanji Group should be assigned to the Precambrian or the Cambrian for lack of convincing fossil evidence. The discovery of ichnofossils, including Rusophycus, Cruziana, Dimorphichnus, Treptichnus, Skolithos, Arenicolites, Palaeophycus, and Helminthopsis, indicates that the upper member of the Zhoujieshan Formation (top Quanji Group) is Cambrian in age, and at least above the Treptichnus (Phycodes) pedum Biozone, the lowermost biozone in the Cambrian. The lower member of the Zhoujieshan Formation should belong to the Cambrian. During the time when the upper member of the Zhoujieshan Formation was deposited, the northern margin of the Qaidam Basin was dominated by the Cruziana Ichnofacies, characterizing a lower-energy shelf (shallow) sea environment with moderate-rich oxygen contents. In addition, the conglomerates in the Hongtiegou Formation of the Quanji Group underlying the Zhoujieshan Formation were generally regarded as tillites. However, the dolostones of the lower member of the Zhoujieshan Formation are, in lithology and geochemistry, different from the typical cap-dolostones of the Doushantuo Formation in South China, so it is necessary to further study the origins of the lower member of the Zhoujieshan Formation and the conglomerates of the Hongtiegou Formation.
The Late Paleozoic Ice Age across Carboniferous and Permian had a significant impact on the Kungurian (Upper Cisuralian series of Permian) Chihsia Formation in South China. This resulted in a unique interval with features such as the lack of reef in Chihsian limestone, widespread stinkstone and nodular/bedded chert. The Chihsia limestone (Kungurian stage) deposited during a time of cooling was resulted from oceanic upwelling. Here we present evidence for this upwelling using several geochemical analyses: bulk organic carbon isotope, biomarker molecular geochemical data, and authigenic silica of the stinkstone member in the lower Chihsia Formation of the Kuangurian stage from the Enshi Section in western Hubei Province, South China. The lower part of the stinkstone member shows a rapid organic carbon isotope excursion with a −3‰ shift triggered by the upwelling of13C-depleted bottom water. The concurrent rapid increasing of authigenic silica content resulted from the enhanced supply of dissolved silica in the upwelling water mass. This upwelling at the Enshi Section also led to relative high TOC content, accounting for the widespread stinkstone in the lower Chihsia Formation during the Kungurian stage in Permian.
Successive evolutionary trends control the genera Paragondolella Mosher and Metapolygnathus Hayashi over the about 20 Ma long Aegean-Tuvalian timespan. In consideration of their evolutionary criteria, these genera have been retained together with Carnepigondolella Kozur and the two new genera proposed herein, Mazzaella (type species M. carnica) and Hayashiella (type species H. nodosa). Mazzaella n. gen. represents a Late Julian side branch of Metapolygnathus, harbouring a platform ornamentation similar to the several million years younger Tuvalian lineage of Carnepigondolella, issued from Hayashiella n. gen. that is intermediary between Metapolygnathus and Carnepigondolella, based on appearance and platform ornamentation.
Thirty three benthic foraminiferal species belong to 23 genera and 16 families have been recorded from the coral reefs of the Callovian Tuwaiq Formation, Khashm Al-Qaddiyah area, Central Saudi Arabia. Three species: Astacolus qaddiyahensis, Nodosaria riyadhensis, Siderolites jurassica are believed to be new. Nearly all identified foraminifera are of Atlantic-Miditeranean affinity. The foraminiferal assemblage recorded in the present work is mixed of open marine, moderately deep marine conditions associations and shallow to deep lagoon. The reefal part of upper Twiaq Formation may have been deposited in shallow water of lower to middle shelf depth (20–50 m) as indicated by abundant corals and benthic foraminifera. The coral fauna and bearing benthic foraminifera indicated moderate water energy.
The Triassic "Green-bean Rock" (GBR) layers were widely recognized around the Early-Middle Triassic boundary interval in the Nanpanjiang Basin,South China. To determine the precise relationship between the GBR layers and the first appearance datum (FAD) of the conodont Chiosella timorensis,four Lower-Middle Triassic sections from the Nanpanjiang Basin,including the Gaimao,Bianyang II,Zuodeng and Wantou sections have been studied in detail. Detailed conodont biostratigraphy convinces us that there is no exact temporal relationship between the GBR layers and first occurrence of Ch. timorensis. Moreover,the numbers of the GBR layers are different from the place to place within the Nanpanjiang Basin,and the time span of the GBR layers was much longer than previously estimated. Global correlations show that the FAD of Ch. timorensis is contemporaneous basinwide and worldwide and more suitable marker defining the Olenekian-Anisian boundary (Early-Middle Triassic boundary) than any other proxies.
Biological dissimilatory reduction of selenite (SeO3 2−) to elemental selenium (Se0) is common,but the mineral formation and the biogenic process remain uncertain. In this study,we examined the Se0 formation during the selenite bioreduction by Bacillus licheniformis SeRB-1 through transmission electron microscope (TEM),energy-dispersive spectrometry (EDS) and X-ray absorption fine structure (XAFS) techniques. Results showed that the reduction process occurred mostly during the exponential phase and early stationary phase,whilst the elemental selenium was produced in these periods. From the TEM images and polyacrylamide gel electropheresis,it is known that the Se0 granule formation is a biologically-induced type,and the cell envelopes are the main biomineralization positions,and particles may go through a process from nucleation to crystallization,under the control of microbes. In fact,the minerals are spherical nanoparticles,occurring as a microcrystal or amorphous form. It is vital to recognize which kinds of proteins and/or polysaccharides act as a template to direct nanoparticle nucleation and growth? This should focus for further studies. This study may shed light on the process of formation of Se(0) nanosphere.
Bryozoan nodules,coralline algae,scleractinian corals and oysters form an important organic buildup,1.2–4.5 m thick in the Langhian-Serravaliann sediments of Egypt. Based on type,shape and size of the substrate,bryozoan nodules take tree-like and globular morphologies. Tree-like specimens reach 10 cm in maximum height and 3 cm in diameter,while Globular ones attain 9 cm in maximum diameter. Most tree-like nodules are perforated with wide or narrow pores,few are non-perforated. Globulars and few tree-like forms are with mamelon-like structures. Perforations on the outer surfaces may indicate a symbiotic relationship between bryozoans and a live plant substrate. Nodules from Homiera and Gharra areas of the Cairo-Suez District with wider perforations may indicate growth in slightly lighter or turbid areas of the continental shelf than those of North Western Desert of narrower perforations. Non-perforated nodules may assume an incrustation on ephemeral substrate.
The first data of geochemical study of the Benevka Section cherty rocks belonging to the Taukha terrane of the Sikhote-Alin Late Jurassic-Early Cretaceous accretionary prism,Russia Far East are presented. These data demonstrate essential distinctions of major,trace and rare earth element concentrations in different parts of the measured stratigraphic section. The lower chert horizons exhibit high Fe2O3 and MnO contents,low concentrations of Al2O3 and TiO2,relatively high V/Y ratio,and extremely low value of negative Ce anomaly. In contrast the upper horizons composed of clayey cherts and siliceous mudstones are characterized by high Al2O3,TiO2 and K2O contents,low Fe2O3 and MnO values,low V/Y ratio,and slightly negative Ce anomaly. In the middle part of the Benevka Section,in which cherts gradually changed to clayey cherts,intermediate geochemical characteristics are present. Based on these data obtained the depositional environments correspond to proximal to the spreding ridge,open-ocean and near continental margin regimes were successfully reconstructed from bottom to top of the Benevka Section,that indicate that significant horizontal movement took place of the sea-floor,on which the cherts were deposited.
The depositional environment of the Upper Permian quartzose sandstone (Kuishan sandstone in Shihezi Formation of Upper Permian) in the North China epicontinental basin is controversial. In order to test the previous hypotheses,we analyzed sedimentological characteristics of the Kuishan sandstones in outcrops and boreholes,and carried out trace element geochemical analysis by electron probe microanalyzer. Three lithofacies were recognized,including normal-graded conglomerate (Cng),trough and planar cross-bedded coarse sandstone (CStpc),and planar cross-bedded medium sandstone (MSpc). Normal-graded conglomerate (Cng) formed in the meandering river or deltaic distributary channels. Trough and planar cross-bedded coarse sandstone (CStpc) formed in meandering river or distributary channels of near-source deltaic plain. Planar cross-bedded medium sandstone (MSpc) formed in the siliciclastic beach with high- to moderate-energy conditions. By the petrology and trace elements analysis,three relatively large-scale transgressions were revealed. Each transgression was reflected by the lower content of Ba and ratios of Fe/Mn,and the high content of B and ratios of B/Ga. The ratios of Ni/Co of all samples are all lower than 2,suggesting oxygen-enriched shallower water environment during deposition of the Kuishan sandstones.
Based on field work,organic geochemical analyses and experimental testing,a six-property assessment method for shale gas is proposed. These six properties include organic matter properies,lithofacies,petrophysical properties,gas content,brittleness and local stress field. Due to the features of continuous distribution over a large area and low resource abundance in shale plays,a sweet spot should have these following properties: (a) TOC > 2%; (b) brittle minerals content (> 40%) and clay minerals (< 30%); (c)Ro (> 1.1%); (d) porosity (> 2%) and permeability (> 0.000 1 mD),and (e) effective thickness (30–50 m). Applying these criteria in the Sichuan Basin,the Silurian Longmaxi shale consists of four prospecting sweet spots,including blocks of Changning,Weiyuan,Zhaotong and Fushun-Yongchuan. Although these four blocks have some similarities,different features were usually observed. After comprehensive analyses using the six-property assessment method,the Fushun-Yongan Block ranks the most favorable sweet spot,followed by the Weiyuan Block. For the other two blocks,the Changning Block is better than the Zhaotong Block. By comparing with the Mississippian Barnett shale,characteristics that are crucial for a high-yielding in the Sichuan Basin include a high content of organic matter (TOC > 2.5%),a moderate thermal maturity (Ro=0.4%–2%),a high content of brittle minerals (quartz: 30%–45%),a high gas content (> 2.5 m3·t−1),and types I and II1 kerogen.