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The Tibetan Plateau, the highest plateau in the world, is relatively difficult to access. Therefore, the stratigraphy and fossils in this area are poorly known, although they are very important for interpreting the palaeogeographical evolution of different tectonic blocks. Here we report the 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 (Mesogondolella idahoensis, M. siciliensis, Vjalovognathus nicolli Yuan, Shen & Henderson sp. nov. 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 Mesogondolella idahoensis and the denticle characters of Vjalovognathus nicolli sp. nov. 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 F...

Meishan Section D with the Wuchiapingian/Changhsingian and Permian/Triassic GSSPs has become the most intensively studied section because it records the whole process of the largest biological extinction during the Phanerozoic. Numerous data including high-precision geochronology, multiple isotope chemostratigraphy, magnetostratigraphy, and high-resolution multiple fossil biostratigraphy have been determined during the last decade. Conodonts are very abundant in the Changhsingian Stage at the Meishan sections and their biostratigraphy together with geochronologic and multiple geochemical data provide a basic temporal framework to calibrate the end-Permian mass extinction and realize global correlation between sections at Meishan and those in other regions of the world. However, major discrepancies exist in various previous studies of conodonts from the Meishan sections. Many different authors have documented very different species ranges based on different concepts and approaches of taxonomy. We here employ a sample population approach to revise and refine the high-resolution conodont biostratigraphic framework for the Changhsingian Stage and end-Permian mass extinction interval across the Permian–Triassic boundary (PTB) at the Meishan sections. Eight zones are recognized from the latest Wuchiapingian to the basal Triassic. They are, in ascending order, the Clarkina longicuspidata Zone in the uppermost Wuchiapingian; the Clarkina wangi Zone, Clarkina subcarinata Zone, Clarkina changxingensis Zone, Clarkina yini Zone, Clarkina meishanensis Zone, Clarkina zhejiangensis–Hindeodus changxingensis Zone in the Changhsingian Stage, and the Hindeodus parvus Zone in the basal Triassic. Conodont evolutionary lineages for the whole Changhsingian are also tentatively established. All species are described in detail and growth series of different specimens for valid species are figured as completely as possible. The temporal relationship of each conodont zone with geochemical excursions, geochronologic calibration and magnetostratigraphical polarity zones are provided, which is critical to understand the tempo of the end-Permian mass extinction.

The Yangtze Platform preserves relatively thick carbonate successions and excellent fossil records across the Ediacaran–Cambrian boundary interval. The intensely studied Meishucun section in East Yunnan was one of the Global Stratotype Section candidates for the Precambrian–Cambrian boundary. However, depositional breaks were suspected in the section and the first appearance of small shelly fossils could not be verified. The Laolin section located in NE Yunnan is more continuous and shows great potential for global correlation of carbon isotope features across the Precambrian–Cambrian boundary. However, the stratigraphic framework and correlations were controversial. We studied and systematically sampled the Laolin section and present here new carbon isotope data for this section. The Laolin section consists of, in ascending order, the Baiyanshao dolostone of the Dengying Formation, the Daibu siliceous dolostone, Zhongyicun dolomitic phosphorite, lower Dahai dolostone and upper Dahai limestone of the Zhujiaqing Formation, and the black siltstone of the Shiyantou Formation. Our data reveal a large negative δ13C excursion (−7.2‰, L1′) in the Daibu Member, which matches the previously published data for the Laolin section, and a large positive excursion (+3.5‰, L4) in the Dahai Member, which was not shown in the published data. The excursion L1′ correlates well with the similarly large negative excursion near the first appearance of small shelly fossils in Siberia and Mongolia. Similar magnitude excursions are also known from Morocco and Oman, for which there are no robust fossil constraints but from where volcanic ash beds have been dated precisely at 542 Ma, thus confirming a global biogeochemical event near the Ediacaran–Cambrian boundary. Our data also indicate that deposition was more continuous at the Laolin section compared with the Meishucun section, where there are no records of a comparable negative excursion near the Ediacaran–Cambrian boundary, nor any comparable positive excursion in the Dahai Member. Therefore, the Laolin section has proven potential to be a supplementary Global Stratotype Section for the Ediacaran–Cambrian boundary on the Yangtze Platform.

Primary carbon isotope trends in marine carbonate rocks are particularly useful for chemostratigraphic correlation and paleoenvironmental reconstruction of the Neoproterozoic Earth System. Differences, however, exist between the published carbonate C-isotope profiles from the Neoproterozoic Yangtze platform and the global C-isotope record through the equivalent time interval. More C-isotope profiles are required for the Yangtze platform from where excellently preserved early animal fossils have been discovered. We studied C, O and Sr isotope compositions and Mn–Sr concentrations of two successions of the Neoproterozoic Doushantuo and Dengying Formations in Guizhou and Zhejiang Provinces, South China. Most of the 87 Sr/ 86 Sr ratios lie above 0.709, higher than the contemporaneous seawater values, and are likely to represent diagenetic alteration and possible leaching of clay detritus. The δ 18 O profiles exhibit more fluctuation than the δ 13 C profiles, indicating that oxygen isotopes are more sensitive to diagenetic effects. Both δ 13 C profiles in Zhejiang and Guizhou show negative excursions to − 3 to − 4‰ in the Doushantuo cap carbonate overlying the Nantuo (Marinoan) diamictite and at the Doushantuo–Dengying boundary, and positive shifts to + 3 to + 4‰ through the rest of the Doushantuo and Dengying Formations. We suggest that oceanic overturn was responsible for both the negative δ 13 C excursion within the Doushantuo cap carbonate and that at the Doushantuo–Dengying boundary. However, the mechanisms for the two overturn events are different. The former overturn occurred under conditions of high temperature and high evaporation rates after thawing of the Nantuo (end-Cryogenian) Snowball Earth that had resulted in the stagnant and stratified ocean under sea ice. The Doushantuo interval witnessed sustained high bioproductivity, elevated rates of organic matter accumulation in deep water and sediment, and progressive δ 13 C stratification in the ocean, CO 2 drawdown to sediments and thus cooling, which led eventually to high latitudinal glaciation, vigorous thermohaline circulation and oceanic overturn at the end of the Doushantuo period. This latter overturn released CO 2 back to the atmosphere, thus raising the temperature and preventing further cooling. High productivity revived subsequently during the Dengying interval. More work will be needed to further constrain and interpret C-isotope evolution across the Precambrian–Cambrian boundary on the Yangtze platform.

Extreme metal enrichments occur in the Lower Cambrian Niutitang Formation, a thick black shale sequence deposited on the Yangtze Platform of South China, and form a regionally distributed conformable polymetallic Ni–Mo–PGE–Au sulfide horizon. The origin for the extreme enrichment of metals in these black shales is discussed based on a comprehensive geochemical investigation of Re–Os isotopes and platinum-group elements. The black shales of the Lower Cambrian Niutitang Formation in Guizhou province yielded an Re–Os isochron age of 535±11 Ma with an initial 187 Os/ 188 Os ratio of 0.80±0.04, which is similar to the initial 187 Os/ 188 Os ratio (0.78±0.19) of the Ni–Mo sulfide ores, but slightly lower than the initial 187 Os/ 188 Os ratio (1.18±0.02) of Lower Cambrian black shales from the Lesser Himalaya, India. A comparison of Os isotope data among the Chinese Ni–Mo sulfide ores, the seafloor massive sulfide deposits and contemporaneous seawater suggests a possible similar hydrothermal forming mechanism for these deposits. The PGE concentrations, Pt anomaly (Pt/Pt⁎), Pt/Pd, Ir/Pd, Au/Pd ratios of the Chinese Ni–Mo sulfide ores are similar to those metal-rich black shales of submarine volcanogenic hydrothermal origin from Czech Republic, Namibia and Canada, but are different from those data of the ocean floor Fe–Mn crusts that have scavenged their PGE and other metals directly from seawater. It is therefore suggested that the Ni–Mo sulfide ores from the Niutitang black shale sequence in South China had a submarine-hydrothermal origin. The anoxic environments and abundant organic matter in the ocean basin also played a key role for the extreme metal enrichments. The discharge of hydrothermal fluids into the Cambrian Ocean may have had a great effect on life during the Cambrian Explosion. © 2007 Elsevier B.V. All rights reserved.

The Lower Cambrian black shale sequence of the Niutitang Formation in the Yangtze Platform, South China, hosts an extreme metal-enriched sulfide ore bed that shows >10,000 times enrichment in Mo, Ni, Se, Re, Os, As, Hg, and Sb and >1,000 times enrichment in Ag, Au, Pt, and Pd, when compared to average upper continental crust. We report in this paper trace- and rare-earth-element concentrations and Pb–Pb isotope dating for the Ni–Mo–PGE–Au sulfide ores and their host black shales. Both the sulfide ores and their host black shales show similar trace-element distribution patterns with pronounced depletion in Th, Nb, Hf, Zr, and Ti, and extreme enrichment in U, Ni, Mo, and V compared to average upper crust. The high-field-strength elements, such as Zr, Hf, Nb, Ta, Sc, Th, rare-earth elements, Rb, and Ga, show significant inter-element correlations and may have been derived mainly from terrigenous sources. The redox sensitive elements, such as V, Ni, Mo, U, and Mn; base metals, such as Cu, Zn, and Pb; and Sr and Ba may have been derived from mixing of seawater and venting hydrothermal sources. The chondrite-normalized REE patterns, positive Eu and Y anomalies, and high Y/Ho ratios for the Ni–Mo–PGE–Au sulfide ores are also suggestive for their submarine hydrothermal-exhalative origin. A stepwise acid-leaching Pb–Pb isotope analytical technique has been employed for the Niutitang black shales and the Ni–Mo–PGE–Au sulfide ores, and two Pb–Pb isochron ages have been obtained for the black shales (531±24 Ma) and for the Ni–Mo–PGE–Au sulfide ores (521±54 Ma), respectively, which are identical and overlap within uncertainty, and are in good agreement with previously obtained ages for presumed age-equivalent strata.

Secular δ13Ccarb and Ceanom profiles in the post-glacial Neoproterozoic and Early Cambrian interval are reported from Guizhou on the southeasten border of the Yangtze platform. South China. Overall, the δ13Ccarb profile drifts to negative values in the postglacial Nantuo and lower to middle Doushantuo Formations, and then to positive values in the upper Doushantuo and Dengying Formations of Neoproterozoic, followed by negative values in the Lower Cambrian Gezhongwu and Niutitang Formations. A detailed investigation of the relationship between the δ 13Ccarb and Ceanom profiles reveals that the main anoxic and oxic episodes are coupled with negative and positive δ 13Ccarbvalues, respectively. This may suggest a control of alternation between ocean stratification and mixing on variations in 13C abundance in the ancient ocean of the investigated areas.

Black shales of the Lower Cambrian Niutitang Formation occurwidely on the Yangtze Platform. In this study, we analyzed black shales from two sections (Zhongnan and Zhijin) in Guizhou Province. The redox-sensitive metal concentration and distribution of black shales from the two sections provide good evidence for the anoxic conditions of the basal Cambrian ocean on the Yangtze Platform. Our geochemical data suggest that the black shales from the Zhongnan section may have deposited in a more strongly anoxic environment than the black shales in the Zhijin section.

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 diagenetico-rigin. 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.l‰. 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‰.–...

The Lower Cambrian black shales of the Niutitang Formation and their lateral equivalents occur widely on the Yangtze Platform. South China. In this study, we examine two sections of the Niutitang Formation in Guizhou Province. We employ a stepwise acid-leaching technique to obtain Pb-isotope compositions of the black shales. At the Zhongnan section, the black shales display large Pb isotope variations, with 206Pb/204Pb of 20.5396–33.5709, and 207Pb/204Pb of 15.8407–16.5782. In contrast, Pb isotope data show a relatively limited range in 206Pb/204Pb (18.2797–18.5972) and 207Pb/204Pb (15.6813–15.7159) at the Zhijin section. Data for all acid-leached black shale samples from the two sections yield a Pb-Pb isochron age of 531 ± 24 Ma. This age may represent the sedimentary age of the black shales. The initial Pb-isotope composition of the black shales fallsnear the upper-crust evolution curve in a Zartman Pb-Pb evolution diagram. Hence, it is likely that the Pb in the black shales may have been deriv...

The Lower Cambrian Niutitang Formation consists of a thick black shale sequence with a regionally distributed conformable Ni Mo polymetallic sulfide horizon and a chert bed at its basal strata on theYangtze Platform, South China. In this paper, we discuss all available data on Re Os isotopes and Platinum Group Element (PGE) distribution pattern of the Ni Mo polymetallic sulfide ore and its host rocks (black shales, cherts, and phosphorites) from Guizhou and Hunan provinces. Our results show that the black shales and the Ni Mo sulfide ore have a high initial 187 Os/ 188 Os ratio of 0.78～0.86, indicating that the Early Cambrian ocean across the Yangtze Platform had a highly radiogenic Os value. This ratio is slightly lower than but still similar to present day seawater, possibly as a result of high continental weathering at that time. The Ni Mo sulfide ore yields a Re Os isochron of 537±10 Ma (MSWD=11.9), possibly representing the depositional age of the Niutitang Formation. The chondrite normalized PGE pattern, Pt anomaly (Pt/Pt *), Pt/Pd, Ir/Pd, Au/Ir and Re/Mo ratios of the Ni Mo sulfide ore and its host rocks from South China indicate a varying source contribution of the PGE and other metals for different rocks. It is suggested that the cherts and Ni Mo sulfide ore may have a significant proportion of PGE and probably other metals deriving from submarine hydrothermal fluids with a mantle signature.

The polymetallic Ni-Mo-PGE-Au sulfide ores occur in the Lowermost Cambrian Niutitang Formation of a thick black shale sequence in Yangtze Platform of South China. The origin for this special type of sulfide ore has been hotly debated. There genetic models have been proposed: (1) extraterrestrial impact origin (Fan et al. 1984); (2) submarine hydrothermal exhalative origin (Coveney et al., 1992; Lott et al. 1999; Steiner et al. 2001); (3) seawater scavenging origin (Mao et al. 2002). In this paper, we discuss the origin for the special type of sulfide ore based on platinum group element geochemistry. We suggest that the chondrite-normalized PGE patterns of the sulfide ores show some distinctive difference from the seawater pattern and may indicate a submarine hydrothermal input for the metal enrichments in the sulfide ore. We defined a new parameter, namely Pt anomaly (Pt/Pt*), and found that the Pt anomaly in the polymetallic Ni-Mo-PGE-Au sulfide ores is similar to those ancient and modern sea-floor massive sulfide deposits. Other platinum group element pairs, such as Pt/Pd, Ir/Pd, and Au/Pd ratios of the Ni-Mo sulfide ores also share some similarity with those of ancient and modern submarine massive sulfide deposits. In conclusion, we support the submarine hydrothermal exhalative origin for the sulfide ores, and suggest that this is a new type of sediment-hosted submarine hydrothermal exhalative sulfide deposits.