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41.
安徽巢湖地区下三叠统综合层序 总被引:15,自引:2,他引:15
印度阶一奥伦尼克阶界线的全球层型候选剖面之一位于安徽巢湖地区;巢湖地区的下三叠统也是国际上同期地层中生物地层序列最有代表性、多重地层学手段应用齐备、研究效果最好的地层序列之一。根据巢湖地区3条代表性下三叠统剖面的岩石地层、生物地层和碳同位素地层的最新研究成果归纳出本区早三叠世综合地层序列,作为区域地层对比研究的标准.巢湖的下三叠统明确包含8个牙形石带和6个菊石带。它们具有区域甚至全球对比意义;巢湖地区早三叠世碳同位素δ^13Ccarb的演变呈现2个显著的漂移周期,这种有特色的碳同位素漂移,不仅具有地层学价值,而且可能对于三叠纪初的生物复苏和生态系演变具有指导意义.在综合地层序列基础上,将3条剖面的古地磁学研究成果链接,形成了巢湖地区完整的早三叠世磁性地层序列,包括5个主要的正向极性带和5个反向极性带,这也是目前在本区乃至华南获得的最完整的早三叠世磁极性序列之一.这些为该区域乃至全球相关地层研究树立了一个基本格架。 相似文献
42.
Yuri Amelin 《Geochimica et cosmochimica acta》2008,72(19):4874-4885
Angrite Sahara 99555 (hereafter SAH), precisely dated by Baker et al. (Baker J., Bizzarro M., Wittig N., Connelly J. and Haack H. (2005) Early planetesimal melting from an age of 4.5662 Gyr for differentiated meteorites. Nature436, 1127-1131), has been proposed as a new reference point for the early Solar System timescale and for calculation of the revised minimum age of our Solar System. The Pb-Pb age of SAH of 4566.18 ± 0.14 Ma, reported by Baker et al., differs from the Pb-Pb age of D’Orbigny, another basaltic angrite, of 4564.42 ± 0.12 Ma (Amelin Y. (2008) U-Pb ages of angrites. Geochim. Cosmochim. Acta72, 221-232), despite the fact that the relative 53Mn-53Cr and 182Hf-182W ages of these meteorites are identical. Here I report U-Pb data for 21 whole rock and pyroxene fractions from SAH, analyzed using the same approach as D’Orbigny (Amelin, 2008). These fractions contain between 1.3 and 8.9 pg of total common Pb, slightly more than analytical blank. Measured 206Pb/204Pb ratios are between 625 and 2817 for D’Orbigny, blank-corrected 206Pb/204Pb ratios are between 1173 and 6675. Eight acid-washed whole rock fractions yielded an isochron age of 4564.86 ± 0.38 Ma, MSWD = 1.5. Data for pyroxene fractions plot mostly above the whole rock isochron, and do not form a linear array in 207Pb/206Pb vs. 204Pb/206Pb isochron coordinates. The 207Pb∗/206Pb∗ model dates of the pyroxene fractions vary from 4563.8 ± 0.3 to 4567.1 ± 0.5 Ma. The difference between whole rock and pyroxene U-Pb systematics may be a result of re-distribution of radiogenic Pb at a mineral grain scale several million years after crystallization. Complexities of Sm-Nd, Lu-Hf, and possibly 26Al-26Mg mineral systematics of SAH, described previously, may be related to the same process that caused the re-distribution of radiogenic Pb. Disturbance of isotopic chronometers renders SAH an imperfect anchor for the early Solar System timescale. The problems with age determination revealed by the studies of SAH call for greater attention in Pb-isotopic dating of angrites and other achondrites. 相似文献
43.
Fumarolic activity of Avachinsky and Koryaksky volcanoes, Kamchatka, from 1993 to 1994 总被引:1,自引:0,他引:1
Yuri A. Taran Charles B. Connor Vyacheslav N. Shapar Alexandre A. Ovsyannikov Arthur A. Bilichenko 《Bulletin of Volcanology》1997,58(6):441-448
Volcanic gas and condensate samples were collected in 1993–1994 from fumaroles of Koryaksky and Avachinsky, basaltic andesite
volcanoes on the Kamchatka Peninsula near Petropavlovsk–Kamchatsky. The highest-temperature fumarolic discharges, 220 °C
at Koryaksky and 473 °C at Avachinsky, are water-rich (940–985 mmol/mol of H2O) and have chemical and isotopic characteristics typical of Kamchatka–Kurile, high- and medium-temperature volcanic gases.
The temperature and chemical and water isotopic compositions of the Koryaksky gases have not changed during the past 11 years.
They represent an approximate 2 : 1 mixture of magmatic and meteoric end members. Low-temperature, near-boiling-point discharges
of Avachinsky Volcano are water poor (≈880 mmol/mol); Their compositions have not changed since the 1991 eruption, and are
suggested to be derived from partially condensed magmatic gases at shallow depth. Based on a simple model involving mixing
and single-step steam separation, low water and high CO2 contents, as well as the observed Cl concentration and water isotopic composition in low-temperature discharges, are the
result of near-surface boiling of a brine composed of the almost pure condensed magmatic gas. High methane content in low-temperature
Avachinsky gases and the 220 °C Koryaksky fumarole, low C isotopic ratio in CO2 at Koryaksky (–11.8‰), and water isotope data suggest that the "meteoric" end member contains considerable amounts of the
regional methane-rich thermal water discovered in the vicinity of both volcanoes.
Received: 2 May 1996 / Accepted: 5 November 1996 相似文献
44.
45.
Yuri I. Sorokin Franco Dallocchio Fernando Gelli Luciano Pregnolato 《Journal of Sea Research》1996,35(4):243-250
Inorganic phosphorus dynamics were investigated with the use of 32P in the hypertrophic Comacchio lagoons (NE Adriatic) during an extremely dense, quasi-permanent bloom of picocyanobacteria. Concentrations of dissolved inorganic phosphate (DIP) in waters of the blooming lagoons were usually near the detection limit (0.01 μmoles·dm−3). DIP uptake rates by microplankton at near-ambient concentrations (0.01 to 0.1 μmoles·dm−3) were in the range of 9.6 to 16.1 nmoles P·dm−3·min−1, and turnover times were 1.5 to 3 min. The turnover time was >40 h in the eutrophic coastal waters of the adjacent Adriatic Sea. The uptake rate of DIP depended on its initial concentration. In water samples artificially enriched with DIP, the uptake rate rose to its maximum of 0.10 to 0.13 μmoles P·dm−3·min−1 (or 6 to 7 μmoles·dm−3·h−1) when the initial concentration of DIP was elevated to 10 to 20 μmoles·dm−3. The potential capacity of microplankton in the water samples to consume and retain DIP was estimated at 25 μmoles·dm−3. Specific features are discussed of phosphorus metabolism in the anthropogenically transformed lagoon ecosystem with an anomalous food web with few animals. 相似文献
46.
Spatial and vertical distributions of elements in sediments of the Colorado River delta and Upper Gulf of California 总被引:1,自引:0,他引:1
Evgueni N. Shumilin Jos D. Carriquiry Víctor F. Camacho-Ibar Dmitry Sapozhnikov Stepan Kalmykov Alberto Snchez Sergio Aguíiga-García Yuri A. Sapozhnikov 《Marine Chemistry》2002,79(3-4)
The abundance of major components (Fe, Ca, K, and organic carbon) and trace elements was analyzed in surface sediments and core samples from the Colorado River delta (CRD) and the Upper Gulf of California (UGC) using instrumental neutron activation analysis.The spatial distribution patterns of the elements studied are consistent with the model of sedimentary dynamics proposed for this area [Mar. Geol. 158 (1999) 125]: intense tidal resuspension of sediments in the delta with subsequent transport of suspended particulate matter in a southerly direction, followed by sedimentation of fine-grained material in a depocenter near the southwestern margin of the UGC. Concentrations of most of the elements are higher in the surface sediments of this depocenter. The gradual mixing of terrigenous and marine biogenic materials, normally expected for the estuarine sediments, was not detected in the CRD–UGC system because of homogenization of the sediments by tides and wind.Vertical profiles of element contents in samples of the sediment core collected in the depocenter area revealed (i) almost no anthropogenic contamination of the area by environmentally important trace elements such as Cr, Co, Sb, and As; (ii) a twofold decrease of Fe, Sc, Cr, and Co in upper core sediments; and (iii) the enrichment of the sediments at 60–62 cm depth in the core, in calcium carbonate, Ca, Sr, and the Eun/Smn shale-normalized ratio along with a depletion in this layer of Fe, Sc, Cr, Co, light rare-earth elements (REEs), and some other elements of terrigenous origin, presumably caused by the dilution of fluvial terrigenous material by biogenic carbonates, which were probably introduced at this level in the sediments by the action of a strong episodic winter storm, followed by the advective transport of shell fragments from the coastal clam banks or as a result of strong planktonic bloom. 相似文献
47.
We have used ex situ atomic force microscopy (AFM), scanning tunneling microscopy and spectroscopy (STM/STS) and X-ray photoelectron spectroscopy (XPS) to study the surfaces of natural arsenopyrite samples that were electrochemically polarized in 1 M HCl, or leached in acidic solutions containing ferric iron salts, and then reacted with aqueous gold (III) chloride at ambient temperatures. For arsenopyrite oxidized on a positive-going potential sweep, progressively increasing amounts of surface Fe(III)-O and As-O species, and of S/Fe and S/As ratios in a non-stoichiometric sulfidic layer were found. The products formed in the sweep to a potential of 0.6 V (Ag/AgCl) of the passivity region are shaped in about 100 nm protrusions of two sorts, which are arranged in micrometer-size separate areas, while they are largely mixed at higher, “transpassive” potentials. The quantities of surface alteration substances notably decrease after leaching in ferric chloride and ferric sulfate acidic solutions. Passivation of arsenopyrite was suggested to associate with the disordered, metal-deficient surface layer having moderate excess of sulfur rather than with the products of arsenopyrite oxidation. Exposure of arsenopyrite to 10−5-10−3 M (pH 2) solutions results in the deposition of 8-50 nm gold particles; only a small fraction of the gold is present as Au(I)-S species. The electrochemical oxidation at 0.6 V or ageing of arsenopyrite in air promotes the subsequent gold deposition; in contrast, the amount of Au deposited on arsenopyrite that was treated by leaching in ferric chloride and sulfate solutions was about 10 times smaller than with polished arsenopyrite samples. It has been concluded that reducing agents formed as intermediates of arsenopyrite decomposition facilitate the Au0 cementation although other factors related to the surface state of the arsenopyrite play a role as well. A decrease in the tunneling current magnitudes with decreasing the Au0 particle size has been revealed using STS. This effect along with the increase by 0.2-0.5 eV in the XPS Au 4f binding energies were tentatively ascribed to retarding the electron transitions by emerging electrostatic charge on gold nanoparticles (Coulomb blockade). Possible mechanisms for the effects, and their potential role in the deposition and hydrometallurgy of “invisible” gold are discussed. 相似文献
48.
The study is motivated by recent findings of the decrease in the momentum transfer from strong winds to sea. The Kelvin–Helmholtz instability (KHI) of a three-fluid system of air, foam and water is examined within the range of intermediately short surface waves. The foam-layer thickness necessary for effective separation of the atmosphere and the ocean is estimated. Due to high density contrasts in the three-fluid system, even a relatively thin foam layer between the atmosphere and the ocean can provide a significant stabilization of the water surface by the wavelength shift of the instability towards smaller scales. It is conjectured that such stabilization qualitatively explains the observed reduction of roughness and drag. 相似文献
49.
50.