An isotopic biogeochemical study of Neoproterozoic and Early Cambrian sediments from the Centralian Superbasin, Australia

Organic matter from Neoproterozoic and Early Cambrian sediments of the Amadeus and Officer basins of the Centralian Superbasin, Australia, has been studied for biomarker distributions and the carbon isotopic compositions of kerogen and individual hydrocarbons. These sediments represent both shallow and deep water marine facies in the older sections and marine and saline lacustrine carbonate deposits in the Cambrian. Hydrocarbon biomarker patterns were found to be quite consistent with the known sedimentary environments and provide valuable insights into the biogeochemical changes which accompanied the transition from a microbially-dominated ocean to the early stages of metazoan radiation. In particular, carbon isotopic data for n-alkyl and isoprenoid lipids presented here, and in earlier studies, showed a reversal in carbon isotopic ordering between the Proterozoic and Phanerozoic. By comparison with the delta 13C of kerogen, n-alkyl lipids from deep-water Proterozoic sediments were enriched in 13C and appear to be derived mainly from heterotrophs whilst open marine Phanerozoic counterparts are 13C depleted and evidently derived mainly from autotrophs. Data from the samples studied here are consistent with a model invoking a change in the redox structure of the ocean, possibly aided by the innovation of faecal pellets.     

An isotopic biogeochemical study of the Green River oil shale

Thirty-five different samples from three different sulfur cycles were examined in this stratigraphically oriented study of the Shell 22x-l well (U.S.G.S. C177 core) in the Piceance Basin, Colorado. Carbon isotopic compositions of constituents of Green River bitumens indicate mixing of three main components: products of primary photoautotrophs and their immediate consumers (delta approximately -30% vs PDB), products of methanotrophic bacteria (delta approximately -85%), and products of unknown bacteria (delta approximately -40%). For individual compounds synthesized by primary producers, delta-values ranged from -28 to -32%. 13C contents of individual primary products (beta-carotane, steranes, acyclic isoprenoids, tricyclic triterpenoids) were not closely correlated, suggesting diverse origins for these materials. 13C contents of numerous hopanoids were inversely related to sulfur abundance, indicating that they derived both from methanotrophs and from other bacteria, with abundances of methanotrophs depressed when sulfur was plentiful in the paleoenvironment. gamma-Cerane coeluted with 3 beta(CH3),17 alpha(H),21 beta(H)-hopane, but delta-values could be determined after deconvolution. gamma-Cerane (delta approximately -25%) probably derives from a eukaryotic heterotroph grazing on primary materials, the latter compound (delta approximately -90%) must derive from methanotrophic organisms. 13C contents of n-alkanes in bitumen differed markedly from those of paraffins generated pyrolytically. Isotopic and quantitative relationships suggest that alkanes released by pyrolysis derived from a resistant biopolymer of eukaryotic origin and that this was a dominant constituent of total organic carbon.     

某些稀有、有色金属矿床及花岗岩中包裹体微量气体色谱分析研究

研究表明:不同成岩成矿作用不但与温度、压力有关,而且微量气体成分及其含量也有明显的规律变化.例如某爆发岩筒中,酸性气体(HCl、HF、H_2S)含量一般高于不活泼气体(N_2等);随着温度的下降,酸性气体含量减少,而后者增加.在某些地区远离花岗岩体矿物包裹体中CO_2含量有规律地增加,对矿物包裹体中微量气体成分及其含量的研究,有助于解决成岩作用机制,成矿阶段划分及矿床成因.同时,对地球化学找矿,隐伏矿体的揭露也有指导意义.包裹体中微量气体的变化可以作为一个地球化学指示剂.我们在自行研制真空爆裂微量气体测量分析仪的基础上,1979年春,首次成功地使用带热解炉的色谱仪测定了矿物包裹体中H_2O和CO_2等微量气体组分.同时对该色谱仪进行了改装,使该仪器更适合于矿物包裹体微量组分的测定及研究.通过近400多个     

Integrated Paleomagnetism and U-Pb Geochronology of Mafic Dikes of the Eastern Anabar Shield Region, Siberia: Implications for Mesoproterozoic Paleolatitude of Siberia and Comparison with Laurentia

This article reports the first joint paleomagnetic and U-Pb geochronologic study of Precambrian diabase dikes in the Anabar Shield and adjacent Riphean cover of Siberia. It was undertaken to allow comparison with similar published studies in Laurentia and to test Proterozoic reconstructions of Siberia and Laurentia. An east-trending Kuonamka dike yielded a provisional U-Pb baddeleyite emplacement age of 1503+/-5 Ma and a virtual geomagnetic pole at 16 degrees S, 221 degrees E (dm=17&j0;, dp=10&j0;). A paleomagnetic pole at 6 degrees N, 234 degrees E (dm=28&j0;, dp=14&j0;) was obtained from five Kuonamka dikes. An east-southeast-trending Chieress dike yielded a U-Pb baddeleyite emplacement age of 1384+/-2 Ma and a virtual geomagnetic pole at 4 degrees N, 258 degrees E (dm=9&j0;, dp=5&j0;). Kuonamka and Chieress poles are interpreted to be primary but do not average out secular variation. Assuming that the Siberian Plate has remained intact since the Mesoproterozoic, except for mid-Paleozoic opening of the Viljuy Rift, then the above results indicate that the Siberian Plate was in low latitudes at ca. 1503 and 1384 Ma, broadly similar to low latitudes determined for Laurentia from well-dated paleopoles at 1460-1420, 1320-1290, and 1267 Ma. This would allow Laurentia and Siberia to have been attached in the Mesoproterozoic, as suggested in several recent studies based on geological criteria. However, because paleomagnetic results from the Anabar Shield region do not average out secular variation and the ages of poles from Siberia and Laurentia are not well matched, it is not yet possible to distinguish between these reconstructions or to rule out other configurations that also maintain the two cratons at low paleolatitudes.     

First Mass-resolved Measurement of High-Energy Cosmic-Ray Antiprotons

We report new results for the cosmic-ray antiproton-to-proton ratio from 3 to 50 GeV at the top of the atmosphere. These results represent the first measurements, on an event-by-event basis, of mass-resolved antiprotons above 18 GeV. The results were obtained with the NMSU-WIZARD/CAPRICE98 balloon-borne magnet spectrometer equipped with a gas-RICH (Ring-Imaging Cerenkov) counter and a silicon-tungsten imaging calorimeter. The RICH detector was the first ever flown that is capable of identifying charge-one particles at energies above 5 GeV. The spectrometer was flown on 1998 May 28-29 from Fort Sumner, New Mexico. The measured p&d1;/p ratio is in agreement with a pure secondary interstellar production.     

两例强海洋气旋的诊断分析

本文介绍了北美东海岸两例(1972年11月16—18日和1982年1月9—11日)强海洋气旋的诊断分析。这两例气旋都沿一强低层斜压带生成,而且它们也都随一接近的对流层高空短波槽而加深。1972年11月16—18日的风暴沿卡罗来纳海岸线,在低层辐合加强和气旋性涡旋的形成有利于早期气旋生成医前方发展起来,在气旋的东北部有效的海洋加热和水汽通量有助于低层斜压性的加强和气旋路径上暖湿气团的不稳定。当地面低压上游大约300公里处有一普通的对流层中部低槽存在时,气旋开始爆发性加深(35百帕/12小时)。应注意的是,在气旋开始加深阶段,其中心附近有很强的对流和内部特别大的气压梯度,表明非绝热过程在其急剧发展阶段的作用。1982年1月9—11日气旋的形成和加深对对流层中上部旺盛的低压槽/较强的急流系统以及大尺度斜压性的反应,比1972年11月的气旋要强一些。除气旋后部,海洋热通量一般都很小。当气旋爆发性加深时,没有大范围的对流和对流不稳定。1982年的风暴强度达到峰值时是在冷水区,而1972年的风暴达到最大强度时,是在墨西哥湾流的暖水区。在1982年的个例中,上层锋生可以有助于对流层上部低压槽加强和使在下游发展。