温室气体源汇及其对气候影响的研究现状

温室气体对全球气候变化将产生深远的影响。本文拟从温室气体源汇研究以及温室气体对气候环境的影响等方面论述温室气体研究进展。尽管目前国内外对主要的温室气体源与汇研究报道很多,但不同的研究结果不尽一致,有些研究间甚至出现相反的结论。温室气体增加对气候的影响及其检测,主要是利用不同复杂程度的数值模式进行研究。     

海进体系域碳氧同位素地球化学响应——以黔西南地区三叠系为例

层序地层研究表明，位于扬子地块西南缘的黔西南地区在中三叠世末期（相当于Ladinian-Carnian期）出现了一次与全球同步的大规模海侵，形成了一个向上变深的碳酸盐岩台地淹没沉积层序。垄头组顶部和竹竿坡组分别是海进体系域（TST）的下、上部分。碳、氧同位素研究表明，垄头组顶部自下而上δ（^18O）持续增大，而δ（^13 C）先逐渐增大，后在顶部界面附近快速下降，反映了垄头组顶部在暴露环境下氧化作用的结果。竹竿坡组δ（^13 C）自下而上逐渐增大，δ（^13 C）总体呈现逐渐减小趋势，反映了海平面变化特征。研究认为，海进体系域的δ（^13 C）和δ（^18 O）演化不但反映了海平面和沉积环境变化，同时对密集段（CS）、层序界面和古暴露面等也有很好的识别作用，在层序地层研究中具有重要的意义。     

Episodes of late Holocene aridity recorded by stalagmites from Devil's Icebox Cave, central Missouri, USA

Two stalagmites from Devil's Icebox Cave, central Missouri, display similar δ¹³C and δ¹⁸O values and trends during the late Holocene. Positive δ¹³C excursions at 3.5-2.6 ka and 1.2-0.9 ka are interpreted to reflect drier conditions. These elevated stalagmite δ¹³C values could have plausibly been driven by increasing C₄ plant abundances over the cave or an increased contribution of bedrock carbon, both of which could reflect decreased effective moisture. A lack of corresponding oxygen isotopic anomalies during these intervals suggests that neither mean annual temperature nor the seasonality of precipitation changed concomitantly with dryness. Both of the δ¹³C excursions identified in our stalagmite record are roughly coincident with dry intervals from a number of sites located across the Great Plains.     

爆裂法作为快速测定流体包裹体中二氧化碳（和其它气体）含量的手段及其在勘探中的使用：以中国山东和河北省金矿为例

The acoustic decrepitation method heats a small monomineralic sample and counts pressure impulses as the inclusions burst when they develop high internal pressures.For aqueous fluids,the decrepitation temperature is correlated with the homogenisation temperature,but gas rich fluids give a distinct and characteristic low temperature decrepitation peak which can be used to recognize gas rich fluid inclusions.This information is useful in exploration for Au deposits,which are frequently associated with CO_2 rich and sometimes CH_4 rich fluids. This distinctive decrepitation occurs because the CO_2 rich inclusion fluids expand according to the gas law and develop internal pressures high enough to burst the host mineral grain at temperatures well below their homogenisation temperatures.In contrast,aqueous fluids condense to a liquid and vapour phase during post-entrapment cooling.Upon subsequent heating their internal pressures do not increase significantly until after homogenisation to a single phase occurs and hence they do not decrepitate"prematurely"as gas rich inclusions do. This behaviour is usually regarded as an annoyance in conventional microthermometric homogenisation studies,but can readily be used as an exploration aid to find mineralisation deposited from such gas rich fluids.Decrepitation results on samples from Cowra Ck, NSW,Australia,which have also been microthermometrically measured for CO_2 content,show that amounts of less than 5 mole % CO_2 are easily distinguished by decrepitation and amounts as low as 1 mole % CO_2 may be determinable. Examples of the use of acoustic decrepitation in the study of 6 gold mines in the Shandong and Hebei provinces of China are discussed.     

交会图和Carbon软件在火山碎屑岩识别中的应用

针对火山岩储层的特殊性(复杂性、离散性和随机性),应用交会图及Carbon软件对火山岩测井解释中岩性识别问题进行了研究。该方法的技术关键是交会图的选取,以交会图和Carbon软件为基础实现对岩性的识别。将研究方法应用在海拉尔地区火山碎屑岩岩性识别问题中,取得了很好的效果,岩性解释符合率80%。     

Tilt corrections over complex terrain and their implication for CO<Subscript>2</Subscript> transport

Observational data from sonic anemometers are commonly rotated from sonic to streamline coordinates, a procedure that is called tilt correction. Tilt corrections are often used to post-process air velocity data collected from sonic anemometers to allow objective interpretation of air flow data relative to the Earth. Since streamline coordinates depend on dynamical characteristics of the flow, the tilt correction depends not only on temporal and spatial variations of the flow, but also on local circulations. We found that ensemble- averaged slope flows are approximately parallel to the terrain slope close to the ground within the canopy layer, but not above, due to the influence of the diurnal variation of local vertical circulations. As a result, the diurnal variation of the observed vertical velocity in streamline coordinates at 21.5 m above the ground over 11-m tall forest canopies can be opposite to that calculated from the continuity equation. To estimate CO₂ transport over sloping terrain, a workable reference coordinate system is needed such that multiple sonic anemometers have a common reference relative to the Earth. Streamline coordinate systems can be the choice of the common reference coordinate system only if flow, at least ensemble-averaged flow, is parallel to terrain slopes. The choice of the reference coordinate system and its implication in investigation of CO₂ transport are discussed. The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

岩溶发育对温室气体CO2的调节能力研究

温室效应是当今世界上许多国家及其政府关注的重要问题之一。从地质角度研究全球最大碳库－－碳酸盐岩在其岩溶发育过程中对温室气体ＣＯ２的调节能力,从而为更全面,定量地考察温室气体ＣＯ２循环提供新思路及依据。     

Carbon isotopic fractionation by desorption of shale gases

Geochemical studies of shale gas and conventional reservoirs within the Triassic Yanchang Formation of Xiasiwan and Yongning Field, Ordos Basin show that methane is isotopically depleted in ¹³C as compared to δ¹³C₁ calculated by the Ro based on the relationship between δ¹³C₁ and Ro. Geochemical fractionation during the adsorption/desorption process of shale system may play a significant part in influencing δ¹³C₁ values of shale gas. Two shale core samples from confined coring of the Yanchang Formation were adopted segmented desorption experiments to examine this phenomenon. The results show that the δ¹³C₁ of desorbed gas changes little in the first few phases of the experiments at low desorption levels, but become less negative rapidly when the fraction of desorbed methane exceeds 85%. The desorption process for the last 15% fraction of the methane from the shale samples shows a wide variation in δ¹³C₁ from −49‰ to −33.9‰. Moreover, δ¹³C₁ of all desorbed methane from the shale samples is substantially depleted in ¹³C than that calculated by Ro, according to Stahl and Carey's δ¹³C₁–Ro equation for natural gas generated from sapropelic organic matter. This shows some gases with isotopically enriched in ¹³C cannot be desorbed under the temperature and pressure conditions of the desorption experiments. This observation may be the real reason for the δ¹³C₁ of shale gases and conventional reservoirs becomes more negative in Xiasiwan and Yongning Fields, Ordos Basin. The magnitude of the deviation between the δ¹³C₁ of shale gas and that calculated by Ro may be related to the adsorption capacity of shale or the proportion of absorbed gases. In this way, we may be able to evaluate the relative adsorption capacity of shale in geological conditions by δ¹³C₁ of the shale gas, or by δ¹³C₁ of conventional gas which generated by the shale with certainty. The δ¹³C₁ of conventional gas in Dingbian and Yingwang Fields have no deviation because the TOC value of the hydrocarbon source rock is relatively low.     

Characteristics and origin of carbon isotopes of n-alkanes in crude oils from the western Pearl River Mouth Basin,South China sea

The quantitative characterization of carbon isotopes of n-alkanes is commonly carried out in organic geochemical studies. Possible controls on carbon isotopes include source organic matter, maturity, fractionation during oil expulsion and migration, and the mixing of different oils. In this study of the origin of crude oils in the western Pearl River Mouth Basin, the influences of all of these factors have been considered in reaching a conclusion. Carbon isotopes of n-alkanes in the crude oils, and the extracts of the two effective source rocks (the Wenchang and Enping formations) in the basin, exhibit clear differences. The Wenchang source rocks have heavy δ¹³C values that remain almost constant or become slightly heavier with increasing carbon number. The Enping source rocks have light δ¹³C values that become lighter with increasing carbon number. Two groups of oils in this area were identified based on the carbon isotopes of the n-alkanes; groupIoils are similar to extracts of the Wenchang source rocks. However, the groupIIoils are different from both the Wenchang and Enping source rocks and the carbon isotopic profiles of their n-alkanes exhibit a “V” feature with increasing carbon number. The results of artificial thermal maturation experiments indicate that, from the early stage to the peak stage of oil generation (with EasyRo between 0.64% and 1.02%), the δ¹³C values of n-alkanes in the pyrolysis oils become heavier by about 3‰ with increasing thermal maturity, but the shape of the carbon isotopic profiles are not significantly changed. Calculated δ¹³C values of n-alkanes in “mixed” artificial pyrolysis oils indicate that the mixture of oils generated from the same source rocks with different maturities could not change the carbon isotopic profile of the n-alkanes, however, a mixing of the Wenchang and Enping oils could give the “V” feature in the profiles, similar to the groupIIoils in this area. The groupIIoils appear to be mixed Wenchang and Enping oils, the latter being the dominant component in the mixture. We conclude that the source organic matter and the degree of mixing are the main factors controlling the carbon isotopic characteristics of n-alkanes in crude oils in the western Pearl River Mouth Basin.