火星生命研究的进展与前景

关于火星是否存在或曾经存在生命的争论由来已久。有人以ALH84001火星陨石新鲜破裂面上的大量碳酸盐小球体和多环芳香烃（PAHs）为主要依据，推论火星至少在13～36亿 aBP前很可能有生命形态存在。然而，很多人认为ALH84001陨石的各种特性可以是非生物成因的。由于地球上的生物在超过115℃的温度下很难存活（火星可与之类比），争论的焦点逐渐集中在碳酸盐球体的形成温度上。也有研究者关注该陨石上有机物质的来源问题。对ALH84001陨石的综合学科研究提出了互相矛盾的证据。综述了自1996年以来在国外各种主要期刊上发表的关于 ALH84001陨石与火星生命的研究成果（也包括了一些对其他火星陨石的研究），认为目前尚不能断言火星生命存在与否。对火星继续深入探索以获取进一步的证据是十分必要的。以美国国家航空和宇航局（NASA）Odys sey宇宙飞船起始的火星探测计划将引发新一轮火星生命研究的热潮。     

Carbonate platform evolution: from a bioconstructed platform margin to a sand-shoal system (Devonian, Guilin, South China)

ABSTRACT The depositional organization and architecture of the middle–late Devonian Yangdi rimmed carbonate platform margin in the Guilin area of South China were related to oblique, extensional faulting in a strike‐slip setting. The platform margin shows two main stages of construction in the late Givetian to Frasnian, with a bioconstructed margin evolving into a sand‐shoal system. In the late Givetian, the platform margin was rimmed with microbial buildups composed mainly of cyanobacterial colonies (mostly Renalcis and Epiphyton). These grew upwards and produced an aggradational (locally slightly retrogradational) architecture with steep foreslope clinoforms. Three depositional sequences (S3–S5) are recognized in the upper Givetian strata, which are dominated by extensive microbialites. Metre‐scale depositional cyclicity occurs in most facies associations, except in the platform‐margin buildups and upper foreslope facies. In the latest Givetian (at the top of sequence S5), relative platform uplift (± subaerial exposure) and associated rapid basin subsidence (probably a block‐tilting effect) caused large‐scale platform collapse and slope erosion to give local scalloped embayments along the platform margin and the synchronous demise of microbial buildups. Subsequently, sand shoals and banks composed of ooids and peloids and, a little later, stromatoporoid buildups on the palaeohighs, developed along the platform margin, from which abundant loose sediment was transported downslope to form gravity‐flow deposits. Another strong tectonic episode caused further platform collapse in the early Frasnian (at the top of sequence S6), leading to large‐scale breccia release and the death of the stromatoporoid buildups. Siliceous facies (banded cherts and siliceous shales) were then deposited extensively in the basin centre as a result of the influx of hydrothermal fluids. The platform‐margin sand‐shoal/bank system, possibly with gullies on the slope, persisted into the latest Frasnian until the restoration of microbial buildups. Four sequences (S6–S9), characterized by abundant sand‐shoal deposits on the margin and gravity‐flow and hemipelagic deposits on the slope, are distinguished in the Frasnian strata. Smaller‐scale depositional cyclicity is evident in all facies associations across the platform–slope–basin transect. The distinctive depositional architecture and evolution of this Yangdi Platform are interpreted as having been controlled mainly by regional tectonics with contributions from eustasy, environmental factors, oceanographic setting, biotic and sedimentary fabrics.     

Fluid-bearing alkaline carbonate melts as the medium for the formation of diamonds in the Earth''s mantle: an experimental study

We have experimentally studied the formation of diamonds in alkaline carbonate–carbon and carbonate–fluid–carbon systems at 5.7–7.0 GPa and 1150–1700 °C, using a split-sphere multi-anvil apparatus (BARS). The starting carbonate and fluid-generating materials were placed into Pt and Au ampoules. The main specific feature of the studied systems is a long period of induction, which precedes the nucleation and growth of diamonds. The period of induction considerably increases with decreasing P and T, but decreases when adding a C–O–H fluid to the system. In the range of P and T corresponding to the formation of diamonds in nature, this period lasts for tens of hours. The reactivity of the studied systems with respect to the diamond nucleation and growth decreases in this sequence: Na₂CO₃–H₂C₂O₄·2H₂O–C>K₂CO₃–H₂C₂O₄·2H₂O–C>>Na₂CO₃–C>K₂CO₃–C. The diamond morphology is independent of P and T, and is mainly governed by the composition of the crystallization medium. The stable growth form is a cubo-octahedron in the Na₂CO₃ melt, and an octahedron in the K₂CO₃ melt. Regardless of the composition of the carbonate melt, only octahedral diamond crystals formed in the presence of the C–O–H fluid. The growth rates of diamond varied in the range from 1.7 μm/h at 1420 °C to 0.1–0.01 μm/h at 1150 °C, and were used to estimate, for the first time, the possible duration of the crystallization of natural diamonds. From the analysis of the experimental results and the petrological evidence for the formation of diamonds in nature, we suggest that fluid-bearing alkaline carbonate melts are, most likely, the medium for the nucleation and growth of diamonds in the Earth's upper mantle.     

Predicting average annual groundwater levels from climatic variables: an empirical model

On the basis of one-dimensional theoretical water flow model, we demonstrate that the groundwater level variation follows a pattern similar to recharge fluctuation, with a time delay that depends on the characteristics of aquifer, recharge pattern as well as the distance between the recharge and observation locations. On the basis of a water budget model and the groundwater flow model, we propose an empirical model that links climatic variables to groundwater level. The empirical model is tested using a partial data set from historical records of water levels from more than 80 wells in a monitoring network for the carbonate rock aquifer, southern Manitoba, Canada. The testing results show that the predicted groundwater levels are very close to the observed ones in most cases. The overall average correlation coefficient between the predicted and observed water levels is 0.92. This proposed empirical statistical model could be used to predict variations in groundwater level in response to different climate scenarios in a climate change impact assessment.     

大庆徐家围子地区深部致密砂砾岩气层识别

大庆徐家圈子地区深部致密砂砾岩储层的骨架成分除了含有石英、长石外，还含有许多酸性喷发岩，而且各种骨架成分的含量随深度变化比较大；复杂的岩性使得气的影响被岩性的影响所淹没，从而造成常规气层识别方法失效。针对这一问题，应用神经网络方法准确求取地层颗粒密度和泥质含量，然后对中子和密度测井值进行岩性影响校正和泥质影响校正，使得求出的中子和密度孔隙度仅受地层气的影响，最后将得到的中子和密度孔隙度进行对比，应用中子和密度孔隙度的差异识别气层。     

中国油气储层地质研究面临的挑战和发展方向

论述了我国采取“稳定东部 ,发展西部”的油气战略后 ,油气地质所面临的形势 ,以及油气工业的发展对储层地质提出四个领域的挑战 :深部储层、挤压盆地储层、低渗透储层和碳酸盐岩储层 ;这些都是石油勘探开发中久攻不克的难题。根据我国陆上东西部油气区的勘探开发实际和近年的储层研究实践 ,文章系统多视角地分析了这四个难题 ,并提出了相应客观的研究思路和研究方向。     

湖南涟源凹陷构造演化与油气成藏研究

涟源凹陷经历了2个主要构造演化阶段:晚古生代海相碳酸盐岩夹碎屑岩盖层建造和中生代陆相沉积,现今的逆掩冲断构造样式和构造格局基本定型于燕山期。油气藏的形成经历了早、晚两期,早期形成于印支运动主幕,燕山运动主幕遭到破坏,部分经重新分配后形成次生气藏;晚期形成于燕山运动主幕以后,属原生油气藏。涟源凹陷中部褶断带的紧闭背斜是寻找次生气藏的首选区域,而宽缓向斜中的隐伏隆起则是寻找晚期原生油气藏的靶区。     

试论碳酸盐岩上覆红土的形成模式及演化趋势

据长期对岩溶及红土化作用等的研究成果,本文全面系统地分析了碳酸盐岩上覆红土的形成及演化规律,提出了一个新的碳酸盐岩上覆红土的形成模式,进而深入阐明了碳酸盐岩上覆红土的演化规律及其在现代气候条件下的演化趋势等,在解决岩溶及红土学术界存在的碳酸盐岩上覆红土的形成、碳酸盐岩与上覆红土之间的相互关系及其发展演化规律等一系列重大疑难问题上向前迈进了一步,对相关学科的发展将产生积极的推动作用.     

测氡法快速确定油气田边界及深度

本介绍了运用测氡法快速确定大庆××油气田边界，估算其埋藏深度试验，结果表明，该方法具有可行性和实用性。由于所做工作有限，尚属经验性探讨，还必须从理论和实践上进一步地工作，进而充实、完善它。