地表喀斯特沉积中藻类作用的观察研究

本文通过对我国,南斯拉夫及英国的一些典型地表喀斯特沉积样品的微观观察(偏光显微镜及扫描电镜观察),并综合前人成果,讨论了多种陆相淡水碳酸盐沉积物(石灰华、藻微礁、钙壳核、荒漠叠层石及钙结壳等)沉积过程中藻类(蓝藻、硅藻、绿藻、红藻及轮藻的)钙化作用(充填、结壳及代换作用)、捕获和粘结作用、同化作用和分泌作用,并提出了一种地表喀斯特沉积中新的藻类作用的可能类型——构架作用(shoring effect)。     

Some Problems Concerning Geologic Structure with Double Layers in Urban Underground Lifeline Engineering

Underground lifeline engineering(ULE for short)in modern city demands the ap-preciation of an active fault in buried bedrock.Generally speaking,a large numberof urban geological textures of a basement may all be simplified into a dual geologicaltexture model,i.e.,the upper part of the basement consists of loose covering layerand the lower part consists of bedrock.The study of an active fault should includethree parts of contents,i.e.,to determine the lower time limit of activity of thefault,and the time limit must be recognized by both of designing engineers and geolo-gists;on the basis of the studies of repetition periods of earthquake occurrence to deter-mine whether the fault moves or not during the allowed time of efficacy of buildingsand constructions;for the sake of engineering practice,the active rate of the faultmust be given.The fault with different active mechanism has different effects on theULE.The authors studied the effect of lateral non-uniform overburden site on theULE by means of the su     

Sulfur redox reactions: Hydrocarbons,native sulfur,Mississippi Valley-type deposits,and sulfuric acid karst in the Delaware Basin,New Mexico and Texas

Hydrocarbons, native sulfur, Mississippi Valley-type (MVT) deposits, and sulfuric acid karst in the Delaware Basin, southeastern New Mexico, and west Texas, USA, are all genetically related through a series of sulfur redox reactions. The relationship began with hydrocarbons in the basin that reacted with sulfate ions from evaporite rock to produce isotopically light ( ³⁴S = -22 to -12) H₂S and bioepigenetic limestone (castiles). This light H₂S was then oxidized at the redox interface to produce economic native sulfur deposits ( ³⁴S = -15 to +9) in the castiles, paleokarst, and along graben-boundary faults. This isotopically light H₂S also migrated from the basin into its margins to accumulate in structural (anticlinal) and stratigraphic (Yates siltstone) traps, where it formed MVT deposits within the zone of reduction ( ³⁴S = -15 to +7). Later in time, in th zone of oxidation, this H₂S reacted with oxygenated water to produce sulfuric acid, which dissolved the caves (e.g., Carlsbad Cavern and Lechuguilla Cave, Guadalupe Mountains). Massive gypsum blocks on the floors of the caves ( ³⁴S = -25 to +4) were formed as a result of this reaction. The H₂S also produced istopically light cave sulfur ( ³⁴S = -24 to -15), which is now slowly oxidizing to gypsum in the presence of vadose drip water.     

结构—功能—生境框架下的西南喀斯特生态系统脆弱性研究进展

特殊的地质背景与生态环境叠加强烈的人类活动,导致中国西南喀斯特地区生态系统呈现显著的脆弱性特征。从生态系统敏感性和适应性角度出发,喀斯特生态系统结构、功能和生境对外界扰动响应的脆弱性特征研究已取得一定进展,尤其是借助物种多样性、生态系统生产力、土壤水分/养分等指标揭示了喀斯特生态系统对土地利用/覆被变化、石漠化等过程的敏感性等方面,但综合野外试验、数值模拟、数理统计等手段的生态系统敏感性定量化研究仍较薄弱。在生态系统适应性方面,虽然具有喜钙、耐旱以及石生等特性的植物种群通过形态结构和生理功能的自我调节能够呈现出对岩溶环境的适应性,但喀斯特生态系统对人类干扰和气候变化等环境胁迫响应的适应机制仍缺乏长期的生物及理化过程研究。今后,应针对生态系统结构、功能、生境间的正反馈机制,增强系统组分的耦合分析,加强喀斯特生态系统脆弱性驱动机制研究与定量评估,突出系统脆弱性在石漠化遏制和生态恢复重建中的关键地位。     

Evolution of fluid flow and heat distribution over geological time scales at the margin of unconfined and confined carbonate sequences - A numerical investigation based on the Buda Thermal Karst analogue

Hydrogeological processes acting at the margins of confined and unconfined thick carbonate sequences are particularly interesting due to a complex system evolution including partial uplift of fully confined carbonate systems and subsequent erosion of cover layers. We provide insights into this evolution by simulating coupled density-dependent fluid flow and heat transport based on the Buda Thermal Karst (BTK) system (Hungary) in a 2D vertical plane. Applying an equivalent porous medium (EPM) approach using the Heatflow-Smoker finite element model, scenario modelling of three evolutionary steps was carried out between the fully-confined carbonate stage through to partly and completely unconfined conditions over the western ridge. The numerical simulations were used to derive the main evolutionary characteristics of groundwater flow and heat transport patterns for the unconfined and confined parts of the hydrogeologic system. The initial fully-confined state led to the development of thermal convection cells due to the insulating role of the low-permeability confining layer, which facilitates buoyancy-driven flow by restricting the dissipation of heat. Over geological time, these cells were gradually overprinted by gravity-driven flow and thermal advection due to uplift of the west ridge. The limited thickness of the cover allowed sufficient water infiltration into the system, which led to increased cooling. Further uplifting led to a prevalence of gravity-driven groundwater flow. The results highlight the critical role of confining formations on flow patterns, and their effect on heat distribution and dissipation over geological time scales. The results have important implications for heat accumulation as well as for the development of a deep geothermal energy potential in confined carbonates.     

贵州猫场超大型铝土矿床成因浅析

猫场铝土矿床位于大威岭背斜北东端猫场穹窿背斜。由于寒武系碳酸盐岩古喀斯特侵蚀面,经长期风化溶蚀淋滤作用,在古喀斯特正地形上先形成粘土层,粘土层进一步风化溶蚀经脱硅、脱铁形成三水铝石的矿源层,而古喀斯特负地形则为铝土矿的沉积提供了充足的场所。本文通过对含矿岩系的特征分析,结合沉积相与古地理环境等研究,揭示了猫场铝土矿床的形成严格受大地构造和古喀斯特地形的控制。     

贵州织金洞世界地质公园喀斯特景观特征及其形成演化分析

织金洞世界地质公园,位于贵州高原西部,园区内喀斯特景观总体可概括为洞穴、峡谷、天生桥、天坑、高峰丛、丘陵、单面山与象形山、水文遗迹等8大类,它们以下三叠统海相碳酸盐岩为物质基础,有序、集中分布于织金洞、绮结河、东风湖三片相对独立,却又以绮结河为纽带紧密相连的喀斯特区域内,共同构成一个以洞穴、峡谷、天生桥、天坑为核心,形态雄伟、典型、优美、珍稀的高原喀斯特景观群。同时在对公园岩溶景观特征及区域地质背景进行分析和研究的基础上,系统研究和探讨了织金喀斯特,及织金洞、绮结河、东风湖三大地貌单元的形成演化过程,并认为它们的发育模式由地下喀斯特逐渐过渡至地表喀斯特,系统完整地纪录了贵州高原喀斯特的演化历程。     

中国喀斯特关键带岩石风化碳汇评估及其生态服务功能

喀斯特地区的岩石风化固碳被认为是全球遗漏碳汇之一,中国喀斯特地区的分布面积达344万km²,目前对其岩溶碳汇缺乏精确、系统的评估,对碳汇产生的机制仍存在争议。本文通过对喀斯特地区碳汇研究的回顾,详细介绍了适用于喀斯特地区固碳速率的估算方法,并对喀斯特地区的岩石风化碳汇进行再评估,然后将地球关键带科学概念引入喀斯特生态系统,阐述喀斯特关键带碳汇研究对生态系统服务和功能的意义。研究结果表明,中国喀斯特地区每年因岩溶作用产生的碳汇为4.74 Tg C yr^-1,未来中国需要加强岩石—土壤—水体—生物—大气复杂交互系统的基础数据收集,以明确各界面碳通量,对喀斯特关键带碳汇进行多尺度、多方法、全方位联合评估,在改善喀斯特生态系统功能、科学管理区域和国家碳收支及全球变化研究等方面为政府和学者提供参考。