江西修水二叠系-三叠系界线地层树枝状微生物岩状岩石成因初解

江西修水二叠系-三叠系界线地层有一段特殊构造的地层，下部为灰色部分和红色部分组成的斑状构造，上部为灰色部分和黄色部分组成的树枝状构造。这种树枝状构造的岩石与前人报道自重庆老龙洞剖面的微生物岩非常相似。岩石薄片观察表明，树枝状构造的暗色部分为残留的灰泥岩；浅色部分为灰岩经过重结晶、白云石化去白云石化作用改造而成。在暗色的残留灰岩里有保存很好的丰富的球状微生物化石。研究认为，岩石中暗色部分和浅色部分的原始组分是同时沉积的；是成岩作用控制了浅色部分的形成。这一成果应当对认识老龙洞剖面树枝状微生物岩的成因有借鉴作用。     

济南泉域排泄区岩溶地下水水化学特征

文章通过分析研究济南泉域排泄区地下水水化学成分特征及形成过程,结合岩溶地下水的补径排条件,揭示了不同位置、不同深度循环的水质存在差异的原因。为保护泉水、优化泉域内地下水的开采方案提供了依据。     

鄂尔多斯盆地南部奥陶系马五段去白云石化成因及模式

通过研究马五段去白云石化作用的成因及发生模式,可进一步了解鄂尔多斯盆地南部奥陶系碳酸盐岩储集层成岩和物性的演化.通过岩心与薄片的观察,结合地球化学方法,和对白云岩的碳、氧同位素与微量元素的测定,分析了去白云石化作用成因及成岩演化过程,并结合物性资料分析去白云石化作用对储集层的影响,建立了研究区去白云石化的作用模式.结合...     

湖北随州薛家店地区灯影组去白云石化特征及意义

湖北随州薛家店地区灯影组去白云石化特征及意义翟永红郭成贤（江汉石油学院，湖北荆沙４３４１０２）关键词去白云石化方解石储层灯影组湖北随州去白云石化是一种白云石被方解石交代的成岩现象。目前，国内外有关文献报道，但多侧重于实验室研究机理和条件的研究，如Ｄｅ...     

激光探针稳定同位素分析技术的现状及发展前景

以揭示碳酸盐岩和硫酸盐岩相伴沉积时发生的复合岩溶形成机制为目的 ,采用室内模拟实验方法 ,利用反应路径模型研究了水流路径上碳酸盐岩→硫酸盐岩 (简称层序 1)和硫酸盐岩→碳酸盐岩 (简称层序 2 )两种层序时发生的地球化学作用 ,根据质量平衡原理 ,计算了水岩间发生的地球化学作用强度 ;探讨了硫酸盐岩成因、岩溶发育的环境温度对复合岩溶的影响。结果表明 ,复合岩溶形成机理与可溶岩层序关系密切 ,层序 1中 ,发生两种可溶岩的溶解作用 ;层序 2中 ,除硫酸盐岩 (石膏和半水石膏 )溶解外 ,碳酸盐岩 (白云岩 )发生的是去白云化作用。这些作用间通过不同的机制相互促进 ,导致复合岩溶较单一可溶岩的岩溶更发育。复合岩溶的发育程度还受溶液 pH值和环境温度影响 ,溶液pH值降低、环境温度升高都利于复合岩溶发育。     

Dedolomitization and calcite cementation in the Middle Devonian Winnipegosis Formation in Central Saskatchewan,Canada

Limestone consisting of finely to medium crystalline calcite mosaics is present in the upper part of the Winnipegosis Formation on the east‐central margin of the Elk Point Basin where the overlying Prairie Evaporite deposits have been removed. This type of crystalline limestone is interpreted as dedolomite, based on petrographic observations. The δ¹⁸O and δ¹³C values of the Winnipegosis dedolomite vary from ?12·8‰ to ?11·9‰ VPDB (Vienna Pee Dee Belemnite) and from ?0·5‰ to +1·7‰ VPDB, respectively; both values are significantly lower than those for the corresponding dolomite. The ⁸⁷Sr/⁸⁶Sr ratios of the dedolomite are significantly higher, between 0·7082 and 0·7087. The spatial distribution and geochemical data of the Winnipegosis dedolomite suggest that dedolomitization was related to an influx of fresh groundwater and dissolution of the Prairie Evaporite anhydrite during the latest Mississippian to the Early Cretaceous when the basin was subjected to uplift and erosion. The Winnipegosis dedolomite displays a series of replacement fabrics showing progressive calcitization of dolomite, including the occurrence of dedolomite restricted along fractures and adjacent areas, dolomite patches ‘floating’ in the dedolomite masses and massive dedolomite with sparsely scattered dolomite relicts. However, the characteristic fabrics resulting from dedolomitization documented in the literature have not been observed in the Winnipegosis dedolomite. Coarsely to very coarsely crystalline, subhedral to euhedral calcite cement is restricted in the dedolomite. The petrographic features, isotopic compositions and homogenization temperatures, coupled with the burial history of the Winnipegosis Formation, constrain the precipitation of the calcite cement from a mixing of basinal brines and fresh groundwater during Late Cretaceous to Neogene time. The more negative C‐isotopic signatures of the calcite cement (?5·3‰ to ?2·3‰ VPDB) probably reflect a hydrocarbon‐derived carbon.     

塔里木盆地柯坪地区中寒武统藻白云岩去白云岩化研究

对塔里木盆地柯坪地区中寒武统去白云岩化现象进行了研究。去白云岩化限于渗透性较好的藻白云岩,并且只有靠近含膏层段的藻白云岩才发生去白云岩化。从微观上看,发生去白云岩化的藻灰岩与藻灰云岩含有明显的去白云岩化交代残余,白云石残余呈碎斑状或树枝状。树枝状白云石残余含有大量的方解石包裹体,同时具有较高的Ca/Mg比,为高钙白云石,去白云岩化较彻底,形成藻灰岩;碎斑状白云石残余成分较均一,接近化学计量白云石(Ca/Mg比接近1),去白云岩化程度较弱,形成藻灰云岩。藻灰云岩的δ18O值(平均值为-6.7‰)明显低于邻近的白云岩(平均值为-5.3‰),同时高于藻灰岩(平均值为-9.5‰)。与未发生去白云岩化的藻白云岩相比,藻灰岩与藻灰云岩的孔隙度要明显降低。     

Dolomitization,gypsum calcitization and silicification in carbonate–evaporite shallow lacustrine deposits

This paper describes and interprets the mineral and facies assemblages that occur in carbonate–evaporite shallow lacustrine deposits, considering the importance of the processes pathway (i.e. dolomitization, gypsum calcitization and silicification). The Palaeogene deposits of the Deza Formation (Almazán Basin, central‐northern Spain) are selected as a case study to determine the variety of physicochemical processes taking place in carbonate–evaporite shallow lakes and their resulting diagenetic features. Dolostones are the predominant lithology and are composed mainly of dolomite with variable amounts of secondary calcite (5 to 50%), which mainly mimic lenticular gypsum (pseudomorphs). Five morphological types of dolomite crystal were identified as follows: dolomite tubes, dolomite cylinders, rhombohedral dolomite, spheroidal and quasi‐rhombohedral dolomite, and cocoon‐shaped dolomite. The dolomite cylinders and tubes are interpreted as the dolomitized cells of a widespread microbial community. The sequence of diagenetic processes started with growth of microlenticular interstitial gypsum in a calcareous mud deposited on the playa margin mudflats, and that sometimes included microbial sediments. Immediately following growth of gypsum, dolomite replaced the original calcite (or possibly aragonite) muds, the microbial community and the gypsum. Partial or total replacement of gypsum by dolomite was related mainly to the biomineralization of endolithic microbial communities on gypsum crystals. Later calcitization took place under vadose, subaerial exposure conditions. The development of calcrete in distal alluvial settings favoured the release of silica and subsequent silicification on the playa margin mudflats. Stable isotope compositions of calcite range from ?9·02 to ?5·83‰ δ¹³C_PDB and ?7·10 to 1·22‰ δ¹⁸O_PDB; for the dolomite, these values vary from ?8·93 to ?3·96‰ δ¹³C_PDB and ?5·53 to 2·4‰ δ¹⁸O_PDB. Quartz from the cherts has δ¹⁸O_SMOW values ranging from 27·1 to 31·1‰. Wide variation and relatively high δ¹⁸O_SMOW values for dolomite indicate evaporitic and closed hydrological conditions; increased influx of meteoric waters reigned during the formation of secondary calcite spar.     

滇东北毛坪和会泽超大型铅锌矿床粗—巨晶碳酸盐岩成因及其找矿指示意义

云南毛坪和会泽铅锌矿床是川滇黔碳酸盐岩型铅锌成矿域的重要组成部分,是滇东北铅锌矿集区内两个最具代表性的超大型矿床。靠近铅锌矿体常见透镜状、囊状产出的蚀变围岩,因呈麻点状而被俗称为“麻石”,空间上与断裂、矿化结伴出现,是重要找矿标志。本文以这种麻点状的蚀变围岩为主要研究对象,通过大比例尺坑道剖面精细测量、岩相分析、电子探针分析、X射线微区衍射分析、主量—微量元素分析,研究其物质组成、组构特征及形成过程。根据组构特征将蚀变围岩分为两类,Ⅰ类呈砂糖状,矿物颗粒主要为粗晶结构(0.5~1 mm)的白云石和方解石,被褐色伊利石等黏土矿物胶结;Ⅱ类呈斑点状,矿物颗粒主要为巨晶结构(1~3 mm)的方解石和白云石,重结晶现象明显,被黑色泥质和有机质胶结。通过手标本观察、镜下鉴定和综合分析,将Ⅰ类蚀变围岩定名为弱大理岩化粗晶泥质白云岩,Ⅱ类蚀变围岩定名为去白云石化巨晶灰岩。两类蚀变围岩的主量元素特征相比,Ⅰ类中SiO₂、Al₂O₃、K₂O含量较高。微量元素特征显示两类蚀变围岩中主要矿化元素(Zn、Pb)明显富集。稀土元素特征显示,Ⅰ类中稀土元素含量均高于Ⅱ类,其中Ⅱ类与矿化白云岩稀土元素特征相似。两类蚀变围岩是同一流体系统不同阶段的产物,构建其成岩作用模式:弱大理岩化粗晶泥质白云岩(Ⅰ类)的原岩为钙质泥岩,高盐度卤水下渗,在岩性界面处与泥岩和白云岩反应形成泥质白云岩,沉积稳定后受构造运动影响,热液流体沿断裂上升,在有利地段形成泥质白云岩大理岩化(结构上改变);去白云石化巨晶灰岩(Ⅱ类)比弱大理岩化粗晶泥质白云岩(Ⅰ类)蚀变更强烈,经历矿化、大理岩化作用和去白云石化(结构和成分上改变)而形成。综合分析认为两类蚀变围岩与铅锌矿体在时间、空间、成矿物质和成矿流体等方面都具有密切的成因联系,提出大理岩化、去白云石化作用对该类矿床成矿与找矿均具有重要的指示意义。     

广东红岩黄铁矿床的地质特征与成矿机制

本矿床形成于成岩晚期,为弱改造层控型。黄铁矿具典型的球粒、胶状和生物交代结构。含矿岩系东岗岭组白云岩含TFe高、Al_2O_3低,并具缝合线和铁白云石等标志。主要控矿因素为古水下隆起、沉积相(礁滩组合)和成岩环境。成矿机制主要与有机物、礁滩沉积以及成岩过程中的白云岩化、退白云岩化和压溶作用有关。