白云岩的成因研究现状及最新进展

白云岩是主要由白云石组成的碳酸盐岩,对其成因的研究一直是沉积岩石学的热点。主要有原生白云石直接沉淀、次生交代和其他成因模式。目前普遍接受的主流成因模式是白云岩由石灰岩经过变化而成的,即石灰岩白云石化。     

对白云岩形成机理的再认识

在碳酸盐岩体系中,白云岩通常能形成最好的储层。对白云岩成因演化和储层展布的认识直接决定勘探部署。而白云岩成因是碳酸盐岩岩石学中最复杂、争论时间最久、最难解决的问题之一。根据机理的不同,当前各种主要的白云岩成因模式可划分为两大类:原生白云石模式和次生白云石化模式。虽然原生白云石的例子已被大量发现,但它们是否属真正的原生白云石仍需后续研究;理清白云岩成因问题,对认识白云岩及其相关的碳酸盐岩储层的油气勘探工作尤为重要。     

川东北地区三叠系飞仙关组白云化流体的Ca/Mg比定量估算

作为川东北地区三叠系飞仙关组天然气气藏最重要储集岩的粒屑白云岩和结晶白云岩的成因始终是沉积和石油地质学家高度关注的研究热点之一.在总结川东北地区三叠系飞仙关组不同类型白云岩形成温度的基础上,通过已有的白云化流体Ca/Mg值和温度之间关系式获得了川东北地区三叠系飞仙关组白云化流体的Ca/Mg值的主要分布范围.结果表明:不同类型白云岩对应的白云化流体具有不同的Ca/Mg值,同时证实了三叠纪海水或与之有关的海源流体、三叠纪海水与大气淡水混合流体的Ca/Mg值都符合在40～130℃区间、甚至更高温度下白云化(白云石沉淀)作用的要求,微晶白云岩和具原始结构的粒屑白云岩可能与地表—近地表的低温、小Ca/Mg值混合流体中相对快速的白云石沉淀作用有关,并形成了相对细的他形白云石;结晶白云岩(包括结构类似的过渡岩石类型、白云石胶结物)可能与埋藏的高温、大Ca/Mg值三叠纪海水或与之有关的海源流体中相对缓慢的白云石沉淀作用有关,并形成了相对粗的自形白云石.白云化流体的Ca/Mg值估算,可望为川东北地区三叠系飞仙关组优质储层白云岩的成因研究提供一些有价值的基础资料.     

柴西下干柴沟组湖相白云岩特征及成因分析

对柴达木盆地西部地区下干柴沟组湖相白云岩的岩石组构、矿物成分、主微量元素地球化学及碳氧同位素特征进行研究,并分析白云岩成因。研究区白云岩沉积环境为浅水相对封闭湖相环境,白云岩以泥晶白云岩为主,层状、块状分布,见藻云岩、膏质白云岩及颗粒云岩,有序度普遍较低。主量元素中Mg2+/Ca2+比值低,Mn、Fe、Na、Sr元素含量高,指示沉积环境水体盐度较高和相对封闭;微量元素中稀土元素具有轻稀土相对富集、Eu负异常特征,反映低温浅埋藏的成岩环境;氧同位素为较低的负值,反映整体咸化水体特征,碳同位素为较低的正值或负值,主要是受到大气水影响和生物的影响。研究认为白云石形成于准同生期相对封闭咸化环境中,白云石化流体中Mg2+主要来源于大气水的淋滤和深部卤水,少数来自于藻类的分解;Mg2+通过蒸发、盐类矿物沉淀而富集,富Mg2+流体通过回流渗透交代方解石发生白云石化。     

苏北盆地黄桥地区富CO_2流体对二叠系龙潭组砂岩储层的改造与意义

富CO_2流体-砂岩相互作用是砂岩储层次生孔隙的重要形成机制。苏北黄桥地区作为中国重要的CO_2气产区,富CO_2流体对上二叠统龙潭组砂岩储层的改造问题备受关注。为揭示富CO_2流体的作用特征及其对储层的影响,对黄桥地区典型钻井开展了系统的岩心描述和岩矿鉴定,并进行了微区原位观测和相关地球化学分析。结果表明,在靠近CO_2流体活动强烈的断裂带部位(特别是断层上盘),砂岩中碳酸盐胶结物基本溶蚀殆尽,仅存少量交代成因菱铁矿,同时钾长石类碎屑溶蚀非常强烈,并伴随高岭石等矿物沉淀,以及石英次生加大,还发育片钠铝石等指示高浓度CO_2作用的特征矿物,形成与CO_2流体作用相关的特征矿物组合(片钠铝石+高岭石+次生石英+菱铁矿);而在远离断裂的部位,受CO_2流体影响较弱,溶蚀作用也较弱,有较多的次生方解石沉淀,形成了以方解石+菱铁矿为主的自生矿物组合。前者次生孔隙发育,后者则更加致密。据此提出了深源断裂主控下与富CO_2流体作用相关的储层发育模式,为油气勘探和开发提供了新的思路。     

中国中西部盆地海相白云岩主要形成机制与模式

塔里木、四川及鄂尔多斯盆地是中国中西部海相白云岩的主要发育地区。三大盆地重点层系海相白云岩新近的成因研究表明,大规模准同生白云岩和埋藏成因白云岩的发育均与蒸发台地密切相关。蒸发台地中由海水浓缩形成的富Mg~(2+)卤水一方面在准同生期,通过蒸发泵和下渗机制交代碳酸钙沉积物而形成与蒸发岩共生的准同生白云岩,另一方面作为富含Mg~(2+)的地层孔隙水,在准同生-浅埋藏期乃至中、深埋藏期,通过侧向渗透、侧向与垂向压实排挤和垂向热对流机制与粗结构的碳酸钙沉积物发生交代反应,在蒸发岩系周边和上下形成广泛分布的埋藏成因白云岩。与热流体作用有关的白云石化主要依靠构造断裂、裂缝、不同级次的层序界面、孔洞层等输导体系发生,分布较局限。热流体云化常表现为对先期白云岩进行叠加改造而形成热水改造白云岩。热流体性质不一,可以是深埋藏混合热水、深部循环水、地幔深部的岩浆热液等。白云石(岩)的生物成因不仅表现为微生物作用导致白云石直接沉淀,还表现为生物的存在与活动为白云石化作用提供Mg~(2+)和云化流体通道。由微生物和宏观藻释放出Mg~(2+),在埋藏期对方解石进行交代是各种富含藻类的灰岩中部分白云石的重要形成机制。生物扰动可明显改善岩石的孔渗性,从而显著促进白云石化作用的发生。     

湖相白云岩成因模式及其储集性

湖相白云岩的成岩作用是非常规油气储层中非常活跃的话题,其成因模式以及储集性的研究对以碳酸盐岩为储层的油气勘探具有重要意义。通过综述前人关于湖相碳酸盐岩领域的研究成果,总结出以下几点:湖相白云岩成因模式主要有原生生物成因、准同生成因以及热液成因;湖相白云岩的储集空间类型包括以生物体腔孔为代表的原生孔、酸性流体作用下形成的溶蚀孔洞、白云石化作用或重结晶作用形成的晶间孔以及构造应力作用下形成的裂缝等4大类;其物性和孔隙结构分别受控于沉积环境及生物种类、酸性流体的溶蚀能力、白云岩化模式以及构造活动强度和岩石脆性等。以上研究成果可为湖相碳酸盐岩,乃至其他成因的碳酸盐岩物性影响因素以及油气地质意义研究提供借鉴参考。     

渤海湾盆地歧口凹陷沙河街组一段下亚段湖相白云岩及其与海相白云岩的差异

渤海湾盆地歧口凹陷古近系沙河街组一段下亚段湖相白云岩主要为颗粒白云岩和泥晶白云岩两大类,常与泥质岩成薄互层或与其他碳酸盐岩互层产出。该湖相白云岩有序度较低,类似于海相准同生白云岩;Mg/Ca值偏离正常的化学计量值,具有富钙特征,说明其为快速交代的产物;碳氧同位素、Z值分析结果则反映了湖水的咸化程度较高。根据低海平面期蒸发浓缩盐水在湖底形成密度层并向灰质沉积层中回流渗透导致白云石化发生的机理,建立了歧口凹陷沙一下亚段湖相白云岩的成因模式。湖相白云岩的分布特征及其与海相白云岩的差异分析表明,湖相白云岩具有分布面积小、白云石化作用不彻底等特征,油气储集性能较为局限。     

准噶尔盆地乌夏地区二叠系风城组云质岩类成因研究

准噶尔盆地乌夏地区风城组发育的云质岩类是一套特殊成因的、重要的油气储层。岩石学、扫描电镜能谱和稳定同 位素分析表明,发生白云岩化作用的母岩是火山凝灰物质,白云岩化的流体来自风城组干旱气候条件下形成的咸化滨浅湖 卤水以及下伏佳木河组和石炭系残留的富镁海水。凝灰岩中富含大量的斜长石,其中的富钙长石在二氧化碳参与下水解蚀变, 沉淀方解石（即方解石化）。后期富镁卤水渗滤早期形成的方解石,成岩交代形成白云岩。富镁流体运移受火山喷发产生的 热流驱动,产生热对流环。同时,乌夏断裂同生逆掩活动加快深层富镁流体上侵,并使流体在层间快速渗透、流动。构造 作用产生的裂缝或断裂对白云岩的形成及优质储层分布起到决定性控制作用。     

云南会泽超大型铅锌矿田热液白云岩的成因及地质意义

川滇黔铅锌矿集区会泽超大型铅锌矿田赋矿地层石炭系摆佐组碳酸盐岩广泛发育热液白云岩化。本文通过岩相学、主量和微量元素分析讨论了热液白云岩的成因、成矿流体来源及演化。热液白云岩包括热液流体交代早期微-细晶白云岩形成的细-中晶白云岩和交代灰岩形成的粗晶白云岩。细-中晶白云岩中的部分白云石在阴极发光下显示核边和环带结构特征,与早期成岩阶段形成的微-细晶白云岩具有相似的稀土元素含量和分布模式,继承了原岩稀土元素组成特征。粗晶白云岩呈厚层状和团块状产出,ΣREE含量相对较低,并且相对亏损轻稀土,表明稀土元素主要源于灰岩,热液流体(盆地卤水)活化迁移了部分轻稀土元素。近矿粗晶白云岩受MVT铅锌成矿流体交代,具有较高的Fe和Mn含量,白云石在阴极发光下呈亮红色,可能为矿化过程中与盆地流体有关的粗晶白云岩溶解再沉淀的产物。脉石方解石的Fe、Mn、ΣREE和Y含量相对较高,并显示轻-中稀土元素富集、Ce异常不显著的特征,暗示成矿流体(深循环酸性卤水)可能萃取了基底岩石中的稀土元素和成矿金属。脉石方解石的Y/Ho值与近矿粗晶白云岩相似,指示成矿流体与碳酸盐岩围岩也发生了反应。结合前人的研究,我们认为热液白云...     

The terrestrial fauna of the Late Triassic Pant-y-ffynnon Quarry fissures,South Wales,UK and a new species of Clevosaurus (Lepidosauria: Rhynchocephalia)

Pant-y-ffynnon Quarry in South Wales yielded a rich cache of fossils in the early 1950s, including articulated specimens of new species (the small sauropodomorph dinosaur Pantydraco caducus and the crocodylomorph Terrestrisuchus gracilis), but no substantial study of the wider fauna of the Pant-y-ffynnon fissure systems has been published. Here, our overview of existing specimens, a few described but mostly undescribed, as well as freshly processed material, provides a comprehensive picture of the Pant-y-ffynnon palaeo-island of the Late Triassic. This was an island with a relatively impoverished fauna dominated by small clevosaurs (rhynchocephalians), including a new species, Clevosaurus cambrica, described here from a partially articulated specimen and isolated bones. The new species has a dental morphology that is intermediate between the Late Triassic Clevosaurus hudsoni, from Cromhall Quarry to the east, and the younger C. convallis from Pant Quarry to the west, suggesting adaptive radiation of clevosaurs in the palaeo-archipelago. The larger reptiles on the palaeo-island do not exceed 1.5?m in length, including a small carnivorous crocodylomorph, Terrestrisuchus, and a possible example of insular dwarfism in the basal dinosaur Pantydraco.     

The effect of water on accessory phase solubility in subaluminous and peralkaline granitic melts

The solubilities of columbite, tantalite, wolframite, rutile, zircon and hafnon were determined as a function of the water contents in peralkaline and subaluminous granite melts. All experiments were conducted at 1035 °C and 2 kbar and the water contents of the melts ranged from nominally dry to approximately 6 wt.% H₂O. Accessory phase solubilities are not affected by the water content of the peralkaline melt. By contrast, solubilities are affected by the water content of the subaluminous melt, where the solubilities of all the accessory phases examined increase with the water content of the melt, up to 2 wt.% H₂O. At higher water contents, solubilities are nearly constant. It can be concluded that water is not an important control of accessory phase solubility, although the water content will affect diffusivities of components in the melt, thus whether or not accessory phases will be present as restite material. The solubility behaviour in the subaluminous and peralkaline melts supports previous spectroscopic studies, which have observed differences in the coordination of high field strength elements in dry vs. wet subaluminous granitic glasses, but not for peralkaline granitic glasses. Lastly, the fact that wolframite solubility increases with increasing water content in the subaluminous melt suggests that tungsten dissolved as a hexavalent species.     

Quaternary stresses revealed by calcite twinning inversion: insights from observations in the Savonnières underground quarry (eastern France)

Calcite samples were extracted both from the rock matrix and the superficial coating of a karstified fault plane of an underground quarry, located in the eastern border of the Paris basin. The karstification is dated as Quaternary. Analysis of mechanical calcite twinning reveals that only the calcite matrix has also undergone a compression trending WNW that can be attributed to the Mio-Pliocene alpine collision. Both coating and matrix have undergone a strike-slip regime with σ₁ roughly trending north–south, that could correspond to the regional present-day state of stress, a strike-slip compression rather trending NNW, modified by local phenomena. To cite this article: M. Rocher et al., C. R. Geoscience 335 (2003).     

HYDROGEOLOGY

正20141756 Chen Ruige(Mathematical College,China University of Geosciences,Beijing100083,China);Zhou Xun Numerical Simulation of Groundwater Level Fluctuation in a Coastal Confined Aquifer with Sloping Initial Groundwater Level Induced by the Tide(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(7),2013,p.1099-1104,6 illus.,16 refs.) Key words:confined water,groundwater level     

METAMORPHIC PETROLOGY

正20141408 Cai Jia(Institute of Geology,Chinese Academy of Geological Sciences,Beijing100037,China);Liu Fulai Petrogenesis and Metamorphic P-T Conditions of Garnet-Spinel-Biotitebearing Paragneiss in Danangou Area,Daqingshan-Wulashan Metamorphic Complex Belt(Acta Petrologica Sinica,ISSN1000-0569,CN11-1922/P,29(7),     

SERIALS

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GEOPHYSICAL EXPLORATION

正20142386An Guoying(China Aero Geophysical Survey and Remote Sensing Center for Land and Resources,Beijing 100083,China)Application of Satellite Remote Sensing in Regional Hydrogeological Investigation:Taking Cenozoic Strata in Wenquan Sheet(1∶250 000)of Karakoram Range as an Example(Geosci-     

QUATERNARY GEOLOGY & GEOMORPHOLOGY

正20141016An Chengbang(Key Laboratory of Western China’s Environmental Systems,Ministry of Education,Lanzhou University,Lanzhou 730000,China);Zhao Yongtao Lake Records during the Last Glacial Maximum from Xinjiang,NW China and Their Climatic Impli-     

PETROLEUM GEOLOGY

正20141538 Cao Qing(School of Earth Sciences and Engineering,Xi’an Petroleum University,Xi’an 710065,China);Zhao Jingzhou Characteristics and Significance of Fluid Inclusions from Majiagou Formation,Yichuan Huangling Area,Ordos Basin(Advances in Earth Science,ISSN1001-8166,CN62-1091/P,28(7),2013,p.819-828,7 illus.,3 tables,43 refs.)     

GEOCHEMISTRY

正20142002 Wei Hualing(Institute of Geophysical and Geochemical Exploration,Chinese Academy of Geological Sciences,Langfang065000,China);Zhou Guohua Element Content and Mineral Compositions in Different Sizes of Soil in Tongling Area,Anhui Province(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(11),2013,p.1861