白云石形成过程中的热力学与动力学基础及白云岩形成环境划分

CaMg(CO3)2在现代海水中是过饱和的,但是前人的研究发现在实验室标准状态下(25℃,1atm)无法从海水中直接沉淀出白云石,所以,白云石的形成不是一个单纯的热力学问题,而是一个动力学问题。依据白云石形成的热力学和动力学特征,将白云岩的形成环境划分为表生成岩环境与埋藏成岩环境。表生成岩环境按白云岩发育位置又分为:潮坪-澙湖蒸发环境、环礁潜流面与深?粱肪场B癫爻裳腋萘魈褰胩逑?的方式又分为:与裂缝相关的埋藏成岩、与缝合线相关的埋藏成岩、与岩溶相关的埋藏成岩和与渗透回流相关的浅埋藏成岩。分别对所划分的各成岩环境进行了详细的岩石学与地球化学特征分析与讨论。     

Geology and petrology of the Hormuz dolomite, Infra-Cambrian: Implications for the formation of the salt-cored Halul and Shraouh islands, Offshore, State of Qatar

Geological investigations of the Halul and the Shraouh islands, offshore Qatar, indicate that most of their calcareous rocks, which display abundant stromatolitic bedding, belong to the Infra-Cambrian Hormuz Series. Mineralogical, petrological, and geochemical analyses show that these calcareous rocks consist dominantly of dolomite and have formed in a reducing depositional environment. Faint laminations and small streaks of organic matter furnish evidence for the involvement of algal mats in their genesis and indicate their formation in an intertidal to supratidal setting. The Halul and Shraouh dolomites experienced extensive recrystallization and sulfatization during the emplacement of the Halul and Shraouh salt domes that form the cores of the islands. During mobilization and ascent of the salt, the dolomite recrystallized, and its Sr initial ratios were abnormally enhanced by the incorporation of ⁸⁷Sr from a source, which is more radiogenic than the attendant seawater at the time of the dolomite formation near the Proterozoic–Cambrian boundary. Geochemical analysis show that Si, Al, Ti Zr, and % of insoluble residue are highly correlative, suggesting the presence of detrital minerals such as rutile and zircon. A paleosabkha model may well agree with this chemical signature. However, the Infra-Cambrian age of the Hormuz rocks and the presence of stromatolitic layers containing organic materials in the studied rocks, suggest that organogenic dolomitization could be an alternative dolomitization model.     

塔西南地区海相碳酸盐岩勘探突破新领域:寒武系白云岩

塔里木盆地西南地区近期勘探方向集中在奥陶系的碳酸盐岩,但成效不大,勘探也陷入迟滞。基于钻井解剖及成藏关键要素分析认为:塔西南地区奥陶系碳酸盐岩不仅储层欠发育,而且油气充注欠佳;中下寒武统白云岩储层优于奥陶系石灰岩储层,而且盐膏层盖层发育,基底卷入断裂欠发育,盐下油气保存条件较优越,有利于形成大规模的寒武系自生自储油气藏;塔西南古隆起北斜坡长期稳定发育的古构造是勘探突破的主攻方向,和田河气田周缘的古隆起斜坡区中下寒武统成藏条件优越,有望获得新的大发现。     

Dissolution Kinetics of Dolomite in Water at Elevated Temperatures

Kinetic experiments of dolomite dissolution in water over a temperature range from 25 to 250°C were performed using a flow through packed bed reactor. Authors chose three different size fractions of dolomite samples: 18–35 mesh, 35–60 mesh, and 60–80 mesh. The dissolution rates of the three particle size samples of dolomite were measured. The dissolution rate values are changed with the variation of grain size of the sample. For the sample through 20–40 mesh, both the release rate of Ca and the release rate of Mg increase with increasing temperature until 200°C, then decrease with continued increasing temperature. Its maximum dissolution rate occurs at 200°C. The maximum dissolution rates for the sample through 40–60 mesh and 60–80 mesh happen at 100°C. Experimental results indicate that the dissolution of dolomite is incongruent in most cases. Dissolution of fresh dolomite was non-stoichiometric, the Ca/Mg ratio released to solution was greater than in the bulk solid, and the ratio increases with rising temperatures from 25 to 250°C. Observations on dolomite dissolution in water are presented as three parallel reactions, and each reaction occurs in consecutive steps as

西藏措勤盆地白垩系白云岩地球化学特征及其成因分析

通过岩石学、阴极发光、同位素和岩石地球化学等方法对青藏高原措勤盆地郎山组白云岩进行了成因研究.研究表明本区白云岩岩石类型主要为中-细晶白云岩和灰质白云岩,阴极发光主体呈棕红-暗棕红色光,并且具有高的有序度和低的CaCO3摩尔含量.地球化学分析表明岩石U含量(1.5～45.2×10-5)和U/Th(0.89～68)明显高于一般的海相碳酸盐;高的87Sr/86Sr(0.710092～0.711719)同位素比值,表明在成岩过程中Sr的加入.白云岩δ18O值为-15.13‰～-6.94‰,平均-8.7‰,δ13C为-0.56‰～2.53‰,平均1.7‰,反映出白云岩具有较高的盐度指数Z值(118.0～128.0)和成岩温度(50.77～95.95℃),表明形成于超成浓缩海水环境并具较高的成岩温度.综合分析认为本区白云岩属于埋藏成因,并在后期由于淡水加入发生去白云化作用.     

油气田典型岩石三轴压缩变形破坏与声发射活动特征——四川盆地震旦系白云岩及页岩的破坏过程

随着二氧化碳地质封存、深部地热开采、地下储气库建设、页岩气开发、二次驱油/驱气等工业应用的快速发展,与地下流体注入有关的诱发地震活动呈现一定的增加趋势.利用声发射实验观测油气田典型岩石在三轴压缩条件下变形破坏过程与声发射活动特征,对研究注水诱发地震过程有着重要意义.本文利用四川盆地现场采集的震旦系白云岩及页岩,采用实验室声发射技术观测研究岩石三轴压缩变形破坏过程中地震波速度等物性参数及声发射事件时空分布特征.实验结果表明:震旦系白云岩及页岩在变形破坏过程中均有一定的声发射活动.根据声发射定位结果,声发射主要集中在破坏前后的较短时间内,页岩的层理面为结构弱面,控制最终破坏面的形态及声发射特征.根据应力-应变结果,白云岩在压缩的后期阶段有一定的扩容现象,但页岩在整个压缩阶段均没有明显扩容现象.研究结果表明四川盆地较古老的白云岩及页岩具有脆性破坏特征,地下流体注入容易诱发微震活动,形成裂缝,有利于页岩气压裂开采.微震活动有利于监测裂缝的发生发展,但同时在页岩气开发及二氧化碳地质封存时应采取相应的预防控制措施进行安全合理的储盖层管理,避免灾害性诱发地震的发生.     

山东省枣庄市侯孟熔剂用白云岩矿地质特征及开发利用前景

侯孟熔剂用白云岩矿位于枣庄市台儿庄区张山子镇东南,区内圈定了1个矿体,呈层状产出,矿体赋存于震旦纪土门群石旺庄组地层中,受地层层位控制,产出稳定.矿物成分主要为白云石,矿石结构以泥微晶结构为主,块状构造,矿石自然类型为灰色细晶白云岩.该矿床为滨海泻湖相沉积的层状石灰岩经白云岩化形成的交代型白云岩矿床,矿石主要有用组分含...     

Thermochemical sulphate reduction in the Upper Devonian Cairn Formation of the Fairholme carbonate complex (South-West Alberta, Canadian Rockies): evidence from fluid inclusions and isotopic data

The Fairholme carbonate complex is part of the extensively dolomitized Upper Devonian carbonate reefs in west-central Alberta. The studied formations contain moulds (up to 10 cm in diameter), which are filled partially with (saddle) dolomite, quartz and calcite cements. These cements precipitated from a mixture of brines that acquired high salinity by dissolution of halite and brines derived from evaporated sea water. The fluids were warm (homogenization temperature of primary fluid inclusions of 76 to 200 °C) and saline (20 to 25 wt% NaCl equivalent) and testify to thermochemical sulphate reduction processes. The latter is deduced from S in solid inclusions, CO₂ and H₂S in volatile-rich aqueous inclusions and depleted δ¹³C values down to −26‰ Vienna Pee Dee Belemnite. High ⁸⁷Sr/⁸⁶Sr values (0·7094 to 0·7110) of the cements also indicate interaction of the fluids with siliciclastic sequences. The thermochemical sulphate reduction-related cements probably formed during early Laramide burial. Another (younger) calcite phase, characterized by depleted δ¹⁸O values (−23·9‰ to −13·9‰ Vienna Pee Dee Belemnite), low Na (27 to 37 p.p.m.) and Sr (39 to 150 p.p.m.) concentrations and non-saline (∼0 wt% NaCl equivalent) fluid inclusions, is attributed to post-Laramide meteoric water.     

贵州云台山岩石特征及其峰丛—峰林地貌成景意义

云台山峰丛—峰林的成景岩石主要为白云岩和（含）灰质白云岩,灰岩仅在峰丛—峰林基坐部分见及。成景岩石结构主要为颗粒结构和晶粒结构,且颗粒结构（颗粒和填隙物）、晶粒结构（晶粒白云石和少量泥质、少量陆源碎屑）在空间上各自顺层偏集呈层分布。此外,白云岩孔隙发育,孔隙类型有孔洞和裂隙两种,区内构造运动改造了原来的孔隙,加宽、加深其横纵向展布,增强孔隙的连通性,使原来较细级孔隙相互贯通成较大一级孔隙网,在水的溶蚀及机械崩塌等地质作用下成景。     

塔里木盆地中央隆起中部中下奥陶统白云石类型及形成机理

根据岩心及薄片观察,按照矿物晶体的大小、形状以及自形程度的差异,将塔里木盆地中央隆起中部中下奥陶统碳酸盐岩地层中的白云石分为6种类型,包括泥微晶白云石、粉—细晶自形—半自形漂浮状白云石、粉—细晶半自行—他形白云石、粉—细晶自形(环带)白云石、细—粗晶他形白云石、粗晶鞍形白云石。综合不同类型白云石的结构特征、碳氧锶同位素值、阴极发光等特征,认为中下奥陶统白云石主要由三种成岩作用形成:泥微晶白云石主要是在准同生期由回流白云石化形成;大部分粉—粗晶白云石是在埋藏期由埋藏白云石化形成,其中浅埋藏期是大规模白云石化的阶段;粗晶鞍形白云石主要由与高温热液活动相关的热液白云石化形成。