西藏措勤盆地白垩系白云岩地球化学特征及其成因分析   总被引：4，自引：1，他引：3  

李亚林  黄永建  王成善  朱利东  王立成  魏玉帅 《岩石学报》2008,24(3)

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.  相似文献   

羌塘盆地中央隆起带南侧隆额尼-昂达尔错古油藏白云岩地球化学特征及成因意义   总被引：2，自引：1，他引：1  

刘建清  陈文斌  杨平  陈文西  付休根 《岩石学报》2008,24(6):1379-1389

以系统的岩石学及沉积相分析为基础,深入探讨了隆额尼-昂迭尔错古油藏白云岩及其伴生灰岩的地球化学特征,认为该区白云岩化作用主要集中在古地理相对高点的潮上高能带、潮坪环境及台地边缘藻丘礁三个沉积相带内,白云岩及伴生灰岩在地球化学特征方面表现出近岸及淡水作用的深刻影响,和前人关于混合水白云岩化作用气候和古地理条件的基本论断是一致的.淡水作用依据主要体现在:①白云岩及伴生灰岩中不溶残渣特征表现为潮湿的古气候环境;②与白云岩伴生灰岩中Sr、Na含量与美国密苏里、田纳西等地淡水成因灰岩Sr、Na含量十分相近;③灰岩及白云岩中微量元素B含量及Sr/Ba指数、Sr/Ca指数,常量元素中m、Fe/Mn指数均反映出该区碳酸盐岩形成于近岸的碳酸盐台地环境,灰岩及白云岩均曾受到淡水的深刻作用和影响.该区白云岩过程中除Sr有明显的带出现象,Na、K有明显带入现象,大部分元素仍保存了其原始的组成特点.  相似文献   

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     

Sobhi Nasir  Hamad Al-Saad  Abudlrazak Alsayigh  Oliver Weidlich 《Journal of Asian Earth Sciences》2008,33(5-6):353-365

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.  相似文献   

Petrological and geochemical constraints on diagenesis and deep burial dissolution of the Ordovician carbonate reservoirs in the Tazhong area,Tarim Basin,NW China     

《Marine and Petroleum Geology》2016

Deeply buried (4500–7000 m) Ordovician carbonate reservoirs in the Tazhong area, Tarim Basin, NW China show obvious heterogeneity with porosity from null in limestones and sweet dolostones to 27.8% in sour dolostones, from which economically important oils, sour gas and condensates are currently being produced. Petrographic features, C, O, Sr isotopes were determined, and fluid inclusions were analyzed on diagenetic calcite, dolomite and barite from Ordovician reservoirs to understand controls on the porosity distribution. Ordovician carbonate reservoirs in the Tazhong area are controlled mainly by initial sedimentary environments and eo-genetic and near-surface diagenetic processes. However, vugs and pores generated from eogenetic and telogenetic meteoric dissolution were observed to have partially been destroyed due to subsequent compaction, filling and cementation. In some locations or wells (especially ZG5-ZG7 Oilfield nearby ZG5 Fault), burial diagenesis (e.g. thermochemical sulfate reduction, TSR) probably played an important role in quality improvement towards high-quality reservoirs. C2 calcite and dolomite cements and barite have fluid inclusions homogenization temperatures (Ths) from 86 to 113 °C, from 96 to 128 °C and from 128 to 151 °C, respectively. We observed petrographically corroded edges of these high-temperature minerals with oil inclusions, indicating the dissolution must have occurred under deep-burial conditions. The occurrence of TSR within Ordovician carbonate reservoirs is supported by C3 calcite replacement of barite, and the association of sulfur species including pyrite, anhydrite or barite and elemental sulfur with hydrocarbon and ¹²C-rich (as low as −7.2‰ V-PDB) C3 calcite with elevated Ths (135–153 °C). The TSR may have induced burial dissolution of dolomite and thus probably improved porosity of the sour dolostones reservoirs at least in some locations. In contrast, no significant burial dissolution occurred in limestone reservoirs and non-TSR dolostone reservoirs. The deeply buried sour dolostone reservoirs may therefore be potential exploration targets in Tarim Basin or elsewhere in the world.  相似文献   

Dolomite microstructures between 390° and 700 °C: Indications for deformation mechanisms and grain size evolution     

《Journal of Structural Geology》2016

Dolomitic marble on the island of Naxos was deformed at variable temperatures ranging from 390 °C to >700 °C. Microstructural investigations indicate two end-member of deformation mechanisms: (1) Diffusion creep processes associated with small grain sizes and weak or no CPO (crystallographic preferred orientation), whereas (2) dislocation creep processes are related with larger grain sizes and strong CPO. The change between these mechanisms depends on grain size and temperature. Therefore, sample with dislocation and diffusion creep microstructures and CPO occur at intermediate temperatures in relative pure dolomite samples. The measured dolomite grain size ranges from 3 to 940 μm. Grain sizes at T_max >450 °C show an Arrhenius type evolution reflecting the stabilized grain size in deformed and relative pure dolomite. The stabilized grain size is five times smaller than that of calcite at the same temperature and shows the same Arrhenius-type evolution. In addition, the effect of second phase particle influences the grain size evolution, comparable with calcite. Calcite/dolomite mixtures are also characterized by the same difference in grain size, but recrystallization mechanism including chemical recrystallization induced by deformation may contribute to apparent non-temperature equilibrated Mg-content in calcite.  相似文献   

任丘油田雾迷山组白云岩储集层的渗透性试验研究   总被引：6，自引：0，他引：6       下载免费PDF全文

韩宝平 《地质科学》2000,35(4):396-403

运用815.02型电液伺服岩石力学试验系统对任丘油田雾迷山组18块白云岩岩芯的渗透性进行了测试.结果表明,溶蚀孔洞型中-亮晶藻屑白云岩和角砾岩,初始和峰值渗透率均较高(分别为143.10×10^-7-206.00×10^-7Darcy和386.80×10^-7-790.00×10^-7Darcy),而且破坏强度较低(35.8MPa-55.3MPa);裂隙型白云岩初始渗透率为1.48×10^-7-23.40×10^-7Darcy,峰值渗透率32.13×10^-7-202.10×10^-7Darcy;泥质白云岩和硅质白云岩,岩性致密,初始渗透率几乎为零,峰值渗透率66.00×10^-7-152.20×10^-7Darcy,而且其破坏强度最高可达107.50MPa.同时运用Amray 1000B型电子扫描显微镜和9310型微孔结构分析仪研究了空隙发育对渗透性的影响.  相似文献   

塔里木盆地古城地区奥陶系鹰山组白云岩特征及孔隙成因     

王珊  曹颖辉  杜德道  张亚金  刘策 《岩石学报》2020,36(11):3477-3492

奥陶系鹰山组白云岩是塔里木盆地的重点勘探领域,优质白云岩储层是制约其勘探的关键难题。本文在前人研究基础之上,结合多口井岩心薄片观察、同位素、微量元素等地球化学分析,对古城地区奥陶系鹰山组白云岩成因、孔隙成因以及储层主控因素进行了深入研究,认为古城地区鹰山组发育粉晶、粉细晶、细晶、细中晶、中晶、粗晶6种白云岩。粉晶和粉细晶白云岩碳、锶同位素分布范围均与同时期灰岩一致;氧同位素值与同时期白云石一致或偏正;锶元素含量相对较高;稀土元素与同时期灰岩分配模式相同。以上特征表明该类白云岩形成于蒸发海水环境,为准同生海源成因。细晶、细中晶、中晶及粗晶白云岩碳同位素值与同期灰岩总体一致;氧同位素值与正常海相白云石一致或偏负;锶同位素值与灰岩背景值一致或偏高;锶元素含量相对较低;大部分样品Eu正异常。以上特征揭示该类白云岩主要为中浅埋藏成因,并且叠加了早期淡水溶蚀及晚期埋藏-热液改造。孔隙成因分析表明高能缓坡滩是孔隙形成的物质基础、准同生暴露溶蚀是孔隙形成的关键、早期白云石化有利于孔隙的继承和保存,构造破裂和埋藏-热液溶蚀对孔隙起到有利的改造作用。白云岩规模优质储层受控于云化滩和断裂热液溶蚀改造,二者叠合之处为规模优质储层发育区。这一认识为研究区下一步勘探部署提供了重要依据。  相似文献   

Formation,diagenesis and palaeoenvironmental significance of upper Ediacaran fibrous dolomite cements     

Yongjie Hu  Chunfang Cai  Dawei Liu  Chelsea L. Pederson  Lei Jiang  Anjiang Shen  Adrian Immenhauser 《Sedimentology》2020,67(2):1161-1187

Neoproterozoic marine dolomite cements represent reliable, albeit complex, archives of their palaeoenvironment. Petrological and high-resolution geochemical data from well-preserved fibrous dolomite and pyrite in the upper Ediacaran (ca 551·1 to 548·0 Ma) Dengying Formation in south-west China are presented and discussed here. The aim of this research is to reconstruct the redox state of late Ediacaran shallow seawater and porewater in the Sichuan Basin using early marine diagenetic fabrics. Based on crystalline texture and axis, four basic types of fibrous dolomite cements formed penecontemporaneously in a microbialite reef setting at the platform margin: (i) bladed dolomites (replacement from a high-Mg calcite precursor); (ii) fascicular fast dolomites (replacement from an aragonitic precursor); (iii) fascicular slow dolomites; and (iv) radial slow dolomites. The latter two fabrics are considered direct marine porewater precipitates due to their length-slow character, cathodoluminescent zonation, and enriched copper and cobalt concentrations. Marine cements yield rare earth element and yttrium patterns comparable to modern seawater and represent a refined set of archive data relative to previously published bulk dolostones. Redox-sensitive elements and cathodoluminescence indicate that the fascicular fast dolomites formed in suboxic seawater, while fascicular slow and radial slow dolomites formed in euxinic marine porewaters. Microbial sulphate reduction during the formation of fascicular slow and radial slow dolomites is recognized by nanometre-scale spheroidal ankerite and sulphur-containing dolomite, and intergrown pyrite grains with U-shaped δ³⁴S transects. Data shown here suggest predominantly suboxic shallow late Ediacaran seawater and euxinic marine porewaters, with microbial activity promoting the direct precipitation of dolomite.  相似文献   

Sublimation of the Martian CO₂ Seasonal South Polar Cap     

Frédéric Schmidt  Bernard Schmitt  Francois Forget  Patrick Martin  Jean-Pierre Bibring  the OMEGA Team 《Planetary and Space Science》2010,58(10):1129-1138

The polar condensation/sublimation of CO₂, that involve about one fourth of the atmosphere mass, is the major Martian climatic cycle. Early observations in visible and thermal infrared have shown that the sublimation of the Seasonal South Polar Cap (SSPC) is not symmetric around the geographic South Pole.Here we use observations by OMEGA/Mars Express in the near-infrared to detect unambiguously the presence of CO₂ at the surface, and to estimate albedo. Second, we estimate the sublimation of CO₂ released in the atmosphere and show that there is a two-step process. From Ls=180° to 220°, the sublimation is nearly symmetric with a slight advantage for the cryptic region. After Ls=220° the anti-cryptic region sublimation is stronger. Those two phases are not balanced such that there is 22% ± 9 more mass the anti-cryptic region, arguing for more snow precipitation. We compare those results with the MOLA height measurements. Finally we discuss implications for the Martian atmosphere about general circulation and gas tracers, e.g. Ar.  相似文献   

川东北飞仙关组白云岩的主要类型、地球化学特征和白云化机制   总被引：17，自引：9，他引：8  

黄思静  佟宏鹏  刘丽红  胡作维  张雪花  郇金来  黄可可 《岩石学报》2009,25(10):2363-2372

四川盆地东北部蕴藏有丰富的烃类资源,三叠系飞仙关组的白云岩是最主要的储层和产层,这使得飞仙关组白云岩成为人们近年来高度关注的对象.按照结构,我们可以将飞仙关组白云岩分为三种端元类型:微晶白云岩、具原始结构的粒屑白云岩和结晶白云岩,在一个向上变浅的剖面旋回中,这三种白云岩分别位于旋回的顶部、上部和中下部.微晶白云岩和具原始结构的粒屑白云岩具有较高的锰含量和较低的包裹体均一化温度,白云化流体的δ~(18O) 值(从白云石的包裹体均一化温度和δ~(18O) 值反演,以下同)介于大气水和海水之间,反映这类白云岩形成于有大气水参与的相对开放的沉积-成岩环境中,蒸发泵作用(对于微晶白云岩)和混合水作用(对于具原始结构的粒屑白云岩)可能是其主要的形成机制;结晶白云岩(表现为好储层)具有很低的锰含量和较高的包裹体均一化温度,白云化流体的δ~(18O) 值显著高于早三叠世海水,表明这类白云岩形成于相对封闭的埋藏成岩环境,白云化流体具较高的温度和盐度,但到目前为止,还没有一个已有模式可以较好地解释这类白云岩的成因.  相似文献