鄂尔多斯盆地南缘铜川地区三叠系延长组油页岩中“钙质结核”的成因初探          下载免费PDF全文

马　瑶李文厚  刘江斌李智超 《地质科学》2018,(2):458-469

在鄂尔多斯盆地南缘铜川地区野外露头三叠系延长组长7段油页岩中发现了一些“钙质结核”,野外露头中呈层状发育于长7段油页岩中,形态为“透镜状”、“椭球状”、“飞碟状”,直径大小约为10～70 cm。为探明其岩石类型和主要岩石组分,运用显微镜薄片鉴定、电子探针实验、能谱分析等方法,对结核体进行岩石学特征分析。在此基础上,对其成因进行初步探讨。岩石学特征显示,霸王庄和宜君套滩剖面的“钙质结核”主要成分为重结晶方解石和晶粒方解石,具“球粒状”结构,岩石类型为灰岩;瑶曲聂家河剖面结核体主要岩石类型为泥-粉晶白云岩。分析认为这些“钙质结核”其野外产状和岩石成分,符合热水沉积碳酸盐岩和受热液活动影响的特征,并且铜川地区在长7期具备热液活动的条件。初步认为这些“钙质结核”为湖底热液活动成因的湖相碳酸盐岩。  相似文献   

Tectonics and Topography of the Tibetan Plateau in Early Miocene   总被引：1，自引：0，他引：1  

WU Zhenhan  YANG Yan  Patrick J. BAROSH  WU Zhonghai  ZHANG Yaoling 《《地质学报》英文版》2014,88(2):410-424

Early Miocene stratigraphy, major structural systems, magmatic emplacement, volcanic eruption, vegetation change and paleo-elevation were analyzed for the Tibetan Plateau after regional geological mapping at a scale of 1:250,000 and related researches, revealing much more information for tectonic evolution and topographic change of the high plateau caused by Indian-Asian continental collision. Lacustrine deposits of dolostone, dolomite limestone, limestone, marl, sandstone and conglomerate of weak deformation formed extensively in the central Tibetan Plateau, indicating that vast lake complexes as large as 100,000–120,000 km2 existed in the central plateau during Early Miocene. Sporopollen assemblages contained in the lacustrine strata indicate the disappearance of most tropical-subtropical broad-leaved trees since Early Miocene and the flourishing of dark needleleaved trees during Early Miocene. Such vegetation changes adjusted for latitude and global climate variations demonstrate that the central Tibetan Plateau rose to ca. 4,000–4,500 m and the northeastern plateau uplifted to ca. 3,500–4,000 m before the Early Miocene. Intensive thrust and crustal thickening occurred in the areas surrounding central Tibetan Plateau in Early Miocene, formed Gangdise Thrust System(GTS) in the southern Lhasa block, Zedong-Renbu Thrust(ZRT) in the northern Himalaya block, Main Central Thrust(MCT) and Main Boundary Thrust(MBT) in the southern Himalaya block, and regional thrust systems in the Qaidam, Qilian, West Kunlun and Songpan-Ganzi blocks. Foreland basins formed in Early Miocene along major thrust systems, e.g. the Siwalik basin along MCT, Yalung-Zangbu Basin along GTS and ZRT, southwestern Tarim depression along West Kunlun Thrust, and large foreland basins along major thrust systems in the northeastern margin of the plateau. Intensive volcanic eruptions formed in the Qiangtang, Hoh-Xil and Kunlun blocks, porphyry granites and volcanic eruptions formed in the Nainqentanglha and Gangdise Mts., and leucogranites and granites formed in the Himalaya and Longmenshan Mts. in Early Miocene. The K2O weight percentages of Early Miocene magmatic rocks in the Gangdise and Himlayan Mts. are found to increase with distance from the MBT, indicating the genetic relationship between regional magmatism and subduction of Indian continental plate in Early Miocene.  相似文献   

Uranium distribution in the lacustrine calcareous clastic-evaporite sequence in the western Qaidam Basin,and implications for U behavior in concentration of closed water     

YANG Yibo  FANG Xiaomin  LI Minghui  APPEL Erwin  ZHANG Weilin  LIU Xiaoming 《《地质学报》英文版》2014,88(Z1):168-169

正Uranium(U)provides especially useful information for reconstructing paleoredox conditions due to its unique geochemical properties and behavior in supergene environments.The proxy potential under suboxic-oxic  相似文献   

A 1,100-year palaeoenvironmental record inferred from stable isotope and trace element compositions of ostracode and plant caryopses in sediments of Cattle Pond,Dongdao Island,South China Sea   总被引：1，自引：0，他引：1  

Xiaodong Liu  Liguang Sun  Gangjian Wei  Yuhong Wang  Hong Yan  Kexin Liu  Xiaohong Wu 《Journal of Paleolimnology》2008,40(4):987-1002

Abundant ostracode valves (Cyprinotus cingalensis) and caryopses of Urochloa paspaloides, a terrestrial grass, were well preserved in the lacustrine sediments of the Cattle Pond on Dongdao Island, South China Sea. Oxygen and carbon isotopes, and elements (Ca, Mg) were analyzed on ostracode valves and plant caryopses in this study. The δ¹⁸O_ostracode and δ¹³C_ostracode exhibited a positive and statistically significant correlation, and showed a decreasing trend toward the top of sediment sequence with some fluctuations, indicating a gradual increase in effective moisture. The Mg/Ca ratios in the ostracode shells, generally used as a proxy for salinity changes in lake water, showed a trend toward lower values in the upper samples, reflecting a gradual decrease of salinity in the lake. The δ¹³C_org values in the plant caryopses of the upper 14 cm of sediment have lower values than those in the bottom sediments, suggesting less water and salinity stress. These results indicate increasing effective moisture and rainfall intensity over the past ∼1,100 years on Dongdao Island.  相似文献   

The gravel fans of upper Glen Roy,Lochaber, Scotland: their importance for understanding glacial,proglacial and glaciolacustrine dynamics during the Younger Dryas cold period in an Atlantic margin setting     

《Proceedings of the Geologists' Association. Geologists' Association》2017,128(1):83-109

Over the past 200 years significant research effort has gone into explaining the origin of the obvious former shorelines in Glen Roy (the so-called “Parallel Roads”). The large gravel deposit at the mouth of Glen Turret has attracted similar interest, but a solution to its origin and age remains contested: the same applies to the associated gravel fans in upper Glen Roy. This paper presents the results of systematic mapping and instrumental levelling of these features and new evidence from two previously unrecorded gravel fans in the nearby Allt Chonnal valley. Interpretation of altitudinal and lithofacies data indicates that all the fans (including the one at the mouth of Glen Turret) were deposited in a series of ice-dammed lakes during the Loch Lomond Stadial (Younger Dryas). The largest gravel fans were deposited in the shallow lake heads of the 260 m, 325 m and 350 m lakes in upper Glen Roy, infilling these areas to the extent that deposition was in part subaerial. The absence of foreset bedding from the deposits is explained by the relatively shallow depth of lake waters, which inhibited development of classic Gilbert-type deltas and encouraged Hjulström-type fans. The previous assumption that gravel deposition into the 325 m and 350 m lakes was relatively limited is shown to be erroneous. The Allt Chonnal gravel fans, deposited into these lakes, have an estimated combined volume of 6,000,000 m³ deposited in about 200 years. Significant gravel deposition into these former lakes continued at least until glaciers started to retreat in Glen Roy. When glacier retreat began, gravel deposition was reduced by over 85%. This research also concludes that the glacier which deposited the Turret fan emanated from Glen Gloy, supplied not only by ice from the south but also from ice that spilled into Glen Gloy from the adjacent Great Glen. The Loch Lomond Stadial (LLS) ice cap mapped in the Monadhliath Mountains was connected to the west Highland ice cap, which at the time filled the Great Glen. Regional equilibrium line altitude (ELA) estimates, based solely on the Monadhliath LLS ice cap evidence, may therefore be altitudinally too high.  相似文献   

Re-sedimented deposits in the rift section of the Campos Basin     

《Marine and Petroleum Geology》2017

An integrated petrologic-sedimentologic-stratigraphic-seismic study of the Lagoa Feia Group, rift section of the Campos Basin, has shown that rift sedimentation was dominantly intrabasinal (carbonate and stevensitic deposits), with siliciclastic deposits restricted to the proximity of graben border faults. The bivalve bioclastic rudstones (“coquinas”) that constitute the rift reservoirs show commonly limited abrasion of the bioclasts, and were deposited both on basement highs and lows throughout the rift section. Although in situ deposits of stevensite ooids and peloids occur dominantly at the base of the succession, these particles are ubiquitous to the entire rift section, mixed in variable proportion with siliciclastic and carbonate sediments. The environmental conditions required for the formation of stevensite and the growth of bivalves are mutually exclusive, as stevensite forms only at pH greater than 10, while bivalves cannot tolerate pH greater than 9. The common mixture of well-rounded basaltic rock fragments with angular, granitic-gneissic rock fragments and feldspars in the sandstones and conglomerates indicates recycling of epiclastic deposits from the early rift section, combined with first-cycle contribution from the plutonic basement. The studied cores show no evidence of subaerial exposure, and there is a lack of bioturbation, suggesting harsh environmental conditions. The rift deposits are dominantly massive or faintly-laminated, with diffuse facies boundaries. Structures indicative of unidirectional or oscillatory flow are subordinate. Integration of seismic, sedimentologic and petrographic evidence indicates that the Campos Basin rift section is formed mostly by re-sedimented gravitational deposits. The onset of the rift sedimentation occurred in synformal depressions, where bivalve banks or stevensite ooids were formed in shallow lacustrine environments under variable alkalinity conditions. With the development of half-grabens and concentration of the tectonic activity along the border faults, recurrent tectonic events promoted the mixing and gravitational re-deposition of stevensitic, clastic and bioclastic sediments in deeper, fault-bounded troughs. Large-scale units, hundreds of meters thick, were generated by major tectonic events, whereas compositional variations in the scale of meters were possibly a product of lake-level climatic fluctuations. Thus, due to syn-rift and mainly to post-rift erosion (the Neo-Aptian unconformity), the preserved rift section of the Lagoa Feia Group comprises mostly sediments deposited in the central troughs of the half-graben structures. Marginal sediments were extensively eroded and re-sedimented as gravity-driven mixed deposits. This new model, constructed form the integration of seismic, stratigraphic, sedimentologic and petrologic data, diverges substantially from the presently accepted model for the sedimentation of the rift section, opening new possibilities for the exploration of Campos Basin, as well as of similar settings, as in the adjacent Santos Basin.  相似文献   

Stable isotope characterisation of co-existing carbonates from the Holocene Gallocanta lake (NE Spain): palaeolimnological implications     

A. Luzón  M. J. Mayayo  A. Pérez 《International Journal of Earth Sciences》2009,98(5):1129-1150

The sedimentary succession of Gallocanta lake, a closed saline lake located in the Iberian Range (NE Spain), documents two successive lacustrine stages: (1) brackish lake stage and (2) shallow saline lake stage. The saline stage corresponds to the present-day situation in which the lake water properties are mainly controlled by a strongly negative annual water balance. The carbonates of the brackish lake stage have relatively constant δ¹⁸O values, however, they are rather high (δ¹⁸O_Do = 2.4‰ and δ¹⁸O_Cc = 4.5‰ mean values) suggesting a hydrologically closed lake with a long residence time of the waters. δ¹⁸O values of carbonates from the saline stage vary greatly, and are lighter than in the previous stage (δ¹⁸O_Do = 0.5‰, δ¹⁸O_Cc = −0.7‰, δ¹⁸O_Mgs = −2.3‰ mean values). These carbonates also precipitated in a hydrologically closed lake, but in equilibrium with a lake water of more variable isotopic composition. The δ¹³C values for carbonates of both stages reflect a mixing of different pools of carbon, but during saline stage δ¹³C values have been more controlled by the equilibrium of the lake waters with atmospheric CO₂. During the current stage, calcite and dolomite precipitate in Gallocanta lake mainly during spring and summer, although dolomite precipitation is more favoured towards the summer. Magnesite precipitates at the beginning of autumn, when the first rainfall re-dissolves the saline surface crust, producing saline waters with a high Mg²⁺ content. The isotopic composition of lake waters sampled in 2005 are far higher than those calculated from the carbonates. It is considered that this could be due to two factors: either because there have not been many extremely dry years (like the year 2005) during the development of the lake, or because the physical and chemical characteristics of the lake waters in such conditions are not appropriate for the development of these minerals.  相似文献   

陆相断陷湖盆T-R层序的特点及其控制因素--以东营凹陷古近系沙河街组三段层序地层为例   总被引：23，自引：13，他引：10       下载免费PDF全文

操应长  姜在兴  夏斌  杨伟利 《地质科学》2004,39(1):111-122

一般认为经典层序的湖(海)平面变化轨迹为正弦曲线,且可分出低位稳定、上升、高位稳定和下降4个阶段。按照Vail的层序地层学理论,每个三级层序由3个体系域组成,目前也有人认为划分出4个体系域更合适。但在断陷湖盆中,发育了一种特殊的层序,其湖平面变化呈折线,仅可分出上升阶段(T)和下降阶段(R),缺失稳定阶段,我们将此类层序称为T-R层序。潮湿气候条件下的幕式构造运动和沉积物快速充填是T-R层序形成的关键。层序发育的早期阶段,幕式构造运动产生新生可容空间,决定了T旋回的发育,形成了以深水泥岩、页岩等沉积为特征的湖侵域;晚期阶段,沉积物快速充填减少可容空间,决定了R旋回的演化,形成了以前积式砂体为特征的湖退域。T-R层序与油气勘探关系密切,湖侵域烃源岩发育,湖退域储层发育,并具有良好的生储盖组合条件。  相似文献   

Characteristics of Carbonate Reservoir and Its Forming Conditions in Continental Lake Basin of China     

Jiangmin Du  Pengyu Long  Peng Yang  Qiang Ding  Xiuyin Hu  Wei Li  Yang Bai  Jun Sheng 《地球科学进展》2020,35(1):52-69

For decades of exploration, geologists have made great achievements in the exploration of lacustrine carbonate rocks. By dissecting four typical cases of lacustrine carbonate rocks, such as Lucaogou Formation of Permian in Junggar Basin, Da'anzhai Section of Jurassic in Sichuan Basin, Cretaceous in Yin'e Basin and Oligocene in Qaidam Basin, the reservoir characteristics, hydrocarbon generating capacity and reservoir forming model of source rocks were analyzed. The results show that: \mathrm{①} Lacustrine carbonate reservoirs are generally dense, with nano-micron reservoir space as the main reservoir space, including dolomite intergranular pore, organism cavity and accumulation pore, micro-fracture system and its corrosion expansion pore. Saline environment is beneficial to dolomitization and can improve the reservoir capacity of lacustrine carbonate rocks, but most of the permeability is less than 0.1 mD. \mathrm{②} Lacustrine carbonate rocks have not only reservoir capacity, but also can be used as source rocks. The abundance of organic matter is not high and the maturity is generally low. However, dispersed soluble organic matter in source rocks can generate and expel hydrocarbons in large quantities at low maturity stage, which has high liquid hydrocarbon yield. \mathrm{③} Oil and gas reservoirs are characterized by "high initial production, large reduction of production and long-term low and stable production", and are typical "fracture-pore" reservoirs. Fracture networks provide migration pathways in the process of primary migration and accumulation of oil and gas in geological history and oil and gas exploitation nowadays. \mathrm{④} Oil and gas reservoirs are "continuous" unconventional reservoirs, which often form regional oil and gas field groups together with conventional reservoirs in adjacent areas. The research results lay a theoretical foundation for re-evaluating the exploration potential of lacustrine carbonate rocks.  相似文献   

湖相碳酸盐岩烃源岩有机显微组分分类及其岩石学特征——以酒西盆地为例   总被引：4，自引：0，他引：4  

涂建琪  陈建平  张大江  程克明  陈建军  杨智明 《岩石学报》2012,28(3):917-926

酒西盆地主力烃源岩为下白垩统下沟组和赤金堡组暗色半深湖相-深湖相的白云质泥岩和泥质白云岩,是典型的湖相碳酸盐岩烃源岩。通过对酒西盆地下白垩统二百多块湖相碳酸盐岩烃源岩详细的有机岩石学研究,解剖了湖相碳酸盐岩烃源岩中有机质的赋存形式,揭示了藻纹层为有机质纹层的主要发育形式,其与富泥晶白云石纹层和富粘土纹层构成湖相碳酸盐岩烃源岩特有的"三元式纹层"沉积结构,系统总结了各显微组分的光性、成因、生烃性及分布规律,提出了以全岩和干酪根为基础的湖相碳酸盐岩有机显微组分分类方案,首次鉴定出对酒西盆地油气有贡献的主要生烃组分为腐泥无定形体、腐殖无定形体以及浮游藻类体、孢粉体、壳屑体五种有机显微组分。  相似文献