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91.
A study on two closed salt lake basins, Tal Chapar and Parihara in the eastern margin of the Thar Desert, Rajasthan, was carried
out to unravel late Quaternary geomorphic evolution of these saline lakes. Both lakes are elliptical in shape bordered by
stabilised dunes, and are oriented in a NE-SW direction, i.e., in the direction of the prevailing summer monsoon wind. Both
lakes have been formed in the wind-shadow zones of isolated hills of Precambrian quartzite. Our study indicates that the late
Quaternary sediments in the lakes began with the cyclic deposition of laminated fine silt layers (0.5 m thick), rich in organic
matter, alternating with ripple cross-bedded sand layers (each ∼1.5–2 m thick). Sand layers that are moderately sorted are
separated by laminated silt-clay layers with gypsum/calcite and this unit occurs in the upper most 4 m sequence in deeper
sections. The presence of gypsum crystals within the laminated sediments suggests a high concentration of Ca in the inflowing
water.
At Parihara Lake the organic carbon-rich sediments at 95 cm depth was dated to 7,375 + 155/−150 year BP. At Tal Chapar radiocarbon
dates of 7,190 + 155/−150 and 9,903 + 360/−350 was obtained from the sediments rich in organic carbon occurring at a depth
of 1.35 m and 1.80 m, respectively. The study reveals strong hydrologic oscillations during the past ∼14,000 year BP (13,090 + 310/−300 year
BP).
Quaternary geomorphic processes, especially the strong aeolian processes during dry climatic phases, played a major role in
the formation of the lake basins, as well as the fringing linear dunes. Geochemical and mineralogical analyses of the lacustrine
sediments, supported by radiocarbon dates indicate the existence of an ephemeral lake earlier than ∼13,000 year BP as sediments
began to be deposited in a lacustrine environment implying sustained runoff in the catchments. A freshwater lake formed between
9,000 year and 7,000 year BP. The lake dried periodically and this strong fluctuating regime continued until about ∼7,000 year
BP. Mid-Holocene was wet and this was possibly due to higher winter rains A saline lake existed between 6,000 year and 1,300 year
BP and finally present day semi arid conditions set in since 1,200 year BP. Remnants of a habitation site (hearth and charred
bones) on stabilised dune at Devani near Tal Chapar were dated to 240 ± 120 year, while that at Gopalpura was dated to 335 ± 90 year.
These historical sites on stabilised dunes were, according to the local accounts, settlements of people who used the lake
brine for manufacturing salt. 相似文献
92.
川滇震旦系灯影组葡萄石的沉积环境 总被引:1,自引:0,他引:1
川镇地区震旦系地层发育,其中,灯影组含葡萄石。本文记述云南宜良九乡震旦系剖面以及川滇地区震旦系葡萄石,并探讨其沉积环境。 相似文献
93.
通过地面调查及钻井地质资料分析,对柴达木盆地干柴沟地区第三系湖盆边缘斜坡带沉积体系构成进行分析研究,该体系主要由扇三角洲沉积体系,水下洪积扇-近岸浊流沉积体系,辫状河三角洲沉积体系,常态湖三角洲沉积体系和湖泊沉积体系组成。对其成因地层格架及湖盆充填模式进行了探讨分析。 相似文献
94.
95.
钠长石岩分布不太广泛 ,研究程度较低。通过研究 ,本文将钠长石岩分为接触带型、层状型、顺层角砾岩型、脉型及岩体型 5类。其中以层状钠长石岩型分布较广 ,意义较大。层状及与之紧密相伴的顺层角砾状钠长石岩有特定的矿物组合、化学成分及岩石组合 ,层状及角砾状钠长石岩产在一定的地层层位中 ,形成于特殊的沉积环境 ,且有一定的时空分布规律 ,并伴有特殊的 Au,Cu,Pt- Zn- Ag,Ba,Fe,B等矿产。因此笔者认为钠长石岩系特定地质条件下的产物。目前对其成因有岩浆岩、热液交代 +充填、热水沉积等不同认识 ;热水来源也有岩浆水、地下水、变质水等多种观点。本文作者认为层状及角砾状钠长石岩为热水沉积形成的 ,成岩流体属含 Na- Mg- Si- Al± Fe,Ba,B的 HCO3- ,CO32 - 碱性溶液 ,成岩物质来自基底富钠岩石。 相似文献
96.
硅灰石表面改性实验研究 总被引:18,自引:0,他引:18
实验以湖北大冶硅灰石为原料,初步探讨了硅灰石表达改性的工艺条件。经沉降体积法、表面接触角、红外光谱等方法检测和填充橡胶试验证实,硅灰石得到了改性且其填充性能有明显的提高。 相似文献
97.
回顾了沉积混杂碉的研究历史,指出了沉积混杂岩的分布位置和形成机制,重新给出了沉积混杂岩的定义,依据沉积混杂作用的不同方式划分为四种类型,重力垮塌和重力汉混杂作用,冰筏混杂作用,古喀斯特混杂作用和损落混杂作用,最后探讨了海底混杂岩块的来源和搬运方式。 相似文献
98.
湘西南高涧群的地球化学特征及其意义 总被引:3,自引:0,他引:3
湘西南高涧群主要是一套浅变质沉积碎屑岩系,由变质泥岩、板岩和变质粉砂岩组成,原岩颗粒小。变质作用对岩石化学成分没有大的改变,岩石具有相近的风化蚀变指数(平均CIA=75)风化蚀变矿物主要为伊利石-白云母-蒙脱石组合。主要化学成分反映沉积物来源于中性和基性火成岩区。浅变质沉积岩中大多数微量元素亏损,元素Cu,Zn,Co,Ti,Cr等在研究区的南部和北部具有相似的共生组合。并且稀土元素的分布模式基本相同,稀土的总量与岩性有关。上述特点显示了高涧群沉积物来源相同,亲石元素共生组合相似;Au,Ag,As,Sb,Sr,Ba等存在一定的分异,Ba/Co比值,Sr/Ba比值和δCe值表明,它是主要在浅深海-深海相还原环境下的产物。 相似文献
99.
Petroleum inclusions in sedimentary basins: systematics, analytical methods and applications 总被引:21,自引:0,他引:21
Fluid dynamics in sedimentary basins is of tremendous interest, both from a scientific and an economic point of view. Integration between fluid inclusion and present-day fluid data provides the time aspect necessary for reconstruction of fluid flow paths, and can be used for mapping fluid dynamics both on a regional basin scale or on the more local scale of petroleum reservoirs. This paper presents a review of analytical and modelling methods for petroleum in fluid inclusions. Essentially, four types of data for petroleum inclusions can be established through analysis and modelling: (1) textures (which give indirect information of the time aspect), (2) fluid composition, (3) fluid properties and (4) pressure–temperature of trapping. During the last decade, development of analytical methods for determination of inclusion fluid compositions has taken place. Traditional correlation studies for characterisation of maturity and source facies may now therefore include fluid inclusion data. The development has also been directed towards an improved understanding of the physical properties of petroleum inclusions. Although these methods are in their early stages concerning precision and accuracy, data necessary for fluid flow modelling, such as fluid densities, viscosities, pressure and temperature, can be estimated. 相似文献
100.
东安牛头寨地区锑矿床控制因素及成因探讨 总被引:1,自引:0,他引:1
锑矿床严格受构造控制,表现出逐级控矿特征:区域性F1断裂、牛头寨复式背斜及北北东、北北西、北西向次级断裂,分别控制着锑矿带、锑矿床的空间展布及锑矿脉的形态、产状与规模。地层岩石建造对成矿的控制,主要表现在赋矿地层中的白云岩、硅质岩等易碎裂,为矿液的运移提供了有利的通道。部分含矿地层的Sb高丰度,还可能成为矿提供了矿源。已有的研究表明,锑矿床的硫同位素组成具有岩浆硫特征,并混入了部分围岩沉积硫。石英的氢氧同位素组成反映出岩浆流体与变质水混入溶液特征。矿物包裹体的爆裂温度平均为157℃。石英的包裹体成分测试结果,揭示了矿液为K-Na-Ca-Cl型富硅的弱碱性溶液。矿床成因厘定为岩浆期后中低温热液脉状充填矿床。 相似文献