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1.
田雯  陈刚  李文厚  吕剑文  李建东  杨超 《地质通报》2016,35(203):454-460
受古岩溶作用的影响,鄂尔多斯盆地靖边气田高桥区块形成了层位较稳定的溶蚀孔洞白云岩储层。利用钻井岩心、铸体薄片、阴极发光及地球化学手段等,对研究区马五41段白云岩储层埋藏环境下建设性成岩作用进行了系统研究。研究表明,区内埋藏环境下建设性成岩作用有埋藏白云石化作用、埋藏溶解作用、裂缝作用等。研究区晶粒白云岩C、O同位素比值与奥陶纪海水的C、O同位素值相比明显偏负,表明地层经历了埋藏白云石化作用,埋藏白云石化作用使得岩石体积缩小、岩石孔隙度有所增加,有利于晶间孔的形成。埋藏溶解作用可形成大量的溶蚀孔、洞、缝等储集空间,为油气的储集成藏提供了有利的场所。裂缝的发育增加了溶蚀孔洞的连通性,有效地提高了储层的孔隙度与渗透率。上述3种建设性成岩作用相互叠加配合,使得裂缝与原本存在的孔隙配套,对良好油气储集空间的形成起了决定性控制作用。  相似文献   

2.
鄂尔多斯盆地中央气田奥陶系马家沟组马五段白云岩是重要的油气储集层,多年来,马家沟组白云岩的成因问题一直是地质研究者讨论的热点话题.对马五段白云岩的C、O、Sr同位素地球化学资料的分析表明,孔洞充填的白云石(含鞍状白云石)和白云岩的δ13C、δ18O值极其近似,且白云岩的δ18OPDB值比奥陶纪海水值要偏负1.752‰～4.395‰(平均2.911‰);成岩流体(水)的占δ18OSMOW平均值为+8‰,比当时海水值偏正;87Sr/86Sr比值比奥陶纪海水87Sr/86Sr比值要高.从C、O同位素数据上看,形成白云岩和沉淀于孔洞中的白云石(含鞍状白云石)的流体为同源流体;造成白云岩的δ18O值偏负的原因主要是埋藏条件的"温度效应";87Sr/86Sr比值偏高可能是交代流体来自或流经了富含放射成因Sr的铝硅酸盐基底或硅质碎屑岩.这些特征表明马五段白云岩很可能形成于埋藏环境.  相似文献   

3.
川中磨溪—高石梯地区栖霞组发育滩相白云岩,目前对滩相中差异白云石化机理不明确,导致难以预测优质白云岩储层的分布。在岩石学和地层特征研究基础上,通过分析不同类型白云岩的微量元素及碳、氧、锶同位素特征,结合颗粒滩类型和构造背景,系统研究了该区不同类型白云岩的成因机理及模式。结果显示:研究区栖霞组白云岩中白云石以细晶为主,中晶和粗晶次之,晶形多为半自形—自形。白云岩具有明显的残余颗粒结构,表明原始岩性为颗粒灰岩。细晶、细—中晶白云岩的阴极发光整体较暗,呈暗红色至红色,稀土元素配分模式与同期灰岩相似,白云岩的87Sr/86Sr比值大部分落于二叠纪海水的87Sr/86Sr比值范围之内,表明白云岩的成岩流体与海水沉积的灰岩具有同源性。白云岩的δ13C值（3.73‰~4.19‰）与同期灰岩δ13C值（3.61‰~4.93‰）相近,表明白云岩与灰岩具有一致的碳源。从灰岩到白云岩,Sr含量明显减少且Mn含量有所增加,说明灰岩经过一定的成岩作用被交代形成白云岩,该类白云岩为埋藏条件下地层中富Mg2+的流体交代孔隙型颗粒灰岩而成;中—粗晶白云岩的阴极发光呈红色,具明显环带特征,且具有高的Mn含量、低Sr/Ba比值及铕的正异常,87Sr/86Sr比值高于同期海水值,δ18O值在-8.06‰~-8.52‰,为颗粒灰岩在埋藏期受持续、充足的云化流体供给而成,较高的包裹体均一温度和δ18O值明显偏负均指示埋藏白云化作用过程还受到局部高温的影响。总体而言,埋藏白云岩化是该区白云岩的主要成因,地层中富镁的流体在压力和热对流的双重影响下进行迁移,促进白云岩化流体的运移,但局部地区鞍形白云石的形成遭受了后期不同程度的热液改造作用。  相似文献   

4.
研究了南京汤山观音台组顶部、仑山组和红花园组底部的微量元素、稀土元素和碳、氧同位素,基于观音台组顶部白云岩中白云石和方解石δ~(18)O 值的相似性,认为它是在成岩作用初期由交代作用形成的准同生白云岩。依据同位素分析,所研究层段的碳酸盐岩主要形成于埋藏成岩环境,未经历大气淡化成岩阶段。依据地层多重划分概念修订了观音台组和仑山组的界线。依据碳同位素与有关地区对比探讨了寒武系与奥陶系界线,界线附近δ~(13)C 值仅见小的负偏移,反映这一时期海平面的升降幅度较小。  相似文献   

5.
碳酸盐岩碳、氧同位素对古气候、古环境及成岩流体示踪具重要的指示意义。通过对羌塘盆地南部昂达尔错地区QZ-11井、QZ-12井布曲组岩心观察、薄片鉴定及碳氧同位素分析,结果表明:研究区布曲组是在炎热、半干旱-半潮湿古气候条件下,在台地边缘礁滩环境发育的一套碳酸盐岩沉积;岩性包括灰岩,白云岩及过渡性岩类,白云岩主要发育在高位体系域晚期台缘浅滩微相中,白云岩包括保留先驱灰岩原始组构的颗粒白云岩、泥微晶白云岩及先驱灰岩原始组构不可见的晶粒白云岩;研究区内的碳酸盐岩δ~(13)C_(PDB)分布范围为1.5‰~4‰,δ18OPDB分布范围为-7.6‰~-12.1‰,其中灰岩的δ~(13)C_(PDB)分布范围为1.5‰~2.9‰,普遍高于同期全球海水碳同位素值,推测可能与高位体系域晚期强蒸发及生物繁盛有关,白云岩和过渡性岩类中δ~(13)C_(PDB)分布范围为1.4‰~4‰,说明为继承先驱灰岩中碳同位素组成,局部可能受到白云石化流体的改造;氧同位素组成虽然普遍低于同期海水值,但白云岩中保留先驱灰岩原始组构的颗粒白云岩氧同位素值仍高于灰岩,表明其形成与蒸发环境有关,而细晶白云岩、中粗晶白云岩氧同位素组成呈逐步降低趋势,表明可能受埋藏阶段温度升高的影响。  相似文献   

6.
塔深1井寒武系白云岩储层同位素流体地球化学示踪   总被引：3，自引：0，他引：3  
通过对塔里木盆地沙雅隆起阿克库勒凸起东部塔深1井寒武系白云岩岩石学特征及成岩成因分析,影响塔深1井寒武系地层流体改变主要成岩有准同生期、埋藏期和后期热液改造期等.塔深1井寒武系白云岩及充填孔、洞、缝内方解石的氧、碳、锶同位素地球化学特征表明:准生期白云岩δ~(13)C_(PDB)值(0.9‰～1.8‰)偏正、δ~(18)C_(PDB)值(-10.1‰～-4.2‰)偏负反映准同生期泥微晶白云石成因属于高盐度的海水使得碳酸盐泥发生白云石化;埋藏期白云岩碳、氧随重结晶作用加强,白云岩晶粒由细向粗变化值随埋深增加,由于同位素分馏作用而偏负,δ~(18)C_(PDB)值(-10.02‰～-5.7‰)呈明显的下降,但δ~(13)C_(PDB)值(-1.4‰～0‰)组成变化不大;后期热液白云岩在热液作用下δ~(18)C_(PDB)值普遍低于-10‰(δ~(18)C_(PDB)/‰-13.1～-9.4,δ~(13)C_(PDB)/‰-2～-0.647);基质方解石δ~(18)C_(PDB)值为-10.1‰～-10.13‰,δ~(13)C_(PDB)值为-1.48‰～-1.62‰;充填孔洞缝粗-巨晶方解石δ~(18)C_(PDB)值为-10.89‰～-14.28‰,δ~(13)C_(PDB)值为-2‰～-3.09‰,反映准同生期→埋藏期→后期热液晶粒大小由泥微晶→细晶→中晶→粗晶氧碳同位素值逐渐变小偏负,据~(87)Sr/~(86)Sr(0.707 284～0.746 888)值均远高于现今海洋中海水的锶同位素组成(0.708)及围岩的锶同位素(0.707 284),说明鞍形白云石以及方解石结晶时的孔隙流体不是残余在岩石孔隙中的同生期海水,而是外来的富含锶的流体,也就是深部热液流体.渗透回流白云石化、埋藏白云石化和高温热液白云石化等特征表明白云岩形成于超盐度、埋藏和高温热液等3种不同的环境,因此影响储层形成与分布,从而影响对白云岩的勘探.  相似文献   

7.
梁茹  苏中堂  马慧  方继瑶  林良彪 《沉积学报》2021,39(6):1506-1516
川西地区栖霞组白云岩成因及其与峨眉山玄武岩喷发热事件关系颇有争论。在野外剖面、岩心观察基础上,通过岩石学、全岩及矿物微区地球化学分析方法对其研究,结果表明川西地区栖霞组白云岩（石）可分为残余砂屑白云岩、晶粒白云岩以及鞍状白云石、脉体充填白云石四类。残余砂屑白云岩与晶粒白云岩均呈块状,阴极发光较暗,稀土配分模式与泥微晶灰岩相似,δ13C、87Sr/86Sr多处于同期海水范围内,δ18O略偏负,Ce负异常,残余砂屑白云岩Eu呈负异常,而晶粒白云岩Eu多为正异常。微区δ13C、δ18O分析显示,残余砂屑白云岩的白云石雾心与亮边内δ13C均处于同期海水范围内,δ18O亮边较雾心偏负;晶粒白云岩中不同大小的晶粒白云石微区δ13C、δ18O显示相近特征,表明这两类白云岩均为海水浅埋藏成因,但受到后期热流体叠加改造。曲面他形粗晶鞍状白云石充填于裂隙与溶蚀孔洞内,镜下具波状消光特征,发亮红色光,δ13C与二叠纪海水相近,δ18O明显负偏,Eu呈正异常,指示鞍状白云石为热液成因。脉体白云石岩石学与地球化学特征表明其为晚期埋藏成因。川西地区栖霞组白云岩主体为浅埋藏成因,峨眉山玄武岩喷发期热液对其叠加改造,仅西南地区充填裂隙与溶洞的鞍形白云石为热液成因。  相似文献   

8.
显微取样碳氧同位素分析技术利用高聚焦激光束与碳酸盐岩样品作用,是一种在显微薄片下对岩石特定组构产生CO2的有效方法,其空间分辨率20～50μm,δ13C和δ18O的最好分析精度可达±0.22‰(σ),可以为碳酸盐岩碳氧同位素提供“高分辨率、原位”数据,微区分析是同位素测试发展的重要方向。用该技术对川东北飞仙关组鲕粒白云岩地球化学特征进行的研究表明,它可避免样品不纯带来的解释上的误差,为解释鲕粒白云岩成因提供了较为准确的地球化学信息,可进一步认识川东北飞仙关组鲕粒白云岩的成因问题。各种产状白云石的δ13C‰(PDB)值均大于当时海水值,说明白云石化流体没有淡水注入;而δ18O‰(PDB)分布较为离散,伴随白云石晶体大小增加,δ18O‰(PDB)值明显偏负,说明白云石化作用过程经历了埋藏加深、温度升高的过程,并且白云石化流体远离卤水源,其咸化程度减弱,为鲕粒白云岩的卤水渗透回流成因提供了有力的证据。  相似文献   

9.
川东兴隆场地区长兴组白云岩地球化学特征及流体来源   总被引：1，自引：0，他引：1  
四川盆地东部长兴组—飞仙关组礁滩相储层为重要的天然气勘探目的层,优质储层的岩性多为白云岩,且主要分布于开江-梁平陆棚的东西两侧。川东兴隆场地区位于开江-梁平陆棚西侧有利相带的东南端,长兴组白云岩层段为该区主力产气层,且白云岩主要分布在台地边缘礁滩相等易于发生暴露的高能沉积相带。明确了白云岩宏观分布的控制因素,以岩石结构及Mg/Ca值和有序度为基础,结合岩石地球化学特征,对川东兴隆场地区上二叠统长兴组白云岩成因进行分析。研究结果表明兴隆场地区长兴组白云岩是在埋藏条件下,同层位的泥晶灰岩及泥灰岩中封存的浓缩海水通过压实作用排挤进入碳酸盐沉积物交代灰岩形成的。有如下证据:①飞仙关组沿缝合线发育的自形白云石化学组成(CaO含量均值30.94%,MgO含量均值20.76%)与长兴组白云石化学组成(CaO含量均值30.51%,MgO含量均值21.28%)相近,表明二者成因及白云化流体具有相似性,推断压实流体可能为长兴组白云岩白云化流体;②长兴组白云岩δ13C介于1‰～2.5‰之间,δ18O介于-6‰～-4‰之间,分布在同期古海水的δ13C(0～5.8‰)、δ18O(-7.5‰～-3.5‰)变化范围内,并与全球典型埋藏白云岩δ13C、δ18O分布区间一致,说明白云化流体具有同期海水性质,且形成于埋藏成岩环境中;③长兴组白云岩的87Sr/86Sr值(0.707108～0.707507)覆盖在了川东北晚二叠世海水Sr同位素(0.706620～0.707742)的变化范围内,证明白云化流体来源于同期海水;④长兴组白云岩稀土元素表现为LREE亏损、HREE富集的海水稀土元素特征,表明白云化流体具有海源流体的性质;⑤长兴组碳酸盐岩Fe含量均较低(<2000×10-6),但长兴组白云岩相对于灰岩具有较高的Mn含量(69×10-6～90×10-6,均值为76×10-6)和较强的阴极发光性,反映了白云岩形成于埋藏的还原环境中。  相似文献   

10.
中国南方灯影峡期(晚前寒武纪)是白云岩广泛发育的海洋碳酸盐沉积时期,在灯影组.中部发育从海水直接沉积、沉淀的原生白云岩,目前仍保留其原始组构特征。从40个原生白云石(岩)中测得:泥晶白云石的δ13C值为3.64‰,δ18O值为-1.17‰(n=6);藻白云岩的δ13C值为3.52‰,δ18O值为-1.86‰(n=15);海水纤状白云石胶结物δ13C值为2.90‰,δ18O值为-2.65‰(n=8);海水刃状白云石胶结物的δ13C值为2.96‰,δ18O值为-2.41‰(n=8);泥晶纹层和海水纤状白云石胶结物的δ13C值为2.79‰,δ18O值为-3.13‰。40个岩样的δ13C平均值为3.25‰±0.44‰,δ18O平均值为-2.12‰±0.98‰(均以PDB标准)。对于灯影峡期海相白云岩的原始δ13C和δ18O值,不采用所有样品的平均值,而是采用原生白云石沉积物与海水白云石胶结物δ13C值和δ18O值两个图示分布区重叠部分的最重同位素值,即：δ13C值为4.43‰(PDB标准),δ18O值为-0.62‰(PDB标准),将其作为灯影峡期海洋碳酸盐岩的原始同位素组成。对海水原生白云石胶结物包裹体盐度进行了测定,海水δ18O计算值为2.90‰(SMOW标准),用原始δ18O值计算的原生白云石形成时的海水温度为40.8 ℃。这说明中国南方灯影峡期的海洋为炎热的较高的海水温度环境。  相似文献   

11.
Summary The Xiluvo complex of central Mozambique is made up of coarse- to fine-grained calciocarbonatites (sövites and alvikites), heavily altered lamprophyres and syenitic rocks that intruded the Precambrian basement ca. 120Ma ago. The carbonatites have fractionated rare earth element patterns (chondrite-normalized La/Yb=30–80) and markedly negative Rb, K, P, Zr and Ti anomalies in mantle-normalized incompatible element diagrams. The 18O (+7 to +8), 13C (–5), and the age-corrected 87Sr/86Sr (0.7032–0.7033) and 143Nd/144Nd (0.51263–0.51262) indicate an origin in the mantle. A few carbonatitic samples have higher 18O (+13), indicating interaction with high-18O crust or late-stage fluids. The chemical and isotopic compositions of the Xiluvo carbonatites and nearby carbonatites of similar age in Malawi indicate very similar sources, characterized by time-integrated depletion of Rb with respect to Sr and of Sm with respect to Nd. These characteristics point to a source similar in many respects to those of other East African carbonatites and to those of some ocean island basalts, with the additional influx of components possibly located in the African lithospheric mantle.  相似文献   

12.
The reasons for the isotopic heterogeneity of the mantle are analyzed in this paper on the basis of published isotopic data. It was shown that the observed variations in the Sr, Nd, Hf, and Pb isotopic compositions of oceanic basalts cannot be explained by mixing of a finite number of homogeneous reservoirs (components). The considerable variations in the contents of Rb, Sr, Sm, Nd, Lu, Hf, U, Th, and Pb and ratios of these and other trace elements in tholeiitic basalts indicate that the chemical heterogeneity of mantle-derived rocks is inherited in part from their sources. Oceanic tholeiitic basalts show a tight correlation between the variances of Nd, Hf, Sr, and Pb isotopic ratios and the variances of respective radiogenic additions that could be accumulated in these rocks over a time period of 〈t〉 = 1.8 Gyr. This paradox clearly indicates that variations in all the mentioned isotopic systems in the mantle cannot be understood without the analysis of the geochemical heterogeneity of rocks.The close to lognormal distributions of lithophile trace elements in oceanic tholeiitic basalts and the character of correlations between them suggest that magmatic differentiation was the major mechanism of the formation of chemical heterogeneity in the mantle. The role of metasomatism in the global transport of trace elements and formation of the geochemically heterogeneous mantle is probably rather limited. Intrusive processes within the mantle could result in the development of chemical and, after a period of time, isotopic anomalies in the mantle. Simple calculations show that long-lived geochemical anomalies related to alkaline magmatism could be responsible for EM-I type isotopic anomalies, and geochemical anomalies produced in the mantle by enriched tholeiitic melts could be sources of EM-II type isotopic anomalies. The analysis of the distribution of the isotopic compositions of mantle-derived igneous rocks in various “isochron” coordinates suggested that the formation of geochemical anomalies in the mantle is a long-term process lasting for hundreds of millions of years. Nonetheless, trends approaching 4.5 Ga were never observed in such diagrams, i.e., the mantle is in general rejuvenated in all isotopic systems. Both on global and local scales, there are no mantle domains that have remained geochemically closed and isolated since the Earth’s formation. The entire mantle is involved in material exchange processes.The development of isotopic systems in the mantle was explored by means of statistical modeling accounting for the tendency of a continuous increase in the chemical heterogeneity of the mantle source and the tendency of obliteration of the isotopic heterogeneity owing to the convective mixing in the mantle. The modeling demonstrated that the character of the isotopic heterogeneity of the mantle is statistically consistent with the character of its chemical heterogeneity. The mantle isotopic anomalies HIMU, EM-I, and EM-II were generated by two simultaneous processes: the magmatic differentiation of mantle material and its not very efficient mixing.  相似文献   

13.
The skarn complex of Traversella was formed at the expense of various rock types (calcic hornfels, gneiss, dolomitic marble) occurring in the contact aureole of the dioritic intrusion of Traversella (30±5 Ma). Application of phase equilibria has fixed the temperature of the primary stage of skarn formation between 550° C to 625° C. Similar applications indicate a larger range of temperature (525° C to 300° C) for the secondary stage. The different types of skarn (primary stage) are enriched in REE relative to the corresponding precursor rock (T.R.=126 ppm (protolith) to 228 ppm (inner zone) for the skarn on gneisses; T.R.=14 ppm to 71 ppm for the skarn on calcic hornfelses; T.R.=12 ppm to 200 ppm for the skarn on dolomitic marbles), but all the inner zones of these different types of skarn show a similar REE distribution with a slight LREE fractionation and no Eu anomaly. It is inferred that the primary metasomatic fluid has a parallel REE pattern. The oxygen isotope composition of water in equilibrium with the early stage of skarn at T=600° C ranges from 8.3 per mil to 8.9 per mil. At the beginning of the first hydroxylation stage (secondary stage), the fluid σ 18O remains in the range observed in the primary stage but within it, there is a sharp decrease from 8.0 per mil to 5.0 per mil. During the sulphidation stage, the fluid σ 18O decreases more gradually from 5.0 per mil to 3.0 per mil. The I Sr of the early skarn silicates ranges from the values observed in the dolomitic marbles (0.70874 to 0.70971) to the I Sr of the intrusion (0.70947 to 0.71064). During the secondary stage, there is a progressive increase of the minerals I Sr up to 0.71372. The REE pattern of the primary metasomatic fluid does not put any precise constraint on the primary fluid source. On the other hand, both stable and radiogenic isotopes suggest that the early high-temperature metasomatic fluid was isotopically equilibrated with the dioritic intrusion. This implies that this early fluid is either exsolved from the crystallizing intrusion or a metamorphic water previously equilibrated with the intrusion. During the secondary stage, the replacement of the early anhydrous phases by hydrated parageneses is accompanied by the mixing with meteoric fluid as indicated by stable (σ 18O) and radiogenic (87Sr/86Sr) isotopes.  相似文献   

14.
The present work reports on the temporal variations of Sb, As, V and Mo concentrations in the surface freshwater reaches of the Gironde Estuary (SW France). Dissolved (<0.2 and <0.02 μm) and particulate Sb, As, V and Mo concentrations were measured in samples collected with high temporal resolution (every 30 min) during two consecutive tides at a fixed station located upstream of the city of Bordeaux and the maximum turbidity zone (MTZ). In addition, measurements of suspended particulate matter concentration, physico-chemical parameters, Cl− concentration, water depth, current velocity and particulate Th concentration were performed either at the same time resolution or continuously. The data obtained suggested that variations in particulate As, V and Mo concentrations were most probably related to tidal cycling near the sampling site of fine grained particles from the MTZ located downstream. Significant differences in the behavior of the dissolved target oxyanions, mostly present in the <0.02 μm fraction, occurred. The behavior of Sb was conservative. Variations of the dissolved As and V concentrations showed similar cycling trends, strongly related to tidal cycles. These As and V cycles were interpreted as a mixing between upstream freshwater and downstream water enriched in dissolved As and V by desorption from the MTZ particles. The observed trend in the variation of the dissolved Mo was more complex than that of As and Sb and attributed to the mixing of the water bodies mentioned above coupled to a point source input of dissolved Mo from an intra-estuarine source. The contribution of this suspected Mo source to the dissolved Mo concentrations measured at the sampling site was estimated from the ratio of dissolved Mo to dissolved As concentrations. The additional dissolved Mo signal, coupled to the monitored ebb and flood length and associated current velocities, suggested an anthropogenic input which may derive from industrial activity near the city of Bordeaux. Extrapolating these results to the annual scale suggested that this dissolved Mo may be equivalent to 45-90% of the annual dissolved Mo flux into the Garonne Branch, highlighting the importance to further investigate the origin and behavior of Mo in the fluvial estuary near Bordeaux.  相似文献   

15.
Investigations on S, C, O, Sr, and Pb isotopes in ores, gangue, and country rocks of the Chaudfontaine ore deposit confirm that interbedded barite and white sparry calcites are cogenetic. They emphasize the marine origin of S and the nonmarine origin of the metals. They underline the important role played by the bacterial reduction at the site of deposition. Hypotheses concerning the source of the metals and the nature of the brines involved in their transportation are briefly discussed.  相似文献   

16.
贵州安龙坡脚剖面新苑组位于扬子地台和右江盆地交汇处,为中三叠世台缘斜坡相沉积,在该组中上部发现了牙形石动物群,除少量分枝分子外,都归属于Neogondolella属,建立了4个牙形石带,自下而上分别为:Neogondolella bulgarica、Neogondolella bifurcata、Negondolella constricta、Neogondolella constricta cornuta(未见顶界)带。时代为中三叠世安尼中晚期,其特殊的古地理位置,对系统研究与对比罗平生物群、盘县动物群的古生态环境,以及区域地层对比、地层格架建立,探讨该时期盆地演化提供了基础资料。  相似文献   

17.
It is shown that globular phyllosilicates subjected to deep categenesis are abundant in Middle Riphean sandstones and siltstones (lower subformation of the Arymas Formation) of the Olenek High. Their detailed structural-crystallochemical characteristics are given. Secondary alterations of globules and the associated pelletal minerals at different stages of lithogenesis (illitization, chloritization, ferrugination, disintegration, and so on) are considered. Structural-crystallochemical characteristics of Fe-illite and Fe2+-Mg-chlorite in globules, pellets, separate clayey strata among glauconite-bearing sandstones and siltstones (hereafter, sandy-silty rocks), and mudstone interlayers are also presented. Possible mechanisms of the formation of these minerals are discussed.  相似文献   

18.
Hamamayagi thermal spring (HTS) is located along the North Anatolian Fault Zone. The thermal spring has a temperature of 36°C, with total dissolved solids ranging from 485.6 to 508.5 mg/L. Hard, brittle, and gray limestones Permian aged are the reservoir rocks of the HTS. δ18O–δ2H isotope ratios clearly indicate a meteoric origin for the waters. The δ34S value of sulfate in the thermal water is nearly 4.1‰ and implies a diagenetic environment characterized by reduced sulfur compounds. The δ13C ratio for dissolved inorganic carbonate in the HTS lies between −1.78 and −1.62‰, showing that it originates from the dissolution of fresh-water carbonates. Quartz geothermometry suggests a reservoir temperature of 52–85°C for the Hamamayagi geothermal field, but chalcedony geothermometers suggest reservoir temperatures between 30 and 53°C.  相似文献   

19.
J. D. HUDSON 《Sedimentology》1978,25(3):339-370
In interpreting the results of a petrographic and isotopic study of concretions, a range of subjects is discussed including the original texture of the Oxford Clay sediment, Jurassic palaeotemperatures, the diagenetic history of pore-waters and the palaeo-hydrology of central England. The concretions are all composed predominantly of calcite. They include precompactional, pyrite-rich concretions that later suffered an eposide of brecciation, and others that only commenced to form after compaction had crushed ammonite shells included in the bituminous clay sediment. Petrographic, chemical, and especially carbon isotope data demonstrate a dominantly organic source for the carbon in the early formed concretions. Oxygen isotopes indicate formation at the same temperatures (13-16°C) at which benthic molluscs were living. Concretion growth in pelleted, anaerobic mud proceeded concurrently with bacterial sulphate reduction and pyrite precipitation. Cracking of the concretions started at this stage: in a few concretions, the cracks were also partially filled with brown calcite. During post-compactional growth, δ13C increased and pyrite content decreased, showing waning organic influence; δ18O decreased. The brecciated concretions were intruded by clay in which baryte crystals grew; finally, most remaining voids were filled with strongly-ferroan calcite of δ18O about—7 PDB and δ13C about O PDB. This must indicate strong depletion of the pore waters in 18O. Mechanisms that might lead to this are reviewed. It is concluded that the sequence of mineralogical and chemical changes is most readily explained if originally marine porewaters, first modified by bacterial activity, were flushed from the compacting clays by water of ultimately meteoric origin. This had its source in palaeo-aquifers beneath the Oxford Clay. Speculative attempts are made to relate this history to the geology of the region.  相似文献   

20.
We present new original data on the geochemistry of scandium in the coals of Asian Russia, Mongolia, and Kazakhstan. In general, the studied coals are enriched in Sc as compared with the average coals worldwide. Coal deposits with abnormally high, up to commercial, Sc contents were detected in different parts of the study area. The factors for the accumulation of Sc in coals have been identified. The Sc contents of the coals depend on the petrologic composition of coal basins (composition of rocks in their framing) and the facies conditions of coal accumulation. We have established the redistribution and partial removal of Sc from a coal seam during coal metamorphism. The distribution of Sc in deposits and coal seams indicates the predominantly hydrogenic mechanism of its anomalous concentration in coals and peats. The accumulation of Sc in the coals and peats is attributed to its leaching out of the coal-bearing rocks and redeposition in a coal (peat) layer with groundwater and underground water enriched in organic acids. The enrichment of coals with Sc requires conditions for the formation of Sc-enriched coal-bearing rocks and conditions for its leaching and transport to the coal seam. Such conditions can be found in the present-day peatland systems of West Siberia and, probably, in ancient basins of peat (coal) accumulation.  相似文献   

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