Palaeoenvironmental significance of Late Permian palaeosols in the South‐Eastern Iberian Ranges,Spain     

RAÚL DE LA HORRA  Ma ISABEL BENITO  JOSE LÓPEZ‐GÓMEZ  ALFREDO ARCHE  JOSÉ F. BARRENECHEA  JAVIER LUQUE 《Sedimentology》2008,55(6):1849-1873

The Late Permian (Wuchiapingian) Alcotas Formation in the SE Iberian Ranges consists of one red alluvial succession where abundant soil profiles developed. Detailed petrographical and sedimentological studies in seven sections of the Alcotas Formation allow six different types of palaeosols, with distinctive characteristics and different palaeogeographical distribution, to be distinguished throughout the South‐eastern Iberian Basin. These characteristics are, in turn, related to topographic, climatic and tectonic controls. The vertical distribution of the palaeosols is used to differentiate the formation in three parts from bottom to top showing both drastic and gradual vertical upwards palaeoenvironmental changes in the sections. Reconstruction of palaeoenvironmental conditions based on palaeosols provides evidence for understanding the events that occurred during the Late Permian, some few millions of years before the well‐known Permian‐Triassic global crisis.  相似文献   

Methane‐related microbial gypsum calcitization in stromatolites of a marine evaporative setting (Münder Formation,Upper Jurassic,Hils Syncline,north Germany)     

GERNOT ARP  CHRISTIAN OSTERTAG‐HENNING  SELÇÜK YÜCEKENT  JOACHIM REITNER  VOLKER THIEL 《Sedimentology》2008,55(5):1227-1251

Fossil stromatolites may reveal information about their hydrochemical palaeoenvironment, provided that assignment to a specific microbial community and a corresponding biogeochemical mechanism of formation can be made. Tithonian stromatolites of the Münder Formation at Thüste, north Germany, have traditionally been considered as formed by intertidal cyanobacterial communities. However, thin sections of the stromatolites show elongated angular traces of former gypsum crystals in a dense arrangement, but no algal or cyanobacterial filament traces. Moreover, high Fe²⁺ and Mn²⁺ contents, oxygen‐isotope and sulphur‐isotope ratios of carbonate‐bound sulphates, and sulphurized hydrocarbon biomarkers of the stromatolitic carbonate indicate that CaCO₃ precipitation occurred near the oxic–anoxic interface as a result of intensive bacterial sulphur cycling rather than photosynthetic activity. Furthermore, anaerobic oxidation of methane by Archaea may have driven CaCO₃ precipitation in deeper parts of the biofilm community, as reflected by high concentrations of squalane with a strongly negative δ¹³C in conjunction with evaporite pseudomorphs showing extremely low δ¹³C_Carb ratios. Consequently, the Thüste stromatolites are now interpreted as having initially formed by gypsum impregnation of biofilms. Subsequently, early Mg‐calcitic calcitization within the biofilms occurred because of combined bacterial iron, manganese and sulphate reduction, with an increasing contribution of anaerobic oxidation of methane with depth. This model plausibly explains the prominent preservation of signals derived from oxygen‐independent metabolic pathways, whereas virtually no geochemical record exists for an aerobic community that may, nevertheless, have prevailed at the stromatolite surface. Photic‐zone stromatolites with a prominent signal of anaerobic oxidation of methane may be common in, and indicative of, oxygen‐depleted sulphate‐bearing environments with high rates of methane production, conditions that possibly were fulfilled at the Archaean to Proterozoic transition.  相似文献   

东秦岭二郎坪群中火山成因块状硫化物矿床地质地球化学特征及其成因讨论   总被引：4，自引：1，他引：3  

燕长海  徐勇航  彭翼  赵太平 《矿床地质》2008,27(1):14-27

二郎坪群是东秦岭造山带重要的组成部分,其火山建造中广泛发育有火山成因块状硫化物(VMS)矿床.文章总结并分析了南阳盆地东、西两侧二郎坪群中3个典型矿床(刘山岩、水洞岭和上庄坪)的研究资料,把二郎坪群VMS矿床分为3类:Zn-Cu型矿床(刘山岩矿床);Zn-Cu型与Zn-Pb-Cu型矿床(水洞岭矿床);Zn-Pb-Cu型矿床(上庄坪矿床).从刘山岩矿床到水洞岭矿床,再到上庄坪矿床,铜的含量减少,铅的含量增多.二郎坪群VMS矿床矿石富集LREE、Ce负异常及Eu正异常,说明矿床为热液成因.石英和重晶石中流体包裹体的氢氧同位素特征表明,成矿流体主要来自建造水,南阳盆地以西,矿床成矿流体中伴有较多古大气降水.矿石的硫同位素特征说明,二郎坪群VMS矿床中的硫可能为地幔岩浆硫和海水硫的混合硫.围岩与矿石的铅同位素组成基本一致,说明矿石和围岩可能来源于相似的物源区,成矿元素主要来源于地幔或下地壳深源物质,而水洞岭矿床明显有上地壳浅源物质的混染.研究表明,南阳盆地以西的水洞岭和上庄坪矿床可能形成于大陆边缘海环境,盆地规模较小,受陆源物质影响较大;而南阳盆地以东的刘山岩矿床可能形成于远洋盆地,盆地到达成熟阶段.用地震泵模式可解释二郎坪群VMS矿床的成因机制.  相似文献   

Chemical weathering of carbonates and silicates in the Han River basin,South Korea     

Jong-Sik Ryu  Kwang-Sik Lee  Ho-Wan Chang  Hyung Seon Shin 《Chemical Geology》2008,247(1-2):66-80

A detailed investigation of the fluvial geochemistry of the Han River system allows to estimate the rates of chemical weathering and the consumption of CO₂. The Han River drains approximately 26,000 km² and is the largest river system in South Korea in terms of both water discharge and total river length. It consists of two major tributaries: the North Han River (NHR) and the South Han River (SHR). Distinct differences in basin lithology (silicate vs. carbonate) between the NHR and SHR provide a good natural laboratory in which to examine weathering processes and the influence of basin geology on water quality. The concentrations of major elements and the Sr isotopic compositions were obtained from 58 samples collected in both summer and winter along the Han River system in both 2000 and 2006. The concentrations of dissolved loads differed considerably between the NHR and SHR; compared with the SHR, the NHR had much lower total dissolved solids (TDS), Sr, and major ion concentrations but a higher Si concentration and ⁸⁷Sr/⁸⁶Sr ratio. A forward model showed that the dissolved loads in the NHR came primarily from silicate weathering (55 ± 11%), with a relatively small portion from carbonates (30 ± 14%), whereas the main contribution to the dissolved loads in the SHR was carbonate weathering (82 ± 3%), with only 11 ± 4% from silicates. These results are consistent with the different lithologies of the two drainage basins: silicate rocks in the NHR versus carbonate rocks in the SHR. Sulfuric acid derived from sulfide dissolution in coal-containing sedimentary strata has played an important role in carbonate weathering in the SHR basin, unlike in the NHR basin. The silicate weathering rate (SWR) was similar between the NHR and SHR basins, but the rate of CO₂ consumption in the SHR basin was lower than in the NHR basin due to an important role of sulfuric acid derived from pyrite oxidation.  相似文献   

运用3DEEMs及荧光偏振方法研究pH、离子强度及浓度效应对腐殖酸荧光光谱特性的影响   总被引：6，自引：0，他引：6  

梅毅  吴丰昌  王立英  白英臣 《地球化学》2008,37(2):165-173

利用三维荧光激发.发射光谱(3DEEMs)及荧光偏振法研究了3例腐殖酸和1例湖泊溶解有机物(DOM)在不同腐殖酸浓度、离子强度和pH条件下的荧光光谱特性.实验结果表明,随着浓度增大,各腐殖酸样的荧光强度增大,其中垃圾渗滤液腐殖酸和Pahokee泥炭腐殖酸的荧光峰出现红移.随着浓度进一步增大,腐殖酸的荧光偏振值增大,由此推断在此浓度范围内腐殖酸由于分子间的排斥作用使其构型出现伸展.离子强度增大导致腐殖酸及阿哈湖DOM的荧光强度降低.随着氯化钾(KCI)浓度增大,Fluka腐殖酸的荧光峰A蓝移,荧光峰B的荧光偏振值出现减小,推测是由于静电中和作用使其荧光基团发生卷曲造成的.离子强度对其余腐殖酸样和阿哈湖DOM的其他荧光特性没有明显的影响.总的来说,pH值的变化对腐殖酸和湖泊DOM的荧光特征的影响是很明显的.随着pH值增大,腐殖酸和湖泊DOM的荧光强度增强.而pH值减小时,Fluka腐殖酸和Pahokee泥炭腐殖酸的荧光峰(A峰)蓝移,当pH值降到5时,Fhka腐殖酸的荧光峰突然红移到最大,随后又继续蓝移;垃圾渗滤液腐殖酸和阿哈湖DOM的荧光峰位无明显的漂移.所有样品的荧光偏振值都减小(但阿哈湖DOM的A峰变化不大),但在pHi≤5时又增大,这种现象表明随着pH值降低,腐殖酸和湖泊DOM中有机大分子发生卷曲,但在pH≤5时由于羧基的质子化又以平面伸展构型出现在溶液中.  相似文献   

DEM analysis of the crack propagation in brittle clays under uniaxial compression tests   总被引：2，自引：0，他引：2  

Luis F. Vesga  Luis E. Vallejo  Sebastian Lobo‐Guerrero 《国际地质力学数值与分析法杂志》2008,32(11):1405-1415

  相似文献   

Numerical estimation of REV and permeability tensor for fractured rock masses by composite element method   总被引：2，自引：0，他引：2  

S.‐H. Chen  X.‐M. Feng  S. Isam 《国际地质力学数值与分析法杂志》2008,32(12):1459-1477

The Monte Carlo method is used to generate parent stochastic discrete fracture network, from which a series of fractured rock samples of different sizes and orientations are extracted. The fracture network combined with a regular grid forms composite element mesh of the fractured rock sample, in which each composite element is composed of sub‐elements incised by fracture segments. The composite element method (CEM) for the seepage is implemented to obtain the nodal hydraulic potential as well as the seepage flow rates through the fractured rock samples. The application of CEM enables a large quantity of stochastic tests for the fractured rock samples because the pre‐process is facilitated greatly. By changing the sizes and orientations of the samples, the analysis of the seepage characteristics is realized to evaluate the variation of the permeability components, the existence of the permeability tensor and the representative element volume. The feasibility and effectiveness are illustrated in a numerical example. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Biaxial test simulations using a packing of polygonal particles   总被引：1，自引：0，他引：1  

A. A. Peña  A. Lizcano  F. Alonso‐Marroquin  H. J. Herrmann 《国际地质力学数值与分析法杂志》2008,32(2):143-160

The mechanical response of cohesionless granular materials under monotonic loading is studied by performing molecular dynamic simulations. The diversity of shapes of soil grains is modelled by using randomly generated convex polygons as granular particles. Results of the biaxial test obtained for dense and loose media show that samples achieve the same void ratio at large strains independent of their initial density state. This limit state resembles the so‐called critical state of soil mechanics, except for some stress fluctuations, which remain for large deformations. These fluctuations are studied at the micro‐mechanical level, by following the evolution of the co‐ordination number, force chains and the fraction of the sliding contacts of the sample. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

库车坳陷大北地区下白垩统巴什基奇克组储层成因地质分挝   总被引：6，自引：0，他引：6       下载免费PDF全文

张荣虎  张惠良  寿建峰  沈扬  李昌 《地质科学》2008,43(3)

塔里木盆地库车坳陷大北地区白垩系巴什基奇克组储层以细一中粒岩屑砂岩为主夹少量长石岩屑砂岩,杂基为铁泥质和泥质(2%～10%).胶结物以方解石(3%～15%)为主.粘土矿物以伊利石、绿泥石和伊/蒙混层为主,不含高岭石,伊/蒙混层中的蒙皂石含量一般为(15～20)%;主要孔隙组合为残余原生粒问孔-溶蚀孔-微孔隙,占储集空间总量的(50～90)%,其次为构造缝-溶蚀孔,主要的孔隙类型为溶蚀孔和裂缝,总体属于低孔低渗-特低孔特低渗储层.综合分析认为:阶段性的前陆构造逆冲推覆作用对沉积旋回性、水体盐度变化及物源区距离变化的控制至关重要;构造活跃期扇三角洲前缘环境中形成的差分选中-粗砂岩、近源快速堆积造成的高岩屑含量、干旱成湖导致的高碳酸盐胶结和早成岩期相对深埋-后期持续快速深埋压实作用,是特低孔特低渗储层的主要成因;而较优质储层足构造平缓期辫状河三角洲前缘环境中形成的分选好的中-细砂岩、早期表生溶蚀及弱碳酸盐胶结作用、早期构造破裂的复合作用及其叠加效应的结果.  相似文献   

Flexural isostatic response of the Alps to increased Quaternary erosion recorded by foreland basin remnants,SE France     

Jean‐Daniel Champagnac  Peter Van Der Beek  Gaël Diraison  Samuel Dauphin 《地学学报》2008,20(3):213-220

We test the hypothesis that flexural isostatic compensation of the mass removed by enhanced Quaternary erosion is responsible for uplift of the Western European Alps and their forelands. We use two well‐preserved and well‐dated (1.8 Ma) abandonment surfaces of foreland basin remnants in SE France (the Chambaran and Valensole plateaux) as passive benchmarks for tilting of the foreland. Estimating their initial slope from morphometric scaling relationships, we determine bulk post‐depositional tilting of 0.5–0.8% for these surfaces. The calculated isostatic response of the Alpine lithosphere to erosional unloading, using the method recently proposed by Champagnac et al. [Geology 35 (2007) 195–198] , yields a predicted tilting of 0.3–0.4% in the considered areas, explaining approximately half of the determined post‐depositional tilting. Such long‐term deformation being insensitive to cyclic loading/unloading because of glaciations, we suspect the other half to be related to as yet undetermined long‐wavelength and long‐lived tectonic process(es).  相似文献