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951.
青藏高原北缘哈拉湖近800年来 湖泊沉积及其环境意义* 总被引:5,自引:5,他引:5
文章以青藏高原北缘高山祁连山湖泊——哈拉湖作为研究对象,利用放射性核素210 Pb和137 Cs测年资料,通过对此高海拔湖泊沉积碳酸盐氧碳同位素、碳酸盐含量、总有机碳含量、磁化率等环境代用指标的分析,揭示了这一地区近800年来的气候环境变化过程。分析表明哈拉湖记录的气候环境变化经历了3个阶段:1206~1700A.D.环境较为寒冷、湿润,并有持续变湿的趋势;1700~1920A.D.环境由冷湿的状况趋向温暖干旱,1771年之后,环境保持相对稳定;1920~2002A.D.是自1206年以来最为温暖干旱的阶段。 相似文献
952.
混合沉积是一种特殊的沉积类型,研究程度较低。金家地区处于东营凹陷的斜坡带,该区古近系沙河街组第四段上亚段发育了碳酸盐与陆源碎屑的混合沉积,研究认为该混合沉积为古湖泊内的混合沉积,可划分为混积砂滩亚相、混积砂坝亚相及半深湖混积亚相,混合沉积物既包括同层混合沉积物(灰质砂岩、砂质灰岩、泥质灰岩等),又包括互层混合沉积物(砂岩与颗粒灰岩互层沉积等),研究区的混合沉积受当时构造运动、碎屑物质供给量、湖平面的变化等诸多因素控制。 相似文献
953.
Wind tunnel experiments were carried out to measure the spatial distribution in equilibrium transport of four types of mixed sand. The flux profiles of each grain size group were calculated. It is found that the vertical distribution of mean grain size has a close relation with the grain size distribution in the sand bed. In a log-linear plot, the flux profiles of main grain size groups are all straight lines and their slopes are nearly equal. It is also found that the ratio of transport rate of each size group to the whole transport rate is directly proportional to the mass ratio of each size group in the sand bed and the proportion value is only dependent on the grain size. This harmonious law is applicable to all four types of mixed sand used in the experiment. 相似文献
954.
沉积物粒度对水合物形成的制约:来自IODP 311航次证据 总被引:1,自引:0,他引:1
对取自IODP 311航次(东北太平洋Cascadia大陆边缘)所有5个站位、采样间距约为1.5 m的614件沉积物样品,利用Beckman Coulter LS 230激光粒度仪进行了沉积物粒度分析,获得了沉积物粒度随深度变化特征,进而与水合物层位的替代指标进行了位置对比,这些指标包括特殊沉积构造(soupy和mousse like构造)、测井数据(LWD)推算出来的水合物饱和度(Sh)、岩芯红外图像和实际钻取的含水合物沉积物等。发现沉积物粒度分别为31~63 μm和63~125 μm的2组较粗粒径的沉积物数量变化增多的位置与水合物出现层位之间存在较好的位置对应关系。如在U1326站位海底以下5~8 m、21~26 m、50~123 m、132~140 m、167~180 m、195~206 m、220~240 m深度位置出现了沉积物粒度明显偏向粗粒的趋势,而这些位置正好对应于大多数特殊沉积构造出现的深度,也对应于水合物饱和度(Sh)值相对较高的深度,并与一些实际钻取的赋含水合物的浊积沙层观察结果一致。因此,初步研究后认为,沉积物粒度在水合物形成过程中扮演了重要角色,天然气水合物可能偏向形成于粒度大于31 μm的粗粒沉积物中。
相似文献
955.
采用一系列温和的化学降解法对松辽盆地南部嫩江组烃源岩的干酪根进行连续的选择性化学降解,并对不同降解产物进行色谱—同位素比值质谱分析。研究表明碱性水解和脱硫产物以一元脂肪酸和正构烷烃为主,其中正构烷烃碳同位素分布曲线呈现一定的“负倾”(即随碳数增加呈现逐渐贫13C)趋势;一元脂肪酸以C16和C18为主,具有明显的偶碳优势,与同碳数的正构烷烃具有相似的碳同位素组成。氧化产物则以一元脂肪酸和α,ω 二元脂肪酸为主,一元脂肪酸低碳数部分呈现“负倾”趋势,高碳数部分则呈现“正倾”的趋势;α,ω 二元脂肪酸与低碳数的一元脂肪酸具有相似的分布,表明它们可能具有相同的母源。对比研究表明JL 30抽提物中正构烷烃可能存在混源的影响,其碳同位素组成是多源混合的结果。 相似文献
956.
Hsueh-Yu Lu 《Environmental Geology》2007,51(6):1029-1041
A new method has been developed to estimate the hydraulic conductivity in unconsolidated aquifers. The method uses bulk geochemical
compositions correlated with hydraulic conductivities measured by pumping tests. The concept is based on a general rule that
hydraulic conductivity is principally controlled by grain-size distribution and particle shape,both of which relate to mineralogical
composition. Using a MINLITH algorithm, normative mineralogical compositions can be derived from bulk geochemical compositions
economically and expediently, and then correlated to the hydraulic conductivity determined by pumping tests in the field.
In this study, 202 sediment samples from nine unconsolidated aquifers were analyzed by X-ray fluorescence. Although hydraulic
conductivity does not show a definite relationship with geochemical compositions, it does demonstrate a linear logarithmic
equation to the content of normative earthy minerals. However, linear regressed equations should not be applied to aquifers
composed of medium to coarse sand and gravel sizes due to interference from lithic fragments. In addition, this equation tends
to overestimate hydraulic conductivity possibly because the effect of compaction is ignored in this study. 相似文献
957.
A Combined Three-Dimensional Geological-Geostatistical-Numerical Model of Underground Excavations in Rock 总被引:1,自引:1,他引:1
Summary. This paper exploits geological and borehole geotechnical data obtained in the exploratory phase of a tunneling project to
investigate in a first place if the kriging interpolation scheme may effectively reproduce the spatial variability of rock
mass quality (Rock Mass Rating, RMR) in the vicinity of tunnels. For this purpose a quick solver in Fortran has been developed
that performs variography analysis of 3D spatial data, fast kriging estimations of RMR between borehole sampling locations
at the centroids of the elements of the numerical model, and model validation. For the purpose of an integrated underground
excavation design, a step further is made by incorporating into the 3D mechanical numerical model of the rock mass, the three-dimensional
(3D) solid geological model, thus coupling the geology with the ground (geotechnical) model (i.e. each element of the numerical
model is assigned a geological material). The mechanical properties of each finite difference cell (or Representative Elementary
Volume) of the ground model were then prescribed according to its geological type, the spatial heterogeneity of the rock mass
expressed quantitatively with the kriging model, and the upscaling calculations of the mechanical properties of the intact
rocks determined in the laboratory, based on the size-effect (strength dependence on size) and Damage Theory. Furthermore,
a preliminary numerical simulation of the advance of unsupported tunnels in the model of the heterogeneous rock mass was performed
for illustration purposes. 相似文献
958.
959.
V. N. Sergeev M. A. Semikhatov M. A. Fedonkin A. F. Veis N. G. Vorob’eva 《Stratigraphy and Geological Correlation》2007,15(2):141-160
Expounded in this work are the results of critical consideration of published and original data on biologic nature and appearance chronology of different groups of Archean and Lower Proterozoic (3.5–1.65 Ga) paleontological remains known from geological record. Conclusions are substantiated by morphological analysis of structurally preserved microfossils, their facies distribution, and by inferable genesis and principal evolutionary trends of Archean stromatolites. A special attention is paid to variations of organic and carbonate carbon isotope composition in sedimentary successions with paleontological remains and to recent information about discovered, most ancient biomarkers of large groups of organic world. As a result of this approach, a detailed model of Precambrian organic world evolution is suggested. 相似文献
960.
Cosmas Kongnyuy Shang Muharrem Satir Emmanuel Nkonguin Nsifa Jean-Paul Liégeois Wolfgang Siebel Heiner Taubald 《International Journal of Earth Sciences》2007,96(5):817-841
We present a geochemical and isotopic study that, consistent with observed field relations, suggest Sangmelima late Archaean
high-K granite was derived by partial melting of older Archaean TTG. The TTG formations are sodic-trondhjemitic, showing calcic
and calc-alkalic trends and are metaluminous to peraluminous. High-K granites in contrast show a potassic calc-alkaline affinity
that spans the calcic, calc-alkalic, alkali-calcic and alkalic compositions. The two rock groups (TTG and high-K granites)
on the other hand are both ferroan and magnesian. They have a similar degree of fractionation for LREE but a different one
for HREE. Nd model ages and Sr/Y ratios define Mesoarchaean and slab-mantle derived magma compositions respectively, with
Nb and Ti anomalies indicating a subduction setting for the TTG. Major and trace element in addition to Sr and Nd isotopic
compositions support field observations that indicate the derivation of the high-K granitic group from the partial melting
of the older TTG equivalent at depth. Geochemical characteristics of the high-K granitic group are therefore inherited features
from the TTG protolith and cannot be used for determining their tectonic setting. The heat budget required for TTG partial
melting is ascribed to the upwelling of the mantle marked by a doleritic event of identical age as the generated high-K granite
melts. The cause of this upwelling is related to linear delamination along mega-shear zones in an intracontinental setting. 相似文献