The structural and sedimentological setting of the Quaternary deposits in Al-Ain area, UAE   总被引：1，自引：0，他引：1  

Mohamed A. El-Ghawaby  Mohamed I. El-Sayed 《Journal of Arid Environments》1997,35(4):627-640

Quaternary sediments represent the main constituent which covers an ENE–WSW elongated depression some 25 km long and 10 km wide (Al-Ain area). This depression is encountered between two north and south low fault scarps and is located perpendicular to the Al Jaww plain and Jabel Hafit axes.Four main types of Quaternary surface deposits were identified belonging to: flood plain and braided channels; desert plain; aeolian sand; and sabkha. The first type shows many pedogenic and non-pedogenic features of which are dolocrete, calcrete and gypcrete.An ENE–WSW closely-spaced dip-slip, stepping pattern fault set could be traced in dolocretized-calcretized braided channel deposits, on the south margin of this depression, where the relationship between fault geometry, displacement and geomorphology suggest a model of either graben or half-graben. The role of this system in developing the landscape of Al-Ain is well documented near the surface but a comprehensive study to assess its role in the sub-surface is needed.  相似文献   

东南极、西南极4000年以来生物活动强度变化与南极冰芯的对比          下载免费PDF全文

曹俊忠  李天杰 《极地研究》1997,9(4):20-23

利用南极中山站地区的冰退速率和奈拉湖湖相沉积物中的硫浓度分布特征推算了奈拉湖的沉积速度。以硫元素浓度作为湖相沉积物中生物活动强度的指标，对比了西南极长城站地区西湖沉积物和东南极中山站奈拉湖沉积物中生物活动强度的变化趋势，并与Ｄ１０冰芯中反映海洋生物活动强度的指标ＣＨ３ＳＯ－３的浓度变化趋势作对比。结果表明，４０００ａＢ．Ｐ．以来三者的历史变化趋势是明显一致的，１８５０～１１５０ａＢ．Ｐ．是生物活动的最宜期，这是全球环境变化在不同地点、不同类型沉积物中的表现。  相似文献   

南极长城站地区西湖底沉积物化学元素分布规律及其环境意义   总被引：3，自引：0，他引：3       下载免费PDF全文

李锋  李天杰 《极地研究》1997,9(4):24-29

利用南极长城站地区西湖底沉积物的化学元素背景值，对西湖底沉积物元素的时序分布规律及其指示的环境意义作了较细致的研究。研究表明，湖底沉积物元素的时序变化规律与站区自然环境变化密切相关。尽管元素的时序变化滞后于自然环境的波动，但对研究长城站地区自然环境演变仍具有一定的指示意义。尤其是Ｓ元素的异常变化，可能揭示出长城站地区两次规模较大的火山活动。  相似文献   

风成沉积物磁组构与中国黄土区第四纪风向变化   总被引：12，自引：4，他引：12       下载免费PDF全文

吴汉宁  岳乐平 《地球物理学报》1997,40(4):487-494

通过对黄土高原几个剖面黄土样品磁化率各向异性的初步研究，发现了风成沉积物中的磁组构特征，且它的形成受沉积作用控制并与黄土高原形成时的古风场有关，即风成沉积物磁化率椭球体主轴方向及各轴比值与磁性颗粒分布排列方式亦即与空气动力条件相关．阐明了风成沉积物磁组构形成机制及其与古风向的关系，提出一种能够定量研究黄土高原形成时古风场的方法，为研究黄土高原形成演化和第四纪以来气候变化提供了基础数据．  相似文献   

山东济阳坳陷岩层空隙比与应力传递速度的相关性研究          下载免费PDF全文

卜凡泉  王尤培 《地震地质》1997,19(1):25-30

统计了不同深度测层的群井降水附加应力从开始传递到水位响应的间隔时段，在此基础上建立了应力在地层中传递深度－时间相关模式，进行了有关参数反演，并结合相关地质、气象等资料，提出了岩层空隙比－应力传递速度的相关模型。该模型说明了应力传递速度与岩层结构、构造的内在联系，为不同类型应力在不同空隙比岩层中的单层传播速度、组合层段传播所需时间计算提供了简单、有效的方法，也为识别降水引起的附加应力对深井水位动态的干扰提供了依据  相似文献   

INVESTIGATIONS ON EROSIONAL PROCESSES OF COHESIVE SEDIMENT USING AN IN-SITU MEASURING DEVICE     

Rosi LIEM Research Engineers  Institute of Hydraulic Engineering  Water Resources Management  Aachen Univer-s of Technology  Germany Volker SPORK Research Engineers  Institute of Hydraulic Engineering  Water Resources Management  Aachen Univer- 《国际泥沙研究》1997,(3)

I.INTRODUCTIONToconstructanidealmeasuringdeviceforin-situstUdiesincomparisontolaboratorydeVicesastrongeremphasishastobesetonthehandlingoftheSystemandtheresistanceunderwater,whichaughtbethereasonwhynotmanyapproachesonrealin-situinvestigationwerecaaccedoutlately.Sincetheedupandtheconstructionseemtodemandahigheramountofcostsandeffort,quasiin-siamstudieswerecAnedoutrefetringtoanundisturbedsedimentsampledrawnfromthesedimentbedoutofthewaterintothesamplingchamberofameasuringdevice.Evenifthisisa…  相似文献   

The relationship between glacial activity and sediment production: evidence from a 4450-year varve record of neoglacial sedimentation in Hector Lake, Alberta, Canada   总被引：3，自引：0，他引：3  

Eric M. Leonard 《Journal of Paleolimnology》1997,17(3):319-330

A 4450-year sequence of varves, spanning the entire Neoglacialinterval, has been recovered from Hector Lake, Alberta. The varve record is compared to records of regional glacial history toevaluate therelationship between alpine glacial activity and sediment production. Glacial controls on sediment production vary with the timescale considered. Long-term variations in sedimentation rate, of centuries to millennial duration, reflect changes in ice extent of the same timescale. Superimposed on these long-term changes is decadal-scale variability that is complexly related to upvalley ice extent. Over the short term, high sedimentation rates may be associated with glacier maximum stands, or with periods of glacier advance or recession. Overthe last millennium at least, highest sedimentation rates appear to have been associated with transitional periods, preceding or post-dating maximum ice stands, rather than with times of maximum ice extent.  相似文献   

Differential sedimentation versus coring artifacts: a comparison of two widely used piston-coring methods   总被引：1，自引：0，他引：1  

André F. Lotter  Josef Merkt  Michael Sturm 《Journal of Paleolimnology》1997,18(1):75-85

In order to compare two widely used piston-coring techniques, parallel cores were taken with both a Kullenberg and a Livingstone corer in the deepest part of Soppensee (25 m), a small eutrophic Swiss lake containing varved sediments. The cores were taken within a horizontal distance of 3 m and yield comparable stratigraphic records. Differences in millimetre-scale microstructure are attributed to primary sedimentation processes at the water/sediment interface. Sediment thin-sections, as well as sediment x-radiograph investigations, reveal no difference in microstructure that could unequivocally be attributed to one of the coring methods used. The differences in deposition are therefore thought to reflect the inherent variability of lacustrine sedimentation in Soppensee.Major differences in overall core recovery do occur, however, in organic-rich, highly porous sediments. These variations are primarily attributed to differential gas expansion. Actual sediment-accumulation rates can therefore only be correctly estimated if the sedimentary record can be constrained within a high-resolution temporal framework, e.g. by annual laminations.  相似文献   

Sesquiterpenoids in sediments of a hypersaline lagoon: A possible algal origin     

V. O. Elias  A. M. A. De Barros  A. B. de Barros  B. R. T. Simoneit  J. N. Cardoso 《Organic Geochemistry》1997,26(11-12)

Core samples were collected in Lagoa Vermelha, a hypersaline lagoon located about 100 km east of Rio de Janeiro (Brazil). The sediment composition is predominantly carbonate in amounts up to 93%. Analysis of δ¹³C of the total organic matter in the sediments showed that marine organic matter predominates throughout the core (δ¹³C ranges from −15.84 to −22.64‰ vs. PDB). Organic carbon contents (TOC) ranged from 0.81 to 13.28%. A series of cadinane-type sesquiterpenoids can be recognized in the gas chromatography-mass spectrometry data. Essentially the same components are present in all the samples, with variations only in their relative abundances. The most abundant compounds are α- and β-cubebene, α- and β-cedrene, cadinenes (different isomers), α-curcumene and calamenene, with minor amounts of calarene, humulene, calacorene and cadalene. Since this lagoon is surrounded by dunes with only minor vegetation typical of this environment (grasses, small non-resinous shrubs and no forest) with no potential source for sesquiterpenoids, a terrestrial origin for these compounds is excluded and an algal origin is more consistent with the locale and the recognition of sesquiterpenoids (including cadinol) in microbial mats from the lagoon. Only the natural product precursor sesquiterpenoids are present in the microbial mats with no detectable diagenetic derivatives (e.g. calamenene and cadalene). This indicates that the compounds in the mats are from recent input and those found in the sediments are most likely derived from former algal biomass in this lagoon, a fact confirmed by the recognition of a series of diagenetic aromatic components in the sediments. Surface sediments contain n-alkanes with no even-to-odd predominance indicating that microbial activity is higher in shallower sediments. Moreover, mass fragmentograms (m/z 191) of biomarkers revealed the presence of 17α(H),21β(H)-hopanes, the mature isomers, together with their ββ precursors and low amounts of the intermediates with the βα configuration (moretanes). This indicates a contribution of mature organic matter to these immature sediments.  相似文献   

Mercury pollution in two gold mining areas of the Brazilian Amazon     

S. Rodrigues Filho  J.E.L. Maddock 《Journal of Geochemical Exploration》1997,58(2-3)

Gold has been exploited intensively in the Brazilian Amazon during the past fifteen years using garimpo methods (small-scale gold mining). In this study, two gold mining areas were investigated, the municipalities of Pocone and Alta Floresta located in the state of Mato Grosso. Central Brazil. The elemental mercury (Hg) used in amalgamating the gold, the final stage of the ore dressing process, has caused abnormal Hg concentrations in waterways. This has occurred principally in the Amazon region, where most of the ore prospected is alluvial. Background levels of metals were determined by analyzing sediments and soils located upstream of the anthropogenic inputs and unaffected by mining activities. The study aimed to evaluate the pollution level in sediments and soils, taking into account drainage waters directly affected by gold mining. ‘Geoaccumulation indexes’ (Igeo) of Hg in sediments from both study areas were used to assesses the pollution level in the aquatic environment. The geoaccumulation indexes of Hg in sediments of the Bento Gomes River in Pocone indicate a relatively high degree of pollution at some sites, even reaching class 4 (1.85 mg/kg). However, when the river reaches the Pantanal swamp, Hg concentrations drop considerably to 0.30 mg/kg. This drop seems to be due to accumulation of metals in the sediments of a lake (sampling site PG-24), which retains most of the sediments transported by the Bento Gomes River. Accumulation of metals in the lake also occurred for Cu, Pb, Zn, Fe and Mn. In the region of Alta Floresta, total Hg concentrations in sediments of the Teles Pires River were studied in the grain size fractions < 74 μm and > 74 μm. Hg concentrations in bottom sediments of this river were higher than those found in the Pocone region, with increases of 1.5 to 30 times the background, and thus reaching an Igeo up to class 5.  相似文献