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941.
地球轨道根数变化与第四纪冰期 总被引:1,自引:0,他引:1
介绍了米兰柯维奇(Milankovitch)天文气候学理论和第四纪地质时期以来冰期的研究进展。研究结果表明,地球上的冰体积具有近10万yr的变化周期,并伴有近4万yr和2万yr的变化周期,它们是由于地球的轨道根数变化导致的气候变迁所致;不同的地球物理资料中均存在上述类似的变化周期,表明气候变迁所导致的变化是全球性效应,证实米兰柯维奇天文理论是基本正确的;对天文气候学理论作了简要介绍,指出了米兰柯维奇天文气候学理论的可能不足,对引起最近百万yr以来的近10万yr气候变化周期的可能天文机制也作了介绍。 相似文献
942.
Classifications of urban settlements have traditionally used total employment data in place of basic (export-oriented) employment data. While urban analysis agree upon the superiority of basic employment data for these classifications, usually only total employment data are available. This paper uses the Arizona Community Data Set, a unique survey-generated body of information that describes the major economic characteristics of numerous Southwestern communities and includes both basic and total employment data, to explore the extent to which misclassification results when using total employment data. 相似文献
943.
我国钾盐资源的开发利用 总被引:14,自引:3,他引:14
本文以基础统计资料为主,首先叙述了我国钾盐资源的基本情况及其分布特点和勘查程度,介绍国内钾资源开发利用的现状,就如何开发利用我国钾资源,解决国内钾肥短缺问题提出了一些建议. 相似文献
944.
945.
达坂山公路隧道冻土工程问题和工程防治措施 总被引:2,自引:0,他引:2
达坂山公路隧道位于高海拔寒冷地区,自然条件非常独特(高寒、低氧、多雨雪、冬季较长等),地质条件又很复杂,这些不利因素为工程的设计和施工带来了许多新问题,最为突出的是:工程的冻害及水害的防治;隧道的开挖、贯通和营运,改变了原有的温度场、应力场和地下水的迳流排泄途径;传统施工方法受到挑战等.隧道工程的冻害及水害的防治是关系到隧道能否正常营运的关键.为了克服和解决以上问题,经过反复研究和论证,采取了必要的的工程措施和先进的施工方法,确保了该隧道的顺利竣工和正常营运,为建设同类隧道积累了宝贵的经验. 相似文献
946.
947.
山东省牛庄洼陷古近系沙河街组沙三中亚段储集层成岩作用研究 总被引:12,自引:1,他引:12
山东省牛庄洼陷古近系沙河街组沙三中亚段储集层岩石类型以长石岩屑砂岩和岩屑长石砂岩为主,岩石结构成熟度和成分成熟度均较低。砂岩成岩作用包括压实作用、胶结作用、交代作用、溶解作用等。压实作用主要有刚性颗粒发生脆性破裂、颗粒之间呈线接触和凹凸接触、岩石碎屑颗粒呈明显的定向排列、塑性颗粒挤压变形或刚性颗粒嵌入变形颗粒中、粘土质碎屑被挤压变形发生假杂基化等五种表现形式。胶结物主要有泥质胶结物、碳酸盐胶结物、自生粘土矿物和自生石英、长石。交代作用主要有石英交代长石颗粒、碳酸盐胶结物交代石英、长石及岩屑颗粒、碳酸盐胶结物之间的相互交代。发生溶解作用的主要是石英、长石和岩屑颗粒,胶结物中主要是碳酸盐矿物。目前研究区沙三中亚段储集层成岩演化处于晚成岩A期。影响成岩作用的主要因素为岩石成分、沉积环境、孔隙流体性质等。成岩作用对储集物性的影响主要表现在孔隙度和渗透率的变化,其中压实作用和胶结作用使储层原生孔隙迅速减少、渗透率降低,使得储集物性变差;而溶解作用是次生孔隙发育的主要因素,从而改善砂岩的储集性能。 相似文献
948.
《International Geology Review》2012,54(3):341-360
ABSTRACTThe Upper Triassic Langjiexue Group, which lies immediately south of the Yarlung-Tsangpo Suture Zone in the Shannan area of southeastern Tibet, represents an important part of the Tethyan Himalayan Sequence (THS). Its provenance and palaeogeography have been the subject of debate. We present new data on petrographic composition, whole-rock geochemistry, and detrital zircon U–Pb geochronology to constrain the provenance of the Langjiexue Group. The dominance of quartz grains and felsic volcanic lithic fragments suggests that the sandstones are litho-quartzose. The trace element geochemical signatures (V–Ni–Th*10, Co/Th–La/Sc, Eu/Eu*–Th/Sc) suggest derivation from felsic igneous sources. The detrital zircon age spectra display three major peaks: a Meso-to-Neoproterozoic peak (1200–900 Ma, 7–18%), a Neoproterozoic-to-Late Cambrian peak (750–500 Ma, 32–65%), and a Late Carboniferous-to-Late Triassic peak (300–200 Ma, 11–33%). The maximum depositional age of early Carnian (236–235 Ma) is obtained by calculating weighted average ages of the youngest zircons (≤250 Ma). The youngest age cluster (300–200 Ma) is incompatible with sources from neighbouring terranes, including the South Qiangtang terrane, Lhasa terrane, THS, and Higher Himalayan Crystalline. Correlations of the Permian–Triassic zircons with those of time-equivalent strata in northwest Australia, west Burma, and the Banda Arc unveil a potential connection to the Tasmanides along the convergent margin of eastern Australia. The New England Orogen (300–230 Ma) could have supplied the Langjiexue Group with magmatic materials via continent-scale drainage systems or a submarine fan complex. This scenario provides a new perspective into the transport of detritus from distal orogens to sedimentary basins thousands of kilometres away. 相似文献
949.
Root‐related rhodochrosite and concretionary siderite formation in oxygen‐deficient conditions induced by a ground‐water table rise 下载免费PDF全文
Maciej J. Bojanowski Elżbieta Jaroszewicz Adrijan Košir Maciej Łoziński Leszek Marynowski Anna Wysocka Arkadiusz Derkowski 《Sedimentology》2016,63(3):523-551
Sedimentological, mineralogical, stable carbon and oxygen isotope determinations and biomarker analyses were performed on siderite concretions occurring in terrestrial silts to understand their formation and to characterize the sedimentary and diagenetic conditions favouring their growth. High δ13C values (6·4‰ on average) indicate that siderite precipitated in an anoxic environment where bacterial methanogenesis operated. The development of anoxic conditions during shallow burial was induced by a change in sedimentary environment from flood plain to swamp, related to a rise of the ground‐water table. Large amounts of decaying plant debris led to efficient oxygen consumption within the pore‐water in the peat. Oxygen depletion, in combination with a decrease in sedimentation rate, promoted anoxic diagenetic conditions under the swamp and favoured abundant siderite precipitation. This shows how a change in sedimentary conditions can have a profound impact on the early‐diagenetic environment and carbonate authigenesis. The concretions contain numerous rhizoliths; they are cemented with calcium‐rhodochrosite, a feature which has not been reported before. The rhodochrosite cement has negative δ13C values (?16·5‰ on average) and precipitated in suboxic conditions due to microbial degradation of roots coupled to manganese reduction. The exceptional preservation of the epidermis/exodermis and xylem vessels of former root tissues indicates that the rhodochrosite formed shortly after the death of a root in water‐logged sediments. Rhodochrosite precipitated during the initial stages of concretionary growth in suboxic microenvironments within roots, while siderite cementation occurred simultaneously around them in anoxic conditions. These suboxic microenvironments developed because oxygen was transported from the overlying oxygenated soil into sediments saturated with anoxic water via roots acting as permeable conduits. This model explains how separate generations of carbonate cements having different mineralogy and isotopic compositions, which would conventionally be regarded as cements precipitated sequentially in different diagenetic zones during gradual burial, can form simultaneously in shallow burial settings where strong redox gradients exist around vertically oriented permeable root structures. 相似文献
950.
V. S. N. Murty V. Ramesh Babu L. V. G. Rao Charuta V. Prabhu V. Tilvi 《Journal of Earth System Science》2000,109(2):267-277
Time-series data on upper-ocean temperature, Vessel-Mounted Acoustic Doppler Current Profiler (VM-ADCP) measured currents
and surface meteorological parameters have been obtained for the first time in the southern Bay of Bengal at 7‡N, 10‡N, and
13‡N locations along 87‡E during October–November, 1998 under BOBMEX-Pilot programme. These data have been analysed to examine
the diurnal variability of upper oceanic heat budget and to estimate the eddy diffusivity coefficient of heat in the upper
layer. Diurnal variation of near-surface temperature is typical at northern location (13‡N) with a range of 0.5‡C while the
diurnal range of temperature is enhanced to 0.8‡C at the central location (10‡N) due to intense solar radiation (1050 W/m2), clear skies and low wind speeds. At the southern location (7‡N), the diurnal variation of temperature is atypical with
the minimum temperature occurring at 2000 hrs instead of at early morning hours. In general, the diurnal curve of temperature
penetrated up to 15 to 20 m with decreasing diurnal range with depth. The VM-ADCP measured horizontal currents in the upper
ocean were predominantly easterly/northeasterly at southern location, north/northerly at central location and northwesterly
at northern location, thus describing a large-scale cyclonic gyre with the northward meridional flow along 87‡E. The magnitudes
of heat loss at the surface due to air-sea heat exchanges and in the upper 50 m layer due to vertical diffusion of heat are
highest at the southern location where intense convective activity followed by overcast skies and synoptic disturbance prevailed
in the lower atmosphere. This and the estimated higher value (0.0235 m2/s) of eddy diffusivity coefficient of heat in the upper ocean (0–50 m depth) suggest that 1-D processes controlled the upper
layer heat budget at the southern location. On the other hand, during the fair weather conditions, at the central and northern
locations, the upper layer gained heat energy, while the sea surface lost (gained) heat energy at northern (central) location.
This and lower values of eddy diffusivity coefficient of heat (0.0045 and 0.0150 m2/s) and the northward intensification of horizontal currents at these locations suggest the greater role of horizontal heat
advection over the 1-D processes in the upper ocean heat budget at these two locations. 相似文献