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排序方式： 共有138条查询结果，搜索用时 31 毫秒
71.
JAN LUNDQVIST 《Geografiska Annaler: Series A, Physical Geography》2010,92(3):411-420
In the mountain area of Swedish Lapland, landforms with semicircular or horse‐shoe ridges encircling hummocky ground occur. They are interpreted as landslide or avalanche deposits directly upon, from or adjacent to down‐wasting ice. Since they are restricted to the vicinity of fault scarps in the Pärvie fault system the releasing factor is suggested to be displacement of bedrock blocks or related seismic activity. 相似文献
72.
The fan-delta reservoir play has become an important exploration target within the Junggar Basin, especially in the Mabei area within the Mahu Sag, where a fan-delta oil and gas pool has been recently discovered. The sedimentary characteristics, distribution patterns and formation mechanisms of the fan-delta clastic bodies in Lower Triassic Baikouquan Formation (T1b) were studied using seismic, well log and core data accompanied by a flume tank experiment and a modern analogue depositional study. The T1b in the Mabei area is composed of a fan delta consisting of fan-delta plain (including debris flow deposits, sheetflood deposits, braided channel deposits, and floodplain deposits), fan-delta front (including subaqueous reworked sheetflood deposits and distal sheetflood deposits) and muddy lake deposits. The sheetflood deposits, characterised by moderately sorted conglomerates with brown matrix, form during the peak flooding. They are widespread and sheet-like, occupying the major portion of the fan-delta plain. The braided channel deposits are characterised by well-sorted and clast-supported conglomerates and pebbly sandstones, formed later during the falling flow stage. Owing to the decline in volume and velocity, and the formation of continuously braided fluid flow, the sediments of the flood period are reworked, generating the braided channels. Laterally, the braided channels occur as belts of clastic bodies surrounded by continuous sheetflood deposits. Vertically, the braided channels are interbedded between the sheetflood deposits. The subaqueous reworked sheetflood deposits are characterised by greyish-green, well-sorted and clast-supported conglomerates, whereas the distal sheetflood deposits are characterised by well-sorted sandstones, intercalated with mudstone. The subaqueous reworked sheetflood and distal sheetflood deposits are a distal partly subaqueous extension of the main sheetflood deposits, albeit reworked by basinal currents and waves. The distal sheetflood deposits form on distal fringes of the sheetfloods and are more thoroughly reworked by longshore and wave currents. The braided channel, subaqueous reworked sheetflood and distal sheetflood deposits can form high-porosity reservoirs. These findings challenge the common view and suggest that the channelised facies on the fans are not the main flood events; rather, the more extensive sheetfloods are the major flood events. 相似文献
73.
The 85°E Ridge, located in the Bay of Bengal of the northeastern Indian Ocean is an enigmatic geological feature as it possesses unusual geophysical signatures. The ridge's internal structure and mode of eruptions are unknown due to lack of deep seismic reflection and borehole data control. Here, we analyze 10 km of long-streamer seismic reflection data to unravel the ridge's internal structure, and thereby to enhance the understanding of how the ridge was originated and grew over a geologic time. Seismic facies analysis reveals the ridge structure consisting of volcanic vent and several stratigraphic units including packs of prograding clinoforms. The clinoform sequences are interpreted as volcanic successions, and led to the formation of lava-delta fronts. Interpreted features of lava-fed deltas and intervening erosional surfaces, and mass flows along ridge flanks suggest that the 85°E Ridge is a volcanic construct, and was built by both subaqueous and multiphase sub-marine volcanism during the Late Cretaceous (approximately from 85 to 80 Ma). At later time, from Oligocene-Miocene (∼23 Ma) onwards the ridge was buried under the thick sediments of the Bengal Fan system. 相似文献
74.
The Upper Cretaceous Prairie Canyon Member of the Mancos Shale, Book Cliffs, Utah, contain outstanding examples of prodeltaic turbidity and hyperpycnal flow deposits. Sandstone‐rich, heterolithic and mudstone‐rich channel fills occur near the north‐west entrance to Tusher Canyon, Gunnison Butte and Bootlegger Wash. Mudstone‐rich and heterolithic‐rich hyperpycnal channel deposits are mostly unbioturbated, locally displaying a few specimens of Phycosiphon incertum, Protovirgularia dichotoma, Rosselia socialis, Schaubcylindrichnus coronus and Palaeophycus tubularis. Sandstone‐rich channel deposits consist of wave‐reworked turbidites and hyperpycnites, containing Helminthoidichnites tenuis, Lockeia siliquaria, Phycodes isp., Phycosiphon incertum, Protovirgularia dichotoma, Rosselia socialis, Skolithos linearis and Fugichnia. Scolicia isp. and Chondrites isp. occur locally. Strata along the south‐west entrance of Tusher Canyon record deposition in a prodelta turbidite lobe, but far from its axis. With the exception of a few specimens of Ophiomorpha isp., bioturbation is restricted to the top of the succession, where Curvolithus simplex, Gyrochorte comosa, Lockeia siliquaria, Palaeophycus tubularis and Ptychoplasma excelsum occur. Strata at Hatch Mesa record deposition in a hyperpycnal lobe, near to its axis. Sandstone beds include Curvolithus simplex, Gyrochorte comosa, Ophiomorpha nodosa, Palaeophycus tubularis, Phycosiphon incertum, Protovirgularia dichotoma, Ptychoplasma excelsum, Schaubcylindrichnus freyi, Skolithos linearis, large specimens of Rosselia socialis and indeterminate crustacean burrows. Chondrites isp. is present in the mudstone. High rates of both episodic and sustained sedimentation, degree of substrate consolidation, freshwater discharge and water turbidity are the most important stress factors in both channels and lobes. Taxonomic composition, uneven distribution of bioturbation through the successions, and overall low ichnodiversity help to distinguish these prodeltaic deposits from bathymetrically equivalent offshore strata in the same basin. Hyperpycnal flow deposits are formed in a wide variety of environmental settings, therefore displaying high ichnological variability. Such variability is summarized by characterising ichnofaunas from four different depositional settings: (i) lakes; (ii) shelf deltas; (iii) shelf‐edge deltas; and (iv) deep‐marine systems. 相似文献
75.
A criterion, allowing one to assess conditions likely togenerate gap flows and/or hydraulicjumps in stratified flows over a mountain ridge or a mountain pass,is derived. It is based on the one-dimensional reduced-gravity shallow-watertheory generalized to a three-dimensional orography with moderate streamwisevariations by introducing a variable effective flow cross-section. In this way,the hydraulic jump and gap flow are accommodated within the same model. Theresulting steady hyperbolic problem is shown to require the boundaryconditions to be expressed in terms of Riemann invariants. The latter yield the flow betweentwo given sites in a unique way. In particular, it is possible to relateunambiguously the existence of a hydraulic jump/gap flow and its energydiscontinuity to the boundary conditions. A simple method of flow interpolationand energy discontinuity calculation between two sites is presented. 相似文献
76.
建立了一种在非规则结构化网格上求解平面二维浅水流动的有限体积方法。通过采用地形在离散网格内双线性变化及离散网格界面间地形连续的地形逼近方法和应用可以有效处理间断问题的Roe格式来离散浅水方程中的对流项,并通过VanLeer提出的状态插值法提高格式精度。在计算原始变量在网格内的插值梯度时,采用最小二乘方法求变量的最优梯度代替差分计算梯度,从而可采用任意形状的不规则四边形网格离散计算域。计算实例表明,该方法能够计算间断问题并能够处理各种复杂流态的过渡,具有较好适应性和计算精度,能够满足不同实际问题的计算要求。 相似文献
77.
78.
J.V. Gardner P. Dartnell L.A. Mayer J.E. Hughes Clarke B.R. Calder G. Duffy 《Geomorphology》2005,64(3-4):133-166
A high-resolution multibeam survey of the northwest Florida shelf mapped six relict shelf-edge deltas, each with a drowned barrier–island system developed on its south and southwestern rims. The deltas appear to have formed during periods of sea-level stasis that occurred between 58,000 and 28,000 years ago. The barrier islands formed on the deltas during periods of slow regression during this same time interval. Large fields of asymmetric dunes are found on the delta surfaces as well as on the south and southwestern flanks of the deltas. The asymmetry and orientation of the dunes suggest that a northward-flowing current was sheared by the presence of the delta topography, and as a result, the upper layer of the flow continued to the north, whereas the lower layer was steered by the topography. The topographic steering accelerated the northward flow around the south and southwestern flanks with speeds adequate to form large dunes. The flow slowed after rounding southwestern flank but accelerated again as it encountered the next delta flank to the north. The age of the dune formation is unknown, and no northward-flowing geostrophic flow has been reported in the literature from this area. 相似文献
79.
以鄂尔多斯盆地延长组长8-长6致密储集层为例,采用地质统计数学(Levy Sim)和沉积地层正演模拟对沉积非均质性进行研究。结果表明,地质统计学Levy函数能够有效地表征非均质性参数,不仅可以表征油藏尺度(岩心、露头和测井曲线尺度),而且也可以有效刻画岩石微观尺度的非均质性。而三维正演地层模拟方法 Sedsim则能够有效地模拟浅水三角洲砂体的空间展布。沉积地层正演模拟与非传统地质统计学相结合,能够更真实地定量刻画不同尺度的沉积非均质性,该方法不仅有效地解决了不同尺度沉积储集层、烃源岩及盖层非均质性定量表征的难题,而且为非常规油气成藏研究提供了新思路与新的定量评价方法。 相似文献
80.