Slump blocks, intraformational conglomerates and associated erosional structures in Pennsylvanian fluvial strata of eastern Canada   总被引：2，自引：0，他引：2  

H. W. VAN DE  POLLI. M. PATEL 《Sedimentology》1989,36(1):137-145

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Modern carbonate and terrigenous clastic sediments on a cool water, high energy, mid-latitude shelf: Lacepede, southern Australia   总被引：1，自引：0，他引：1  

NOEL P. JAMES  YVONNE BONE†  CHRISTOPHER C. VON DER  BORCH‡ VICTOR A. GOSTIN† 《Sedimentology》1992,39(5):877-903

The wide Lacepede Shelf and narrow Bonney Shelf are contiguous parts of the south-eastern passive continental margin of Australia. The shelves are open, generally deeper than 40 m, covered by waters cooler than 18°C and swept by oceanic swells that move sediments to depths of 140 m. The Lacepede Shelf is proximal to the ‘delta’of the River Murray and the Coorong Lagoon. Shelf and upper slope sediments are a variable mixture of Holocene and late Pleistocene quartzose terrigenous clastic and bryozoa-dominated carbonate particles. Bryozoa grow in abundance to depths of 250 m and are conspicuous to depths of 350 m. They can be grouped into four depth-related assemblages. Coralline algae, the only calcareous phototrophs, are important sediment producers to depths of 70 m. Active benthic carbonate sediment production occurs to depths of 350 m, but carbonate sediment accumulation is reduced on the open shelf by continuous high energy conditions. The shelf is separated into five zones. The strandline is typified by accretionary sequences of steep shoreface, beach and dune carbonate/siliciclastic sediments. Similar shoreline facies of relict bivalve/limestone cobble ridges are stranded on the open shelf. The shallow shelf, c.40–70 m deep, is a wide, extremely flat plain with only subtle local relief. It is a mosaic of grainy, quartzose, palimpsest facies which reflect the complex interaction of modern bioclastic sediment production (dominated by bryozoa and molluscs), numerous highstands of sea level over the last 80 000 years, modern mixing of sediments from relatively recent highstands and local introduction of quartz-rich sediments during lowstands. The middle shelf, c.70–140 m deep, is a gentle incline with subtle relief where Holocene carbonates veneer seaward-dipping bedrock clinoforms and local lowstand beach complexes. Carbonates are mostly modern, uniform, clean, coarse grained sands dominated by a diverse suite of robust to delicate bryozoa particles produced primarily in situ but swept into subaqueous dunes. The deep shelf edge, c. 140–250 m deep, is a site of diverse and active bryozoa growth. Resulting accumulations are characteristically muddy and distinguished by large numbers of delicate, branching bryozoa. The upper slope, between 250 and 350 m depth, contains the deepest platform-related sediments, which are very muddy and contain a low diversity suite of delicate, branching cyclostome bryozoa. This study provides fundamental environmental information critical for the interpretation of Cenozoic cool water carbonates and the region is a good model for older mixed carbonate-terrigenous clastic successions which were deposited on unrimmed shelves.  相似文献   

A CORER FOR SAMPLING SHALLOW-MARINE SANDS     

H. K. J. VAN DEN  BUSSCHE J. J. H. C. HOUBOLT 《Sedimentology》1964,3(2):155-159

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THE INFLUENCE OF RAINFALL ON TRANSPORT OF BEACH SAND BY WIND     

P. M. VAN DIJK  L. STROOSNIJDER  J. L. M. P. DE LIMA 《地球表面变化过程与地形》1996,21(4):341-352

This paper deals with the effect of rainfall on the process of wind erosion of beach sands and presents results from both field and wind tunnel experiments. Although sediment transport by splash is of secondary importance on coastal dunes, splash–saltation processes can move sediments in conditions where no motion is predicted by aeolian processes. The effect of raindrop impact on the movement of soil particles by wind was measured on a sand beach plain using an acoustic sediment sampler. In general, an increase of particle movement by wind at the sensor heights was observed during rainfall. Rainfall also affected the wind erosion process during and after rain by changing the cohesive conditions of the surface. The influence of the surface moisture content on the initiation of wind erosion and on the vertical distribution of transported sand particles was studied in a wind tunnel. Moisture significantly increased threshold wind velocities for the initiation of sediment transport and modified vertical sediment profiles.  相似文献   

CHANGES IN MORPHOLOGY AT THE MARGIN OF THE GREENLAND ICE SHEET (LEVERETT GLACIER), IN THE PERIOD 1943–1992: A QUANTITATIVE ANALYSIS     

FRANK G. M. VAN TATENHOVE 《地球表面变化过程与地形》1996,21(9):797-816

Changes in ice-marginal morphology near Leverett glacier, a small outlet glacier at the western margin of the Greenland ice sheet, are determined from a photogrammetrical analysis. To be able to compare two datasets from subsequent years with measurements at different coordinates, kriging was used for interpolation. In this study the kriging standard error is used to evaluate the relative accuracy of the resulting maps. Aerial photographs of 1943, 1968 and 1985 were compared. In the period 1943–1968 an area of 0.2 × 10⁶ m² was deglaciated. Approximately 1.1 × 10 m³ of material is deposited in this area. The southern part of the deglaciated area is characterized by ice-cored moraines, while moraines without ice core were formed in the north. Differences in depositional products reflect differences in meltwater activity and probably ice-marginal thermal regime. During deglaciation a small proglacial sandur decreased in altitude by 3.2 ± 0.1 m. From the early 1970s Leverett glacier advanced over a previously deglaciated area. During this advance, small ice-marginal accumulations were incorporated and eroded by the advancing glacier. Erosion products were for a substantial part stored in the proglacial sandur. About 1.2 ×10⁵ m² of the northern part of an ice-cored moraine complex decreased in altitude by −3.6 ± 0.1 m from 1943 to 1968 and over 2.7 × 10⁴ m² by −2.7 ± 0.1 m during 1968–1985. The spatial patterns of altitude change were analysed in relation to topomorphological parameters as exposition and slope angle and areas occupied by lakes. The estimated energy used to melt the subsurface ice of the ice-cored moraine is 1.4–2.2 W m² (1943–1968) and 1.0–1.6 W m² (1968–1985). These values are 30–50 times larger than the geothermal heat flux. For the expected average debris concentration of the ice core (< 10 per cent by volume) the deviation of the surface energy balance forced by climate change will be small and encompass an insignificant part of the total estimated energy used for melting.  相似文献   

AN EULEREAN FINITE ELEMENT MODEL FOR PENETRATION IN LAYERED SOIL     

P. VAN DEN BERG  R. DE BORST  H. Hutink 《国际地质力学数值与分析法杂志》1996,20(12):865-886

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Origin of lunar high‐titanium ultramafic glasses: Constraints from phase relations and dissolution kinetics of clinopyroxene‐ilmenite cumulates     

James A. VAN ORMAN  Timothy L. GROVE 《Meteoritics & planetary science》2000,35(4):783-794

Abstract— Phase equilibrium and dissolution kinetics experiments on synthetic late‐stage magma ocean cumulates are used to place constraints on hypotheses for the origin of lunar high‐Ti ultramafic glasses. Models for the production of high‐Ti lunar magmas have called for either (1) assimilation of late‐stage clinopyroxene‐ilmenite cumulates at shallow levels or (2) sinking of clinopyroxene‐ilmenite cumulates to form a hybrid mantle source. To satisfy the constraints of our experiments, we propose an alternative model that involves shallow‐level reaction and mixing of cumulates, followed by sinking of hybrid high‐Ti materials. This model can fulfill compositional requirements imposed by the pristine lunar glass suite that are difficult to satisfy in assimilation models. It also avoids difficulties that arise in overturn models from the low solidus temperatures of clinopyroxene‐ilmenite cumulates. Partially molten clinopyroxene‐ilmenite cumulates become gravitationally unstable with respect to underlying mafic cumulates only when they have cooled to within ～30°C of their solidus (～1125°C at 100 km depth). At these temperatures, the viscosity of mafic cumulates is too high to allow for growth and descent of clinopyroxene‐ilmenite diapirs on the appropriate time scale. Reaction and mixing between late‐stage liquids and mafic cumulates at shallow levels would produce a refractory hybrid material that is negatively buoyant at higher temperatures and could sink more efficiently to the depths inferred for production of high‐Ti ultramafic glasses.  相似文献   

Das Alpenvorland im Zenit des Eiszeitalters,I. SCHAEFER,Publisher F. Steiner,Stuttgart 1995 (2 Vols: 405 + 672 pp) DM/FrS 248 ISBN 3-315-05957-1     

JAAP J. M. VAN DER MEER 《第四纪科学杂志》1997,12(1):81-81

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SOIL ERODIBILITY PARAMETERS UNDER VARIOUS CROPPING SYSTEMS OF MAIZE     

P. M. VAN DIJK  M. VAN DER ZIJP  F. J. P. M. KWAAD 《水文研究》1996,10(8):1061-1067

For four years, runoff and soil loss from seven cropping systems of fodder maize have been measured on experimental plots under natural and simulated rainfall. Besides runoff and soil loss, several variables have also been measured, including rainfall kinetic energy, degree of slaking, surface roughness, aggregate stability, soil moisture content, crop cover, shear strength and topsoil porosity. These variables explain a large part of the variance in measured runoff, soil loss and splash erosion under the various cropping systems. The following conclusions were drawn from the erosion measurements on the experimental plots (these conclusions apply to the spatial level at which the measurements were carried out). (1) Soil tillage after maize harvest strongly reduced surface runoff and soil loss during the winter; sowing of winter rye further reduced winter erosion, though the difference with a merely tilled soil is small. (2) During spring and the growing season, soil loss is reduced strongly if the soil surface is partly covered by plant residues; the presence of plant residue on the surface appeared to be essential in achieving erosion reduction in summer. (3) Soil loss reductions were much higher than runoff reductions; significant runoff reduction is only achieved by the ‘straw system’ having flat-lying, non-fixed plant residue on the soil surface; the other systems, though effective in reducing soil loss, were not effective in reducing runoff.  相似文献   

Archaeological and palaeoecological indications of an abrupt climate change in The Netherlands,and evidence for climatological teleconnections around 2650 BP     

B. VAN GEEL  J. BUURMAN  H. T. WATERBOLK 《第四纪科学杂志》1996,11(6):451-460

A sudden and sharp rise in the ¹⁴C content of the atmosphere, which occurred between ca. 850 and 760 calendar yr BC (ca. 2750–2450 BP on the radiocarbon time-scale), was contemporaneous with an abrupt climate change. In northwest Europe (as indicated by palaeoecological and geological evidence) climate changed from relatively warm and continental to oceanic. As a consequence, the ground-water table rose considerably in certain low-lying areas in The Netherlands. Archaeological and palaeoecological evidence for the abandonment of such areas in the northern Netherlands is interpreted as the effect of a rise of the water table and the extension of fens and bogs. Contraction of population and finally migration from these low-lying areas, which had become marginal for occupation, and the earliest colonisation by farming communities of the newly emerged salt marshes in the northern Netherlands around 2550 BP, is interpreted as the consequence of loss of cultivated land. Thermic contraction of ocean water and/or decreased velocity and pressure on the coast by the Gulf Stream may have caused a fall in relative sea-level rise and the emergence of these salt marshes. Evidence for a synchronous climatic change elsewhere in Europe and on other continents around 2650 BP is presented. Temporary aridity in tropical regions and a reduced transport of warmth to the temperate climate regions by atmospheric and/or oceanic circulation systems could explain the observed changes. As yet there is no clear explanation for this climate change and the contemporaneous increase of ¹⁴C in the atmosphere. The strategy of ¹⁴C wiggle-match dating can play an important role in the precise dating of organic deposits, and can be used to establish possible relationships between changing ¹⁴C production in the atmosphere, climate change, and the impact of such changes on hydrology, vegetation, and human communities.  相似文献