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11.
Ian Douglas 《地球表面变化过程与地形》1987,12(5):481-495
The variety of active, exhumed, and buried limestone landforms of northern England, North Wales, and the Isle of Man arises in part from the way in which Dinantian (Lower Carboniferous) sedimentation was affected by a tilt-block basement structure evolved during the closure of the Iapetus Ocean suture to the north, and partly to subsequent plate tectonic movements associated with the closure of the proto-Tethys ocean, the opening of the Atlantic Ocean and the Alpine orogeny. Landforms created during the Dinantian now form important exhumed and buried landscape features. The Permian half-graben structures of the eastern Irish Sea-Cheshire-Worcester Basins account for many of the contrasts between the upland karsts of the Pennines and the lowland karsts of coastal areas. 相似文献
12.
Uranium-series ages have been obtained for 87 speleothems collected from nine major cave systems in the Craven district of northern England. Large systems such as Ease Gill Caverns, the West Kingsdale caves, and Gaping Gill-Ingleborough Cave, which contain relict high-level tunnels, are found to be older than 350,000 years (the limit of the 230Th/234U dating method). There is little evidence to indicate a significant enlargement of these passages since this time. Estimates of the age of Victoria Cave from 234U/238U isotopic ratios suggest that the cave has been fully relict for more than 500,000 years. Ages of in situ speleothems immediately adjacent to local base level cave streams show that mean maximum downcutting rates in limestone channels are about 2 to 5 cm 1000 yr. These rates are significantly lower than those obtained from direct measurements on limestone bedrock in stream channels but are comparable to areal denudation rates based on solute budgets. Using the present elevation of caves with respect to adjacent valley floor levels, mean maximum valley entrenchment rates are found to range between 5 cm/ky and < 20cm/ky, which corresponds to 6 m to < 24 m of lowering per glacial/interglacial cycle. These rates suggest that upper beds of the limestone were incised to form the Yorkshire Dales between 1 and 2 million years ago. The results indicate that the erosional effects of individual glaciations are not as severe as previously proposed in the literature. 相似文献
13.
Limestone and ophiolite rocks are common across the eastern Mediterranean and many of the highest mountains are formed in these rock types. In northwest Greece, Pleistocene glacial erosion was much more effective on limestone terrain where pronounced glacial incision and subglacial glacio-karst processes produced locally-complex topography. This enabled Pleistocene glaciers to form on a range of slope orientations in contrast to ophiolite terrains, where glaciers were strongly controlled by aspect. On limestone terrains, the largest ice masses formed on south-facing slopes, whereas in neighbouring higher mountains formed in ophiolite, glaciers were much more restricted and predominantly formed on north- and east-facing slopes. 相似文献
14.
Siegfried Siegesmund Akos Török Andre Hüpers Christian Müller Werner Klemm 《Environmental Geology》2007,52(2):385-397
High levels of SO2 and particulate pollution enable the rapid development of gypsum-rich weathering crusts in Budapest. Two types of white crusts,
thin and thick ones, and two forms of black crusts, laminar and framboidal ones, were studied in limestone buildings of the
parliament and Citadella. The percentage of crust cover and damage categories were documented on selected walls. Petrographic,
XRD, XRF and sulphur isotope analyses were performed under laboratory conditions to understand the mechanism of crust formation.
White crusts found both on exposed and sheltered walls display a calcite-rich layer with gypsum, while black crusts are enriched
with gypsum. The sulphur isotopic composition of white and black crusts overlaps, but the crusts are slightly enriched in
heavy isotopes compared to rainwater. S content, Si/Al ratios and particulates in black crusts suggest that air pollution
(SO2, dust) contributes to black crust formation. The accumulation of sulphur and Zn enrichment of white crusts were also documented
indicating that under high pollution levels, even these compound can accumulate on exposed facades. 相似文献
15.
Hanifi Canakci 《Environmental Geology》2007,53(4):915-922
This paper focuses on an investigation of the possible causes for the collapse of limestone caves in Gaziantep, Turkey. The
city contains a lot of man-made caves, at a shallow depth, of various width and length. These caves were mainly excavated
to provide work or storage space. As the city has been growing fast with increased population, many structures were constructed
over these caves. Recently, two caves collapsed and five houses were damaged. These caves are all made of limestone and it
was observed after the collapse that the limestone was saturated with water due to sewer pipe leakage and surface water. Tests
were carried out on the limestone and it was determined that the compressive strength of limestone decreases by about 50%
and the tensile strength decreased by about 80% when saturated with water. It was concluded that the reduced strength of the
limestone combined with additional loads due to the factors mentioned above seem to be the main reason for these collapses. 相似文献
16.
A model of the early evolution of karst aquifers in limestone in the dimensions of length and depth 总被引:5,自引:0,他引:5
《Journal of Hydrology》2001,240(3-4):206-224
A new model of the early evolution of limestone karst aquifers in the dimensions of length and depth is presented. In its initial state the aquifer consists of a rock massive with evenly spaced fractures of about 50 μm aperture widths with an hydraulic conductivity of 10−7 ms−1. In addition to this a coarser network of prominent fractures with aperture widths of several 100 μm is also present. Boundary conditions of constant recharge 450 mm/year, or constant head from the input of allogenic streams are imposed. First the position of the water table in the aquifer is calculated, then dissolutional widening during a time step in all the fractures below the water table is found by use of the well-known nonlinear dissolution kinetics of limestone. This is iterated and the position of the water table as well as the fracture widths are found as a function of time. In the case of constant recharge to a karst plateau, the water table in any case drops to base level and conduits there propagate from the spring headwards. If constant head conditions are valid the position of the water table remains almost stable and conduits propagate along the water table from the input towards the spring. There is competition between conduit evolution along prominent fractures and along tight fissures close to the water table. In any case under constant head conditions one of these pathways wins, and early karst evolution is terminated by a breakthrough event with an explosive increase of the flow through the aquifer until constant head conditions break down. Depending on the boundary conditions of constant head or constant recharge or a combination of both it is possible to describe models of cave genesis, which have been derived from field evidence, such as the water table models of Swinnerton and Rhoades as well as the four-state model by Ford and Ewers (Can. J. Earth Sci., 15 (1978) 1783). 相似文献
17.
四川攀钢石灰石矿曾发生多次大规模滑坡,给矿山生产造成巨大损失。以其中规模较大的H3滑坡为研究对象,分析探讨该边坡的失稳原因,建立边坡失稳概念模型,并用离散单元法论证该边坡概念模型的合理性。 相似文献
18.
John Gunn 《地球表面变化过程与地形》1981,6(6):595-597
Recent work by Láng (1977) on solutional erosion rates in limestone drainage basins in relation to rainfall contains serious errors and has a questionable logical basis. Although much sounder, Smith and Atkinson's (1976) work on erosion rates in relation to runoff also requires modification as it greatly overestimates erosion rates in two areas of New Zealand. Greater resolution could probably be obtained by relating autogenic runoff to the rate of solution by autogenic waters and by computing separate relationships for areas where solution takes place under open and closed system equilibrium conditions. These factors should be taken into account in the experimental design of future studies. 相似文献
19.
20.
The Lune River Quarry at Ida Bay, Tasmania exposes numerous palaeokarst features developed in the Ordovician Gordon Limestone. These palaeokarst features contain carbonate and siliciclastic deposits probably representing Late Devonian to early Late Carboniferous and Late Carboniferous karstification and sedimentation. Five facies of palaeokarst deposits are recognised, namely megabreccia, graded‐bedded carbonate, laminated sandstone/siltstone, diamictite/quartz‐lithic sandstone and coarse crystalline calcite. Pyrite, dolomite and sphalerite were emplaced in the palaeokarst deposits after the Carboniferous. These deposits are probably associated with a phase of hydrothermal cave development in Exit Cave, which adjoins the quarry. Pyrite weathering accounts for the abundance of gypsum speleothems and cave breakdown in Exit Cave. 相似文献