Rates of cave and landform development in the Yorkshire Dales from speleothem age data     

Melvyn Gascoyne  Derek C. Ford  Henry P. Schwarcz 《地球表面变化过程与地形》1983,8(6):557-568

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   

Effect of a kelp forest on coastal currents   总被引：1，自引：0，他引：1  

George A. Jackson  Clinton D. Winant 《Continental Shelf Research》1983,2(1):75-80

Ocean currents supply a kelp ecosystem with nutrients, planktonic food, and larvae. We have found that these currents in a kelp forest (Macrocystis pyrifera) are slower than currents outside. At the Pt. Loma, San Diego, California, site that we studied, current velocities were about a third of those outside. A comparison of frequency spectra shows that semi-diurnal frequencies are preferentially passed by the kelp. This effect of a kelp forest on the currents that nurture it is similar to that of a terrestrial forest on local winds.  相似文献   

The seismicity of Kohistan, Pakistan: Source studies of the Hamran (1972.9.3), Darel (1981.9.12) and Patan (1974.12.28) earthquakes     

James Jackson  Graham Yielding 《Tectonophysics》1983,91(1-2)

Long period body waves are examined to show that the Hamran (1972.9.3), Darel (1981.9.12) and Patan (1974.12.28) earthquakes in Kohistan had focal depths of about 8–10 km. All involved high angle reverse faulting (thrusting) and had seismic moments of about 2.2 to 2.7·10²⁵ dyne cm. These shallow depths contrast with the deeper hypocentres found in the Hindu Kush and northeast Karakoram to the north and in Hazara to the south. The Hamran and Patan shocks were assigned depths of 45 km by the ISC, indicating that even well-recorded events in this region may have focal depths in error by 30 km  相似文献   

The impact of a major Quaternary river capture on the alluvial sediments of a beheaded river system, the Rio Alias SE Spain   总被引：1，自引：0，他引：1  

Elizabeth Maher  Adrian M. Harvey  Derek France 《Geomorphology》2007,84(3-4):344

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Initiation and growth of salt-based thrust belts on passive margins: results from physical models   总被引：1，自引：0，他引：1  

Tim P. Dooley  Martin P. A. Jackson  Michael R. Hudec 《Basin Research》2007,19(1):165-177

Scaled sandbox models simulated primary controls on the kinematics of the early structural evolution of salt‐detached, gravity‐driven thrust belts on passive margins. Models had a neutral‐density, brittle overburden overlying a viscous décollement layer. Deformation created linked extension–translation–shortening systems. The location of initial brittle failure of the overburden was sensitive to perturbations at the base of the salt. Salt pinch‐out determined the seaward limit of the thrust belt. The thrust belts were dominated by pop‐up structures or detachment folds cut by break thrusts. Pop‐ups were separated by flat‐bottomed synclines that were partially overthrust. Above a uniformly dipping basement, thrusts initiated at the salt pinch‐out then consistently broke landward. In contrast, thrust belts above a seaward‐flattening hinged basement nucleated above the hinge and then spread both seaward and landward. The seaward‐dipping taper of these thrust belts was much lower than typical, frictional, Coulomb‐wedge models. Towards the salt pinch‐out, frictional resistance increased, thrusts verged strongly seawards and the dip of the taper reversed as the leading thrust overrode this pinch‐out. We attribute the geometry of these thrust belts to several causes. (1) Low friction of the basal décollement favours near‐symmetric pop‐ups. (2) Mobile salt migrates away from local loads created by overthrusting, which reduces the seaward taper of the thrust belt. (3) In this gravity‐driven system, shortening quickly spreads to form wide thrust belts, in which most of the strain overlapped in time.  相似文献   

Geomorphic constraints on the active tectonics of southern Taiwan     

Lucy A. Ramsey  Richard T. Walker  James Jackson 《Geophysical Journal International》2007,170(3):1357-1372

Taiwan is a region of rapid active tectonics, yet the study of the tectonic processes that shape the interior of the island is difficult due to the high rates of erosion and dense vegetation. We use digital topography to look for indications of active deformation preserved in the local geomorphology. In particular, anomalies in the regional pattern of drainage are used to infer zones of enhanced tectonic activity. The apparent anticlockwise rotation of major river systems in plan view indicates the presence of a diffuse zone of left-lateral shear running down the southeastern side of Taiwan. Asymmetries in the catchments of individual drainage basins show the influence of varying rates of uplift across southern Taiwan, with the most rapid uplift close to Taitung at the indentation point of the Luzon arc with the Chinese continental margin. Our interpretations, though based predominantly on remote-sensing observations, are consistent with the available field evidence. This study demonstrates the usefulness of drainage basins as tectonic markers in the quantification of regional strain and uplift, which may have wider applicability in other deforming parts of the world.  相似文献   

A comprehensive model inter-comparison study investigating the water budget during the BALTEX-PIDCAP period   总被引：2，自引：0，他引：2  

D. Jacob  B. J. J. M. Van den Hurk  U. Andræ  G. Elgered  C. Fortelius  L. P. Graham  S. D. Jackson  U. Karstens  Chr. Köpken  R. Lindau  R. Podzun  B. Rockel  F. Rubel  B. H. Sass  R. N. B. Smith  X. Yang 《Meteorology and Atmospheric Physics》2001,77(1-4):19-43

Summary A comparison of 8 regional atmospheric model systems was carried out for a three-month late summer/early autumn period in 1995 over the Baltic Sea and its catchment area. All models were configured on a common grid using similar surface and lateral boundary conditions, and ran in either data assimilation mode (short term forecasts plus data assimilation), forecast mode (short term forecasts initialised daily with analyses) or climate mode (no re-initialisation of model interior during entire simulation period). Model results presented in this paper were generally post processed as daily averaged quantities, separate for land and sea areas when relevant. Post processed output was compared against available analyses or observations of cloud cover, precipitation, vertically integrated atmospheric specific humidity, runoff, surface radiation and near surface synoptic observations. The definition of a common grid and lateral forcing resulted in a high degree of agreement among the participating model results for most cases. Models operated in climate mode generally displayed slightly larger deviations from the observations than the data assimilation or forecast mode integration, but in all cases synoptic events were well captured. Correspondence to near surface synoptic quantities was good. Significant disagreement between model results was shown in particular for cloud cover and the radiative properties, average precipitation and runoff. Problems with choosing appropriate initial soil moisture conditions from a common initial soil moisture field resulted in a wide range of evaporation and sensible heat flux values during the first few weeks of the simulations, but better agreement was shown at later times. Received September 8, 2000 Revised April 3, 2001  相似文献   

Beaches and dunes of developed coasts: Nordstrom, Karl F. Cambridge University Press, Cambridge, 2000, 338 pages+xiii, 57 figures (b&w photographs and b&w diagrams), 8 tables, UK£45, US$74.95, Hardback, ISBN 0 521 47013 7     

Derek J. McGlashan 《Geomorphology》2001,36(3-4)

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DNAPL Remediation: Which 'New Paradigm' Will Prevail?     

Richard E. Jackson 《Ground Water Monitoring & Remediation》2001,21(3):54-58

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DNAPL Removal from a Heterogeneous Alluvial Aquifer by Surfactant- Enhanced Aquifer Remediation     

John T. Londergan  Hans W. Meinardus  Paul E. Manner  Richard E. Jackson  Chris L. Brown  Varadarajan Dwarakanath  Gary A. Pope  Jon S. Ginn  Sam Taffinder 《Ground Water Monitoring & Remediation》2001,21(3):71-81

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