Criteria for the instability of upper-stage plane beds     

J. R. L. ALLEN  M. R. LEEDER 《Sedimentology》1980,27(2):209-217

Calculations of the critical dimensionless bed stresses that obtain when upper-stage plane beds should revert to ripple and dune bed forms are presented. Strong support is given to the Bagnold ‘universal’ plane-bed instability criterion and to a modified criterion suggested by Allen over a wide range of solids grain size. A reinterpretation of the mechanism of plane bed instability is based upon the extent to which significant grain concentrations in plane bed flows increase apparent fluid viscosity and decrease turbulence production over potential bed defects, thereby preventing ripple or dune propagation and growth.  相似文献   

Apparent redox potential discontinuity (aRPD) depth as a relative measure of sediment oxygen content and habitat quality     

Travis G GERWING  Alyssa M ALLEN GERWING  Diana JHAMILTON  Myriam ABARBEAU 《国际泥沙研究》2015,(1)

As hypoxic conditions spread in our oceans, indices that quickly and efficiently assess oxygen content in sediment pore water, and habitat quality are increasingly becoming desirable. Depth to the appa...  相似文献   

LOS LAVADORES: DISCOVERING PLACE IN THE ANDES     

CASEY D. ALLEN 《Geographical review》2012,102(3):364-371

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A history of atmospheric tritium gas (HT) 1950–2002     

JAMES D. HAPPELL  GÖTE ÖSTLUND  ALLEN S. MASON 《Tellus. Series B, Chemical and physical meteorology》2004,56(3):183-193

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Report of the Editor     

PETER HOMEWOOD  PHILIP ALLEN  JUDITH McKENZIE 《Sedimentology》1991,38(1):199-202

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Involutions in the Middle Pleistocene (Anglian) Barham Soil, eastern England: a comparison with thermokarst involutions from arctic Canada     

JULIAN B. MURTON  COLIN A. WHITEMAN  PETER ALLEN 《Boreas: An International Journal of Quaternary Research》1995,24(3):269-280

Involutions in the early Anglian Barham Soil at Newney Green, Essex, and Badwell Ash, Suffolk, in eastern England, are attributed to soft-sediment deformation during an episode of regional thermokarst development. The involutions show a striking resemblance in morphology and size to thermokarst involutions within a palaeo-thaw layer at Crumbling Point, western arctic Canada. By analogy with the thermokarst involutions, the involutions in the Barham Soil are reinterpreted to have formed by loading during the melting of an ice-rich layer at the top of Anglian permafrost. This period of thermokarst development may have coincided with an episode of intra-Anglian climatic amelioration. Reinterpretation of the Barham Soil involutions implies that many other Pleistocene involutions in Britain may have formed during periods of thermokarst development rather than by active-layer cryoturbation.  相似文献   

Zircons from Syros, Cyclades, Greece--Recrystallization and Mobilization of Zircon During High-Pressure Metamorphism   总被引：27，自引：1，他引：27  

TOMASCHEK  FRANK; KENNEDY  ALLEN K.; VILLA  IGOR M.; LAGOS  MARKUS; BALLHAUS  CHRIS 《Journal of Petrology》2003,44(11):1977-2002

Zircons were studied from high-pressure/low-temperature metamorphosedmeta-igneous lithologies from Syros. These rocks carry severalzircon generations related to each other by dissolution–reprecipitationprocesses. One generation is pristine zircon that shows growthzoning, relatively elevated contents of trivalent cations andhigh Th/U ratios. The other end-member is a skeletal zircongeneration with negligible trivalent cation contents and lowTh/U ratios (  相似文献   

Large transverse bedforms and the character of boundary-layers in shallow-water environments     

J. R. L. ALLEN 《Sedimentology》1980,27(3):317-323

Theoretical work, laboratory studies, and field observations indicate that the oscillatory boundary layers generated by the tidal wave differ fundamentally in dynamics and kinematic structure from the unidirectional boundary layers of rivers. Unique to the former are mass-transport currents attributable to: (1) the wave motion itself, and (2) bed curvature in the presence of the oscillatory flow. The implication of this difference for bed-material transport is that the larger flow-transverse bedforms of shallow-water environments are divisible hydraulically between two major classes: (A) those related to tidal conditions, under which the fluid reverses in direction of flow with each reversal of the tide, permitting the initiation and maintenance of bed features by the spatially reversing, curvature-related mass transport, and (B) those related strictly to rivers and river-like flows, in which the fluid motion is unidirectional, and therefore the only mechanisms available for bedform initiation and maintenance are those creating a finite spatial lag between the transport rate and the bed waviness. Forms of Class B are best called dunes and bars, and only those attributable to Class A should be termed sand waves. The latter, restricted to oscillatory boundary layers of tidal origin, apparently correspond to the very much smaller; but also commonly symmetrical, ripple marks produced in wind-wave oscillatory boundary layers.  相似文献   

Space weathering on airless bodies: Resolving a mystery with lunar samples     

Carl M. PIETERS  Larry A. TAYLOR  Sarah K. NOBLE  Lindsay P. KELLER  Bruce HAPKE  Richard V. MORRIS  Carl C. ALLEN  David S. McKAY  Susan WENTWORTH 《Meteoritics & planetary science》2000,35(5):1101-1107

Abstract— Using new techniques to examine the products of space weathering of lunar soils, we demonstrate that nanophase reduced iron (npFe⁰) is produced on the surface of grains by a combination of vapor deposition and irradiation effects. The optical properties of soils (both measured and modeled) are shown to be highly dependent on the cumulative amount of npFe⁰, which varies with different starting materials and the energetics of different parts of the solar system. The measured properties of intermediate albedo asteroids, the abundant S‐type asteroids in particular, are shown to directly mimic the effects predicted for small amounts of npFe⁰ on grains of an ordinary chondrite regolith. This measurement and characterization of space weathering products seems to remove a final obstacle hindering a link between the abundant ordinary chondrite meteorites and common asteroids.  相似文献   

A QUANTITATIVE MODEL OF CLIMBING RIPPLES AND THEIR CROSS-LAMINATED DEPOSITS   总被引：1，自引：0，他引：1  

J. R. L. ALLEN 《Sedimentology》1970,14(1-2):5-26

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