Toxic Metals in Ground Water of the Front Range, Colorado     

Ronald W. Klusman  Kenneth W. Edwards 《Ground water》1977,15(2):160-169

  相似文献   

Weathering processes in baked sediments and their effects on archaeomagnetic field-intensity measurements     

M.F. Barbetti  M.W. McElhinny  D.J. Edwards  P.W. Schmidt 《Physics of the Earth and Planetary Interiors》1977,13(4):346-354

Thellier-type measurements of ancient field intensity on specimens of clay and other sediments, which were apparently well-baked and oxidised in ancient times, often fail to give consistent results over part or even most of the blocking-temperature spectrum. It is suggested that post-baking chemical alteration, or weathering, leading to the presence of hydrated Fe minerals, is a major cause of non-ideal behaviour in such material. The behaviour of hypothetical specimens containing either goethite or lepidocrocite can be predicted using simple models, and actual examples are given from two sites in southern Australia which show some similarities with the predicted model behaviour. The results of the Thellier measurements, after interpretations, agree closely with previously published results from the northern hemisphere for the period 4700-4200 yr. B.P. The presence of hydrated minerals may not be readily detected by methods other than the Thellier technique and, if so, would result in estimates of the ancient geomagnetic field strength that are systematically too low.  相似文献   

Oceanography and marine biology,annual review: Volume 20. Margaret Barnes (ed.). Aberdeen University Press. 777 pp, 19 plates. Price £45.00. ISBN 0 08 028460 4     

A.J. Edwards  S. Howard 《Marine pollution bulletin》1983,14(8):315-316

  相似文献   

Week-end field meeting: The Upper Eocene—Lower Oligocene beds of the Isle of Wight: 6–8 October 1972     

B. Daley  N. Edwards 《Proceedings of the Geologists' Association. Geologists' Association》1974,85(2):281-292

  相似文献   

Oolitic iron formations in Northern Australia     

A. B. Edwards 《International Journal of Earth Sciences》1959,47(2):668-682

Summary Recent exploration in northern Australia has discovered three shallow water oolitic iron formations, one of Permian age, and two of Upper Proterozoic age. The Permian formation resembles the oxidized oolitic chamositic formations of south-eastern England, but contains more detrital quartz and felspar.The two Precambrian iron formations, consist, below the zone of weathering, of oolites of hematite and of a chamosite-like substance, in a siderite cement, together with well-rounded quartz grains, and are interlayered with sandstones with a chamosite-like cement. Within the zone of weathering the siderite and chamosite are more or less completely replaced by quartz, but with preservation in detail of original textures.Published by permission of the Commonwealth Scientific and Industrial Research Organization (CSIRO).  相似文献   

A late Wisconsin and Holocene vegetation history from the central brooks range: Implications for Alaskan palaeoecology     

Linda B. Brubaker  Harriet L. Garfinkee  Mary E. Edwards 《Quaternary Research》1983,20(2):194-214

Five pollen diagrams reveal late Wisconsin and Holocene vegetation changes in the Walker Lake/Alatna Valley region of the central Brooks Range, approximately 100 km west of the area studied by D. A. Livingstone (1955, Ecology36, 587–600). New insights into the vegetation history of this region are provided by calculations of pollen influx and by the use of linear discriminant analysis to separate Picea glauca and P. mariana pollen. Three major pollen zones are identified: (1) a basal herb zone, characterized by high percentages of Cyperaceae, Gramineae, Salix, and Artemisia, and low total pollen influx; (2) a shrub Betula zone with increased total pollen influx and very high percentages of Betula pollen, predominantly in the size range of B. nana and B. glandulosa; and (3) and Alnus zone dominated by Alnus pollen. Lakes currently within the boreal forest or near tree line show relatively high percentages of Picea pollen in the Alnus zone. Several striking vegetation changes occurred between ca. 10,000 and 7000 yr B.P. Between ca. 11,000 and 10,000 yr B.P., Populus balsamifera pollen percentages as great as 30% indicate that this species was present at low-elevation sites near Walker Lake. These populations declined abruptly ca. 10,000 yr ago and have never regained prominence. About 8500 yr B.P., Picea glauca pollen reached 10–15%, indicating the arrival of P. glauca in or near the study area. P. glauca populations evidently decreased ca. 8000 yr ago, when Picea pollen percentages and influx fell to low values. About 7000 yr B.P., Alnus pollen percentages and influx rose sharply as alder shrubs became established widely. Picea once more expanded ca. 5000 yr ago, but these populations were dominated by P. mariana rather than P. glauca, which increased slowly at this time and may still be advancing northward. Some vegetation changes have been remarkably synchronous over wide areas of interior Alaska, and probably reflect responses of in situ vegetation to environmental changes, but others may reflect the lagged responses of species migrating into new areas.  相似文献   

Interhemispheric anti-phasing of rainfall during the last glacial period   总被引：1，自引：0，他引：1  

Xianfeng Wang  Augusto S. Auler  R. Lawrence Edwards  Hai Cheng  Emi Ito  Maniko Solheid 《Quaternary Science Reviews》2006,25(23-24):3391

We have obtained a high-resolution oxygen isotopic record of cave calcite from Caverna Botuverá (27°13′S, 49°09′W), southern Brazil, which covers most of the last 36 thousand years (ka), with an average resolution of a few to several decades. The chronology was determined with 46 U/Th ages from two stalagmites. Tests for equilibrium conditions show that oxygen isotopic variations are primarily caused by climate change. We interpret our record in terms of meteoric precipitation changes, hence the variability of South American Monsoon (SAM) intensity. The oxygen isotopic profile broadly follows local insolation changes and shows clear millennial-scale variations during the last glacial period with amplitudes as large as 3‰ but with smaller centennial-scale shifts (<1‰) during the Holocene. The overall record is strikingly similar to, but strongly anti-correlated with, a number of records from the Northern Hemisphere.We compared our record to other precisely dated contemporaneous records from Hulu Cave eastern China. Minima in δ¹⁸O (wet periods, intense SAM) at our site are synchronous with maxima in δ¹⁸O (dry periods, weak East Asian Monsoon, EAM) in eastern China (within precise dating errors) and vice versa. This anti-phased precipitation relationship between two low-latitude locations may be interhemispheric in extent, based on comparison with records from other sites. Precipitation anti-phasing may be related to north–south shifts in the mean position of the intertropical convergence zone (ITCZ) and asymmetry in Hadley circulation in two hemispheres, associated not with seasonal changes as observed today, but with millennial-scale climate shifts. The millennial-scale atmospheric see-saw patterns that we observe could have important controls and feedbacks on climate within hemispheres because of water vapor's greenhouse properties.  相似文献   

The Validity of Similarity Theory in the Roughness Sublayer Above Forests   总被引：1，自引：0，他引：1  

I. J. Simpson  G. W. Thurtell  H. H. Neumann  G. Den Hartog  G. C. Edwards 《Boundary-Layer Meteorology》1998,87(1):69-99

Flux-gradient relationships based upon similarity theory have been reported to severely underestimate scalar fluxes in the roughness sublayer above forests, as compared to independent flux estimates (for example, eddy covariance or energy balance measurements). This paper presents the results of a unique three-month investigation into the validity of similarity theory in the roughness sublayer above forests. Eddy covariance and flux-gradient measurements of carbon dioxide (CO²) exchange were compared above a mixed deciduous forest at Camp Borden, Ontario, both before and after leaf senescence. The eddy covariance measurements used a Li-Cor infrared gas analyzer, and the flux-gradient (similarity theory) measurements featured a tunable diode laser Trace Gas Analysis System (TGAS). The TGAS resolved the CO² concentration difference to 300 parts per trillion by volume (ppt) based upon a half-hour sampling period. The measured enhancement factor (the ratio of independent flux estimates, in this case eddy covariance, to similarity theory fluxes) was smaller and occurred closer to the canopy than in most previous investigations of similarity theory. Very good agreement between the eddy covariance and similarity theory fluxes was found between 1.9 and 2.2 canopy heights (h^c), and the mean enhancement factors measured before and after leaf senescence were 1.10 plusmn; 0.06 and 1.24 ± 0.07, respectively. Larger discrepancies were measured closer to the canopy (1.2 to 1.4 h^c), and mean enhancement factors of 1.60 ± 0.10 and 1.82 ± 0.11 were measured before and after leaf senescence, respectively. Overall, the Borden results suggest that similarity theory can be used within the roughness sublayer with a greater confidence than previously has been believed.  相似文献   

Peat extraction, conservation and the rural economy in Northern Ireland     

MM Cruickshank  RW TomlinsonD BondPM DevineCJW Edwards 《Applied geography (Sevenoaks, England)》1995,15(4)

Northern Ireland has a tradition of peat cutting; 78 per cent by area of remaining lowland bogs and 46 per cent of blanket bogs have been cut in the past. Since the early 1980s, machine peat extraction for fuel and horticulture has increased, against a background of changing economic support for agriculture, high rural unemployment and agricultural underemployment. Cutting fuel peat can reduce household fuel costs and some peat fuel is sold to gain income. Horticultural peat is cut mainly for sale. Expansion of machine extraction, with possible environmental impacts, occurred as interest in peatland conservation increased. Potential conflict arises between local economic needs and conservation. Machine cutting for fuel is widespread, but affects only 2.6 per cent of the blanket peat area; horticultural extraction is more localized and is only one-fifth of the extent of fuel extraction. Altitude, distance from roads, land ownership and rights, turbary, religious affiliation, local economic needs and the role of government departments all contribute to explaining the distribution and extent of extraction.  相似文献   

UUThTh systematics and the precise measurement of time over the past 500,000 years     

R. Lawrence Edwards  J.H. Chen  G.J. Wasserburg 《Earth and Planetary Science Letters》1987,81(2-3)

We have developed techniques to measure the²³⁰Th abundance in corals by isotope dilution mass spectrometry. This, coupled with our previous development of mass spectrometric techniques for²³⁴U and²³²Th measurement, has allowed us to reduce significantly the analytical errors in²³⁸U²³⁴U²³⁰Th dating and greatly reduce the sample size. We show that 6 × 10⁸ atoms of²³⁰Th can be measured to ±30‰ (2σ) and 2 × 10¹⁰ atoms of²³⁰Th to ±2‰. The time over which useful age data on corals can be obtained ranges from a few years to 500 ky. The uncertainty in age, based on analytical errors, is ±5 y (2σ) for a 180 year old coral (3 g), ±44 y at 8294 years and ±1.1 ky at 123.1 ky (250 mg of coral). We also report²³²Th concentrations in corals (0.083–1.57 pmol/g) that are more than two orders of magnitude lower than previous values. Ages with high analytical precision were determined for several corals that grew during high sea level stands 120 ky ago. These ages lie specifically within or slightly postdate the Milankovitch insolation high at 128 ky and support the idea that the dominant cause of Pleistocene climate change is Milankovitch forcing.  相似文献