Cyclicity in the late Precambrian Elatina Formation,South Australia: Solar or tidal signature?     

G. E. Williams 《Climatic change》1988,13(2):117-128

New observations from two late Precambrian (~800-650 Ma) sedimentary rhythmites in South Australia (Reynella Siltstone and Chambers Bluff Tillite) reveal cycles structurally similar to the ~12-laminae cycles of the ~650-Ma Elatina Formation but which comprise from 15 to 26 or more laminae. The new data are difficult to accomodate in depositional models for the Elatina Formation whereby its laminae are regarded as annual and the cyclicity ascribed to solar variability (Williams and Sonett, 1985) or to the combined influences of the sunspot cycle and the lunar nodal tide (Zahnle and Walker, 1987). If, however, the long-term Elatina Cycle and not the individual lamina is taken as a yearly climatic signal, the Elatina and other rhythmites studied may be interpreted as the deposits of marine ebb-tidal deltas that record variability in the velocity and range of paleo-ebb tides. The basic laminae-cycles would represent lunar fortnightly cycles of diurnal and/or semidiurnal laminae, commonly truncated through non-deposition at neap tides. Despite numerous empirical similarities between the Elatina and sunspot series, the ebb-tidal model for deposition is preferred because it accounts plausibly for observations from all three rhythmites studied.  相似文献   

DISCUSSION OF PAPERS     

Michael Price  Ann Williams 《Ground water》1988,26(6):798-798

  相似文献   

全球地学断面图数字化指南     

H.-J.Gotze  R.T.Williams  周琦  刘心铸 《地球学报》1993,14(2):185-195

  相似文献   

The common agricultural policy and the general environmental policies concerned with agriculture in the European Community and their implications for fertilizer consumption     

A. J. Williams 《Marine pollution bulletin》1994,29(6-12):500-507

This paper traces the major developments in the European Common Agricultural Policy (CAP) and related environmental policy and examines their impact on the use of crop nutrients. The objectives of the CAP were set out in the Treaty of Rome in 1957 and have not been explicitly revised. The Community has, however, progressed from being a significant importer to a major exporter of food. Various changes in the policy measures/reforms, have been implemented, each to control the continuing increase in farm output. The latest of these in May 1992 reduced commodity prices towards world market levels, introduced 15% set aise for arable land, as well as agreeing a number of agri-environmental measures. Further changes are anticipated following the Uruguay Round of the General Agreement on Tariffs and Trade (GATT) and as new trade agreements are reached with the countries of the former Eastern Bloc. Inevitably, existing farm systems will be subject to careful reappraisal. The Community's environmental objectives were added to the Treaty in 1987 with the passing of the European Single Act. The interaction between agriculture and the environment has been a prominent concern. The Directive 91/676, which seeks to protect water against pollution caused by nitrate from agricultural sources, is the first Directive to have a major direct impact on farm practive. The Fifth Environmental Action Plan for 1993–2000 ‘Towards Sustainability’ selects agriculture as one of five industries for specific attention. The plan seeks an extensification of agriculture and a reduction in the use of chemicals. Changes in the amount of plant nutrients from both farmyard manure and mineral fertilizers used in agriculture are quantified. Methods of determining the efficiency with which they are utilized are assessed. New advisory techniques which will improve the efficiency of nutrient use on the farm are considered, as are the implications for the future demand for nutrients from mineral fertilizers. This paper is the view of the European Fertilizer Manufacturers Association.  相似文献   

Reply to 'Can magnetic-force microscopy determine micromagnetic structures?' by Grütter and Allenspach     

W. Williams  V. Hoffmann  F. Heider  T. Göddenhenrich  C. Heiden 《Geophysical Journal International》1994,116(2):506-507

  相似文献   

Tourism, Technology and Competitive Strategies By A. Poon     

Bob Garnham 《New Zealand geographer》1995,51(2):62a-63

  相似文献   

Desertification,drought and landcare: Australia's role in an international convention to combat desertification     

Martin Williams  Megan McCarthy  Geoff Pickup 《The Australian geographer》1995,26(1):23-32

  相似文献   

Factors Affecting Efficient Aquifer Restoration at In Situ Uranium Mine Sites     

James L. Osiensky  Roy E. Williams 《Ground Water Monitoring & Remediation》1990,10(2):107-112

In situ mining of uranium typically requires the injection of a reactive leaching solution (lixiviant) such as sodium carbonate/bicarbonate, ammonium carbonate/bicarbonate, or sulfuric acid, and an oxidant such as hydrogen peroxide or oxygen into an ore-bearing, confined aquifer. It also requires the environmental restoration of the source aquifer. The stratigraphy of sandstone uranium deposits typically consists of interbedded layers of poorly consolidated sands and clays and gravels deposited in fluvial or coastal environments. The parameters that influence the migration of lixiviant during mining and restoration in these environments include induced hydraulic gradients, hydrodynamic dispersion, heterogeneity, anisotropy, physicochemical reactions, leakage into and/or through confining layers, and convergence of flow lines due to partial well penetration.
The effectiveness of the various methods of aquifer restoration is sit -specific and is dependent upon the site hydrogeology and hydrogeochemistry, and the chemistry of the lixiviant. Each method of aquifer restoration has advantages and disadvantages. Selection of the most effective and economically feasible method requires detailed knowledge of the site-specific hydrogeologic conditions.  相似文献   

Time-scale calibration by high-precision UPb zircon dating of interstratified volcanic ashes in the Ordovician and Lower Silurian stratotypes of Britain     

R.D. Tucker  T.E. Krogh  R.J. Ross Jr.  S.H. Williams 《Earth and Planetary Science Letters》1990,100(1-3)

High initial parent/daughter element ratios and a unique dual decay scheme make UPb zicron ages more precise and reliable than most isotopic ages, and thus inherently superior for time-scale calibration. Employing improved techniques to the conventional method of UPb dating, we have analyzed microgram-size (2–12 × 10⁻⁸ g) zircon fractions from biostratigraphically controlled volcanic ashes and dated key Paleozoic time-markers with a precision better than 1% (±2Ma). Four of the stratotype samples from Britain for which fission-track ages [1] were previously reported have yielded improved ages of:438.7 ± 2.0Ma for the lower Silurian zone of Coronograptus cyphus from Llandovery strata at Dob's Linn, southern Scotland;457.5 ± 2.2 Ma for a Middle Ordovician Caradoc (Longvillian) ash near Bala, North Wales, and;465.7 ± 2.1and464.6 ± 1.8 Ma for the Didymograptus artus Zone and the type Didymograptus Murchisoni Zone, respectively, of the Llanvirn Series at Arenig Fawr and Abereiddi Bay, Wales. Another sample from the zone of Dicellograptus anceps (P. pacificus Subzone) of the Ashgill Series at Dob's Linn has been dated at445.7 ± 2.4Ma, suggesting placement of the Ordovician-Silurian time boundary at approximately 441 Ma. A sixth bentonite from Caradocian age strata of North America (Spechts Ferry Shale, Decorah Formation, Missouri) is453.7 ± 1.8Ma old, indicating that the Rocklandian Stage of the Mohawkian Series is only slightly younger than the Longvillian Stage of the Caradoc Series in Britain.  相似文献   

Monitoring active volcanoes and mitigating volcanic hazards: the case for including simple approaches     

Richard E. Stoiber  Stanley N. Williams 《Journal of Volcanology and Geothermal Research》1990,42(1-2)

Simple approaches to problems brought about eruptions and their ensuing hazardous effects should be advocated and used by volcanologists while awaiting more sophisticated remedies. The expedients we advocate have all or many of the following attributes: only locally available materials are required; no extensive training of operators or installation is necessary; they are affordable and do not require foreign aid or exports; they are often labor intensive and are sustainable without outside assistance. Where appropriate, the involvement of local residents is advocated. Examples of simple expedients which can be used in forecasting or mitigating the effects of crises emphasize the relative ease and the less elaborate requirements with which simple approaches can be activated. Emphasis is on visual observations often by untrained observers, simple meteorogical measurements, observations of water level in lakes, temperature and chemistry of springs and fumaroles, new springs and collapse areas and observations of volcanic plumes. Simple methods are suggested which can be applied to mitigating damage from mudflows, nuées ardentes, tephra falls and gas discharge. A review in hindsight at Ruiz includes the use of both chemical indicators and simple mudflow alarms. Simple expedients are sufficiently effective that any expert volcanologist called to aid in a crisis must include them in the package of advice offered. Simple approaches are a critical and logical complement to highly technical solutions to hazardous situations.  相似文献