The age of the Earth and the oldest rocks     

STEPHEN MOORBATH 《Geology Today》1985,1(3):75-79

The ages of rocks and minerals can be determined by measuring the accumulation of the products of radioactive decay within them. The results provide a time–scale for the Earth and for the major geological events which have shaped the Earth's continental crust since it first started to separate from the mantle at least 3700 million years ago. The Earth itself is about 4600 million years old.  相似文献   

A NEW PARAMETER FOR AEROMAGNETIC SURVEYING*     

STEPHEN THYSSEN-BORNEMISZA 《Geophysical Prospecting》1967,15(2):204-207

The author proposes the parameter Δ²/ΔT¹ for possible application in aeromagnetic surveying making use of already available gradiometer systems equipped with sensors separated vertically.  相似文献   

Three modelling approaches for seasonal streamflow droughts in southern Africa: the use of censored data     

EMMA L. TATE  STEPHEN N. FREEMAN 《水文科学杂志》2013,58(1):27-42

Abstract

Three approaches to modelling the duration of streamflow droughts at eight southern African sites are considered; a non-parametric method (that of Kaplan-Meier) is compared with the fitting of two simple parametric models: the exponential and Weibull. All techniques allow the instantaneous probability of a drought coming to an end to differ between wet and dry seasons, using the concept of censored data. Model-fitting is discussed, and the Kaplan-Meier estimates permit an assessment of the fit of the parametric models, with the aim of finding a parsimonious model for the data, which can be used for predictive purposes. In most cases considered herein, either the exponential or Weibull approach is found to be adequate.  相似文献   

Using Contents Addressable Filestore for rapid access to a large cartographic data set†     

STEPHEN WISE 《International journal of geographical information science》2013,27(2):111-120

Abstract

The need for rapid access to large amounts of data is one of the central problems in the field of geographical information systems. This paper describes the use of a hardware solution to this problem, in the particular case of selecting digitized boundary data from a very large file. The hardware is International Computers'(ICL's) award winning Contents Addressable Filestore (CAFS) which is a special unit fitted to ICL disc drives allowing the fast selection of records from large files. By reformatting the boundary data, it was possible to perform searches using CAFS. A command-driven package was written to allow users to select the boundaries for any named zone or zones, display them on a graphics terminal and write them out in a format suitable for input to the GIMMS package. This package was tested on a file containing the boundaries of all the wards of Great Britain. After reformatting, this file was 6 Mbytes in size, but by means of CAFS could be searched interactively with response times of the order of 5-10 seconds.  相似文献   

Modelling the temporal element in land information systems     

STEPHEN PRICE 《International journal of geographical information science》2013,27(3):233-243

Abstract

This paper considers the use of a modern programming language (Modula-2) to develop a data model for a lot-based land information system. The emphasis is on the importance of maintaining the history of the lots, and a data model is developed which incorporates the history of each lot.  相似文献   

CONSTRUCTING,VISUALIZING, AND ANALYZING A DIGITAL FOOTPRINT*   总被引：1，自引：0，他引：1  

STEPHEN D. WEAVER  MARK GAHEGAN 《Geographical review》2007,97(3):324-350

ABSTRACT. Herein, we discuss the desire for new technology, the need for security, and the right to privacy; in doing so, we argue that each of these concerns comprises an important, tripartite debate. To highlight the complexities in this problem, we define our notion of a “digital footprint” and introduce Big Foot—specialized software created for the research described here to facilitate visualization and exploration of the data that comprise Stephen Weaver's personal digital footprint. Using Big Foot we demonstrate how multiple digital personae can be created from the data that constitute one unique digital footprint and provide a methodology for understanding the good and bad impacts that new technologies may have on future societies. One of the primary arguments of this work is that the debate—though not formally recognized—is currently before contemporary society and must receive sufficient attention.  相似文献   

The Range of Spinel Compositions in Terrestrial Mafic and Ultramafic Rocks   总被引：33，自引：10，他引：33  

BARNES  STEPHEN J.; ROEDER  PETER L. 《Journal of Petrology》2001,42(12):2279-2302

Compositional fields for spinels from a wide variety of mafic–ultramaficigneous rock types and tectonic environments have been determinedfrom a global database of over 26 000 analyses. These fieldsare defined using contoured data density plots based on thespinel prism, and plots of T iO₂ vs ferric iron, for mantlexenoliths, ophiolitic rocks, continental layered intrusions,alkalic and lamprophyric rocks, tholeiitic basalts, Alaskanultramafic complexes and komatiites. Several trends appear regularlyin the various environments: a trend of widely variable Cr/(Cr+ Al) at low Fe²⁺/(Mg + Fe²⁺) (the Cr–Al trend); increasingFe³⁺, Fe²⁺/(Mg + Fe²⁺) and T iO₂ at constant Cr/(Cr + Al) (Fe–Ti trend); a trend found primarily in kimberlites, similar toFe–T i but at constant Fe²⁺/(Mg + Fe²⁺); and an unusualtrend of increasing Al found only in layered intrusions. TheCr–Al and Fe–T i trends are both found to varyingdegrees in tholeiitic basalts. The Cr–Al trend is prevalentin rocks that have equilibrated over a range of pressures, whereasthe Fe–T i trend is dominantly due to low-pressure fractionation.The most Cr-rich chromites found in nature occur in boninites,diamond-bearing kimberlites, some komatiites and ophioliticchromitites. Exceptionally reduced chromites are found in somekomatiites and in ophiolitic chromitites. Detrital chromitesfrom the Witwatersrand conglomerates are of komatiitic provenance. KEY WORDS: basalt; chromite; kimberlite; ophiolite; spinel  相似文献   

Flood Risk Management for Caravan Parks in New South Wales     

STEPHEN YEO 《The Australian geographer》2003,34(2):195-209

A survey of 71 caravan parks in coastal NSW indicates a high exposure to flooding. Most parks in NSW are flood-prone. A growing number of long-term residents in the 1980s, and essentially immovable manufactured homes in the 1990s, significantly increased flood risk. However, many parks are ill-equipped to deal with flooding: a high turnover of park managers means that most have no direct experience of floods; attitudes of denial prevail; most parks have no means of raising community flood awareness; and the process of flood response planning is patchy and of poor quality. Key strategies for the reduction of flood risk are suggested, including a more rigorous implementation of tighter regulations that better guard the health and safety of park residents, and the equipping of park managers to self-manage risk.  相似文献   

The Late Devensian Lateglacial palaeoenvironmental record from Whitrig Bog, SE Scotland. 2. Chironomidae (Insecta: Diptera)   总被引：1，自引：0，他引：1  

STEPHEN J. BROOKS  J. JOHN LOWE  FRANCIS E. MAYLE 《Boreas: An International Journal of Quaternary Research》1997,26(4):297-308

Changes in chironomid midge larval assemblages in Lateglacial (c. 13.5–10 ka yr BP) lake sediments from Whitrig Bog are used to infer climatic (temperature) change. The earliest sediments contain few, predominantly cold stenothermic taxa. This fauna is replaced by an assemblage dominated by thermophilic taxa, indicating rising temperatures. The relatively warm Interstadial is punctuated by at least two brief cold oscillations which are characterized by the return of certain cold-water taxa and the demise of some elements of the thermophilic fauna. The earlier of the two oscillations was apparently shorter and colder than the second. The highest Lateglacial Interstadial temperatures were attained either shortly before or after the first cold oscillation. This timing of the Lateglacial thermal maximum is apparently later than has been previously inferred from fossil beetle data. The Lateglacial Interstadial is terminated by the Loch Lomond (Young Dryas) Stadial, which is indicated in this monolith by an abrupt return of cold stenothermic Chironomidae and the virtual elimination of thermophilic taxa. Temperatures during the Younger Dryas appear to have been colder than during either of the previous minor cold oscillations. Climatic inferences from chironomid analysis broadly support and augment conclusions drawn from sediment chemistry and palynological evidence derived from the same monolith, although there is evidence that the vegetation and chironomid responses to early postglacial warming were out of phase.  相似文献   

Sedimentological aspects of the Humber Group (Upper Jurassic) of the South Central Graben, UK North Sea     

JOHN A. HOWELL  STEPHEN S. FLINT  CATHERINE HUNT 《Sedimentology》1996,43(1):89-114

Complex structure, poorly understood sedimentology and poor biostratigraphic control make the Upper Jurassic Humber Group of the South Central Graben one of the least understood and most complex hydrocarbon reservoirs of the North Sea. Detailed logging of available core from 19 exploration wells has been combined with an improved understanding of the relevance of trace fossils and a recognition of important base-level variations to provide a greatly enhanced understanding of the depositional system active within the area at that time. A new sedimentological model, based upon the distribution of facies and facies associations, illustrates that Upper Jurassic structure and consequent basin geometry were the principal controls upon the distribution of depositional environments. Rifting and second-order transgression controlled the back-stepping onlap patterns observed and higher frequency base-level fluctuations controlled the internal architecture of individual sandbodies. The model presented accounts for features of these deposits that were previously considered anomalous, such as the thickness of bioturbated sandstones, paucity of foreshore deposits and complex age relationships of sands.  相似文献