Diving deep on a Pleistocene reef in eastern Jamaica     

STEPHEN K. DONOVAN  DAVID A. T. HARPER 《Geology Today》1998,14(1):26-30

Exhumed early Pleistocene reefs along the eastern coast of Jamaica expose deep-water environments downslope from the more familiar, shallow-water reef frameworks. Such environments have quite different faunas from the shallow parts of the reefs, including common 'Palaeozoic-type' biotas like the brachiopods and crinoids. These animals are found in deeper-water settings around the Caribbean today; however, these biotas are not readily available nor easily studied. The slightly older Pleistocene faunas are much more accessible and informative. Here the past may be the key to the present.  相似文献   

Continental/Cordilleran ice interactions: a dominant cause of westward super-elevation of the last glacial maximum continental ice limit in southwestern Alberta, Canada     

EDWARD C. LITTLE  LIONEL E. JACKSON Jr.  THOMAS S. JAMES  STEPHEN R. HICOCK  ELIZABETH R. LEBOE 《Boreas: An International Journal of Quaternary Research》2001,30(1):43-52

In southwestern Alberta, Canada, a westward-rising last-glacial-maximum continental ice limit has been identified. This limit is defined by the upper elevation of Canadian Shield erratics deposited by last-glacial-maximum continental ice along the flanks of prominent ridges and buttes within the region. The interpolation between ice-limit data points has produced two distinct slope profiles: 2.9 m/km to the east, and 4.2 m/km to the west of Mokowan Butte. Three hypotheses are proposed to explain this westward rise of the last-glacial-maximum continental ice limit: (1) regional tectonic uplift, (2) glacio-isostatic uplift, and (3) continental ice-flow convergence due to topographic obstacles and interaction with montane ice. Inferred long-term rates of tectonic uplift and glacio-isostatic modelling show that these two mechanisms account for less than 25% of the observed absolute elevation increase of the limit between the Del Bonita uplands and Cloudy Ridge in southwestern Alberta. The remaining rise in elevation of the continental ice-sheet margin in this region is thought to result from continental ice-flow convergence due to the combined effects of the regional topography and interaction with montane glaciers to the west. The steeper rise in the former continental ice surface west of Mokowan Butte can be explained by the topographic obstruction and interaction with montane glaciers in the area of the Rocky Mountain front.  相似文献   

DATA ANALYSIS IN THE SHOT NOISE LIMIT.PART Ⅲ:ADAPTIVE DATA SMOOTHING FILTERS     

STEPHEN E.BIALKOWSKI 《地理学报(英文版)》1990,(4)

Digital filter smoothing methods for shot-noise-limited data are addressed in this study.The preferredmethod is based on a Gaussian filter in which the width of the Gaussian filter function is varied dependingon the estimate of the second derivative of the raw data.This filter is developed from the standpoint ofmaximum likelihood parameter estimation of the probability density function which describes shot-noise-limited data.The smoothing filter is tested and compared with the conventional sequential regressionfilter.This adaptive Gaussian smoothing filter works better than both the sequential regression and theadaptive Gaussian filter derived for normal noise.For data containing both high-and low-frequencycomponents,the limiting step in the adaptive filter is an estimation of the smoothing interval.Methodsfor determining an optimum smoothing interval are discussed.With the optimized smoothing interval,the adaptive Gaussian filter works well for data sets with a wide range of varying frequency components.In particular,synthetic data typical of atomic emission spectra are used to test this smoothing filter.  相似文献   

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