Characteristic features of pockmarks on the North Sea Floor and Scotian Shelf   总被引：6，自引：0，他引：6  

MARTIN HOVLAND  ALAN G. JUDD†  LEWIS H. KING‡ 《Sedimentology》1984,31(4):471-480

This paper presents the results of a comparative study of pockmarks and associated features appearing on both sides of the North Atlantic: on the Scotian Shelf off Nova Scotia and in the northern North Sea. Pockmarks are formed in seabed material consisting of soft silty clay. The seismic, sonar and lithologic characteristics of the sediments on the Scotian Shelf are remarkably similar to those found in the northern North Sea. Sediment clouds suspended in the water column immediately over the seabed have previously been observed on side-scan records associated with gas-charged sediments on corresponding shallow-seismic records. These and similar observations strongly suggest that most pockmarks are caused by gas efflux through the seafloor. However, the detailed mechanism of formation and the origin of the gas in the sediments is still unknown.  相似文献   

Alluvial fan and lacustrine sediments from the Stephanian A and B (La Magdalena, Ciñera—Matallana and Sabero) coalfields, northern Spain     

ALAN P. HEWARD 《Sedimentology》1978,25(4):451-488

Vertical sequence analysis within 1500-2500 m thick coarse-grained coalfield successions allows six sedimentary associations to be distinguished. These are interpreted in terms of depositional environments on, or related to alluvial fans which fringed a fault bounded source region. (i) Topographic valley and fanhead canyon fills: occurring at the bases of the coalfield successions and comprising sporadically reddened, scree, conglomeratic thinning and fining upward sequences, and fine-grained coal-bearing sediments. (ii) Alluvial fan channels: conglomerate and sandstone filled. (iii) Mid-fan conglomeratic and sandstone lobes: laterally extensive, thickly bedded (1-25 m) and varying from structureless coarse conglomerates and pebbly sandstones, to stratified fine conglomerates and cross-bedded sandstones. (iv) Interlobe and interchannel: siltstones, fine-grained sheet sandstones, abundant floras, thin coals and upright trees. (v) Distal fan: 10 cm-1.5 m thick sheet sandstones which preserve numerous upright trees, separated by silt-stones and mudstones with abundant floras, and coal seams. The sheet sandstones and normally arranged in sequences of beds which become thicker and coarser or thinner and finer upwards. These trends also occur in combination. (vi) Lacustrine: coals, limestones, and fine-grained, low-energy, regressive, coarsening upward sequences. Proximal fan sediments are only preserved in certain basal deposits of these coalfields. The majority of the successions comprise mid and distal alluvial fan and lacustrine sediments. Mid-fan depositional processes consisted of debris flows and turbulent streamflows, whilst sheetfloods dominated active distal areas. A tropical and seasonal climate allowed vegetation to colonize abandoned fan surfaces and perhaps resulted in localized diagenetic reddening. Worked coals, from 10s cm-20 m thick, occur in the distal fan and lacustrine environments. These alluvial fan deposits infill‘California-like’basins developed and preserved along major structural zones. In many of their characteristics, in particular the occurrence of thinning and fining, and thickening and coarsening upward sequences and megasequences, these sediments have similarities to documented ancient submarine fan deposits.  相似文献   

Glass-rich, Cordierite-Biotite Rhyodacite, Valle Ninahuisa, Puno, SE Peru: Petrological Evidence for Hybridization of 'Lachlan S-type' and Potassic Mafic Magmas   总被引：1，自引：0，他引：1  

SANDEMAN  HAMISH A.; CLARK  ALAN H. 《Journal of Petrology》2003,44(2):355-385

The Revancha dyke, a 24·1 Ma,  相似文献   

植被冠层热点的季相和日相变化     

苏理宏  李小文  A.Stralher  E.Tsvetsinskay  王锦地 《遥感学报》2002,6(4):241-245

随着热点卫星Triana的即将发射，地表热点季相和日相变化的研究变得日益重要。以几种植被冠层为例，采用计算机模拟的方法考查冠层热点的季相和日相变化。  相似文献   

Recent shallow marine ostracods from high latitudes: implications for late Pliocene and Quaternary palaeoclimatology   总被引：2，自引：0，他引：2  

ELISABETH M. BROUWERS  THOMAS M. CRONIN  DAVID J. HORNE  ALAN R. LORD 《Boreas: An International Journal of Quaternary Research》2000,29(2):127-142

New information about modern high-latitude marine ostracod faunas and about their occurrence in late Pliocene and Quaternary sequences promotes the application of these microfossils to palaeoenvironmental, palaeobiogeographical and palaeoclimatological problems. Five poorly known species (Cluthia cluthae, Finmarchinella logani, Roundstonia globulifera, Roundstonia macchesneyi and Semicytherura complanata) from North Atlantic, North Pacific and Arctic areas are confirmed as extant and are used to demonstrate the potential of marine ostracods as tools for palaeoclimate studies. The genus Bonnyannella Athersuch, 1982 is shown to be a junior synonym of Roundstonia Neale, 1973.  相似文献   

North American Quaternary cold-tolerant turtles: distributional adaptations and constraints   总被引：1，自引：0，他引：1  

J. ALAN HOLMAN  KENNETH D. ANDREWS 《Boreas: An International Journal of Quaternary Research》1994,23(1):44-52

The painted turtle, Chrysemys picta , and the snapping turtle, Chelydra serpentina , occur in aquatic habitats north of Lake Superior in boreal forest and cold prairie areas across Canada, and have by far the most northern range of any modern North American chelonian taxa. These two species are also the dominant turtles of the North American Pleistocene glacial ages and were among the first species to invade formerly glaciated areas at the end of the Wisconsinan. These Pleistocene occurrences are documented here. Several remarkable behavioral, physiological and reproductive adaptations that may act together to allow these species to survive in such northern areas are discussed.  相似文献   

Kyoto flexibility mechanisms in EU accession countries: will they make a difference?     

DIANA ÜRGE-VORSATZ  ALEKSANDRA NOVIKOVA  ALAN WATT 《Climate Policy》2013,13(3):179-196

What potential effect do flexible mechanisms under the Kyoto Protocol have on energy efficiency, fuel switching and the development of renewable energy sources for the eight post-communist EU Member States that accessed in 2004? These countries are chief candidates for hosting Joint Implementation (JI) projects and for participating in international emission trading, which may assist the implementation and financing of projects in these target areas. The potentials and barriers to Joint Implementation are reviewed, as well as the conditions under which international emission trading can influence the energy use of the selling country. Different strategies adopted by the host countries towards the application of these instruments, and their impact on sustainable energy development, are examined. The article concludes that the Kyoto flexibility mechanisms may play a positive, but rather limited, role in the sustainable energy development of the region, but the barriers to Joint Implementation may shift the emphasis towards transactions under the framework of international emission trading. If innovative mechanisms are tied to sustainable development goals, this may mobilize the energyefficiency potentials of these countries. An attractive opportunity exists to achieve energy efficiency and emission reductions, utilizing the revenues from allowance sales through ‘green investment’ schemes.  相似文献   

Conflation Automated map compilation     

ALAN SAALFELD 《International journal of geographical information science》2013,27(3):217-228

Abstract

Map compilation, or conflation, is now being accomplished by computer. Interactive routines manipulate the graphic images of two different digital maps of the same region in order to permit map similarities and differences to be recognized more easily. Rubber-sheeting one or both of the maps permits an operator or the computer to align the maps in stages through methods of successive approximation and to review each new alignment. The computer recognizes matches using mathematical relations of geometric position and graph network configuration to test for feature matches and, when the tests are satisfied, corresponding features can be flagged automatically as matches or highlighted for review by the operator. Techniques and methods developed for conflation systems have important applications in other areas of automated cartography and in image processing and computer graphics  相似文献   

UK Developments in Environmental GIS     

ALAN J. STRACHAN  NEIL STUART 《International journal of geographical information science》2013,27(1):17-20

  相似文献   

BRAZILIAN IMMIGRATION TO THE UNITED STATES AND THE GEOGRAPHICAL IMAGINATION*     

ALAN P. MARCUS 《Geographical review》2009,99(4):481-498

ABSTRACT. In the late 1980s more than 1 million Brazilians left Brazil without returning. Today an estimated 2 million Brazilians live abroad, 1.2 million of them in the United States. In this article I show that Brazilians migrate for a variety of reasons, including the geographical imagination. Why are so many Brazilians leaving for the United States? What are their geographical imaginations, and how are they described in their migration process? Using primary and secondary data and multiple methods, I address these questions by providing insights into Brazilian migrants' place perceptions, experiences, and reasons for migrating, focusing on the geographical imagination. Those migrants who end up returning to Brazil are more likely to cite financial and curiosity reasons for having migrated. A web of transnational religious and social networks sustains those immigrants who remain in the United States. Reasons for migrating are not economic alone; rather, they are based on interrelated and complex factors that range from adventure to curiosity, the cultural influence of the United States, family members, education, and escape.  相似文献