Times of sand: Sedimentary history and archaeology at the Sigatoka Dunes,Fiji     

Atholl Anderson  Richard Roberts  William Dickinson  Geoffrey Clark  David Burley  Antoine de Biran  Geoffrey Hope  Patrick Nunn 《Geoarchaeology》2006,21(2):131-154

The orthodox archaeological sequence at the Sigatoka Dunes site (VL 16/1) in Fiji proposes three phases of occupation spanning Fijian prehistory, each associated with a period of dune stability. It has been taken as the standard model of Fijian prehistory for more than 30 years. Recently, however, it has been argued that there is no stratigraphic support for three discrete levels and that the occupation history was fragmented, complex, and continuous within a volatile dune system. We present new data, from optical and radiocarbon dating, to argue that a three‐phase model, although somewhat more complex in detail, remains the most robust interpretation of site history. The longest stable phase (Level 2) began 2500–2300 cal yr B.P. and is possibly associated with relatively low ENSO frequency. Substantial sand dune accumulation began after ˜1300 cal yr B.P. © 2006 Wiley Periodicals, Inc.  相似文献   

Environmental archaeology: Theoretical and practical approaches     

Richard W. Yerkes 《Geoarchaeology》2006,21(8):878-880

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The eSTAR network – agent architectures for astronomy     

A. Allan  T. Naylor  E. S. Saunders 《Astronomische Nachrichten》2006,327(8):767-770

The eSTAR Project uses intelligent agent technologies to carry out resource discovery, submit observation requests and analyze the reduced data returned from a meta‐network of robotic telescopes. Linking ground based telescopes with astronomical satellites, and using the emerging field of intelligent agent architectures to provide crucial autonomous decision making in software, the project has succeeded in combining data archives and research class telescopes, along with distributed computing nodes, to build an ad‐hoc peer‐to‐peer heterogeneous network of resources. We present the current operations paradigm of the eSTAR network and describe the direction in which the project intends to develop over the next few years. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Modelling Watersheds as Spatial Object Hierarchies: Structure and Dynamics   总被引：1，自引：0，他引：1  

Lawrence E. Band  Christina L. Tague  Soren E. Brun  David E. Tenenbaum  & Richard A. Fernandes 《Transactions in GIS》2000,4(3):181-196

The generation, transport and fate of non-point source pollutants in surface water systems is recognized as a major threat to water supplies, aquatic and coastal ecosystems. The transformation and movement of water, carbon and nutrients through watersheds integrates a set of ecosystem processes along hydrologic flowpaths. Human individual and institutional interactions with these processes involve direct addition or abstraction of these substances, or the alteration of land cover and drainage systems. In natural and developed catchments, these processes often vary at granularities ranging from below the level of a hillslope, up through regional watersheds. This suggests the need for the development of hierarchical analysis tools that can address the integration of a set of biophysical, biogeochemical and socioeconomic processes over a spectrum of scales. We describe and illustrate the use of a watershed model implemented as a spatial object hierarchy, representing successively contained landform classes associated with class specific processes as member functions. The model has been linked in a range of looser and tighter couplings with GRASS and ArcView, supplemented by specific terrain analytical functions. We illustrate the data and model system for an instrumented catchment monitored as part of the Baltimore Ecosystem Study (BES), a Long Term Ecological Research (LTER) site centering on integrated carbon, water and nutrient cycling.  相似文献   

High-Resolution Non-Hydrostatic Simulations of Flash-Flood Episodes with Grid-Nesting and Ice-Phase Parameterization     

J. Stein  E. Richard  J. P. Lafore  J. P. Pinty  N. Asencio  S. Cosma 《Meteorology and Atmospheric Physics》2000,72(2-4):203-221

Summary ?Simulations of two heavy rainfall events south of the Alps have been conducted with a non-hydrostatic model at horizontal resolutions ranging from 40 to 2.5 km. Emphasis is placed on the assessment of two recent model developments: a detailed explicit mixed phase microphysical scheme and a two-way interactive grid nesting method. In the high-resolution simulations, the impact of the ice phase was found to be quite substantial, accelerating the propagation of the surface front and modifying the spatial distribution of the rainfall. Simulations carried out with two-way interactive grid nesting yielded more realistic overall precipitation patterns, particularly at the finest horizontal resolution. Received March 22, 1999/Revised June 28, 1999  相似文献   

Modal metasomatism in the Kaapvaal craton lithosphere: constraints on timing and genesis from U–Pb zircon dating of metasomatized peridotites and MARID-type xenoliths     

Jürgen Konzett  Richard A. Armstrong  Detlef Günther 《Contributions to Mineralogy and Petrology》2000,139(6):704-719

Modal metasomatism in the Kaapvaal craton lithosphere is well documented in upper mantle xenoliths sampled by both group I (mainly late Cretaceous) and group II (mainly early Cretaceous to late Jurassic) kimberlites in the Kimberley area. The metasomatic style is characterized by introduction of K, H and large ion lithophile/high field strength (LIL/HFS) elements into the lithospheric mantle leading to the crystallization of hydrous potassic phases such as phlogopite and/or K-amphibole. Textures indicate that the hydrous phases either replace pre-existing assemblages in peridotites, forming the metasomatized peridotite suite (phlogopite–K-richterite–peridotites: PKPs) or crystallize from K-rich melts, forming the mica–amphibole–rutile–ilmenite–diopside (MARID) suite of xenoliths. These K-rich assemblages become potential low melting source components for alkaline incompatible trace element enriched magmas. The timing of metasomatism and its temporal and possible genetic relation to kimberlite magmatism is poorly constrained because of the rarity of phases in the metasomatic assemblages suitable for precise dating. Here we present precise sensitive high resolution ion microprobe (SHRIMP) U–Pb formation ages of 88 ± 2 (1σ=1 standard deviation) and 82 ± 3 Ma data for zircons from a K-richterite–phlogopite-bearing metasomatized peridotite (PKP) and a MARID xenolith respectively, sampled by a group I kimberlite. Both average PKP and MARID zircon ages are indistinguishable from emplacement ages of group I kimberlites in the Kimberley area dated at 83 ± 4 (2σ) and 84 ± 0.9 Ma. One exceptionally old age spot of 102 ± 5 Ma from a PKP zircon provides evidence for modal metasomatism predating group I kimberlite emplacement by several millions of years with minor resetting of the U–Pb isotopic system of most analyzed PKP zircons to a group I emplacement age. Detailed textural and mineral chemical analysis, including high energy X-ray mapping and analysis of fluid inclusion daughter crystals, indicates a complex reaction history for both PKPs and MARIDs. U–Pb zircon ages from this study combined with literature data and experimentally derived models for MARID formation are used to suggest that MARID-formation is concurrent and genetically related to both group I and II kimberlite magmatism in the Kimberley area. MARID and PKP zircon ages are also consistent with the idea first proposed by Dawson and Smith (Geochim Cosmochim Acta 41: 309–323, 1977) that metasomatized peridotites may form from interaction of hydrous fluids expelled by solidifying MARID-type melts with peridotitic wall rocks. Received: 13 December 1999 / Accepted: 13 April 2000  相似文献   

Constraints on Cation Order in Calcium-rich Sedimentary Dolomite   总被引：2，自引：0，他引：2  

Richard J. Reeder 《Aquatic Geochemistry》2000,6(2):213-226

Most sedimentary Ca-rich dolomite in pre-Holocenerocks is known to exhibit a fine-scale modulation inTEM images, reflecting a domain structure of which onecomponent is a low-symmetry variant of dolomite. Thevarious structural models proposed for thelow-symmetry component involve Ca–Mg order patternsthat are different from that in dolomite. Caution istherefore required for interpretation of X-raydiffraction data, which average over the entirestructure. The average structures of two Ca-richdolomites having a structural modulation are refinedusing single-crystal intensity data. The resultsindicate a poor fit using a dolomite model, which isconsistent with the findings from TEM and electrondiffraction indicating that one component of thedomain structure is different than dolomite. Resultsalso indicate that average model A and B cation siteshave mixed Ca–Mg occupancy, which provides someconstraints on possible models for the low-symmetrydomains.  相似文献   

Ready for IPCC-2001: Innovation and Change in Plans for the IPCC Third Assessment Report     

Richard H. Moss 《Climatic change》2000,45(3-4):459-467

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Climatic and Demographic Consequences of the Massive Volcanic Eruption of 1258     

Richard B. Stothers 《Climatic change》2000,45(2):361-374

Somewhere in the tropics, a volcanoexploded violently during the year 1258, producing amassive stratospheric aerosol veil that eventuallyblanketed the globe. Arctic and Antarctic ice coressuggest that this was the world's largest volcaniceruption of the past millennium. According tocontemporary chronicles, the stratospheric dry fogpossibly manifested itself in Europe as a persistentlycloudy aspect of the sky and also through anapparently total darkening of the eclipsed Moon. Basedon a sudden temperature drop for several months inEngland, the eruption's initiation date can beinferred to have been probably January 1258. Thefrequent cold and rain that year led to severe cropdamage and famine throughout much of Europe.Pestilence repeatedly broke out in 1258 and 1259; itoccurred also in the Middle East, reportedly there asplague. Another very cold winter followed in1260–1261. The troubled period's wars, famines,pestilences, and earthquakes appear to havecontributed in part to the rise of the Europeanflagellant movement of 1260, one of the most bizarresocial phenomena of the Middle Ages. Analogies can bedrawn with the climatic aftereffects and Europeansocial unrest following another great tropicaleruption, Tambora in 1815. Some generalizations aboutthe climatic impacts of tropical eruptions are madefrom these and other data.  相似文献   

A Concise History of Dutch River Floods     

Richard S. J. Tol  Andreas Langen 《Climatic change》2000,46(3):357-369

Based on a brief account of 1,000 years of river floods and flood management in the Dutch Rhine delta, it is argued that vulnerability to river floods depends on the complex interaction of economics, institutions, politics and, to a limited extent, climate. Response functions and thresholds for climate change impacts should take this complexity into account rather than assuming society to be constant or evolving in a straightforward manner.  相似文献