Noble gas measurements in the L/LL5 chondrite Knyahinya     

Bernard LAVIELLE  Seraphin TO  ERIC GILABERT 《Meteoritics & planetary science》1997,32(1):97-107

Abstract— The L/LL5 chondrite Knyahinya had an approximately spherical shape, and as it experienced a single stage exposure history, it represents a very interesting object to study depth profiles of cosmic-ray-produced nuclide concentrations. Such data are required to improve and to validate model calculations of production rates. We report Ne, Ar, Kr and Xe isotopic abundances in five bulk samples. The adopted procedure of noble gas extraction included two pyrolysis steps at 450 °C and 650 °C, respectively, followed by a combustion step in pure O₂ at 650 °C before melting the sample. This procedure allows for the separation of a significant fraction of the trapped Kr and Xe, leading to an enrichment of the cosmic-ray produced component, which is released in the melting step. The isotopic composition of the trapped Xe component measured in the combustion step is found to be identical with the OC-Xe composition (Lavielle and Marti, 1992) and supports the suggestion that ordinary chondrites formed in a homogeneous trapped noble gas reservoir. Cosmic-ray produced Kr and Xe components and depth profiles were measured, including for the first time a ⁸¹Kr profile. The calculated exposure age of 39.5 ± 1.0 Ma, based on the ⁸¹Kr-Kr method, is found to be in excellent agreement with previous determinations. The concentrations of trapped and fissiogenic noble gas components are clearly lower than those generally observed in type 5 ordinary chondrites and may suggest diffusion losses before a meter-sized object was exposed to the cosmic radiation.  相似文献   

Evaluating delta asymmetry using three‐dimensional facies architecture and ichnological analysis,Ferron ‘Notom Delta’, Capital Reef,Utah, USA     

WEIGUO LI  JANOK P. BHATTACHARYA  YIJIE ZHU  DANIEL GARZA  ERIC BLANKENSHIP 《Sedimentology》2011,58(2):478-507

Delta asymmetry occurs where there is strong wave influence and net longshore transport. Differences in the morphology and facies architecture between updrift and downdrift sides of asymmetric deltas are potentially significant for exploration and exploitation of resources in this class of reservoirs. Although delta asymmetry has been recognized widely from modern wave‐influenced deltaic shorelines, there are few documented examples in the ancient record. Based on an integrated sedimentological and ichnological study, the along‐strike variability and delta asymmetry within a single parasequence (Ps 6) is documented in continuously exposed outcrops of the Cretaceous Ferron Sandstone Member of the Mancos Shale Formation near Hanksville in southern Utah. Two intra‐parasequence discontinuity surfaces are recognized which allow subdivision of the parasequence into three bedsets, marked as Ps 6‐1 to Ps 6‐3. Four facies successions are recognized: (i) wave/storm‐dominated shoreface; (ii) river‐dominated delta front; (iii) wave/storm‐reworked delta front; and (iv) distributary channel and mouth bar. Dips of cross‐strata within distributary‐mouth bars and shorefaces show a strong downdrift (southward) component. Ps 6‐3 predominantly consists of river‐dominated delta‐front deposits, whereas Ps 6‐1 and Ps 6‐2 show an along‐strike facies change with shoreface deposits in the north, passing into heterolithic, river‐dominated delta‐front successions south to south‐eastward, and wave/storm‐reworked delta‐front deposits further to the south‐east. Trace fossil suites correspondingly show distinct along‐strike changes from robust and diverse expressions of the archetypal Cruziana Ichnofacies and Skolithos Ichnofacies, into suites characterized by horizontal, morphologically simple, facies‐crossing ichnogenera, reflecting a more stressed, river‐dominated environment. Further south‐eastward, trace fossil abundance and diversity increase, reflecting a return to archetypal ichnofacies. The overall facies integrated with palaeocurrent data indicate delta asymmetry. The asymmetric delta consists of sandier shoreface deposits on the updrift side and mixed riverine and wave/storm‐reworked deposits on the downdrift side, similar to that observed in the modern examples. However, in contrast to the recent delta asymmetry models, significant paralic, lagoonal and bay‐fill facies are not documented in the downdrift regions of the asymmetric delta. This observation is attributed to a negative palaeoshoreline trajectory during delta progradation and subsequent transgressive erosion. The asymmetric delta was induced by net longshore transport from north to south. The forced regressive nature of the delta precludes significant preservation of topset mud.  相似文献   

Editorial     

TERRY COPPOCK  ERIC ANDERSON 《International journal of geographical information science》2013,27(2):99-100

This paper addresses the problems associated with the integration of data between incongruent boundary systems. Currently, the majority of spatial boundaries are designed in an uncoordinated manner with individual organizations generating individual boundaries to meet individual needs. As a result, current technologies for analysing geospatial information, such as geographical information systems (GISs), are not reaching their full potential. In response to the problem of uncoordinated boundaries, the authors present an algorithm for the hierarchical structuring of administrative boundaries. This algorithm applies hierarchical spatial reasoning (HSR) theory to the automated structuring of polygons. In turn, these structured boundary systems facilitate accurate data integration and analysis whilst meeting the spatial requirements of selected agencies. The algorithm is presented in two parts. The first part outlines previous research undertaken by the authors into the delineation of administrative boundaries in metropolitan regions. The second part outlines the distinctly different constraints required for administrative-boundary design in rural areas. The development of the algorithm has taken place in a GIS environment utilizing Avenue, an object-orientated programming language that operates under ArcView, the desktop software developed and distributed by ESRI.  相似文献   

Selection of calibration objective fonctions in the context of rainfall-ronoff modelling in a Sudanese savannah area     

ERIC SERVAT  ALAIN DEZETTER 《水文科学杂志》2013,58(4):307-330

Abstract

In the context of rainfall-runoff modelling carried out on the Sudanese savannah area in the northwest of the Ivory Coast, attempts are being made to reconstitute the flow at the outlets of catchments in 10 day time steps. By using algorithms with automatic fitting procedures for the parameters, it appeared necessary to make a choice concerning the calibration objective functions to be used. The paper presents the algorithms, data and objective functions that have been used. The results obtained from the calibrations made have been analysed. That analysis was done principally with the help of a comparative evaluation modulus which takes into account elements other than the value of the objective function alone and which enables the quality of the results to be picked out from a hydrological point of view. At the conclusion of the analysis, the objective function defined by Nash seems to stand out quite clearly in relation to the other formulae examined.  相似文献   

THE RISE,FALL, AND RECONFIGURATION OF THE MEXICAN EJIDO*     

ERIC P. PERRAMOND 《Geographical review》2008,98(3):356-371

ABSTRACT. After the Mexican Revolution of 1910 the Mexican federal government created a communal resource‐holding institution, the ejido, to redress long‐standing land‐tenure inequality. Between the 1930s and the late 1970s, the period of active redistribution of federalized and previously private resources, half of Mexico's entire area was transferred to the ejido sector. Local ejidos became the driving political and economic force at the municipio level for agrarian reform, redistributing local power and affirming the national stamp of the Partido Revolucionario Institucional, the dominant national party of the twentieth century. Although the 1992–1993 reforms to Article 27 of the Mexican Constitution prohibited any future expansion of communal lands and allowed privatization of communal resources, few widespread privatization schemes have taken hold in the vast majority of ejidos. In this article I provide examples of this new communal framework and its implications, with illustrations based on fieldwork in the states of Guanajuato and Sonora.  相似文献   

Determinism within human–environment research and the rediscovery of environmental causation     

GABRIEL JUDKINS  MARISSA SMITH  ERIC KEYS† 《The Geographical journal》2008,174(1):17-29

The popularity of the work Guns, germs and steel (GGS) has served to bring the question of human–environment connections once again to the forefront of popular thought. We assert that the recent success of GGS represents both a persistence of environmental determinist logic and a contemporary trend that privileges the environment as the primary influence on human–environment relationships. The historical development of the human–environment field is reviewed from the cultural and political ecology (CAPE) perspective, with particular attention to illustrating the varying emphasis between humans and their environment. GGS is situated within this developing field through a critical analysis of the arguments and methods forwarded by Jared Diamond. The book is found to mirror earlier environmental determinism by failing to take into account many of the advances in human–environmental thought since the early twentieth century. Its popular success suggests the pitfalls of failures to acknowledge the complex, intertwined and indivisible relationship that exists among humans and their environment. Furthermore, there is evidence that the environmental determinism espoused in GGS has caught the attention of international development policymakers potentially influencing future outlays of aid and assistance to the developing world. These conclusions raise cautionary flags against repeating past theoretical mistakes by accepting simplistic, causal explanations based largely on a deterministic conception of the natural environment.  相似文献   

Grand Canyon Geology, S. S. Beus and M. Morales (eds).     

ERIC ROBINSON 《Geology Today》1991,7(6):231-231

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The relation between glacial ages and terrestrial magnetism     

ERIC OLAUSSON  BJÖRN SVENONIUS 《Boreas: An International Journal of Quaternary Research》1973,2(3):109-115

An attempt is made to show that the change of angular momentum of the earth, caused by glaciations, may compensate the slowing down effect from tidal friction forces and even reverse the polarity in the terrestrial magnetic field.  相似文献   

Petrology and Geochemistry of Basalts from the Red Sea Axial Rift at 18? North     

EISSEN  JEAN-PHILIPPE; JUTEAU  THIERRY; JORON  JEAN-LOUIS; DUPRE  BERNARD; HUMLER  ERIC; AL'MUKHAMEDOV  ALEXANDER 《Journal of Petrology》1989,30(4):791-839

Detailed studies by submersible were carried out in the axialzone of the Red Sea Rift near 18?N during the Soviet Red Seaexpedition of the Oceanological Institute of the Academy ofSciences (December 1979–March 1980). The initial bathymetric,magnetic and seismic surveys established the general organizationof the symmetric tectonic steps (1–3) descending towardsthe axial rift. The 4–5 km wide inner floor of the riftwas explored during 21 dives. It is occupied by 100–300m high, young pillowed volcanoes, isolated or grouped to formelongated hills, frequently cut by open fissures except in thezone of most recent extrusion. The 42 samples collected are typical plagioclase ? olivine ?clinopyroxene ? spinel, more or less porphyritic mid-ocean ridgebasalts whose compositions were mainly controlled by polybaricfractionation of plagioclase, olivine and minor clinopyroxene.They have been separated into porphyritic and sub-aphyric groupsusing modes and mineralogical criteria. Mineral-liquid equilibria,crystal zonation, and modal proportions indicate some magmamixing but probably only of closely related magma batches withineach described group, as can occur inside a single magma chamber.Crystal accumulation is believed to have played a significantrole in only a few porphyritic samples. Three sub-groups (from less to more evolved; (a) FeO^*/MgO<1?22;(b) 1?16<FeO^*/MgO < 1?48; and (c)FeO^*/MgO>1?49) weredistinguished on the basis of glass and whole-rock major elementchemistry. Glass compositions follow the multisaturated cotectic-likecurve for MORB-type basalts and show a general evolution verycomparable to what is observed on the Mid-Atlantic Ridge near36?N, but arc less diverse than in the FAMOUS area. ⁸⁷Sr/⁸⁶Sr,¹⁴³Nd/¹⁴⁴Nd, and ²⁰⁶Pb/²⁰⁴Pb data for 4 samples show strongsimilarities to those from the Mid-Atlantic and East PacificRidges, and indicate no continental contamination despite thefact that they have been produced during recent continentalbreak-up and ocean opening. ²⁰⁶Pb/²⁰⁴Pb values, Th/Ta vs. Th/Tbcorrelations, and rare earth element patterns allow recognitionof three different groups of samples, indicating that the RedSea Rift near 18?N is fed by a heterogeneous mantle source.The chondrite-normalized LREE.  相似文献   

Properties of debris flow deposits and source materials compared: implications for debris flow characterization   总被引：1，自引：0，他引：1  

ERIC BARDOU  PASCAL BOIVIN†  HANS-RUDOLF PFEIFER‡ 《Sedimentology》2007,54(2):469-480

In the Alps, debris flow deposits generally contain <5% clay‐size particles, and the role of the surface‐charged <2 μm particles is often neglected, although these particles may have a significant impact on the rheological properties of the interstitial fluid. The objective of this study was to compare debris flow deposits and parent materials from two neighbouring catchments of the Swiss Alps, with special emphasis on the colloidal constituents. The catchments are small in area (4 km²), 2·5 km long, similar in morphology, but different in geology. The average slopes are 35–40%. The catchments were monitored for debris flow events and mapped for surface aspect and erosion activity. Debris flow deposits and parent materials were sampled, the clay and silt fractions extracted and the bulk density, <2 mm fraction bulk density, particle size distribution, chemical composition, cation exchange capacity (CEC) and mineralogy analysed. The results show that the deposits are similar to the parent screes in terms of chemical composition, but differ in terms of: (i) particle size distribution; and (ii) mineralogy, reactivity and density of the <2 mm fraction. In this fraction, compared with the parent materials the deposits show dense materials enriched in coarse monocrystalline particles, of which the smallest and more reactive particles were leached. The results suggest that deposit samples should not be considered as representative of source or flow materials, particularly with respect to their physical properties.  相似文献