陆良彩色沙林旅游地学与保护

陆良彩色沙林为晚第三纪砂砾岩层中的溯源侵蚀冲沟地貌景观,世界罕见的自然奇观之一,具有较高的旅游和地理、地质研究价值。彩色沙林承继了陆良上亿年的地质发展史,淀积了10亿年来的砂、砾、矿物等物质,而形成、发育在近2Ma间,现仍处于缓慢发展阶段的溯源侵蚀冲沟中。彩色沙林景观应坚持“经营、建设、保护”并重的方针。     

The possible contribution of circumferential fault intrusion to caldera resurgence

In the geological record, the intrusion of substantial amounts of magma into circumferential faults and ring fractures is commonly observed. Finite element modelling is used here to investigate the strain field that may be expected from such intrusive events. Two simple vertical scenarios are explored, one for a caldera with a central block of thickness to diameter ratio of ~1:1 (similar to Rabaul) and one with a ratio much less than 1:1 (similar to the Valles type). Surface deformation in both cases is similar with central uplift, the development of a moat (or trough) like feature just outside of the intersection of the azimuth of the intruded ring fault and the free surface, and broader scale tumescence at a scale several times larger than the calderas radius. The response of the block and sub-caldera magma chamber for the two scenarios, however, is different. The blocks are in effect squeezed; the high aspect ratio one deforms upwards at the surface and downwards at its base, whereas the low aspect ration one experiences up arching (or bending) of the central part of the caldera block. Central uplift still occurs when only a short arc of a ring fracture system or a circumferential fault is intruded. In both models, tumescence in the centre of the caldera from single ring dyke intrusion can only account for decimetres to metres of surface uplift. Repeated intrusions over tens to hundreds of thousands of years, however, may cause incremental up doming of the caldera block leading to larger scale resurgent features. The amount of uplift possible due to squeezing of a high aspect ratio block is limited. It is proposed, however, that where bending of plate-like blocks occur above a decompressible and/or malleable magma body, ring fault intrusion may be a significant contributor to resurgence. In the simple conceptual models shown here, the amount of ring dyke-induced central uplift will be >40–50% of the width of the ring complex. In the geological record the accumulation of intrusions into some ring fractures has led to annular or arcuate plutons of hundreds of meters to several kilometres in thickness. At certain calderas such intrusions may be a control on the marked concentration of uplift within the restricted area defined by the caldera faults. The complex nature of the horizontal displacements associated with the intrusion of ring and arcuate dykes is also explored. Intrusion into ring fracture zones will tend to take place into those sectors of the annular zone which are perpendicular to the least compressive stress vector. This may be a factor in the observed difference for caldera evolution in extensional and compressional areas. The unrest at several modern calderas is tentatively related to circumferential fault intrusion.Editorial responsibility: J. Stix     

Stable Carbon and Nitrogen Isotopic

The perennially ice-covered lakes in the McMurdo Dry Valleys, Antarctica, are part of the coldest and driest ecosystem on earth. To understand lacustrine carbon and nitrogen cycling in this end-member ecosystem, and to define paleolimnological proxies for ice-covered lakes, we measured the stable carbon and nitrogen isotopic composition of particulate organic matter (POM) and benthic organic matter (BOM) within the lakes of Taylor Valley. The ¹³C compositions of seasonally ice-free edges of the lakes (moats) are enriched relative to under-ice organic matter. Thus, the organic carbon isotopic composition of buried sediments may be a proxy for sample position within the lake. In the moats, ¹³C values are governed by limited CO₂diffusion across benthic cyanobacterial cell membranes. During a high glacial melt (2001–2002) season, both ¹³C_POM and ¹³C_BOM in the moats were more depleted than during previous low melt years. We propose that this occurred in response to higher [CO₂]_(aq) and/or reduced growth rates resulting from turbidity-induced light limitation. Though moats and under-ice environments are usually poorly connected, during the 2001–2002 season, the enrichment of the ¹³C_POM values at 6 m depth in the stream-proximal sites relative to deep-profile sites implies enhanced connectivity between these environments. The ¹³C compositions of BOM and POM profiles in Lake Hoare and Lake Fryxell indicate that these lakes are dominated by benthic productivity. In contrast, in Lake Bonney, the similarity of the ¹³C values of BOM and POM indicates the pelagic component dominance in the carbon cycle.     

BOOK REVIEWS

Book Reviewed in this article: Redundant Spaces in Cities and Regions? Studies in Industrial Decline and Social Change . J. Anderson, S. Duncan and R. Hudson. eds. The Social Consequences and Challenges of New Agricultural Technologies . Gigi M. Berardi and Charles C. Geisler, eds. Determinants of Fertility in Developing Countries, Vol. I, Supply and Demand for Children . Rodolfo A. Bultao and Ronald D. Lee, eds. Computer Mapping: Progress in the‘80s . James R. Carter. Washington: Colonial Africa . A. J. Christopher. Geography of the Soviet Union . J. P. Cole. Chicago Mapmakers, Essays on the Rise of the City's Map Trade . Michael P. Conzen, ed. Changes in the Land: Indians, Colonists and the Ecology of New England . William Cronon. Mizner's Florida: American Resort Architecture . Donald W. Curl. Geographical Studies on the Soviet Union: Essays in Honor of Chauncy D. Harris . George Demko and Roland J. Fuchs, eds. Fluvial Hydrology . S. Lawrence Dingman. Pueblo Indian Water Rights: Struggle For a Precious Resource . Charles T. DuMars, Marilyn O'Leary and Albert E. Utton. Women in the Cities of Asia: Migration and Urban Adaptation . James T. Fawcett, Siew-Ean Khoo, and Peter C. Smith, eds. America's National Parks and Their Keepers . Ronald A. Foresta. Neighborhood Revitalization and the Postindustrial City . Dennis E. Gale. China in Canada: A Dialogue on Resources and Development . R. Louis Gentilcore, ed. China: The 80s Era . Norton Ginsburg and Bernard A. Lalor, eds. Boulder, CO: Global Resources: Challenges of Interdependence . Martin I. Glassner, ed. River Networks . Texas: A Geography . Terry G. Jordan with John L. Bean, Jr. and William M. Holmes. The American Frontier: An Archaeological Study of Settlement Pattern and Process . Kenneth E. Lewis. Water Resources, Geography and Law . Olen Paul Matthews. A Field Guide to American Houses . Virginia and Lee McAlester. Population: Patterns, Dynamics, and Prospects . James L. Newman and Gordon E. Matzke. Wood, Brick, and Stone, The North American Settlement Landscape, Vol. 1: Houses . Allen G. Noble. Historical Analysis in Geography . William Norton. The Displaced Worker and Community Response: Case Study of Portsmouth, Scioto County, Ohio . H. Milton Patton and Janet W. Patton. Disaster Management: Warning Response and Community Relocation . Ronald W. Perry and Alvin H. Muskatel. The Anthropology of Space: Explorations into the Natural Philosophy and Semantics of the Navajo . Rik Pinxten, Ingrid van Dooren, and Frank Harvey. What STYLE Is It? A Guide To American Architecture . John C. Poppeliers, S. Allen Chambers, Jr., and Nancy B. Schwartz. Appalachia: A Regional Geography—Land, People and Development . Karl Raitz and Richard Ulack. An Introduction to Urban Geography . John R. Short. Ford, A Village in the West Highlands of Scotland: A Case Study of Repopulation and Social Change in a Small Community . John B. Stephenson. Income and Jobs: USA Diagnosing the Reality . George Sternlieb and James W. Hughes. Weather and Climate of the Antarctic . W. Schwerdtfeger. History and Ecology: Studies of the Grassland, James C. Malin . Robert P. Swierenga, ed. Optimal Control of Spatial Systems . K. C. Tan and R. J. Bennett. Social Science and Revolutions . Stan Taylor. The Global Textile Industry . Brian Toyne, Jeffrey S. Arpan, David A. Ricks, Terence A. Shimp and Andy Barnett. Integrated Water Development: Water Use and Conservation Practice in Western Colorado . James L. Wescoat, Jr. Proceedings of the First International Symposium on Maps and Graphics for the Visually Handicapped . Joseph W. Wiedel, ed.     

BOOK REVIEWS

Book Reviewed in this article: Latin America: Case Studies . Richard G. Boehm and Sent Visser Locality and Rurality: Economy and Society in Rural Regions . Tony Bradley And Philip Lowe The City and the Grassroots . Manuel Castells Geopolitics and Conflict in South America. Quarrels among Neighbors . Jack Child Post-Industrial America: A Geographical Perspective . David Clark Coastal Research: UK Perspectives . Malcolm W. Clark A Rural Policy for the EEC? Hugh Clout Peasant Agriculture in Assam: A Structural Analysis . M. M. Das . Environmental Change and Tropical Geomorphology . I. Douglas and T. Spencer Advances in Abandoned Settlement Analysis: Application to Prehistoric Anthrosols in Colombia, South America . Robert C. Eidt Measuring Culture . Jonathan L. Gross and Steve Rayner North America: A Human Geography . Paul Guinness and Michael Bradshaw A Geographical Bibliography for American Libraries . Chauncy D. Harris et al. Geography and the Urban Environment: Progress in Research and Applications, Vol. VI . D. T. Herbert and R. J. Johnston Changes in Global Climate: A Study of the Effect of Radiation and Other Factors During the Present Century . K. Ya . Kondrat'ev . Rural Development and the State: Contradictions and Dilemmas in Developing Countries . David A. M. Lea and D. P. Chaudhri The Martial Metropolis: U.S. Cities in War and Peace . Roger W. Lotchin The Climate of the Earth . Paul E. Lydolph . Weather and Climate . Paul E. Lydolph . Spatial Divisions of Labor: Social Structures and the Geography of Production . Doreen Massey . Panorama of the Soviet Union . N. Mikhailov . Soviet Armenia . K. S. Demirchian . USSR: Geography of the Eleventh Five-Year Plan Period . K. Spidchenko . Planung und Verwirklichung der Wiener Ringstrassenzone (Planning and Materialization of the Ringstrasse-Zone of Vienna). Kurt Mollik , Hermann Reining , Rudolf Wurzer . The American West Transformed: The Impact of the Second World War Gerald D. Nash . An Overview of the Survey of Income and Program Participation . Dawn Nelson , David Mc Millen, and Daniel Kasprzyk . Phenomenology, Science and Geography: Spatiality and the Human Sciences . John Pickles . Biological Diversification in the Tropics . Ghillean T. Prance Die Wanderviehwirtschaft im gebirgigen Westen der U.S.A. und ihre Auswirkungen im Naturraum . Gisbert Rinschede . Social and Economic Aspects of Radioactive Waste Disposal: Considerations for Institutional Management . World-Wide Weather . K. Takahashi Coastal Geomorphology in Australia . B. G. Thom Settlement System in Rural India: A Case Study of the Lower Ganga-Yamuna Doab . Ram Chandra Tiwari . Computer Programming for Geographers . David J. Unwin and John A. Dawson . Late Quaternary Environments of the Soviet Union . A. A. Velichko, ed . H. E. Wright , Jr. and C. W. Barnosky Ethics in Planning . Martin Wachs     

Morphology and Chemistry of Placer Gold from Attappadi Valley, Southern India

We report the morphological, textural and chemical characteristics of gold grains in stream gravels from the Siruvani River in Attappadi Valley, southern India. The placer gold deposits contain both primary grains with jagged grain contours and secondary grains with smooth grain margins. The primary and secondary gold grains are also distinguished by marked contrast in microtextures with the latter displaying a range of corrosion textures including striations, etch pits and chemical corrosion cavities that coalesce to form honey-comb patterns. Some of these cavities are filled with fine clay derived from lateritic weathering front. While the primary grains are characterized by high silver content (up to 35.77 wt.%) with marginal overgrowths of high purity gold, the secondary grains show exceedingly high fineness (1000 Au/Au+Ag) levels (up to 984) with no marked compositional variation indicating selective extraction of Ag and/or reprecipitation of Au. From morphological and chemical characteristics, we propose that the high purity gold grains were not derived directly from primary sources, but underwent chemical refinement in the weathering front before they were transferred to the fluvial systems. Our findings have important implications for gold exploration in the Attappadi Valley.     

Engineering geologic and geotechnical analysis of paleoseismic shaking using liquefaction effects: field examples

The greatest impediments to the widespread acceptance of back-calculated ground motion characteristics from paleoliquefaction studies typically stem from three uncertainties: (1) the significance of changes in the geotechnical properties of post-liquefied sediments (e.g., “aging” and density changes), (2) the selection of appropriate geotechnical soil indices from individual paleoliquefaction sites, and (3) the methodology for integration of back-calculated results of strength of shaking from individual paleoliquefaction sites into a regional assessment of paleoseismic strength of shaking. Presented herein are two case studies that illustrate the methods outlined by Olson et al. [Engineering Geology, this issue] for addressing these uncertainties.

The first case study is for a site near Memphis, Tennessee, wherein cone penetration test data from side-by-side locations, one of liquefaction and the other of no liquefaction, are used to readily discern that the influence of post-liquefaction “aging” and density changes on the measured in situ soil indices is minimal. In the second case study, 12 sites that are at scattered locations in the Wabash Valley and that exhibit paleoliquefaction features are analyzed. The features are first provisionally attributed to the Vincennes Earthquake, which occurred around 6100 years BP, and are used to illustrate our proposed approach for selecting representative soil indices of the liquefied sediments. These indices are used in back-calculating the strength of shaking at the individual sites, the results from which are then incorporated into a regional assessment of the moment magnitude, M, of the Vincennes Earthquake. The regional assessment validated the provisional assumption that the paleoliquefaction features at the scattered sites were induced by the Vincennes Earthquake, in the main, which was determined to have M7.5. The uncertainties and assumptions used in the assessment are discussed in detail.     

Situated justice in environmental decision-making: Lessons from river management in Southeastern Australia

The practical application of environmental justice in natural resource management depends upon moving beyond generic principles to situated understanding. This understanding in turn requires knowledge of both historical and geographical contexts, including how decision-making frameworks develop and the nature of the biophysical environment itself. This paper examines these requirements based on case material from the Hunter Valley, New South Wales. In the Hunter Valley, the colonial history of river management was one of the creation, and subsequent inclusion and exclusion, of particular ‘stakes’ from the decision-making process, resulting in a narrowly defined ‘community of justice’ that became institutionalised at the catchment scale. However, even within this restricted community, distributive injustices occurred due to a failure of policy to engage with environmental variability at both spatial and temporal scales. This combination of procedural injustice and environmental variability also resulted in ecological injustice - that is a disconnected or even antagonistic human-nature relationship that restricted the opportunity to redress the severe degradation of riverine ecosystems that had occurred since European settlement. In the light of these examples, broader challenges in the application of environmental justice to river management are explored in terms of ecological complexity and contested perceptions of environmental health. Based on this material, a historically and geographically situated, ecologically informed vision of environmental justice is proposed as an essential part of sustainable river management.     

Assessing gaps in irrigated agricultural productivity through satellite earth observations—A case study of the Fergana Valley,Central Asia

Improving crop area and/or crop yields in agricultural regions is one of the foremost scientific challenges for the next decades. This is especially true in irrigated areas because sustainable intensification of irrigated crop production is virtually the sole means to enhance food supply and contribute to meeting food demands of a growing population. Yet, irrigated crop production worldwide is suffering from soil degradation and salinity, reduced soil fertility, and water scarcity rendering the performance of irrigation schemes often below potential. On the other hand, the scope for improving irrigated agricultural productivity remains obscure also due to the lack of spatial data on agricultural production (e.g. crop acreage and yield). To fill this gap, satellite earth observations and a replicable methodology were used to estimate crop yields at the field level for the period 2010/2014 in the Fergana Valley, Central Asia, to understand the response of agricultural productivity to factors related to the irrigation and drainage infrastructure and environment. The results showed that cropping pattern, i.e. the presence or absence of multi-annual crop rotations, and spatial diversity of crops had the most persistent effects on crop yields across observation years suggesting the need for introducing sustainable cropping systems. On the other hand, areas with a lower crop diversity or abundance of crop rotation tended to have lower crop yields, with differences of partly more than one t/ha yield. It is argued that factors related to the infrastructure, for example, the distance of farms to the next settlement or the density of roads, had a persistent effect on crop yield dynamics over time. The improvement potential of cotton and wheat yields were estimated at 5%, compared to crop yields of farms in the direct vicinity of settlements or roads. In this study it is highlighted how remotely sensed estimates of crop production in combination with geospatial technologies provide a unique perspective that, when combined with field surveys, can support planners to identify management priorities for improving regional production and/or reducing environmental impacts.     

Dispersion Pattern of PGE and Ag in Chromiferous Ultramafic Suite of Rocks in Sukinda Valley,India

Potential chromite ore deposits of India are situated in Sukinda, Odisha, which may also be considered as a potential resource for platinum group elements (PGEs). This paper reports on PGE geochemistry in twenty six samples covering chromite ores, chromitites and associated ultramafic rocks of the Sukinda ultramafic complex. Platinum group element contents range from 213 to 487 ppb in the chromite ore body, from 63 to 538 ppb in rocks that have chromite dendrites or dissemination and from 38 to 389 ppb in associated olivine–peridotite, serpentinite, pyroxenite and brecciated rocks. The PGEs are divided into two sub‐groups: IPGE (Ir, Os, and Ru) and PPGE (Pd, Pt, and Rh) based on their chemical behaviour. The IPGE and PPGE in these three litho‐members show a contrasting relationship e.g. average IPGE content decreases from chromite to chromitite and associated rocks while PPGE increases in the same order. Appreciable Ag in chromitite (270–842 ppb) is recorded. Positive correlation between IPGE with Cr₂O₃ and with Al₂O₃ is observed while these are negatively correlated with MgO. Covariant relationships between Au and Mg in rocks devoid of chromite and between Ag and Fe in chromitite sample are observed. Chromite in all seams and some chromitite samples exhibit an IPGE‐enriched chondrite normalized pattern while PPGE are highly fractionated and show a steep negative slope, thereby indicating that PGE in the parental melt fractionates and IPGE‐compatible elements prefer to settle with chromite. The rocks devoid of chromite and rocks containing accessory chromite exhibit a nearly flat pattern in chondrite‐normalized PGE plots and this suggests a limited fractionation of PGE in these rocks. Variation in the distribution pattern of PGE and Ag in three typical litho‐members of the Sukinda Valley may be related to multiple intrusion of ultramafic magma, containing variable volume percentage of chromite.