Two decades of progress in periglacial research     

JAMES B. BENEDICT 《Boreas: An International Journal of Quaternary Research》1989,18(1):86-86

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Within-valley asymmetry and related problems of Neoglacial lateral moraine development at certain Jotunheimen glaciers, southern Norway     

JOHN A. MATTHEWS  JAMES R. PETCH 《Boreas: An International Journal of Quaternary Research》1982,11(3):225-247

A difference in the size of Neoglacial lateral moraines on either side of a valley axis (within-valley asymmetry of lateral moraine development) is described. Analysis of clast roundness has revealed subangular material in latero-terminal and terminal moraines; lateral moraines, however, exhibit a compositional gradient of increasing angularity with distance from the former glacier snout. Comparisons with clasts of known origin suggest that this 'roundness gradient' may be explained with reference to either or both of two hypotheses: (1) a variable proportion of supraglacial (or englacial) to subglacial transported material; and (2) the variable composition of regolith incorporated by a push mechanism from the valley sides. Within-valley asymmetry is inferred to result where the supply of debris to lateral moraines from these sources is unequal either side of a valley axis. Both interpretations are also consistent with the relatively large size of latero-terminal sections of end moraines. In order to account for the discrepancy between moraine size and apparent debris supply rates, it is suggested that the largest lateral moraines may have been formed over a longer time scale than the 'Little Ice Age', and that reworking of deposits may have occurred. The supply of debris to the north-facing lateral moraine at Nordre Illåbreen has been so great that it has developed into a rock glacier; this suggests the possibility that subglacial material and valley-side regolith, as well as supraglacial material, contributes to the formation of ice-cored rock glaciers.  相似文献   

Interlobate ice-sheet dynamics during the Last Glacial Maximum at Whitburn Bay, County Durham, England     

BETHAN J. DAVIES  DAVID H. ROBERTS  COLM Ó COFAIGH  DAVID R. BRIDGLAND  JAMES B. RIDING  EMRYS R. PHILLIPS  DEREK A. TEASDALE 《Boreas: An International Journal of Quaternary Research》2009,38(3):555-578

This research reconstructs ice-sheet processes operating during the Late Devensian in northeast England. The article assesses the lithostratigraphy of the Devensian glacial tills of Whitburn Bay, eastern County Durham, and presents the first detailed analysis of petrological, geochemical and biostratigraphical data to reconstruct lithostratigraphy, provenance and iceflow pathways. Two Devensian tractions tills (the Blackhall and Horden tills) are separated by a boulder pavement, pointing to a switch in ice-bed conditions and the production of a melt-out lag prior to deposition of the upper traction till, the Horden Till. The Blackhall Till contains Magnesian Limestone, Carboniferous Limestone, Whin Sill dolerite and Old Red Sandstone, suggesting a northwesterly source, probably from the Midland Valley and the Southern Uplands. The Horden Till contains erratics and heavy minerals derived from crystalline bedrock sources in the Cheviot Hills and northeast Scotland. Within the Horden Till are numerous sand, clay and gravel-filled canals incised downwards into the diamicton which are attributed to a low-energy, distributed, subglacial canal drainage system. Coupled with hydro-fractures and the boulder pavement, this suggests that a partially decoupled, fast-flowing ice stream deposited the Horden Till. The uphill, landward direction of ice movement indicates that the ice stream was confined in the North Sea Basin, possibly by the presence of Scandinavian Ice.  相似文献   

Phase differences between bed configuration and flow in natural environments, and their geological relevance     

J. R. L. ALLEN 《Sedimentology》1973,20(2):323-329

In nature where unsteady flows prevail, the characters of bed configurations lag, or differ in phase from, the flow conditions. This is demonstrated from quantitative data for dune beds in the Fraser River (Canada) and the Gironde Estuary (France), where the flow conditions change ahead of the bed form by as much as 1/4 period. Qualitative evidence for lag abounds, for instance, substantially unmodified dunes exposed during low water. The existence of lag appears to confuse attempts to establish from field data the relationships between bed-form properties and flow conditions and, at the same time, makes difficult the confident application to field situations of formulae based on steady-state experiments or theories. Unfamiliar types of field study and experiments are needed to increase understanding of the degree and precise significance of lag.  相似文献   

PHYSICO‐GEOCHEMICAL AND MINERAL COMPOSITION OF NEEM TREE SOILS AND RELATION TO ORGANIC PROPERTIES          下载免费PDF全文

WILLIAM C. MAHANEY  JOAN VOROS  RAMANATHAN KRISHNAMANI  RONALD G.V. HANCOCK  SUSAN AUFREITER  MICHAEL W. MILNER  CHRISTOPHER C.R. ALLEN 《Geografiska Annaler: Series A, Physical Geography》2016,98(2):143-154

The Neem tree, the oil of which has a long history of pesticide, fertilizer and medicinal use in India, has been studied extensively for its organic compounds. Here we present a physical, mineralogical and geochemical database resulting from the analyses of two Neem soil profiles (epipedons) in India. Neem tree derivatives are used in the manufacture of a variety of products, from anti‐bacterial drugs and insecticides to fertilizers and animal feeds. A preliminary geochemical and mineralogical analysis of Neem soils is made to explore the potential for chemical links between Neem tree derivatives and soils. Physical soil characteristics, including colour, texture and clay mineralogy, suggest the two pedons formed under different hydrological regimes, and hence, are products of different leaching environments, one well‐drained site, the other poorly drained. Geochemically, the two Neem soils exhibit similarities, with elevated concentrations of Th and rare earth elements. These elements are of interest because of their association with phosphates, especially monazite and apatite, and the potential link to fertilizer derivatives. Higher concentrations of trace elements in the soils may be linked to nutritional derivatives and to cell growth in the Neem tree.  相似文献   

THE GEOPOLITICS OF EUGENICS AND THE EXCLUSION OF PHILIPPINE IMMIGRANTS FROM THE UNITED STATES     

JAMES A. TYNER 《Geographical review》1999,89(1):54-73

ABSTRACT. From 1898 to 1936, Philippine immigrants were routinely excluded from the United States, where incipient practices of eugenic “science” and geopolitics were informing social policy. Concomitant with emergent theories of evolution, a geopolitically informed eugenics forewarned of possible racial competition and societal degeneration. Immigration legislation emerged as an effective social policy to exclude perceived undesirable, and racially distinct, immigrant groups, ostensibly to protect race and state.  相似文献   

Multiple-Step Predictive Control for Offshore Structures   总被引：13，自引：0，他引：13  

李华军  Sau-Lon JAMES HU 《中国海洋工程》1999,(3)

—Ocean wave propagation is slow,visible and measurable,so a wave theory can be used to approxi-mately predict the imminnent wave force on an offshore structure based on measured,real-time wave elevation nearthe structure.This predictability suggests the development of a more efficient algorithm,than those that have beendeveloped for structures under wind and seismic loads,for the active vibration control of offshore structures.Thepresent study delveops a mutiple-step predictive optimal control(MPOC)algorithm that accounts for multiple-step external loading in the determibation of optimal control forces.The control efficiency of the newly developedMPOC algorithm has been investigated under both regular(single-frequency)and irregular(multiple-frequency)wave loads,and compared with that of two other well-known optimal control algorithms:classical linear optimalcontrol(CLOC)and instantaneou optimal control(IOC).  相似文献   

Reply: Redepositional or Climate Event in Iberia During the Boreal     

JUDY R. M. ALLEN  BRIAN HUNTLEY  WILLIAM A. WATTS 《第四纪科学杂志》1997,12(1):75-75

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Chemical mass balance and rates of mineral weathering in a high-elevation catchment,west glacier lake,wyoming     

JIM B. FINLEY  JAMES I. DREVER 《水文研究》1997,11(7):745-764

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大数据驱动下的数字古地理重建：现状与展望     

张蕾  钟瀚霆  陈安清  赵应权  黄可可  李凤杰  黄虎  刘宇  曹海洋  祝圣贤  穆财能  侯明才  JAMES G. Ogg 《高校地质学报》2020,26(1):73

古地理学是一门强数据依赖性学科,古地理重建作为古地理学的核心任务之一,着眼于研究地质历史时期地球表面的地理、生物、气候面貌及其演化规律。随着大数据时代的来临,海量古地理数据的不断积累和计算机技术的高速发展使得标准化、智能化的数字古地理重建成为可能。文章通过介绍国内外与古地理相关的代表数据库及团队,总结其优缺点,提出大数据驱动下的数字古地理重建核心思路:(1)建立标准化的古地理学知识体系;(2)建立开放互动、动态更新的古地理数据库,并利用机器阅读技术等拓展数据来源;(3)建立标准化的古地理学数据质量控制体系;(4)利用机器学习技术建立各类型古地理重建模型,深度挖掘数据;(5)以可实时更新的智能数字地图集或多维动画形式输出成果。  相似文献