Continuum and age: comments*     

RICHARD A. SHAKESBY  ALASTAIR G. DAWSON  JOHN A. MATTHEWS 《Boreas: An International Journal of Quaternary Research》1989,18(1):84-85

  相似文献   

Arguing about Earth expansion     

RICHARD WILDING 《Geology Today》1989,5(2):53-54

  相似文献   

Oxygen isotopic record of silicate alteration in the Shergotty—Nakhla—Chassigny meteorite Lafayette     

CHRISTOPHER S. ROMANEK  EUGENE C. PERRY  ALLAN H. TREIMAN  RICHARD A. SOCKI  JOHN H. JONES  EVERETT K. GIBSON 《Meteoritics & planetary science》1998,33(4):775-784

Abstract— Samples from a suite of Shergotty—Nakhla—Chassigny (SNC) meteorites were analyzed for their O isotopic ratios by a modified version of the laser fluorination technique. Measured isotopic ratios (¹⁷O/¹⁶O and ¹⁸O/¹⁶O) from bulk samples of the Shergottites, EETA79001, Shergotty and Zagami; the Nakhlite Lafayette; and Chassigny are similar to those reported in the literature, as are those from olivine and pyroxene mineral separates from Lafayette. Iddingsite, a preterrestrial alteration product of Lafayette, was measured for the first time as a separate phase. Oxygen isotopic ratios increase with the percentage of iddingsite in a sample to a maximum δ¹⁸O of 14.4% for a ～90% separate. Based on these measurements, end-member iddingsite has a δ¹⁸O of 15.6%, which places it among other ¹⁸O-enriched secondary phases (carbonate and silica) observed in SNC meteorites. The relatively large difference in δ¹⁸O between iddingsite and the olivine and pyroxene it replaces (～11%) is typical of low-temperature alteration products. A range of crustal fluid δ¹⁸O values can be interpreted from the δ¹⁸O for end-member iddingsite, assuming isotopic equilibrium was achieved during low-temperature hydrous alteration (<100 °C; Treiman et al., 1993). The calculated range of values, ?15 to 5%, depends on many factors including: (1) the modal mineralogy of iddingsite, (2) potential isotopic exchange among other O-bearing phases such as host silicate and carbonate, and (3) exchange with evolved or exotic O reservoirs on Mars. Despite the lack of constraints, the calculated range is consistent with isotopic exchange, and possibly equilibria, among components of the CO₂-carbonate-iddingsite-H₂O system at low temperature. The SNC meteorite samples in this study have Δ¹⁷O values that are indistinguishable from bulk Mars (0.30%), except for a single, small sample of iddingsite that has an anomalous Δ¹⁷O of ～1.4%. While analytical difficulties make isotopic measurements for this sample problematic, the Δ¹⁷O is similar in direction to Δ¹⁷O reported for waters extracted from bulk samples of Lafayette (Karlsson et al., 1992). If the Δ¹⁷O for iddingsite is confirmed, it can be concluded that evolved or exotic fluids on Mars have contributed volatiles to the O reservoir from which iddingsite formed 130 to 700 Ma ago.  相似文献   

HONDURAS: WHEN THE SAINTS ARRIVE     

RICHARD SYMANSKI 《Geographical review》1998,88(4):571-579

ABSTRACT. Hurricane Mitch, the most deadly hurricane to strike the Western Hemisphere in two centuries, killed at least 10,000 people in Honduras, Nicaragua, and El Salvador and left tens of thousands homeless. Some needed food; others, medical attention. Americans, Europeans, Mexicans, and others almost immediately responded to the widespread devastation by sending large donations of food, clothing, and medicine. Six weeks after Mitch struck the Honduran mainland, the author traveled to Honduras with the aim of photographing the physical damage and its effect on humans. In San Pedro Sula he was sidetracked by the issue of where the refugees were being housed and whether they were receiving the donations that had been sent on their behalf. This essay narrates that search and what he found.  相似文献   

An Indicator of Our Pressure on the Land: New Zealand's Ecological Footprint     

KATHRYN B. BICKNELL  RICHARD J. BALL  ROSS CULLEN  HUGH R. BIGSBY 《New Zealand geographer》1998,54(2):4-11

Sustainability has become a primary goal for much of the legislation which governs resource management in New Zealand. A major difficulty associated with sustainable development objectives, however, is the absence of reliable indicators to measure progress towards the goal of sustainability. The ‘ecological footprint’ provides an estimate of the amount of ecologically productive land required on a continuous basis to sustain current levels of resource consumption and waste assimilation for a given population. By comparing the ecological footprint of a community with the amount of land available, we can more clearly determine whether our current consumption patterns are likely to be sustainable. This paper explores the use of ecological footprint analysis within a New Zealand context. Modifications to the existing procedure for calculating an ecological footprint are proposed, and estimates based on the modified procedures are presented for New Zealand.  相似文献   

A study on assimilating potential vorticity data     

YONG LI  RICHARD MÉNARD  LARS PETER RIISHØJGAARD  STEPHEN E. COHN  RICHARD B. ROOD 《地球，A辑:动力气象学与海洋学》1998,50(4):490-506

  相似文献   

MAPPING KENTUCKY'S FRONTIER TRAILS THROUGH GEOGRAPHICAL INFORMATION AND CARTOGRAPHIC APPLICATIONS*     

KARL B. RAITZ  JEFFREY E. LEVY  RICHARD A. GILBREATH 《Geographical review》2010,100(3):312-335

Historical first‐generation frontier roads in America's trans‐Appalachian West often evolved from buffalo and Indian trails into pioneer routeways such as Daniel Boone's Trace and, eventually, into twentieth‐century hard‐surface highways. Period cartographers found these routes difficult to document accurately, and present‐day scholars often depict them only on small‐scale maps, which simply illustrate connections between origin and destination points. Accurately mapping Kentucky's first‐generation roads at large scale requires detailed site and contextual topographic information over long distances, but historical maps, diaries, surveyors' reports, and other period documents often lack sufficient detail for route‐related sites to support mapping. Use of gis software enables positioning historical routes onto U.S. Geological Survey contour‐ and hill‐shaded base maps by mapping verifiable locations and linking them through interpretation of best‐choice routes that consider frontier migrants' transportation priorities, such as direction, distance, gradient, and land‐surface character.  相似文献   

Interannual variability of annual streamflow and the Southern Oscillation in Costa Rica     

RICHARD K. GEORGE  PETER WAYLEN  SADÍ LAPORTE 《水文科学杂志》2013,58(3):409-424

Abstract

This study illustrates the association between annual and seasonal streamflow characteristics on six Costa Rican rivers and the Southern Oscillation Index (SOI). Annual discharge from rivers within the Pacific watershed are clearly positively associated with contemporary values of the SOI and experience significant reductions in both mean and variance in El Ninõ years. The considerable practical implications of this finding to a country in which over 60% of national electrical power comes from hydroelectric schemes is illustrated using quantile estimates from various models. Rivers draining towards the Caribbean show less clear and coherent patterns of associations. The observed associations with seasonal flows on some rivers appear to be the opposite of those on the Pacific, and may even vary during the course of a year at a site. The exact nature of the response seems to be closely related to the elevation of the gauge site. The larger the proportion of the basin at elevations above about 500–1000 m the greater the similarity to the Pacific pattern, suggesting that the marked topographic divide between the two coastal watersheds does not correspond to the divide in associations between streamflow and the SOI.  相似文献   

Testate amoebae as a proxy for reconstructing Holocene water table dynamics in southern Patagonian peat bogs          下载免费PDF全文

SIMON VAN BELLEN  DMITRI MAUQUOY  RICHARD J. PAYNE  THOMAS P. ROLAND  TIM J. DALEY  PAUL D. M. HUGHES  NEIL J. LOADER  F. ALAYNE STREET‐PERROTT  EMMA M. RICE  VERÓNICA A. PANCOTTO 《第四纪科学杂志》2014,29(5):463-474

Testate amoebae are abundant and diverse in Sphagnum peat bogs and have been used extensively as indicators of past water table depths. Although these unicellular protists are widely dispersed with globally similar hydrological preferences, regional variations in communities demand region‐specific transfer functions. Here we present the first transfer function for southern Patagonian bogs, based on 154 surface samples obtained from transects in five bogs sampled in 2012 and 2013. Significant variance was explained by pH, electrical conductivity and, in particular, water table depth. Transfer functions for water table were constructed using weighted averaging and evaluated by cross‐validation and independent test sets. The optimal transfer function has predictive ability, but relatively high prediction errors given the wide range in sampled water tables. The use of independent test sets, as well as cross‐validation, allows a more rigorous assessment of model performance than most previous studies. For a subset of locations we compare surface and subsurface samples to demonstrate significant differences in community composition, possibly due to vertical zonation. Our results provide the first quantification of hydrological optima and tolerances for several rare species, which may include Southern Hemisphere endemics and pave the way for palaeohydrological reconstructions in southern Patagonian bogs.  相似文献   

Glacial meltwater erosion and sedimentation as evidence for multiple glaciations in west Wales     

NEIL F. GLASSER  JAMES L. ETIENNE  MICHAEL J. HAMBREY  JEREMY R. DAVIES  RICHARD A. WATERS  PHILIP R. WILBY 《Boreas: An International Journal of Quaternary Research》2004,33(3):224-237

This article presents the results of a geomorphological and sedimentological investigation of former glacial meltwater drainage in the region of the lower Afon Teifi, one of the major rivers of southwest Wales. Former drainage characteristics in the region are reconstructed concentrating on palaeo-drainage routes associated with successive Pleistocene glaciations and their role in the Quaternary evolution of the lower Teifi. Mapping of these features throughout a c. 100 km ² area reveals a complex evolution in the establishment of the present-day drainage system, with evidence for the following surface channel types: (i) type 1 channels of primary subglacial origin cut during the late Devensian (late Wisconsinan/late Weichselian) glaciation; (ii) type 2 channels representing either pre-late Devensian subaerial fluvial run-off, unconnected to the course of the preglacial Afon Teifi, or originating as subglacial chute channels; (iii) type 3 channels developed as subglacially modified pre-late Devensian tributaries of the Afon Teifi. Two further features are also described: (iv) type 4 channels are drift-plugged abandoned preglacial courses of the Afon Teifi, and (v) type 5 channels formed as lateglacial and post-late Devensian gorges which bypass type 4 channels. A relative chronostratigraphy based on channel geomorphology and sedimentology reveals an evolutionary sequence considerably more complicated than identified in previous studies, with extensive modification of the lower Afon Teifi region by glacial meltwater during at least two periods of Pleistocene glaciation.  相似文献