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211.
A survey of women AAG members in applied geography shows a geographical concentration in the Washington metropolitan area and an employment concentration in the private sector. The typical educational preparation is a master's degree. Job titles reflect the importance of planning, environmental issues, and cartography; cartography is cited as the most helpful career skill. Respondents want the AAG to promote geography and to help graduates in finding careers. 相似文献
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213.
Kurt A. Refsnider Gifford H. Miller Marilyn L. Fogel Bianca Fréchette Roxane Bowden John T. Andrews G. Lang Farmer 《Quaternary Research》2014
The mineralogy and isotopic compositions of subglacially precipitated carbonate crusts (SPCCs) provide information on conditions and processes beneath former glaciers and ice sheets. Here we describe SPCCs formed on gneissic bedrock at the bed of the Laurentide Ice Sheet (LIS) during the last glacial maximum on central Baffin Island. Geochemical data indicate that the Ca in the crusts was likely derived from the subglacial chemical weathering Ca-bearing minerals in the local bedrock. C and Sr isotopic analyses reveal that the C in the calcite was derived predominantly from older plant debris. The δ18O values of the SPCCs suggest that these crusts formed in isotopic equilibrium with basal ice LIS preserved in the Barnes Ice Cap (BIC). Columnar crystal fabric and the predominance of sparite over micrite in the SPCCs are indicative of carbonate precipitation under open-system conditions. However, the mean δ18O value of the calcite crusts is ~ 10‰ higher than those of primary LIS ice preserved in the BIC, demonstrating that SPCCs record the isotopic composition of only basal ice. Palynomorph assemblages preserved within the calcite and basal BIC ice include species last endemic to the Arctic in the early Tertiary. The source of these palynomorphs remains enigmatic. 相似文献
214.
Data from accelerator mass spectrometer radiocarbon dated sediment cores and Huntec high-resolution seismic profiles were used to investigate the age and origin of the sediments in the Eastern Basin of Hudson Strait. The data indicate that the ice-contact and glacial-marine sediments on the basin flanks and much of the upper sequence in the deep floor of the basin were produced during the Noble Inlet advance (8.9 to 8.4 ka), the last northward expansion of the Labrador Dome on to southeastern Baffin Island. On the northern flank of Eastern Basin one sequence of ice-contact sediments and glacial-marine deposits overlies bedrock; the glacial-marine sediments are transitional upslope to ice-contact sediments, and form at least two successive ice-sheet grounding zones. The earliest abundance peaks of benthic Foramininfera in glacial-marine sediments date ca. 8.6 and 8.4 ka, and correlate to sediments near the base of the 58-m-thick glacial-marine section in the deepest part of Eastern Basin. This correlation suggests that Noble Inlet ice was grounded throughout Eastern Basin during the early part of its advance. In later stages the thinning ice produced grounding zones on the basin flanks while glacial-marine sediments were deposited in the deep basin. © 1998 John Wiley & Sons, Ltd. 相似文献
215.
Jonathan D. Phillips Heather Golden Karen Cappiella Bain Andrews Tamara Middleton David Downer Deonna Kelli Lee Padrick 《地球表面变化过程与地形》1999,24(1):23-39
In agricultural basins of the southeastern coastal plain there are typically large disparities between upland soil erosion and sediment delivered to streams. This suggests that colluvial storage and redistribution of eroded soil within croplands is occurring, and/or that processes other than fluvial erosion are at work. This study used soil morphology and stratigraphy as an indicator of erosion and deposition processes in a watershed at Littlefield, North Carolina. Soil stratigraphy and morphology reflect the ways in which mass fluxes associated with cultivation transform the local soils. Fluvial, aeolian and tillage processes were all found to be active in the redistribution of soil. The soil transformations are of five general types. First, erosion and compaction in the cultivated area as a whole result in the thinning of Arenic and Grossarenic Paleudults and Paleaquults to form Arenic, Typic and Aquic Paleudults and Paleaquults. Second, redistribution of surficial material within the fields results in transitions between Arenic and Typic or Aquic subgroups as loamy sand A and E horizons are truncated or accreted. Third, aeolian deposition at forested field boundaries leads to the formation of compound soils with podzolized features. Fourth, sandy rill fan deposits at slope bases create cumulic soils distinct from the loamy sands of the source area or the darker, finer terrace soils buried by the fan deposits. Finally, tillage and fluvial deposition in upland depressions results in the gradual burial of Rains (poorly drained Typic Paleaquults) soils. Results confirm the importance of upland sediment storage and redistribution, and the role of tillage and aeolian processes as well as fluvial processes in the region. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献