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81.
Late Pleistocene and Holocene vegetational and climatic change have been studied palynologically at a site at 1750 m elevation in the subandean vegetation belt near Popayán, in the southern Colombian Andes. Time control on the pollen record is based on six AMS 14C ages, ranging from possibly Middle Pleniglacial time (around 50000 yr BP) to 1092 ± 44 yr BP. Because of the presence of two hiatuses only the Middle Pleniglacial and Late Holocene periods (the last 2300 yr BP) are represented. Pollen data indicate the presence of closed subandean forest during glacial time. Changes in the contribution of pollen originating from the uppermost and lowermost subandean forest belts, changes in the contribution of a number of other subandean forest taxa, and changes in species composition between the three pollen zones, suggest that the climate during the Middle Pleniglacial was markedly colder, and perhaps also wetter, than during the Late Holocene. Pollen assemblages from the Late Holocene indicate that the landscape has been affected by deforestation and agriculture since at least 2300 yr BP, but that human impact decreased in the last 780 yr BP. © 1998 John Wiley & Sons, Ltd. 相似文献
82.
Hermann Kreutzmann 《GeoJournal》1998,46(4):255-265
This paper critically discusses Samuel Huntington's contribution to development studies. Long before his currently debated work on the clash of civilizations, Huntington wrote on the political order in changing societies. In this highly influential book of the late 1960s he argued on the basis of modernization theory for strong governments to accompany the inevitable and universal process of modernization. His clash of civilizations seems to argue from different assumptions. It insists on the essential differences between cultures based on religion. These cultural differences would now give rise to the most important conflict constellations. In his earlier and later work Huntington insists on the primacy of Western values and the need to defend them. The author critiques the assumptions, concepts and some of the empirical evidence of Huntingtons recent study. 相似文献
83.
We present a method based on the combination of elevation and geoid anomaly data together with thermal field to map crustal and lithospheric thickness. The main assumptions are local isostasy and a four-layered model composed of crust, lithospheric mantle, sea water and the asthenosphere. We consider a linear density gradient for the crust and a temperature dependent density for the lithospheric mantle. We perform sensitivity tests to evaluate the effect of the variation of the model parameters and the influence of RMS error of elevation and geoid anomaly databases. The application of this method to the Gibraltar Arc System, Atlas Mountains and adjacent zones reveals the presence of a lithospheric thinning zone, SW–NE oriented. This zone affects the High and Middle Atlas and extends from the Canary Islands to the eastern Alboran Basin and is probably linked with a similarly trending zone of thick lithosphere constituting the western Betics, eastern Rif, Rharb Basin, and Gulf of Cadiz. A number of different, even mutually opposite, geodynamic models have been proposed to explain the origin and evolution of the study area. Our results suggest that a plausible slab-retreating model should incorporate tear and asymmetric roll-back of the subducting slab to fit the present-day observed lithosphere geometry. In this context, the lithospheric thinning would be caused by lateral asthenospheric flow. An alternative mechanism responsible for lithospheric thinning is the presence of a hot magmatic reservoir derived from a deep ancient plume centred in the Canary Island, and extending as far as Central Europe. 相似文献
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A'Hearn Michael F. Boehnhardt Hermann Kidger Mark West Richard M. 《Earth, Moon, and Planets》1997,78(1-3):3-3
Earth, Moon, and Planets - 相似文献
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Hermann D. Bermúdez Jenny García Wolfgang Stinnesbeck Gerta Keller José Vicente Rodríguez Michael Hanel Jens Hopp Winfried H. Schwarz Mario Trieloff Liliana Bolívar Francisco J. Vega 《地学学报》2016,28(1):83-90
The discovery of a new Cretaceous/Palaeogene (K/Pg) bathyal marine sequence on Gorgonilla Island, SW Colombia, extends the presence of Chicxulub impact spherule deposits to the Pacific region of northern South America and to the Eastern Pacific Ocean. The Gorgonilla spherule layer is approximately 20 mm thick and consists of extraordinarily well‐preserved glass spherules up to 1.1 mm in diameter. About 70–90% of the spherules are vitrified, and their chemical composition is consistent with Haiti (Beloc) impact glass spherules. Normal size‐grading, delicate spherule textures, welded melt components and an absence of bioturbation or traction transport suggest that the Gorgonilla spherule layer represents an almost undisturbed settling deposit. 相似文献
88.
Winter storm- and summer thunderstorm-related loss events with regard to climate change in Germany 总被引:1,自引:1,他引:0
Friedrich-Wilhelm Gerstengarbe Peter C. Werner Hermann Österle Olaf Burghoff 《Theoretical and Applied Climatology》2013,114(3-4):715-724
The development of winter storm- and summer thunderstorm-related loss events within the next decades in Germany was investigated with regard to change in frequency and intensity caused by climate changes. As a first step, observed meteorological data were connected with insurance data on a statistical basis. A regional climate model was then used to estimate future climate development. Using the statistical relations between meteorological and insurance data, the development of climate-driven damages was calculated. Results show that an increase of loss events can be expected within the next decades. These results show loss ratios shifting from higher return periods to smaller ones. In progressive decades, all these loss events become regionally more differentiated. 相似文献
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90.
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