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131.
Tectono-thermal modeling of the Yinggehai Basin,South China Sea 总被引:1,自引:0,他引:1
Lijuan?HeEmail author Liangping?Xiong Jiyang?Wang Jihai?Yang Weiliang?Dong 《中国科学D辑(英文版)》2001,44(1):7-13
Based on the observed data, the average value of surface heat flow in the Yinggehai Basin is calculated and it turns out to
be 84.1 mW/m2. The thermal evolution of the basin since the Cenozoic era has been attempted by tectono-thermal modeling. Three-phase extension
made the basin become hotter and hotter, reaching its climax in paleo-temperature history since 5.2 Ma. And nowadays, the
basin is in the heat flow decreasing period. During the Cenozoic era, the basement heat flow remained at 50–70 mW/m2 all the time. This is related to the degree of each extension phase, stretching rate mode and also the limited basin scale.
Modeling results also show that, the surface heat flow is controlled mainly by the basement heat flow, and less than 20% comes
from radiogenic heat production in the sediments of the basin 相似文献
132.
Ramzi Touchan Elena Xoplaki Gary Funkhouser Jürg Luterbacher Malcolm K. Hughes Nesat Erkan Ünal Akkemik Jean Stephan 《Climate Dynamics》2005,25(1):75-98
This study represents the first large-scale systematic dendroclimatic sampling focused on developing chronologies from different
species in the eastern Mediterranean region. Six reconstructions were developed from chronologies ranging in length from 115 years
to 600 years. The first reconstruction (1885–2000) was derived from principal components (PCs) of 36 combined chronologies.
The remaining five, 1800–2000, 1700–2000, 1600–2000, 1500–2000 and 1400–2000 were developed from PCs of 32, 18, 14, 9, and
7 chronologies, respectively. Calibration and verification statistics for the period 1931–2000 show good levels of skill for
all reconstructions. The longest period of consecutive dry years, defined as those with less than 90% of the mean of the observed
May–August precipitation, was 5 years (1591–1595) and occurred only once during the last 600 years. The longest reconstructed
wet period was 5 years (1601–1605 and 1751–1755). No long term trends were found in May–August precipitation during the last
few centuries. Regression maps are used to identify the influence of large-scale atmospheric circulation on regional precipitation.
In general, tree-ring indices are influenced by May–August precipitation, which is driven by anomalous below (above) normal
pressure at all atmospheric levels and by convection (subsidence) and small pressure gradients at sea level. These atmospheric
conditions also control the anomaly surface air temperature distribution which indicates below (above) normal values in the
southern regions and warmer (cooler) conditions north of around 40°N. A compositing technique is used to extract information
on large-scale climate signals from extreme wet and dry summers for the second half of the twentieth century and an independent
reconstruction over the last 237 years. Similar main modes of atmospheric patterns and surface air temperature distribution
related to extreme dry and wet summers were identified both for the most recent 50 years and the last 237 years. Except for
the last few decades, running correlation analyses between the major European-scale circulation patterns and eastern Mediteranean
spring/summer precipitation over the last 237 years are non-stationary and insignificant, suggesting that local and/or sub-regional
geographic factors and processes are important influences on tree-ring variability over the last few centuries. 相似文献
133.
Iodine contents of soils developed over the major rock formations of the northern zone of the Eastern Pontide Tectonic Belt
(Northeastern Turkey) have been investigated with respect to soil-parent rock relationship, effect of topography, elevation,
and climate to construe its effect on the health of the local population. Samples were collected from the A and B horizons
of the soils developed over the major stratigraphic units constituting the eastern Pontides, including the Lower Basic Complex
of Jurassic-Lower Cretaceous age, the Berdiga limestone (Jurassic-lower Cretaceous), the Dagbasi granitoid (Upper Cretaceous),
volcano-sedimentary sequence of Upper Cretaceous age, ore-bearing and barren dacites of Upper Cretaceous age, and Neogene
alkaline basalts. Chemical analyses of soil samples indicate significantly lower iodine abundances for all the soils studied
(5–28 ppm) in comparison to the average abundance of iodine in analogous soils of other parts of the world (22–93 ppm). The
concentration of iodine in soils developed over the same geologic formation decrease with increasing elevation. In certain
cases, this decrease may reach up to 70%. Goiter is highly common throughout this region in Turkey. The results of this study
suggest that the iodine deficiency of region’s soils may be a principal underlying cause for this area of Turkey being an
endemic goiter region. 相似文献
134.
Laurent Millet Boris Vannière Valérie Verneaux Michel Magny Jean Robert Disnar Fatima Laggoun-Défarge Anne Véronique Walter-Simonnet Gilles Bossuet Elena Ortu Jacques-Louis de Beaulieu 《Journal of Paleolimnology》2007,38(4):525-539
This study focuses on the response of lacustrine littoral chironomid communities to late glacial changes in limnological,
environmental and climate conditions in the Mediterranean context. Late glacial chironomid (Diptera: Chironomidae) assemblages,
organic petrography and geochemistry were analysed in a sediment core from the littoral zone of Lago dell’Accesa (Tuscany,
Italy), where the lake-level fluctuations and the vegetation history have been previously reconstructed. Comparison of the
chironomid stratigraphy to other proxies (pollen assemblages, organic petrography and geochemistry, lake-level) and regional
climate reconstruction suggested the predominant influence of lake-level changes on the littoral chironomid fauna. The main
lowering events that occurred during the Oldest and the Younger Dryas were followed by higher proportions of taxa typical
of littoral habitats. A complementary study of organic matter suggested the indirect impact of lake-level on the chironomids
through changes in humic status and habitat characteristics, such as the type of substrate and aquatic macrophyte development.
Several chironomid taxa, such as Glyptotendipes, Microtendipes and Cricotopus type patens, were identified as possible indicators of low lake-level in the late glacial records. Nevertheless, this study suggested
that parallel analyses of organic matter and chironomid assemblages may be needed to circumvent misinterpretation of littoral
chironomid assemblage stratigraphy. There was a weak response of the chironomid assemblages to small lake-level lowerings
that corresponded to the Older Dryas and Preboreal oscillations. A higher level of determination, e.g. to the species group
level, may be necessary to increase the sensibility of the indicators to lake-level changes. 相似文献
135.
136.
137.
1985年在甘肃文县屯寨乡洋汤寨的天池庙的大樑上发现了一条新的关于1879年7月1日武都8级地震的新的历史记载。该记载表明武都8级地震在这里的地震烈度至少达到了Ⅹ度。 相似文献
138.
139.
140.
铂族元素矿床特征及成因分类探讨 总被引:5,自引:0,他引:5
在收集国内外铂族元素矿床地质特征的基础上,审视了国内外不同学者对铂族元素矿床的分类方案,综合矿床容矿岩石类型、共生元素组合、矿化类型和矿床类型并结合形成环境,对铂族元素矿床进行了系统的总结和分类,划分为四类十二亚类。同时重点论述了具有开发前景的典型铂族元素矿床的基本特征、成矿物质来源和形成环境及成矿的关键问题。 相似文献