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131.
132.
Fischer图解及其在旋回层序研究中的应用──以北京西山张夏组为例 总被引:11,自引:0,他引:11
Fischer图解(又称为容纳空间图解)为人们研究沉积旋回在空间上的叠置规律、相对海平面变化、层序级次的划分以及地层层序对比等提供了一种客观实用的方法。本文较详细地讨论了该图解的绘制方法及应注意的问题。运用该图解,将北京西山下苇甸剖面张夏组划分为1个大的三级旋回层序和4个四级旋回层序,根据图解反映的相对海平面变化讨论了旋回层序与构造运动间的关系,提出华北板块晚寒武世之前的"翘翘板运动"应始于中寒武世张夏期之早期到中期。 相似文献
133.
En‐De Wang Chang‐Ik Han Jian‐Ming Xia Jian‐Fei Fu Guang‐Su Li San‐Shi Jia Ye‐Kai Men 《Geological Journal》2016,51(3):480-498
The Anshan–Benxi iron producing area, which is located at the northeastern margin of the North China Craton, is the main distribution area of Archaean BIFs in China. In their eastern part, including the Gongchangling and Waitoushan deposits, BIFs mainly are hosted in the Archaean middle Anshan Group. Amphibolites are widely distributed in the iron‐bearing rock series, reflecting the tectonic setting of BIFs. Amphibolites not only have MORB‐like compositional characteristics, but also have island arc‐like ones, and they are consistent with back‐arc basin basalts (BABB). In the study area, the protolith of amphibolites belongs to Okinawa‐type BABB; it indicates that tectonic setting of BIFs is the intra‐continental back‐arc basin. In the study area, the formation of sedimentary basins for BIFs had been associated with oceanic plate subduction. Amphibolites from Gongchangling deposit are characterized by relative enrichments in LILE and LREE, and depletions in HFSE. This indicates that they had a relatively large influence of subduction in their formation. Amphibolites from Waitoushan deposit are characterized by relative enrichments in LILE without conspicuous depletions in HFSE, indicating relatively low subduction rates. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
134.
Min Sun Chao Yuan Wenjiao Xiao Xiaoping Long Xiaoping Xia Guochun Zhao Shoufa Lin Fuyuan Wu A. Kröner 《Chemical Geology》2008,247(3-4):352-383
Gneissic rocks in the Chinese Altai Mountains have been interpreted as either Paleozoic metasedimentary rocks or Precambrian basement. This study reports geochemical and geochronological data for banded paragneisses and associated gneissic granitoids collected along a NE–SW traverse in the northwestern Chinese Altai. Petrological and geochemical data suggest that the protoliths of the banded gneisses were possibly immature sediments with significant volcanic input and that the gneissic granitoids were derived from I-type granites formed in a subduction environment. Three types of morphological features can be recognized in zircons from the banded gneisses and are interpreted to correlate with different sources. Zircons from five samples of banded paragneiss cluster predominantly between 466 and 528 Ma, some give Neoproterozoic ages, and a few yield discordant Paleoproterozoic to Archean ages. Zircon Hf isotopic compositions indicate that both juvenile/mantle and crust materials were involved in the generation of the source rocks from which these zircons were derived. In contrast, zircons occur ubiquitously as elongated euhedral prismatic crystals in the four samples of the gneissic granitoids, and define single populations for each sample with mean ages between 380 and 453 Ma. The general absence of Precambrian inheritance and positive zircon ?Hf values for these granitoids suggest insignificant crustal contribution to the generation of the precursor magmas. Our data can be interpreted in terms of a progressive accretionary history in early to middle Palaeozoic times, and the Chinese Altai may possibly represent a magmatic arc built on a continental margin dominated by Neoproterozoic rocks. 相似文献
135.
136.
一次暴雪过程前后近地层物理量场特征分析 总被引:1,自引:1,他引:1
利用铁塔风梯度观测资料和超声风温仪观测资料,对2008年1月18—21日暴雪前后,湖北黄石长江岸边近地层风场和湍流作了计算分析,探索其异常变化特征,为认识黄石地区暴雪近地层发生发展的物理过程提供依据。结果表明,暴雪前,风向转变,水平风速和垂直风速明显增大,湍流通量的输送较活跃,湍流动能和湍流强度有显著峰值出现;降雪过程结束后,湍流动能再次增大后缓慢减弱。可见此次暴雪过程前后近地层物理量场有异常变化 相似文献
137.
On 21–22 July 2012, torrential rains hit North China, with the daily precipitation record at Beijing station reaching 160.6 mm; this event is named the Beijing 7–21 case. This paper assesses the likelihood of the occurrence of local torrential rains, such as the Beijing 7–21 case, from the perspective of climate variability. In particular, the influence of the Pacific Decadal Oscillation (PDO) is assessed. There were five extreme events, with daily precipitation records equal to or larger than 160.6 mm, at Beijing station during the period 1951–2012; all of these events happened during negative phases of the PDO. The present analysis indicates that precipitation events more extreme than the Beijing 7–21 case should happen more than once per decade during negative phases of the PDO, but only about once every four decades during positive PDO phases. The negative phase of the PDO is found to be associated with a much greater probability of daily records of southerly winds in North China during summer. Strong southerly summer monsoons are deemed favorable for increasing the occurrence of local extreme rainfall over North China. 相似文献
138.
利用长株潭地区地面空气质量监测资料、常规地面气象资料及NCEP再分析资料和MODIS火点监测资料,结合HYSPLIT4后向轨迹模式,对2014年10月1718日长株潭地区一次严重霾天气过程的空气污染特征和成因进行综合分析。研究表明,长株潭地区此次严重霾天气污染事件的主要污染物为PM2.5,安徽南部和江西西北部地区秸秆焚烧产生的颗粒物,经高空偏东北气流引导输送到长株潭地区,是这次大范围烟霾天气的主要来源。长株潭地区西部高空槽区宽广,槽前西南气流较为强盛,地面受均压场控制,水平风速弱,为严重霾污染天气的维持提供了有利的环流条件。中低层逆温和大气底层湿度的增加,使污染物粒子不断累积;近地面连续静(小)风和风向的频繁转变,不利于污染物粒子的水平扩散;中下层弱的下沉气流、较低的混合层高度有利于污染物的垂直累积,为此次重度霾污染天气的发展、加强提供了有利的气象条件。 相似文献
139.
Affected by climate change and policy factors, Kazakhstan is the country with the most severe ecological degradation and grassland conflicts in Central Asia. Therefore, studying the state of grassland carrying resources in Kazakhstan is particularly important for understanding the responses of grassland ecosystems to climate change and human activities. Based on Kazakhstan's remote sensing data and animal husbandry statistics, this study analyzes the patterns of changes in grassland ecosystems in Kazakhstan based on the supply and consumption of these ecosystems. The results show that: 1) From 2003 to 2017, the number of livestock raised in Kazakhstan showed a trend of sustained and steady growth. Due to freezing damage, the scale of livestock farming decreased in 2011, but a spatial difference in the livestock farming structure was not obvious. 2) The fluctuation of grassland supply in Kazakhstan has increased, while the consumption due to animal husbandry has also continued to increase, resulting in an increasing pressure on the grassland carrying capacity. 3) Between 2003 and 2017, the overall grassland carrying status of Kazakhstan have been abundant, but the grassland carrying pressure index has shown a steadily increasing trend, the grassland carrying pressure is growing, and it is mainly determined by grassland productivity. The greater pressure in lower Kyzylorda state, the southern Kazakhstan state of the cultivated land and the northern Kazakhstan state has gradually expanded to include the agro-pastoral zone and the semi-desert zone. 相似文献
140.
Position-domain integrity risk-based ambiguity validation for the integer bootstrap estimator 总被引:1,自引:0,他引:1
Integrity monitoring for ambiguity resolution is of significance for utilizing the high-precision carrier phase differential positioning for safety–critical navigational applications. The integer bootstrap estimator can provide an analytical probability density function, which enables the precise evaluation of the integrity risk for ambiguity validation. In order to monitor the effect of unknown ambiguity bias on the integer bootstrap estimator, the position-domain integrity risk of the integer bootstrapped baseline is evaluated under the complete failure modes by using the worst-case protection principle. Furthermore, a partial ambiguity resolution method is developed in order to satisfy the predefined integrity risk requirement. Static and kinematic experiments are carried out to test the proposed method by comparing with the traditional ratio test method and the protection level-based method. The static experimental result has shown that the proposed method can achieve a significant global availability improvement by 51% at most. The kinematic result reveals that the proposed method obtains the best balance between the positioning accuracy and the continuity performance. 相似文献