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B.M. Besly C.J. Cleal 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(1):50-65
An extensive regional stratigraphic hiatus has been proposed in the Asturian to Stephanian foreland basin successions lying to the north of the main Variscan deformation belt, stretching from north west Europe to eastern North America. The hiatus is inferred on megafloral grounds and involves the absence of most if not all of Stephanian Substages B and C. If present it would have great significance for the understanding of regional basin dynamics in the later stages of the Variscan orogeny. However, its existence has been strongly contested. One of the keys to this hypothesis is the correct identification and interpretation of plant fossils from the Warwickshire Coalfield (Central England). The published identifications are here shown to be incorrect, and revised determinations taken in conjunction with other stratigraphic data from Central England suggest that a regional hiatus is not present in the early-mid Stephanian, and that any stratigraphic hiatuses at other horizons in the succession are of purely local extent. A review of known occurrences of the Asturian and Stephanian successions in basins stretching from eastern Canada to Germany suggests that, while facies developments may be similar, there is little uniformity in stratigraphic style and little evidence for a major Stephanian hiatus. 相似文献
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The age models of fluvio-lacustrine sedimentary sequences are often subject of discussions in paleoclimate research. The techniques employed to build an age model are very diverse, ranging from visual or intuitive estimation of the age-depth relationship over linear or spline interpolations between age control points to sophisticated Bayesian techniques also taking into account the most likely deposition times of the type of sediment within the sequence. All these methods, however, fail in detecting abrupt variations in sedimentation rates, including the possibility of episodes of no deposition (hiatus), which is the strength of the method presented in this work. The new technique simply compares the deposition time of equally thick sediment slices from the differences of subsequent radiometric age dates and the unit deposition times of the various sediment types. The percentage overlap of the distributions of these two sources of information, together with the evidence from the sedimentary record, helps to build an age model of complex sequences including abrupt variations in the rate of deposition including one or many hiatuses. 相似文献
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The Eocene succession of the El Basatin Section in Gebel Mokattam, east of Cairo, consists, from base to top, of two main units; the Mokattam and Maadi Formations. The Mokattam Formation consists of two Members, the Building Stone Member and the Giushi Member. The Upper Building Stone Member yielded six species of Nummulites belonging to the Upper Lutetian. These species are: Nummulites farisi Hussein et al., 2004; Nummulites cf. praegizehensis Boukhary and Hussein-Kamel, 1993; Nummulites cf. gizehensis(Forsk?l, 1775); Nummulites discorbinus(Schlotheim 1820) and Arxina schwageri(Silvestri, 1928) emended by Boukhary et al. 2012 and Nummulites crassichordatus Boukhary et al., 2010. The Giushi Member yielded three species that indicate a Bartonian age. These species, which continued from their first appearance in the Upper Building Stone Members, are N. discorbinus, A. schwageri and N. crassichordatus. The Maadi Formation, which has been previously considered to be of Bartonian–Priabonian age, is devoid of fossils in the study section. The two members of the Mokattam Formation represent a carbonate platform facies. The deposition of the Upper Building Stone Member was disturbed during the Lutetian by slumping and a convolute-bedding interval, indicating a short hiatus. The subsequent regression resulted in a very shallow marine to near-shore facies in the above Maadi Formation. 相似文献
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Deposystems are complex and governed by discrete depo events with variable intervals of stasis or erosion in between. Since shoreface sediments indicate sea level, depo events of shoreline facies are discrete samples of sea level. Only if these samples are sufficiently regular and frequent will the shoreline trajectory in the space domain accurately reflect the sea-level curve in the time domain. This study presents a method to convert shoreline trajectory in the space domain to sea-level curve in the time domain from artificial miniature deltas. One obtains the depo sequence as function of time and uses it to: convert depo sequence from time-to space domain, correlate depo sequence to shoreline trajectory in the space domain, and convert shoreline trajectory from space-to time domain. For natural deltas one would extract the depo set in the frequency domain, i.e. the probability density function of stasis intervals between depo events from the experimental depo sequence and use it to: convert shoreline trajectory from space-to time domain, and infer a range of possible sea-level curves. This method therewith explicitly includes the uncertainty of the inferred sea-level curve. 相似文献
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1971-2012年青藏高原春季风速的年际变化及对气候变暖的响应 总被引：2，自引：0，他引：2
利用青藏高原73个气象台站的观测资料和日本气象厅JRA-55再分析资料,通过引入年际增量和动能收支方程,分析了1971-2012年高原春季风速的年际变化特征及其对气候变暖的响应。结果表明,在气候变暖的背景下高原风速呈减弱的趋势,随着变暖趋缓风速的变化也趋于平稳。春季高原风速与气温的线性趋势是相反的,但在年际尺度上二者表现出同位相的变化,当青藏高原、中南半岛和印度半岛的地面气温偏高,北亚和东亚地区的地面气温偏低时,有利于高原地面风速增大,反之风速减小。20世纪末青藏高原及其周边地区的升温速率表现为北快南缓,高原南、北侧气温差异减小,而东、西向的气温差异增大,风速趋于减弱;21世纪初高原中部及其南侧地区以升温为主,高原东北侧和东亚地区以降温为主,南、北向气温差异较小,高原风速的变化也趋于平缓,东、西向气温差异有减小的趋势,对应高原东部风速有所增大。青藏高原及其邻近地区的热力差异及其变化速率的不均衡改变了对流层大气的斜压性,进而通过两种途径影响青藏高原的风速,一方面是近地面层气压梯度力的直接作用,另一方面是高层动能向低层的输送。此外,还指出JRA-55再分析风速资料比ERA-Interim和NCEP/NCAR资料在青藏高原的适用性更强。 相似文献
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全球变暖趋缓研究进展 总被引：16，自引：5，他引：11
近十几年来,全球年平均表面温度上升趋势显示出停滞状态,即全球变暖趋缓,这引起了国际社会的广泛关注,同时也引发了对全球变暖的质疑,各国气候学家正努力就全球变暖趋缓的事实、原因及其可能影响展开研究。本文综述了目前国内外对全球变暖趋缓的研究结果。多数科学家认可近十几年来全球变暖停滞的事实,并认为太阳活动处于低位相、大气气溶胶（自然和人为）增加以及海洋吸收热量是变暖停滞的可能影响因子,其中海洋（尤其是700米以下的深海）对热量的储存可能是变暖停滞的关键。国际耦合模式比较计划第5阶段中的模式并未精确地描述各种有利降温影响因子的近期位相演变,因而其模拟的近期增暖趋势较观测偏强。由此推断,变暖停滞主要是自然因素造成的,并且预测变暖趋缓将在近几年或几十年内结束（依赖于太平洋年代际振荡的位相转变）,未来气温将仍主要受到温室气体增加的影响而表现出明显的上升趋势。因此,目前的全球变暖趋缓不大可能改变到本世纪末全球大幅度变暖带来的风险。本综述展望未来的研究热点包括:精确估算全球气温和海洋热含量的变率及其不确定性,海洋年代际信号（太平洋以及大西洋的年代际振荡）的转型机制,存储在深海的热量将在何时返回海洋表面及其对区域气候的潜在影响。 相似文献
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