Stratigraphical Time——Correlation and Mass Extinction Event Near Permian——Triassic Boundary in South China

Shaw's method used to correlate 40 sections across the Permo-Triassic boundary in South China is applied in the paper. Two steps are adopted to get an Integral Composite Section (ICS) by synthesizing these data : First , South China is divided into five areas and composite section developed for each area . Then the second step . the Changxing composite section is regarded as a composite standard (CSRS) while the ICS is produced by matching the CSRS with composite sections of the other areas. Three biozones in the Changxingian and two biozones in the Griesbachian can be discerned on the basis of computing Z values in the ICS. These biozones are marked by the Z values which quantitatively represent their time ranges ; therefore , they may increase accuracy of stratigraphic time correlation . The mass extinction at the end of the Permian is an abrupt event that is supported by the relative rate of extinction near the P/T boundary . About 90% of invertebrate species died out by the end of the Permian . The duration of the mass extinction is rather short ,approximately 0.018Ma .

Some Evidence for a Possible Extraterrestrial Event at/near Permian-Triassic Boundary

A selection of evidence, including a carbon isotopic excursion, iridium anomaly, fullerenes (C 60 and C 70 ) with trapped noble gases, microspherules and shocked quartz, is discussed in this paper. All the evidence in hand favors the hypothesis that the PTB event was probably related to an extraterrestrial cause, and the impact would lead to great physical change, including large volcanic eruptions on the earth's surface. The ET markers for the CTB event could be considered only as an example, and cannot be taken as a unique standard of an ET event.

Wildfire events at the Triassic-Jurassic boundary of the Tabas Basin,Central Iran

This paper presents organic geochemical evidence pointing to the occurrence of wildfire events at the Triassic-Jurassic boundary in Central Iran.The studied outcrop section(the Kamarmacheh Kuh section)is comprised of the Upper Triassic Nayband Formation which passes conformably into the Lower Jurassic Ab-e-Haji Formation with no sharp boundary.Organic petrographical studies reveal a higher concentration of semi-fusinite macerals and microscopic charcoal at the boundary between studied formations.This observation can be an evidence for widespread wildfire events at the Triassic-Jurassic boundary of the studied area.Following these fires,vast areas of land were exposed for erosion and large volumes of clastic sediments were provided due to increased run-off.This agrees well with previous sedimentological and stratigraphical studies suggesting a major change in the depositional conditions from marine to non-marine at the Triassic-Jurassic boundary of the Tabas Basin.These findings can have important implications about paleo-depositional settings of the studied formations and the nature of the associated organic matter.

GEOLOGICAL MARKS OF A POSSIBLE EXTRATERRESTRIAL IMPACT EVENT ON THE BOUNDARY BETWEEN SINIAN/CAMBRIAN IN TIANMENSHAN IN WESTERN HUNAN

Geologic marks related to extraterrestrial impact events, such as impact split gravels, impact brecciate layers, impact dikes, microirghizites, microtektites, especially meteoritic residues, were discovered on the boundary between Sinian/Cambrian at Tianmenshan of Western Hunan, which may possibly demonstrate that an extraterrestrial impact event has ever occurred there on the S/C boundary.

Experimental investigation of closed-loop active control to modulate coherent structures by mu-level method

The experimental research on zero-net-mass-flux jet closed-loop active control was conducted in the wind tunnel.The mu-level method successfully detected burst events of the coherent structures. The streamwise velocity signals in the turbulent boundary layer were measured by HWA. The drag reduction rate of 16.7% is obtained comparable to that of the open-loop control and saves 75% of the input energy at the asynchronous 100 V/160 Hz control case, which reflects the advantages of the closed-loop control. The experimental findings indicate that the intensity increases in the near-wall region.The perturbation of the PZT vibrators on the skewness factor is concentrated in the region y+< 60. The generation of highspeed fluids is depressed and the downward effect of high-speed fluids weakens. The alteration of energy distribution and the discernible impact of modulation between structures of varying scales are observed. The correlation coefficient exhibits a strong positive correlation, which indicates that the large-scale structures produce modulation effect on small-scale ones.The occurrence of burst events is effectively suppressed. The disturbance has the characteristics of stable periodicity,positive and negative symmetry, low intermittency, and high pulsation strength. The conditional phase waveform shows that the fluctuation amplitude increases, indicating amplitude modulation effects on coherent structures.

Urban Boundary-Layer Stability and Turbulent Exchange during Consecutive Episodes of Particle Air Pollution in Beijing,China

Based on measurements at the Beijing 325-m Meteorological Tower,this study reports an analysis of atmospheric stability conditions and turbulent exchange during consecutive episodes of particle air pollution in Beijing(China),primarily due to haze and dust events(15–30 April 2012).Of particular interest were relevant vertical variations within the lower urban boundary layer(UBL).First,the haze and dust events were characterized by different atmospheric conditions,as quite low wind speed and high humidity are typically observed during haze events.In addition,for the description of stability conditions,the bulk Richardson number(RiB) was calculated for three different height intervals: 8–47,47–140,and 140–280 m.The values of RiB indicated an apparent increase in the occurrence frequency of stably-stratified air layers in the upper height interval—for the 140–280-m height interval,positive values of RiB occurred for about 85% of the time.The downward turbulent exchange of sensible heat was observed at 280 m for the full diurnal cycle,which,by contrast,was rarely seen at 140 m during daytime.These results reinforce the importance of implementing high-resolution UBL profile observations and addressing issues related to stably-stratified flows.

Elemental Geochemical Anomaly in the Sinian Doushantuo Formation-Dengying FormationBoundary in Miaohe, Hubei

: No research has been made on such a lower rank boundary as the Sinian Doushantuo Formation-Dengying Formation boundary in the eastern region of the Yangtze Gorges. Elemental geochemical determination has revealed anomalies of REE and other trace elements around the boundary, which have relatively high contents than those in its overlying and underlying beds. The authors therefore think that a catastrophic event once occurred in the Miaohe area at the end of the Doushantuoan Period, which caused the mass extinction of the Miaohe biota.

Sedimentary-volcanic tuffs formed during the early Middle Triassic volcanic event in Guizhou Province and their stratigraphic significance

The sedimentary-volcanic tuff (locally called “green-bean rock”) formed during the early Middle Triassic volcanic event in Guizhou Province is characterized as being thin, stable, widespread, short in forming time and predominantly green in color. The green-bean rock is a perfect indicator for stratigraphic division. Its petrographic and geochemical features are unique, and it is composed mainly of glassy fragments and subordinately of crystal fragments and volcanic ash balls. Analysis of the major and trace elements and rare-earth elements (REE), as well as the related diagrams, permits us to believe that the green-bean rock is acidic volcanic material of the calc-alkaline series formed in the Indosinian orogenic belt on the Sino-Vietnam border, which was atmospherically transported to the tectonically stable areas and then deposited as sedimentary-volcanic rocks there. According to the age of green-bean rock, it is deduced that the boundary age of the Middle-Lower Triassic overlain by the sedimentary-volcanic tuff is about 247 Ma.

Analysis of platinum-group elements in drill core samples from the Meishan Permian-Triassic boundary section, China

There is a long-standing controversy of what triggered the extinction at the Permian-Triassic boundary, the most severe mass extinction in the geologic record, including flood basaltic volcanism and/or bolide impact hypothesis. In order to clarify various pieces of evidence for the mass extinction event at the Permian-Triassic boundary, some researchers from some laboratories throughout the world have made a comprehensive study on a group of samples from the Meishan area of China. Some fresh core samples from the Permian-Triassic boundary in the Meishan area were analyzed in this study. The results showed that there is no Ir anomaly. Moreover, the PGEs patterns of those samples show obvious differentiation characteristics, that is different from the case encountered in meteorites. So no evidence supports the hypothesis of extraterrestrial impact. In contrast, the PGEs patterns are similar to those of Siberian and Emeishan basalts, which indicates that those PGEs are derived mainly from the basalts, lending a support to the correlation between mass extinction at the Permian-Triassic boundary and flood basaltic volcanism. This study has also confirmed the results for samples from section C prior to the analysis of the samples.

The fungal and acritarch events as time markers for the latest Permian mass extinction:An update

The latest Permian extinction(252 Myr ago)was the most severe in the geologic record.On land,widespread Late Permian gymnosperm/seed-fern dominated forests appear to have suffered rapid and almost complete destruction,as evidenced by increased soil erosion and changes in fluvial style in deforested areas,signs of wildfires,replacement of trees by lower plants,and almost complete loss of peat-forming and fire-susceptible vegetation.Permian-Triassic boundary strata at many sites show two widespread palynological events in the wake of the forest destruction:The fungal event,evidenced by a thin zone with>95%fungal cells(Reduviasporonites)and woody debris,found in terrestrial and marine sediments,and the acritarch event,marked by the sudden flood of unusual phytoplankton in the marine realm.These two events represent the global temporary explosive spread of stress-tolerant and opportunistic organisms on land and in the sea just after the latest Permian disaster.They represent unique events,and thus they can provide a time marker in correlating latest Permian marine and terrestrial sequences.

The Tectonic and Climate Change Across the Oligocene-Miocene Boundary in Northern Tibetan Plateau

From the planktonic foraminiferal and nannofossil events across the Oligocene/Miocene boundary (OMB) to the major transient glaciation at this epoch boundary,Mi-l,the paleoclimate,stratigraphic and paleontologic events showed a prominent change across the OMB.However,the previous work was mainly about the marine deposits,especially the ocean drilling data.Whatever,the continental strata,such as the alluvial and lacustrine sedimentation in

小说语篇建构的三重维度:事件基础、语境边界及主体意向性——以《外婆的日用家当》为例

小说语篇建构是在事件基础、语境边界和主体意向性三个维度下进行的,是三个维度之间辩证和依存关系的结果呈现。事件基础是作者针对一定的交际情景而建构起来的典型事件和用例事件,确定了小说语篇的内容和结构;语境边界是作者在特定社会环境下的认知维度,制约着小说语篇的意义和交际功能;主体意向性是作者在语境边界内针对特定社会生活的心智模型的体现,决定着小说语篇所要表达的思想和观点。

开放领域新闻中基于自适应决策边界的突发事件识别和分类研究

[目的/意义]网络新闻是获取突发事件情报的重要来源之一,提高海量网络新闻中突发事件的识别准确率和分类效果,并减少非突发事件新闻造成的开放集识别问题和降低人工标注非突发事件新闻的成本,这是当前突发事件识别与分类研究的重要课题。[方法/过程]选择BERT预训练模型获得文本的特征表示,融合不同层级之间的语义信息增强文本表示的质量,采用自适应决策边界模型,学习各突发事件类别在高维语义表示空间上的球形最佳决策边界,根据新闻样本的文本表示和各突发事件类别的球形最佳决策边界的欧几里得距离,检测出突发事件新闻并判断突发事件的类别,并在CEC公开数据集和实时爬取的中文新闻数据集CEN上对模型的有效性进行验证。[结果/结论]实验结果表明,本文模型在CEC数据集和CEN数据集上的宏F1值分别为98.46%和95.80%,与基准模型相比,本文模型的宏F1值分别提升了5.15%和19.69%。模型应用展示了提出方法在解决实际问题时的有效性。[局限]未考虑突发事件新闻可能存在多标签的情况。

下侏罗统辛涅缪尔阶-普林斯巴阶界线地质事件研究进展

早侏罗世经历了赫塘期、辛涅缪尔期、普林斯巴期和土阿辛期,其中土阿辛期大洋缺氧事件(T-OAE)被广泛研究。但在辛涅缪尔阶-普林斯巴阶界线处,δ^(13)C_(org)及δ^(13)C_(carb)曲线均发生负偏,局部伴随黑色页岩沉积。其在英国、法国、意大利、葡萄牙以及中国等地区都有记录,碳同位素的变化伴随着环境、气候的变化,研究显示该事件可能是全球性的,被称为“S-P界线事件”(SPBE)。此次地质事件与T-OAE事件类似,也显示了一次大洋缺氧事件,其发生时有轻碳同位素被排入了大气系统中,但是轻碳同位素的来源尚不明确,部分学者认为是大火成岩省喷发时排放的轻碳物质注入了海洋-大气系统所致。目前对该事件的研究主要集中于欧洲海相地层,其对陆地生态系统的影响还知之甚少。我国四川盆地下侏罗统湖相沉积发育良好,下侏罗统自流井组东岳庙段沉积有与大安寨段(T-OAE发生层段)类似的黑色页岩及介壳灰岩,其有机碳同位素负偏,显示了S-P界线事件的影响,其与T-OAE类似也对四川盆地早侏罗世古湖泊产生了影响。

奖赏预测误差对时间顺序记忆和来源记忆的影响

先前研究表明,事件边界会增强边界处来源记忆、削弱跨边界的时间顺序记忆,但对于两者之间是否存在一种权衡关系,以及内在的、具有社会性意义的变化作为事件边界是如何影响记忆的,尚鲜有研究。本研究以奖赏预测误差(reward prediction errors,RPE)作为事件边界,通过两个行为实验和一个ERP实验,探讨RPE事件边界对时间顺序记忆和来源记忆的影响。结果发现,RPE事件边界增强了边界处信息的来源记忆,高RPE事件边界引发了记忆权衡效应;相对于事件内/非边界条件,跨事件/边界条件记忆的正确提取诱发出更大的N400波幅,时间顺序记忆的激活主要集中在头皮中前部,来源记忆的激活主要集中在头皮中后部。本研究表明,事件边界的切分强度是影响记忆权衡效应的重要因素,N400成分可能是反映事件边界对情景记忆的整合与切分的重要指标。

网络化热方程的集中事件触发控制

本文对热方程建模的分布式参数化多智能体系统进行研究,设计了基于事件触发控制下的一致性边界控制器,将网络化热方程的状态驱动到相同的稳定状态.其中每一个子系统的边界信息能被测量,并且所有的智能体由无向静态拓扑连接.事件触发控制器由以下两部分组成:一是基于网络拓扑的边界局部交互作用,驱动所有子系统达到相同的状态;二是由事件触发条件建立的触发时刻.本文证明了在事件触发的边界一致性控制下两个连续触发时刻之间存在最小停留时间以避免Zeno现象;同时利用李雅普诺夫函数分析并保证了闭环系统的稳定性和适定性.最后,给出了由5个热方程组成的多智能体系统的仿真算例,结果证实了本文所设计事件触发控制器的真实性.

山东重大基础地质问题研究进展

在1∶50万山东省大地构造相图编制和大地构造相综合研究的基础上,作者对山东重大基础地质问题提出了新的划分方案。山东地块是经多期增生和碰撞、镶嵌、叠覆而成的,其漫长的地质构造演化具明显的阶段性,可分为前南华纪、南华纪——中三叠世和晚三叠世——第四纪三大构造演化阶段。大地构造分区分为陆块区、造山系和叠加造山——裂谷系,划分出3个I级构造单元、5个II级构造单元、18个III级构造单元和55个IV级构造单元。基于鲁东和鲁西地区在地层建造、岩浆活动、构造格局和成矿作用等存在的重大差异性,新厘定的渤海陆块作为华北陆块区之下的II级构造单元。厘定大别——苏鲁造山带的北部边界、鲁西陆块与渤海陆块的边界。对古元古代荆山群、粉子山群形成的构造环境进行了深入探讨,认为是弧后盆地靠近大陆边缘一侧的构造背景,在古元古代晚期的造山过程中,粉子山群和荆山群等均卷入了造山过程,其中荆山群发生了深俯冲及高压麻粒岩相变质作用。胶东地区构造——岩浆事件和金矿成矿作用受控于特提斯、古亚洲洋和太平洋三大构造域,金矿形成于中生代构造体制转折和岩石圈减薄的动力学背景,与华北板块和扬子板块碰撞及太平洋板块的俯冲机制存在密切成因关系。

三叠纪全球海水的锶同位素组成及主要控制因素

三叠纪是地球环境的重大变革时期,海水锶同位素组成的研究也较为困难。三叠纪海水的87S r/86S r值或是在短时间内剧烈变化(如早三叠世),或是在较长时间内保持稳定(如中三叠世—晚三叠世早期);已公布的全球海水锶同位素曲线也具有显著的不一致性。早三叠世约10 M a时间中海水87S r/86S r值在海平面上升的背景下反而急剧增加,其控制因素与二叠/三叠纪生物绝灭事件之后的生态空白、尤其是全球古陆缺乏植被的保护和相应的侵蚀作用加剧有关;早三叠世末全球生态环境的逐步恢复(尤其是大陆植被的复苏)以及该时间间隔中的火山作用是全球海平面上升背景下早三叠世末—中三叠世早期海水87S r/86S r值的下降的主要控制因素;中三叠世—晚三叠世早期海水87S r/86S r值的长时间稳定主要与全球海平面持续上升的背景下,大范围分布的陆表海对放射性成因锶的保护作用有关;古特提斯洋的关闭、西米里亚大陆与欧亚大陆的碰撞造山、以及全球海平面的显著下降造成了晚三叠世中期以后再次出现的海水87S r/86S r值增加。

应用测井技术识别碎屑岩与碳酸盐岩地质事件及其差异

应用测井技术识别地质事件时,对具有隐蔽测井信息结构变化的识别涉及较少,限制了认知地质事件的精度和可靠性。而根据测井记录的地质响应及其相关测井信息组合特征,研究重要地质事件的多样性与测井曲线之间的成因关系,以及测井曲线纵、横向变化与地质演变的成因关系,可以探索性地解决上述问题。运用该方法可识别出碎屑岩和碳酸盐岩地质事件并推断其成因机理。通过对地质事件表现形式多样性的分析,提出了碎屑岩地质事件的识别和论证方法;通过同成因地质界面的识别与追踪,提出了碳酸盐岩"同期异相"地层对比问题的识别方法和依据。地层的岩性成因机制不同,碎屑岩和碳酸盐岩地层的地质事件研究方法也有所不同,二者的识别差别在于地质界面的追踪依据不同、地质界面的测井响应特征不同以及测井信息与地质界面识别的对应关系不同。应用该方法,成功解决了大港油田、普光气田以及澳大利亚等国内外油气探区地质研究中地质界面识别的关键问题。

大洋缺氧事件的碳稳定同位素响应

从碳稳定同位素组成及其分馏机理出发 ,系统探讨了大洋缺氧事件与海相碳酸盐和有机碳稳定同位素分馏之间的关系。缺氧事件期间 ,由于生物大批死亡和快速埋藏 ,其分解消耗海水中大量的溶解氧 ,引起大洋水体缺氧 ,富含 1 2 C的有机质从而得以大量保存 ;相应地大气和海水中富 1 3 C,同期海相碳酸盐岩碳同位素 δ值 (δ1 3C)正偏。在世界各地缺氧事件层内 ,无一例外地碳酸盐岩碳稳定同位素出现了不同程度的正偏 ,Cenomanian- Turonian 界线偏幅达～2‰。海相碳酸盐与有机质碳稳定同位素变化不仅可以提供地质历史中有机碳埋藏量的记录。研究全球碳循环变化 ,还可能追溯有机碳风化和埋藏速率的变化 ,定性地恢复大气 p CO2 变化。