Signature of palaeo-ice-stream stagnation: till consolidation induced by basal freeze-on

A combination of glaciological theory and geological observations was used to investigate the possibility of till consolidation being driven by basal freeze-on beneath a stagnating, mid-latitude palaeo-ice stream. We focused on the case of the Baltic Ice Stream that advanced into Denmark at c. 15ka BP and which left behind a characteristic till sequence consisting of a strong and well-consolidated till crust underlain by weak and poorly consolidated till. Our hypothesis is that basal freezing caused the markedly higher consolidation of the uppermost till layer. The freezing may have either triggered or simply just accompanied ice-stream stoppage. To test the feasibility of this hypothesis, we have developed a numerical model that couples ice-stream dynamics to time-dependent changes of till properties. Despite relatively mild palaeo-climatic conditions in this area during Late Pleistocene deglaciation (˜0°C), the ice-stream model is capable of producing basal freezing when the effect of horizontal advection of cold ice is included. Our simulations of till response to basal freezing are based on thermodynamic concepts adapted from permafrost studies. Dewatering of till by basal freeze-on may lead to overconsolidation (OCR>10). Based on the history of effective pressure changes in the till, we can predict postglacial till strength profiles using the SHANSEP method. In a series of numerical experiments we have examined the response of till strength to basal freeze-on induced beneath a decaying ice sheet. We have come reasonably close to reproducing shear strength profiles for till deposited by the Baltic Ice Stream. These observations are most consistent with palaeo-ice-stream stagnation triggered by basal freezing and followed by abrupt retreat (<100 years) due to high surface ablation rates (>10 ma^-1).     

Estimation of Pore Water Concentrations from DGT Profiles: A Modelling Approach

The technique of Diffusional Gradients in Thin-films (DGT) can be used in situ to obtain high resolution profiles of trace-metals in sediment pore waters. Substances sampled by DGT continuously diffuse through a diffusion layer comprising a hydrogel prior to being immobilized by binding to a resin layer. DGT therefore measures a time averaged flux from the pore water to the resin. Interpretation of this flux as pore water concentration is problematic for two reasons. Firstly, the pore water concentration adjacent to the sampler may become depleted by the DGT induced flux. Secondly, if there are steep vertical chemical gradients in the pore waters, they may relax by diffusion along the gradient within the gel layer. The extent of relaxation depends on the diffusion coefficient, gradient steepness, and diffusion layer thickness. Two dimensional (2D) numerical models of DGT deployments in horizontally uniform sediments were used to investigate to what extent DGT measured profiles accurately reproduced (a) the shape of pore water concentration profiles, and (b) the magnitude of pore water concentrations. A method is developed which translates high resolution DGT measured flux profiles into reliable estimates of pore water concentrations. Linear relationships are given which estimate the minimum DGT measured peak width (as a function of diffusion layer thickness) that ensures accurate reproduction of the shape and the magnitude of peaks in pore water concentrations. Peaks in DGT profiles obtained from assemblies with diffusion layer thicknesses of 0.3 mm (0.5 mm) should be at least 1.2 mm (1.8 mm) wide for their shape to reflect accurately their true shape in the pore water, and at least 1.7 mm (2.7 mm) wide to ensure the peak concentration is accurately estimated.     

Late Mesozoic East Asian Magmatic Province: Structure,Magmatic Signature,Formation Conditions

Geotectonics - Abstract—The Late Mesozoic volcanic province of East Asia is considered in relation to global geological events. The main structure-forming events and largest magmatic...     

风化壳剖面的定年研究

风化壳时间序列的建立是提取有关信息的根本前提。然而,风化壳的定年一直被认为是一道国际难题。近年来,风化作用及风化壳剖面的研究越来越受到人们的关注,有关风化壳定年的研究也取得了一些重要进展。本对此进行了归纳和总结,并对各种方法进行了评述。     

原油族群划分及其地球化学意义

本文阐述了原油族群与组群的概念及其在地球化学研究中的意义,分析了造成同一族群不同组群的原油之间地球化学特征差异的成因.在总结了前人研究工作的基础上提出,油藏内原油的地球化学特征除了受源岩有机相的制约外,还受到烃源岩的成熟度以及油气在成藏过程和成藏后所经历的各种地质、地球化学因素的影响,这些因素主要包括生物降解和水洗作用、流体岩石相互作用及地质色层作用、油气在运移过程中的相控分馏作用、热蚀变作用、不同期次聚集的原油的混合作用、浸析作用和热化学硫还原作用等.因此,必须在充分认识原油在运移、聚集和成藏后所经历的地球化学变化,划分原油族群以及在对造成不同组群原油组成差异的成因分析的前提下,才能客观地分析油气来源、进行油源对比,而不能以原油在化学组成上的异同性及其相关的地球化学参数作为油源对比的唯一依据.并介绍了原油族群划分的方法和应注意的问题.     

Signature of Precambrian extension events in the southern Siberian craton

We investigate extension events in the southern Siberian craton between 1.8 and 0.7 Ga. Signature of Late Paleoproterozoic within-plate extension in the Northern Baikal region is found in 167 4± 29 Ma dike swarms. A Mesoproterozoic extension event was associated with intrusion of the 1535 ± 14 Ma Chernaya Zima granitoids into the Urik-Iya graben deposits. Neoproterozoic extension recorded in the Sayan-Baikal dike belt (740-780 Ma dike complexes) was concurrent with the breakup of the Rodinia supercontinent and the initiation of the Paleoasian passive margin along the southern edge of the Siberian craton. The scale of rifting-related magmatism and the features of the coeval sedimentary complexes in the southern Siberian craton indicate that Late Paleoproterozoic and Early Mesoproterozoic extension did not cause ocean opening, and the Paleoasian Ocean opened as a result of Neoproterozoic rifting.     

Epeiric Sea Formation on Neoproterozoic Supercontinent Break-up: A Distinctive Signature in Coastal Storm Bed Amalgamation

Literature review underlines uncertainty in the configuration of the Neoproterozoic supercontinent, (with Rodinia and Palaeopangaea reconstructions enjoying wide support), that stems primarily from inadequate palaeomagnetic data. Nonetheless, breakup of this supercontinent at ca. 0.65 Ga was conducive for epeiric sea formation globally. In the Vindhyan basin, India, a carbonate depositing sea developed over a fluvial-aeolian plain, at approximately 0.6 Ga. The top part of the Vindhyan Supergroup, the Upper Bhander Sandstone, was, however, able to prograde because of a decline in the rate of relative sea level rise. Within this general setting, temporal increases in this rate caused storm deposition at the coastline, largely in a supralittoral setting. Bizarre amalgamation of these storm beds without erosion likely owes its origin to severe curtailment of the velocity of the downwelling flow on the very gentle, muddy coastal slopes, and is thought to be a hallmark of deposition in an open epeiric setting. The storm domination in the Bhander embayment shelf is compatible with the Palaeopangaea supercontinental configuration.     

全球沉积盆地结构与构造演化背景——洲际经-向超长构造剖面对比

沉积盆地地层及其结构可记录盆地构造演化过程,而盆地演化则记录了不同历史时期的构造背景。为系统认识盆地 构造演化及其演化背景,本文在全球构造理论指导下,收集全球上百个重要沉积盆地资料,编制了洲际超经向长剖面 2 条:(1) 印度—西伯利亚—北美—南美经向超长剖面;(2)非洲东海岸—地中海—欧洲—北冰洋沿岸—西伯利亚—澳大利亚超长剖面。 它们成为探讨沉积盆地结构特征、构造演化对比的重要基础,由此获得的主要认识包括:超长剖面是全球沉积盆地分类的 基础,不同类型的沉积盆地有序并列。盆地构造演化和发育受控于板块构造边界作用以及基底沉降作用。不同的盆地类型 在时间演化和空间分布具有密切成因联系。从板块边缘出发一般为大洋盆地、海沟、弧前盆地、弧后前陆盆地、前陆盆地、 克拉通盆地、裂谷盆地、被动陆缘盆地。位于欧亚板块的各个盆地均受到阿尔卑斯造山运动(喜马拉雅运动)影响,亚洲 大陆盆地群发育及其后期改造受古亚洲、特提斯和西太平洋构造域控制。受板块边界作用影响,相同板块上的不同盆地群 之间具有密切的构造—沉积联系和构造事件响应。全球油气最富集的巨型盆地主要出现于板块内部、远离挤压板块边界的 环境下。     

AIRS红外高光谱资料反演大气水汽廓线研究进展

随着卫星遥感关键技术的突破,卫星光谱分辨率达到了分辨大气成分单个谱线的水平,研究人员开始了大量通道同时反演大气廓线和多种微量成分的研究.针对AIRS(Atmospheric Infrared Sounder)就红外高光谱资料反演大气水汽廓线的研究进展进行了评述,从训练数据、通道信息的提取及降维、反演算法和反演精度改进4个方面对反演晴空大气水汽廓线的研究现状进行了分析与讨论.AIRS资料反演大气水汽廓线的训练数据通常选用威斯康星大学提供的全球晴空反演训练样本集CIMSS (Cooperative Institute for Meteorological Satellite Studies,University of WisconsinMadison)和SARTA(Stand-Alone Radiative Transfer Algorithm)辐射传输模式模拟的亮温辐射值.归纳总结了2种通道信息的提取及降维方法:一是采用有效的方法来完成光谱信息压缩,对常用的主成分分析和独立分量分析方法进行了对比,认为独立分量分析更为可行.二是通道选择,即保留部分含有较多大气廓线信息量的通道,达到降维目的.在进行通道选择时要注意针对不同地区气候类型、下垫面、季节以及即时天气条件,选择不同的通道组合.介绍了3种反演算法:特征向量统计法、牛顿非线性迭代法和神经网络法.对比发现特征向量统计法简单易行,但精度不够理想;牛顿非线性迭代法精度虽高但计算耗时长,因此不适合业务使用;神经网络计算速度快、精度也能达到要求,具有很好的前景.对目前的几种样本分类方法及附加因子进行了对比分析,对反演算法精度的改进提出了一些有益的设想.最后对晴空辐射订正及云天大气水汽廓线反演进行了简要介绍,提出了该领域未来的一些研究方向.     

塔里木盆地地震反射异常体特征剖面

<正> 在塔里木盆地地震剖面上,异常反射多,内容丰富,包含了诸多沉积、构造现象。依据异常反射的外型特征和内部反射结构,可将其归纳为9种类型:丘状、下切状、楔状、丘状斜交前积、蘑菇状、树枝状、枕状、下凹状和透镜状等(图1)。这些地震异常体为一群特殊的地质体。可以是生物礁、生物滩、河道砂体、浊积砂岩体、水下扇、火成岩等,其中的绝大多数都具有较高的孔隙度和渗透率,是好的储集体。     

Signatures of Divergence and Self-Organization in Soils and Weathering Profiles

Complex system behaviors such as self-organization are difficult to address in geology. System evolution often cannot be directly observed and, in geology models and theory, must be reconciled with field evidence. However, self-organization can be addressed within the historical-interpretive paradigm by applying a measure of the degree of self-organization of geologic features, using standard interpretive methods to determine the nature of changes, and determining whether those changes result in an increase or decrease in organization. In this way, stable non-self-organizing convergent development can be distinguished from unstable chaotic self-organizing divergent development. Kolmogorov entropy (K-entropy) was used as a measure of the self-organization of soil profiles in eastern North Carolina. In general, the profiles are low in K-entropy, indicating a generally high level of predictability and information in the vertical arrangement of pedogenetic horizons. As a broad generality, the study profiles appear to be decreasing in entropy if or when surface erosion is minimal and increasing in entropy otherwise. However, results show that whether the profiles demonstrate evidence of convergent or divergent behavior is determined by the relative rates or magnitudes of three main processes: (1) horizon differentiation in surficial horizons by the formation of transitional AE or A&E horizons due to secondary podzolization, (2) thickening of the solum at the weathering front, and (3) surface erosion. There is no direct relationship between the degree of pedogenic development and self-organization. The results suggest that complex system behaviors are controlled by, and can be linked to, specific pedologic and geomorphic processes and that soils and regoliths may be characterized by both convergent and divergent developmental pathways.     

Signature of Himalayan orogenic features in Brahmaputra River sediments,Bangladesh: Evidence from single-grain heavy mineral chemistry

The present study describes results obtained from the chemistry of detrital heavy minerals i.e. pyroxene, amphibole, biotite, garnet, epidote and Fe-Ti oxides in fluvial sediments of the northern Brahmaputra River (Bangladesh) with an aim to determine conditions of their petrogenesis and provenance. The primary and secondary genera of ferromagnesian minerals occurred in calc-alkaline and peraluminous subduction zone. In which, the garnets are Fe-rich, indicating mostly almandine component (Alm₆₅–Pyp₁₆–Grs₈–Sps₆ averagely), occurred in medium to high grade metasedimentary rocks in the Lesser Himalaya (LH), along the Main Central Thrust (MCT) and the eastern Himalayan syntaxis. Besides, the fingerprint of omphacite and actinolite owe to ascertain the co-existence of garnet developed in ultrahigh-pressure (UHP) eclogites that may also be drained from the Tso Morari massif. Augite to aegirine-augite pyroxenes emphasizes Fe enrichment in basaltic systems and high to ultrahigh grade metamorphic rocks, which are exposed in the LH, Shillong Plateau, Mikir Hills, South Tibetan Detachment System (STDS), eastern Himalayan syntaxis and Tso Morari massif. Geochemistry and thermobarometry of the primary magmatic amphiboles and biotites manifest the source of granitoid and granodiorite like bodies, and their windows are exposed in the Bomi–Chayu, Gangdese arcs and the western Arunachal Himalaya. Again, metamorphosed Fe-Ti oxide minerals are well-exposed along the NE Lesser Himalaya, where magmatic derivative of Fe-Ti oxide minerals were modified through the diffusional processes in low-grade metamorphism (534–562 °C with 10^–22.1–10^?21.5 fo₂). Integrating the aforementioned discussion with the thermochronology, it is evident that the eastern Himalayan syntaxis is the major source of sediment flux, which is carried mostly by the upper Himalayan tributaries i.e. Yigong, Parlung, Dibang and Lohit. Also, the lower Himalayan tributaries i.e. Subansiri and Manas drain the sequestered derivatives dominantly from the Arunachal Himalayan. Tso Morari eclogites (NW Himalaya) have also contribution somewhat of dense minerals to the Tsangpo-Brahmaputra River system. Thus, scrutinizing the fingerprint of single-grain detrital minerals provides key information regarding the source terrains and tectonics of the Himalayan sequences.     

Collapse,Connectivity, and Galaxy Populations in Supercluster Cocoons: the Case of A2142

Astronomy Reports - The largest galaxy systems in the cosmic web are superclusters, overdensity regions of galaxies, groups, clusters, and filaments. Low-density regions around superclusters are...     

大气廓线物理反演的最优化方法进展

从最优化数学理论角度对大气廓线物理反演以及卫星辐射率资料直接同化中的最优化算法进行了回顾。分析了各种方法的优点和缺点、联系和差别。总结了卫星大气遥感反演问题的求解思路。对大气廓线反演研究中几种主要的目标函数和寻优策略进行了分析,着重分析了目前作为各数值预报中心和卫星数据处理中心业务数值产品核心算法的牛顿非线性迭代法的不足之处,并对其改进途径进行了探讨。引入了Levenberg-Marquardt方法及信赖域方法用于大气廓线反演,使反演算法的收敛性质得到改善。     

北京地区典型土壤剖面分子标志物分布特征

对北京地区具代表性的环境功能区土壤剖面中的藿烷、甾烷、芳香甾烷类分子标志物含量及组成变化进行了分析。在10个土壤剖面中都检测到了不同浓度的藿烷与甾烷系列化合物,其中水稻田（B9）和城区绿地（B7）这些化合物的含量最高,在农田（B6、B9）和城区绿地（B7）表层土壤中还检测到了少量的三芳甾烷。土壤剖面中藿烷和甾烷含量随深度的增大而降低,在表层30 cm深度范围内的变化较大,30 cm以下其含量波动甚微,但不同深度土层中藿烷和甾烷化合物的指纹特征相近。表明表层土壤均不同程度受到了化石燃料及其衍生物的影响,并且土壤剖面不同深度土壤中藿烷和甾烷具有相关性,受石油类燃烧污染源的影响较大,煤燃烧污染影响的比重相对较小,而且深部土壤的藿烷与甾烷主要来源于表层土壤。     

海上地震勘探GI枪子波数值模拟

GI枪震源已经逐步成为海上地震勘探的主要激发方式。常规气枪只有一个腔室,而GI枪具有G腔和I腔2个腔室,能够较好地压制气泡振荡。基于自由气泡振动理论,分析GI枪的激发机制,在考虑气泡壁的热传导作用和流体粘度对气泡振动影响的基础上,建立了海上勘探GI枪子波数值模型,并对气泡的振动过程和远场地震子波进行了数值模拟。结果表明:当G腔内气体释放所形成的气泡体积达到最大时,I腔内气体的释放有效地抑制了气泡的收缩,气泡壁运动速度明显减小,气泡变得稳定;GI枪激发所产生的子波具有明显的峰值和较小的旁瓣,有利于高分辨率海上地震勘探。     

Life Recovery of 1995 Kobe Earthquake Survivors in Nishinomiya City: A Total-Quality-Management-Based Assessment of Disadvantaged Populations

The main objectives of this study were (1) to examine what has beenrecovered and what has not yet been recovered in Nishinomiya City five years after the GreatHanshin-Awaji Earthquake, and (2) to find current service needs for the earthquake survivors,especially for the disadvantaged populations. Disadvantaged populations are minorities in society, andtheir needs and opinions are often ignored and not reflected in the services or mitigation policy,despite the fact that they are the ones who are affected most by various hazards. At the same time, becauseof their unique characteristics and positions in society, their needs differ from the majorityof the society. Six hundred eighty-six opinion cards were collected in nine grassroots workshopsessions with various disadvantaged groups in Nishinomiya City, such as the physically challenged,the visually impaired, the elderly living in public housing, junior and senior high school students,mothers with small children, and those who lost their own homes because of the earthquake. Theseopinion cards were sorted out and analyzed by using a TQM(Total Quality Management)-basedassessment method. Since the TQM-based assessment method allows bottom-up integration ofopinions from each individual, it helps us identify unique needs of the disadvantaged groupsand reflect their opinions in mitigation plan and policies. The main findings of this study include (1)the city redevelopment cannot be achieved without integrating the viewpoints of thedisadvantaged; (2) the social support was a key resource for both mental health and community development;and (3) disaster experiences and adaptation produced civic mindedness among people in a community.