Crack-filling clays and weathered cracks in the DPRI 1800 m core near the Nojima Fault, Japan: Evidence for deep surface-water circulation near an active fault     

Shin-Ichi Uda  Aiming Lin  Keiji Takemura 《Island Arc》2001,10(3-4):439-446

Abstract Crack-filling clays and weathered cracks were observed in the Disaster Prevention Research Institute, Kyoto University (DPRI) 1800 m cores drilled from the Nojima Fault Zone, which was activated during the 1995 Hyogo-ken Nanbu earthquake (Kobe earthquake). The crack-filling clays consist mainly of unconsolidated fine-grained materials that fill opening cracks with no shear textures. Most of the cracks observed in the DPRI 1800 m cores are yellow-brown to brown in color due to weathering. Powder X-ray diffraction analyses show that the crack-filling clays are composed mainly of clay minerals and carbonates such as siderite and calcite. Given that the top of the borehole is approximately 45 m above sea level, most of the core is far below the stable groundwater table. Hence, it is suggested that the crack-filling clays and weathered cracks in the cores taken at depths of 1800 m were formed by the flow of surface water down to the deep fractured zone of the Nojima Fault Zone during seismic faulting.  相似文献   

Storm deposits and storm-generated coarse carbonate breccias on a pelagic outer shelf (South-East Basin, France)   总被引：2，自引：0，他引：2  

Michel Seguret  Alexis Moussine-Pouchkine  Guilherme Raja Gabaglia  & Frederic Bouchette 《Sedimentology》2001,48(2):231-254

Uppermost Jurassic limestones of the South‐East Basin (France) are organized into four facies associations that were deposited in four distinct zones: (1) peritidal lagoonal limestones; (2) bioclastic and reefal limestones; (3) pelagic lime mudstones; (4) lime mudstones/calcarenites/coarse breccias. Calcarenite deposits of zone 4 exhibit sedimentary structures that are diagnostic of deposition under wave‐induced combined flow. In subzone 4a, both vertical and lateral transitions from lime mudstone/calcarenite to breccia indicate in situ brecciation under wave‐cyclic loading. Breccias were produced by heterogeneous liquefaction of material previously deposited on the sea floor. Deposits in subzone 4a record relatively long periods (>400 kyr) of sedimentation below wave base, alternating with periods of deposition under wave‐induced currents and periods of in situ deformation. In this zone, storm waves were attenuated by wave–sediment interaction, and wave energy was absorbed by the deformation of soft sediment. With reference to present‐day wave attenuation, water depths in this zone ranged between 50 and 80 m. Landwards of the attenuation zone, in zone 3, storm waves were reduced to fair‐weather wave heights. Storm wave base was not horizontal and became shallower landwards. As a consequence, water depth and wave energy were not linearly related. On a small area of the seaward edge of subzone 4a, cobbles were removed by traction currents and redeposited in subzone 4b. There, they formed a 100‐m‐thick wedge, which prograded over 3 km and was built up by the stacking of 5‐ to 20‐m‐thick cross‐stratified sets of coarse breccia. This wedge records the transport and redeposition of cobbles by a high‐velocity unidirectional component of a combined flow. The increase in flow velocity in a restricted area is proposed to result from flow concentration in a channel‐like structure of the downwelling in the gulf formed by the basin. In more distal subzone 4c, the hydrodynamic effect of wave‐induced currents was quasi‐permanent, and brecciation by wave–sediment interaction occurred only episodically. This indicates that, seawards of the attenuation zone, hydrodynamic storm wave base was deeper than mechanical storm wave base. Uppermost Jurassic carbonates were deposited and soft‐sediment deformed on a hurricane‐dominated ramp of very gentle slope and characterized by a zone of storm wave degeneration, located seawards of a zone of sedimentation below wave base.  相似文献   

Long-distance correlation between tectonic-controlled, isolated carbonate platforms by cyclostratigraphy and sequence stratigraphy in the Devonian of South China   总被引：5，自引：1，他引：5  

Daizhao Chen  Maurice E. Tucker  Maosheng Jiang  & Jingquan Zhu 《Sedimentology》2001,48(1):57-78

During the early Middle Devonian in South China, an extensive carbonate platform was broken up through extension to create a complex pattern of platforms, and interplatform basins. In Givetian and Frasnian carbonate successions, five depositional facies, including peritidal, restricted shallow subtidal, semi‐restricted subtidal, intermediate subtidal and deep subtidal facies, and 18 lithofacies units are recognized from measured sections on three isolated platforms. These deposits are arranged into metre‐scale, upward‐shallowing peritidal and subtidal cycles. Nine third‐order sequences are identified from changes in cycle stacking patterns, vertical facies changes and the stratigraphic distribution of subaerial exposure indicators. These sequences mostly consist of a lower transgressive part and an upper regressive part. Transgressive packages are dominated by thicker‐than‐average subtidal cycles, and regressive packages by thinner‐than‐average peritidal cycles. Sequence boundaries are transitional zones composed of stacked, high‐frequency, thinner‐than‐average cycles with upward‐increasing intensity of subaerial exposure, rather than individual, laterally traceable surfaces. These sequences can be further grouped into catch‐up and keep‐up sequence sets from the long‐term (second‐order) changes in accommodation and vertical facies changes. Catch‐up sequences are characterized by relatively thick cycle packages with a high percentage of intermediate to shallow subtidal facies, and even deep subtidal facies locally within some individual sequences, recording long‐term accommodation gain. Keep‐up sequences are characterized by relatively thin cycle packages with a high percentage of peritidal facies within sequences, recording long‐term accommodation loss. Correlation of long‐term accommodation changes expressed by Fischer plots reveals that during the late Givetian to early Frasnian increased accommodation loss on platforms coincided with increased accommodation gain in interplatform basins. This suggests that movement on faults resulted in the relative uplift of platforms and subsidence of interplatform basins. In the early Frasnian, extensive siliceous deposits in most interplatform basins and megabreccias at basin margins correspond to exposure disconformities on platforms.  相似文献   

Cyclic strength and deformation of crushable carbonate sand     

Masayuki Hyodo  Noritaka Aramaki  Masayuki Itoh  Adrian F.L. Hyde 《Soil Dynamics and Earthquake Engineering》1996,15(5):331-336

Cyclic triaxial tests have been carried out on a skeletal carbonate sand from the west coast of Eire. Results are presented for undrained cyclic shear tests on samples with 80% of relative density consolidated under both isotropic and anisotropic conditions. Failure was defined as a 5% double amplitude cyclic strain and a 5% peak axial strain for stress-reversal and non-reversal stress conditions, respectively. Using this definition the cyclic strength for isotropically consolidated samples was affected by the confining pressure although the angular platey nature of the sand resulted in higher cyclic strengths than for a comparable silica sand. For anisotropically consolidated samples the cyclic strength increased with increasing initial static shear stress while on the other hand the cyclic strength normalised in the usual way with respect to the initial confining pressure decreased as this pressure increased.  相似文献   

碳酸盐矿物的阴极发光性与其Fe,Mn含量的关系   总被引：40，自引：2，他引：40  

黄思静 《矿物岩石》1992,12(4):74-79

根据不同地区和时代84件碳酸盐样品的阴极发光和Fe,Mn元素分析,在本次研究使用的仪器和实验条件下,方解石和白云石的阴极发光性与其Fe,Mn含量之间存在如下关系:Mn<40μg/g(ppm)时,其阴极发光性主要受Mn的绝对含量控制,当Mn<20μg/g时,不具阴极发光;Fe>5000μg/g时,其阴极发光性与Fe的绝对含关系更为密切,当Fe>10000μg/g时,不具阴极发光;Mn>40μg/g,Fe<5000μg/g时,其阴极发光性受Fe/Mn比值的显著控制,此时当Fe/Mn<7时,具强的阴极发光,30>Fe/Mn>7时,具中等强度的阴极发光,Fe/Mn>30时,具弱的阴极发光。两个热液碳酸岩中单晶白云石样品的阴极发光性和稀土元素含量间的关系说明,碳酸盐矿物的阴极发光性可能还与某些稀土元素的存在有关,它们可能是某些样品具低激活电压和长发光余辉的原因。  相似文献   

泥盆纪海相碳酸盐岩碳同位素组成及演变   总被引：4，自引：0，他引：4       下载免费PDF全文

陈代钊  陈其英  江茂生 《沉积与特提斯地质》1995,(5):22-28

根据对六景泥盆系碳酸盐岩碳同位素组成的系统分析表明：从落霍柯夫期到布拉格期海洋中的δ~１３Ｃ是逐渐变重，埃姆斯期明显变轻．艾菲尔期又开始变重，特别是基维特期有较明显的正向偏移，并继续向上变重，至弗拉斯期与法门期之交达到最大，尔后逐渐变轻，反映了泥盆纪海洋碳同位素组成的演变趋势．这和泥盆纪（二级）海平面的变化趋势是基本一致的，反映海洋碳同位素组成与海平面变化及相关的气候和海洋、大气中ＣＯ_２含量的成因联系。弗拉斯阶－法门阶界线附近δ~１３Ｃ的变化型式表明其间发生的生物绝灭事件是海平面升降和缺氧环境的周期性扩展等因素的累积效应的结果．  相似文献   

碳酸盐岩米级旋回层序的成因类型及形成机制   总被引：3，自引：1，他引：3       下载免费PDF全文

梅冥相 《沉积与特提斯地质》1993,(6):34-43

在前人研究及自己野外观察的基础上,本文把碳酸盐岩米级旋回层序归为四大类:深水非对称米级旋回层序、L-M米级旋回层序、潮下碳酸盐米级旋回层序、潮坪碳酸盐米级旋回层序。米级旋回层序的形成机制是与米兰柯维奇旋回有关的高频率海平面振荡变化旋回所形成的间断-加积旋回沉积作用,它们的识别标志主要是岩石类型、界面特征、产出环境等。碳酸盐岩米级旋回层序的规则的垂直叠加形式是识别三级旋回层序的基础。  相似文献   

Cretaceous stratigraphy and palaeoenvironments of the Southern Petén Basin, Guatemala     

Eric Fourcade  Luis Piccioni  Jos Escrib  Eduardo Rosselo 《Cretaceous Research》1999,20(6):793

The Cretaceous deposits of the Southern Petén Basin, an oil-producing province, are located to the south of the Yucatan Platform and to the east of the Chiapas Carbonate Platform of Mexico. The succession in the southern part of this basin has been studied both in wells and at outcrop by microfacies analysis. It is composed of 5000 m of shallow marine carbonates and evaporites with a few thin layers of pelagic limestones rich in organic carbon and planktic foraminifera deposited during peak transgressions or maximum flooding. The sedimentation of this thick succession was not continuous, and the section is punctuated by subaerial erosional bounding surfaces and a single hardground which marks the final drowning of the carbonate platform during the late Maastrichtian. New age determinations have been obtained on the basis of planktic and benthic foraminifera from the Aptian to Santonian Cobán Formation, D, C, B and A Members. Cobán C (Albian) and B (Cenomanian) Members are the present oil reservoirs. The rudist and alveolinid limestones of late Campanian and Maastrichtian age referred to the Campur Formation in the Southern Petén Basin are here reassigned to the Angostura Formation, as recognized in the Chiapas area. The Actela Formation is defined here to encompass the limestone breccia deposits that occur at the Cretaceous–Tertiary boundary and extend into the Parvularugoglobigerina eugubina Zone of early Danian age. The D, C, B and A Members of the Cobán Formation and the Angostura Formation represent second order transgressive and regressive trends in a passive margin area where the deposits indicate a succession of various environments, including fluviatile, salinas, shallow marine carbonate platform, outer shelf and intrashelf basin. High subsidence rates, sea-level changes and tectonic uplift controlled the sedimentation.

Abstract

Les formations crétacées du sud-est du Bassin du Petén, région pétrolière du nord du Guatemala, sont situées au Sud du Yucatan et à l'Est du Chiapas au Mexique. Ces sédiments ont été étudiés à la fois dans deux puits et à l'affleurement par l'analyse des microfaciès. Cet ensemble sédimentaire est composé de 5000 m de carbonates de plate-forme de faible profondeur et d'évaporites, dans lesquels s'intercalent de minces couches de calcaires pélagiques riches en matière organique et en foraminifères planctoniques. Ces calcaires pélagiques se sont déposés lors des maximums de transgressions. La sédimentation de cette épaisse série n'est pas continue et est ponctuée par quelques surfaces d'érosion sub-aérienne et une surface durcie qui souligne l'ennoyage définitif de la plate-forme carbonatée au Maastrichtien terminal. De nouvelles datations ont été obtenues sur la formation Cobán et ses membres D, C, B et A qui s'étagent de l'Aptien au Santonien. Les membres C (albien) et B (cénomanien) constituent les réservoirs productifs. Les calcaires à rudistes et à alveolinidés du Campanien supérieur–Maastrichtien ont été appelés à tort au Petén formation Campur. Ils doivent, selon nous, être attribués à la formation Angostura comme au Chiapas voisin, où affleurent des faciès comparables et de même âge. Une nouvelle formation est créée (formation Actela) pour les brèches calcaires de la limite Crétacé–Tertiaire et de la Zone à Eugubina du Danien inférieur. Les membres D, C, B, A de la formation Cobán et la formation Angostura représentent des cycles transgressifs–régressifs de deuxième ordre. Sur cette marge passive du Petén, les dépôts correspondent à des environnements variés comme des terres émergées soumises à une altération karstique et à des dépôts fluviatiles, des salinas, des plates-formes carbonatées marines, des shelf externes et des bassins intra plate-forme. La sédimentation a été, ici, contrôlée par une forte vitesse de subsidence, les variations du niveau marin et des soulèvements tectoniques.  相似文献   

长庆气田奥陶系风化壳气藏、气源研究   总被引：22，自引：4，他引：18  

戴金星  夏新宇 《地学前缘》1999,6(Z1):195-203

对10年来长庆气田奥陶系风化充气藏气源问题存在的不同观点（上古生界煤成气和奥陶系海相碳酸盐岩气何者为主）及相应的证据进行了总结和讨论,认为“奥陶系自生自储为主”的观点对地质和地球化学现象的解释存在疑问,包括用次要组分来判别混源天然气的主要来源,用不确切的端员气地球化学特征来计算混源比,对本溪组底部岩石的封盖性和下奥陶统碳酸盐岩的原始生烃潜力评价偏高,忽略了石炭系存在能够生成油型气的海相源岩。因此,长庆气田不能作为海相贫有机质的碳酸盐岩生成的大、中型油气田的实例。根据天然气及气源岩的地球化学特征,提出长庆气田奥陶系风化壳气藏气是以上古生界煤成气为主、石炭系海相源岩生成的油型气为辅的混合气。  相似文献   

Effects of groundwater flow on mineral diagenesis, with emphasis on carbonate aquifers     

Hans G. Machel 《Hydrogeology Journal》1999,7(1):94-107

 This article provides a critical synopsis of the effects of groundwater flow on mineral diagenesis. Emphasis is placed on those aspects and processes that change porosity and permeability in carbonate aquifers, because they are of particular importance to human societies as sources of supplies of water for human consumption (drinking, irrigation) and of crude oil and natural gas. Diagenetic settings in carbonates as well as clastics are generally ill defined. This paper proposes a new comprehensive classification of diagenetic settings into near-surface, shallow-, intermediate-, and deep-burial diagenetic settings; hydrocarbon-contaminated plumes; and fractures. These settings are defined on the basis of mineralogy, petroleum, hydrogeochemistry, and hydrogeology. This classification is applicable to all sedimentary basins. Diagenesis is governed by various intrinsic and extrinsic factors that include thermodynamic and kinetic constraints, as well as microstructural factors that may override the others. These factors govern diagenetic processes, such as dissolution, compaction, recrystallization, replacement, and sulfate–hydrocarbon redox-reactions. Processes such as cementation, dissolution, and dolomitization require significant flow of groundwater driven by an externally imposed hydraulic gradient. Other processes, such as stylolitization and thermochemical sulfate reduction, commonly take place without significant groundwater flow in hydrologically nearly or completely stagnant systems that are geochemically "closed." Two major effects of groundwater flow on mineral diagenesis are enhancement and reduction of porosity and permeability, although groundwater flow can also leave these rock properties essentially unchanged. In extreme cases, an aquifer or hydrocarbon reservoir rock can have highly enhanced porosity and permeability due to extensive mineral dissolution, or it can be plugged up due to extensive mineral precipitation. Received, April 1998 · Revised, July 1998 · Accepted, September 1998  相似文献