Mesozoic transtensional basin history of the Eastern Cordillera, Colombian Andes: Inferences from tectonic models     

L.F. Sarmiento-Rojas  J.D. Van Wess  S. Cloetingh 《Journal of South American Earth Sciences》2006,21(4):383

Backstripping analysis and forward modeling of 162 stratigraphic columns and wells of the Eastern Cordillera (EC), Llanos, and Magdalena Valley shows the Mesozoic Colombian Basin is marked by five lithosphere stretching pulses. Three stretching events are suggested during the Triassic–Jurassic, but additional biostratigraphical data are needed to identify them precisely. The spatial distribution of lithosphere stretching values suggests that small, narrow (<150 km), asymmetric graben basins were located on opposite sides of the paleo-Magdalena–La Salina fault system, which probably was active as a master transtensional or strike-slip fault system. Paleomagnetic data suggesting a significant (at least 10°) northward translation of terranes west of the Bucaramanga fault during the Early Jurassic, and the similarity between the early Mesozoic stratigraphy and tectonic setting of the Payandé terrane with the Late Permian transtensional rift of the Eastern Cordillera of Peru and Bolivia indicate that the areas were adjacent in early Mesozoic times. New geochronological, petrological, stratigraphic, and structural research is necessary to test this hypothesis, including additional paleomagnetic investigations to determine the paleolatitudinal position of the Central Cordillera and adjacent tectonic terranes during the Triassic–Jurassic. Two stretching events are suggested for the Cretaceous: Berriasian–Hauterivian (144–127 Ma) and Aptian–Albian (121–102 Ma). During the Early Cretaceous, marine facies accumulated on an extensional basin system. Shallow-marine sedimentation ended at the end of the Cretaceous due to the accretion of oceanic terranes of the Western Cordillera. In Berriasian–Hauterivian subsidence curves, isopach maps and paleomagnetic data imply a (>180 km) wide, asymmetrical, transtensional half-rift basin existed, divided by the Santander Floresta horst or high. The location of small mafic intrusions coincides with areas of thin crust (crustal stretching factors >1.4) and maximum stretching of the subcrustal lithosphere. During the Aptian–early Albian, the basin extended toward the south in the Upper Magdalena Valley. Differences between crustal and subcrustal stretching values suggest some lowermost crustal decoupling between the crust and subcrustal lithosphere or that increased thermal thinning affected the mantle lithosphere. Late Cretaceous subsidence was mainly driven by lithospheric cooling, water loading, and horizontal compressional stresses generated by collision of oceanic terranes in western Colombia. Triassic transtensional basins were narrow and increased in width during the Triassic and Jurassic. Cretaceous transtensional basins were wider than Triassic–Jurassic basins. During the Mesozoic, the strike-slip component gradually decreased at the expense of the increase of the extensional component, as suggested by paleomagnetic data and lithosphere stretching values. During the Berriasian–Hauterivian, the eastern side of the extensional basin may have developed by reactivation of an older Paleozoic rift system associated with the Guaicáramo fault system. The western side probably developed through reactivation of an earlier normal fault system developed during Triassic–Jurassic transtension. Alternatively, the eastern and western margins of the graben may have developed along older strike-slip faults, which were the boundaries of the accretion of terranes west of the Guaicáramo fault during the Late Triassic and Jurassic. The increasing width of the graben system likely was the result of progressive tensional reactivation of preexisting upper crustal weakness zones. Lateral changes in Mesozoic sediment thickness suggest the reverse or thrust faults that now define the eastern and western borders of the EC were originally normal faults with a strike-slip component that inverted during the Cenozoic Andean orogeny. Thus, the Guaicáramo, La Salina, Bitúima, Magdalena, and Boyacá originally were transtensional faults. Their oblique orientation relative to the Mesozoic magmatic arc of the Central Cordillera may be the result of oblique slip extension during the Cretaceous or inherited from the pre-Mesozoic structural grains. However, not all Mesozoic transtensional faults were inverted.  相似文献   

Great earthquakes of variable magnitude at the Cascadia subduction zone   总被引：1，自引：0，他引：1  

Alan R. Nelson  Harvey M. Kelsey 《Quaternary Research》2006,65(3):354-365

Comparison of histories of great earthquakes and accompanying tsunamis at eight coastal sites suggests plate-boundary ruptures of varying length, implying great earthquakes of variable magnitude at the Cascadia subduction zone. Inference of rupture length relies on degree of overlap on radiocarbon age ranges for earthquakes and tsunamis, and relative amounts of coseismic subsidence and heights of tsunamis. Written records of a tsunami in Japan provide the most conclusive evidence for rupture of much of the plate boundary during the earthquake of 26 January 1700. Cascadia stratigraphic evidence dating from about 1600 cal yr B.P., similar to that for the 1700 earthquake, implies a similarly long rupture with substantial subsidence and a high tsunami. Correlations are consistent with other long ruptures about 1350 cal yr B.P., 2500 cal yr B.P., 3400 cal yr B.P., 3800 cal yr B.P., 4400 cal yr B.P., and 4900 cal yr B.P. A rupture about 700-1100 cal yr B.P. was limited to the northern and central parts of the subduction zone, and a northern rupture about 2900 cal yr B.P. may have been similarly limited. Times of probable short ruptures in southern Cascadia include about 1100 cal yr B.P., 1700 cal yr B.P., 3200 cal yr B.P., 4200 cal yr B.P., 4600 cal yr B.P., and 4700 cal yr B.P. Rupture patterns suggest that the plate boundary in northern Cascadia usually breaks in long ruptures during the greatest earthquakes. Ruptures in southernmost Cascadia vary in length and recurrence intervals more than ruptures in northern Cascadia.  相似文献   

Investigation of the effect of aggregate shape and surface roughness on the slake durability index using the fractal dimension approach     

Ersin Kolay  Kamil Kayabali   《Engineering Geology》2006,86(4):271-284

Argillaceous rocks cover about one thirds of the earth's surface. The major engineering problems encountered with weak- to medium-strength argillaceous rocks could be slaking, erosion, slope stability, settlement, and reduction in strength. One of the key properties for classifying and determining the behavior of such rocks is the slake durability. The concept of slake durability index (SDI) has been the subject of numerous researches in which a number of factors affecting the numerical value of SDI were investigated. In this regard, this paper approaches the matter by evaluating the effects of overall shape and surface roughness of the testing material on the outcome of slake durability indices.

For the purpose, different types of rocks (marl, clayey limestone, tuff, sandstone, weathered granite) were broken into chunks and were intentionally shaped as angular, subangular, and rounded and tested for slake durability. Before testing the aggregate pieces of each rock type, their surface roughness was determined by using the fractal dimension. Despite the variation of final values of SDI test results (values of I_d), the rounded aggregate groups plot relatively in a narrow range, but a greater scatter was obtained for the angular and subangular aggregate groups. The best results can be obtained when using the well rounded samples having the lowest fractal values. An attempt was made to analytically link the surface roughness with the I_d parameter and an empirical relationship was proposed. A chart for various fractal values of surface roughness to use as a guide for slake durability tests is also proposed. The method proposed herein becomes efficient when well rounded aggregates are not available. In such condition, the approximate fractal value for the surface roughness profile of the testing aggregates could be obtained from the proposed chart and be plugged into the empirical relation to obtain the corrected I_d value. The results presented herein represent the particular rock types used in this study and care should be taken when applying these methods to different type of rocks.  相似文献   

Subsidence due to peat oxidation and impact on drainage infrastructures in a farmland catchment south of the Venice Lagoon   总被引：1，自引：0，他引：1  

G. Gambolati  M. Putti  P. Teatini  G. Gasparetto Stori 《Environmental Geology》2006,49(6):814-820

Large agricultural areas reclaimed in the past century, south of the Venice Lagoon, have experienced significant land subsidence due to oxidation of peat organic soils. This has exposed the region to flood hazard particularly during severe storms and has contributed to increase the marginal management cost of the infrastructures (ditches, levees, pumping stations) designed to operate the drainage system. Direct measurements and indirect evidence from the channel network suggest a land settlement between 1.5 and 2 m over the past 70 years. This paper provides an overview of the problem with important information on its most recent evolution.  相似文献   

Glacial survival of blockfields on the Varanger Peninsula, northern Norway     

Jakob Fjellanger  Leif Srbel  Henriette Linge  Edward J. Brook  Grant M. Raisbeck  Franoise Yiou 《Geomorphology》2006,82(3-4):255-272

For more than hundred years it has been debated whether blockfields in mountain summit areas can be used to delimit the vertical extent of Pleistocene ice sheets. In this study the relationship between blockfields, developed in quartzites and sandstones on the Varanger Peninsula, northern Norway, and glacially derived features have been evaluated. Erratics and circular ablation moraines are superimposed on the blockfields and lateral meltwater channels are eroded into them. Glacial striations and other signs of glacial sculpturing are restricted to low-lying areas with channelled ice flow. Relative ages of the blockfields and the features in them are inferred, and the first measurements of in-situ produced cosmogenic nuclides from the Varanger Peninsula are reported. We conclude that the blockfields have survived underneath at least one thick, cold-based ice sheet. Thus, these blockfields cannot be used as indicators of ice-free conditions as previously suggested for southern Norway. Our results have implications for the potential for land surface preservation beneath ice sheets and for glacial reconstructions in northern Fennoscandia.  相似文献   

The relationship between depth, age and gravity in the oceans   总被引：2，自引：0，他引：2  

A. G. Crosby  D. McKenzie  J. G. Sclater 《Geophysical Journal International》2006,166(2):553-573

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江苏省矿山的主要生态环境问题及治理对策     

徐翠云 《中国地质灾害与防治学报》2006,17(2):160-163

江苏的经济发展较快,对矿产资源的需求量亦大。多年来的无序开采,对生态环境造成很大的破坏和影响,出现了山体植被遭受破坏、土地被占用、环境受污染、诱发地面沉降、地面塌陷等一系列问题,已影响到国民经济的发展。随着省人大和省政府关于限制开山采石和保护环境等政策、法规出台和落实,近几年乱采滥挖现象基本得到了有效的遏制。人们的环保意识得到了加强,不少矿山已逐步开始对环境治理,且初见成效。文章介绍了江苏生态环境现状、存在的主要问题和治理对策,以期引起各级政府和广大民众在对矿产资源开采的同时更要注重环境保护。  相似文献   

Semi-Analytic Modelling of Subsidence   总被引：2，自引：0，他引：2  

Peter A. Fokker  Bogdan Orlic 《Mathematical Geology》2006,38(5):565-589

This paper presents a forward model for subsidence prediction caused by extraction of hydrocarbons. The model uses combinations of analytic solutions to the visco-elastic equations, which approximate the boundary conditions. There are only a few unknown parameters to be estimated, and, consequently, calculations are very fast. The semi-analytic model is applicable to a uniform and layer-cake stratigraphy, with visco-elastic parameters changing per layer, and an arbitrary depletion pattern. By its capabilities to handle a multi-layered visco-elastic subsurface, the semi-analytic model fills the gap between the analytic single-layered elastic models available to date and the more elaborate numerical, e.g. finite element, models.  相似文献   

蒙脱石脱水作用与地面沉降关系的研究展望   总被引：7，自引：0，他引：7  

杨献忠杨祝良  陈敬中胡存礼袁平  魏乃颐 《岩石矿物学杂志》2005,24(6):659-665

粘土矿物在地面沉降中的作用、粘土矿物的脱水作用对地面沉降的影响等日益成为评价和防治地质、工程、水文、环境等问题的关键,也一直是相关领域的研究难题而逐渐引起高度重视。本文回顾了蒙脱石层间水性质、层间水化膨胀和脱水收缩的影响因素,提出蒙脱石层间的固溶体特征,在总结蒙脱石脱水作用与地面沉降关系研究成果的基础上,提出了用蒙脱石脱水作用研究地面沉降的思路。最后讨论了用蒙脱石的脱水作用研究地面滞后沉降及沉降趋势预测的可能性。  相似文献   

南海西南部曾母盆地早中新世以来沉降史分析   总被引：2，自引：2，他引：2       下载免费PDF全文

吴庐山 邱 燕解习农  刘晓峰江 涛 《中国地质》2005,32(3):370-377

采用回剥法和局部均衡模式研究曾母盆地早中新世以来的沉降史，并探讨了该盆地构造演化特征。曾母盆地自早中新世以来经历了17．5-11．6Ma、11．6-5．5Ma、5．5-3．0Ma和3．0-0Ma的4次快速沉降作用，其构造演化受控于曾母地块与南沙地块及婆罗洲地块的碰撞和盆地两侧的万安-卢帕尔断裂与廷贾走滑断裂的综合作用，可划分为南北双向挤压（晚始新世-早中新世）、走滑改造（中中新世-晚中新世）和区域沉降（上新世-第四纪）3个演化阶段。  相似文献