Appraisal of storm beach buffer width for cyclonic waves     

F.-C. Lee  John R.-C. Hsu  W.-H. Lin 《Coastal Engineering》2011

The loss of beach sand from berm and dune due to high waves and surge is a universal phenomenon associated with sporadic storm activities. To protect the development in a coastal hazard zone, hard structures or coastal setback have been established in many countries around the world. In this paper, the requirement of a storm beach buffer, being a lesser extent landward comparing with the coastal setback to ensure the safety of infrastructures, is numerically assessed using the SBEACH model for three categories of wave conditions in terms of storm return period, median sand grain size, berm width, and design water level. Two of the key outputs from the numerical calculations, berm retreat and bar formation offshore, are then analysed, as well as beach profile change. After having performed a series of numerical studies on selected large wave tank (LWT) test results with monochromatic waves using SBEACH, we may conclude that: (1) Berm erosion increases and submerged bar develops further offshore as the storm return period increases for beach with a specific sand grain size, or as the sand grain reduces on a beach under the action of identical wave condition; (2) Higher storm waves yield a large bar to form quicker and subsequently cause wave breaking on the bar crest, which can reduce the wave energy and limit the extent of the eroding berm; (3) A larger buffer width is required for a beach comprising small sand grain, in order to effectively absorb storm wave energy; and (4) Empirical relationships can be tentatively proposed to estimate the storm beach buffer width, from the input of wave conditions and sediment grain size. These results would benefit a beach nourishment project for shore protection or design of a recreational beach.  相似文献   

不同饵料对真蛸亲体产罗同量、受精卵孵化率及初孵幼体大小的影响     

刘兆胜  刘永胜  郑小东  曲海波 《海洋科学》2011,35(10):81-85

分别采用文蛤（Meretrix meretrix）、菲律宾蛤仔（Ruditapes philippinarum）、缢蛏（Sinonovacula constrzcta）、许氏平鲌（Sebastodes fuscescens）投喂处于产卵、护卵期的真蛸（Octopus vulgaris）亲体,通过测量亲蛸摄食量、产卵量、...  相似文献   

西畴县近48年来降水及气温小波分析     

刘云生  黄国平  王顺江 《云南地理环境研究》2011,23(2):90-92

利用连续小波分析1962～2009年西畴县年降水量和年平均气温序列的小波变化特征,揭示了西畴县降水量与平均气温存在多时间尺度的周期变化特征。其中降水有2个明显的特征时间尺度,分别是4年和8年,平均气温存在以准2～4年为周期的周期振荡。此外,也可以看出近48年来,平均气温存在明显升高的趋势,降水也有减少的趋势,为掌握西畴县的气候变化规律及今后的气象预报服务工作提供了一定的参考价值。  相似文献   

Kinematics and geochronology of multistage ductile deformation along the eastern Alxa block,NW China: New constraints on the relationship between the North China Plate and the Alxa block     

《Journal of Structural Geology》2013

The NE-trending Bayanwula Shan–Lang Shan is an important tectonic belt lying between the North China Plate (NCP) to the east and the Alxa block to the west. An understanding of its nature and the timing of deformation are essential to understand the relationship between the NCP and the Alxa block. Two phases of ductile deformation have been observed in this belt. Large-scale top-to-the-west ductile thrusting characterized the early deformation in the Bayanwula Shan–Lang Shan. Nearly east–west trending quartz stretching lineations and lineations formed by amphibole and biotite are well developed. Different types of sheath and oblique folds with east–west trending fold hinges are also developed in the region. The shear strain of this ductile thrust is up to 17. The ductile deformation may have resulted from the top-to-the-west thrusting of the northern part of the NCP over the Alxa block, and may have occurred ca. 351 Ma (biotite ⁴⁰Ar/³⁹Ar age). Later ductile deformation was expressed as NE-trending sinistral shear along the entire Bayanwula Shan–Lang Shan and likely occurred ca. 250 Ma (biotite and muscovite ⁴⁰Ar/³⁹Ar ages); this shear may have resulted from the collision between the Yangtze and North China plates to the south during the Triassic. Combined with recently obtained detrital zircon U–Pb ages for the area, the ductile deformation events in the eastern Alxa block indicate that the block may not have been part of the NCP, at least before the end of the Devonian. Both blocks were located in the Paleo-Asian Ocean during the Paleozoic and collided or amalgamated with each other at the end of the Devonian.  相似文献   

Floral biodiversity and geology of the Talcher Basin,Orissa, India during the Permian–Triassic interval     

Shreerup Goswami  Kamal Jeet Singh 《Geological Journal》2013,48(1):39-56

The review paper provides an updated account of the previous and recently published records concerning the palaeobiology and the geology of the Talcher Basin of Orissa State, India. We conclude that fossil floral species in this basin originated in the earliest Permian Talchir Formation and evolved and diversified through the Karharbari Fm., Barakar Fm., Barren Measures Fm. and the uppermost Kamthi Fm. (Late Permian–Triassic). The megaflora and the palynology of the different formations of the basin are also discussed briefly. The geological setting of the basin along with the status of different formations (especially the Kamthi Formation) has been redefined. The post‐Barakar Fm. rocks, earlier retained in the Raniganj/Kamthi, Panchet and Mahadeva formations in this basin, have been critically assessed and redefined as the Lower and Upper Kamthi formations of Late Permian and Triassic ages, respectively. Accordingly, the geological map of the basin has been modified. Permian deposits (particularly the Barakar and the lower Kamthi formations) not only have the best preserved flora but also possess the highest diversity, whereas the upper Kamthi Triassic sediments have a meagre number of taxa. The plant diversity of the basin has been discussed in detail to interpret the development of the flora, evolutionary trends and palaeoenvironments of the basin. The patchy Gangamopteris vegetation of the Talchir glacial phase has ultimately evolved and diversified through time (Karharbari Fm. to Lower Kamthi Fm.) and gave rise to the thick dense swampy forests consisting of large Glossopteris trees and other shade‐loving under‐storied pteridophytes. Several groups of plants including spores and pollen have disappeared in a ladder pattern during the Permian–Triassic interval (Lower Kamthi–Upper Kamthi Fm.) and, similarly, in steps, many new fore‐runners appeared in the Upper Kamthi Formation. Records of marine acritarchs and ichnofossils in this basin at various Permian–Triassic levels demonstrate that there were marine influences. These features suggest a paralic (coastal marine to deltaic) mode of origin of the coal beds and associated sediments in the basin. The present study also advocates the continued survival of plants, rather than a mass extinction near the vicinity of the Permian–Triassic (P–T) boundary in this basin. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

川东北地区三叠系飞仙关组白云化流体的Ca/Mg比定量估算     

胡作维  黄思静  李志明  郇金来  张文涛  梁瑞 《地质学报》2013,87(1):110-118

作为川东北地区三叠系飞仙关组天然气气藏最重要储集岩的粒屑白云岩和结晶白云岩的成因始终是沉积和石油地质学家高度关注的研究热点之一.在总结川东北地区三叠系飞仙关组不同类型白云岩形成温度的基础上,通过已有的白云化流体Ca/Mg值和温度之间关系式获得了川东北地区三叠系飞仙关组白云化流体的Ca/Mg值的主要分布范围.结果表明:不同类型白云岩对应的白云化流体具有不同的Ca/Mg值,同时证实了三叠纪海水或与之有关的海源流体、三叠纪海水与大气淡水混合流体的Ca/Mg值都符合在40～130℃区间、甚至更高温度下白云化(白云石沉淀)作用的要求,微晶白云岩和具原始结构的粒屑白云岩可能与地表—近地表的低温、小Ca/Mg值混合流体中相对快速的白云石沉淀作用有关,并形成了相对细的他形白云石;结晶白云岩(包括结构类似的过渡岩石类型、白云石胶结物)可能与埋藏的高温、大Ca/Mg值三叠纪海水或与之有关的海源流体中相对缓慢的白云石沉淀作用有关,并形成了相对粗的自形白云石.白云化流体的Ca/Mg值估算,可望为川东北地区三叠系飞仙关组优质储层白云岩的成因研究提供一些有价值的基础资料.  相似文献   

Amenity migration to the global south: Implications for community development     

《Geoforum》2013

Despite a growing trend of migration to countries in the global South fueled by their natural amenities (i.e., natural amenity migration), research on this topic has predominantly been conducted in the global North. This is problematic given the notable socioeconomic, attitudinal, and behavioral differences between amenity migrants (often urbanites from developed countries) and local people (often rural residents of developing countries). Grounded in community field theory, this study begins to fill this gap in the literature by increasing our understanding of the ways in which local residents and amenity migrants interact in the amenity-rich community of Nuevo Arenal, Costa Rica. We found that linguistic, cultural, and spatial barriers (real and perceived) created a social climate in which the interaction between local residents and amenity migrants was primarily based on mundane interactions and did not lead to social integration. This proved to be a hindrance to the creation of the community field, which led to a lack of joint planning and participation in activities and projects that sought to improve the overall living conditions in the community. Explanations of these findings and the implications of such a divide are offered.  相似文献   

The geology of Ewarara Intrusion,Giles Complex,Central Australia     

A. D. T. Goode  G. W. Krieg 《Australian Journal of Earth Sciences》2013,60(2):185-194

Ewarara is a small layered ultramafic intrusion which forms part of the Giles Complex. The flat‐lying body displays both sub‐horizontal and vertical layering, which appear to have different origins. Petrographically the intrusion consists of a lower olivine bronzitite unit and an upper pyroxenite unit. These display a small cryptic variation with the upper layer being the more iron‐rich. Many of the primary igneous textures have been destroyed by deformational effects but the intrusion retains many features of a body formed by gravity accumulation of crystals precipitating from a magma. Crystallisation of the magma is believed to have occurred near the base of the crust.  相似文献   

川西北中二叠统栖霞组白云岩储层特征及控制因素          下载免费PDF全文

郝毅  周进高  张建勇  倪超  谷明峰  辛勇光 《沉积与特提斯地质》2013,33(1):68-74

本文以四川盆地西北部钻井岩心及露头剖面样品的镜下岩石学特征为基础,以微区多参数实验分析数据为依据,对四川盆地西北部中二叠统栖霞组白云岩储层进行了研究。认为栖霞组白云岩储层类型主要为结晶型白云岩及残余颗粒型白云岩。储集空间主要为晶间孔、晶间溶孔、粒间孔、溶蚀孔洞以及裂缝。白云岩储层的发育主要受到沉积微相、早期白云石化作用、晚期白云石化作用、溶蚀作用以及构造作用等因素控制。其中浅滩沉积微相是储层形成的环境基础;早期白云石化作用是储层保存的重要条件;溶蚀作用及构造裂缝是储层改善的关键因素;而晚期白云石的生成则对储集空间有一定的破坏作用。  相似文献   

Late Triassic volcanic activity in South-East Asia: New stratigraphical,geochronological and paleontological evidence from the Luang Prabang Basin (Laos)     

《Journal of Asian Earth Sciences》2013

In South-East Asia, sedimentary basins displaying continental Permian and Triassic deposits have been poorly studied. Among these, the Luang Prabang Basin (North Laos) represents a potential key target to constrain the stratigraphic and structural evolutions of South-East Asia. A combined approach involving sedimentology, palaeontology, geochronology and structural analysis, was thus implemented to study the basin. It resulted in a new geological map, in defining new formations, and in proposing a complete revision of the Late Permian to Triassic stratigraphic succession as well as of the structural organization of the basin. Radiometric ages are used to discuss the synchronism of volcanic activity and sedimentation.The Luang Prabang Basin consists of an asymmetric NE-SW syncline with NE-SW thrusts, located at the contact between Late Permian and Late Triassic deposits. The potential stratigraphic gap at the Permian–Triassic boundary is therefore masked by deformation in the basin. The Late Triassic volcaniclastic continental deposits are representative of alluvial plain and fluvial environments. The basin was fed by several sources, varying from volcanic, carbonated to silicic (non-volcanic). U–Pb dating of euhedral zircon grains provided maximum sedimentation ages. The stratigraphic vertical succession of these ages, from ca. 225, ca. 220 to ca. 216 Ma, indicates that a long lasting volcanism was active during sedimentation and illustrates significant variations in sediment preservation rates in continental environments (from ∼100 m/Ma to ∼3 m/Ma). Anhedral inherited zircon grains gave older ages. A large number of them, at ca. 1870 Ma, imply the reworking of a Proterozoic basement and/or of sediments containing fragments of such a basement. In addition, the Late Triassic (Carnian to Norian) sediments yielded to a new dicynodont skull, attributed to the Kannemeyeriiform group family, from layers dated in between ∼225 and ∼221 Ma (Carnian).  相似文献