Rates of tafoni weathering on uplifted shore platforms in Nojima-Zaki,Boso Peninsula,Japan     

Yukinori Matsukura  Norikazu Matsuoka 《地球表面变化过程与地形》1991,16(1):51-56

Many tafoni occur on the faces of marine cliffs on three uplifted shore platforms with different altitudes and with known ages of emergence. The mean value of the ten largest depths of tafoni, D (cm), was obtained and the period of their formation, t (years), was estimated. The relationship between the two variables was found to be D = 20·3 × (1?e^?0.005t).  相似文献   

Frost weathering and the saturation of coastal rocks     

A. S. Trenhaile  D. W. Mercan 《地球表面变化过程与地形》1984,9(4):321-331

Measurements were made of the water content in coastal rocks, by simulating tidal oscillations in the laboratory, and by field measurement in eastern Canada. If rapid freezing takes place upon exposure to the air, saturation levels may be high enough to permit frost weathering in fine grained rocks in the lower portions of the intertidal zone. Near the high tidal level, however, it may be dependent upon a supply of water from the ice foot and from melting snow. If freezing is slow, frost action may be inhibited by desorption of the rocks while they are exposed by the ebb tide. There was no evidence of a level of permanent sea water saturation within the intertidal zone. Ambient temperature and humidity may affect the rate of rock desorption.  相似文献   

Simulation of pebble abrasion on coastal benches by transgressive waves     

Gordon E. Bigelow 《地球表面变化过程与地形》1984,9(4):383-390

Tumbler simulations of abrasion processes affecting rocks on basaltic marine benches have clarified the effects of mass and volume of rock fragments on their rate of wear. Several experiments indicate that rate of basalt wear increases with mass in the interval 1 g to 8 g, but is not related to volume of fragments abraded in seawater. Relatively small quantities of rock flour suspended in the immersant seawater substantially reduced the rate of basalt wear. Basalt and calcareous beachrock responded differently in systems with both rock types tumbling together. Examination of the cuttings from these low-energy encounters suggests that abrasion on elevated benches along exposed seacoasts reduces virtually all clastic material to particles of silt size or smaller, producing essentially no sand.  相似文献   

探讨渤海及周边地区海洋平台抗震设防水准   总被引：3，自引：0，他引：3       下载免费PDF全文

彭艳菊  吕悦军  唐荣余  沙海军 《地震学报》2005,27(6):647-655

介绍了美国API规范的内容，并将南加利福尼亚和中国渤海海域地震活动特征与地震危险性进行对比. 对比结果表明，无论在地震活动的频度与强度还是地震危险性分析结果上，渤海都比南加州弱. API规范指出，对于南加利福尼亚地区的永久性建筑， 强度设计水准取重现期200 a，变形设计水准取几百至几千年. 我国相关规范规定的海洋平台强度设计和变形设计水准分别取500 a和10 000 a，过于保守. 同时，与其它建构筑物的抗震水平相比较，甲类建筑变形设计水准取设计基准期100 a内超越概率2%~3%，乙、丙类取50 a内2%~3%，考虑海洋平台易于引起严重的次生灾害，变形设计水准取设计基准期30 a内1%（相当于重现期3 000 a）应是安全的. 基于上述对比分析， 同时考虑到经济承受能力以及与现行标准的连贯性， 建议我国海洋石油平台的强度设计水准和变形设计水准分别取200 a和3 000 a.   相似文献   

大港滩海区埕北断阶带古近系层序界面的识别方法     

曲希玉  刘立  刘娜  吴文波 《世界地质》2007,26(4):484-491

通过对大港滩海区埕北断阶带层序地层的研究，将研究区古近系划分为3个三级层序，总结了5种识别层序界面的方法：①地震识别法；②钻井识别法；③测井识别法；④古生物组合识别法；⑤地球化学识别法。在研究区，方法①表现为区域性的上超和削截；方法②表现为岩性和泥岩颜色的突变；方法③表现为各种曲线和地层倾角的突变；方法④表现为古生物组合类型的变化；方法⑤表现为Fe^2＋／Mn^2＋值由下向上由逐渐增大，转为突然变小。其中方法①、③、④是层序界面的主要识别标志，方法②可作为参考标志，而方法⑤的应用效果较差。  相似文献   

金矿尾矿库对近海生态环境的影响   总被引：1，自引：0，他引：1  

张永伟  李世华  姜景文  王庆兵 《水文地质工程地质》2002,29(3):40-43

近海生态环境具有特殊敏感性，金矿尾矿库座落于这一地区，会对大气、地表水、地下水及防风树木产生影响。为此，我们概化了水文地质条件，选取了合理的参数，建立了模型，重点分析了金矿尾矿库对地下水水位的影响。  相似文献   

厦门台地倾斜年变畸变现象与1994年东山海外7.3级地震     

徐智明  张远城 《福建地震》2002,(3)

1994年 9月 1 6日东山海外 7 3级地震前一年左右 ,厦门台地倾斜E -W分量年变发生严重畸变 ,正常年变规律图象明显被破坏 ,异常出现后 1 1个月 ,东山海外发生强震。该现象可以作为闽粤近海强震的一个重要前兆指标  相似文献   

中国近海天然气水合物找矿前景   总被引：38，自引：3，他引：38  

祝有海  吴必豪  卢振权 《矿床地质》2001,20(2):175-181

天然气水合物是一种新型能源，在海底沉积物和陆上永远冻土带中均有广泛分布。西太平洋是全球三大天然气水合物成矿带之一，在其中已发现许多水合物矿床或矿点。中国近海，包括南海、东海和台湾东部海域，具备良好的天然气水合物成矿条件和找矿前景，并已在这些海域中发现了一系列的找矿标志。南海的西沙海槽、台湾西南陆坡和台西南盆地、笔架南盆地及其东缘增生楔、东沙群岛东南坡、南部陆坡区，东海的冲绳海槽和台湾东北部海域是中国近海最有利的天然气水合物找矿远景区。  相似文献   

Modelling the Quaternary evolution of shore platforms and erosional continental shelves     

A. S. Trenhaile 《地球表面变化过程与地形》2001,26(10):1103-1128

A mathematical model was used to investigate the effect of glacially induced fluctuations in sea level on the evolution of wave‐cut shore platforms and erosional continental shelves during the Quaternary. The model used two deep‐water wave sets, which were used to calculate breaker height and depth, and the force of the waves at the waterline, according to the width and bottom roughness of the surf zone and the gradient of the submarine slope. The model also incorporated an erosional threshold related to the strength of the rocks, the number of hours each year in which the water level is at each intertidal elevation and the amount and persistence of the debris at the cliff foot. Most runs were made using a sea level model that consisted of 26 glacial cycles from 2 million to 0·9 million years ago, and nine, of approximately twice the amplitude and wavelength, in the last 0·9 million years. The model emphasized the dynamic association between the contemporary intertidal platform and the continental shelf. Both surfaces trend towards a state of static equilibrium under oscillating sea level conditions, when attenuated waves are unable to continue eroding the rock. If there has not been enough time to reduce the gradient of the shallower portions of the continental shelf, however, intertidal shore platforms can be in a temporary, though possibly long‐lasting, state of dynamic equilibrium. The model suggests that most platforms are, at least in part, inherited from one, or in many cases more, interglacial stages when sea level was similar to today's. Copyright © 2001 John Wiley & Sons, Ltd.  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