Rapid incision of the Colorado River in Glen Canyon – insights from channel profiles,local incision rates,and modeling of lithologic controls     

Kristen L. Cook  Kelin X. Whipple  Arjun M. Heimsath  Thomas C. Hanks 《地球表面变化过程与地形》2009,34(7):994-1010

The Colorado River system in southern Utah and northern Arizona is continuing to adjust to the baselevel fall responsible for the carving of the Grand Canyon. Estimates of bedrock incision rates in this area vary widely, hinting at the transient state of the Colorado and its tributaries. In conjunction with these data, we use longitudinal profiles of the Colorado and tributaries between Marble Canyon and Cataract Canyon to investigate the incision history of the Colorado in this region. We find that almost all of the tributaries in this region steepen as they enter the Colorado River. The consistent presence of oversteepened reaches with similar elevation drops in the lower section of these channels, and their coincidence within a corridor of high local relief along the Colorado, suggest that the tributaries are steepening in response to an episode of increased incision rate on the mainstem. This analysis makes testable predictions about spatial variations in incision rates; these predictions are consistent with existing rate estimates and can be used to guide further studies. We also present cosmogenic nuclide data from the Henry Mountains of southern Utah. We measured in situ ¹⁰Be concentrations on four gravel‐covered strath surfaces elevated from 1 m to 110 m above Trachyte Creek. The surfaces yield exposure ages that range from approximately 2·5 ka to 267 ka and suggest incision rates that vary between 350 and 600 m/my. These incision rates are similar to other rates determined within the high‐relief corridor. Available data thus support the interpretation that tributaries of the Colorado River upstream of the Grand Canyon are responding to a recent pulse of rapid incision on the Colorado. Numerical modeling of detachment‐limited bedrock incision suggests that this incision pulse is likely related to the upstream‐dipping lithologic boundary at the northern edge of the Kaibab upwarp. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

深圳市观澜断裂第四纪活动性研究   总被引：2，自引：1，他引：1  

马浩明  陈庞龙 《华南地震》2009,29(3):17-24

观澜断裂是深圳陆域地区规模最大的北北西向断裂。通过地质地貌调查、联合钻孔探测及地质年代测定等技术方法对观澜断裂的第四纪活动性进行了详细考察与综合研究。结果表明：穿越低丘陵台地地貌区的观澜断裂两侧未见地貌差异或现代构造形变现象;4个典型地质露头和2条钻孔联合剖面显示断裂没有扰动上覆第四系．观澜大布巷钻孔探测剖面还获得了断裂上覆冲洪积砂层底部12．6±2．4Ka的光释光测年数据;断裂物质主要由碎裂岩、构造角砾岩、硅化岩等组成．可见硅质被膜及半固结岩屑或岩粉状物质;7个断层样品的电子自旋共振测试结果显示断裂的最新活动年龄为距今21．1±2．1万年。结合12条浅层地震测线探测未发现断裂错移第四纪覆盖层底界的事实．得出了观澜断裂最新一次活动发生在中更新世晚期．自晚更新世中期以后没有新的近地表活动的结论。  相似文献   

北京市浅层剪切波速与隐伏构造关系研究     

玄月  吴涛  刘轩  李伟华  王金萍 《华北地震科学》2014,32(2):25-28

以北京平原区地震钻孔为基础资料,建立三维剪切波速速度模型,获得了2个代表性的波速剖面,研究其与地质构造和隐伏断裂之间的关系,结果表明：北京平原区新构造运动和隐伏断裂活动对晚第四纪地层沉积和发育具有控制作用,而且浅层剪切波速的差异性也为隐伏构造的位置确定提供了帮助。  相似文献   

3 万年来亚洲降水与大气环流变化重建和模拟综述     

廖梦娜  于革 《地理科学进展》2014,33(6):807-814

区域性的湖泊水位能反映有效降水及气候变化,已成为重建第四纪降水和水量平衡最重要的指标。亚洲分布着几乎全球各种成因类型的湖泊,第四纪湖泊演化在全球第四纪研究中占有重要地位。多年来通过对地貌学、沉积学、生物地球化学和考古学的研究重建了各个区域的湖泊水位变化,并据此建立了湖泊演变数据库,作为研究第四纪亚洲区域气候变化的重要基础。本文介绍湖泊水位气候理论的发展历程,回顾晚第四纪亚洲湖泊水位研究的历史;分析晚第四纪亚洲从西到东不同区域湖泊水位变化历史和地域特征,并根据晚第四纪冰期和间冰期的两个特征期湖泊空间变化特征,从古气候模拟的角度探讨了气候驱动机制下湖泊水位变化的成因。  相似文献   

亚热带第四纪沉积型红土与风化壳型红土的磁学特征对比     

杨立辉  叶玮  郑祥民  周立旻  苏优 《地理科学》2015,35(11):1475-1481

对浙江新昌玄武岩、花岗岩风化壳红土和江西南昌第四纪沉积型红土剖面的磁学特征进行了分析,结果表明,同一气候区内风化壳红土的磁学特征受母质特征影响较大。随着风化强度的增加,强磁性的玄武岩风化壳磁化率先减小后增加,磁性矿物颗粒先变粗后变细,弱磁性的花岗岩风化壳磁化率逐渐增加,磁性矿物颗粒逐渐变细。第四纪沉积型红土剖面中,均质红土磁化率远大于网纹红土,磁性矿物颗粒亦较网纹红土层细。这些差别说明了第四纪沉积型红土剖面中均质红土与网纹红土不完全相同的物质来源。  相似文献   

粒度分析在中国第四纪黄土古气候研究中的应用现状     

刘冬雁  李巍然  彭莎莎  王玲 《中国海洋大学学报(自然科学版)》2010,40(2)

中国黄土是记录第四纪古气候信息的重要载体,作者就第四纪黄土研究中涉及的粒度测量、常用粒度指标、敏感粒度、粒度年龄模型以及粒度指标时间序列周期分析等方面的应用现状作了回顾。前人研究结果表明:不同前处理方法对粒度测量结果有较大影响;传统粒度指标应用广泛;敏感粒度的确定是反演古环境的关键;粒度指标时序谱分析是古气候定量化研究的重要方法之一;粒度年龄模型仍是较可信的建立地层年代序列的方法。  相似文献   

平面影像到QTM像元的转换算法及精度分析     

孙文彬  赵学胜 《地理与地理信息科学》2007,23(1):20-23

平面影像数据到四元三角网(Quaternary Triangular Mesh,QTM)像元的转换是实现全球QTM格网影像无缝建模的首要任务。提出基于面积权的数据转换方法,给出不同类型的权重及格网值的计算,并利用ArcGIS中256级灰度的Wsiearth.tif图像数据分析了转换精度。结果表明:将4 km分辨率的影像数据转换到12层的QTM像元时,转换误差在0~2灰度内占96.27%,对一般应用的影响可以忽略不计。  相似文献   

江苏建湖庆丰剖面孢粉组合及其古环境     

赵希涛  吴学忠 《海洋科学》1991,(4)

本文通过对庆丰剖面的孢粉分析,得出了孢粉组合,恢复了建湖地区自晚更新世玉木亚间冰期以来的古植被及古气候,探讨了地层时代和晚第四纪环境变迁等问题。  相似文献   

Generation of calc-alkaline andesite of the Tatun volcanic group (Taiwan) within an extensional environment by crystal fractionation     

《International Geology Review》2012,54(9):1156-1171

The Pliocene–Pleistocene northern Taiwan volcanic zone (NTVZ) is located within a trench-arc–back-arc basin and oblique arc–continent collision zone. Consequently the origin and tectonic setting of the andesitic rocks within the NTVZ and their relation to other circum-Pacific volcanic island-arc systems is uncertain. Rocks collected from the Tatun volcanic group (TTVG) include basaltic to andesitic rocks. The basalt is compositionally similar to within-plate continental tholeiites whereas the basaltic andesite and andesite are calc-alkaline; however, all rocks show a distinct depletion of Nb-Ta in their normalized incompatible element diagrams. The Sr-Nd isotope compositions of the TTVG rocks are very similar and have a relatively restricted range (i.e. I_Sr = 0.70417–0.70488; εNd_(T) = +2.2 to +3.1), suggesting that they are derived directly or indirectly from the same mantle source. The basalts are likely derived by mixing between melts from the asthenosphere and a subduction-modified subcontinental lithospheric mantle (SCLM) source, whereas the basaltic andesites may be derived by partial melting of pyroxenitic lenses within the SCLM and mixing with asthenospheric melts. MELTS modelling using a starting composition equal to the most primitive basaltic andesite, shallow-pressure (i.e. ≤1 kbar), oxidizing conditions (i.e. FMQ +1), and near water saturation will produce compositions similar to the andesites observed in this study. Petrological modelling and the Sr-Nd isotope results indicate that the volcanic rocks from TTVG, including the spatially and temporally associated Kuanyinshan volcanic rocks, are derived from the same mantle source and that the andesites are the product of fractional crystallization of a parental magma similar in composition to the basaltic andesites. Furthermore, our results indicate that, in some cases, calc-alkaline andesites may be generated by crystal fractionation of mafic magmas derived in an extensional back-arc setting rather than a subduction zone setting.  相似文献   

基于六边形网格的球面Voronoi图生成算法     

贲进  童晓冲  张衡  江刚武 《测绘科学技术学报》2006,23(5):328-330

利用二十面体施奈德等积多面体投影构建了球面多分辨率六边形层次网格;通过边界四元组将六边形单元分解到四元三角形及其子单元中处理;利用改进的四元三角网编码方案建立了网格的数字空间、单元层次编码模型和不同实体在球面上的表达方法.在此基础上,提出了球面Voronoi图的生成算法.实验结果表明该算法与现有算法相比具有更高精度.  相似文献