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基于古地磁和AMS14C定年结果,对长江三角洲太湖平原的WJ孔进行岩性特征、矿物磁学、粒度分析及有孔虫化石研究,拟重建WJ孔记录的晚第四纪以来沉积环境演变过程与海侵事件,并探讨环境磁学参数对河口三角洲地区沉积环境演化的指示意义.研究结果表明,WJ孔可以划分为中更新世阶段I、中更新世阶段II、晚更新世、全新世四个阶段,沉积地貌环境分别为:河湖、滨海-阶地、河口坝-河口湾-潮滩与阶地、湖沼平原.WJ孔揭示了三次海侵事件,分别为中更新世晚期海侵,晚更新世MIS5海侵和晚更新世MIS3海侵.其中记录的MIS5e海侵最为强盛,MIS3后期也存在一次海侵加强事件.另外,滨海潮滩-河口坝环境的沉积物磁性特征明显,χlf、SIRM、HIRM等为显著高值. 相似文献
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珠江三角洲的新构造运动及其与三角洲演化的关系 总被引：4，自引：0，他引：4
综合已有资料。重新对珠江三角洲的新构造运动进行了系统的分析．分析结果表明该地区的新构造运动以断裂活动和断块差异升降运动为主要特征．这些特征在珠江三角洲的演化过程中起着非常重要的作用。大多数在第四纪形成或重新活化的基底断裂把三角洲切割成一系列的断块，并且在垂直运动上以沉降为主导，为珠江三角洲的第四系沉积创造了空间。另外，第四系两期河流相砂砾层分布的差异反映了古河道在晚更新世海侵后、全新世海侵前所发生的变迁。这主要是断裂活动的结果。因此，在珠江三角洲的形成和演化过程中。新构造运动既影响着三角洲的沉积又控制着河道的变迁． 相似文献
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由滨海相沉积样品反映的东南沿海海岸升降速率 总被引：1，自引：0，他引：1
收集了闽、粤、桂、琼4省（区）海岸带的^14C测年自45000aB.P.以来共490个演海相样品，依据文献[1]广东中山石歧45000aB.P，以来的渐进上升水动型海平面变化曲线，计算了相应地区晚更新世及全新世以来海岸地壳的升降速率，结果表明，除粤西和粤东一些地区及海南省外，东南沿海海岸部份地壳的升降速率，结果且明，除粤西和粤东一些地区及海南省外，东南沿海海岸份地区晚更新世及全新世时期和中期地壳主要表现为下沉，全新世中晚期特别是晚期主要反映为上升，珠江三角洲晚更新世中晚期以来主要表现为继承性下沉，现代地壳形孪测量反映的地壳升降较多地区与一述趋向大致相似，广东惠来县东60km下新礁海域及珠江三角洲灯笼沙等15个地区，是地壳升降异常速率较高地区。 相似文献
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东南沿海末次盛冰期古海平面标志与地震的关系──-100m以下最低海平面问题质疑 总被引：1，自引：0，他引：1
东南沿海末次盛冰期（２１～１４ｋａＢ．Ｐ，）滨海相沉积垂相分布多在海拔３８～－５０．８ｍ的范围内，以正向分布（海平面附近及以上）、正负向混合分布及负向（海平面以下）分布在断块交界区或其附近，是强震的主要发生地。在滨海相沉积垂向分布愈离散的区段，其地震活动性也愈强，本研究地区不存在末次盛冰期－１００ｍ以下的最低海平面，那些局部在外陆架海底发现的－１００ｍ以下的滨海相沉积，可能与地壳呈长趋势下沉作用有关 相似文献
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珠江三角洲沉积物的岩石磁学性质及其环境意义 总被引：1，自引：0，他引：1
选取珠江三角洲区域位于广州番禺的PD钻孔进行沉积物岩石磁学和环境磁学记录的研究. 岩石磁学实验表明钻孔大部分沉积物以低矫顽力的磁铁矿类矿物为主要控磁矿物, 但仍存在少量铁硫化物. 在有机质丰富的灰黑色黏土沉积中, 铁硫化物含量增加, 成为影响沉积物磁性特征的主要矿物, 标志着海退后富含有机质而缺氧的沼泽环境. 以赤铁矿和针铁矿类矿物为主要控磁矿物的花斑黏土, 表明了一个较长时期的暴露风化过程, 代表着沉积间断. 在以磁铁矿类矿物作为主要载磁矿物的沉积物中, 磁铁矿浓度及粒度的变化主导磁化率(κ)、饱和等温剩磁(SIRM)等环境磁学参数的变化, SIRM/κ 和χarm/SIRM的大小旋回响应于海平面的升-降过程, 它们的高值反映了磁性矿物粒度变细、海平面上升. 在沉积学分析的基础上, 根据环境磁学参数截然不同的变化规律, 结合微体古生物数据, 将珠江三角洲沉积物代表的环境分为两次显著的海平面上升－下降旋回, 晚更新世和全新世的海侵又包含若干个比较明显的次级海平面波动过程. 相似文献
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全新世以来珠江三角洲的地层层序和演变过程 总被引：2，自引：0，他引：2
本文基于对90个拥有全新世14C年代数据的钻孔进行详细的沉积物特征和年代地层分析,讨论了全新世珠江三角洲的地层特征及全新世以来的充填过程.全新世珠江三角洲沉积物覆盖在末次冰期冰盛期形成的风化侵蚀面与底砾层之上.最大海侵面位于松软海相淤泥层位.在受潮汐冲刷区域,最大海侵面表现为侵蚀面.全新世沉积层序自下向上在古河谷为河流相、河漫滩-河口湾相、河口湾-三角洲相,在古河间地为滨海相、河口湾相和三角洲相.全新世沉积层垂向堆积序列绝大部分表现为下粗上细的正向序列,且不具有典型Gilbert三角洲的前积层、顶积层等沉积层序.受控于独特而复杂的地貌边界,古珠江河口湾在高水位体系域的演变模式不同于世界其他大型三角洲,而是一个多源复合、不同尺度河流沉积体独立并行发展,最后复合成的三角洲.全新世以来珠江三角洲的演变可以分为5个阶段：第一阶段12~8kaBP,全新世海侵未达三角洲中部地区,直至约9kaBP以后,南部一些地势较低的地区才开始受海进影响,出现一些海陆交互相沉积;第二阶段8~6kaBP,海面快速上升,珠江三角洲大部分地区接受海进沉积;第三阶段6~4kaBP,全新世海侵达到盛期,古珠江三角洲地区大面积为河口湾,且受系列岛屿的阻隔分为两部分,上部是与河流相接的半封闭的内古海湾;下部是与海洋相接的外古海湾,两部分仅由若干峡口相通,河流沉积物主要在内古海湾中堆积充填;第四阶段4~2kaBP,在复杂边界对河流与海洋动力的重塑和改造作用下,内古海湾各区域的沉积同时进行,独自发展;第五阶段2kaBP至今,该阶段三角洲的演变已不再是单纯的自然过程,而是自然和人类共同塑造的过程. 相似文献
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从沉积物特征谈太湖的演变 总被引：3，自引：5，他引：3
通过太湖湖底淤泥层中的微体古生物及其物理化学分析,在西太潮W1孔发现多门类海相化石。海相化石出现的时间约在1100—5000aB.P.之间。据此提出西太湖在全新世期间曾遭受海侵,因而支持了太湖形成于泻湖的说法,同时,还提出海水进入太湖的时间,比以往学者推测的早2000多年。 相似文献
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珠江三角洲地区断裂比较发育 ,晚第四纪以来的活动方式皆具有垂直差异运动特征 ,且大多数都呈隐伏状态。文中在对三角洲发育阶段分析的基础上 ,利用已有钻孔资料 ,沿断裂两侧寻找位置相互靠近、且能揭露出时代和堆积环境相同的地层层位的一对或多对钻孔进行对比。根据断裂两侧相同层位现今所处海拔高度的差异确定它们沉积以来的垂直位移量 ,再根据该层位的测年数据计算断裂的垂直位移速率。共计算了 5条断裂晚第四纪以来的垂直位移速率 ,位移速率值为 0 14～0 4 7mm/a 相似文献
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Uplift of the shoreline in tectonically‐active areas can have a profound influence on geomorphology changing the entire process dynamics of the coast as the landforms are removed from the influence of the sea. Over decadal timescales it is possible for the landforms to return to their pre‐earthquake condition and this paper examines the re‐establishment of mixed sand and gravel beaches on the coast of Wellington, New Zealand, subsequent to an uplift event in 1855. Over 60 topographic profiles were surveyed, seven sets of aerial photographs from a 67 year period were mapped and sediment size analyses conducted in order to quantify the nature of beach change following uplift, and associated relative sea level fall. These data were supported by surveys using ground penetrating radar. It is found that uplift raised the gravel beaches out of the swash zone thereby removing them from the littoral zone. Intertidal rocky reefs which occur between each embayment were also uplifted during the same event and completely interrupted the longshore transport system. Continued input of gravel material to the littoral zone allowed beaches to re‐establish sequentially along the coast as each embayment was infilled with sediment. This reconnection of the embayments with the longshore drift system is associated with the beach planform being initially drift dominated during infill but then switching to swash alignment once the embayment becomes infilled. This has resulted in shoreline accretion of over 100 m in some places, at rates of up to 4 m/yr, covering shore protection works built in the past few decades. The ability of the shore to adjust back to its pre‐uplift condition appears to be a function of the accommodation space created during uplift and the rate of sediment supply. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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The Trabucador Bar is a barrier coast linking the main lobe of the Ebro Delta with its southern spit. This coastal stretch, which may be considered as a microtidal transgressive barrier, is the most vulnerable area of the deltaic coast to storm-induced geomorphologic changes. During the second week of October 1990 a severe storm affected the Ebro Delta causing serious erosion, in which the Trabucador Bar was one of the most damaged zones. A breach 800 m long and with a maximum depth of 0·4 m below the mean water level was created. During the breaching process approximately 70 000 m3 of sand were removed from the subaerial barrier in a few hours. Three factors are normally responsible for the loss of sediment, longshore transport gradient, offshore transport and overwash processes, most of the eroded sediment (60 000 m3) was transported towards the inner bay due to overwash processes. The post-storm recovery of the zone was slow and far from complete, as the breach remained a conduit for onshore sediment transport under a regime of breaking and reforming waves. An artificial dune was subsequently constructed to close the breach and thus allow beachface recovery. 相似文献
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根据福州盆地2个钻孔地层放射性元素(铀、钍、钾)含量的变化特点,结合孢粉分析等结果,探讨了地层放射性元素含量变化与岩性、沉积环境的关系。沉积地层中的放射性元素含量与沉积物粒度、岩性等密切相关,在泥质沉积(如淤泥、黏土)中含量较高,在砂质沉积中较低,在砾石层中介于前两者之间。同时,放射性元素含量的高低还与古气候环境有关,温暖潮湿的环境放射性元素含量较高,凉爽干燥的环境含量较低 相似文献
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Julian Vrbancich 《Geophysical Prospecting》2009,57(4):633-651
Previous studies using commercial airborne electromagnetic equipment that is not optimized for marine surveying have demonstrated the use of airborne electromagnetic methods for measuring water depth and estimating sediment thickness. A new prototype helicopter time-domain airborne electromagnetic system, SeaTEM(0), is now under development for bathymetric surveying. The first sea trial of the SeaTEM(0) system took place over Broken Bay, New South Wales, Australia, in shallow water up to ∼30 m in depth. Broken Bay was chosen because the separate paleodrainage systems for the Hawkesbury River, Brisbane Water and Pittwater, which join in Broken Bay give rise to paleovalleys infilled with unconsolidated sediments, ranging in thickness between 0 m (bedrock outcrop) and ∼200 m. The survey area also included a tombolo with a beach either side, which provided the opportunity to measure water depth through a surf zone. Sediment thickness and water depth is predicted from stitched layered-earth inversion of data based on a simplified two-layer model that represents seawater and sediment overlying a resistive half-space basement (bedrock). The resulting bathymetric profiles show agreement typically to within ∼±1 m and ∼±0.5 m with known water depths in areas less than 20 and 6 m deep respectively. The inverted depth profile of the second (sediment) layer is noisy; however, the profiles reveal coarse topographic features of paleovalleys to depth limits of ∼60 to 80 m below sea level in 20 to 30 m water depth, as well as resolving bedrock ridges and exposed reefs in shallow waters. 相似文献