琼东南盆地地壳伸展深度依赖性及其动力学意义

地壳或岩石圈尺度内伸展因子随深度变化特征对于理解岩石圈演化有重要的指示意义.我们利用南海北部大陆边缘琼东南盆地区深反射地震剖面的地壳分层模型,计算了沿剖面上地壳与全地壳的伸展因子.结果表明:琼东南盆地区具有明显的地壳尺度内伸展的深度相关性（上地壳尺度伸展因子变化范围为1.0~2.0,全地壳尺度的伸展因子变化范围为1.2~2.5）;琼东南盆地各构造单元内的上地壳与全地壳伸展具有明显的非均一性(长昌凹陷上地壳尺度伸展最大,乐东—陵水凹陷其次,松南—宝岛凹陷最小;长昌凹陷和松南—宝岛凹陷的地壳尺度伸展因子较乐东—陵水凹陷大) 与各向异性(南东—北西剖面较之北东—南西向剖面地壳伸展因子大).这些结果预示着琼东南盆地区地壳伸展优势方向为北西向,盆地区东西部的伸展过程或伸展机制可能差异较大拟或存在太平洋岩石圈俯冲角空间差异或地幔岩浆产出时空差异.结合研究区相关研究成果,推断地壳伸展因子的深度相关性可能是共轭大陆边缘低角度拆离控制的简单剪切系统内伴随地幔挤出的动力学现象.     

南美地区下地幔速度界面结构研究

下地幔间断面是地球内部结构研究的重要课题,对于理解地球深部的动力过程具有重要意义.美国西部密集地震台网记录到的南美洲太平洋地区深震的短周期波形资料有利于震源下方下地幔间断面的研究.本文收集了美国西北太平洋地震台网和犹他大学地震台网所记录的南美洲西部俯冲地区15个深震的19组短周期垂向台网资料,并利用4次根倾斜叠加方法提取震源下方下地幔中速度界面上发生转换的次生震相SdP,据此发现南美洲西部下方下地幔中800~1200 km深度范围内存在明显的转换点集中,主要分布在900,1000和1100 km三个深度附近,三个速度界面具有不同的起伏形态,应为在研究区域双层地幔对流中间边界层.     

地震海洋学方法在研究南海东北部海水水体结构中的应用

反射地震方法一般用于地下地质结构的探测.本文采用南海东北部的一条地震测线记录,通过对水体反射信号的处理,获取了该测线上海水的声速剖面,并获得了海水水体结构的直观图像.在反射地震剖面上,可以看出南海东北部上层海水结构较为稳定,没有明显的水体侵入痕迹,但中、深层海水中内波较为发育,这与物理海洋学上的研究结果是一致的.本文通过设计合理的数据模型说明了地震海洋学这种方法的可行性,并对地震海洋学的工作方法和方向上提出了一些意见和建议.     

Occurrence of brackish water phytoplankton species at a closed coral reef in Nansha Islands, South China Sea

The phytoplankton assemblage of Zhubi Reef, a closed coral reef in Nansha Islands (South China Sea, SCS) was studied in June 2007. A total of 92 species belonging to 53 genera and four phyla have been identified. The dominant taxa in the lagoon were the diatom Chaetoceros and cyanobacteria Nostoc and Microcystis, while in reef flats were cyanobacteria Trichodesmium erythraeum, dinoflagellates Gymnodinium and Prorocentrum. The species richness and diversity were consistently lower in the lagoon than in reef flats. Classification and nMDS ordination also revealed significant dissimilarity in phytoplankton community structure between the reef flat and lagoon, with statistical difference in species composition and abundance between them (ANOSIM, p = 0.025). Nutrient concentrations also spatially varied, with ammonium-enrichment in the lagoon, while high Si-concentration existed in reef flat areas. Both nutrient levels and currents in SCS may play important roles in determining the composition and distribution of microalgae in Zhubi Reef and SCS.     

Daily morphological changes determined by high‐energy events on an embayed beach: a qualitative model

This paper examines the daily morphological responses of Sununga Beach, an embayed beach located on the south‐eastern Brazilian coast, to storms in the South Atlantic Ocean. The main mechanisms and timing of beach erosion and accretion, the relationship between wave height and direction, and beach volume changes are considered, to establish a qualitative model for short‐term embayed beach morphological changes. The methodology consisted of daily topographic surveys during the month of May in 2001, 2002, and 2003, using an RTK‐GPS (real‐time kinematics – global positioning system). Weather and wave model results were used to correlate hydrodynamics and beach morphology. The results indicate that the morphodynamics of Sununga Beach are characterized by a process of beach rotation, which occurred more or less clearly during all three surveys. Unlike what has been commonly described in the literature for longer time intervals and alternations of fair and stormy weather, the beach rotation processes on Sununga Beach occurred under conditions of moderate‐to‐high wave energy change (wave heights greater than 2 m). An integrated evaluation of the behaviour of the meteorological aspects, together with beach morphology, enabled us to recognize that extra‐tropical cyclones were the most important agent in remobilizing the beach planform, whether in beach rotation or in cross‐shore erosion. Copyright © 2010 John Wiley & Sons, Ltd.     

Coastal dune rock development and Holocene climate changes in South China

Coastal dune rocks in China are eolian sands cemented by calcium carbonate under subaerial conditions, widely distributing on the tropical and subtropical coasts of South China. Particular temperature and precipitation as well as local wave and landform conditions are required for the formation of the dune rocks. A correspondence was found between Holocene environmental changes and coastal dune rock development by comparing the features of the sea-level and climate changes in the Holocene period with the ages, scales, and cementation of the dune rocks on the South China coasts. The findings provide well grounded explanation for some problems unresolved in the past researches on the coastal dune rock in South China: (1) There were no dune rocks with ages older than 6000 years in South China because the dune rocks formed before 6000 a BP were covered by the sea water that rose in the later period; (2) the dune rocks with ages of around 3000 a BP were widely found in South China today because the coastal dunes were cumulated on a large scale at that time as a result of temperature falling after the end of Megathermal; (3) Medieval Warm Period was the main period for the eolian dunes to be cemented into the coastal dune rocks in South China; (4) lack of dune rocks of younger than 1000 a BP was accounted for by that the climate conditions in recent one thousand years were not suitable for the cementation.     

南海南部陆坡晚第四纪沉积物稀土元素及环境意义

采用电感耦合等离子质谱(ICP-MS)法,对南海南部86GC柱状沉积物样品的稀土元素(REE)含量进行测量,并对其地球化学特征进行系统分析。结果表明,自大约31kaBP以来,该海域的沉积物具有基本相同的物质来源,物源区的气候环境变化可能是影响沉积物中REE指标纵向变化的主要因素。各指标的综合分析显示,末次冰期南海南部海域的沉积物源区具有较强的化学风化作用,冰后期则相对减弱,这就意味着南海南部及周边地区末次冰期期间依然盛行热带气候,冰后期的气候环境则可能较为多变。另外,在柱状样深度分别为17cm和100cm处均记录了指标的突变,前者可能是8k事件在南海南部的记录,后者代表的事件还有待进一步研究。     

南黄海中古生代残留沉积地层的地震成像

文中展示了南黄海中古生代沉积地层的成像结果,显示南黄海隆起区存在较稳定的中古生代沉积地层残留区.南黄海中古生代残留沉积地层的成像问题一直是地震资料处理的难点,主要原因是以海底鸣震为主的层间多次波和与中古生界顶界面相关的长程多次波非常发育,致使有效反射波无法准确识别.本文利用平面波域层间多次波的可预测性,对地震数据平面波分解之后进行预测反褶积,较好地消除了层间多次波.利用速度差异分离长程多次波,在有效波速度无法确定的条件下,先从低速的、可以确认的多次波开始进行分离,逐步确认并分离多次波,同时逐步进行有效波的确认和成像速度的尝试,最终得到合适的成像速度场和多次波被充分分离的数据.成像结果对南黄海残留盆地研究有一定借鉴意义.     

南海北部第四系厚度分布图的编制与简要说明

收集南海北部大量多道地震和钻井资料,编制了该区域首幅第四系厚度分布图。第四系等厚线总体呈NEE向,特别是珠江口外大陆架最明显,莺歌海、琼东南呈NW-EW-NE向弧形,珠江口大陆架南部存在次一级NW向等厚线。第四系等厚线分布形态明显受到断裂构造控制。