全新世以来广西主要河口近岸沉积物粘土分布及富集特征

Clay Distribution and Accumulation in Sediments of Main Estuary along Guangxi Coast Since Holocene

关键词:  近岸  粘土  分布  关系  富集

Key words:  near shore  clay  distribution  relationship  accumulation

摘要:

[目的]了解粘土在广西主要河流出海口近岸的分布、变化、联系和富集特征。[方法]对钦州湾-廉州湾近岸浅海区沉积物进行取样测试,分析了4个钻孔43个岩芯样品和表层样品52个,阐明了该河口湾区全新世以来粘土分布、粒级分配、相互联系以及沉积环境、物源与富集。[结果]该区粘土广泛分布,钻孔粘土为0%~48.64%,表层为0%~62.10%,来源以河流和海岸侵蚀为主;垂向上粘土随环境变化而波动,总体上为下降趋势或者波动维持,但自晚全新世1m以来均为转折增加,多是F粒级的升高;粘土最细F粒级为主导因素,粒级分配显示该区粘土有一定的内在稳定性,与陆架浅海反相,高F粒级及其比例具有河相和河口湾指示意义。表层粘土是对全新世以来的继承和发展,F粒级比例在0.65以上,最高达0.84,显示河流影响的稳定性和加强迹象;粘土对动力沉积环境变化响应灵敏,环境选择性强。[结论]结合了粘土本底值的表层沉积物粘土富集系数C/C'显示,粘土主要在钦州湾口水下斜坡、钦州湾口与三娘湾的结合部近岸以及湾口西南部富集,与潮流控制的低能动力沉积环境分区相对应。

Abstract:

[Objective] The distribution, variation, relationship and accumulation of clay were analyzed in main estuary in Guangxi coast in order to understand their characteristics.[Methods] Four boreholes and 52 surficial sediments were sampled from outer Qinzhou Bay to western Beihai waters. Based on the sediment sampling and laboratory sample test data, the clay distribution, composition and variation were estimated since Holocene.[Results] The clay widely appears in studied area ranging from 0%~48.64% in boreholes and 0%~62.10% in surficial sediments with inputting from river runoff and coast erosion. Vertical clay's concentration varies in waving way in boreholes, which generally showed a decreasing trend but transited since late Holocene 1m and increased.F grain takes main part of clay and indicates river-facies and estuary-facies opposite to shallow shelf. Developed from late Holocene, the finest F grain of surficial sediments takes account the ratio of 0.65 in average and reaches the maximum of 0.84, revealing river's control maintains and enhances. The clay demonstrates a sensitive response to dynamic sedimentary environment by means of average grain size and grain parameters.[Conclusion] Combining clay's background value and enriching index C/C', main clay accumulating areas include the mouth of Qingzhou Bay, the intersection of Qingzhou Bay and Sanniang Bay, and southwestern part of studied area, corresponding to deeper and tide controlled low energy areas.