南海北部晚中新世红绿韵律层成因的矿物学和地球化学约束  

Mineralogical and geochemical constraints on the origin of rhythmic layering of Late Miocene reddish-brown and greenish-gray sediments in the northern South China Sea

作　　者：董宏坤 万世明[1,3] 刘畅 赵德博 曾志刚[1,2] 李安春[1] DONG Hongkun;WAN Shiming;LIU Chang;ZHAO Debo;ZENG Zhigang;LI Anchun(Key Laboratory of Marine Geology and Environment,Institute of Oceanology,Chinese Academy of Sciences,Qingdao 266071,China;University of Chinese Academy of Sciences,Beijing 100049,China;Laboratory for Marine Geology,Qingdao National Laboratory for Marine Science and Technology,Qingdao 266061,China;International Ocean Discovery Program,Texas A&M University,College Station,TX,77845,USA)

机构地区：[1]中国科学院海洋研究所海洋地质与环境重点实验室,山东青岛266071 [2]中国科学院大学,北京100049 [3]青岛海洋科学与技术国家实验室海洋地质过程与环境功能实验室,山东青岛266071 [4]International Ocean Discovery Program,Texas A&M University,College Station,TX,77845,USA

出　　处：《地学前缘》2022年第4期42-54,共13页Earth Science Frontiers

基　　金：国家自然科学基金项目(42125602,42076052);中国科学院战略性科技先导专项(XDB40010100)。

摘　　要：沉积物颜色是其物质组成和形成环境的重要标志,对古海洋古环境重建有特殊指示意义。国际大洋发现计划(IODP)368航次在南海北部钻取的U1502站沉积岩心中发现了上百米红褐色-绿灰色韵律沉积层,但其成因不明。为探究其物源和红绿韵律沉积层的成因,我们对该站位岩心样品开展了矿物学和地球化学分析,包括粒度、黏土矿物、常微量元素和Sr-Nd同位素组成、有机碳含量及碳酸盐碳氧同位素组成分析。物源分析表明,U1502站沉积物陆源输入以珠江为主而吕宋次之,红层相对绿层有稍多的吕宋物质贡献。地球化学指标指示红绿沉积层的形成没有遭受热液、冷泉流体的影响,其形成是南海晚中新世构造演化和冰期-间冰期旋回中水体通风、底层水氧化还原环境改变及早期成岩作用共同影响的结果。结合以前南海北部沉积物源研究及沉积物颜色频谱分析,推测红绿层可能分别对应了间冰期-冰期时间尺度。指标重建指示了红绿层分别形成于偏氧化和偏还原的底层水氧化还原环境。自中中新世以来随着吕宋岛弧与欧亚板块碰撞,南海海盆从开放的环境变得相对封闭,其深部通风和氧化还原条件开始呈现典型的冰期-间冰期旋回模式。红层对应了间冰期高海平面时期南海深层水通风良好、水体偏氧化的沉积环境,而绿层则指示了冰期低海平面时期南海层化加强、水体偏还原的环境。不同的氧化还原条件控制了早期成岩作用中致色含铁自生矿物如赤铁矿的形成与转化,最终引起沉积层颜色韵律变化。Sediment color is an important indicator of sediment composition and formation environment and can be used for the reconstruction of paleoceanographic environments.During the International Ocean Discovery Program(IODP)Expedition 368,hundreds of meters of rhythmic reddish-brown and greenish-gray sedimentary layer were found in the sediment core at Site U1502 in the northern South China Sea(SCS);however,the origin of the rhythmic layers remains unclear.In order to understand its causes,we carried out mineralogical and geochemical analyses of core samples on grain size,clay minerals,major and trace elements,Sr-Nd isotopic compositions,organic carbon contents and carbonate C-O isotopic compositions.The sediments are mainly sourced from the Pearl River,with a minor contribution from the Luzon Island and the material input was slightly higher in the reddish-brown layer than in the greenish-gray layer.The geochemical indicators showed that the formation of the reddish-brown and greenish-gray layers was not affected by hydrothermal and cold seep fluids,rather it was influenced by a combination of tectonic evolution of SCS in the Late Miocene and changes of deep-water ventilation and redox environment and early diagenesis during the glacial-interglacial cycle.Combined with the previous provenance studies in northern SCS and spectral analysis of sediment color in this study,we suggest that the reddish-brown and greenish-gray layers may be associated respectively with the interglacial and glacial periods.The redox indicator indicated that the reddish-brown and greenish-gray layers were formed respectively in more oxidative and more reductive bottom water environments.Since the Middle Miocene,following the collision between the Luzon arc and Eurasian plate,the SCS basin evolved from an open environment to a relatively closed marginal sea,and its deep ventilation and redox conditions began to reflect typical glacial-interglacial cycling.The reddish-brown layer corresponds to the sedimentary environment with well ventilated an

关 键 词：南海北部 晚中新世 红绿层沉积物 矿物地球化学 沉积物源 氧化还原条件 

分 类 号：P736.21[天文地球—海洋地质] P534.621[天文地球—海洋科学] P539.7