西沙群岛宣德环礁水下沙洲动力地貌特征及其成因机制  

Morphodynamic characteristics and genetic mechanism of the submarine sandbanks in Xuande Atoll, Xisha Islands

作　　者：何其江 沈爱斯 刘刚[2,3] 丁咚 瞿洪宝[2,3] 刘根[4] 苟鹏飞 HE Qijiang;SHEN Aisi;LIU Gang;DING Dong;QU Hongbao;LIU Gen;GOU Pengfei(College of Marine Geosciences,Ocean University of China,Qingdao 266100,China;Key Laboratory of Marine Geology Resources and Environment of Hainan Province,Haikou 570206,China;Marine Geological Survey Institute of Hainan Province,Haikou 570206,China;Third Institute of Oceanography,Ministry of Natural Resources,Xiamen 361005,China)

机构地区：[1]中国海洋大学海洋地球科学学院,青岛266100 [2]海南省海洋地质资源与环境重点实验室,海口570206 [3]海南省海洋地质调查研究院,海口570206 [4]自然资源部第三海洋研究所,厦门361005

出　　处：《海洋地质与第四纪地质》2023年第1期1-12,共12页Marine Geology & Quaternary Geology

基　　金：海南省自然科学基金项目“西沙宣德环礁碳酸盐台地动力地貌特征和成因机制及发育演化研究”(421QN0963);“晚第四纪以来琼州海峡西口沉积演化过程与海砂成矿模式研究”(422QN420)。

摘　　要：海底地形地貌研究可以揭示海底表面形态特征,探索海底物质结构及其形成、演化和分布规律。通过单波束测深、单道地震、海底表层沉积物取样和潮汐水文水动力实测等方法,开展了宣德环礁水文要素和水动力条件定量化研究,对宣德环礁水下沙洲动力地貌特征及动力作用下形成机制进行了探讨。研究结果表明:宣德环礁潟湖内水深50~55 m及60 m发育的礁滩体和埋藏珊瑚礁,与全新世50~60 m的低海平面时期发育的系列特征地貌应为同时期形成,水深50~55 m处的地貌边界很可能保留了早全新世时期古潟湖礁盘地貌轮廓形态;宣德环礁潟湖发育5类动力地貌特征形态的水下沙洲,环礁底层涨落潮流是塑造水下沙洲的主要现代动力因素。在常态天气下,涨落潮流输运的砂质沉积物足以在原有地形的基础上沉积和发育形成现今水下沙洲地貌形态。影响水下沙洲发育的主要因素由强至弱依次为气候变化引起的海平面升降,地形基础(珊瑚礁格架、礁盘岸线、口门)和涨落潮流。Submarine geomorphology can reveal the topographic characteristics of seafloor, which is helpful to understand the composition,formation, evolution, and distribution of the sediment. The hydrologic elements and hydrodynamic conditions in Xuande Atoll, Xisha, Islands,South China Sea were quantitatively investigated by the combination of single beam sounding, single-channel seismology, sampling of surface sediments, and hydrodynamic measurements. Furthermore, the morphodynamic characteristics and genetic mechanism of submarine sandbanks were discussed in detail. Results show that the coral reef frame and buried corals that developed in water depth of 50~55 m and 60 m in the atoll lagoon were formed in the same period of typical landforms that formed in the 50~60 m depth during the lower sea level period of the Holocene in South China Sea. It is likely that the boundary of the submarine geomorphology developed in water depth of 50~55 m retained the paleo-lagoon reef morphology of the Early Holocene. Five types of submarine sandbanks with own morphodynamic characteristics were identified in the atoll lagoon where tidal currents at the bottom are the main modern dynamic factors that shape the submarine sandbanks. Under normal weather condition, tidal currents in the study area are strong to transport sandy sediments and shape the geomorphology of present submarine sandbanks on the previous topography formed during sea level fluctuations. The sea level fluctuations are induced by climate change,followed by topographic foundation(coral frame, reef shoreline, reef gate) and tidal currents, and are the main factors that control the development of submarine sandbanks in the study area.

关 键 词：水下沙洲 动态地貌 水动力条件 成因机制 宣德环礁 

分 类 号：P736.15[天文地球—海洋地质]