潟湖岩芯沉积对海平面变化和物源的响应——以中沙环礁潟湖为例  

Sedimentary characteristics of a drilling core from the Zhongsha atoll lagoon:responses to sea level and provenance changes

作　　者：龙根元 陈万利 陈波 吴时国 张从伟 姜海滨 魏浩天 李秋环 LONG Genyuan;CHEN Wanli;CHEN Bo;WU Shiguo;ZHANG Congwei;JIANG Haibin;WEI Haotian;LI Qiuhuan(Key Laboratory of Marine Geology,Resources and Environment of Hainan Province,Haikou 571127,China;Marine Geological Institute of Hainan Province,Haikou 571127,China;Laboratory of Marine Geophysics and Georesources,Institute of Deep-sea Science and Engineering,Chinese Academy of Sciences,Sanya 572000,China;Ocean University of China,Qingdao 266100,China;School of Marine Science,Sun Yat-sen University,Zhuhai 519083,China)

机构地区：[1]海南省海洋地质资源与环境重点实验室,海口570206 [2]海南省海洋地质调查院,海口570206 [3]中国科学院深海科学与工程研究所,三亚572000 [4]中国海洋大学海洋地球科学学院,青岛266100 [5]中山大学海洋科学学院,珠海519083

出　　处：《海洋地质前沿》2024年第6期26-38,共13页Marine Geology Frontiers

基　　金：海南省海洋地质资源与环境重点实验室开放课题项目(HNHYDZZYHJKF003,HNHYDZZYHJKF017);南海地质构造研究项目(T100731);海南省科技计划三亚崖州湾科技城联合项目(2021JJLH0047);中国博士后科学基金(2021M703667);广东省区域联合基金-青年基金(2021A1515110844)。

摘　　要：基于中沙环礁潟湖的50.5m钻孔岩芯,采用薄片观察、测年、主微量元素和碳氧同位素分析等方法,探讨了钻孔岩芯的层序地层、沉积微相和地球化学特征。结果显示该处沉积过程对晚第四纪海平面变化和物源有明显响应。结合测年结果,将岩芯的生物礁灰岩划分为10个更新世层序,且可与MIS5—MIS23阶段间冰期海水高位时期相对应。元素Sr和U的含量变化随深度加大而呈现阶梯式下降,这是由于冰期海水低位时期碳酸盐岩台地反复暴露使得老地层接受更长时间淡水成岩作用从而导致元素累积流失更多,且数值下降处可以指示层序界面。该钻孔钻遇的珊瑚礁多发育在高位体系域的进积阶段,推测是由于晚第四纪时期海平面变化速度快,且呈现迅速上升而缓慢下降的特征引起的。物源贡献因子分析结果显示,陆源物质来源、文石和高镁方解石来源、低镁方解石来源和鸟类粪便来源等4类物源影响礁灰岩的主量元素组成。本研究还揭示出现今潟湖钻遇的珊瑚礁地层有对晚第四纪10万a短偏心率周期的海平面变化响应较好,体现潟湖和台地边缘珊瑚礁的差异生长是造成现今环礁潟湖水深较大的原因之一,对解释现代环礁由来有一定的启示意义。Based on thin-section observation,dating results,analysis of major and minor elements and carbon and oxygen stable isotopes,the sequence stratigraphy,sedimentary facies and geochemical characteristics of a 50.5-m drill core in the atoll lagoon were examined and its significance for paleoclimate and paleoenvironment was ex-plored.Results show that sedimentary features well responded to the Late Quaternary sea level change and provenance.Using dating results,ten Pleistocene sequences were correlated with interglacial stages during Mar-ine Isotope Stages 5-23.The gradual decrease in Sr and U values is due to the longer duration of exposure and meteoric diagenesis of the older sequence relative to the younger sequence in the carbonate platform,clearly indic-ating the existence of a sequence boundary.The reef facies were formed mainly during sea level fall,indicating progradational growth of the reef.Rapid sea level rise and slow sea level fall lead to reef facies preferring to grow in the highstand systems tracts of the sequences.Four potential sources were identified from the combined PMF(positive matrix factorization)factor profiles and factor contributions.Our results indicate the drilling reef layers in the modern lagoon can well reflect the sea level change controlled by the eccentricity cycles of 100 ka and that greater reef thickening of aggradational reef in the marginal platform than that of progradational reef in the lagoon,which enriched our understanding of the evolutional processes of the atoll with a deep lagoon.

关 键 词：生物礁 沉积微相 地球化学 晚第四纪海平面变化 中沙环礁潟湖钻孔 

分 类 号：P736[天文地球—海洋地质]