| 西沙群岛琛航岛全新世珊瑚礁的起始发育时间及其海平面指示意义 |
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| 引用本文： | 覃业曼,余克服,王瑞,姜伟,许慎栋.西沙群岛琛航岛全新世珊瑚礁的起始发育时间及其海平面指示意义[J].热带地理,2019,39(3):319-328. |
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| 作者姓名： | 覃业曼 余克服 王瑞 姜伟 许慎栋 |
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| 作者单位： | （广西大学 a. 广西南海珊瑚礁研究重点实验室；b. 珊瑚礁研究中心；c. 海洋学院；d. 林学院；南宁 530004） |
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| 基金项目： | 国家自然科学基金重点项目（91428203）；广西科技项目（AD17129063、AA17204074） |
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| 摘 要： | 以西沙群岛琛航岛珊瑚礁钻孔为材料，通过高精度铀系测年技术测定了全新世底界的年代；同时利用MAT-253同位素质谱仪和电感耦合等离子体质谱仪测定了0~20 m层段δ13C、δ18O和锶元素的质量分数，以U-Th年龄为基础，结合δ13C、δ18O和锶元素的质量分数均在16~17 m之间明显降低这一特点，得到琛航岛全新世珊瑚礁的起始发育时间为距今7 900 a前，不整合于晚更新世的珊瑚礁体（年代老于110 ka）之上，全新世礁体的厚度为16.7 m。考虑研究区域新构造活动相对稳定，以及南海现代珊瑚礁的礁坪面与大潮低潮面基本一致，琛科2井的钻孔井位高于现代礁坪约2.9 m，推测其起始发育时的位置在现代海平面大潮低潮面之下约13.8 m，即西沙群岛海域7 900 a前的海平面在现代海平面以下约13.8 m，近7 900 a以来海平面上升了至少13.8 m。这一结果为理解全新世南海珊瑚礁的发育历史及海平面变化提供了新的信息。
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| 关 键 词： | 全新世 珊瑚礁 起始发育时间 海平面 西沙群岛琛航岛 |
The Initiation Time of the Holocene Coral Reef at the Chenhang Island (Xisha Islands) and Its Significance as a Sea Level Indicator |
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| Qin Yeman,Yu Kefu,Wang Rui,Jiang Wei and Xu Shendong.The Initiation Time of the Holocene Coral Reef at the Chenhang Island (Xisha Islands) and Its Significance as a Sea Level Indicator[J].Tropical Geography,2019,39(3):319-328. |
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| Authors: | Qin Yeman Yu Kefu Wang Rui Jiang Wei and Xu Shendong |
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| Institution: | （Guangxi University a. Guangxi Laboratory on the Study of Coral Reefs in the South China Sea; b. Coral Reef Research Center of China; c. School of Marine Sciences; d. Forestry College, Nanning 530004, China） |
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| Abstract: | This study relies on analyses of the top layer of the material extracted from Well Chenke-2, which is part of a coral reef drilling program in the south-east of Chenhang Island, Xisha Islands. The age of the material at the bottom of the borehole was determined by high-precision uranium dating technology. Five coral samples were selected for the U-Th dating. The five groups of data can be clearly dated to the Holocene or to the Pleistocene. The Holocene part includes samples CK2-15, CK2-16, and CK2-17. Their age was determined as 7 914 ± 67, 7 552 ± 73, and 7 584 ± 55 years, respectively. The Pleistocene part includes samples CK2-18 and CK2-19. Their age was determined as 112 700 ± 700 and 128 100 ± 1 000 years, respectively. Furthermore, a MAT-253 isotope mass content of δ13C, δ18O, and strontium in 21 whole rock samples extracted in the depth interval 0-21 m. Based on the contents of these three elements, the interval can be divided into two parts. The content of δ13C, δ18O, and strontium in the depth interval 0-16 m is higher, with average values of 0.647‰, -3.392‰, and 0.843%, respectively, than that in the depth interval 17-21 m, with average values of -3.185‰, -7.994‰, and 0.174%, respectively. On the basis of the U-Th age, and considering that the contents of δ13C, δ18O, and strontium decrease evidently between 16 and 17 m, it can be concluded that the boundary between the Holocene and the Pleistocene corals is located at a depth between 16 and17 m in Well Chenke-2, and that the age of the corals determined by uranium dating in the upper part of the boundary represents the initiation time of the Holocene reefs. Therefore, it is concluded that the Holocene coral reefs in Chenhang Island started to develop 7 900 years ago, basically simultaneously with most of the Holocene reefs in the Indo-West Pacific, Central Pacific, and Caribbean. The Holocene reefs are 16.7 m thick, and are in unconformity with the late Pleistocene coral reefs (aged 110 ka). Considering the relative stability of the Neotectonic activities in the study area, as well as the fact that the reef flat of the modern coral reefs in the South China Sea is basically located at the low tide height, and that the borehole of Well Chenke-2 is located approximately 2.9 m above the modern reef flat, it is speculated that the top of Well Chenke-2 was originally located about 13.8 m below the low tide level of the modern sea. In other words, the sea level at Xisha Islands 7 900 years ago was about 13.8 m below the modern sea level. This result provides new information for understanding the development history of the Holocene coral reefs in the South China Sea and the sea level changes in the area. |
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| Keywords: | Holocene coral reef initiation time sea level the Chenhang Island (Xisha Islands) |
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