Late Quaternary reef growth and sea level in the Maldives (Indian Ocean)
Late Quaternary reef growth and sea level in the Maldives (Indian Ocean)
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DOI：
10.1016/j.margeo.2008.01.004
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发表时间：
2008-04
期刊：
影响因子：
2.9
通讯作者：
E. Gischler;J. Hudson;Andrzej Pisera
中科院分区：
文献类型：
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作者：
E. Gischler;J. Hudson;Andrzej Pisera
基于旋转钻井和放射性和U系列测年，我们提出了第一个全面的数据全新世珊瑚礁解剖和海平面上升，以及在马尔代夫的下伏更新世石灰岩的性质和年龄。马尔代夫中部Rasdhoo环礁全新世生物礁由4种相组成：（1）粗壮分枝珊瑚相，（2）珊瑚藻相，（3）穹状珊瑚相，（4）碎屑砂和碎石相。边缘礁以分枝珊瑚相和珊瑚藻相为主，泻湖礁以穹状珊瑚相和碎屑相为主。此外，在边缘礁的较低核心部分发现了微生物岩结壳。微生物岩形成于全新世早期的礁洞中。全新世生物礁厚度为14.5 ~>22 m。珊瑚礁的生长早在8.5 kyr BP就开始了。边缘礁以维持模式增生，速率>15 m/kyr。海平面上升速率从7-6 kyr BP显著减缓，随后以<1 m/kyr的速率逐渐上升。泻湖礁以追赶模式增生，速率约为4 m/kyr。尽管在这项研究中没有发现海平面高于现在的迹象，但从数据中并不完全清楚海平面是否在全新世晚期逐渐上升到或超过现在的水平。所研究的全新世生物礁中的海底胶结作用相当弱，可能是高加积速率的结果，即，可用于整合的时间短。更新世珊瑚颗粒灰岩遇到一个核心在14.5米低于目前的水平和三个U系列的日期表明沉积在海洋同位素阶段5E约。135 kyr BP.
Based on rotary drilling and radiometric and U-series dating, we present the first comprehensive data on Holocene reef anatomy and sea-level rise as well as nature and age of underlying Pleistocene limestone in the Maldives. Holocene reefs in Rasdhoo Atoll, central Maldives, are composed of four facies including (1) robust-branching coral facies, (2) coralline algal facies, (3) domal coral facies, and (4) detrital sand and rubble facies. Branching coral and coralline algal facies predominate the marginal reefs and domal corals and detrital facies preferentially occur in a lagoon reef. In addition, microbialite crusts are found in lower core sections of marginal reefs. Microbialites formed during the early Holocene in reef cavities. Holocene reef thickness ranges from 14.5 m to >22 m. Reef growth started as early as 8.5 kyr BP. Marginal reefs accreted in the keep-up mode with rates of >15 m/kyr. Rate of sea-level rise significantly slowed down from 7–6 kyr BP and subsequently gradually rose with rates <1 m/kyr. The lagoon reef accreted in the catch-up mode with rates of around 4 m/kyr. Even though no indications of a higher than present sea level were found during this study, it is not entirely clear from the data whether the sea gradually rose to or exceeded present level in the late Holocene. Submarine cementation in Holocene reefs studied is rather weak, presumably as a consequence of high accretion-rates, i.e., short time available for consolidation. Pleistocene coral grainstone was encountered in one core at 14.5 m below present level and three U-series dates indicate deposition during marine isotope stage 5e ca. 135 kyr BP.