Holocene sedimentary evolution of a mid-ocean atoll lagoon, Maldives, Indian Ocean
Holocene sedimentary evolution of a mid-ocean atoll lagoon, Maldives, Indian Ocean
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DOI：
10.1007/s00531-014-1068-8
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发表时间：
2015-01-01
影响因子：
2.3
通讯作者：
Gischler, Eberhard
中科院分区：
文献类型：
--
作者：
Klostermann, Lars;Gischler, Eberhard
根据对马尔代夫拉兹虎环礁泻湖岩心的详细分析，已识别出六种碳酸盐相、一种土壤相和一种泥炭相。碳酸盐和稀有不透明颗粒的丰度用点计数器进行了量化。用X射线衍射仪测定了样品的矿物组成。使用聚类分析进行相的统计描述是基于点计数、矿物学和结构分析。6种碳酸盐相丰度由高到低依次为：软体动物-珊瑚-藻类浮岩-红藻岩(30%)、软体动物-珊瑚-红藻赤藻-红藻岩相(23%)、软体动物-珊瑚-藻类围岩-浮岩(23%)、软体-珊瑚-藻类围岩(13%)、软体-珊瑚泥岩-软体动物泥岩(9%)和软体动物泥岩(2%)。碳酸盐岩相代表泻湖背景沉积，主要由细粒沉积组成，事件沉积沉积了输送的粗粒生物礁成分。对57个碳酸盐样品和1个泥炭样品进行了放射性测年，涵盖了从10kyr BP到今天的全新世海侵。将泻湖的沉积资料与当地的两条海平面曲线进行对比，可以识别出三个体系域：(1)以岩溶和土壤沉积为特征的低水位体系域；10kyrBP；(2)以泥炭和碳酸盐为特征的海侵体系域，间隔10-6.5kyBP；(3)以碳酸盐沉积为主的高水位体系域，进一步划分为3个阶段(6.5-3kyrBP、3-1kyrBP和1-0kyrBP)。全新世海侵期间，沉积速率持续增加，在3~1kyr BP期间达到最大值1.4m/Kyr。现代(1-0kyrBP)平均沉积速率平均为0.6m/kyr。一个简单的计算表明，在全新世高水位期间，两个过程(背景沉积和沙坪进积)可能会填满泻湖的可容纳空间，但这些过程不足以填满群岛更大的环礁泻湖。
Based on detailed analyses of cores covering the lagoon of Rasdhoo Atoll, Maldives, six carbonate facies, one soil, and one peat facies have been identified. The abundance of carbonate and rare opaque grains was quantified with a point counter. X-ray diffractometry was used to measure mineralogical composition of samples. The statistical delineation of facies using cluster analysis was based on point count, mineralogical, and textural analyses. In decreasing abundance, the six carbonate facies are classified as mollusk-coral-algal floatstone to rudstone (30 %), mollusk-coral-red algae rudstone (23 %), mollusk-coral-algal wackestone to floatstone (23 %), mollusk-coral wackestone (13 %), mollusk-coral mudstone to wackestone (9 %), and mollusk mudstone (2 %). The carbonate facies represent lagoonal background sedimentation, mostly consisting of fine sediments, and event sedimentation depositing transported coarse-grained reefal components. Fifty-seven carbonate samples and one peat sample were dated radiometrically, covering the Holocene transgression from 10 kyrs BP until today. Comparing the sediment accumulation data of the lagoon with two local sea-level curves, three systems tracts can be identified: (1) a lowstand systems tract characterized by karst and soil deposition >10 kyrs BP, (2) a transgressive systems tract with peat and carbonate separated by hiatus 10-6.5 kyrs BP, and (3) a highstand systems tract dominated by carbonate sedimentation 6.5-0 kyrs BP and further divided into three stages (6.5-3, 3-1, and 1-0 kyrs BP). During the Holocene transgression, sedimentation rates increased continuously to a maximum of 1.4 m/kyr during 3-1 kyrs BP. Modern (1-0 kyrs BP) mean sedimentation rates average 0.6 m/kyr. A simple calculation suggests that two processes (background sedimentation and sand apron progradation) will probably fill up the accommodation space of the lagoon during the Holocene highstand, but these processes will not suffice to fill the larger atoll lagoons of the archipelago.