三亚海岸珊瑚礁地层成因演化与工程地质分区

珊瑚礁是一类特殊的工程建设场地,受地质成因、生物作用、海洋水动力环境和地质环境演化等多方面影响。开展珊瑚礁场地工程地质分区研究,不仅对认识珊瑚礁岩土层的成因和变化规律、分析评价珊瑚礁场地的工程地质条件等具有重要的理论意义,而且对未来南海岛礁工程建设具有重要指导作用。在现场地质调查的基础上,采用现场原位测试、室内试验和钻探岩芯分析等综合技术手段,分析了三亚珊瑚礁地层的演化历史,对地层结构特征、矿物成分、化学成分和土层物理力学性质进行了深入分析,将三亚海岸珊瑚礁场地划分为泻湖沉积区、砂坝堆积区和水下珊瑚生长堆积区;对各工程地质分区的工程特性和建设适宜性进行了分析评价。研究成果可以对珊瑚礁场地的地质调查、工程规划和设计提供指导和借鉴。     

珊瑚礁海岸水动力学问题研究综述

珊瑚礁水动力学是一个涉及生态、环境、地质和工程学的交叉课题,其水动力学研究不仅为珊瑚礁海域生态系统的维护和海岸线的演变提供一定的理论参考,还能为海岸的防灾减灾以及岛礁工程的建设提供一定的决策依据。回顾了国内外珊瑚礁海岸水动力问题的研究与进展,从现场观测、理论模型、物理模型试验和数值模型4个方面对当前该领域的研究进展进行了综述,并提出今后现场观测研究对象可关注南中国海的珊瑚岛礁,理论分析方法可侧重考虑非线性波浪理论,物理模型试验可采用大型波浪水槽和港池来复演现场尺度的水动力问题,数值模型可采用计算流体力学（Computational Fluid Dynamics,CFD）方法对波浪与珊瑚礁相互作用进行精细化模拟,本文旨在为今后国内珊瑚礁水动力学方面的相关研究提供一定的借鉴和参考。     

基于应力-应变曲线的礁灰岩脆性特征评价EI北大核心CSCD

脆性是岩石类材料的重要性质。针对南海某岛礁在某深度范围内的珊瑚格架灰岩、砾块灰岩、砾屑灰岩及砂屑灰岩的钻孔芯样,开展室内物理性质测试及压缩试验。研究表明,礁灰岩的物理力学性质与其沉积组构和成岩作用密切相关;基于峰后应力降的相对大小和绝对速率的脆性指标计算方法能够反映礁灰岩的破坏特征;围压对礁灰岩的脆性指标影响显著,随着围压的增大,试样的脆性指标呈现趋势性降低;单轴压缩条件下,低孔隙率的砂屑灰岩脆性指标与水泥砂浆类似,同时高于格架灰岩及砾块灰岩;随着孔隙率的增大,砂屑灰岩和砾屑灰岩的脆性指标减小,饱和单轴抗压强度也与孔隙率呈负相关关系。     

Incorporation of strontium into reef coral skeletal carbonate

Two thousand and twenty well-characterized coral specimens from 17 localities have been analyzed for Sr. Seventy-three genera and subgenera, mostly hermatypic scleractinians, are represented. For some genera, specimens living in surface reef environments are compared with those from 18.3 m depths on the same reefs. Growth rates for some species have also been measured at these depths at one of the sampling sites. Skeletal strontium for a given genus decreases with increasing water temperature, a relationship which previously eluded detection. Aragonite deposited by corals living on the reef at a depth of 18.3 m contains more strontium than the skeletal aragonite of the same coral genera from shallow-water, surface environments. Quantitative treatment of the data for Acropora, one of the most abundant and widely distributed of the reef-building corals, suggests that the observed strontium variations may reflect variations in the rate of skeletal calcification, rather than direct dependence upon temperature or water depth. There is evidence for ‘species effects’, apparently unrelated to growth rate differences, in that certain coral genera are consistently enriched or depleted in skeletal strontium content relative to other genera living in the same reef environments under identical ambient conditions. Temperature, salinity, water depth, seawater composition, and/or other such parameters may in part determine the levels of trace element concentration in carbonates deposited by corals and other marine invertebrates, but it would appear that these variables more directly affect physiological processes which in turn control skeletal chemistry.     

珊瑚岛礁工程地球物理方法初探

梳理了国内珊瑚岛礁岩土工程物探调查的现状,结合钻孔原位测试,采用成熟的物探方法对珊瑚岛礁进行综合地球物理勘探,说明了各种物探方法的场地适应性和效果。主动源面波探测效果好,面波视速度剖面很好地反映了珊瑚碎屑层与礁灰岩的地层层序;水域地震反射波对外礁坪、向海坡、外海的沉积层界面反映清晰,发现某岛礁的西南、东北端的水底形态不对称,沉积层差异大,可能与珊瑚礁成长的海洋水动力环境有关。孔内电阻率原位测试数据表明,松散珊瑚碎屑层与礁灰岩的电阻率差异很小,在同一数量级,总体上无法采用电法类勘探方法进行地质分层。     

Nutrient enrichment on coral reefs: Is it a major cause of coral reef decline?

Coral reefs are degrading worldwide at an alarming rate. Nutrient over-enrichment is considered a major cause of this decline because degraded coral reefs generally exhibit a shift from high coral cover (low algal cover) to low coral cover with an accompanying high cover and biomass of fleshy algae. Support for such claims is equivocal at best. Critical examination of both experimental laboratory and field studies of nutrient effects on corals and coral reefs, including the Elevated Nutrient on Coral Reefs Experiment (ENCORE) enrichment experiment conducted on the Great Barrier Reef, does not support the idea that the levels of nutrient enrichment documented at anthropogenically-enriched sites can affect the physiology of corals in a harmful way, or for most cases, be the sole or major cause of shifts in coralalgal abundance. Factors other than nutrient enrichment can be significant causes of coral death and affect algal cover, and include decreased abundance of grazing fishes by fishing, and of grazing sea urchins to disease; grazing preferences of remaining grazers; temperature stress that kills coral (i.e., coral bleaching) and creates more open substrate for algal colonization; sedimentation stress that can weaken adult corals and prevent coral recruitment; coral diseases that may be secondary to coral bleaching; and outbreaks of coral predators and sea urchins that may be secondary effects of overfishing. Any factor that leads to coral death or reduces levels of herbivory will leave more substrate open for algal colonization or make the effects of even low-level enrichment more severe. Factors that contribute to an imbalance between production and consumption will result in community structure changes similar to those expected from over-enrichment. Over-enrichment can be and has been the cause of localized coral reef degradation, but the case for widespread effects is not substantiated.     

珊瑚礁地层钻探取心技术研究及应用

人工吹填珊瑚岛礁地层结构比较特殊,以珊瑚砂和珊瑚碎屑为主,取心和成孔难度较大。以南海某岛礁地质钻探取心工程实践为例,针对地层岩性特点,采用一系列对应技术措施：上部松散或弱胶结砂砾层采取跟管钻进和无水干钻取心技术;礁灰岩全漏失地层设计了一套掏砂钻具进行掏砂,确保井眼干净;软硬互层采用超前侧喷钻头;粉砂质地层采取小口径钻具无水干钻取心技术等。该技术在18个钻孔实施中取得了良好的效果,可为后续珊瑚礁地层钻探取心提供借鉴。     

基于珊瑚礁岛分区分层的淡水形成过程研究

为了探究土的分层特征对珊瑚礁岛下淡水透镜体形成的意义,在南海某珊瑚礁岛采用钻孔取样,分析每个钻孔不同层位样品的粒度。根据水平和垂直方向上的粒度特征,确定岛的水平分区和垂直分层;根据每个钻孔所代表的范围,确定每个水平分区的面积;根据每个钻孔中不同颗粒级配的样品所代表的厚度,确定每个垂直分层厚度。礁灰岩以上松散层的不同分区和分层的颗粒级配控制地层的渗透性,垂直和水平方向的渗透性特征控制淡水透镜体形成的难度、淡水透镜体的总厚度以及过渡带的厚度。根据岛的总面积和垂直分层数建立数值模型,得到不同时间、不同水平位置和垂直深度的地下水浓度特征的模拟结果。     

A preliminary study on the environmental condition of the coral reef habitat

The present investigation was carried in coral reef areas of Palk Bay, Madapam. Palk Bay corals were found disturbed by human beings due to oil pollution, waste discharge from processing units and discharge of domestic household wastes from the nearby Mandapam town. Environmental conditions of the coral reef habitat in the Palk Bay, Mandapam was analyzed for a period of six months at fortnightly intervals for March to August 2001 on the coral reef areas. Temperature, pH, Dissolved Oxygen (DO), Biological Oxygen Demand (BOD) and Total Organic Carbon (TOC) were analyzed at five different stations of Palk Bay, Madapam. The maximum mean values of temperature, pH, DO, BOD and TOC for the four experimental and control stations were 32.6°C, 8.7, 7.02ppm, 8.29ppm and 2.13% and 31.5°C, 8.3, 7.98ppm, 5.71ppm and 0.48% respectively. The sampling stations were selected on the basis of their importance.     

The durability of bioclastic sediments and implications for coral reef deposit formation

The generation and composition of carbonate sediment within tropical carbonate settings is controlled by the skeletal production of CaCO₃ in conjunction with physical, biological and chemical processes which act to break down and disperse skeletal remains. Using the results of detailed tumbling barrel experiments, this paper discusses the role the physical durability of common constituents of reef sediment plays in the composition of coral reef deposits. The durability of the skeletal remains of six reef sediment constituents was determined experimentally using tumbling barrels. Results indicate that constituent durability varies considerably amongst common reef sediment constituents. Calcareous algae Halimeda was the least durable constituent tested, followed by larger benthic foraminifera Baculogypsina sphaerulata and Marginopora vertebralis and the pelecypod Fragum fragum. Two species of branching coral (Acropora sarmentosa and Acropora nasuta) were found to be the most resistant to physical destruction. These findings provide increased power to interpret reef and island deposits and the potential role skeletal durability plays in the retention of constituent skeletons within coral reef associated sedimentary systems.     

不同结构类型珊瑚礁灰岩弹性波特性研究

基于岩石弹性波特性的地震方法是目前地球物理勘探中最主要的方法,岩石中弹性波传播速度是联系岩石物理力学特性与地质学的有效桥梁。对于海相生物成因的珊瑚礁灰岩而言,其弹性波特性研究是了解珊瑚礁体内部整体性质的有效途径。研究表明,珊瑚礁灰岩的弹性纵波速度与干密度、回弹值呈线性正相关关系,与孔隙度呈线性负相关关系。不同结构类型珊瑚礁灰岩弹性波特性表现出显著的差异性,珊瑚骨架灰岩和珊瑚砾块灰岩均匀性较好,珊瑚砾屑灰岩和珊瑚砂屑灰岩离散性较大。基于珊瑚礁灰岩纵波速度与干密度、孔隙度以及回弹值之间的关系,结合某珊瑚礁体钻孔岩芯沿深度变化的回弹值信息以及岩芯薄片光学检测结果,提出一个基于纵波速度的珊瑚礁灰岩质量等级的划分标准,具有一定的可靠度和适用性。运用岩石二相体模型基本原理,建立了修正的时间平均公式,而不同结构类型珊瑚礁灰岩弹性波特性均符合雷莫亨特-加德纳方程。     

黔南晚石炭世旋回珊瑚礁群落演化研究

发育于黔南地区的扁坪—岩板寨晚石炭世旋回珊瑚礁由3个旋回组成,每个旋回都具有较高的生物含量和生物多样性。根据生物的丰度和功能可识别出叶状藻-"不明管状物"群落、Ivanovia cf.manchurica群落、Tubiphytes群落和Fomitchevella群落。旋回珊瑚礁的演化过程可划分为6个阶段。分析表明,礁体形成过程中曾一度出现了高能的环境,第二、三旋回经历了迅速的环境变化。     

岛礁吹填珊瑚砂力学行为与颗粒破碎特性试验研究

珊瑚砂是岛礁陆域吹填唯一的材料,因其特殊的海洋生物成因和孔隙结构特征,珊瑚砂颗粒在常规工程应力水平下就会发生破碎。通过对取自南海某吹填岛礁的珊瑚砂开展室内三轴固结排水剪切试验,研究珊瑚砂强度、变形参数和颗粒破碎程度随相对密实度、围压的演变规律,并与其他研究成果中的南海珊瑚砂强度参数进行对比分析。研究结果表明:珊瑚砂应变软化及剪胀特征随有效围压的增大、密实度的减小而逐渐减弱;在常规应力范围内,得到珊瑚砂峰值摩擦角和临界状态摩擦角的取值范围分别为33°～58°和28°～47°,且均随有效围压的增大而减小;建立了珊瑚砂割线模量E₅₀与相对密实度、有效围压间的关系式;珊瑚砂峰值摩擦角与修正相对破碎指数B_r^*间的关系可用指数为负数的幂函数关系式拟合,且当颗粒破碎程度较高时,峰值摩擦角随修正相对破碎指数的增大而减小的趋势变缓;珊瑚砂修正相对破碎指数随塑性功的增大近似以双曲线的形式增长,密实度对两者间的关系影响不大。该研究成果可为南海岛礁基础设施的安全设计提供参考。     

Vitality of reef coral populations off Key Largo,Florida: Recruitment and mortality

Recently, questions about the health of the coral reefs of the Florida Keys have been raised. Estimates of net recruitment and mortality of reef corals on Carysfort Reef, Key Largo, Florida, suggest that these populations declined over the 14 month interval studied. The greatest rate of change on Carysfort Reef, the most well developed reef in the northern Keys, occurred in the zone of richest coverage by corals. Water pollution associated with the tremendous increase in the human population of South Florida in the last twenty years may be contributing to the reef's decline.     

Enhancement of regional variations in salinity and temperature in a coral reef lagoon, New Caledonia

The variability in salinity and temperature in the southwest lagoon of New Caledonia (2100 km²) under non-storm conditions is analysed using a 4-year dataset (1997–2001). Seasonal and interannual variations in salinity are amplified nearshore. Temperature is larger in bays than in the open lagoon during summer, the reverse is true in winter. El Niño Southern Oscillation (ENSO) related nearshore temperature variations parallel those at regional scale, but with seasonal variations amplified. Haline stratification, if any, is enhanced in coastal areas. To cite this article: S. Ouillon et al., C. R. Geoscience 337 (2005).     

Effects of differential tectonic uplift on Late Quaternary coral reef diagenesis,Huon Peninsula,Papua New Guinea

Mineralogical, petrological and geochemical analyses of corals and associated skeletal limestones taken from three transects across the Late Quaternary raised coral reefs of the Huon Peninsula, Papua New Guinea, show that tectonic uplift can be related to the degree of subaerial diagenesis of the reefs. Where the uplift rate is high, Pleistocene corals frequently retain their aragonite mineralogy, even though the annual rainfall is relatively high. In contrast, similar age corals from low‐uplift areas are consistently altered neomorphically to calcite. The transformation of reef skeletal limestones shows a similar, but less pronounced, trend to the corals. Chemical analysis shows that the neomorphic calcite crystals of coral skeletons from the low‐uplift areas have relatively higher Sr and Mg concentrations, compared with those in high‐uplift areas. This may indicate that neomorphism of corals in the low‐uplift terraces takes place at a relatively higher rate and an earlier stage than that in the high‐uplift areas. The pattern of diagenesis of the Huon reefs can be explained by the effects of tectonic uplift on the regional hydrological regime. First, lower uplift rates allow a raised reef or any part of it to remain in the meteoric phreatic zone for a relatively long time. Second, river gorge slopes from low‐uplift regions have lower gradients and reef terraces in these areas have more extensive raised lagoon depressions than in high‐uplift areas. Thus, there is less runoff and consequently more extensive vadose percolation in the former areas. Third, the resulting low‐relief topography in low‐uplift areas prompts formation of soils on the terraces, and further increases the ability of interaction between coral reefs and formation water.     

A baseline study of trace metals in a coral reef sedimentary environment,Lakshadweep Archipelago

Surficial and core samples collected from the sedimentary microenvironments of Lakshadweep Archipelago were analysed for their trace metal contents. The synoptical relations in spatial distributions with respect to environmental conditions such as pH, organic carbon and sediment texture were inter-correlated. Some of the metals exhibited good correlations with Fe/Mn, which reflect their similarity in distribution rather than anthropogenic enrichment. Inter-relating the variations in metal—pH relationships with metal—organic carbon, in general, those which exhibited positive correlations with pH, displayed negative interactions with organic carbon content and vice versa. Comparatively, higher values of Fe in the mangrove area of one of the islands highlight the possibility of precipitation of Fe as iron sulphides, which are common in mangrove ecosystem. Based on the contamination factors for Pb, Zn and Cd, as well as the geo-accumulation index of Cd, it can be generalised that some of the islands remain polluted with respect to these elements. An evaluation based on pollution load index shows that none of the islands surveyed for this study posed a serious threat in trace metal pollution. Bray Curtis similarity index was computed to find out the similarity among metals/islands, using non-transformed data of metal concentrations. Group linkage clustering technique was used for drawing dendrograms to show the similarity among them.     

Return of the coral reef hypothesis: basin to shelf partitioning of CaCO3 and its effect on atmospheric CO2

Differences in the rate of coral reef carbonate deposition from the Pleistocene to the Holocene may account for the Quaternary variation of atmospheric CO2. Volumes of carbonate associated with Holocene reefs require an average deposition rate of 2.0 x 10(13) mol/yr for the past 5 ka. In light of combined riverine, midocean ridge, and ground-water fluxes of calcium to the oceans of 2.3 x 10(13) mol/yr, the current flux of calcium carbonate to pelagic sediments must be far below the Pleistocene average of 1.2 x 10(13) mol/yr. We suggest that sea-level change shifts the locus of carbonate deposition from the deep sea to the shelves as the normal glacial-interglacial pattern of deposition for Quaternary global carbonates. To assess the impact of these changes on atmospheric CO2, a simple numerical simulation of the global carbon cycle was developed. Atmospheric CO2 as well as calcite saturation depth and sediment responses to these carbonate deposition changes are examined. Atmospheric CO2 changes close to those observed in the Vostok ice core, approximately 80 ppm CO2, for the Quaternary are observed as well as the approximate depth changes in percent carbonate of sediments measured in the Pacific Ocean over the same time interval.