我国生物礁研究的发展

黄汲清教授研究我国南方二叠系，引发了我国对古代生物礁的研究工作。６０年代起我国开始对古代生物礁的研究。现代珊瑚礁研究从２０年代末兴起，８０年代以来正在深入发展，同全球变化研究和珊瑚礁开发紧密联系，拓展了研究领域，积累了许多新知。     

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。     

海南岛三亚湾海滩研究*

海南岛三亚湾及其周边海滩可分为两种主要类型:一类是岩礁海岸海滩,发育于基岩和珊瑚礁岛波影区或珊瑚礁平台后侧,多为背叠式砂砾滩,滩窄、坡陡,具有数道陡坎,在岛礁背风侧常发育不同阶段的连岛坝,如白排人工岛西南端海滩、鹿回头湾大洲后侧及对岸的海滩、鹿回头湾和小东海海滩;另一类是沙坝海岸海滩,发育于向外海敞开的大沙坝的向海侧,海湾内砂质沉积物丰富,形成滩脊式或背叠式砂质滩,滩面宽坦,物质较细,如三亚湾和大东海海滩。因湾口朝向与湾内岛礁分布发育情况不同,湾内受常浪和台风强浪作用的强度与频率不同,加之现代泥沙补给情况的差异,这一类海滩的形态结构亦不尽相同。如三亚湾西侧近岬角处,波能辐聚,动力强,侵蚀作用突出,滩面呈近直线形倾斜,并形成两道陡坎;三亚湾中部,受岛礁保护,滩面宽阔,波浪消能空间充足,物质丰富,发育滩脊型海滩,滩面呈上凸形,基本稳定;三亚湾东侧,虽有岛礁掩蔽,但由于人为修建的绿地草坪带和水泥碎砖石小径等,建设高度过低, 束狭了激浪带的自由作用宽度,减小了波浪消能范围,破坏了海滩的整体结构,同时阻断了沙坝向海滩的供沙, 使滩面坡度加大,物质粗化,局部与小径相接处形成侵蚀陡坎、椰树等倾斜,呈侵蚀状态。     

An analysis of problems related to dredging in a coral atoll: Kavaratti,Lakshadweep, Indian Ocean

Detailed survey on various aspects has indicated the presence of calcareous sands in the lagoons of Lakshadweep (Arabian Sea) suitable for a number of industries. No data are available about the effect of mining the deposits on these atolls. This paper attempts to analyze the data collected in studying the channel that has been dredged in connection with development of the harbor at Kavaratti lagoon Maximum depth in the lagoon is 3 m Outside the depth increases rapidly within a short distance of about 100 m Sediment in the lagoon is derived from the destruction of the reefs and consists of corals, halimeda, molluscan shells, foraminifers, and red algae Presently sands are being dredged from the lagoon and dumped in the sea and these sands are lost as there is a steep slope outside A study of shoreline records for the beaches adjacent to the dredging site shows that the shoreline is an area of accretion. It is quite possible that removal of 1 or 2 meters of sands from the lagoon floor will not affect the equilibrium if the reef is not disturbed Dredging of coral sands for different purposes is known from Fiji, Johnson Island, offshore Apia and no adverse effect has been noticed Removal of limited quantity of sands is recommended, since in a closed system of such atolls like Kavaratti there is always a surplus of sediment transported to the deep sea. The surplus sediment opens the way to sediment dredging. However, reef areas should not be disturbed since the reef is the most important sediment-generating site Studies on growth rate, currents, tides, and bathymetry should be continued to detect the adverse effect simultaneously with dredging The views expressed in this paper are entirely those of the author and no organization is responsible for them.     

Shoreline variability of an urban beach fronted by a beachrock reef from video imagery

This contribution presents the results of a study on the shoreline variability of a natural perched urban beach (Ammoudara, N. Crete, Greece). Shoreline variability was monitored in high spatio-temporal resolution using time series of coastal video images and a novel, fully automated 2-D shoreline detection algorithm. Ten-month video monitoring showed that cross-shore shoreline change was, in some areas, up to 8 m with adjacent sections of the shoreline showing contrasting patterns of beach loss or gain. Variability increased in spring/early summer and stabilized until the end of the summer when partial beach recovery commenced. Correlation of the patterns of beach change with wave forcing (as recorded at an offshore wave buoy) is not straightforward; the only discernible association was that particularly energetic waves from the northern sector can trigger changes in the patterns of shoreline variability and that increased variability might be sustained by increases in offshore wave steepness. It was also found that the fronting beachrock reef exerts significant geological control on beach hydrodynamics. Hydrodynamic modelling and observations during an energetic event showed that the reef can filter wave energy in a highly differential manner, depending on its local architecture. In some areas, the reef allows only low-energy waves to impinge on the shoreline, whereas elsewhere penetration of higher waves is facilitated by the low elevation and limited width of the reef or by the presence of an inlet. Wave/reef interaction can also generate complex circulation patterns, including rip currents that appeared to be also constrained by the reef architecture.     

Origins and development of Holocene coral reefs: a revisited model based on reef boreholes in the Seychelles, Indian Ocean

 Until recently, concepts of coral reef growth and accumulation have been predominantly based on a Darwinian model. In this, the upwards and outwards growth of a reef core (a coral framework) takes place over a foreslope consisting of reef talus, with the simultaneous filling of the back-reef lagoon by reef-derived debris. The principal adaptations of this pattern relate to the influence of relative changes in sea level and commonly ignore oceanographic factors such as storm frequency and severity. Boreholes through the outer edge of a fringing reef in the Seychelles, western Indian Ocean, reveal a record of Holocene sediment accumulation first established approximately 8 ka ago. Faunal and floral associations show that growth of this body began in relatively deep water but that this shallowed to <5 m within 1 ka. Subsequent accumulation was of “keep-up” style but, as the rate of sea-level rise slowed, shoaling became more frequent and aggradation was limited by reducing accommodation space. Constructional facies are characterised either by massive corals, including Leptastrea, Porites and faviids, or by branching corals, typically Acropora of the danai-robusta group. Coral surfaces may be encrusted by red algae, foraminifera and vermetids, and are commonly bored by filamentous algae, clionids and molluscs. However, detrital facies are volumetrically dominant, and the paucity of a constructional framework requires a re-evaluation of models of reef accretion. New models relate the geometry of accretion to the interplay between extreme storm events and fairweather hydrodynamic conditions. These suggest that a contiguous framework forms in areas of moderate fairweather energy without extreme storm events. Severe storms destroy the continuity of reef structures and generate increasing volumes of coarse detritus. Low storm severity, coupled with low fairweather hydrodynamic energy, may promote the accumulation of fine-grained reef-derived sediments that inhibit framework growth. While ecology reflects year-by-year sea conditions, lithology and structure are controlled by exceptional storms, with the effects of changing sea level superimposed. Received: 30 November 1998 / Accepted: 4 November 1999     

Carbonate sediments of Elizabeth and Middleton Reefs close to the southern limits of reef growth in the southwest Pacific

Elizabeth and Middleton Reefs are atoll-like structures that have developed on top of volcanic edifices and are close to the southern environmental limit of reef development in the southwest Pacific. Reef morphology and vertical accretion rates during the Holocene appear similar to those on other more tropical reefs. Sediment samples were collected from the lagoon of both reefs and around the flanks of Middleton Reef. A distinctly chlorozoan assemblage was observed with coral, molluscs, Halimeda, coralline algae and foraminifers being the dominant sediment constituents. Lagoon sediment samples show little variation within or between reefs, lacking the concentric zonation characteristic of larger atolls. Samples collected from the flanks of Middleton Reef, and subsurface material from vibrocores, differ compositionally from the surficial lagoon sand and were typically more tropical in character. A comparison of the sediment constituents from these reefs with those of samples from within a fringing reef and from the shelf around Lord Howe Island, further south, indicated regional patterns in sediment composition. Halimeda rapidly decreased in abundance with increased latitude, and appeared confined to deeper water, whereas coralline red algae increased significantly. The rapid change in these major sediment contributors is coincident with the general decrease in coral growth rates with latitude. This reinforces the notion that the latitudinal limit of reef development is constrained by factors other than coral growth alone.     

珊瑚礁岩体完整性评价方法

目前,针对珊瑚礁的钻探勘察工作十分有限,获取完整的珊瑚礁地质信息则更加困难,而开展珊瑚礁的研究对我国海洋资源的开发和利用具有重要意义。结合西沙琛航岛地质调查,应用数字钻孔摄像技术,获得大量第一手地质资料,由于传统的岩体完整性指数（RMDI）法并不完全适用于珊瑚礁岩体的评价,考虑到珊瑚礁岩体的孔洞尺寸效应,提出珊瑚礁孔密度的概念,并建立孔密度函数和块度函数,从而改变传统RMDI法中的? 值,重新构建珊瑚礁岩体完整性密度函数（DIDF）,最终确定珊瑚礁RMDI值,对珊瑚礁岩体的完整性进行评价,并应用于南海西沙群岛琛航岛数字钻孔摄像工程地质勘测中CK1孔的完整性评价,与其他评价结果一致,结果表明：高精度的钻孔图像能为珊瑚礁岩体完整性评价提供可靠的结果;孔密度函数能反映钻孔壁孔洞对珊瑚礁岩体影响程度的轴向分布状况;DIDF能反映钻孔孔壁珊瑚礁岩体完整程度的轴向分布状况;RMDI法用于评价珊瑚礁岩体完整性是可行的,能实现全孔或局部孔段的珊瑚礁岩体完整性评价。     

海南岛鹿回头现代珊瑚岸礁发育史

海南岛南部鹿回头现代珊瑚岸礁发育很好, 是我国久负盛名的岸礁研究区。礁区南北两侧是基岩组成的山岭, 中央为宽约2km的连岛砂洲, 砂洲由礁块和生物碎屑堆积而成。连岛砂洲两侧为海湾, 西北侧称三亚湾, 东南侧为小东海, 海湾中发育有现代珊瑚岸礁。     

The hydrodynamic and sedimentary setting of nearshore coral reefs, central Great Barrier Reef shelf, Australia: Paluma Shoals, a case study

The Great Barrier Reef (GBR) shelf contains a range of coral reefs on the highly turbid shallow inner shelf, where interaction occurs with terrigenous sediments. The modern hydrodynamic and sedimentation regimes at Paluma Shoals, a shore‐attached ‘turbid‐zone’ coral reef, and at Phillips Reef, a fringing reef located 20 km offshore, have been studied to document the mechanisms controlling turbidity. At each reef, waves, currents and near‐bed turbidity were measured for a period of ≈1 month. Bed sediments were sampled at 135 sites. On the inner shelf, muddy sands are widespread, with admixed terrigenous and carbonate gravel components close to the reefs and islands, except on their relatively sheltered SW side, where sandy silty clays occur. At Paluma Shoals, the coral assemblage is characteristic of inner‐shelf or sheltered habitats on the GBR shelf (dominated by Galaxea fascicularis, up to >50% coral cover) and is broadly similar to that at Phillips Reef, further offshore and in deeper water. The sediments of the Paluma Shoals reef flats consist of mixed terrigenous and calcareous gravels and sands, with intermixed silts and clays, whereas the reef slope is dominated by gravelly quartz sands. The main turbidity‐generating process is wave‐driven resuspension, and turbidity ranges up to 175 nephelometric turbidity units (NTU). In contrast, at Phillips Reef, turbidity is <15 NTU and varies little. At Paluma Shoals, turbidity of >40 NTU probably occurs for a total of >40 days each year, and relatively little time is spent at intermediate turbidities (15–50 NTU). The extended time spent at either low or high turbidities is consistent with the biological response of some species of corals to adopt two alternative mechanisms of functioning (autotrophy and heterotrophy) in response to different levels of turbidity. Sedimentation rates over periods of hours may reach the equivalent of 10 000 times the mean global background terrigenous flux (BTF) of sediment to the sea floor, i.e. 10 000 BTF, over three orders of magnitude greater than the Holocene average for Halifax Bay of <3 BTF. As elsewhere along the nearshore zone of the central GBR, dry‐season hydrodynamic conditions form a primary control upon turbidity and the distribution of bed sediments. The location of modern nearshore coral reefs is controlled by the presence of suitable substrates, which in Halifax Bay are Pleistocene and early Holocene coarse‐grained (and relatively stable) alluvial deposits.     

Pliocene‐Quaternary history of Futuna Island,south Vanuatu,southwest Pacific

U‐series ages from thermal ionisation mass spectrometry are reported here for the raised coral reefs of Futuna Island, which lies adjacent to the eastern margin of the backarc Futuna Trough in south Vanuatu, southwest Pacific. U‐series ages from coral from the lowest raised reef indicate that its upper part is most likely to be ca 210 ka, whereas the most elevated raised reef has a likely age of ca 520 ka (range 600–440 ka). The inferred Pliocene‐Quaternary history for Futuna Island and the adjacent Futuna Trough is: (i) formation of the Pliocene—Early Quaternary basaltic‐andesite cone in a southeast part of the Vanuatu Island Arc; (ii) inception of the Futuna Trough (adjacent to the west margin of Futuna Island) since 1.8 Ma; (iii) subsequent uplift of the volcanic cone above sea‐level caused ～500 m of its upper part to be removed by marine erosion; (iv) the island then subsided and at least 160 m of limestone was deposited on the truncated cone; and (v) during the period 520 ka to ca 210 ka seven fringing reefs formed at the margin of the cone as the island was uplifted. Since ca 210 ka Futuna further subsided and, as a result, the post ca 210 ka history of the island is obscure.     

Response of reef coral communities to sea-level rise: a Holocene model from Mauritius (Western Indian Ocean)

The fringing reef at Pointe-au-Sable (Mauritius, Indian Ocean) was used to examine the effects of Holocene sea-level rise on coral growth. This reef is about 1000 m wide and comprises a forereef slope (30 m maximum depth), a narrow reef crest and a very shallow backreef (1·5 m maximum depth). Four major coral communities were recognized, which developed within relatively narrow depth ranges: a Pachyseris/Oulophyllia community (deeper than 20 m), an Acropora‘tabulate’Faviid community (20–6 m); a robust branching Acropora community (less than 6 m) and a Pavona community (less than 10m). Three high-recovery cores show the Holocene reef sequence is a maximum of 19·3 m thick and comprises four coral biofacies which are similar to counterparts identified in modern communities: robust branching, tabular-branching, robust branching-domal and foliaceous coral facies. A minimum sea-level curve for the past 7500 years was constructed. Using distribution patterns of coral biofacies and radiocarbon dates from corals, reconstruction of reef growth history indicates that both offshore and onshore reef zones were developing coevally, aggrading at rates of 4·3 mm year^?1 from 6900 years B.P. The reef caught up with sea-level only after sea-level stabilized. Changes in coral community and reef growth rates were driven principally by increasing water agitation due to the decrease in accommodation space. Based on the composition of the successive coral assemblages, the reef appears to have grown through successive equilibrium stages.     

Mapping Shoreline Variability of Two Barrier Island Segments Along the Florida Coast

Recent projections of global climate change necessitate improved methodologies that quantify shoreline variability. Updated analyses of shoreline movement provide important information that can aid and inform likely intervention policies. This paper uses the Analyzing Moving Boundaries Using R (AMBUR) technique to evaluate shoreline change trends over the time period 1856 to 2015. Special emphasis was placed on recent rates of change, during the 1994 to 2015 period of active storm conditions. Small segments, on the order of tens of kilometers, along two sandy barrier island regions on Florida’s Gulf and Atlantic coasts were chosen for this study. The overall average rate of change over the 159-year period along Little St. George Island was ??0.62?±?0.12 m/year, with approximately 65% of shoreline segments eroding and 35% advancing. During periods of storm clustering (1994–2015), retreat rates along portions of this Gulf coast barrier accelerated to ??5.49?±?1.4 m/year. Along the northern portion of Merritt Island on Florida’s Atlantic coast, the overall mean rate of change was 0.22?±?0.08 m/year, indicative of a shoreline in a state of relative dynamic equilibrium. In direct contrast with the Gulf coast shoreline segment, the majority of transects (65%) evaluated along the oceanfront of Merritt Island over the long term displayed a seaward advance. Results indicate that episodes of clustered storm activity with fairly quick return intervals generally produce dramatic morphological alteration of the coast and can delay natural beach recovery. Additionally, the data show that tidal inlet dynamics, shoreline orientation, along with engineering projects, act over a variety of spatial and temporal scales to influence shoreline evolution. Further, the trends of shoreline movement observed in this study indicate that nearshore bathymetry—the presence of shoals—wields some influence on the behavior of local segments of the shoreline.     

中国海洋的珊瑚-珊瑚礁: 南海中央区珊瑚-珊瑚礁生物多样性特征

珊瑚是地球上最古老的原住民,具有近6×108年的发育史,弱势群居、喜温和原地长成是珊瑚的基本特征。作者介绍了珊瑚-珊瑚礁的基本特征,综述了跨十年调查的研究区珍贵照片资料和相关认识,指出中国是全球主要的珊瑚-珊瑚礁国家,地位举足轻重;珊瑚-珊瑚礁作为地球生物多样性的代表,造岛、固礁、护鱼、防护岛岸流失,形成南海四大群岛280余座岛、礁、滩、沙,所构建庞大海洋生态系统是无与伦比的海洋生态资源和寸土寸金的南海海洋国土。提出划分南海珊瑚-珊瑚礁为中央区和周缘区2个分布区,阐述了南海中央区珊瑚-珊瑚礁的基本特征,系统汇集报道了间隔10年2个科考航次调查在浅水礁盘浮潜、至20 m水深浅潜-深潜和礁盘及开展岛、礁、滩、沙地质调查的发现,包括科学定名46种六放石珊瑚和6种八放软珊瑚等成果,同时,收集了西沙、中沙、东沙和南沙群岛海域的相关调查航次珊瑚照片;进一步阐述了单体环礁和复合环礁的特征及分布,并进行了初步对比,指出永乐环礁是南海唯一一个真正的切合达尔文模式的环礁,也是环礁发展到最高阶段的产物,构成现代海洋珊瑚-珊瑚礁形成演化研究最好的天然实验室。     

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。     

Microborer ichnocoenoses in Quaternary corals from New Caledonia: reconstructions of paleo-water depths and reef growth strategies in relation to environmental changes

Coral reef growth and development depend on several environmental factors, including tectonic and climatic parameters and local ecological drivers. Reef growth is especially sensitive to sea-level variations. Paleo-water depth reconstructions are essential tools used to determine reef growth patterns during different periods of reef growth. Assemblages of corals and/or coralline algae have been commonly used in such paleodepth reconstructions. This study shows that using microendolith ichnocoenoses can sometimes provide better accuracy than traditional coralgal analyses, particularly in the depth-range 0–10 m where coralgal assemblages usually show broad distribution ranges. Holocene and Pleistocene cores from two barrier reef sites on the west coast of Grande Terre in New Caledonia are examined here. Holocene reef development at these sites feature examples of microendolith ichnocoenoses that document rapid environmental changes and small sea-level variations of about 2–5 m in amplitude, and record these changes with more accuracy than coral and coralline algae assemblages which are highly dependant on the hydrodynamic energy of the setting. During the Pleistocene, which was less chronologically constrained, the microendolith ichnocoenoses also reflect paleo-water depths and reef-growth patterns at different periods of reef history.     

Impacts of human activities and natural inputs on heavy metal contents of many coral reef environments along the Egyptian Red Sea coast

In order to monitor the heavy metals effect coming from both human activities and natural inputs on coral reef environments of the Egyptian Red Sea coast, metal concentrations in thirty- eight coral reef species and nearby sediment samples collected from seven studied sites were analyzed. Four sites represent impacted areas; included from south to north Hamrawein, Safaga and Hurghada Harbours and Ras El-Behar Area. Wadi El-Gemal represents natural input area while Qola'an and Kalawye Reefs are the control areas. Heavy metal contents were measured in both coral skeletons and nearby marine sediments. Both impact areas as well as natural inputs area recorded the highest values of metals compared with the control ones. However, heavy metal contents recorded high values in sediments of Hamrawein Harbour, while coral species recorded high values in Wadi El-Gemal area. Generally, metal variations in coral reef species reflect natural conditions and human activity. On the other hand, there are no clear relationships between concentrations of heavy metals in coral reef species and those in sediments.     

Shoreline change analysis along the coast between Kanyakumari and Tuticorin of India using remote sensing and GIS

Shoreline is one of the rapidly changing landform in coastal area. So, accurate detection and frequent monitoring of shorelines are very essential to understand the coastal processes and dynamics of various coastal features. The present study is to investigate the shoreline changes along the coast between Kanyakumari and Tuticorin of south India, where hydrodynamic and morphologic changes occur continuously after the December 2004 tsunami. Multi-date satellite data of Indian Remote Sensing (IRS) satellites (1999, 2000, 2003, 2005, and 2006) are used to extract the shorelines. The satellite data is processed by using the ERDAS IMAGINE 9.1 software and analyzed by ArcGIS 9.2 workstation. The different shoreline change maps are developed and the changes are analyzed with the shoreline obtained from the Survey of India Toposheets (1969). The present study indicates that accretion was predominant along the study area during the period 1969–1999. But recently (from 1999 onwards), most of the coastal areas have experienced erosion. The study also indicates the reversal of shoreline modifications in some coastal zones. The coastal areas along the headlands have experienced both erosion and accretion. Though the coastal erosion is due to both natural and anthropogenic activities, the coastal zones where sand is mined have more impacts and relatively more rate of erosion than that of other zones. Improper and in-sustainable sand mining leads to severe erosion problem along this area. So the concept of sustainable management should be interpreted in the management of the near-shore coastal sand mining industry.     

浙江桐庐冷坞二叠纪生物礁的发育模式

礁体底部具脉状层理的潮坪相碎屑沉积,礁体内部藻叠层岩夹层的存在,及礁体上部为煤系地层覆盖等都表明冷坞生物礁是一个典型的二叠纪岸礁;海绵骨架岩的存在表明它是个骨架型岸礁。     

Are carbonate barrier islands mobile? Insights from a mid to late-Holocene system,Al Ruwais,northern Qatar

Barrier islands are important landforms in many coastal systems around the globe. Studies of modern barrier island systems are mostly limited to those of siliciclastic realms, where the islands are recognized as mobile features that form on transgressive coastlines and migrate landward as sea-level rises. Barrier islands of the ‘Great Pearl Bank’ along the United Arab Emirates coast are the best-known carbonate examples. These Holocene islands, however, are interpreted to be anchored by older deposits and immobile. The mid-Holocene to late-Holocene depositional system at Al Ruwais, northern Qatar, provides an example of a mobile carbonate barrier island system, perhaps more similar to siliciclastic equivalents. Sedimentological and petrographic analyses, as well as ¹⁴C-dating of shells and biogenic remains from vibracored sediments and surface deposits, show that after 7000 years ago a barrier system with a narrow back-barrier lagoon formed along what is now an exposed coastal zone, while, contemporaneously, a laterally-extensive coral reef was forming immediately offshore. After 1400 years ago the barrier system was forced to step ca 3 km seaward in response to a sea-level fall of less than 2 m, where it re-established itself directly on the mid-Holocene reef. Since that time, the barrier has retreated landward as much as 1000 m to its current position, exposing previously-deposited back-barrier lagoonal sediment at the open-coast shoreline. In modern neritic warm-water carbonate settings mobile barrier island systems are rare. Their construction and migration may be inhibited by reef formation, early cementation, and the relative inefficiency of sourcing beach sediments from open carbonate shelves. Carbonate barrier island systems likely formed more commonly during geological periods when ramps and unrimmed shelves predominated and in calcite seas, when meteoric cementation was minimized as a result of initial calcitic allochem mineralogy. As with their siliciclastic analogues, however, recognition of the influence of these transient landforms in the rock record is challenging.