Characteristics and distribution patterns of reef complexes on the carbonate platform margin in deep water areas: the western South China Sea

As a potential oil and gas reservoir, reef complexes have been a research focus from petroleum geologists for a long time. There are favorable conditions for the development of reef complexes in the South China Sea; however, their internal structures, evolution and distribution are still poorly understood. Based on 2D and 3D seismic data, the internal structures and evolution patterns of the reef complexes on the carbonate platform margin in the deep water areas over the western South China Sea were studied in detail. The result shows that two types of reef complexes, i.e., fault controlling platform margin reef complexes and ramp reef complexes have been developed in the study area. The reef complexes have independent or continuous mound or lenticular seismic reflections, with three internal structures (i.e., aggrading, prograding and retrograding structures). There are different growth rates during the evolution of the reef complexes, resulting in the formation of catch-up reefs, keep-up reefs and quick step reefs. The study also reveals that different platform margin reef complexes have different internal structures and distributions, because of the different platform types. These results may be applied to the exploration and prediction of carbonate platform margin reef complexes in other areas that are similar to the study area.     

四川盆地晚二叠世长兴期古海洋台洼与陆棚边缘礁滩对比研究

以长兴组台地边缘礁滩储层发育认知为指导,将三维与二维地震资料相结合,开展台洼边缘礁滩与台地边缘礁滩的沉积背景、发育模式、古地貌的综合对比研究,对四川盆地中部蓬溪-武胜台洼边缘礁滩发育演化特征进行分析,提出了四川盆地东南部泰来、永兴场及义和地区3种台洼边缘礁滩发育模式。受开江-梁平陆棚、峨眉地裂运动以及微古地貌影响,泰来地区以台洼边缘礁滩沉积为主,永兴场地区沉积低能生屑滩,义和地区发育成排生物礁带及点礁。从长兴期整个四川盆地沉积格局分析,蓬溪-武胜台洼边缘礁滩与开江-梁平陆棚边缘礁滩整体沉积格局相似,但台洼边缘生物礁滩纵向发育规模偏小,横向分布面积广泛。     

川东北宣汉盘龙洞长兴组生物礁剖面沉积相分析

结合区域构造、地层概况、岩相古地理等方面的背景资料,对宣汉盘龙洞上二叠统长兴组生物礁地层剖面进行了观测描述。通过室内镜下岩石薄片鉴定分析,识别出主要岩石类型为礁灰岩、礁云岩、生屑灰岩、颗粒灰岩及晶粒白云岩。根据露头观察和室内镜下岩石薄片鉴定分析,结合岩石学、古生物等沉积相标志的研究,认为该剖面发育开阔台地、台地边缘生物礁和台地边缘浅滩三种沉积相类型,其中台地边缘生物礁发育,可进一步识别出礁基、礁核和礁前亚相,礁核以骨架礁和障积礁为主;台地边缘浅滩进一步划分为粒屑滩、鲕粒滩等亚相。初步总结出了该剖面的沉积相模式,并对该剖面的沉积演化序列和识别标志进行了讨论。     

Seismic geomorphology and growth architecture of a Miocene barrier reef,Browse Basin,NW-Australia

The Cenozoic succession of Browse Basin is characterized by a carbonate system, that developed from a non-tropical ramp in Eocene-lower Miocene times to a tropical rimmed platform in the middle Miocene. The evolution of the platform was unraveled through the interpretation of the seismic geomorphology and borehole data of the middle Miocene tropical reef system. The first reef structures developed during the early middle Miocene as narrow linear reef belts with an oblique orientation with respect to shelf strike direction. Subsequently, they prograded toward the platform margin to form a barrier reef with a minimum length of 40 km. The barrier reef itself comprises three distinct ridges separated by progradational steps. The second and third step are separated by a karstified horizon, which is interpreted to represent the global sea-level fall shortly before the Serravallian/Tortonian boundary. The following third ridge formed in a slightly downstepped position during the sea-level lowstand and initial transgressive phase. Further sea-level rise during the early Tortonian first drowned the barrier-reef system and subsequently also the patch reefs and relic atolls that had established in a backstepped position in the platform interior. The similar evolution of the Browse Basin reef system and other contemporaneous carbonate systems indicates a strong impact of eustatic sea-level changes. Relatively large subsidence rates in the study area possibly augmented the eustatic sea-level rise in the Tortonian and hence contributed to the drowning of the reef system. However, the initiation and final demise of the reef system was also governed by global and regional climate variations. The first seismically-defined reefs developed simultaneous to a maximum in the transport capacity of the Indonesian throughflow, which brings warm low-salinity waters to the North-West Shelf. Reef drowning followed the restriction of this seaway close to the middle to early Miocene boundary. This near closure of the Indonesian seaway possibly led to a regional amplification of the global middle to late Miocene cooling trend and hampered the potential of the reef system to keep up with the rising sea-level.     

海上退役平台改作鱼礁体的稳定性及流场效应研究

海洋油气平台在达到作业寿命后必须进行废弃处置,将海上退役平台改作人工鱼礁投放,对优化渔业资源、促进海洋经济持续发展具有重要意义。基于平台拆卸结构,共制作了箱状、管状、柱状、网状4种典型鱼礁实物模型,通过室内模拟试验和数值模拟研究,分析了不同鱼礁类型单体的稳定性和流场效应。结果表明：开口率0.1至0.8的箱状礁的稳定性均能满足要求,但开口率高于0.6的箱状礁难以形成连续的背涡流区域,设计时应使开口率低于0.6;管状礁应选择堆叠放置方式投放,且堆叠层数与稳定性和流场造成能力均呈正相关,在设计时尽量提高管状礁的堆叠层数;柱状礁设计时应尽量降低其重心,并减小迎流投影面的中空面积投放;基于平台的钻井架、火炬臂、栈桥设计的3种网状礁,均满足礁体稳定条件,且均能形成大范围的背涡流区域,可作为人工鱼礁投放。研究成果为平台造礁礁体结构设计提供了理论依据与实践基础,对海上退役平台的废弃处置具有一定的参考价值。     

基于QuickBird影像上珊瑚礁发育状况监测实验研究

珊瑚礁生态系统具有很高的生物多样性和重要的生态功能。20世纪80年代以后全球范围内珊瑚礁的大面积退化引起了人们广泛的关注。利用高分辨多光谱QuickBird影像,基于珊瑚礁几何参数与发育指数对南沙典型岛礁发育进行遥感监测,在珊瑚礁体迎风面水域由破波形成的纹理特征表明了海面粗糙度与水下礁坪的发育特性。结果表明,南沙岛礁受地质与气候的影响发育程度不一,半月礁发育较好,发育指数为0.38,仙娥礁发育指数为0.27。建立几何参数等指标能够监测南沙珊瑚礁的发育状况,可对珊瑚礁的保护提供科学依据。     

Reef exploration in the East Sengkang Basin,Sulawesi, Indonesia

Reconnaissance seismic shot in 1971/72 showed a number of well defined seismic anomalies within the East Sengkang Basin which were interpreted as buried reefs. Subsequent fieldwork revealed that Upper Miocene reefs outcropped along the southern margin of the basin. A drilling programme in 1975 and 1976 proved the presence of shallow, gas-bearing, Upper Miocene reefs in the northern part of the basin. Seismic acquisition and drilling during 1981 confirmed the economic significance of these discoveries, with four separate accumulations containing about 750 × 10⁹ cubic feet of dry gas in place at an average depth of 700 m. Kampung Baru is the largest field and contains over half the total, both reservoir quality and gas deliverability are excellent. Deposition in the East Sengkang Basin probably started during the Early Miocene. A sequence of Lower Miocene mudstones and limestones unconformably overlies acoustic basement which consists of Eocene volcanics. During the tectonically active Middle Miocene, deposition was interrupted by two periods of deformation and erosion. Carbonate deposition became established in the Late Miocene with widespread development of platform limestones throughout the East Sengkang Basin. Thick pinnacle reef complexes developed in the areas where reef growth could keep pace with the relative rise in sea level. Most reef growth ceased at the end of the Miocene and subsequent renewed clastic sedimentation covered the irregular limestone surface. Late Pliocene regression culminated in the Holocene with erosion. The Walanae fault zone, part of a major regional sinistral strike-slip system, separates the East and West Sengkang Basins. Both normal and reverse faulting are inferred from seismic data and post Late Pliocene reverse faulting is seen in outcrop.     

Impact of strong easterly trade winds on carbonate petroleum exploration - Relationships developed from Caicos Platform,southeastern Bahamas

Brisk, persistent easterly trade wind influences define Holocene patterns of carbonate sedimentation across the Caicos Platform (southeastern Bahamas). Resultant predictive sedimentary facies models based on trade wind influences are more widely applicable to the exploration for subsurface carbonate plays than are existing models based on the northern Bahamas facies patterns, which are characterized by gentle trade winds and strong platform-margin-related oceanic processes (swells and tidal currents). The Caicos Platform relationships may be more applicable because many ancient shallow carbonate depositional environments were within the trade wind belts and commonly within broad intracratonic seas that were little influenced by oceanic processes.The grainstone-dominated Caicos Platform exhibits reservoir potential over much of its surface, in contrast to northern Bahamian platforms, where oceanic tidal currents or swells and gentle easterly trade winds confine higher energy environments with reservoir potential to platform margins. Strong easterly trade winds across Caicos Platform promote widespread Holocene platform-interior oolitic, skeletal and grapestone grainstone bodies on this platform. Orientations of ooid sand bodies vary depending on preexisting topography, water depth and bottom energy. Shallow subtidal ooid sand shoals orient parallel to these winds. Ooid sands developed along older shorelines orient parallel to the shorelines but prograde perpendicular into these winds. Deeper platform-interior oolitic sands exist as widespread, sheet-like deposits. These trade winds allow reefs and ooids to coexist in many settings, permit isolated linear reefs to flourish on certain leeward platform margins, and promote effective off-bank transport of carbonate sands that create onlapping grainstone wedges. These relationships are very applicable to the rock record.Strong trade wind influences, such as seen on Caicos Platform, better explain the occurrence of Cretaceous reef and/or oolitic grainstone reservoirs developed well in from platform margins (Fairway Field in East Texas; Black Lake Field in Louisiana) than do existing northern Bahamian models. Depositional models based on conditions in the northern Bahamian models would predict low-energy facies in these platform-interior settings. A trade-wind-driven depositional model, characterized by strong persistent easterlies, also better explains the origin of the onlapping wedge of skeletal grainstones at Poza Rica oilfield in Mexico.The Caicos Platform easterly trade-wind-driven depositional model should generally apply to any ancient shallow carbonate environment that developed 5–22° north or south of the paleoequator, whether or not a platform margin was near by. Future carbonate exploration or exploitation should always factor in not only geological age, but also physiographic, latitudinal and climatic setting at a global and local scale.     

Strange bedfellows—a deep-water hermatypic coral reef superimposed on a drowned barrier island; southern Pulley Ridge,SW Florida platform margin

The southeastern component of a subtle ridge feature extending over 200 km along the western ramped margin of the south Florida platform, known as Pulley Ridge, is composed largely of a non-reefal, coastal marine deposit. Modern biostromal reef growth caps southern Pulley Ridge (SPR), making it the deepest hermatypic reef known in American waters. Subsurface ridge strata are layered, lithified, and display a barrier island geomorphology. The deep-water reef community is dominated by platy scleractinian corals, leafy green algae, and coralline algae. Up to 60% live coral cover is observed in 60–75 m of water, although only 1–2% of surface light is available to the reef community. Vertical reef accumulation is thin and did not accompany initial ridge submergence during the most recent sea-level rise. The delayed onset of reef growth likely resulted from several factors influencing Gulf waters during early stages of the last deglaciation (∼14 kyr B.P.) including; cold, low-salinity waters derived from discrete meltwater pulses, high-frequency sea-level fluctuations, and the absence of modern oceanic circulation patterns. Currently, reef growth is supported by the Loop Current, the prevailing western boundary current that impinges upon the southwest Florida platform, providing warm, clear, low-nutrient waters to SPR. The rare discovery of a preserved non-reefal lowstand shoreline capped by rich hermatypic deep-reef growth on a tectonically stable continental shelf is significant for both accurate identification of late Quaternary sea-level position and in better constraining controls on the depth limits of hermatypic reefs and their capacity for adaptation to extremely low light levels.     

琼东南盆地南部早中新世碳酸盐岩台地的地震解释

The southern uplift of the Qiongdongnan Basin is a deepwater area in which no wells have beens drilled. The Miocene-Quaternary strata in the Xisha Islands, which are located 40–100 km to the south, are composed of carbonate reef formations. Paleotectonic and paleogeographic analyses of the basin suggest that the southern uplift experienced favorable geological conditions for the development of carbonate reefs during the Miocene.The high-impedance carbonates have high amplitudes and low frequencies on seismic profiles. The reefs are distributed on paleotectonic highs and are thicker than the contemporaneous formations. A forward model of the variation in carbonate thickness based on lithological and velocity information from wells in nearby regions can simulate the seismic response of carbonates with different thicknesses. We identified several important controlling points for determining the thickness of carbonates from seismic profiles, including the pinchout point,the λ/4 thickness point, and the λ/2 thickness point. We depict a carbonate thickness map in the deepwater area of the southern Qiongdongnan Basin based on this model. The carbonate thickness map, the paleotectonic and paleogeographic background, and the seismic response characteristics of reefs suggest that the carbonates that developed on the southern uplift of the Qiongdongnan Basin during the Miocene were mainly an isolated carbonate platform peninsula and ramp deposits. It consisted of gentle ramp platform, steep slope platform,platform depression, gravity flow, and reef bank facies.     

The use of remote sensing and linear wave theory to model local wave energy around Alphonse Atoll,Seychelles

This paper demonstrates a practical step-wise method for modelling wave energy at the landscape scale using GIS and remote sensing techniques at Alphonse Atoll, Seychelles. Inputs are a map of the benthic surface (seabed) cover, a detailed bathymetric model derived from remotely sensed Compact Airborne Spectrographic Imager (CASI) data and information on regional wave heights. Incident energy at the reef crest around the atoll perimeter is calculated as a function of its deepwater value with wave parameters (significant wave height and period) hindcast in the offshore zone using the WaveWatch III application developed by the National Oceanographic and Atmospheric Administration. Energy modifications are calculated at constant intervals as waves transform over the forereef platform along a series of reef profile transects running into the atoll centre. Factors for shoaling, refraction and frictional attenuation are calculated at each interval for given changes in bathymetry and benthic coverage type and a nominal reduction in absolute energy is incorporated at the reef crest to account for wave breaking. Overall energy estimates are derived for a period of 5 years and related to spatial patterning of reef flat surface cover (sand and seagrass patches).     

西沙海区新近纪碳酸盐岩台地地震响应特征和控制因素

利用西沙海域最新采集的高分辨率二维地震资料及钻井资料,结合前人研究成果,建立了西沙海区高精度层序地层格架;并在西沙海区新近纪识别出点礁、塔礁、台地边缘礁和环礁这4种不同类型生物礁,总结了不同生物礁的地震反射特征.早中新世时,西沙碳酸盐岩台地开始发育,台地数量较少且规模有限;中中新世,随着海平面的持续上升,海平面上升速率...     

西沙海区碳酸盐台地地震反射特征及沉积模式

随着南海海盆的持续扩张,西沙海区整体沉降,从早中新世起西沙碳酸盐台地开始发育,而且在台地之上生长了不同类型的生物礁。通过地震识别认为,西沙海区生物礁在地震剖面上表现为顶底强振幅的丘形连续反射、内部弱振幅杂乱反射;碳酸盐台地表现为顶部强振幅连续平行反射、底部界面局部模糊、内部强弱相间亚平行连续反射。通过对西沙海区地层层序的分析以及大量地震资料的解释认为,在西沙碳酸盐台地的发育早期它受基底构造的控制,而在后期主要受多期海平面变化的影响,其发育演化经历了初始生长—加积—出露—二次生长—淹没等一系列阶段,复杂的演化过程也使西沙碳酸盐岩具有较好的储集条件和油气远景。     

Negotiating uncertainty: Framing attitudes,prioritizing issues,and finding consensus in the coral reef environment management “crisis”

Environmental problems are becoming increasingly unwieldy, particularly those which are highly debated because of their political and financial consequences and have been termed as in “crisis”. In coral reef environments, these considerations spill into decisions on mitigation of reef decline and attendant questions of territorial and resource-access rights. Historical foundations of reef science show that early applications of reef inquiries centered on environmental connection and inevitably led to establishing not only the baseline of reef ecosystems, but also contributed to the evolution of conservation crisis in this environment. This work applies Q-methodology towards determining attitudes, prioritizing statements and finding consensus regarding management issues that are tied to the science of coral reef environments and their conservation “crisis”. This work delineates the social construction of attitudes, perceptions, and foundations of coral conservation science by examining the scientifically-grounded statements that constitute conservation debates. Study participants were comprised of the coral reef science and conservation professional network. The Q-sample (n = 43) was structured around some central debates over the dilemmas and strategies of reef management and decline-mitigation, both recent and long-running. Four attitudes or viewpoints were isolated in terms of their preferred management models, geographic perspectives and the role scientific findings play within these core beliefs. These can be generally described as Community and Locally-centered Humanists, Scientific Idealists, Skeptical and Utilitarian Pragmatists, and Politically-oriented Positivists. Evaluating agreement about central issues showed a high degree of consensus regarding the relative importance of community input in the role of successful reef management while the highest degree of contention was seen in scalar issues such as human-environment feedback systems that are inherent in solving environmental crises.     

江苏小庙洪牡蛎礁的地貌特征及演化

江苏岸外的小庙洪牡蛎礁在海岸地貌学上是一稀有的生物沉积体。这种位于蚀、淤交替岸段潮间带、古礁体和活体共存的牡蛎礁体是我国所仅见。现场观察了牡蛎礁体的地貌特征,并使用GPS和全站仪进行了主要礁体分布与高程的测量,表明礁区地貌面不是一个水平面,相差可达2m以上。礁体顶高主要分布在两个高程上,一是与平均潮位相当,二是比前者低约30cm,略高于小潮平均低潮位。礁体起伏面高出礁坪面多在0.5—1.5m。小庙洪牡蛎礁正处于退化状态,除物理因素造成的侵蚀外,化学溶蚀及人类活动也是侵蚀退化的主要因素。对于礁区内部的礁体,其退化过程为连片礁→环礁→带礁→斑礁→礁坪的顺序。礁体沉积体有三种:原生礁体、与原生礁体脱离的礁块以及已离开原生地的松散堆积体。浪蚀礁坪分布在礁体的迎浪面上,而溶蚀礁坪则分布在礁体密集区。在礁体稀疏区,则覆盖约20—30cm厚的粉沙或淤泥,形成次生的潮坪。     

Variations in architecture and cyclicity in fault-bounded carbonate platforms: Early Miocene Red Sea Rift,NW Saudi Arabia

The Early Miocene was a period of active rifting and carbonate platform development in the Midyan Peninsula, NW Saudi Arabia. However, there is no published literature available dealing with the detailed characterization of the different carbonate platforms in this study area. Therefore, this study aims to present new stratigraphic architectural models that illustrate the formation of different carbonate platforms in the region and the forcing mechanisms that likely drove their formation. This study identified the following features formed during active rifting: a) a Late Aquitanian (N4) fault-block hangingwall dipslope carbonate ramp, b) a Late Burdigalian (N7-N8) isolated normal fault-controlled carbonate platform with associated slope deposits, and c) a Late Burdigalian (N7-N8) attached fault-bounded platform with reef buildups, rimmed shelf developed on a footwall fault-tip within a basin margin structural relay zone that formed coinciding with the second stage of rifting. Variations in cyclicity have been observed within the internal stratigraphic architecture of each platform and also between platforms. High-resolution sequence stratigraphic analysis shows to be parasequences the smallest depositional packages (metre-scale cycles) within the platforms. The hangingwall dipslope carbonate ramp and the attached platform demonstrate aggradational-progradational parasequence stacking patterns. These locations appear to have been more sensitive to eustatic cyclicities, despite the active tectonic setting. The isolated, fault-controlled carbonate platform reveals disorganized stratal geometries in both platform-top and slope facies, suggesting a more complex interplay of rates of tectonic uplift and subsidence, variation in carbonate productivity, and resedimentation of carbonates, such that any sea-level cyclicity is obscure. This study explores the interplay between different forcing mechanisms in the evolution of carbonate platforms in active extensional tectonic regions. Characterization of detailed parasequence-scale internal architecture allows the spatial variation in syn-depositional relative base-level changes to be inferred and is critical for understanding the development of rift basin carbonate platforms. Such concepts may be useful for the prediction of subsurface facies relationships beyond interwell areas in hydrocarbon exploration and reservoir modeling activities.     

刺参对人工礁体设计关键指标的选择性

采用平均聚集率(Mean Attractive Rate,MAR)作为统计分析指标,研究了仿刺参(Apostichopusjaponicas Selenka)对人工礁体结构设计关键指标(孔径、间隙、颜色、夹角)的选择性及其行为特性。结果表明:(1)随着实验时间延长,仿刺参在礁体模型上的聚集数量呈上升趋势;(2)礁体模型在自然光照条件下的聚参效果优于黑暗条件下的聚参效果(P<0.05);(3)孔径组各水平间聚参效果比较:2 cm>4 cm、16 cm>8 cm(P<0.05),4 cm与16 cm间差异不显著;间隙组各水平间聚参效果比较:2 cm>4 cm>6 cm>8 cm(P<0.05);颜色组各水平间聚参效果比较:黑色、蓝色、红色>绿色>白色>透明(P<0.05),黑色、蓝色、红色间差异不显著;夹角组各水平间聚参效果比较:15°>30°>45°、60°>90°、120°(P<0.05),45°与60°差异不显著,90°与120°差异不显著。说明仿刺参适应礁体模型需要一定时间,呈负趋光性。10 g至30 g的仿刺参,对设计指标为2 cm孔径、2 cm间距、深色、15°夹角的人工礁体,具有较好地选择性。     

Formation and evolution of the tertiary carbonate reefs in the Madura Strait Basin of Indonesia

Analysis of 2 D seismic data over 4 500 km in length from the Madura Strait Basin in the East Java Sea reveals seismic re?ection characteristics of reefs and associated sedimentary bodies, including asymmetrical or symmetrical dome re?ections, slope progradational re?ections, chaotic re?ections and discontinuous strong re?ections inside the reef, which onlap the ?ank of the reef. It is concluded that the developmental paleo-environment of most reefs is mainly conducive to shallow marine carbonate platform facies and platform margin facies, based on well core data, variations in seismic facies and strata thickness.The formation and evolution of all reefs are primarily in?uenced by the tectonic framework of the Madura Strait Basin. Platform margin reefs are principally controlled by two types of structures: one is a series of E-W trending Paleogene normal faults, and the other is an E-W trending Neogene inversion structures. In addition, wave actions, tidal currents and other ocean currents play an accelerated role in sorting, rounding and redeposition for the accumulation and evolution of reefs. Tertiary reefs in the MSB can be divided into four types: 1) an open platform coral reef of Late Oligocene to Early Miocene, 2) a platform margin coral reef controlled by normal faults in Late Oligocene to Early Miocene, 3) a platform margin Globigerina moundreef controlled by a "hidden" inversion structure in Early Pliocene, and 4) a platform margin Globigerina mound-reef controlled by thrust faults in the early Pliocene. Patterns of the formation and evolution of reefs are also suggested.     

鱼礁模型对赤点石斑鱼的诱集效果

本文在实验室中水池中观察了赤点石斑鱼在三种不同口径鱼礁模型存在下的行为，结果表明；鱼礁对这种鱼有明显诱集效果，随着模型口径的增大，鱼在礁体放置区分布百分率有增大趋势，而鱼个体平均距离、群体总重心与礁体平均距离和鱼与礁的距离均有减小趋势。可见，口径大小的鱼礁模型有较好的聚鱼效果。     

热带风暴过程中珊瑚礁坪示踪砂运移的现场实验研究

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