The Continental Margins Program in Georgia

From 1984 to 1993, the Georgia Geologic Survey (GGS) participated in the Minerals Management Service-funded Continental Margins Program. Geological and geophysical data acquisition focused on offshore stratigraphic framework stud ies, phosphate-bearing Miocene-age strata, distribution of heavy minerals, nearsurface alternative sources of groundwater, and development of a PC-based Coastal Geographic Information System (GIS). Seven GGS publications document results of those investigations. In addition to those publications, direct benefits of the GGS's participation include an impetus to the GGS's investigations of economic minerals on the Georgia coast, establishment of a GIS that includes computer hardware and software, and seeds for additional investigations through the information and training acquired as a result of the Continental Margins Program. These additional investigations are quite varied in scope, and many were made possible because of GIS expertise gained as a result of the Continental Margins Program. Future investigations will also reap the benefits of the Continental Margins Program.     

共轭大陆边缘工作会议简介

按照板块构造的观点 ,地球上存在 3类大陆边缘 :活动大陆边缘、被动大陆边缘和转换大陆边缘。被动大陆边缘主要分布在大西洋两岸 ,因此也叫大西洋型大陆边缘。经区域地质构造研究表明 ,南海是一个小大西洋 ,它在新生代像大西洋在中、新生代一样 ,是经过大陆岩石圈张裂 (rifting)、破裂分离 (break up)和海底扩张而生成的小洋盆。虽然目前对大西洋的诞生过程比较清楚 ,但对诞生过程中大陆岩石圈在张裂、破裂分离期间岩石圈的变形过程及其特征仍不太了解。为了进行这方面的研究 ,科学家将在破裂分离前连在一起的大西洋两岸大陆边缘 (科学家命…     

Submarine Sand Resources,Southeastern Virginia-Contributions from Year 9 and Year 10 of Virginia's Continental Margins Program

Virginia's year 9 and year 10 funds from the Continental Shelf Program were used to supplement other work funded by the Minerals Management Service in an ongoing Cooperative Agreement focused on the area offshore of southeastern Virginia. Year 9 and year 10 funds facilitated interpretation of subbottom profiles and the analysis of sediment samples from cores and grabs. On Virginia's sediment-starved continental shelf, deposits of material potentially suitable for use as beach nourishment or, perhaps, as construction aggregate occur in three stratigraphic settings, each with specific characteristics of morphology, grain-size gradients, likelihood of discovery, and physical ease of exploitation. All must be verified with a careful program of coring. Modern shoals generally are easier to identify, prove, and access than either filled channels or lenticular facies. Shoals usually are identifiable on nautical charts and characteristically have a definite lower boundarythat can be seen in subbottom profiles. In most cases, the base of the shoal coincides with the level of the surrounding sea floor. Filled channels are readily identifiable on subbottom profiles but may have a narrow, sinuous form and steep lateral gradients in sediment properties. Buried lenticular facies of good-quality sand usually are found only fortuitously. As the lateral and often vertical gradients in geotechnical properties usually are low, the lenticular facies can be mined with a lesser concern for the consequences of violating the deposit's limits than with the other two types of deposit. There are three types of filled paleochannels in the study area. (1) Relatively near-surface, generally small, roughly shore normal channels most likely mark the migration of tidal inlets across the shelf during the most recent transgression. (2) Small, relatively wide and relatively shallow generally shore parallel channels may be filled back-barrier or lagoonal channels. (3) Larger channels trending across the shelf probably result from riverine flow. The complexity of the seismostratigraphy of the Quaternary deposits on south eastern Virginia's inner continental shelf is a result of series of high-frequency (fifth-order, 10-20,000 y), low-amplitude (20-30 m) variations in sea level that occurred during the last highstand, roughly 80,000 to 130,000 BP. The evidence of the small oscillations in sea level is best seen in the regions that were between the shoreline and wave base, today's inner shelf; however, the very low rates of deposition on the shelf make it difficult to correlate specific reflectors or beds or, at times, to distinguish between fifth-and fourth-order changes. Results for the continuing studies already have been used in the determination to mine several hundred thousand cubic meters of sand from Sandbridge Shoal for use on a Navy-owned facility and in consideration of mining greater quantities of sand from Sandbridge and other shoals for use in local beach nourishment and hurricane protection efforts.     

深水大陆边缘的热流演变

由于经济和政治的原因,石油工业为找寻新的石油源区,其勘探地区不断地发生改变,注意力由滨岸(如中东地区)转向近海陆架区,在过去的10年里则移向深水大陆边缘(海平面500～2500m以下)地区。尽管该区域的勘探风险和费用较高,但是石油资源的潜在蕴藏量非常巨大。     

Submarine Sand Resources, Southeastern Virginia-Contributions from Year 9 and Year 10 of Virginia's Continental Margins Program

Virginia's year 9 and year 10 funds from the Continental Shelf Program were used to supplement other work funded by the Minerals Management Service in an ongoing Cooperative Agreement focused on the area offshore of southeastern Virginia. Year 9 and year 10 funds facilitated interpretation of subbottom profiles and the analysis of sediment samples from cores and grabs. On Virginia's sediment-starved continental shelf, deposits of material potentially suitable for use as beach nourishment or, perhaps, as construction aggregate occur in three stratigraphic settings, each with specific characteristics of morphology, grain-size gradients, likelihood of discovery, and physical ease of exploitation. All must be verified with a careful program of coring. Modern shoals generally are easier to identify, prove, and access than either filled channels or lenticular facies. Shoals usually are identifiable on nautical charts and characteristically have a definite lower boundarythat can be seen in subbottom profiles. In most cases, the base of the shoal coincides with the level of the surrounding sea floor. Filled channels are readily identifiable on subbottom profiles but may have a narrow, sinuous form and steep lateral gradients in sediment properties. Buried lenticular facies of good-quality sand usually are found only fortuitously. As the lateral and often vertical gradients in geotechnical properties usually are low, the lenticular facies can be mined with a lesser concern for the consequences of violating the deposit's limits than with the other two types of deposit. There are three types of filled paleochannels in the study area. (1) Relatively near-surface, generally small, roughly shore normal channels most likely mark the migration of tidal inlets across the shelf during the most recent transgression. (2) Small, relatively wide and relatively shallow generally shore parallel channels may be filled back-barrier or lagoonal channels. (3) Larger channels trending across the shelf probably result from riverine flow. The complexity of the seismostratigraphy of the Quaternary deposits on south eastern Virginia's inner continental shelf is a result of series of high-frequency (fifth-order, 10-20,000 y), low-amplitude (20-30 m) variations in sea level that occurred during the last highstand, roughly 80,000 to 130,000 BP. The evidence of the small oscillations in sea level is best seen in the regions that were between the shoreline and wave base, today's inner shelf; however, the very low rates of deposition on the shelf make it difficult to correlate specific reflectors or beds or, at times, to distinguish between fifth-and fourth-order changes. Results for the continuing studies already have been used in the determination to mine several hundred thousand cubic meters of sand from Sandbridge Shoal for use on a Navy-owned facility and in consideration of mining greater quantities of sand from Sandbridge and other shoals for use in local beach nourishment and hurricane protection efforts.     

Geodynamic Settings of the Formation of Microcontinents,Submerged Plateaus,and Nonvolcanic Islands within Continental Margins

During breakup of the continental lithosphere, partial or complete separation of small continental blocks from the mainland frequently occurs, leading to the formation of microcontinents or partially separated submerged plateaus that advance toward the ocean, as well as to emergent nonvolcanic islands. The article reviews the geodynamic settings in which isolated blocks of continental crust can form. Depending on the thermomechanical conditions of continental rifting, such blocks may be preserved as emergent islands or as submerged blocks of continental crust.     

Oceanic and Continental Mantle Fragments in Ophiolites of the Northwestern Pacific Margins: Composition,Age, and Genesis of Sakhalin Peridotites

The paper presents the results from a study of original and published data on the chemical composition and age of mantle peridotites from Sakhalin Island ophiolites. The material and genetic proximity of peridotites from the Berezovsky and Shelting plutons, on the one hand, and mélange zone serpentinites, on the other, have been established. In composition and Fe₂O₃ and MgO variations, Sakhalin peridotites differ radically from those of the Northeast Asia ophiolite complexes (Krasnogorsky Massif, Karaginsky Island Massif, etc.), which are fragments of Pacific Plate mantle. Conversely, Sakhalin peridotites have a subcontinental genesis and are compositionally close to xenoliths of lherzolites from Hankai Microcontinent mantle (southern Sikhote-Alin). The rythmics of alternation in compression and expansion at the margin of the Asian continent in the last 180 million years, caused by cyclical changes in the Pacific spreading rate, have been considered. According to data obtained by U-Pb dating of zircons, the formation of the Berezovsky Massif took place 169–154 Ma ago during Jurassic expansion of the continental margin. Matching age and composition data demonstrate that the Sakhalin ophiolites formed within the marginal sea basin during riftinduced destruction of the periphery of the Hankai Craton. The assumed tectonic setting was close to that reconstructed for the Jurassic Josephine ophiolites of the California margin of the North American continent. The continental genesis of the studied ophiolites agrees with the age and tectonic mode of ophiolite formation for Sakhalin Island.     

大陆架科学钻探CSDP-2井钻探施工的几项关键技术

南黄海连接了扬子块体和海区.是联系朝鲜半岛和东亚大陆边缘演化的重要组成部分。在南黄海中部隆起实施的大陆架科学钻探CSDP-2井,承载着多个科学目标:在建立陆架区晚新牛代以来的标准地层层序基础上.开展古气候与古环境演化研究.探讨东亚大陆边缘的源汇过程;获取南黄海中古生代海相地层,研究扬子块体向东延伸的大地构造格局与岩相古地理.详细评价其油气资源潜力。     

The Continental Shelf of Crete: The Benthic Environment

Abstract. Sediment characteristics determining macrofauna communities were investigated on the continental shelf of Crete. The sedimentary environment of the outer continental shelf of Crete is characterized by a silty substrate with significant decrease in chlorophyll a and organic carbon concentration with depth. Redox potential values indicated an ample supply of oxygen at all depths. Values of most production-related parameters TOC, chlorophyll a , ATP were found at the low end of the range reported from the literature even though the sampling stations were very close to the coastline. Organic carbon to chlorophyll ratios in the sediments indicated that most of the organic material is of phytoplankton origin; the quality of the organic material in the outer shelf, however, seems to be of lower bioavailability.     

大陆架科学钻探CSDP-2井揭示的南黄海中—古生代构造演化框架

<正>0引言"大陆架科学钻探"计划,是一个聚焦中国大陆架以及东亚大陆边缘的形成演化,以中国大陆架的地层、构造、环境和资源等科学问题作为具体目标,以获取连续的大陆架海底岩心为手段,进行多学科多目标综合研究的科学计划。CSDP-2井选址在工作程度较高且科学问题比较聚焦的南黄海,是大陆架科学钻探的第二口科学探井。其科学目标为,获取中—古生界的连     

The structure of shelf and gulf stream motions in the Georgia bight

The structure of the current and temperature fields along 30°N over the mid-shelf and western Blake Plateau in the South Atlantic Bight has been investigated by combining two moored instrument experiments in the summer of 1981. The shelf moorings were part of the second Georgia Bight Experiment (GABEX-II) and the Gulf Stream mooring data on the Blake Plateau have been described by LEE and WADDELL (1983). Empirical Orthogonal Functions (EOF) in the frequency domain are used to extract shelf and Gulf Stream coherent current and temperature fluctuations in the two- to 14-day period band. Three modes are found, of which the first two are interpreted as Gulf Stream meander and frontal eddy circulations. The difference between them is chiefly in the shelf motions; the first mode is primarily restricted to the shelf edge, whereas the second mode penetrates to the 40m isobath. The third mode dominates at mid-shelf and is the only mode that shows strong coherence with the windstress and local sea-level fluctuations. The relationship of the modes to the occurrence of mid- and inner-shelf cold sub-surface intrusions, generated by shelf-edge Gulf Stream frontal eddies, is examined. All three modes are found to play a role in the initiation, growth and decay of these structures.     

Comparison of Modern Zn-Ba-Pb Ore Deposits at Convergent Plate Margins and Fe-Cu-Zn Deposits at Divergent Plate Margins

At divergent plate margins, black smoke forms immediately on contact of ascending hydrothermal solutions with sea water. The black smoke, consisting mainly of black ore (BO) and barite ore (BaO), is rapidly dispersed in seawater leaving behind a dominantly yellow ore (YO). At convergent plate margins, on the other hand, zinc sulfides and associated chalcophilic elements start depositing within the hydothermal mound at mesothermal temperatures, and are largely trapped there to form a mixed yellow, black and barite ore (YO-BO-BaO). The abundance of individual chalcophilic elements within the mixed ore varies by more than four orders of magnitude, with Zn-Pb-Ba-Cu-As-Sb-Cd being the elements most enriched in these deposits. The differing patterns of element deposition in these two tectonic settings is related to the temperature of the hydrothermal fluids, which is a function of water depth and therefore of tectonic setting (mid-ocean ridge vs volcanic arc). In highly sedimented basins, such as the JADE hydrothermal field in the Okinawa Trough, Pb and other chalcophilic elements are leached from the sediment by slowly migrating hydrothermal fluids to form a mixed black-yellow-barite ore (BO-YO-BaO). This type of deposit is the most enriched in Zn-Pb-Ba-As-Sb-Ag in decreasing order of element abundance. These results indicate that black ore (sphalerite plus galena) is most enriched in sedimented-hosted deposits such as the JADE deposit, is moderately enriched in submarine hydrothermal mineral deposits from convergent plate margins and is poorly enriched in submarine hydrothermal mineral deposits from divergent plate margins.     

Sedimentary sulfides in the Nearshore Georgia Bight

Sedimentary sulfide, iron, and organic matter were measured in neritic sediments from the Georgia Bight. The two measured depth integrated sulfur pools, FeS + HS⁻ and FeS₂, tended to decrease with increasing distance from shore out to 33 km. Total iron and organic matter were strongly correlated and both tended to decrease with increasing distance from shore. Sediment depth profiles of organic matter/reduced sulfur suggest relatively constant rates of sulfate reduction over the top 40 cm of sediment. Differences in within-station variance indicated regions of lower and higher spatial/temporal heterogeneity, that may be related to tidally driven circulation patterns. No seasonal cycles were evident in sedimentary sulfides.     

The Polar Floats Program

The Polar Floats Program, an adaptation of midlatitude SOFAR float technology to the polar regions, is used to monitor subsurface circulation patterns over large spatial and temporal scales as well as to track mesoscale features in near realtime. The program is comprised of three major components that are now under development: an 80-Hz float transducer, American and French sea-ice-deployable listening stations using ARGOS data telemetry (ARS and SOFARGOS, respectively), and the software needed for real-time tracking. The adaptation of SOFAR technology to the planar regime demands modifications of the existing design from both environmental and acoustical standpoints. The authors describe the development and use of SOFAR technology within a relatively small sector of the north polar region that encompasses several thousand kilometers around Fram Strait (located between Greenland and Spitsbergen)     

大陆边缘沉积物中的气水合物

气水合物是甲烷或其他低分子气体与水分子的化合物,它在低温和相对高压的条件下仍然是稳定的。水深超过300 m的海洋符合这样的条件。气水合物以冰的集合体形态广泛分布于富含有机质的海洋沉积物中,后者分解后形成了甲烷。近年来对这些化合物的兴趣有两个主要原因:首先,现已查明     

活动大陆边缘的板片窗构造

正俯冲的洋中脊的持续扩张作用将会使该洋中脊两侧的洋壳板片之间形成一个持续加宽的间隙,这个间隙称为板片窗。板片窗往往形成于小于10Ma左右具浮力的大洋岩石圈俯冲时期。板片窗形态依赖于3个主要因素：板块的相对运动、俯冲前的洋脊一转换断层组合样式、俯冲角度。影响板片窗形态的次要因素还有热侵蚀、相变等因素。在板片窗出现的活动大陆边缘,软流圈、岩石圈、大气圈、水圈发生独特的多圈层相互作用,是地球系统最为活跃的地带。由于该地带的洋底消减往往与生长轴呈一定角度相交,不仅引起盆地的不对称消减,而且使得板片窗之上的活动大陆边缘的构造、岩浆、成矿和热效应明显不同于洋中脊平行于俯冲带的消减作用产生的构造、岩浆、成矿和热效应。     

火山边缘的构造:北大西洋/拉布拉多—巴芬体系存在的问题

火山边缘是与大量岩浆的侵入和排出有关的被动边缘 ,就象北大西洋 /拉布拉多—巴芬体系一样 ,这种岩浆作用出现在板块解体和早期的大洋扩张期间或之前。解体之前的火山活动形成了大面积的溢流玄武岩 ,面积达 1 0 6km2。陆—洋边界出现了与板块解体同期的火山活动 ,值得注意的是 ,它形成了向海倾斜的厚火山楔形体和火山沉积层 ( SDV) ,后者组成了地震研究中的向海倾斜反射系列 ( SDRS)。在它们的下部 ,SDV也含有解体前的玄武岩。大多数火山边缘似乎发育成与羽状物有关的热软流层。对于这种关系是否有规律还存在争议 ,这里不进行讨论。火…     

外大陆架划界信息系统中数据交换方法

采用VB.NET作为开发工具,ArcGIS Engine作为开发平台,进行外大陆架划界的数据交换研究,所开发的程序能够实现图元和文件层次的交换。该方法的研究对于我国外大陆架的划界有着非常重要的参考作用。     

大陆边缘与硫化物循环

大陆架边缘陆地与海洋之间过渡带是地球上最重要的界线之一，海洋地球化学家们经常把大陆架边缘作为一个“生物地球化学反应器”。Turchyn与Schrag的研究显示，在大陆架边缘存在化学物质循环的新的重要的信息。