Characteristics of two natural gas seepages in the North Sea

Two occurrences of active gas seepages are described from the North Sea. The southernmost one, situated above a salt diapir in Norwegian block , has been studied and sampled by use of a remotely operated vehicle (ROV). This seepage consists of about 120 single seeps located within a diameter of 100 m. It is estimated to produce 24 m³ of methane gas per day (at ambient pressure, 75 m water depth). Isotope values of the methane gas and higher hydrocarbon gases in the surrounding seafloor sediments, show that their origin is from a deep seated, thermogenic source. No typical gas-induced erosion features are found on the seafloor at this location, probably due to the lack of very fine grained material.The second occurrence is located in U.K. block (Geoteam, 1984), where the seepage is associated with a very large pockmark depression, measuring 17 m in depth and 700×450 m in width. This depression represents an eroded fine grained sediment volume of 7.10⁵ cubic metres. No detailed inspection or sampling of the gas has been performed here. However seismic reflection anomalies are seen on airgun seismic records at various levels down to a depth of at least 1100 m below seafloor. The seeping gas, possibly mixed with liquids, at this location is therefore also expected to be of a thermogenic origin.     

Spatial distribution and geochemistry of the nearshore gas seepages and their implications to natural gas migration in the Yinggehai Basin,offshore South China Sea

About 120 gas seepage vents were documented along the west and southwest coast of the Hainan Island, South China Sea, in water depths usually less than 50 m. The principal seepage areas include the Lingtou Promontory, the Yinggehai Rivulet Mouth, Yazhou Bay, the Nanshan Promontory and the Tianya Promontory. They occur along three major zones, reflecting the control by faults and lateral conduits within the basement. It is estimated that the total gas emission from these seepage vents is 294–956 m³/year. The seepage gases are characterized by a high CH₄ content (76%), heavy δ¹³C₁ values (−38 to −33‰) and high C₁/C_1–5 ratios (0.95–1.0), resembling the thermogenic gases from the diapiric gas fields of the Yinggehai Basin. Hydrocarbon–source correlation shows that the hydrocarbons in the sediments from seepage areas can be correlated with the deeply buried Miocene source rocks and sandstone reservoirs in the central depression. The 2D basin modeling results based on a section from the source rock center to the gas seepage sites indicate that the gas-bearing fluids migrated from the source rocks upward through faults or weak zones encompassed by shale diapirism or in up-dip direction along the sandstone-rich strata of Huangliu Formation to arrive to seabed and form the nearshore gas seepages. It is suggested that the seepage gases are sourced from the Miocene source rocks in the central depression of the Yinggehai Basin. This migration model implies that the eastern slope zone between the gas source area of the central depression and the seepage zone is also favorable place for gas accumulation.     

可燃气体泄漏爆炸下海洋平台数值仿真计算

用等效TNT方法计算了海洋平台复杂结构在油气爆炸冲击波作用下的动态响应,采用MSC.DYTRAN中的多欧拉-拉格朗日耦合方法进行数值模拟研究。用多欧拉域模拟结构内外空气中爆炸冲击波传播情况,用快速耦合方法计算结构和流体的耦合作用。模拟结果显示:在油气爆炸冲击波的作用下,平台舱室变形、失效后破裂,冲击波通过破口传入平台其它舱室;研究了平台各层甲板、舱壁等构件的吸能情况,为平台的结构设计和结构加强打下基础。     

浙江中南部外侧海区的虾类资源

本文根据1986年8月至1987年11月浙江中南部海域(27°00′～29°30′N,125°00′E) 拖虾调查资料,分析了虾类资源的种类、组成,拖虾渔获量及主要种类的分布,提出进一步开发凹管鞭虾,假长缝拟对虾等新的虾类资源的建议,并讨论了合理利用的途径。     

Speculative petroleum systems of the southern Pelotas Basin,offshore Uruguay

The Pelotas Basin of Brazil and Uruguay represents a frontier basin with under-explored hydrocarbon potential. Although oil and gas accumulations have yet to be identified, only 21 exploratory wells have been drilled in an area of more than 330,000 km², 20 of which are located in the Brazilian portion of the basin. A detailed study of the petroleum system of offshore Uruguay has strong potential to contribute to a better characterization of the capacity of the basin to generate and accumulate hydrocarbons. Three stages have previously been recognized during the evolution of Pelotas basin: (1) a prerift phase which preserved Paleozoic and Mesozoic units of the Paraná Basin; (2) an Early Cretaceous volcano-sedimentary synrift phase; and (3) a Cretaceous to Cenozoic postrift phase deposited during the passive margin stage. In this study, we use sequence stratigraphy methodology to interpret 2D multichannel seismic sections of the southern segment of the Pelotas Basin in the Uruguayan Atlantic margin. This analysis allows us to identify depositional sequences, systems tracts and the distribution of the main elements of the potential petroleum systems. Following our analysis, we propose six speculative petroleum systems (SPS) in the Pelotas Basin. The first SPS is related to the prerift phase and is represented by a Lower Permian restricted marine source rock and reservoirs related to Permian to Upper Jurassic aeolian and fluvial sandstones. The second SPS corresponds to the synrift phase and is constituted by a Barremian lacustrine source rock with reservoirs of alluvial/fluvial sandstones of the same age. The other four proposed SPS are associated with the postrift phase, represented by marine source rocks related to Aptian-Albian, Cenomanian-Turonian and Paleocene transgressions, all of which are identified in the region and interpreted in seismic lines from Uruguay. These postrift SPS have predominantly siliciclastic reservoirs represented by Early Cretaceous aeolian sandstones and Cretaceous to Cenozoic deltaic sandstones and turbidites.     

An offshore eddy in the California current system part II: Surface manifestation

Ship and satellite observations taken over the last thirty years show that mesoscale patterns of sea surface temperature (SST) in the California Current System are consistently found throughout the year and usually occur in approximately the same geographical locations. Typically, these patterns are more pronounced in fall/winter than in spring/summer. The temporal and spatial characteristics of these persistent feature were examined with satellite infrared (IR) measurements during winter 1980–1981. In January 1981, a ship surveyed the vertical structure of several physical, chemical, and biological parameters beneath one of these SST features centered near 32°N, 124°W. The surface IR pattern had a length scale of 200 km and a time scale of about 100 days. It disintegrated following the first two storms of the winter season. Motion studies of the pattern in late October indicated an anticyclonic rotation with maximum velocities of 50 cm s^?1 at 50 km from the axis of rotation. As a unit, the pattern advected southward with an average speed of 1 cm s^?1. Thermal fronts, determined from the satellite imagery, were strongest (0.4°C km^?1) along the rim of the pattern and were advected anticyclonically with the pattern; their length scales were 20–30 km in the along-front direction and less than 10 km wide. The hydrographic data revealed a three-layer structure beneath the surface pattern; a 75 m deep surface layer, a cold-core region from 75 to 200 m depth, and a warm-core eddy extending from 250 to 1450 m. The anticyclonic motion of the surface layer was caused by a geostrophic adjustment to the surface dynamic height anomaly produced by the subsurface warm-core eddy. The IR pattern observed from space reflects the horizontal structure of the surface layer and is consistent with a theoretical model of a mean horizontal SST gradient perturbed by a subsurface density anomaly. Ship of opportunity SST observations collected by the National Marine Fisheries are shown to resolve mesoscale patterns. For December 1980, the SST pattern near 32°N, 124°W represented a 2°C warm anomaly compared with the 20-year mean monthly SST pattern.     

An offshore eddy in the California current system Part IV: Plankton distributions

The distribution of plankton across a warm-core eddy system in the California Current 400 km off Point Conception, California was studied in January 1981. The eddy system, about 150 km in diameter at the 7°C isotherm, was made up of a 75 m thick surface layer, a cold-core region extending from 75 m to about 200 m, and a warm-core eddy below 200 m extending to at least 1450 m. Casts for the vertical distribution of chlorophyll/phaeophytin and integrating zooplankton net tows were taken at 37 stations located about 20 km apart on two orthogonal transects across the eddy system. Vertical distributions of microplankton were determined on one section from the eddy center to beyond the eastern edge. Integrated chlorophyll/phaeophytin values were highest to the north and east of the eddy system; across the system itself, there was only a small increase of values near the center. Asymmetrical distributions of maximum concen Current water was being entrained into the center of the eddy system from the northeast. Dinoflagellates were numerically the most important member of the microplankton, especially in the deep chlorophyll maximum. Zooplankton distributions indicated the intermingling of warm and cool water species throughout at least the upper 200 m of the eddy system. Some cold water species were as abundant inside the system as outside to the north and east; their numbers were much reduced in a band surrounding the system where warm water species were most abundant. The presence of species characteristic of different water types throughout the region of the eddy system provides an indication of the mixing that had occurred since the system originally formed. The biological data, together with the physical and chemical results, indicate the importance of frontal boundary processes and lateral entrainment of surrounding water into the eddy system in determining the character and productivity of such systems.     

An offshore eddy in the California current system Part I: Interior dynamics

From January 9 to 17, 1981, detailed observations of the horizontal and vertical structure beneath one of the quasi-permanent semi-stationary mesoscale offshore eddy signatures in the California Current System (CCS) discussed by Bernstein, Breaker and Whritner (1977), Burkov and Pavlova (1980), and Simpson (1982) were made. The vertical sections of temperature and density show the presence of three-layer system. A subsurface warm-core eddy, whose diameter is about 150 km at the 7°C isotherm, is the dominant feature. A warm surface layer, which extends to a depth of 75 m, lies over the eddy. Between the warm surface layer and the subsurface warm-core eddy, there is a cold-core region which extends to a depth of about 200 m. There is a high degree of symmetry about the vertical axis of rotation. Vertical sections of salinity and dissolved oxygen are entirely different from sections of temperature and density. Diagrams of water mass characteristics confirm that the core of the eddy, found between 250–600 m, consists of inshore water from the California Undercurrent (CU). Below about 700 m, local waters from the Deep Poleward Flow (DPF) have been incorporated into the eddy. The observed distributions of properties (T, S, δ_θ, O₂) are inconsistent with a single, local generation process for the eddy system. Radial distributions of angular velocity, normalized gradient velocity and relative vorticity support the use of a Gaussian radial height field as an initial condition in eddy models. Possible reasons why CCS eddies may differ dynamically from Gulf Stream rings are given in the text. At the time the observations were made, the system as a whole was in near geostrophic balance. Local geostrophic balance, however, cannot explain the observed distribution of properties and structure. The observed symmetry in the structure of the eddy system, chemical evidence (Simpson, 1984), biological distributions (Haury, 1984) and satellite images of the CC (Koblinsky, Simpson and Dickey, 1984) suggest that lateral entrainment of warm (oceanic) and cold (coastal) water into the upper two layers of the three-layer system by the subsurface eddy is a likely generation mechanism for the cold-core region. The coastal origin of the frontal structure along the northeastern quadrant and the oceanic origin of the frontal structure along the southwestern quadrant of the eddy system further support lateral entrainment as a generation mechanism for the cold core. This entrainment makes the CCS eddy system different from cold-core rings in the Gulf Stream and rather similar to some warm-core eddies found in the East Australian Current. The presence of CU water in the core of this eddy raises the question of how CU water was transported from the continental slope. Eddy generation mechanisms, other than baroclinic instability of the CC, may be required to explain the distribution, persistence, and core composition of offshore mesoscale eddies in the CCS. There is evidence that barotropic, in addition to baroclinic, processes may be important.     

An offshore eddy in the California current system part III: Chemical structure

From January 9 to 17, 1981, detailed physical, chemical and biological measurements were made through the historical surface signature (Berstein, Breaker and Whritner, 1977; Burkov and Pavlova, 1980; Simpson, 1982) of a warm-core eddy in the California Current System. The data show a three-layer system: surface layer to 75 m, intermediate cold-core region to about 200 m, and the physically dominant subsurface warm-core eddy to about 1400 m. The chemical structure simultaneously possesses characteristics of both warm- and cold-core eddies. This structure results from a complex interplay among non-local eddy generation processes at the time the three-layer system was formed and a continuous set of interactions within the three-layer system, both inshore (cold) and offshore (warm) waters of the California Current and coastal and local biological processes (e.g. this California Current System eddy is $\text{not}$ an isolated structure like some Gulf Stream rings). The dominant biological/chemical process in the euphotic zone is phytoplankton photosynthesis; photosynthetic alteration of the chemical structure below 100 m is much reduced. The effects of heterotrophic activity on the deeper-lying chemical structure, however are not as significant as those of autotrophs on the chemical structure of the euphotic zone. Hence, below 100 m, the distribution and structure of chemical properties is controlled primarily by physical processes. The continuous set of interactions of the three-layer system with coastal and oceanic waters of the California Current make this offshore eddy in the California Current System fundamentally different chemically and biologically from cold-core Gulf Stream rings and rather similar to some of the warm-core eddies found in the East Australian Current.     

Numerical investigation of ocean waves generated by three typhoons in offshore China

The influences of the three types of reanalysis wind fields on the simulation of three typhoon waves occurred in2015 in offshore China were numerically investigated. The typhoon wave model was based on the simulating waves nearshore model(SWAN), in which the wind fields for driving waves were derived from the European Centre for Medium-Range Weather Forecasts(ECMWF) Re-Analysis-Interim(ERA-interim), the National Centers for Environmental Prediction climate forecast system version 2(CFSv2) and cr...     

Suspended sediment transport in surface waters of the California Current off southern California: 1977–78 floods

Floods in southern California during the rainy season of 1977–78 followed four years of severe drought when vegetative cover of drainage areas was at a minimum. LANDSAT Band 5 analyses following these floods suggest extensive transport of suspended sediment to 80 to 100 km from the coastline. Current patterns can be explained by a decaying Davidson Current situation and a large semipermanent cyclonic gyre that controls distribution of surface suspended sediment throughout the California Borderland. This gyre, and associated spinoff eddies, produce three distinct cells of suspended sediment in surface waters. These cells may control sedimentation patterns of terrigenous silt and clay.     

Passive margin evolution and its controls on natural gas leakage in the southern Orange Basin,blocks 3/4, offshore South Africa

Using a 2D seismic dataset that covers part of the southern Orange Basin offshore South Africa, we reconstructed the geological evolution of the basin. This evolutionary model was then used to investigate the occurrence of natural gas within the sedimentary column and the distribution of gas leakage features in relation to the observed sedimentary and tectonic structures developed in the post-rift succession since the Early Cretaceous. The Cretaceous succession has been subdivided into five seismic units. The highest sedimentation rates occur within the Barremian/Aptian (unit C1) and the Turonian/Coniacian (unit C3). Two Cenozoic units (T1 and T2) have been distinguished. These show a sudden decrease in sedimentation rate for the whole of the Cenozoic. Three phases of gravitational tectonics, with two Late Cretaceous phases of mass movement in the northern study area and Cenozoic slumping in the southern study area, have been related to sedimentation rates, sea-level changes, paleoenvironmental evolution and regional tectonics. The occurrence of natural gas leakage follows a coast-parallel distribution within the study area. In the near shore part at water depths shallower than 400 m, massive gas chimneys penetrate through the sediment layers and reach the (near-) surface. Within an intermediate narrow band, between 300 and <500 m water depth, the gas migrates more diffusely through sub-vertical faulted Cretaceous sediments, while in the outer part of the basin, through the Cretaceous and Cenozoic gravitational wedges, only very few signs of gas accumulation and migration can be seen along the faults. A conceptual model has been established with the Aptian source rock generating gas in the outer part of the basin. This source rock underlies the Cenozoic wedge in the south and the thick Cretaceous wedge in the north and is a postulated source for the natural gas within the sedimentary column. This thermogenically generated gas does not migrate directly through the gravitational faults and the above lying sediments, but moves buoyancy driven up-dip along stratigraphic layers, to escape through the sediments to the sea-floor in the inner shelf area.     

Thermohaline variability and geostrophic circulation in the southern portion of the Gulf of California

Data from seven oceanographic cruises in the southern Gulf of California from 1997 to 2002 are used to describe the thermohaline variability and the geostrophic circulation. Baroclinic patterns exhibited spatial and temporal variability. A deepening of isotherms at the center of the section was evident in February 1999, suggesting anticyclonic flow. In May 1998 and November 1997, cyclonic flow was suggested by shoaling of isotherms at the center of the section. Other cruises showed alternating cores of flow into and out of the Gulf (August 1998, September 1997 and October 2002). Neither a seasonal nor a spatial pattern in geostrophic flows was apparent, suggesting that the exchange of waters between the cyclonic flow of Pescadero basin and the interior of the Gulf is complex. Relatively high salinities were recorded during most of the cruises indicating that Gulf of California Water (GCW) was present most of the year. Higher salinities were observed during winter and spring, although during summer, relatively high and low salinities were both observed as surface and subsurface cores. Temperature and salinity characteristics of California Current waters were observed only in August 1995 when they reached as far north as Cerralvo Island at ∼50 dbar. During El Niño conditions in November 1997, a mixed layer (∼70 dbar) and deepening of the thermocline (∼50 dbar) characterized anomalous conditions; during this cruise an asymmetric salinity pattern was observed with low salinities characteristic of Tropical Surface waters at the center and east of the section, while maximum salinities (34.9<S<35.0) and Gulf waters were located in an 80 km wide core next to the Baja California Sur shelf as far north as San Jose Island.     

Stormwater plume detection by MODIS imagery in the southern California coastal ocean

Stormwater plumes in the southern California coastal ocean were detected by MODIS-Aqua satellite imagery and compared to ship-based data on surface salinity and fecal indicator bacterial (FIB) counts collected during the Bight'03 Regional Water Quality Program surveys in February–March of 2004 and 2005. MODIS imagery was processed using a combined near-infrared/shortwave-infrared (NIR-SWIR) atmospheric correction method, which substantially improved normalized water-leaving radiation (nLw) optical spectra in coastal waters with high turbidity. Plumes were detected using a minimum-distance supervised classification method based on nLw spectra averaged within the training areas, defined as circular zones of 1.5–5.0-km radii around field stations with a surface salinity of S < 32.0 (“plume”) and S > 33.0 (“ocean”). The plume optical signatures (i.e., the nLw differences between “plume” and “ocean”) were most evident during the first 2 days after the rainstorms. To assess the accuracy of plume detection, stations were classified into “plume” and “ocean” using two criteria: (1) “plume” included the stations with salinity below a certain threshold estimated from the maximum accuracy of plume detection; and (2) FIB counts in “plume” exceeded the California State Water Board standards. The salinity threshold between “plume” and “ocean” was estimated as 32.2. The total accuracy of plume detection in terms of surface salinity was not high (68% on average), seemingly because of imperfect correlation between plume salinity and ocean color. The accuracy of plume detection in terms of FIB exceedances was even lower (64% on average), resulting from low correlation between ocean color and bacterial contamination. Nevertheless, satellite imagery was shown to be a useful tool for the estimation of the extent of potentially polluted plumes, which was hardly achievable by direct sampling methods (in particular, because the grids of ship-based stations covered only small parts of the plumes detected via synoptic MODIS imagery). In most southern California coastal areas, the zones of bacterial contamination were much smaller than the areas of turbid plumes; an exception was the plume of the Tijuana River, where the zone of bacterial contamination was comparable with the zone of plume detected by ocean color.     

Petroleum composition in the Cuu Long Basin (Mekong Basin) offshore southern Vietnam

The Cuu Long Basin (Mekong Basin) is a rift basin off southern Vietnam, and the most important petroleum producing basin in the country. However, information on petroleum type and characteristics has hitherto been largely unavailable to the public. This paper presents petroleum geochemical data on nine oil samples from four different producing fields in the Cuu Long Basin: the Dragon (Rong), Black Lion (Sutu-Den), Sunrise (Rang ?ong) and White Tiger (Bach Ho) Fields. The oils are highly paraffinic with bimodal normal alkane distributions and show moderate pristane to phytane ratios and a conspicuous hyperbolic decrease in abundance with increasing carbon number of hopane homologues from C₃₀ to C₃₅. The TPP-index of Holba et al. (Holba, A.G., Dzou, L.I., Wood, G.D., Ellis, L., Adam, P., Schaeffer, P., Albrecht, P., Greene, T., Hughes, W.B., 2003. Application of tetracyclic polyprenoids as indicators of input from fresh–brackish water environments. Organic Geochemistry 34, 441–469) is equal to 1 in all samples which in combination with tricyclic triperpane T26/T25 ratios >1 and the n-alkane and hopane distributions mentioned above provide a strong indication of an origin from lacustrine source rocks. This is supported by the absence of marine C₃₀ desmethyl steranes (i.e. 24-n-propylcholestanes) and marine diatom-derived norcholestanes. Based on the overall biological marker distributions, the lakes probably belonged to the overfilled or balanced-fill types defined by Bohacs et al. (Bohacs, K.M., Carroll, A.R., Neal, J.E., Mankiewicz, P.J., 2000. Lake-basin type, source potential, and hydrocarbon character. An integrated sequence-stratigraphic–geochemical framework. AAPG Studies in Geology 46, 3–34). The oils were generated from source rocks at early- to mid-oil-window maturity, presumably Oligocene lacustrine shales that are present in the syn-rift succession. Oils from individual fields may, however, be distinguished by a combination of biological marker parameters, such as the oleanane index, the gammacerane index, the relative abundance of tricyclic terpanes, the proportions of diasteranes and 28-norspergulane, complemented by other parameters. The oils of the Cuu Long Basin show an overall similarity to the B-10 oil from the Song Hong Basin off northern Vietnam, but are markedly different from the seepage oils known from Dam Thi Nai on the coast of central Vietnam.     

Evidence of subsurface anaerobic biodegradation of hydrocarbons and potential secondary methanogenesis in terrestrial mud volcanoes

The assessment of gas origin in mud volcanoes and related petroleum systems must consider post-genetic processes which may alter the original molecular and isotopic composition of reservoir gas. Beyond eventual molecular and isotopic fractionation due to gas migration and microbial oxidation, investigated in previous studies, we now demonstrate that mud volcanoes can show signals of anaerobic biodegradation of natural gas and oil in the subsurface. A large set of gas geochemical data from more than 150 terrestrial mud volcanoes worldwide has been examined. Due to the very low amount of C₂₊ in mud volcanoes, isotopic ratios of ethane, propane and butane (generally the best tracers of anaerobic biodegradation) are only available in a few cases. However, it is observed that ¹³C-enriched propane is always associated with positive δ¹³C_CO2 values, which are known indicators of secondary methanogenesis following anaerobic biodegradation of petroleum. Data from carbon isotopic ratio of CO₂ are available for 134 onshore mud volcanoes from 9 countries (Azerbaijan, Georgia, Ukraine, Russia, Turkmenistan, Trinidad, Italy, Japan and Taiwan). Exactly 50% of mud volcanoes, all releasing thermogenic or mixed methane, show at least one sample with δ¹³C_CO2 > +5‰ (PDB). Thermogenic CH₄ associated with positive carbon isotopic ratio of CO₂ generally maintains its δ¹³C-enriched signature, which is therefore not perturbed by the lighter secondary microbial gas. There is, however, high variability in the δ¹³C_CO2 values within the same mud volcanoes, so that positive δ¹³C_CO2 values can be found in some vents and not in others, or not continuously in the same vent. This can be due to high sensitivity of δ¹³C_CO2 to gas–water–rock interactions or to the presence of differently biodegraded seepage systems in the same mud volcano. However, finding a positive δ¹³C_CO2 value should be considered highly indicative of anaerobic biodegradation and further analyses should be made, especially if mud volcanoes are to be used as pathfinders of the conditions indicative of subsurface hydrocarbon accumulations in unexplored areas.     

浙江南部近海主要鱼类的时空生态位及种间联结性

基于2016年8月（夏季）、11月（秋季）、2017年3月（冬季）、5月（春季）浙江南部近海的鱼类调查数据,利用生态位宽度、生态位重叠、聚类分析、方差比率法、卡方检验、联结系数以及种对共同出现百分率对主要鱼类种间关系进行研究。结果表明：（1）调查共采集鱼类169种,主要鱼类共有26种;（2）在空间维度上,日本鲭（Scomber japonicus）生态位宽度最大（2.83）,青鳞小沙丁（Sardinella zunasi）和芝芜棱鳀（Thryssa chefuensis）生态位重叠值最大（0.97）;在时间维度上,龙头鱼（Harpadon nehereus）生态位宽度最大（1.34）,6组种对时间生态位重叠值等于1.00;在时空维度上,龙头鱼生态位宽度最大（3.50）,青鳞小沙丁与芝芜棱鳀时空生态位重叠值最大（0.97）;（3）方差比率法分析表明,方差比率偏离显著,主要鱼类总体正联结显著,其中170组种对间联结性达到显著水平（$ \chi^2$≥3.841）,联结系数和种对共同出现频率结果表明种间联结性趋于正联结。     

Canyon-infilling and gas hydrate occurrences in the frontal fold of the offshore accretionary wedge off southern Taiwan

We utilized reflection seismic and bathymetric data to infer the canyon-infilling, fold uplift, and gas hydrate occurrences beneath the frontal fold at the toe of the accretionary wedge, offshore SW Taiwan. The lateral migrating paleo-Penghu canyons has cut across the frontal fold with six distinct canyon/channel incisions marked by channel infills. The longitudinal bathymetric profile along the modern canyon course shows a knickpoint of ~300 m relief at this frontal fold, indicating that the rate of fold uplift is greater than that of canyon incision. The age for the initial thrusting of this fontal fold is around 240 kyr ago, as estimated by using the maximum thickness of growth strata of this fold divided by the sedimentation rate obtained from a nearby giant piston core. Bottom simulating reflector (BSR) on seismic sections indicates the base of gas hydrate stability zone. Beneath the frontal fold, there is a widespread occurrence of BSRs, suggesting the highly probable existence of substantial quantities of gas hydrates. A seismic flat spot and a few push-down reflectors below BSR are found lying beneath the anticlinal axis with bathymetric four-way dip closure. The flat spot, cutting across a series of dipping reflections beneath BSR, may indicate the contact between free gas and its underlying formation water. The push-down reflectors beneath BSRs are interpreted to result from abundant free gas hosted beneath the gas hydrate stability zone. The multiple paleo-canyon infills seen along and beneath the frontal fold and above BSRs may provide thick porous sands to host gas hydrates in the frontal fold.     

夏季海南东、南沿岸珊瑚礁区浮游动物群落结构特征研究

于2018年8月对海南东、南海域展开断面调查研究,共获取了18个浮游动物样品,分析了浮游动物的种群分布和群落结构变化,旨在了解不同区域珊瑚礁生态系统的结构与功能。结果表明:海南东、南沿岸共鉴定浮游动物43属62种,浮游幼体23类,分为河口类群、暖水沿岸类群和暖水广布类群共三个生态类群,浮游动物种群组成以桡足类占优势,优势种以亚强次真哲水蚤(Subeucalanus subcrassus)、肥胖箭虫(Sagittaenflata)、异体住囊虫(Oikopleuradioica)、长尾类幼体(Macruralarva)、鱼卵(Fisheggs)、双生水母(Diphyeschamissonis)等种类组成。浮游动物个体丰度、物种丰富度和多样性指数等参数均存在区域性差异,整体呈现为三亚琼海文昌,湿重生物量则为琼海三亚文昌。总体而言,三亚珊瑚礁生态系统的健康状况整体优于文昌和琼海地区,浮游动物种类丰富度与多样性整体呈较高水平。