Geological structure and petroleum resource potential of the North Sea basin

The North Sea basin occupies a spacious depression almost isometric in shape. In the west and northwest, the basin is bordered by the continental crust consolidated during the Precambrian, Caledonian, and Hercynian orogenic epochs, which now forms epiplatformal orogenic structures. They are represented by the London-Brabant uplift and the Arden massif in the southwest and south and the Baltic Shield in the east and northeast. The North Sea basin may be considered as an ancient aulacogen that was transformed in the Early Mesozoic into a complex system of continental rifts and grabens. The sedimentary cover of the basin is represented by a thick (8.5?C12.5 km) Ordovician-Quaternary sequence. Oil and gas generation in the sedimentary cover of the basin is likely connected with four main productive sequences: the coaliferous Upper Carboniferous (Westphalian), the subsalt Zechstein, the Jurassic-Lower Cretaceous (Lotharingian, Toarcian, Kimmeridgian, and Weldian bituminose shales), and the shaly Cenozoic. The large oil and gas reserves in the North Sea??s sedimentary cover (over 280 fields) implies that the above-mentioned sequences have realized their oil-generating potential. The present-day position of the main oil and gas generation zones in the sedimentary section of the North Sea explains the distribution of the oil and gas fields through the basin from the genetic standpoint. The petroleum resource potential of the basin is still significant. In this regard, most promising are the spacious shelf areas, turbidite sediments, deep Paleozoic sequences, and continental slopes in the northern part of the basin, which remains insufficiently investigated.     

The petroleum resource potential of the Bering Sea region

The Bering Sea sedimentary basin comprises the Bering Sea and the adjacent intermontane depressions on the continents. It includes the following subordinate sedimentary basins: the Norton; Bethel; Saint Lawrence; Anadyr; Navarin; Khatyrka; Saint George; Bristol; Cook Inlet; and Aleutian consisting of the autonomous Aleutian, Bowers, and Komandor basins. All of them exhibit significant geological similarity. The Middle and Upper Miocene terrigenous sequences, which are petroliferous through the entire periphery of the Pacific Ocean, are characterized by their high petroleum resource potential in the Bering Sea continental margin as well, which is confirmed by the oil and gas pools discovered in neighboring onshore lowlands. The younger (Pliocene) and older (up to Upper Cretaceous) sedimentary formations are also promising with respect to hydrocarbons. The integral potential oil and gas resources of the Bering Sea sedimentary basin, including the continental slopes, are estimated by the US Geological Survey to be 1120 × 10⁶ t and 965 × 10⁹ m³, respectively.     

Patterns of ctenophore populations in the northeastern part of the Black Sea in 2005

Particular features of the distribution and the dynamics of populations of the ctenophores Mnemiopsis leidyi, Beroe ovata, and Pleurobrachia pileus in the Gelendzhik area in 2005 are studied and compared to their population structure in the previous years. The intensive evolution of the Rim Current, the suppression of the transversal eddy transfer, and other hydrological features of 2005 resulted in an unusually early mass appearance of Beroe in the plankton off the shores of the Caucasus, its prolonged and intensive breeding, and high biomass. This, in turn, caused the suppression of the population of Mnemiopsis, whose abundance and pressure on the mesoplankton in August–September turned out to be several times smaller than in the previous year, when Beroe appeared only in the middle of September.     

Bacterioplankton in the northeastern part of the Black Sea during the summer and autumn of 2005

On the basis of luminescent microscopy using a DAPI dye, the abundance, morphometric characteristics, and biomass of bacteria in the coastal waters off the northeastern part of the Black Sea in 2005 were considered. The material was collected in June, September, and October along the cross section from Golubaya Bay towards the open part of the sea. An analysis of the microorganism development level showed that the bacteria achieved their maximal abundance in September, amounting, in the closest near-shore area, to 2435 × 10³ cells/ml, or 276 mg/m³ of wet weight; the lowest values were characteristic of October. During all the survey periods, coccal forms were prevailing among the microorganisms; regardless of the season, their fraction was maximal at the coastal stations. The greatest prevalence of coccal forms was characteristic of October (83%). The average sizes of the bacterial cells in 2005 varied within 0.073–0.257 μm³. The highest values of the bacterial abundance and biomass, almost in all the cases, were found at coastal stations; with the distance from the coast, a decrease in the bacterioplankton abundance was observed. A comparison of methodically similar data on the concentration of bacteria (dying with acridine orange and DAPI) from 1985 till now shows a trend of the annual growth in the bacterial abundance.     

基于深度域地震成像的中沙海槽盆地东北部结构构造研究

文章基于叠前深度偏移地震成像分析, 结合前人重磁反演等地球物理资料成果, 对中沙海槽盆地东北部结构构造进行探索研究。研究表明: 中沙海槽盆地东北部发育新生代地层, 厚度在1500~2500m之间, 地层层速度为1500~ 3500m·s^-1, 不存在中生界沉积层, 盆地基底为海山或前寒武系基岩及岩浆岩隆起。中沙海槽盆地新生代陆源海相烃源岩丰富, 盆地新生界地层厚度大, 盆地凹陷、断裂发育, 具有一定的油气勘探潜力。     

Geochemical peculiarities of sediments in the northeastern Black Sea

We present the results of chemical determinations of Al, Fe, Mn, Cu, Ni, Co, Cr, Pb, Sb, and As in Black Sea sediments over a profile from the Kerch Strait to the eastern part of a deep depression (2210 m). The lithological and geochemical variations were studied in the horizontal and vertical profiles of sediments up to 3 m thick. The tendencies in the distributions of the studied metals during Pleistocene and Holocene sedimentation were analyzed beginning from Neoeuxinian freshwater deposits via the overlaying Drevnechernomorian beds with elevated contents of sapropel to modern clayey carbonate deposits with coccolithophorids. Statistical factor analysis isolated five factors: two main factors (75% of the total dispersion) and three subordinate factors. The first leading biogenic factor (47% of dispersion) reflects the correlation between С_org, Cu, and Ni; the second terrigenous factor (28% of dispersion) combimes Fe, Al, Cr, and Sb. The chemical composition of the sediments reflects the manifestation of diagenesis of landslide processes and mud volcanism along with sedimentation regularities.     

Genetic aspects of the oil and gas potential of the sedimentary cover in the northeastern part of the Black Sea (within the Russian Economic Zone)

The oil and gas potential of the region under study is assessed using the historical-genetic method developed at the Shirshov Institute of Oceanology of the Russian Academy of Sciences. The predicted distribution of the main oil and gas source formations in the sedimentary cover section is presented; the modern temperature conditions of their occurrence are calculated. Based on these data and the analyses of the distribution of the oil and gas deposits discovered in the adjacent land territories, the possible oil and oil-and-gasbearing prospectives are determined, and specific recommendations for exploration are given.     

Structural plan and prospective petroleum potential of the Jurassic sediments of the Gudauty Rise in the Black Sea

The structural plan and petroleum potential of the Gudauty Rise are considered. This work is based on detailed seismic (reflected wave and common deep point methods) studies and a hydrogas survey performed simultaneously over all the seismic profiles.     

Role of the small-size fraction of mesozooplankton in the pelagic community of the northeastern part of the Black Sea in the autumn

The role of the small-size (SF; 0.1–0.5 mm) and large-size (LF; 0.5–20.0 mm) fractions in the biomass and abundance of mesozooplankton (0.1–20.0 mm) was assessed using the database of samples obtained during the cruises of RV Akvanavt in the northeastern Black Sea in November 2000 and October 2006. The mesozooplankton was collected by means of Juday nets (37/50, filtering gauze 160 μm) and Niskin bottles in two areas: (1) the shelf and continental slope (30–1480 m depth) and (2) the deep sea (depths of more than 1500 m). The plankton net was considerably less effective in collecting the SF of the mesozooplankton (by a factor of 30–36) than the Niskin bottles. When comparing the SF and LF, we estimated the abundance and biomass of the SF in the samples obtained with the Niskin bottles. The abundance of the SF in the deep-sea area was 2.5 times lower compared to the shelf and continental slope, and the LF abundance was 5.0 times lower in the same way. The abundance of the SF constituted 88% of the total mesozooplankton on the shelf and continental slope, and 78% in the deep-sea area. The biomass of the SF was higher as well on the shelf and continental slope. Meroplankton played a significant role in the SF zooplankton abundance (0.5 × 10³ + 0.16 ind. m⁻³) in this area. The SF grazing impact was 10% of the total mesozooplankton grazing on the shelf and continental slope, and 17% in the deepsea area. Appendicularia and nauplii of copepods had the greatest contribution to the mesozooplankton grazing among the SF group.     

Numerical simulation of an intensive upwelling event in the northeastern part of the Black Sea at the IO RAS hydrophysical testing site

The paper discusses mathematical simulation of intensive coastal upwelling observed in the northeastern part of the Black Sea in the water area of the hydrophysical test site of the Shirshov Institute of Oceanology, Russian Academy of Sciences, in September 2013. The simulation was carried out with the MIKE 21/3 Coupled Model FM combined hydrodynamic model of the Danish Hydraulics Institute (DHI). The calculation results are compared with the data of direct instrumental observations carried out in the IO RAS hydrophysical survey area. The essential role of surface wind waves in the formation of the observed temperature profiles is demonstrated, as well as the necessity of taking it into account when considering peculiarities in the vertical circulation of coastal waters.     

The Black Sea basins structure and history: New model based on new deep penetration regional seismic data. Part 1: Basins structure and fill

This work is based upon results of interpretation of about 8872 km-long regional seismic lines acquired in 2011 within the international project Geology Without Limits in the Black Sea. The seismic lines cover nearly the entire Black Sea Basins, including Russia, Turkey, Ukraine, Romania and Bulgaria sectors. A new map of acoustic basement relief and a new tectonic structure scheme are constructed for the Black Sea Basins. The basement of the Black Sea includes areas with oceanic crust and areas with highly rifted continental crust. A chain of buried seamounts, which were interpreted as submarine volcanoes of Late Cretaceous (Santonian to Campanian) age, has been identified to the north of the Turkish coast. On the Shatsky Ridge, probable volcanoes of Albian age have also been recognized. Synorogenic turbidite sequences of Paleocene, Eocene and Oligocene ages have been mapped. In the Cenozoic, numerous compressional and transpressional structures were formed in different parts of the Black Sea Basin. During the Pleistocene–Quaternary, turbidites, mass-transport deposits and leveed channels were formed in the distal part of the Danube Delta.     

南海东北部居里面特征及其石油地质意义

居里面是岩石中铁磁性矿物因温度升高达到居里点而由铁磁性变为顺磁性时的温度界面, 在这个面以下的岩石由于温度超过居里点而被认为几乎无磁性。1985年中美双船地震扩展排列东剖面(ESPE)和1993年中日合作海底地震仪剖面(OBS93)均穿越南海东北部各主要构造带和盆地, 获得了完整的地震及重、磁资料。通过上述剖面的磁测异常反演出其磁居里面, 同时由热流探测资料计算其地温场并从中获取了热居里面(575℃等温面)数据(热居里面是笔者相对于磁居里面而提出的一个新概念, 即指由海底热流探测资料经地温场模拟而获得的居里面)。研究结果表明, 两种方法得到的居里面深度在很多地区并不一致, 表现出显著的差异。笔者认为造成这种差异的主要原因在于, 在有可能存在未知热事件的地区, 计算稳态地温场的前提条件并不成立, 因而由这种方法计算出来的热居里面在这些地区并不能真正反映居里面的深度, 从而形成了它与磁居里面的显著差异。通过计算研究区磁及热居里面并根据其差异可以快速判定该区下部是否存在10Ma以来的热侵事件以及是否有浅层热源, 这对于研究南海东北部新生代含油气盆地深部结构及沉积充填特征与烃源岩成熟生烃作用以及油气运聚成藏规律和油气资源潜力评价等, 均具有重要的油气地质意义和地球科学意义。     

Evaluation of ecosystem status in the shelf-slope zone of the northeastern Black Sea based on the trophic index (TRIX)

The water conditions and trophic status in the shelf-slope zone and bays of the northeastern Black Sea were evaluated on the basis of monitoring data from 2007–2014. It has been shown that the concentrations of nutrients and chlorophyll “a” in the studied area are at the level of the pristine period (of the late 1970s). The concentration of mineral nitrogen in the surface water layer varied from 0.19 to 5.64 μM. The concentration of phosphates differed from analytical zero to 0.56 μM. The concentration of chlorophyll “a” in different seasons ranged from 0.24 to 0.89 μg/L. The trophic index characterizes the status of the marine shelf ecosystem near Gelendzhik city as “excellent” even in the bays. Significant year-to-year differences in the index were not detected. The range between the values of the trophic index in the bays and open sea was low (3.7 and 3.2, respectively).     

Genetic aspects of the petroleum resource potential of marine sedimentary basins

The historical-genetic method developed at the Institute of Oceanology of the Russian Academy of Sciences for the assessment of the petroleum resource potential is discussed with consideration of its main tasks and the successive procedures in its application. Such studies are crowned by a compilation of separate maps demonstrating scales of oil and gas generation and maps of hydrocarbon genesis zoning of basins with outlining centers of oil and gas generation and defining different-phase hydrocarbon-generation zones. The method was tested in over twenty continental-marginal and intracontinental basins studied to a different extent. The sedimentary basins of the Atlantic continental margin off Africa and the Caspian and Black seas were used as objects for applying the historical-genetic method for assessing their petroleum resource potential.     

Radiation of long waves from Black Sea seismic zones

The paper is concerned with analysis of tsunami wave refraction in the Black Sea, radiated from six seismic areas. Numerical results have been obtained on the basis of a radiation model for long wave propagation, with the sources of tsunamis being pointlike and distributed. Translated by Vladimir A. Puchkin.     

Interannual variability of the zooplankton on the shelf of the northeastern Black Sea in the autumn period

The variability of the mesozooplankton stock in the shelf pelagic communities was studied in the late summer and autumn of 2006–2008. The plankton community’s structure and distribution were described for the shoreward transect (Gelendzhik city vicinity). The indirect and direct effect of the ctenophores Mnemiopsis leidyi and Beroe ovata on the mesozooplankton community was studied. The long-term changes in the meso- and macroplankton communities of the Black Sea were analyzed for the period of 2001–2008. The effects of the climatic factors, the water mass circulation, and the factors’ interplay on the mesozooplankton dynamics were assessed. Despite the wide range of the environmental conditions, the stock biomass of Mnemiopsis leidyi appeared to be quite stable within the studied period.     

南太平洋地区盆地形成演化和油气资源潜力分析

本文从南太平洋地区区域构造演化出发,开展盆地类型划分和石油地质条件分析,了解不同类型盆地的油气成藏特征,并分析油气分布规律和资源潜力,以期对未来油气勘探开发国际合作选区提供借鉴。研究表明:（1）南太平洋地区经历了亨特-鲍恩造山运动、澳大利亚板块与南极洲板块分离、塔斯曼海扩张及珊瑚海扩张、巴布亚新几内亚地区的洋壳俯冲和弧-陆碰撞作用,最终形成了澳大利亚东部南缘和海域及新西兰地区以裂谷盆地为主、澳大利亚东部内陆以克拉通盆地为主的包括晚二叠世-三叠纪前陆盆地、古近纪-新近纪前陆盆地、古近纪-现今弧前盆地和弧后盆地6种盆地类型;（2）澳大利亚内陆南缘和东部海域以及新西兰地区裂谷盆地分布广泛,裂谷盆地油气最为富集,但内陆和海域有所差异,内陆南缘裂谷盆地油气资源丰富且石油与天然气的比值约为2:1,而东部海域裂谷盆地因油气成藏条件差,尚无油气发现;（3）根据盆地的剩余可采储量和远景资源量对南太平洋地区的资源潜力进行分析,认为白垩纪-古近纪裂谷盆地和古近纪-新近纪前陆盆地油气资源潜力最大,并优选出吉普斯兰（Gippsland）、塔拉纳基（Taranaki）和巴布亚（Papua）3个有利盆地。     

Crustal features of the northeastern South China Sea: insights from seismic and magnetic interpretations

We interpret seven two-dimensional deep-penetration and long-offset multi-channel seismic profiles in the northernmost South China Sea area, which were collected by R/V Marcus G. Langseth during the TAIwan GEodynamics Research (TAIGER) project in 2009. To constrain the crustal characteristics, magnetic inversion and forward magnetic modeling were also performed. The seismic results clearly show tilted faulting blocks in the upper crust and most of the fault plane connects downward to a quasi-horizontal detachment as its bottom in the south of the Luzon-Ryukyu transform plate boundary. North of the plate boundary, a small-scale failed rifted basin (minimum 5 km in crustal thickness) with negative magnetization probably indicates an extended continental origin. Significant lower crustal material (LCM) was imaged under a crustal fracture area which indicated a continent and ocean transition origin. The thickest LCM (up to 6.5 km) is located at magnetic isochron C15 that is probably caused by the magma supply composite of a Miocene syn-rift volcanic event and Pliocene Dongsha volcanic activity for submarine volcanoes and sills in the surrounding area. The LCM also caused Miocene crustal blocks to be uplifted reversely as 17 km crustal thickness especially in the area of magnetic isochron C15 and C16. In addition, the wide fault blocks and LCM co-existed on the magnetic striped area (i.e. C15–C17) in the south of the Luzon-Ryukyu transform plate boundary. Magnetic forward modeling suggests that the whole thick crustal thickness (>12 km thick) needs to be magnetized in striped way as oceanic crust. However, the result also shows that the misfit between observed and synthetic magnetic anomaly is about 40 nT, north of isochron C16. The interval velocity derived from pre-stack time migration suggests that the crust is composed of basaltic intrusive upper crust and lower crustal material. The crustal nature should refer to a transition between continent and ocean. Thus, the magnetic reversals may be produced in two possible ways: basaltic magma injected along the crustal weak zone across magnetic reversal epoch and because some undiscovered ancient piece of oceanic crust existed. The crustal structure discrimination still needs to be confirmed by future studies.     

Peculiarities of the currents field in the north-western part of the Black Sea

On the basis of the results derived by theoretical analysis [1] and laboratory physical modelling [2] of the circulation seawater and stratification, induced by buoyancy fluxes, the suggestion has been made that, possibly, the Black Sea currents system is three-layered. It has been supposed that an anticyclonic current flows in the basin. To verify this deduction, the data from MHI's archived dataset have been treated, and results from twoad hoc expeditions are submitted here. Analysis of the vertical structure of currents, based on thein situ velocity measurements, using various means and calculations of the geostrophic circulation, has confirmed that a flow with the theoretically predicted parameters may exist in the Black Sea. Translated by Vladimir A. Puchkin.     

Long-term changes in the meiobenthos of the eastern part of the Black Sea

The results of meiobenthic surveys undertaken in 1991, 1999, and 2005 off the Caucasian coasts of the Black Sea are presented. During the period of 1991 to 1999, the number of free-living nematodes increased significantly at all the sampling stations. The mean nematode abundance values grew from 85 ind./10 cm² in 1991 to 1167 ind./10 cm² in 1999. Proportionally, the total metazoan meiofauna density increased from 171 to 1283 ind./10 cm². The abundance of other meiofaunal groups including harpacticoid copepods did not change significantly. As a result of these changes, the ratio of nematodes to copepods (the nematodes-copepods index) increased from 2.5: 1 in 1991 to 26: 1 in 1999 and to 70: 1 in 2005. The number of foraminifers increased twofold. In 1991, they were found only at five stations out of 25. In 1999, foraminifers were presented at all ten stations with a mean density of 212 ind./10 cm². Such changes in the meiobenthic communities could have resulted from cascade transformations of the ecosystem leading to among other changes to a decline in the macrobenthos biomass and the release of nonutilized organic matter in the bottom ecosystems. The differences in the procedures of the sampling and the samples’ processing in the different years may be responsible for the 20–30% variation in the assessment of the meiobenthos’ number.