Hydrocarbons in surficial sediments from the Scotian Shelf

Surface sediments from 20 stations on the Scotian Shelf, collected on a transect from Halifax to Emerald Bank and around Sable Island, have been analyzed for hydrocarbon content and composition by gas chromatography and fluorescence spectrophotometry. Some samples were taken near abandoned exploratory drilling sites in the Sable Island area. Hydrocarbons appear to be mainly derived from biogenic terrestrial sources as evidenced by an inverse correlation of concentration with increasing distance from the mainland and a strong odd carbon preference in the n-alkanes. Contribution from petroleum sources, while minor, was most noticeable between Halifax and Emerald Bank. There is also evidence that the hydrocarbon composition at abandoned exploratory drilling sites has been slightly altered.     

Buried pockmarks on the Top Chalk surface of the Danish North Sea and their potential significance for interpreting palaeocirculation patterns

Three-dimensional (3D) seismic data from the southern Danish North Sea were used to analyse the morphology and spatial distribution of depressions in the Danian Chalk deposit. Previously, these depressions were either interpreted as karst structures or pockmarks. The observed depressions occur in an interval from 25 ms below to 12 ms above the Top Chalk surface. Three types of depressions were differentiated based on their plan-view geometry and their degree of symmetry: Type 1, comprising sub-circular and symmetrical depressions, is the dominant group (ca. 70 %). Type 2, elongated and symmetrical depressions, represents only a small fraction (ca. 5 %). The elongated and asymmetrical depressions of Type 3 compose ca. 25 %. In cross section, each depression type can be either characterised by a V- or a U-shape. The maximum size of the depressions ranges from 50 to 580 m, with an average internal depth of 10 m. We interpret the depressions as pockmarks formed by the expulsion of biogenic or thermogenic fluids at the Danian seafloor. Likely, the initial form of the pockmarks has been circular (Type 1) and was subsequently modified for Types 2 and 3 to an elongated form by currents. The long axis of the pockmarks is interpreted to represent the effective current direction. The inferred direction is sub-parallel to the palaeobathymetric contours. The 3D seismic interpretation of pockmarks presented in this paper contributes to the understanding of fluid migration and palaeocirculation patterns during the sedimentation of the terminal Chalk Group in the southern Danish North Sea.     

MIS3中期以来北黄海中部陆架古环境演化

通过对北黄海中部陆架DLC70-2孔的岩性、粒度、微体古生物以及AMS14C年代学的分析,探讨了研究区MIS3中期以来的古环境演化。研究表明,北黄海中部陆架MIS3中期以来的沉积环境演化与海平面变化存在良好的对应关系,具有明显的阶段性特征:岩芯22.89~18.50 m段(43 639~42 558 cal yr B.P.)对应MIS3中期海平面上升过程中形成的河口湾相,与上覆地层之间存在明显的沉积间断;随着海平面的逐渐上升,海水自14 602 cal yr B.P. 开始侵入研究区,形成了18.50 m以上的沉积地层,自下而上可划分为末次冰盛期以来海平面上升过程中的河口充填相(18.50~10.02 m,14 602~12 602 cal yr B.P.)-新仙女木事件中晚期海平面停滞期间的河流泛滥平原相(10.02~5.10 m,12 602~10 357 cal yr B.P.)-全新世早中期海平面上升过程中的滨海、浅海相(5.10~0 m,10 357~4 913 cal yr B.P.)。岩芯10.02~5.10 m段(12 602~10 357 cal yr B.P.)记录的源自河流泛滥平原沉积的硬质黏土层与新仙女木事件的全球效应密切相关,可作为新仙女木事件在北黄海陆架响应的一个重要证据。     

南海北部陆架西区磷灰石裂变径迹的分析

文中将磷灰石裂变径迹分析用于南海北部陆架西区地热演化研究,报道了位于北部湾盆地、莺琼盆地和珠三拗陷的３口钻井１３个样品磷灰石径迹的测定结果,并依之研究了乌１６－１－２井与莺１井的热演化史的片断,得出乌１６－１－２井区在３０Ｍａ以来地温演化是平稳的,未受过重大热事件的扰动,而莺１井区则曾经历过抬升事件的论断。对所得结论借助于径迹理论模型计算予以检验,肯定了径迹分析用于南海陆架盆地热演化研究的意义,指出在采取岩样问题上有待改进之处。     

Dynamic Features of Infra-Gravity Sea Waves on the Shelf

Doklady Earth Sciences - The dynamic features of shelf infra-gravity sea waves and their relation to the main parameters of gravity sea waves are studied using experimental data obtained from a...     

Characteristic features of salt tectonics offshore North Sinai, Egypt

Salt tectonic along offshore North Sinai was studied using seismic reflection data. The study revealed and identified various types of salt tectonics and structures in the study area. The triggering mechanism of salt tectonics was attributed to the pressure regime initiated from overloading sediments on the Messinian evaporites. The sediment load of 3,000?m exceeds the critical load (more than 1,000?m) and hence creates a pressure zone. The salt-generated structures resulted from thin-skinned extension that is driven by gravity gliding of the overloading sediments above the Messinian evaporite boundary, which acts as a detachment layer. These structures comprise normal growth faults and keystone grabens, trending roughly perpendicular to the slope of the continental margin. Salt tectonics in the study area were also triggered by the deformation of the movement of evaporite layer that causes stretching and fragmentation of the evaporite layer. Moving salt layer took place laterally and vertically, causing lateral and vertical pressures inside the Pliocene sediments. These movements of sediments led to the formation of salt rollers, salt weld, salt diapirs, rollover structures, and fault blocks. The interpretation of seismic data illustrates that the evaporite layer was switched off between the famous reflector M at its top and another reflector N at its base. M reflector is present and can be traced across the whole study area, while the N reflector pinched out in some parts of the study area.     

Geological Structure and Petroleum Potential of the Kara Sea Shelf

Doklady Earth Sciences - On the Kara Sea shelf, there are two sedimentary basins separated by the North Siberian sill. Tectonically, the southern part of the Kara Sea covers the South Kara regional...     

南极海冰和陆架冰的时空变化动态

利用美国冰中心和雪冰中心提供的海冰资料和我国南极考察现场的海冰观测资料, 对南极海冰的长期变化进行了研究.结果表明: 20世纪70年代后期是多冰期; 80年代是少冰期; 90年代南极海冰属于上升趋势, 后期偏多; 区域性变化差别大, 东南极海冰偏多, 西南极海冰即南极半岛两侧特别是威德尔海(Weddell Sea)区和别林斯高晋海(Bellingshausen Sea)的冰明显偏少.东南极和西南极海冰的变化趋势总是反相的.90年代后期普里兹湾的海冰明显偏多, 南极大陆陆架冰外缘线总体没有明显的收缩, 有崩解也有再生的自然变化现象.西南极威德尔海的龙尼冰架(Ronne Ice Shelf)和罗斯海冰架(Ross Ice Shelf)东部崩解和收缩趋势明显, 东南极的冰架也有崩解和收缩, 但没有西南极明显.陆架冰崩解向海洋输送的冰山对全球海平面升高有一定的影响.目前, 南极冰盖断裂崩解形成的冰山, 向海洋输入的水量可使全球海平面上升约14 mm.南极海冰没有随着全球气候温暖化而明显减少, 而是按照东南极和西南极反相的变化规律进行周期性的变化、调整和制约.     

First data on the Cenozoic section of the Bering Sea Chukchi Shelf

The first deep hole (Tsentral’naya-1) drilled on the Russian shelf of the Bering Sea in 2002 recovered the Cenozoic sedimentary section up to depths of 2785 m¹ This paper discusses results from the log, core, and slime study. The section is composed of Paleocene-Quaternary sediments. It comprises nine sequences (from the top downward): upper Miocene-Pliocene sandy-silty; middle-upper Miocene tuffaceous-diatomite, silty-sandy, shale-siltstone, and coquina-sandstone-siltstone; Eocene-lower Miocene coaliferous and sandstone-shale; Paleocene-lower Eocene volcano-sedimentary. These sequences are correlated with onshore stratigraphic units. The section includes three large unconformities: at the base of the Pliocene (depth of 380 m, base of the Aleksandrovka stratigraphic horizon), at the base of the middle Miocene (depth of 1390 m, base of the Avtakul Horizon), and, presumably, at the base of middle Eocene (depth of 1390 m, base of the Tanyurer Horizon). The last unconformity is accompanied by a kaolinite weathering crust. The section drilled into by Tsentral’naya-1 Hole shows common features for the Cenozoic sedimentary cover through the entire Anadyr basin, despite its significant facies variability.     

Characteristic features of the occurrence of gas-fluid emanations on the northeastern slope of Sakhalin Island, Sea of Okhotsk

This paper summarizes the results of combined studies in the areas of the occurrence of gas-fluid emanations in the water column, on the seafloor, and in the upper part of the sedimentary section on the northeastern slope of Sakhalin Island (Sea of Okhotsk). The phenomena typical of methane seeps were characterized in detail: the presence of acoustic anomalies, high concentrations of methane in the water and sediments, and the specific features of the sedimentary section (the textural and structural features, the character of the mineral inclusions and gas hydrates, and the chemical composition). The component composition of the gases (including the accompanying gas hydrates), which is almost free of heavy hydrocarbon homologues of methane; the light carbon isotopic compositions of the methane and carbonate concretions; and the low temperatures of the near-bottom water and sediments suggest that the occurrence of numerous methane emanations is related to gas generation in the upper part of the sedimentary sequence. No evidence was found for the existence of a deep center of gas formation within the seafloor area considered. Typical submarine mud volcanic edifices were also not found.     

Glacial landforms on German Bank, Scotian Shelf: evidence for Late Wisconsinan ice-sheet dynamics and implications for the formation of De Geer moraines

The extent and behaviour of the southeast margin of the Laurentide Ice Sheet in Atlantic Canada is of significance in the study of Late Wisconsinan ice sheet-ocean interactions. Multibeam sonar imagery of subglacial, ice-marginal and glaciomarine landforms on German Bank, Scotian Shelf, provides evidence of the pattern of glacial-dynamic events in the eastern Gulf of Maine. Northwest-southeast trending drumlins and megaflutes dominate northern German Bank. On southern German Bank, megaflutes of thin glacial deposits create a distinct northwest-southeast grain. Lobate regional moraines (>10km long) are concave to the northwest, up-ice direction and strike southwest-northeast, normal to the direction of ice flow. Ubiquitous, overlying De Geer moraines (<10 km long) also strike southwest-northeast. The mapped pattern of moraines implies that, shortly after the last maximum glaciation, the tidewater ice sheet began to retreat north from German Bank, forming De Geer moraines at the grounding line with at least one glacial re-advance during the general retreat. The results indicate that the Laurentide Ice Sheet extended onto the continental shelf.     

The Fault System Controlling Methane Seeps on the Shelf of the Laptev Sea

Doklady Earth Sciences - The paper presents data obtained during the 69th and 72nd expeditions of the research vessel Akademik Mstislav Keldysh (2017, 2018). A mechanism of methane discharge that...     

Offshore Aggregates Resources on the Northern Continental Shelf of the East China Sea

A large‐scale survey for offshore aggregates is carried out on the northern shelf of the East China Sea. Results show that most of them are directly exposed in the Yangtze Shoal and the linear sand ridges system at water depths 25–55 m and 60–120 m, respectively. The components of these deposits belong to fine aggregates in terms of the fineness modulus. The potential resources are as high as 147.8 × 10¹² kg for the Yangtze Shoal yet only 36.68 × 10¹² kg for the sand ridges area, respectively. A preliminary feasibility analysis suggests that the Yangtze Shoal is suitable for dredging under the present conditions of technology and economy.     

Activity and Formation of Sand Waves on Northern South China Sea Shelf

Sand waves on the northern South China Sea shelf had been considered as stable relict bed form. For the industry use of sea bed between stations LF13-2 and LF13-1, a new round of explorations were conducted. The newly obtained data show that both spacings and amplitudes of sand waves are all systematically changing with water depth. Repeated observations since 2003 to 2004 showed that the sea bed is currently active. Due to strong erosion of surface sediment since Dongsha (东沙) uplifting, there are almost no...     

南海北部陆架南北卫浅滩的成因及油气地质意义

世界范围内的陆架调查已经清楚,陆架浅滩是普遍发育于陆架区的一种海底地貌类型。在中国陆架上发育多个知名浅滩,这些浅滩和现今动力条件处于动态平衡状态,为现今潮流沉积体系。然而,南海北部陆架的南北卫浅滩在地貌上被称为陆架浅滩,但其成因却和其他陆架浅滩有着根本不同。根据地震剖面解释结果,本文指出,南海北部珠江口东南陆架上发育的南卫滩、北卫滩和惠州滩都属于构造地形,其下部各对应一个底辟构造。这3个底辟构造并不是孤立的,而是在深部属于同一个较大的背冲构造。这个背冲构造位于南北卫滩的下方,其上几个突出的底辟,则和本文讨论的南卫滩、北卫滩和惠州滩相对应。南卫滩、北卫滩和惠州滩在成因上具有统一的深部背景,从而在平面上构成一个统一的底辟系统,本文称为南北卫滩底辟系统。该底辟系统以北卫滩为中心,包括南卫滩、惠州滩和陆丰滩,形成一个大致呈圆形,直径约50km的区域。在构造上,该底辟系统位于珠一坳陷和东沙隆起之间。南北卫滩底辟系统的发育起因于东沙隆起后在南海东北部形成的挤压应力环境。底辟系统的发育活化了惠陆-东沙含油气系统的输导层,并重新调整了油气运移的势差和势梯度,在环绕南北卫滩底辟系统一定距离的圆周上形成一个有利于油气聚集的环带。已知的油气田基本分布于这个环带上。下一步的油气勘探方向应该考虑围绕这个环带重点展开。同时,应该考虑在南北卫滩底辟系统的中心带内开展气藏的勘探工作。     

南海北部陆架海底沙波基本特征及属性

南海北部陆架海底沙波是否为残留沙波长期存在争议。为配合陆丰油田的开发,在LF13-2和LF13-1站位之间进行了详细的地形、地貌和海底底流测量。观测数据显示,本研究区发育两组海底沙波。两组沙波的分布和当今的海底地形密切相关,沙波的波宽、波高,沙脊的长度及延伸的方向也都和现今的水深密切相关。此外,沙波区的底质、沉积物颜色等也随现今水深的变化而变化。跨年度的测量结果显示,从2003年夏季到2005年冬季,海底沙波发生了明显的变化,除有明显的沙波迁移,并有新的沙波生成外,沙波区的水深也整体变深,研究区东南端平均加深了0.29m。由于东沙海底高原的存在,东沙区底流有了复杂的变化。实际的观测结果显示,在9MKII站位,向南的退潮流明显大于向北的涨潮流,但在AEM-HR站位,WNW向的涨潮流则稍稍大于ESE向的退潮流。9MKII站位测得的最大底流速为48cm/s,有22%的底流速大于20cm/s,这是启动海底沉积物并能形成海底沙波的最小底流速。本文指出,东沙隆起后,由于强烈的底流侵蚀,在东沙区的中陆架和外陆架区几乎没有现代沉积。构成海底沙波的沉积物主要来自海底地层的剥蚀。测深结果显示的海底加深可能和海底剥蚀有关。很明显,海底沙波和现今的海底底流体系有很好的吻合关系,从而是在现今底流体系条件下形成的,而非晚更新世末次冰期的残留沙波。     

Composition and Flux of Holocene Sediments on the Eastern Laptev Sea Shelf, Arctic Siberia

A 467-cm-long core from the inner shelf of the eastern Laptev Sea provides a depositional history since 9400 cal yr. B.P. The history involves temporal changes in the fluvial runoff as well as postglacial sea-level rise and southward retreat of the coastline. Although the core contains marine fossils back to 8900 cal yr B.P., abundant plant debris in a sandy facies low in the core shows that a river influenced the study site until 8100 cal yr B.P. As sea level rose and the distance to the coast increased, this riverine influence diminished gradually and the sediment type changed, by 7400 cal yr B.P., from sandy silt to clayey silt. Although total sediment input decreased in a step-like fashion from 7600 to 4000 cal yr B.P., this interval had the highest average sedimentation rates and the greatest fluxes in most sedimentary components. While this maximum probably resulted from middle Holocene climate warming, the low input of sand to the site after 7400 cal yr B.P. probably resulted from further southward retreat of the coastline and river mouth. Since about 4000 cal yr B.P., total sediment flux has remained rather constant in this part of the Laptev Sea shelf due to a gradual stabilization of the depositional regime after completion of the Holocene sea-level rise.     

Structure of the North Kara Shelf from results of seismostratigraphic analysis

The sedimentary cover section of the North Kara Shelf had been subdivided based on extensive seismic data, and seismic correlation was carried out. The predominant role of Upper Riphean-Middle Paleozoic rocks has been corroborated. A series of relatively deepwater basins filled with primarily terrigenous fly-schoid rocks up to 7–9 km in thickness existed in the Late Riphean-Vendian at the place of the shelf. In the Cambrian, isolated basins merged into a wide and shallow-water basin as a result of the Baikalian reactivation in southeast Severnaya Zemlya and probably in Taimyr. After the pre-Ordovician hiatus, a vast sedimentation basin with a regressive section was formed on the shelf from Ordovician to Late Devonian. Shallow-water marine and near-shore carbonate and carbonate-terrigenous sequences accumulated in this basin and gave way to continental and less frequent near-shore, marine, variegated, and red beds in the Devonian. The thickness of the Ordovician-Devonian sequence reaches 6 km. Since the Mid-Carboniferous, block emergence and deep erosion of Ordovician-Devonian complexes have occurred in the north Kara shelf as a result of Hercynian events in northern Taimyr, Severnaya Zemlya, and in the southern Kara Sea. No Permian-Triassic rifts existed on the North Kara Shelf. At that time, the shelf was an area of erosion. The thickness of the Middle Carboniferous-Cretaceous sequence was insignificant and gradually increased toward Barents Sea troughs. The newly formed Svyataya Anna and Voronin troughs arose due to opening of the Eurasia Basin of the Arctic Ocean. The terrane concept has been subjected to criticism. The available data show that a large epi-Grenvillian continental block existed, and the North Kara region was part of it. Collision of the northern continent with the Paleosiberian Platform in the Late Paleozoic resulted in the formation of the Hercynian fold arc to the south of the North Kara Shelf, and an inverted orogenic arch arose at the place of shelf basin. The individual geological features that distinguish the North Kara Shelf from the Barents Sea troughs and the South Kara Syneclise are emphasized. The ancient pre-Riphean basement, a system of Late Riphean-Vendian relatively deepwater troughs and basins, Hercynian tectonic inversion, deep erosion of the most uplifted part of the arch, and significant block motions are the distinguishing features of the North Kara Shelf.     

我国东海陆架区新生代地层岩石生热率研究

岩石生热率是描述地球内热的一个重要的热物理参数.通过测定岩石样品的密度、放射性元素U、Th、K的含量可以定量计算地壳岩石的生热率.根据东海陆架多口钻井新生代地层样品、东海陆架表层样品和冲绳海槽柱状样品的密度、放射性元素U、Th、K含量对岩石生热率进行了计算.发现东海陆架地区地层岩石的生热率介于0.4～1.7μW/m3之间,落于正常沉积岩生热率范围,比火成岩的生热率要高.同时,岩性对生热率起明显的控制作用,岩性不同,生热率不同.其中,泥岩的生热率最高,而粉沙岩、砂岩的生热率次之.东海区新生代地层的生热率由新到老生热率呈下降的趋势,但,其中玉泉组、龙井组和花港组地层生热率几乎一致.这和该地层的波速特征非常吻合.关系式lnA=1.04-0.2915vp能够较好地描述东海陆架区新生代地层波速和生热率之间的关系.在已知地层层速度的情况下,可以由该式求取地层的生热率.