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The sediment temperature distribution at mud volcanoes provides insights into their activity and into the occurrence of gas hydrates. If ambient pressure and temperature conditions are close to the limits of the gas hydrate stability field, the sediment temperature distribution not only limits the occurrence of gas hydrates, but is itself influenced by heat production and consumption related to the formation and dissociation of gas hydrates. Located in the Sorokin Trough in the northern Black Sea, the Dvurechenskii mud volcano (DMV) was in the focus of detailed investigations during the M72/2 and M73/3a cruises of the German R/V Meteor and the ROV Quest 4000 m in February and March 2007. A large number of in-situ sediment temperature measurements were conducted from the ROV and with a sensor-equipped gravity corer. Gas hydrates were sampled in pressurized cores using a dynamic autoclave piston corer (DAPC). The thermal structure of the DMV suggests a regime of fluid flow at rates decreasing from the summit towards the edges of the mud volcano, accompanied by intermittent mud expulsion at the summit. Modeled gas hydrate dissociation temperatures reveal that the gas hydrates at the DMV are very close to the stability limits. Changes in heat flow due to variable seepage rates probably do not result in changes in sediment temperature but are compensated by gas hydrate dissociation and formation.  相似文献   

3.
High-resolution multichannel seismic data enables the discovery of a previous, undocumented submarine canyon(Huaguang Canyon) in the Qiongdongnan Basin, northwest South China Sea. The Huaguang Canyon with a NW orientation is 140 km in length, and 2.5 km to 5 km in width in its upper reach and 4.6 km to 9.5 km in width in its lower reach. The head of the Huaguang Canyon is close to the Xisha carbonate platform and its tail is adjacent to the central canyon. This buried submarine canyon is formed by gravity flows from the Xisha carbonate platform when the sea level dropped in the early stage of the late Miocene(~10.5 Ma). The internal architecture of the Huaguang Canyon is mainly characterized by high amplitude reflections, indicating that this ancient submarine canyon was filled with coarse-grained sediments. The sediment was principally scourced from the Xisha carbonate platform. In contrast to other buried large-scale submarine canyons(central canyon and Zhongjian Canyon) in the Qiongdongnan Basin, the Huaguang Canyon displays later formation time, smaller width and length, and single sediment supply. The coarse-grained deposits within Huaguang Canyon provide a good environment for reserving oil and gas, and the muddy fillings in Huaguang Canyon have been identified as regional caps. Therefore, Huaguang Canyon is potential area for future hydrocarbon exploration in the northwest South China Sea. Our results may contribute to a better understanding of the evolution of submarine canyons formed in carbonate environment.  相似文献   

4.
High-resolution multichannel seismic data enables the discovery of a previous, undocumented submarine canyon(Huaguang Canyon) in the Qiongdongnan Basin, northwestern South China Sea. The Huaguang Canyon with a NW orientation is 140 km in length, and 2.5 km to 5 km in width in its upper reach and 4.6 km to 9.5 km in width in its lower reach. The head of the Huaguang Canyon is close to the Xisha carbonate platform and its tail is adjacent to the Central Canyon. This buried submarine canyon is formed by gravity flows from the Xisha carbonate platform when the sea level dropped in the early stage of the late Miocene(around 10.5 Ma). The internal architecture of the Huaguang Canyon is mainly characterized by high amplitude reflections, indicating that this ancient submarine canyon was filled with coarse-grained sediments. The sediment was principally scourced from the Xisha carbonate platform. In contrast to other buried large-scale submarine canyons(Central Canyon and Zhongjian Canyon) in the Qiongdongnan Basin, the Huaguang Canyon displays later formation time,smaller width and length, and single sediment supply. The coarse-grained deposits within the Huaguang Canyon provide a good environment for reserving oil and gas, and the muddy fillings in the Huaguang Canyon have been identified as regional caps. Therefore, the Huaguang Canyon is a potential area for future hydrocarbon exploration in the northwestern South China Sea. The result of this paper may contribute to a better understanding of the evolution of submarine canyons formed in carbonate environment.  相似文献   

5.
Nisyros island is a volcano at the eastern edge of the Aegean volcanic arc within the Hellenic arc and trench system along the convergence zone of the Eurasian and African plates. Several fault zones have been mapped and analyzed on the island with fault displacements reaching 100?C150 m as deduced from the morphology and the offset of the stratigraphic formations of the volcano. Seismic activity during 1995?C1998 affected the island with damage along the western edge of the Mandraki town, related to the Mandraki fault. The geological, tectonic and morphological data on land show that the Mandraki fault throw is 80?C100 m and its length about 2 km. Its continuation northwards under the sea was studied within a systematic survey of the broader area of the Kos-Nisyros-Tilos islands; and the bathymetric and lithoseismic data showed the existence of some active tectonic structures. In the area of the Yali-Nisyros Channel the prolongation of the Mandraki fault has a 100 m high submarine scarp between the two sides of the fault. Morphological slopes along the fault are high between 20 and 50% in contrast to slopes of 1?C5% observed on top of the two adjacent tectonic blocks. The general structure both on land and offshore shows a westward tilt contemporaneous to the extension in the E-W direction observed in this area. Observations of the submarine fault during a dive with submersible Thetis showed spectacular landslides and loose rocks along the fault scarp and very abrupt linear topographic change along the strike of the fault. The synthesis of the onshore and offshore data on a digital topographic map shows that the Mandraki fault is a secondary structure of the major F3 fault zone of Nisyros which separates the neotectonic block/horst of Prophitis Ilias in the west from the Emborio/Nikia block in the east. The GPS data from the period 1997?C2001 show excellent agreement with the neotectonic block structure of Nisyros. The seismic hazard of the F3/Mandraki fault zone is discussed together with the volcanic hazard of Yali-Nisyros area with the general conclusion that the expected seismic magnitude of 6.1?C6.3 is significantly higher than that observed in 1995?C1998. The ascent of magma from a chamber 7.5?C8.5 km deep between the Yali and Nisyros islands may trigger tectonovolcanic activity similar to that observed at the end of the 19th century.  相似文献   

6.
围绕中国大洋矿产资源开发的发展计划,概括介绍了大洋海底矿产资源研究的动态、重大成果和发展趋势,希望在我国的大洋工作当中加强系统论指导下的海底成矿系统研究,重视深海探测技术的发展,争取今后在多种资源矿区申请工作中有的放矢、把握主动。  相似文献   

7.
Submarine channels are major morphological features of the sea floor and are important in the transport of sediment to the deep ocean. Although much is known concerning the large-scale distribution of sediment within and surrounding submarine channels, there is little understanding of the fluid dynamic processes that control this sedimentation. Direct measurement of flow velocities and concentrations has proved to be extremely difficult within submarine channels, with the resultant paucity of direct observations making physical laboratory modelling a critical technique for examining the processes that operate in, and control, submarine channel development.Recent experimental and numerical studies have proposed a new model of secondary circulation within submarine channel bends, characterised by a reversal in the orientation of the secondary circulation cell relative to that found in meandering rivers. This new paradigm for submarine channels thus predicts basal flow from the inside to the outside of the bend at a bend apex, with an upper return flow directed towards the inner bend. The reversal in orientation of the secondary flow cell has been linked to the vertical distribution of downstream velocity and associated changes in centrifugal and pressure gradient forces. However, previous work has additionally proposed that shearing of the within-channel flow by overbank flow may also generate secondary flow reversal.This study assesses the applicability of the proposed submarine bend flow model against a range of key channel parameters. We demonstrate that the sense of secondary circulation is the same for all experimental conditions, strongly supporting the new model of secondary flow in submarine channels. Furthermore, investigation of overbank shear induced secondary circulation confirms for the first time that this mechanism can occur, and identifies the channel styles most likely to exhibit this effect. Such shear-induced circulation is, however, shown to be a secondary mechanism, with the vertical distribution of downstream velocity the principal mechanism. In certain channel configurations, the two mechanisms may act to augment one another.  相似文献   

8.
The nature of the sharkbite phenomenon is presented. The physical nature of the faults and their location along the OPTICAN-1 route are described. The morphology of the shark teeth recovered, and the identification and nature of the sharks believed responsible are discussed. A hypothesis as to the cause of the attacks, based on the findings of previous shark-sensory research, is detailed. The methods and results of an experimental program aimed at verifying this hypothesis are summarized. The results of development programs aimed at resolving this problem are presented. Two avenues were pursued: the first was the development of a mechanically protected SL deep-water, repeated lightwave trunk cable for use in areas of high sharkbite risk; the second was the development of a methodology to assess the sharkbite risk in different areas of the world's oceans. The resultant algorithm, for use in specifying the amount of protected cable to be deployed in an SL system is detailed  相似文献   

9.
《Marine Geology》2005,219(1):1-17
The El Arraiche field is a new mud volcano field discovered near the Moroccan shelf edge in the Gulf of Cadiz that consists of 8 mud volcanoes in water depths from 200 to 700 m. The largest mud volcano in the field (Al Idrissi mud volcano) is 255 m high and 5.4 km wide. The cluster was discovered during a survey with the RV Belgica and studied further during Leg 2 of the TTR 12 survey onboard the R/V Prof Logachev. The 2002 surveys yielded detailed multibeam bathymetry over a 700 km2 study area, dense grids of high-resolution seismic data, deep-tow sub bottom profiles, sidescan sonar mosaics over the major structures. Selected video imagery lines, video guided grab samples, dredge samples, gravity cores, and box cores were collected for groundtruthing purposes. Eight mud volcanoes in water depths from 200 to 700 m cluster around two, sub-parallel anticlines and associated active extensional faults. Rock clasts and regional seismic data locate the El Arraiche field over a Late Miocene–Pliocene extensional basin. The onset of mud volcanic activity is estimated at about 2.4 Ma and probably roots in the Cretaceous–Miocene accretionary wedge. Stacked outflows are visible up to a depth of about 500 m below the sea floor. The occurrence of long-lived mud volcanoes bear witness to continued overpressure generation at depth, either by in situ oil and gas generation or by focussed flow and accumulation in the area. Geochemical analyses of pore water from cores demonstrate the presence of thermogenic hydrocarbon processes. The activity of the mud volcanoes is indicated by the thickness of hemi-pelagic sediments covering extruded mud breccia, the occurrence of seep-typical fauna, the degree of mixing between thermogenic and biogenic hydrocarbon processes, or the depth to the base of the sulphate reduction zone. Given its structural setting and the evidence of thermogenic and biogenic hydrocarbons, the area has promising hydrocarbon potential but remains untested.  相似文献   

10.
Several laterally offset and aggradational sinuous submarine channels are contained within a 54 km long segment of the Benin-major Canyon. Axial channel deposits produce high amplitude reflections on three-dimensional (3-D) seismic profiles. Some seismic reflections have U- or V-shaped cross-sectional motifs that were correlated with confidence along linear to meandering paths for distances up to 70 km. They are referred to here as channel-forms (CFs), and are believed to be the axial parts of submarine channels preserved during overall channel floor aggradation. A total of 15 separate CFs were mapped allowing thalweg-gradients, dimensions, and morphology to be studied spatially and through time, providing insight into how submarine canyons fill. Their planform geometry evolved predominantly in a stepwise fashion through alternating periods of cut-and-fill, but more gradual channel migrations are also observed. The largest offsets in successive channel floor position occur after periods of significant vertical CF fill (‘thalweg plugging’—with deposits commonly consisting of lower amplitude, transparent to chaotic seismic reflections). The passage of erosive flows after such periods of fill caused abrupt shifts in channel position, particularly at meander bends, with increased potential for the formation of pseudo meander loop cut-offs. Significant spatial differences in the stacking architecture of CFs are attributed to local slope deformation and perhaps also to a recent channel avulsion just west of the study area. Abrupt channel straightening in the western study area coincides with a period of increased valley-gradient associated with amplification of an underlying anticlinal fold. The youngest CFs in this area show limited aggradation and are characterized by repeated episodes of headward erosion causing knickpoint migration as the recent channel floor tried, unsuccessfully, to establish a smooth graded depth profile. This is in stark contrast to the time-equivalent predominantly aggradational CFs in the eastern study area that show a progressive increase in sinuosity through time.  相似文献   

11.
Sediments of the continental slope are commonly bioturbated by endo- and epibenthic organisms, particularly in and around submarine canyons and channels. This study reviews the architecture and depositional environments associated with canyons and channels on the continental slope, and assesses the key physical and chemical conditions encountered in and around these conduits. Hydrodynamic energy, concentration and quality of organic carbon, dissolved oxygen concentration and sedimentation rate are identified as key controls on the composition of benthic ecosystems in slope environments. Submarine canyons and channels focus a variety of turbid and clear-water currents, all of which serve to increase the concentration of oxygen, labile organic carbon and other nutrients, which tend to elevate the abundance and biodiversity in the seafloor sediments, compared with those of the surrounding slope. Ancient slope channel and canyon systems reflect some of the variation in ichnological assemblages that is seen in modern analogues, although processes of erosion and trace fossil preservation mean that the benthic environment is often incompletely preserved in the ancient record. By integrating current understanding of sedimentology, oceanography, biology and ichnology of slope environments it is possible to provide a first order summary of the inter-relationships between ichnology and depositional environments on the continental slope. The combination of these data has the potential to improve our understanding of changes in deep marine benthic ecosystems through geological time, and to further the use of ichnology in assessing hydrocarbon reservoir presence, quality and performance from bioturbated slope, canyon and channel-levee hydrocarbon reservoirs.  相似文献   

12.
The Yithi submarine canyons,composed of four canyons less than 60 km in length,are located on the narrowest part of the East China Sea(ECS) slope.They extend from the shelf break at 160 m down to water depth of 1 500 m with an average gradient(along the canyon axis) of 3°(<1 000 m) and 0.7°(>1000 m).The sinuosity of the canyons ranges form 1.02 to 1.14 and their pathways extend radially from the shelf break to the axis of the Okinawa Trough.Structural and evolution pattern of the Yithi canyons are mainly controlled by sediment mass-movements and turbidity current and similar with that of the canyons in Ebro continental slope.The whole canyon system consists of three parts:the canyon,the channel and the fan.Slumps and slides often develop in the upper part of canyon where the water depth is less than 1000 m,and the turbidities usually developed on the fan.The scale of turbidites becomes smaller and their inner structures become more regular towards the ends of the canyons.Canyon-fans are often associated with small angle progradational reflection.Most canyon-fans and levees were transversely cut by active normal faults with NEE-SWW trending that are coupled to the modern extension of the Okinawa Trough.According to the age of formation of canyon-fans and sediments incised by canyons,we can infer that the Yithi canyons were formed since the middle the Medio-Pleistocene.  相似文献   

13.
梅山组海底扇作为中央峡谷水道之外最引人注目的大型储集体,是琼东南盆地尤其是深水区常规碎屑岩领域下一步最为重要的勘探对象。总结了琼东南盆地各凹陷钻井资料所揭示的梅山组海底扇差异分布现象,通过研究区大陆架发育特征、陆架坡折带发育特征,结合物源供给与优势海流方向,首次从宏观格局解释了琼东南盆地中央坳陷带不同凹陷海底扇发育地质背景的差异及成因,提出乐东凹陷梅山组大型海底扇主物源来自东北方向海南隆起。通过细化中中新世大海退内部次级海平面旋回特征,首次建立了本区梅山组层序充填与海平面旋回的精确对应关系,从层序成因角度厘清了梅山组各期次海底扇发育演化特征与凹陷级别的有利储层展布特征,并据此提出相应的勘探建议,指出乐东凹陷梅山组中—晚期海底扇储层风险低,是梅山组海底扇领域突破的首选区带;陵水凹陷早期海底扇圈闭有效性较好,是梅山组海底扇大规模成藏的有利勘探方向。该研究为梅山组海底扇领域的勘探部署提供了新思路。  相似文献   

14.
Submarine caves at the Cape of Otranto (SE, Italy) host pseudostalactites. Only recently have they been recognised as originating mainly from the marine tube worm Protula tubularia (Serpulidae, Polychaeta). Their formation depends on the adaptability, life history and behaviour of that species in the cave habitat. The dating of calcareous tubes in the pseudostalactite core represents the first attempt to describe the formation of such bio-construction, and the gregarious behaviour of the species. Calcareous tubes along the core axis of three pseudostalactites removed from the cave lu Lampiùne (Otranto, South East Italy) have been dated using the 14C method. Measures established ages from 2600 to 5000 years for the three structures. This extremely long period (when compared with the life span of each worm) suggests that each tube aggregation is the result of punctuated growth periods alternated with long standstill phases. At the end of a growth period, each tube aggregation was covered with a brownish concretion, completing the pseudostalactite.  相似文献   

15.
Argnani  A.  Tinti  S.  Zaniboni  F.  Pagnoni  G.  Armigliato  A.  Panetta  D.  Tonini  R. 《Marine Geophysical Researches》2011,32(1-2):299-311
Marine Geophysical Research - The southern Adriatic basin is the current foredeep of the Albanide fold-and-thrust belt that runs along the eastern boundary of the Adriatic basin and partly owes its...  相似文献   

16.
Active mud volcanism is a global phenomenon that represents a natural hazard by self-igniting eruptions and the continuous emission of methane gas in both marine and continental settings. Mud domes are often found in compressional tectonic settings such as the Caucasus orogenic wedge. Dashgil mud volcano, the most prominent of >200 features in Azerbaijan, has erupted vigorously in historic times. For several years, we have observed variations in the activity of Dashgil dome, including transients in methane flux, build-up of extrusive mud cones on the main feature, and flexural polygonal cracks adjacent to the main crater lake and new mud cones. In spring 2007, we carried out in situ CPTU (Cone Penetration Testing with Pore Pressure measurement) experiments in the crestal area of Dashgil. Our data suggest that the central portion of the crater lake, which hosts the conduit for gas (and possible mud) ascent, shows both low sediment shear strength (<5–20 kPa) and excess pore fluid pressures between 15 and 30 kPa supra-hydrostatic at 1 m sub-bottom depth. In situ cone resistance as a measure for undrained shear strength is as low as 150 kPa in the conduit, whereas the mud is found rather stiff in all other testing locations (300–700 kPa, probably a result of deeply buried shales of the Maikop formation parts of which now liquefy and ascend). Pore pressure is low in the centre of the conduit, probably because of rapidly migrating gas. It increases to 30 kPa at the lake bottom and deep flank, then decreases upslope on the lake flank, and reaches hydrostatic values at the crater rim. From the overpressured region beneath the fluid-filled crest of Dashgil dome, combined with the other observations, we suspect to currently witness an ongoing period of updoming. The presence of sintered mudstones from explosive eruptions in 1908 and 1928 (and most likely before) suggests that a similar violent activity may occur in the near future.  相似文献   

17.
This study documents the fractal characteristics of submarine mass movement statistics and morphology within the Storegga Slide. Geomorphometric mapping is used to identify one hundred and fifteen mass movements from within the Storegga Slide scar and to extract morphological information about their headwalls. Analyses of this morphological information reveal the occurrence of spatial scale invariance within the Storegga Slide. Non-cumulative frequency-area distribution of mass movements within the Storegga Slide satisfies an inverse power law with an exponent of 1.52. The headwalls exhibit geometric similarity at a wide range of scales and the lengths of headwalls scale with mass movement areas. Composite headwalls are self-similar.One of the explanations of the observed spatial scale invariance is that the Storegga Slide is a geomorphological system that may exhibit self-organized criticality. In such a system, the input of sediment is in the form of hemipelagic sedimentation and glacial sediment deposition, and the output is represented by mass movements that are spatially scale invariant. In comparison to subaerial mass movements, the aggregate behavior of the Storegga Slide mass movements is more comparable to that of the theoretical ‘sandpile’ model. The origin of spatial scale invariance may also be linked to the retrogressive nature of the Storegga Slide. The geometric similarity in headwall morphology implies that the slope failure processes are active on a range of scales, and that modeling of slope failures and geohazard assessment can extrapolate the properties of small landslides to those of larger landslides, within the limits of power law behavior. The results also have implications for the morphological classification of submarine mass movements, because headwall shape can be used as a proxy for the type of mass movement, which can otherwise only be detected with very high resolution acoustic data that are not commonly available.  相似文献   

18.
High-resolution and high-density 2-D multichannel seismic data, combined with high-precision multibeam bathymetric map, are utilized to investigate the characteristics and distribution of submarine landslides in the middle of the northern continental slope, South China Sea. In the region, a series of 19 downslope-extending submarine canyons are developed. The canyons are kilometers apart, and separated by inter-canyon sedimentary ridges. Numerous submarine landslides, bounded by headscarps and basal glide surfaces, are identified on the seismic profiles by their distorted to chaotic reflections. Listric faults and rotational blocks in head areas and compressional folds and inverse faults at the toes of the landslides are possibly developed. Three types of submarine landslides, i.e., creeps, slumps, and landslide complexes, are recognized. These landslides are mostly distributed in the head areas and on the flanks of the canyons. As the most widespread landslides in the region, creeps are usually composed of multiple laterally-coalesced creep bodies, in which the boundaries of singular component creep bodies are difficult to delineate. In addition, a total of 77 landslides are defined, including 61 singular slumps and 16 landslide complexes that consist of two or more component landslides. Statistics show that most landslides are of a small dimension (0.53–18.09 km² in area) and a short runout distance (less than 3.5 km). Regional and local slope gradients and rheological behavior of the displaced materials might play important roles in the generation and distribution of the submarine landslides. A conceptual model for the co-evolution of the canyons and the associated landslides in the study area is presented. In the model it is assumed that the canyons are initiated from gullies created by landslides on steeper sites of the continental slope. The nascent canyons would then experience successive retrogressive landsliding events to extend upslope; at the same time canyon downcutting or incision would steepen the canyon walls to induce more landslides.  相似文献   

19.
The Trans Indus-Salt Range, located in northern Pakistan, is one of the most tectonically active fold-and-thrust belts and comprises three main regions: the Potwar-Salt Range, the Kohat-Surghar Range and the Bannu Basin-Khisor Range. Of these, the Bannu Basin is the least studied and only a handful of publically accessible datasets and publications are available. Recently made public 2D seismic profiles and well data from the Bannu Basin indicate the presence of salt as well as evidence for a main detachment surface which is Neoproterozoic in age. Our findings suggest that the Salt Range Formation could be the main detachment for the entire basin.Interpretation also shows a Miocene-Eocene basin-wide unconformity that marks the Himalayan orogenic event which separates the pre-Himalayan from the syn-Himalayan sedimentary units. On the basis of seismic reflection data, we conclude that the basin experienced three main tectonic settings. An early stage of pre-Himalayan passive tectonic environment is followed by the compressional Himalayan tectonics which resulted in uplifted areas sourcing the fluviatile fill of the subsided basin. During this time, sedimentation from the northern margin of the basin may have influenced the southward flow of salt. This is followed by a more recent stage of thrusting that produced folds and thrusts deforming all of the sedimentary units.Structural geometries suggest that prospective traps are developed mainly in the anticlines outlining the eastern and western boundaries of the Bannu Basin, as well as the southern zone of the basin. Furthermore, the presence of salt diapirism and transpression zones together with numerous oil seeps in and around the basin increase the probability of hydrocarbon accumulation and indicate great potential for future exploration.  相似文献   

20.
南海北部陆坡发育众多海底峡谷,其形成、发育、演化过程都存在较大差异。本文选取南海北部陆坡典型的珠江口外海底峡谷群、东沙海底峡谷、台湾浅滩南海底峡谷和澎湖海底峡谷进行研究,通过高分辨率多道地震数据和多波束测深数据,结合前人研究成果,对4条典型海底峡谷的形态特征、沉积充填特征及结构、形成发育过程及控制因素进行研究。结果表明,南海北部陆缘各个海底峡谷的形成受多个控制因素的影响,其影响程度及方式都有差别。构造活动、海平面变化及沉积物重力流与海底峡谷的演化密切相关,而陆地河流和局部构造因素也以不同方式影响着海底峡谷的发育。对于发育在主动大陆边缘的台湾岛东南侧的澎湖海底峡谷,其板块运动和岩浆活动活跃,其上发育的海底峡谷的控制因素以内营力地质作用为主。而具有被动大陆边缘属性的其他3条峡谷,由于构造运动较少或停止,其上发育的海底峡谷的控制因素以外营力地质作用为主。  相似文献   

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