首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 218 毫秒
1.
In the Great South Basin, within the Eocene section, at time-depths around 700–900 ms two way time below the seafloor, unusual features are observed on 3D seismic data closely associated with polygonal faults. The features, referred to as honeycomb structures (HS), cover an area of ∼600 km2, are packed circular, oval, to polygonal depressions 150–400 m across in plan view and several to 10 + m in amplitude. Polygonal faults rapidly die out at the Marshall Paraconformity, which is overlain by the Oligocene Penrod Formation. Hence the polygonal faults are inferred to have formed prior to the Marshall Paraconformity, and they cross-cut HS features. Consequently the top of the HS probably formed at burial depths of around 375–500 m, which is their decompacted depth below the paraconformity. The interval containing HS is about 125 m vertical thick. There are several possible origins for the HS. The most probable is related to bulk contraction of the sediment volume accompanied by fluid expulsion, which suggests a diagenetic origin, in particular the opal-A/CT transition. There are actually two polygonal fault systems (PFS) present in the area. The Southern Tier 1 PFS lies laterally to the HS and overlaps with it. The Northern PFS (Tier 2) lies above the HS, appears to be independent of the HS, and formed in the upper 200–300 m of the sediment column. The Tier 1 PFS probably formed by shear failure related to the same diagenetic effects that caused the HS.  相似文献   

2.
《Marine and Petroleum Geology》2012,29(10):1932-1942
A dense seismic reflection survey with up to 250-m line-spacing has been conducted in a 15 × 15 km wide area offshore southwestern Taiwan where Bottom Simulating Reflector is highly concentrated and geochemical signals for the presence of gas hydrate are strong. A complex interplay between north–south trending thrust faults and northwest–southeast oblique ramps exists in this region, leading to the formation of 3 plunging anticlines arranged in a relay pattern. Landward in the slope basin, a north–south trending diapiric fold, accompanied by bright reflections and numerous diffractions on the seismic profiles, extends across the entire survey area. This fold is bounded to the west by a minor east-verging back-thrust and assumes a symmetric shape, except at the northern and southern edges of this area, where it actively overrides the anticlines along a west-verging thrust, forming a duplex structure. A clear BSR is observed along 67% of the acquired profiles. The BSR is almost continuous in the slope basin but poorly imaged near the crest of the anticlines. Local geothermal gradient values estimated from BSR sub-bottom depths are low along the western limb and crest of the anticlines ranging from 40 to 50 °C/km, increase toward 50–60 °C/km in the slope basin and 55–65 °C/km along the diapiric fold, and reach maximum values of 70 °C/km at the southern tip of the Good Weather Ridge. Furthermore, the local dips of BSR and sedimentary strata that crosscut the BSR at intersections of any 2 seismic profiles have been computed. The stratigraphic dips indicated a dominant east–west shortening in the study area, but strata near the crest of the plunging anticlines generally strike to southwest almost perpendicular to the direction of plate convergence. The intensity of the estimated bedding-guided fluid and gas flux into the hydrate stability zone is weaker than 2 in the slope basin and the south-central half of the diapiric fold, increases to 7 in the northern half of the diapiric fold and plunging anticlines, and reaches a maximum of 16 at the western frontal thrust system. Rapid sedimentation, active tectonics and fluid migration paths with significant dissolved gas content impact on the mechanism for BSR formation and gas hydrate accumulation. As we begin to integrate the results from these studies, we are able to outline the regional variations, and discuss the importance of structural controls in the mechanisms leading to the gas hydrate emplacements.  相似文献   

3.
Fractures not only control the distribution of oil and gas reservoirs, but also are key points in the research of oil and gas reservoir development programmes. The tectonic fractures in the Lower Cambrian shale reservoirs in the Feng'gang No. 3 block are effective reservoir spaces for hydrocarbon accumulation, and these fractures are controlled by palaeotectonic stress fields. Therefore, quantitatively predicting the development and distribution of tectonic fractures in the Lower Cambrian shale reservoir is important for the exploration and exploitation of shale gas in the Feng'gang No. 3 block. In the present study, a reasonable geological, mechanical and mathematical model of the study area was established based on the faults systems interpreted from seismic data, fracture characteristics from drilling data, uniaxial and triaxial compression tests and experiments on the acoustic emissions (AE) of rocks. Then, a three-dimensional (3-D) finite element method is applied to simulate the palaeotectonic stress field with the superposition of the Yanshan and Himalayan movements and used to predict the fracture distribution. The simulation results indicate that the maximum principal stress value within the study area ranged from 269.97 MPa to 281.18 MPa, the minimum principal stress ranged from 58.29 MPa to 79.64 MPa, and the shear stress value ranged from 91.05 MPa to 106.21 MPa. The palaeotectonic stress field is controlled by the fault zone locations. The fracture development zones are mainly controlled by the tectonic stress fields and are located around the faults, at the end of the fault zones, at the inflection point and at the intersection of the fault zones.  相似文献   

4.
Structural analysis of the Indian Merge 3D seismic survey identified three populations of normal faults within the Exmouth Sub-basin of the North West Shelf volcanic margin of Australia. They comprise (1) latest-Triassic to Middle Jurassic N-NNE-trending normal faults (Fault Population I); (2) Late Jurassic to Early Cretaceous NE-trending normal faults (Fault Population II); and (3) latest-Triassic to Early Cretaceous N-NNE faults (Fault Population III). Quantitative evaluation of >100 faults demonstrates that fault displacement occurred during two time periods (210–163 and 145–138 Ma) separated by ∼20 Myr of tectonic quiescence. Latest Jurassic to Early Cretaceous (145–138 Ma) evolution comprises magmatic addition and contemporaneous domal uplift ∼70 km wide characterised by ≥ 900 m of denudation. The areally restricted subcircular uplift centred on the southern edge of the extended continental promontory of the southern Exmouth Sub-basin supports latest Jurassic mantle plume upwelling that initiated progradation of the Barrow Delta. This polyphase and bimodal structural evolution impacts current hydrocarbon exploration rationale by defining the nature of latest Jurassic to Early Cretaceous fault nucleation and reactivation within the southern Exmouth Sub-basin.  相似文献   

5.
Fault activity and sandstone-body geometries and spread, all bear significant weight to understanding the potential hydrocarbon systems on the NW Barents Shelf. Synthetic seismic modelling of onshore sedimentary successions provides insight into the seismic resolution and expression of various sedimentological features on Edgeøya: (i) sandy growth basins in pro-delta mudstones (ii) paralic sedimentary deposits and (iii) low-angle tidally influenced progradational successions.Synthetic modelling suggests that the lithological contrast associated with sand-infilled growth basins in pro-deltaic shales, even with offsets as small as 50–75 m, will create distinct geometries in seismic data. Modelling suggests that while optimal 90° illumination, low frequency bands and more typical sedimentary velocities around 2000 m/s will generate very clear discernible growth faults, the angular lithological contrast should generate discernible features even with the high velocities and typical 20–30 Hz frequency band of seismic sections on the NW Barents Shelf. Comparing to actual seismic data in which multiples, noise and in places overburden are influential, it is possible to identify growth-fault geometries more confidently, and to link them to larger planar fault activity.Modelling other features identified in the paralic sedimentary system it is apparent that many of the massive channel or lenticular shaped sandstone bodies should be identifiable in the actual seismic, although their expression is less distinct and more easily misinterpreted than that of growth faults. It is apparent that features such as igneous intrusions, unless imaged in a “perfect” survey, can be difficult to properly identify, particularly near-vertical connections. The velocity contrast creates strong impedance along horizontal sections, but heavily fractured igneous intrusions with lower velocities could easily be assumed to be isolated sandstone bodies. While the modelling appreciates the overall wedging nature of the successions, the simplified lithological observations onshore cannot predict the probable erosion/condensation contrast associated with low-angle clinoforms which are visible in the seismic data, and hence not reproduce them easily in the models.  相似文献   

6.
This study examines the structural characteristics of the northern Gulf of California by processing and interpreting ca. 415 km of two-dimensional multi-channel seismic reflection lines (data property of Petróleos Mexicanos PEMEX) collected in the vicinity of the border between the Wagner and Consag basins. The two basins appear to be a link between the Delfín Superior Basin to the south, and the Cerro Prieto Basin to the north in the Mexicali-Imperial Valley along the Pacific–North America plate boundary. The seismic data are consistent with existing knowledge of four main structures (master faults) in the region, i.e., the Percebo, Santa María, Consag Sur, and Wagner Sur faults. The Wagner and Consag basins are delimited to the east by the Wagner Sur Fault, and to the west by the Consag Sur Fault. The Percebo Fault borders the western margin of the modern Wagner Basin depocenter, and is oriented N10°W, dipping (on average) ～40° to the northeast. The trace of the Santa María Fault located in the Wagner Basin strikes N19°W, dipping ～40° to the west. The Consag Sur Fault is oriented N14°W, and dips ～42° to the east over a distance of 21 km. To the east of the study area, the Wagner Sur Fault almost parallels the Consag Sur Fault over a distance of ～86 km, and is oriented N10°W with an average dip of 59° to the east. Moreover, the data provide new evidence that the Wagner Fault is discontinuous between the two basins, and that its structure is more complex than previously reported. A structural high separates the northern Consag Basin from the southern Wagner Basin, comprising several secondary faults oriented NE oblique to the main faults of N–S direction. These could represent a zone of accommodation, or transfer zone, where extension could be transferred from the Wagner to the Consag Basin, or vice versa. This area shows no acoustic basement and/or intrusive body, which is consistent with existing gravimetric and magnetic data for the region.  相似文献   

7.
Although typically interpreted as 2D surfaces, faults are 3D narrow zones of highly and heterogeneously strained rocks, with petrophysical properties differing from the host rock. Here we present a synthetic workflow to evaluate the potential of seismic data for imaging fault structure and properties. The workflow consists of discrete element modeling (DEM) of faulting, empirical relations to modify initial acoustic properties based on volumetric strain, and a ray-based algorithm simulating prestack depth migration (PSDM). We illustrate the application of the workflow in 2D to a 100 m displacement normal fault in a kilometer size sandstone-shale sequence at 1.5 km depth. To explore the effect of particle size on fault evolution, we ran two DEM simulations with particle assemblages of similar bulk mechanical behavior but different particle size, one with coarse (1–3 m particle radii) and the other with fine (0.5–1.5 m particle radii) particles. Both simulations produce realistic but different fault geometries and strain fields, with the finer particle size model displaying narrower fault zones and fault linkage at later stages. Seismic images of these models are highly influenced by illumination direction and wave frequency. Specular illumination highlights flat reflectors outside the fault zone, but fault related diffractions are still observable. Footwall directed illumination produces low amplitude images. Hanging wall directed illumination images the shale layers within the main fault segment and the lateral extent of fault related deformation. Resolution and the accuracy of the reflectors are proportional to wave frequency. Wave frequencies of 20 Hz or more are necessary to image the different fault structure of the coarse and fine models. At 30–40 Hz, there is a direct correlation between seismic amplitude variations and the input acoustic properties after faulting. At these high frequencies, seismic amplitude variations predict both the extent of faulting and the changes in rock properties in the fault zone.  相似文献   

8.
The paleokarst-unconformity at the top of the Ordovician Yingshan Formation in the central Tarim basin was exposed to air for at least 10 Ma, providing favorable conditions for the later formation of high-quality reservoirs. During the karstification process, the fault system plays an important role in controlling the development of paleokarst. This study characterized the fault system through the paleokarst features on the northern slope of the Tazhong High and examined in detail the impacts of the fault system on paleokarst distribution. Formation Micro-Imager logs and seismic curvature change rate were used for characterizing the fault system in different scales. The results revealed three sets of faults in this region. Cross-cutting relationships, unconformities, and relation between faults and karstification indicate Mid-to-Late Ordovician thrust faults, Silurian-Devonian strike-slip faults, and Permian tension faults. “Bright spots” in seismic records calibrated by Formation Micro-Imager logs were used for indicating paleokarst features and different depth distributions, respectively. Furthermore, the study employed spectral decomposition technique to characterize the morphology of paleocave complexes in detail. The results show the Mid-Late Ordovician thrust faults heavily impacted the distribution of paleokarst mainly distributed along master and secondary thrust faults in shallow areas, as well as along master basement-involved thrust faults in deep strata, and along the most pronounced area of paleokarst, Tazhong No. 10 fault zone bounded by back thrusts. The data provides new forecasting information for deep hydrocarbon exploration in paleokarst-related reservoirs of the Yingshan Formation.  相似文献   

9.
A Natural active oil seepage occurs at the intersection of the NW-oriented rift coastal fault and a NE-oriented cross fault which bound the southwest dipping Little Zeit tilted fault block at the southwestern side of the Gulf of Suez, Egypt. Detailed surface geological mapping followed by subsurface mapping using aeromagnetic, seismic and borehole data of Ras El Ush oilfield (the nearest oil field to the seepage) provide a reliable hydrocarbon migration pathway model of the area.The proposed model suggests that hydrocarbons migrated upward at the intersection of a NE-oriented and the NW-oriented rift coastal faults where they found their way to the surface. The Nubia Sandstone occurs south of Ras El Ush oilfield in a trap door structure and probably entrapped some of the migrating hydrocarbons while a probable oil-water-contact at −1000 m which resulted into the migration of hydrocarbon through the damage zone of the northeast fault.The original oil in place of the predicted reservoir is estimated to be more than 47.5 MMBO which encourages the design makers for more investigation of this reservoir to increase its certainty and putting it in the plan of the future investments.  相似文献   

10.
Due to a lack of borehole data, reservoir and seal rock presence in frontier basins is typically inferred from seismic reflection data. However, analysis of the geometry and kinematic development of polygonal fault systems (PFS), which almost exclusively form within very fine-grained strata, provides another, largely untested method to infer reservoir and seal rock presence. We here use very high-quality 3D seismic reflection data from offshore Uruguay and a range of quantitative GIS-based techniques to document the planform and cross-sectional characteristics of a basin-scale (>6400 km2) PFS, and to investigate the role that stratigraphic variations in the Tertiary deep-water host-rock have on its geometrical variability and kinematic development. We demonstrate that a series of likely sandstone-rich deep-water deposits occur at the base of and within the main PFS tier. The geometric characteristics and throw distribution on individual polygonal faults suggest these sandstone-rich deep-water deposits represent a mechanical barrier to fault propagation, thus influencing fault height and areal density and, in some cases, strike. We argue that in largely unexplored, deep-to ultra-deep water basins, such as those characterizing offshore Uruguay, the distribution and geometric attributes of PFS can be used to delineate sandstone-rich reservoir bodies. Furthermore, these characteristics may help exploration geoscientists better understand seal heterogeneity and quality in data-poor basins.  相似文献   

11.
Passive margins such as the Gulf of Mexico are characterized by two distinct styles of faulting. Homogenous sand/shale packages in offshore Texas mostly display basinward-dipping listric normal faults with associated rollover structures cut by synthetic and antithetic faults. The fault traces are generally long and show a linear trend. Stratigraphic packages with a ductile substratum (salt) in offshore Louisiana are characterized by basinward and landward-dipping, short arcuate faults detaching within the salt. The structures consist of a series of half-grabens, with the movement of salt from the front to the back of each fault block. Clay experimental models are used to study the controls of fault geometries in the two structural styles and their interaction to form complex transfer zones. The surface of the clay cake is laser-scanned to enable 3D visualization and accurate measurements of structures. The results suggest that within homogeneous sand-shale packages, the dips of the faults and their locations are primarily dependent on the direction of the drop down of the basal detachment along pre-existing discontinuities, with the slope of the basal discontinuity and the direction of extension providing secondary controls. On the other hand, the dips of fault systems in packages underlain by a ductile substratum are primarily controlled by the slope of the basal detachment. Therefore, the more common regional Roho systems typically form above salt sheets with initial basinward slopes, whereas counter-regional fault systems form above salt sheets with initial landward slopes. The direction of extension and the presence of small pre-existing discontinuities impart only secondary controls when ductile basal units are involved. The faults initiate at the head of ductile layer and propagate downslope. Complex transfer zones develop at the boundary of the ductile substratum due to interference between the two fault styles.  相似文献   

12.
Based on bathymetric data and multichannel seismic data, the Manila subduction system is divided into three segments, the North Luzon segment, the seamount chain segment and the West Luzon segment starts in Southwest Taiwan and runs as far as Mindoro. The volume variations of the accretionary prism, the forearc slope angle, taper angle variations support the segmentation of the Manila subduction system. The accretionary prism is composed of the outer wedge and the inner wedge separated by the slope break. The backstop structure and a 0.5–1 km thick subduction channel are interpreted in the seismic Line 973 located in the northeastern South China Sea. The clear décollement horizon reveals the oceanic sediment has been subducted beneath the accretionary prism. A number of splay faults occur in the active outer wedge. Taper angles vary from 8.0° ± 1° in the North Luzon segment, 9.9° ± 1° in the seamount segment to 11° ± 1° in the West Luzon segment. Based on variations between the taper angle and orthogonal convergence rates in the world continental margins and comparison between our results and the global compilation, different segments of the Manila subduction system fit well the global pattern. It suggests that subduction accretion dominates the north Luzon and seamount chain segment, but the steep slope indicates in the West Luzon segment and implies that tectonic erosion could dominate the West Luzon segment.  相似文献   

13.
Based on new multibeam bathymetric data and about 300 km long single seismic profiles, three topographic units were identified:the canyons, fractural valley and submarine terrace on the north of Chiwei Island where is a structural transition zone between the southern trough and the middle trough. The Chiwei Canyon and the North Chiwei Canyon are two of the largest canyons in the East China Sea (ECS) slope. Topographic features and architectures of them are described. The study shows that both of them are originated along faults. The evolution and spatial distribution of topographic units in the study area are controlled mainly by three groups of faults which were formed and reactive in the recent extensional phase of Okinawa Trough. The Chiwei Canyon was initiated during the middle Pleistocene and guided by F4 that is a N-S trending fault on the slope and F1, a large NW-SE trending fault on the trough. The pathway migration from the remnant channel to the present one of Chiwei Canyon is the result of uplift of tilted fault block that is coupled to the recent extension movements of the southern trough. The submarine terrace is detached from the ECS slope by the NEE-trending fault. The North Chiwei Canyon, developing during the late Pleistocene, is guided by F5, a N-S trending fault, diverted and blocked by the submarine terrace.  相似文献   

14.
Based on new multibeam bathymetric data and about 300 km long single seismic profiles, three topographic units were identified： the canyons, fractural valley and submarine terrace on the north of Chiwei Island where is a structural transition zone between the southern trough and the middle trough. The Chiwei Canyon and the North Chiwei Canyon are two of the largest canyons in the East China Sea （ECS） slope. Topographic features and architectures of them are described. The study shows that both of them are originated along faults. The evolution and spatial distribution of topographic units in the study area are controlled mainly by three groups of faults which were formed and reactive in the recent extensional phase of Okinawa Trough. The Chiwei Canyon was initia- ted during the middle Pleistocene and guided by F4 that is a N--S trending fault on the slope and F1, a large NW--SE trending fault on the trough. The pathway migration from the remnant channel to the present one of Chiwei Canyon is the result of uplift of tilted fault block that is coupled to the recent extension movements of the southern trough. The submarine terrace is detached from the ECS slope by the NEE -trending fault. The North Chiwei Canyon, developing during the late Pleistocene, is guided by FS, a N-S trending fault, diverted and blocked by the submarine terrace.  相似文献   

15.
Reservoirs where tectonic fractures significantly impact fluid flow are widespread. Industrial-level shale gas production has been established from the Lower Cambrian Niutitang Formation in the Cen'gong block, South China; the practice of exploration and development of shale gas in the Cen'gong block shows that the abundance of gas in different layers and wells is closely related to the degree of development of fractures. In this study, the data obtained from outcrop, cores, and logs were used to determine the developmental characteristics of such tectonic fractures. By doing an analysis of structural evolution, acoustic emission, burial history, logging evaluation, seismic inversion, and rock mechanics tests, 3-D heterogeneous geomechanical models were established by using a finite element method (FEM) stress analysis approach to simulate paleotectonic stress fields during the Late Hercynian—Early Indo-Chinese and Middle-Late Yanshanian periods. The effects of faulting, folding, and variations of mechanical parameters on the development of fractures could then be identified. A fracture density calculation model was established to determine the quantitative development of fractures in different stages and layers. Favorable areas for shale gas exploration were determined by examining the relationship between fracture density and gas content of three wells. The simulation results indicate the magnitude of minimum principal stress during the Late Hercynian — Early Indo-Chinese period within the Cen'gong block is −100 ∼ −110 MPa with a direction of SE-NW (140°–320°), and the magnitude of the maximum principal stress during the Middle-Late Yanshanian period within the Cen'gong block is 150–170 MPa with a direction of NNW-SSE (345°–165°). During the Late Hercynian — Early Indo-Chinese period, the mechanical parameters and faults play an important role in the development of fractures, and fractures at the downthrown side of the fault are more developed than those at the uplifted side; folding plays an important role in the development of fractures in the Middle-Late Yanshanian period, and faulting is a secondary control. This 3-D heterogeneous geomechanical modelling method and fracture density calculation modelling are not only significant for prediction of shale fractures in complex structural areas, but also have a practical significance for the prediction of other reservoir fractures.  相似文献   

16.
The Dongpu depression is located in the southern Bohai Bay Basin, North China, and it has abundant oil and gas reserves. There has been no systematic documentation of this depression's temperature field and thermal history. In this article, the present geothermal gradient and heat flow were calculated for 68 wells on the basis of 892 formation-testing data from 523 wells. Moreover, the Cenozoic thermal history was reconstructed using 466 vitrinite reflectance data from 105 wells. The results show that the Dongpu depression is characterized by a medium-temperature field between stable and active tectonic areas, with an average geothermal gradient of 34.8 °C/km and an average heat flow of 66.8 mW/m2. The temperature field in the Dongpu depression is significantly controlled by the Changyuan, Huanghe, and Lanliao basement faults and thin lithosphere thickness. The geothermal gradient twice experienced high peaks. One peak was during the Shahejie 3 Formation depositional period, ranging from 45 °C/km to 48 °C/km, and the second peak was in the middle and late of the Dongying Formation depositional period, ranging from 39 °C/km to 40 °C/km, revealing that the Dongpu depression experienced two strong tectonic rifts during the geothermal gradient high peak periods. The geothermal gradient began to decrease from the Neogene, and the geothermal gradient is 31–34 °C/km at the present day. In addition, these results reveal that source rock thermal evolution is controlled by the paleo temperature field of the Dongying Formation depositional period in the Dongpu depression. This study may provide a geothermal basis for deep oil and gas resource evaluation in the Dongpu depression.  相似文献   

17.
The multichannel seismic data along one long-offset survey line from Krishna-Godavari (K-G) basin in the eastern margin of India were analyzed to define the seismic character of the gas hydrate/free gas bearing sediments. The discontinuous nature of bottom simulating reflection (BSR) was carefully examined. The presence of active faults and possible upward fluid circulation explain the discontinuous nature and low amplitude of the BSR. The study reveals free gas below gas hydrates, which is also indicated by enhancement of seismic amplitudes with offsets from BSR. These findings were characterized by computing seismic attributes such as the reflection strength and instantaneous frequency along the line. Geothermal gradients were computed for 18°C and 20°C temperature at the depth of BSR to understand the geothermal anomaly that can explain the dispersed nature of BSR. The estimated geothermal gradient shows an increase from 32°C/km in the slope region to 41°C/km in the deeper part, where free gas is present. The ray-based travel time inversion of identifiable reflected phases was also carried out along the line. The result of velocity tomography delineates the high-velocity (1.85–2.0 km/s) gas hydrate bearing sediments and low-velocity (1.45–1.5 km/s) free gas bearing sediments across the BSR.  相似文献   

18.
Between 33°S and 47°S, the southern Chile forearc is affected by the subduction of the aseismic Juan Fernandez Ridge, several major oceanic fracture zones on the subducting Nazca Plate, the active Chile Ridge spreading centre, and the underthrusting Antarctic Plate. The heat flow through the forearc was estimated using the depth of the bottom simulating reflector obtained from a comprehensive database of reflection seismic profiles. On the upper and middle continental slope along the whole forearc, heat flow is about 30–60 mW m–2, a range of values common for the continental basement and overlying slope sediments. The actively deforming accretionary wedge on the lower slope, however, in places shows heat flow reaching about 90 mW m–2. This indicates that advecting pore fluids from deeper in the subduction zone may transport a substantial part of the heat there. The large size of the anomalies suggests that fluid advection and outflow at the seafloor is overall diffuse, rather than being restricted to individual fault structures or mud volcanoes and mud mounds. One large area with very high heat flow is associated with a major tectonic feature. Thus, above the subducting Chile Ridge at 46°S, values of up to 280 mW m–2 indicate that the overriding South American Plate is effectively heated by subjacent zero-age oceanic plate material.  相似文献   

19.
SeaMARC II side-scan images, bathymetry, and single-channel seismic reflection data along the southern Peru—northern Chile forearc area between 16° and 23° S reveal a complex region of morpho-structural, submarine drainage and depression patterns. In the subducting plate area, the NW—SE trending primary normal fault system represented by trench-paralleled scarps was incipiently formed as the Nazca Plate was bent in the outer edge and further intensified as the plate approached the trench. The NE—SW trending secondary normal fault system that consists of discontinuous and smaller faults, usually intersect the primary trench-paralleled fault system. Similar to the Nazca Plate, the overriding continental plate also shows two major NW—SE and NE—SW trending fault systems represented by fault scarps or narrow elongated depressions.The submarine drainage systems represented by a series of canyon and channel courses appear to be partly controlled by the faults and exhibit a pattern similar to the onshore drainage which flows into the central region of the coastal area. Two large depressions occurring along the middle—upper slope areas of the continental margin are recognized as collapse and slump that perhaps are a major result of increased slope gradient. The subsidence of the forearc area in the southern Peru—northern Chile Continental Margin is indicated by: a) drainage systems flowing into the central region, b) the slope collapse and slumps heading to the central region, c) the deepening of the trench and inclining of the lower slope terrace to the central region, and d) submerging of the upper-slope ridge and the Peru—Chile Coast Range off the Arica Bight area.The subsidence of the forearc area in the southern Perunorthern Chile margin is probably attributed to a subduction erosion which causes wearing away and removal of the rock and sedimentary masses of the overriding plate as the Nazca Plate subducts under the South American Plate.  相似文献   

20.
The seafloor morphology and the subsurface of the continental slope of the Olbia intraslope basin located along the eastern, passive Sardinian margin (Tyrrhenian Sea) has been mapped through the interpretation of high-resolution multibeam bathymetric data, coupled with air-gun and sparker seismic profiles. Two areas, corresponding to different physiographic domains, have been recognized along the Olbia continental slope. The upper slope domain, extending from 500 to 850 m water depth, exhibits a series of conical depressions, interpreted as pockmarks that are particularly frequent in seafloor sectors coincident with buried slope channels. In one case, they are aligned along a linear gully most likely reflecting the course of one of the abandoned channels. The location of the pockmarks thus highlights the importance of the distribution of lithologies within different sedimentary bodies in the subsurface in controlling fluid migration plumbing systems. A linear train of pockmarks is, however, present also away from the buried channels being related to a basement step, linked to a blind fault. Two bathymetric highs, interpreted as possible carbonate mounds, are found in connection with some of the pockmark fields. Although the genetic linkage of the carbonate mounds with seafloor fluid venting cannot be definitively substantiated by the lack of in situ measurements, the possibility of a close relationship is here proposed. The lower slope domain, from 850 m down to the base of the slope at 1,200 m water depth is characterized by a sudden gradient increase (from 2° to 6°) that is driven by the presence of the basin master fault that separates the continental slope from the basin plain. Here, a series of km-wide headwall scars due to mass wasting processes are evident. The landslides are characterized by rotated, relatively undeformed seismic strata, which sometimes evolve upslope into shallow-seated (less than 10 m), smaller scale failures and into headless chutes. Slope gradient may act as a major controlling factor on the seafloor instability along the Olbia continental slope; however, the association of landslides with pockmarks has been recognized in several continental slopes worldwide, thus the role of over-pressured fluids in triggering sediment failure in the Olbia slope can not be discarded. In the absence of direct ground truthing, the geological processes linked to subsurface structures and their seafloor expressions have been inferred through the comparison with similar settings where the interpretation of seafloor features from multibeam data has been substantiated with seafloor sampling and geochemical data.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号