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1.
This study aims to constrain the base of the hydrates stability field in structurally complexsites using the case of Woolsey Mound, a fault-controlled, transient, thermogenic hydrates system, in Mississippi Canyon Block 118, northern Gulf of Mexico. We have computed the base of the hydrates stability field integrating results from a recent heat-flow survey, designed to investigate geothermal anomalies along fault zones which exhibit different fluid flux regimes. An advanced “compositional” simulator was used to model hydrate formation and dissociation at Woolsey Mound and addresses the following hypotheses:
- 1.Migrating thermogenic fluids alter thermal conditions of the Hydrate Stability Zone (HSZ), so heat-flow reflects fault activity;
- 2.Gas hydrate formation and dissociation vary temporally at active faults, temporarily sealing conduits for migration of thermogenic fluids;
- 3.High salinity and inclusion of thermogenic gases with higher molecular weight than methane produce opposite effects on the depth to the bottom of the hydrate stability zone.
2.
The Ulleung Basin, East (Japan) Sea, is well-known for the occurrence of submarine slope failures along its entire margins and associated mass-transport deposits (MTDs). Previous studies postulated that gas hydrates which broadly exist in the basin could be related with the failure process. In this study, we identified various features of slope failures on the margins, such as landslide scars, slide/slump bodies, glide planes and MTDs, from a regional multi-channel seismic dataset. Seismic indicators of gas hydrates and associated gas/fluid flow, such as the bottom-simulating reflector (BSR), seismic chimneys, pockmarks, and reflection anomalies, were re-compiled. The gas hydrate occurrence zone (GHOZ) within the slope sediments was defined from the BSR distribution. The BSR is more pronounced along the southwestern slope. Its minimal depth is about 100 m below seafloor (mbsf) at about 300 m below sea-level (mbsl). Gas/fluid flow and seepage structures were present on the seismic data as columnar acoustic-blanking zones varying in width and height from tens to hundreds of meters. They were classified into: (a) buried seismic chimneys (BSC), (b) chimneys with a mound (SCM), and (c) chimneys with a depression/pockmark (SCD) on the seafloor. Reflection anomalies, i.e., enhanced reflections below the BSR and hyperbolic reflections which could indicate the presence of gas, together with pockmarks which are not associated with seismic chimneys, and SCDs are predominant in the western-southwestern margin, while the BSR, BSCs and SCMs are widely distributed in the southern and southwestern margins. Calculation of the present-day gas-hydrate stability zone (GHSZ) shows that the base of the GHSZ (BGHSZ) pinches out at water depths ranging between 180 and 260 mbsl. The occurrence of the uppermost landslide scars which is below about 190 mbsl is close to the range of the GHSZ pinch-out. The depths of the BSR are typically greater than the depths of the BGHSZ on the basin margins which may imply that the GHOZ is not stable. Close correlation between the spatial distribution of landslides, seismic features of free gas, gas/fluid flow and expulsion and the GHSZ may suggest that excess pore-pressure caused by gas hydrate dissociation could have had a role in slope failures. 相似文献
3.
《Marine and Petroleum Geology》2012,35(1):111-118
Potential accumulations of gas hydrates in Alaminos Canyon Block 21 (AC21) in the Gulf of Mexico are thought to occur in a shallow sand-rich interval, stratigraphically separated from sources of free gas below the base of the gas hydrate stability zone (BGHSZ), by an intervening thick layer of clay- and silt-rich sediments. Availability of sufficient gas charge from depth, in addition to local biogenic sourcing is considered key to the formation of gas hydrates in the GHSZ. Implicitly, a detailed understanding of geometries associated with fault and fracture networks in relation to potential gas migration pathways can provide additional confidence that seismic amplitude anomalies are related to gas hydrate accumulations. Delineation of fault and fracture systems from high resolution seismic data in and below the gas hydrates stability zone (GHSZ) was performed using an automated algorithm—Ant Tracking. The capturing of small-scale detail has particular significance at AC21, revealing a pervasive network of typically small-extent discontinuities, indicative of fracturing, throughout this intervening clay- and silt-rich layer of mass-transport deposits (MTDs). Ant Tracking features appear to correlate, to some extent, with potential gas hydrate accumulations, supporting the concept that fracturing possibly provides migration pathways albeit via a tortuous, complex path. This study demonstrates that the Ant Tracking attribute, in conjunction with detailed seismic interpretation and analysis, can provide valuable evidence of potential gas migration pathways. 相似文献
4.
Carl Jörg Petersen Stefan Bünz Steinar Hustoft Jürgen Mienert Dirk Klaeschen 《Marine and Petroleum Geology》2010
The newly developed P-Cable 3D seismic system allows for high-resolution seismic imaging to characterize upper geosphere geological features focusing on geofluid expressions (gas chimneys), shallow gas and gas hydrate reservoirs. Seismic imaging of a geofluid system of an Arctic sediment drift at the Vestnesa Ridge, offshore western Svalbard, provides significantly improved details of internal chimney structures from the seafloor to ∼500 m bsf (below seafloor). The chimneys connect to pockmarks at the seafloor and indicate focused fluid flow through gas hydrated sediments. The pockmarks are not buried and align at the ridge-crest pointing to recent, topography-controlled fluid discharge. Chimneys are fuelled by sources beneath the base of gas hydrate stability zone (GHSZ) that is evident at ∼160–170 m bsf as indicated by a bottom-simulating reflector (BSR). Conduit centres that are not vertically straight but shift laterally by up to 200 m as well as discontinuous internal chimney reflections indicate heterogeneous hydraulic fracturing of the sediments. Episodically active, pressure-driven focused fluid flow could explain the hydro-fracturing processes that control the plumbing system and lead to extensive pockmark formation at crest of the Vestnesa Ridge. High-amplitude anomalies in the upper 50 m of the chimney structures suggest formations of near-surface gas hydrates and/or authigenic carbonate precipitation. Acoustic anomalies, expressed as high amplitudes and amplitude blanking, are irregularly distributed throughout the deeper parts of the chimneys and provide evidence for the variability of hydrate and/or carbonate formation in space and time. 相似文献
5.
Based on the analysis of the high-resolution 3D seismic data from the SW Barents Sea we study the hydrocarbon plumbing system above the Snøhvit and Albatross gas field to investigate the geo-morphological manifestation and the dynamics of leakage from the reservoir. Fluid and gas escape to the seafloor is manifested in this area as mega-pockmarks 1–2 km-wide, large pockmarks (<100 m wide) and giant pockmarks 100–300 m-wide. The size of the mega pockmarks to the south of the study area may indicate more vigorous venting, whilst the northern fluid flow regime is probably characterised by a widespread fluid and gas release. Buried mega depressions and large-to-giant pockmarks are also identified on the base Quaternary and linked to deep and shallow faults as well as to seismic pipes. A high density of buried and seafloor giant pockmarks occur above a network of faults overlying an interpreted Bottom Simulating Reflector (BSR), whose depth coincides with the estimated base of the hydrate stability zone for a thermogenically derived gas hydrate with around 90 mol% methane. Deep regional faults provide a direct route for the ascending thermogenic fluids from the reservoir, which then leaked through the shallow faults linked to seismic pipes. It is proposed that the last episodic hydrocarbon leakage from the reservoir was responsible for providing a methane source for the formation of gas hydrates. We inferred that at least two temporally and dynamically different fluid and gas venting events took place in the study area: (1) prior to late Weichselian and recorded on the Upper Regional Unconformity (URU) and (2) following the Last Glacial Maximum between ∼17 and 16 cal ka BP and recorded on the present-day seafloor. 相似文献
6.
We recorded high-resolution seismic-reflection data in the northern Gulf of Mexico to study gas and gas-hydrate distribution and their relation to seafloor slides. Gas hydrate is widely reported near the seafloor, but is described at only one deep drill site. Our data show high-reflectivity zones (HRZs) near faults, diapirs, and gas vents and interbedded within sedimentary sections at shallow depth (<1 km). The HRZs lie below the gas-hydrate-stability zone (GHSZ) as well as within the zone (less common), and they coincide with zones of shallow water-flows. Bottom simulating reflections are rare in the Gulf, and not documented in our data.We infer HRZs result largely from free gas in sandy beds, with gas hydrate within the GHSZ. Our estimates for the base BHSZ correlate reasonably with the top of HRZs in some thick well-layered basin sections, but poorly where shallow sediments are thin and strongly deformed. The equivocal correlation results from large natural variability of parameters that are used to calculate the base of the GHSZ. The HRZs may, however, be potential indicators of nearby gas hydrate. The HRZs also lie at the base of at least two large seafloor slides (e.g. up to 250 km2) that may be actively moving along decollement faults that sole within the GHSZ or close to the estimated base of the GHSZ. We suspect that water/gas flow along these and other faults such as ‘chimney’ features provide gas to permit crystallization of gas hydrate in the GHSZ. Such flows weaken sediment that slide down salt-oversteepened slopes when triggered by earthquakes. 相似文献
7.
Distribution and expression of gas seeps in a gas hydrate province of the northeastern Sakhalin continental slope, Sea of Okhotsk 总被引：1，自引：0，他引：1
Young Keun Jin Young-Gyun Kim Boris Baranov Hitoshi Shoji Anatoly Obzhirov 《Marine and Petroleum Geology》2011,28(10):1844-1855
Multidisciplinary surveys were conducted to investigate gas seepage and gas hydrate accumulation on the northeastern Sakhalin continental slope (NESS), Sea of Okhotsk, during joint Korean–Russian–Japanese expeditions conducted from 2003 to 2007 (CHAOS and SSGH projects). One hundred sixty-one gas seeps were detected in a 2000 km2 area of the NESS (between 53°45′N and 54°45′N). Active gas seeps in a gas hydrate province on the NESS were evident from features in the water column, on the seafloor, and in the subsurface: well-defined hydroacoustic anomalies (gas flares), side-scan sonar structures with high backscatter intensity (seepage structures), bathymetric structures (pockmarks and mounds), gas- and gas-hydrate-related seismic features (bottom-simulating reflectors, gas chimneys, high-amplitude reflectors, and acoustic blanking), high methane concentrations in seawater, and gas hydrates in sediment near the seafloor. These expressions were generally spatially related; a gas flare would be associated with a seepage structure (mound), below which a gas chimney was present. The spatial distribution of gas seeps on the NESS is controlled by four types of geological structures: faults, the shelf break, seafloor canyons, and submarine slides. Gas chimneys that produced enhanced reflection on high-resolution seismic profiles are interpreted as active pathways for upward gas migration to the seafloor. The chimneys and gas flares are good indicators of active seepage. 相似文献
8.
以墨西哥湾西北部陆坡区为研究区,利用NOAA/AVHRR热红外影像,通过分析1999年Central Mexico 7.0级地震、1999年Oaxaco 7.5级地震和2003年Colima 7.6级地震3次地震期间与墨西哥湾西北部陆坡区海底天然气水合物藏区对应的海表面上方卫星热红外亮温异常的变化,研究了卫星热红外亮温异常与深水海域天然气水合物藏区分布的关系.研究发现,与墨西哥湾西北部陆坡区海底天然气水合物藏区对应的海表面上方,临震前频繁出现孤立的、带状的、强度较大的卫星热红外亮温异常,该研究结果表明,同次和多次地震临震前,该地区频繁出现孤立、带状、强度较大的卫星热红外亮温异常可能与海底蕴藏着天然气水合物藏有关. 相似文献
9.
Pockmarks are observed worldwide along the continental margins and are inferred to be indicators of fluid expulsion. In the present study, we have analysed multibeam bathymetry and 2D/3D seismic data from the south-western Barents Sea, in relation to gas hydrate stability field and sediment type, to examine pockmark genesis. Seismic attributes of the sediments at and beneath the seafloor have been analysed to study the factors related to pockmark formation. The seabed depths in the study area are just outside the methane hydrate stability field, but the presence of higher order hydrocarbon gases such as ethane and/or propane in the expelled fluids may cause localised gas hydrate formation. The selective occurrence of pockmarks in regions of specific seabed sediment types indicates that their formation is more closely related to the type of seabed sediment than the source path of fluid venting such as faults. The presence of high acoustic backscatter amplitudes at the centre of the pockmarks indicates harder/coarser sediments, likely linked to removal of soft material. The pockmarks show high seismic reflection amplitudes along their fringes indicating deposition of carbonates precipitated from upwelling fluids. High seismic amplitude gas anomalies underlying the region away from the pockmarks indicate active fluid flow from hydrocarbon source rocks beneath, which is blocked by overlying less permeable formations. In areas of consolidated sediments, the upward flow is limited to open fault locations, while soft sediment areas allow diffused flow of fluids and hence formation of pockmarks over a wider region, through removal of fine-grained material. 相似文献
10.
Woolsey Mound, a carbonate/hydrate complex of cold seeps, vents, and seafloor pockmarks in Mississippi Canyon Block 118, is the site of the Gulf of Mexico Hydrates Research Consortium’s (GOMHRC) multi-sensor, multi-disciplinary, permanent seafloor observatory. In preparation for installing the observatory, the site has been studied through geophysical, biological, geological, and geochemical surveys. By integrating high-resolution, swath bathymetry, acoustic imagery, seafloor video, and shallow geological samples in a morpho-bio-geological model, we have identified a complex mound structure consisting of three main crater complexes: southeast, northwest, and southwest. Each crater complex is associated with a distinct fault. The crater complexes exhibit differences in morphology, bathymetric relief, exposed hydrates, fluid venting, sediment accumulation rates, sediment diagenesis, and biological community patterns. Spatial distribution of these attributes suggests that the complexes represent three different fluid flux regimes: the southeast complex seems to be an extinct or quiescent vent; the northwest complex exhibits young, vigorous activity; and the southwest complex is a mature, fully open vent. Geochemical evidence from pore-water gradients corroborates this model suggesting that upward fluid flux waxes and wanes over time and that microbial activity is sensitive to such change. Sulfate and methane concentrations show that microbial activity is patchy in distribution and is typically higher within the northwest and southwest complexes, but is diminished significantly over the southeast complex. Biological community composition corroborates the presence of distinct conditions at the three crater complexes. The fact that three different fluid flux regimes coexist within a single mound complex confirms the dynamic nature of the plumbing system that discharges gases into bottom water. Furthermore, the spatial distribution of bio-geological processes appears to be a valid indicator of multiple fluid flux regimes that coexist at the mound. 相似文献
11.
Northern Gulf of Mexico continental slope 总被引：1，自引：0，他引：1
The hummocky continental slope in the northwestern Gulf of Mexico is the result of active salt tectonism and accompanying
faulting. Fluid and gassy hydrocarbons rise through the sediment column and along faults causing the formation of gas hydrates,
gassy sediments, mud volcanoes and mounds, chemosynthetic communities and authigenic carbonates, reefs, and hardgrounds. Salt
activity coupled with processes associated with relative sea level fluctuations create a feedback relationship resulting in
the above-mentioned phenomena as well as others such as seafloor erosion at great water depths. 相似文献
12.
Multichannel seismic reflection data from the continental margin of western India suggest the potential presence of fluid
expulsion features, which may or may not be associated with gas hydrates. No typical bottom simulating reflector was observed
on the reflection seismic section. As a result we look for other evidence in seismic sections in a small corridor of the western
continental margin of India in order to establish the presence of gas hydrates. We study features including venting through
the seafloor, pockmarks, sea floor collapse, faults acting as migration paths for fluid flow, transparent gas-charged sediment,
reduction in amplitude strength, diapirism and mud-volcano. Presence of all these gas-escape features on a seismic section
implies the probable presence of methane within the zone of hydrate stability field. 相似文献
13.
G.J. Crutchley A.R. Gorman I.A. Pecher S. Toulmin S.A. Henrys 《Marine and Petroleum Geology》2011,28(10):1915-1931
Highly concentrated gas hydrate deposits are likely to be associated with geological features that promote increased fluid flux through the gas hydrate stability zone (GHSZ). We conduct conventional seismic processing techniques and full-waveform inversion methods on a multi-channel seismic line that was acquired over a 125 km transect of the southern Hikurangi Margin off the eastern coast of New Zealand’s North Island. Initial processing, employed with an emphasis on preservation of true amplitude information, was used to identify three sites where structures and stratal fabrics likely encourage focused fluid flow into and through the GHSZ. At two of the sites, Western Porangahau Trough and Eastern Porangahau Ridge, sub-vertical blanking zones occur in regions of intensely deformed sedimentary layering. It is interpreted that increased fluid flow occurs in these regions and that fluids may dissipate upwards and away from the deformed zone along layers that trend towards the seafloor. At Eastern Porangahau Ridge we also observe a coherent bottom simulating reflection (BSR) that increases markedly in intensity with proximity to the centre of the anticlinal ridge. 1D full-waveform inversions conducted at eight points along the BSR reveal much more pronounced low-velocity zones near the centre of the ridge, indicating a local increase in the flux of gas-charged fluids into the anticline. At another anticline, Western Porangahau Ridge, a dipping high-amplitude feature extends from the BSR upwards towards the seafloor within the regional GHSZ. 1D full-waveform inversions at this site reveal that the dipping feature is characterised by a high-velocity zone overlying a low-velocity zone, which we interpret as gas hydrates overlying free gas. These results support a previous interpretation that this high-amplitude feature represents a local “up-warping” of the base of hydrate stability in response to advective heat flow from upward migrating fluids. These three sites provide examples of geological frameworks that encourage prolific localised fluid flow into the hydrate system where it is likely that gas-charged fluids are converting to highly concentrated hydrate deposits. 相似文献
14.
《Marine and Petroleum Geology》2012,29(10):1915-1931
Highly concentrated gas hydrate deposits are likely to be associated with geological features that promote increased fluid flux through the gas hydrate stability zone (GHSZ). We conduct conventional seismic processing techniques and full-waveform inversion methods on a multi-channel seismic line that was acquired over a 125 km transect of the southern Hikurangi Margin off the eastern coast of New Zealand’s North Island. Initial processing, employed with an emphasis on preservation of true amplitude information, was used to identify three sites where structures and stratal fabrics likely encourage focused fluid flow into and through the GHSZ. At two of the sites, Western Porangahau Trough and Eastern Porangahau Ridge, sub-vertical blanking zones occur in regions of intensely deformed sedimentary layering. It is interpreted that increased fluid flow occurs in these regions and that fluids may dissipate upwards and away from the deformed zone along layers that trend towards the seafloor. At Eastern Porangahau Ridge we also observe a coherent bottom simulating reflection (BSR) that increases markedly in intensity with proximity to the centre of the anticlinal ridge. 1D full-waveform inversions conducted at eight points along the BSR reveal much more pronounced low-velocity zones near the centre of the ridge, indicating a local increase in the flux of gas-charged fluids into the anticline. At another anticline, Western Porangahau Ridge, a dipping high-amplitude feature extends from the BSR upwards towards the seafloor within the regional GHSZ. 1D full-waveform inversions at this site reveal that the dipping feature is characterised by a high-velocity zone overlying a low-velocity zone, which we interpret as gas hydrates overlying free gas. These results support a previous interpretation that this high-amplitude feature represents a local “up-warping” of the base of hydrate stability in response to advective heat flow from upward migrating fluids. These three sites provide examples of geological frameworks that encourage prolific localised fluid flow into the hydrate system where it is likely that gas-charged fluids are converting to highly concentrated hydrate deposits. 相似文献
15.
Subsurface and seafloor fluid flow anomalies are gaining large interest after the finding of five new hydrocarbon discoveries and observation of large gas flares in the SW Barents Sea. In the present study, we have analysed structural and stratigraphic controls on fluid flow towards the seafloor using gravity cores selected based on subsurface gas anomalies observed on seismic data from the Veslemøy High, SW Barents Sea. The subsurface fluid flow at the Veslemøy High is observed to be controlled by 1) the morphology and orientation of regional faults, structural highs and sedimentary basins, 2) the presence of Paleocene silica ooze deposits that changes microstructure with temperature thereby controlling fluid flow and 3) the location of regional and local open faults formed by glacial loading and unloading. Analysis of extractable organic matter in subsurface Holocene sediments corroborates the active migration pathways inferred from seismic data. Micropalaeontological studies on benthic foraminifera reveal methane seep associated assemblages that confirm the interpretation of subsurface gas anomalies in seismic data. We ultimately link these new results to the geological evolution history of the region to give a comprehensive model for the fluid flow system within the study area. 相似文献
16.
Pelotas Basin has the largest gas hydrate occurrence of the Brazilian coast. The reserves are estimated in 780 trillion cubic feet, covering an area of 45,000 km2. In this work we apply spectral decomposition technique in order to better understand a gas hydrate deep water system, performing a continuous time–frequency analysis of seismic trace, where frequency spectrum is the output for each time sample of the seismic trace. This allows a continuous analysis on the effects of the geologic structures and lithology over frequency content of the seismic wave. Spectral anomalies found were interpreted as variations of hydrates concentration inside the Gas Hydrate Stability Zone (GHSZ), as well free gas accumulations beneath and Below the GHSZ and gas chimneys. We concluded that this technique has a good potential to assist seismic study of structures associated with gas hydrates accumulations. 相似文献
17.
Bin Liu Jiangxin Chen Luis M. Pinheiro Li Yang Shengxuan Liu Yongxian Guan Haibin Song Nengyou Wu Huaning Xu Rui Yang 《海洋学报(英文版)》2021,40(2):136-146
Previous studies of gas hydrate in the Dongsha area mainly focused on the deep-seated gas hydrates that have a high energy potential, but cared little about the shallow gas hydrates occurrences. Shallow gas hydrates have been confirmed by drill cores at three sites(GMGS2 08, GMGS2 09 and GMGS2 16) during the GMGS2 cruise, which occur as veins, blocky nodules or massive layers, at 8–30 m below the seafloor. Gas chimneys and faults observed on the seismic sections are the two main fluid migration pathways. The deep-seated gas hydrate and the shallow hydrate-bearing sediments are two main seals for the migrating gas. The occurrences of shallow gas hydrates are mainly controlled by the migration of fluid along shallow faults and the presence of deep-seated gas hydrates.Active gas leakage is taking place at a relatively high-flux state through the vent structures identified on the geophysical data at the seafloor, although without resulting in gas plumes easily detectable by acoustic methods.The presence of strong reflections on the high-resolution seismic profiles and dim or chaotic layers in the subbottom profiles are most likely good indicators of shallow gas hydrates in the Dongsha area. Active cold seeps,indicated by either gas plume or seepage vent, can also be used as indicators for neighboring shallow gas hydrates and the gas hydrate system that is highly dynamic in the Dongsha area. 相似文献
18.
Gas hydrates along continental margins are commonly inferred from the presence of bottom simulating reflectors (BSRs) on reflection seismic records. Shale and mud diapirs are often observed in the proximity of BSR-inferred gas hydrates. Analysis of data from documented gas-hydrate occurrences suggests that the areas where mud volcanoes exist on the seafloor are promising locations for sediments with high gas-hydrate concentration. Along the western continental margin of India (WCMI), we have identified several anomalous reflections on single-channel, analogue seismic records in the proximity of BSRs, from which the presence of gas-charged sediments and gas seepages was inferred. These features characterize both the shelf-slope region of the WCMI and the adjoining deep-sea areas. The seismic records also reveal mud/shale diapiric activity and pockmarks near the gas hydrates. 相似文献
19.
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
20.
J. Acosta E. Uchupi A. Muñoz P. Herranz C. Palomo M. Ballesteros 《Marine Geophysical Researches》2003,24(1-2):41-57
Circular to elliptical mounds in the Canary Channel with reliefs of 75 to 375 m and diameters of 4 to 8 km partially surrounded by moats with reliefs of 25 to 75 m, were formed by piercement of the seafloor by Mesozoic evaporites. Several long gullies, < 1km wide, with abrupt terminations and pockmarks associated with these mounds were probably eroded by dense brine and hydrocarbon seeps. The salt brines that eroded the gullies were formed where salt diapirs intersect the seafloor, or in the subsurface by circulating ground water heated by igneous activity along the Canary Ridge. If the brines originated in the subsurface they reached the seafloor along faults. Displacement of the surficial sediments by sliding and creep is probably the result of the expulsion of hydrocarbons and/or vertical motion of the Mesozoic evaporites. Microtopographic features along or near the east flank of the Canary Ridge are the creation of uplift of the ridge, hydrothermal activity, mass wasting processes and turbidity currents. 相似文献