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1.
Seafloor mounds are potential geohazards to offshore rig emplacement and drilling operations and may contain evidence of underlying petroleum systems. Therefore, identifying and mapping them is crucial in de-risking exploration and production activities in offshore domains.A 738 km2 high resolution three-dimensional seismic dataset was used to investigate the occurrence, seismic characteristics and distribution of features interpreted as seafloor and buried sediment mounds, at water-depths of 800–1600 m, on the western Niger Delta slope. Fifteen seafloor mounds and eighteen shallowly buried mounds were identified. The seafloor mounds are characterised by lower seismic amplitude anomalies than the surrounding seabed sediments, and overlie vertical zones of acoustic blanking. The buried mounds in contrast are characterised by high amplitude anomalies; they also directly overlie sub-vertical zones of acoustic blanking. Seismic evidences from the features, their distribution patterns and tectono-stratigraphic associations suggest that their formation was controlled by the juxtaposition of buried channels and structural highs and their formation caused by focused fluid flow and expulsion of entrained sediments at the seabed.Considering the acoustic and geometrical characteristics of the mounds and comparing them with mound-shaped features from around the world, we conclude that the mounds most likely comprise heterolithic seafloor extrusions of muds and sands from the Agbada Formation with gas and possibly oil in some of the pore space giving rise to the acoustic characteristics. 相似文献
2.
Located on the West Iberian margin, between Cabo Carvoeiro and Cabo da Roca, the Estremadura Spur is a trapezoidal promontory elongated in an east-west direction, extending until the Tore seamount. Recently a field with more than 70 pockmarks was discovered in the NW region of the Estremadura Spur outer shelf (Lourinhã Monocline). Pockmarks are the seabed culminations of fluid migration through the sedimentary column and their characteristic seabed morphologies correspond to cone-shaped circular or elliptical depressions. The characterization of these features and the understanding of the associated fluid escape process are the main objectives of this work. Here we characterize these structures to understand their structural and stratigraphic control based on: 1) Seismic processing and interpretation of the high resolution 2D single-channel sparker seismic dataset, 2) Bathymetric and Backscatter interpretation and 3) ROV direct observation of the seafloor.The analysis of the seismic profiles allowed the identification of six seismic units, disturbed by the migration and accumulation of fluids. The Estremadura Spur outer shelf has been affected by several episodes of fluid migration and fluid escape during the Pliocene-Quaternary that are expressed by a vast number of seabed and buried pockmarks. At present, the pockmarks are mainly inactive, as the seabed pockmarks are covered by recent sediments. It is concluded that the migration of fluids to the seabed occurred over the Pliocene-Quaternary, as indicated by the buried pockmarks at different depths below the seabed. The vertical stacking of various pockmarks suggests a cyclical fluid flow activity that can possibly be the result of the eustatic sea level variations and the subsequent changes of the hydrostatic pressure. 相似文献
3.
W. Hieke A. Camerlenghi M. B. Cita G. A. Dehghani N. Fusi H. B. Hirschleber L. Mirabile C. Müller A. Polonia 《Marine Geophysical Researches》2009,30(3):161-192
In previous publications, the relationship between the Sirte Abyssal Plain as foreland and the Mediterranean Ridge as accretionary
complex was considered to be simple: the foreland is undeformed, the accretionary complex consumes the foreland, the Messinian
evaporites control the internal structure of the growing complex. The compilation of our own and published data results in
a more complex tectonic pattern and a new geodynamic interpretation. The Sirte Abyssal Plain is imprinted by extensional tectonics
which originated independently from and prior to the approaching process of accretion. The structural setting of the pre-Messinian
and Messinian Sirte Abyssal Plain is responsible for the highly variable thickness of Messinian evaporites. The foreland setting
in the Sirte Abyssal Plain also controls the internal structure of the Mediterranean Ridge, at least between the deformation
front and Bannock Basin, following sediment deformation within the accretionary wedge with a dominating inherited SW-NE orientation.
The taper angle of the post-Messinian Mediterranean Ridge is unusually small compared with other accretionary wedges. In the
studied area, within a distance of about 45 km from the deformation front, there is no appreciable dip in the décollement.
Therefore, the slope of the outer 45 km of the Mediterranean Ridge is considered to be caused only by gravitational spreading
of Messinian evaporites deposited on the slope of pre-Messinian accretionary wedge. As a consequence, the Mediterranean Ridge
underlying such slope is interpreted to belong to the foreland. The allochthonous evaporites overlie autochthonous evaporites
of the Sirte Abyssal Plain. The NE-dipping décollement (and thus of the true tectonically driven deformation front) is expected
to initiate at about the present position of Bannock Basin. The Sirte Abyssal Plain, the adjacent Cyrene Seamount and neighbouring
seafloor relief on the African continental margin are considered to be the product of tectonic segmentation of the continental
crust. 相似文献
4.
Differences in fluids origin, creation of overpressure and migration are compared for end member Neogene fold and thrust environments: the deepwater region offshore Brunei (shale detachment), and the onshore, arid Central Basin of Iran (salt detachment). Variations in overpressure mechanism arise from a) the availability of water trapped in pore-space during early burial (deepwater marine environment vs arid, continental environment), and b) the depth/temperature at which mechanical compaction becomes a secondary effect and chemical processes start to dominate overpressure development. Chemical reactions associated with smectite rich mud rocks in Iran occur shallow (∼1900 m, smectite to illite transformation) causing load-transfer related (moderate) overpressures, whereas mechanical compaction and inflationary overpressures dominate smectite poor mud rocks offshore Brunei. The basal detachment in deepwater Brunei generally lies below temperatures of about 150 °C, where chemical processes and metagenesis are inferred to drive overpressure development. Overall the deepwater Brunei system is very water rich, and multiple opportunities for overpressure generation and fluid leakage have occurred throughout the growth of the anticlines. The result is a wide variety of fluid migration pathways and structures from deep to shallow levels (particularly mud dykes, sills, laccoliths, volcanoes and pipes, fluid escape pipes, crestal normal faults, thrust faults) and widespread inflationary-type overpressure. In the Central Basin the near surface environment is water limited. Mechanical and chemical compaction led to moderate overpressure development above the Upper Red Formation evaporites. Only below thick Early Miocene evaporites have near lithostatic overpressures developed in carbonates and marls affected by a wide range of overpressure mechanisms. Fluid leakage episodes across the evaporites have either been very few or absent in most areas. Locations where leakage can episodically occur (e.g. detaching thrusts, deep normal faults, salt welds) are sparse. However, in both Iran and Brunei crestal normal faults play an important role in the transmission of fluids in the upper regions of folds. 相似文献
5.
Stéphanie Dupré Jean Mascle Jean-Paul Foucher François Harmegnies John Woodside Catherine Pierre 《Geo-Marine Letters》2014,34(2-3):153-168
The Menes caldera is a fault-controlled depression (~8 km in diameter) at ~3,000 m water depth in the western province of the Nile deep-sea fan off NW Egypt, comprising seven mud volcanoes (MVs) of which two are active. Based on multichannel and chirp seismic data, temperature profiles, and high-resolution bathymetric data collected during the 2000 Fanil, 2004 Mimes and 2007 Medeco2 expeditions, the present study investigates factors controlling MV morphology, the geometry of feeder channels, and the origin of emitted fluids. The active Cheops and Chephren MVs are 1,500 m wide with subcircular craters at their summits, about 250 m in diameter, generally a few tens of metres deep, and filled with methane-rich muddy brines with temperatures reaching 42 °C and 57 °C respectively. Deployments of CTDs and corers with attached temperature sensors tracked these warm temperatures down to almost 0.5 km depth below the brine lake surface at the Cheops MV, in a feeder channel probably only a few tens of metres wide. Thermogenic processes involve the dissolution of Messinian evaporites by warm fluids likely sourced even deeper, i.e. 1.7 and 2.6 km below the seabed at the Cheops and Chephren MVs respectively, and which ascend along listric faults. Seepage activity appears broadly persistent since the initiation of mud volcanism in the Early Pliocene, possibly accompanied by lateral migration of feeder channels. 相似文献
6.
Differences in fluids origin, creation of overpressure and migration are compared for end member Neogene fold and thrust environments: the deepwater region offshore Brunei (shale detachment), and the onshore, arid Central Basin of Iran (salt detachment). Variations in overpressure mechanism arise from a) the availability of water trapped in pore-space during early burial (deepwater marine environment vs arid, continental environment), and b) the depth/temperature at which mechanical compaction becomes a secondary effect and chemical processes start to dominate overpressure development. Chemical reactions associated with smectite rich mud rocks in Iran occur shallow (∼1900 m, smectite to illite transformation) causing load-transfer related (moderate) overpressures, whereas mechanical compaction and inflationary overpressures dominate smectite poor mud rocks offshore Brunei. The basal detachment in deepwater Brunei generally lies below temperatures of about 150 °C, where chemical processes and metagenesis are inferred to drive overpressure development. Overall the deepwater Brunei system is very water rich, and multiple opportunities for overpressure generation and fluid leakage have occurred throughout the growth of the anticlines. The result is a wide variety of fluid migration pathways and structures from deep to shallow levels (particularly mud dykes, sills, laccoliths, volcanoes and pipes, fluid escape pipes, crestal normal faults, thrust faults) and widespread inflationary-type overpressure. In the Central Basin the near surface environment is water limited. Mechanical and chemical compaction led to moderate overpressure development above the Upper Red Formation evaporites. Only below thick Early Miocene evaporites have near lithostatic overpressures developed in carbonates and marls affected by a wide range of overpressure mechanisms. Fluid leakage episodes across the evaporites have either been very few or absent in most areas. Locations where leakage can episodically occur (e.g. detaching thrusts, deep normal faults, salt welds) are sparse. However, in both Iran and Brunei crestal normal faults play an important role in the transmission of fluids in the upper regions of folds. 相似文献
7.
Gideon Almagor 《Marine Georesources & Geotechnology》2013,31(1):83-105
Abstract The continental margin of northern Sinai and Israel consists of a seaward‐inclined wedge, made up predominantly of foreset beds of mainly Nile‐derived clastics. They overlie seaward‐thickening Messinian (Upper Miocene) evaporites. Detailed bathymetric and seismic surveys reveal large areas of sea floor disturbances off northern Sinai and in several places off Israel, expressed by a complex block topography of the outer continental shelf and slope. These disturbed areas appear to be gigantic, deep‐seated, compound rotational slumps over down‐slope flowing evaporites. Many of the disturbances are above landward lobes of evaporites which fill buried Late Miocene erosion channels of the pre‐Messinian retreat of the sea. Flowage of the evaporites was presumably caused by excessive pore pressures, generated by the Pliocene‐Quaternary overload, in confined layers of the elastics interbedded within the evaporites. 相似文献
8.
In order to understand the structure and evolution of the Mediterranean Ridge accretionary complex, it is necessary to understand the structure and history of its foreland. The Ionian Abyssal Plain is one of the varying types of foreland. The state of knowledge for that is presented. Its contour and detailed relief are described for the first time. Based on published and hitherto unpublished seismic data, information on the thickness of the Plio-Quaternary and on the Messinian evaporites are presented. Of particular interest are data concerning the pre-Messinian reflectors. They indicate a pattern of tilted blocks and horst-like features created in pre-Messinian time by tensional tectonics. Varying subsidence continued, however, during Messinian time and controlled the thickness of evaporites. At some places (e.g. Victor Hensen Seahill) vertical tectonics seem to be still active. The main tectonic structures of the Ionian Abyssal Plain are not related to the process of the present accretion and subduction at the Africa/Eurasia plate boundary but are pre-existing and should influence the internal structure of the Mediterranean Ridge which is still growing at the expense of the foreland. As a consequence of our structural evidence, we favour the following interpretation: the Ionian Abyssal Plain is not a remainder of the Jurassic Tethyan ocean but originated by extensive attenuation of continental crust. 相似文献
9.
The Hind Sandstone Member of the Carboniferous Craven Basin occurs within a thick succession of marine mudstone and is here interpreted as a sandstone injectite complex. Injectites take the form of (i) sills; (ii) upwards emplaced dykes; (iii) downwards emplaced dykes; (iv) a sedimentary laccolith; and (v) sandstone bodies remobilised in-situ. The remobilised and injected sand originated from small turbidite scour fills and potentially a more significant sand body such as a submarine slope gully fill. The sedimentary laccolith appears to jack-up the units it injects, and is filled by sandstone with a chaotic fabric suggestive of brecciation of partly cemented sand. The laccolith and sill-dominated nature are suggestive of relatively shallow remobilisation. Sills are commonly laterally gradational with upwards emplaced dykes, and in some cases these feed apparently downwards emplaced dykes. A series of flow structures are preserved within some of the injectites, and these provide clues to the emplacement history. Crack propagation direction is inferred from the orientation of undulating crests developed on the upper and lower surfaces of injectites. Peak-flow is indicated by scour marks, resembling flute and tool marks, which are superimposed onto these undulating surfaces. Internal flow structures highlighted by pyrite mineralistion record the waning stage of injection. The observed flow structures suggest that the apparent crack propagation direction was generally oblique to the peak flow, and nearly perpendicular to the direction of late-stage fluidised sediment flow. Crack propagation relates to the local stress field, whilst injection flow may be related to the local pore pressure distribution. Recognition of this suite of structures may provide a useful interpretational tool for other injectites in both core and outcrop. Pore fluid overpressure which drove injection developed through the migration of petroleum and mineralising fluids from the underlying Bowland Shales and older limestones. A complex brecciated fracture network within the mudstones underlying the injectites records fluid migration pathways. Sliced blocks and thin sections from injectites reveal flow structures defined by iron pyrite mineralisation. The trigger is here related to growth of compressional structures and associated syn-sedimentary slumps which occur at the same stratigraphic level as the injectites. 相似文献
10.
Morphostructure of the Egyptian Continental Margin: Insights from Swath Bathymetry Surveys 总被引：1，自引：0，他引：1
Jean Mascle Olivier Sardou Lies Loncke Sébastien Migeon Laurent Caméra Virginie Gaullier 《Marine Geophysical Researches》2006,27(1):49-59
In the Eastern Mediterranean, offshore Egypt, the Nile continental margin is characterized by a large deep water turbiditic
system known as the Nile Deep Sea Fan. This post-Miocene terrigenous construction covers an approximately 10 km-thick sedimentary
pile, including 1–3 km of Messinian salt layers. Systematically collected swath bathymetric data proved to be the most powerful
tool to discover, describe and study many sea floor features of this sedimentary construction which reflects competition between
active tectonic, sedimentary, and geochemical processes. Gravity tectonics, triggered by underlying mobile salt layers, construction
of channel-levee systems, the passage of turbidite flows, sedimentary slope failures at various scales, massive mud expulsions
and fluid seepages are all interfering to shape the Nile Deep Sea Fan seabed. 相似文献
11.
A. T. Jones J. M. Kennard G. A. Logan E. Grosjean J. Marshall 《Geo-Marine Letters》2009,29(4):233-248
Multibeam swath bathymetric data collected in 95–120 m water depth on Australia’s North West Shelf revealed two distinct populations
of sand waves: a laterally extensive, low-amplitude composite form comprising superimposed dunes and ripples, and a laterally
restricted form which has unusually high bedform heights and slopes. These large subaqueous sand waves comprise bioclastic
ooid/peloid sand. Significantly, evidence of seabed fluid flow was detected in association with the high-amplitude sand waves.
This evidence includes seabed pockmarks approximately 2–15 m in diameter imaged with side-scan sonar, tubular and massive
carbonate concretions dredged from the seabed, and potential active venting of a fluid plume from the seabed observed during
an underwater camera tow. Molecular and isotopic analyses of carbonate concretions collected from within pockmarks associated
with the high-amplitude sand waves indicate that the fluids from which they precipitated comprise modern seawater and are
not related to thermogenic fluids or microbial gases. The fluid flow is interpreted to be driven by macrotidal currents flowing
over the relatively steep slopes of the high-amplitude sand waves. Pockmarks and carbonate concretions then develop where
the interstitial flows are confined and focused by subsurface ‘mounds’ in a shallow seismic reflector. 相似文献
12.
Our understanding of burial diagenesis within carbonates is often limited by poor constraints on available fluid volumes and geochemistry. However, regional stratigraphic and burial history data are often readily available. Using these data to develop numerical models which couple sedimentological and hydrological basin evolution, we estimate the volumes and geochemistry of fluids that were available to drive dolomitisation and Pb-ore genesis within the Carboniferous, Derbyshire Platform of northern England. Current conceptual models of these processes invoke tectonic release of burial-induced overpressure developed within adjacent Dinantian basins as a drive for reactive fluid flow to the platform. Our simulations show that compaction-driven flow may lead to a supply of fluids that is more complex in its temporal evolution than may be expected. Spatial variations in the rate of fluid expulsion from different sediments lead to a staggered delivery of fluids from different sources. Rapid fluid expulsion within deeper sediments leads to a downwards-decreasing pressure gradient that subsequently draws down fluid from within overlying sediments. Thus, early fluid supply to the platform is sourced from the deep basins while later fluid supply descends from above the platform as well as from the sides. We suggest that such a flow development may have important implications for the relative timing and distribution of a sequence of diagenetic products within the platform. This hypothesis is tested using volume estimates from our simulations. We conclude that although this staggered fluid supply model may be applicable generically, it appears that it is only valid for explaining mineralisation in the Derbyshire Platform. Fluid volumes supplied to the platform are insufficient to explain dolomitisation. Our simulations are supported by a sensitivity analysis that identifies that compaction-driven flow in this system is strongly controlled by the rate of burial and sediment permeabilities within the compacting basins. 相似文献
13.
14.
D. Emery 《Marine and Petroleum Geology》1991,8(4)
A phase of ferroan burial calcite from the Middle Jurassic Lincolnshire Limestone exhibits a systematic spatial arrangement of oxygen isotopic characteristics. Mean δ18O values of the ferroan calcites from each of 15 core and outcrop localities over a study area 25 × 25 km were obtained. These values show a marked depletion from west to east across the study area of approximately 3‰, such that the oxygen isotopic composition of the ferroan calcites can be contoured. The systematic change in oxygen isotopic composition across the study area is believed to have recorded the thermal gradient in the limestone during ferroan calcite precipitation. This thermal gradient can be partially attributed to approximately 200 m of differential burial of the Lincolnshire Limestone across the study area during the Chalk deposition, with a maximum burial of 550 m to the east of the area at this time. A component of up-dip fluid flow (from east to west) through the formation is required to generate the temperature enhancements above those predicted for conduction alone by simple differential burial. Using a finite-difference step computer program, rates of fluid flow during ferroan calcite precipitation are calculated to be approximately 25 m/year. This rate of fluid flow is considerably greater than rates usually predicted for buried sedimentary basins. The causes of such rapid, probably relatively short-lived flow-rates may be the sudden dewatering of adjacent shales, the release of overpressure within the formation of interest, seismic pumping, or fluid circulation round a supracrustal convective loop. 相似文献
15.
The morphologies and genesis of mega-pockmarks near the Xisha Uplift, South China Sea 总被引：6，自引：0，他引：6
Qiliang Sun Shiguo WuMartin Hovland Peng LuoYintao Lu Tailai Qu 《Marine and Petroleum Geology》2011,28(6):1146-1156
Pockmarks are normally regarded to be manifestations of fluids escape through the seabed. Kilometer-wide depressions, here called mega-pockmarks occur as widespread features near the Xisha Uplift, northern South China Sea. Most of the pockmarks observed in this area are multi-kilometers and much larger than normal-pockmarks reported worldwide. The maximum diameter observed is 3210 m and the maximum depth observed is 165.2 m based on multibeam data and 2D seismic data. The pockmarks are circular, elliptical and crescentic in plan view. Seismic profiles show that the genesis of pockmarks is related to fluid (gas and/or pore water) escape. According to the fluids pathways, the pockmarks fall into four types: (1) gas chimney-related; (2) depositional boundary-related; (3) gas chimney and inclined structure (fault)-related; (4) inclined structure-related. Bottom currents are strong and complex in the study area. The multibeam data and seismic profiles indicate that they may play an important role on extension, maintenance and shaping of pockmarks. The research of the study area is in its initial stage, and the identification of these features as indicators of fluid flow is probably useful for hydrocarbon exploration. 相似文献
16.
《Marine Geology》1999,153(1-4):147-160
Magnetostratigraphic and biostratigraphic results are presented from Neogene deposits in the Taza–Guercif Basin, located at the southern margin of the Rifian Corridor in Morocco. This corridor was the main marine passageway which connected the Mediterranean with the Atlantic during Messinian times. Correlation of the biostratigraphy and polarity sequence of the Taza–Guercif composite section to the astronomical time scale, allows an accurate dating of three subsequent events in the Rifian Corridor. (1) The oldest marine sediments marking the opening of the Rifian Corridor were deposited at 8 Ma. At this age, a deep (600 m) marine basin developed in the Taza–Guercif area, marked by deposition of precession-controlled turbidite–marl cycles. (2) Paleodepth reconstructions indicate that a rapid (5 m/ka) shallowing of the marine corridor took place at the Tortonian/Messinian boundary, at an age of 7.2 Ma. This shallowing phase is primarily related to active tectonics, although a small glacio-eustatic sea level lowering also took place. (3) The Taza–Guercif Basin was emergent at an age of 6.0 Ma and, subsequently, continental sedimentation continued well into the Early Pliocene. We suggest that shallowing and restricting the marine passageway through the Rifian Corridor actually initiated the Messinian salinity crisis, well before the deposition of the Messinian evaporites in the Mediterranean. 相似文献
17.
The Levantine Basin in the South-eastern Mediterranean Sea is a world class site for studying the initial stages of salt tectonics driven by differential sediment load, because the Messinian evaporites are comparatively young, the sediment load varies along the basin margin, they are hardly tectonically overprinted, and the geometry of the basin and the overburden is well-defined. In this study we analyse depositional phases of the evaporites and their structural evolution by means of high-resolution multi-channel seismic data. The basinal evaporites have a maximum thickness of about 2 km, precipitated during the Messinian Salinity Crisis, 5.3–5.9 Ma ago. The evaporite body is characterized by 5 transparent layers sequenced by four internal reflections. We suggest that each of the internal reflection bands indicate a change of evaporite facies, possibly interbedded clastic sediments, which were deposited during temporal sea level rises. All of these internal reflections are differently folded and distorted, proving that the deformation was syn-depositional. Thrust angles up to 14° are observed. Backstripping of the Pliocene–Quaternary reveals that salt tectonic is mainly driven by the sediment load of the Nile Cone. The direction of lateral salt displacement is mainly SSW–NNE and parallel to the bathymetric trend. Apparent rollback anticlines off Israel result rather from differential subsidence than from lateral salt displacement. In the south-eastern basin margin the deposition of the Isreali Slump Complex (ISC) is coeval with the onset of salt tectonic faulting, suggesting a causal link between slumping processes and salt tectonics.
The superposition of ‘thin-skinned’ tectonics and ‘thick-skinned’ tectonics becomes apparent in several locations: The fold belt off the Israeli Mediterranean slope mainly results from active strike-slip tectonics, which becomes evident in faults which reach from the seafloor well below the base of the evaporites. Owing to the wrenching of the crustal segments which are bounded by deep-rooted fault lines like the Damietta–Latakia, Pelusium and Shelf Edge Hinge line the setting is transpressional south of 32°N, where the fault lines bend further towards the west. This adds a component of ‘thick-skinned’ transpression to the generally ‘thin-skinned’ compressional regime in the basin. Above 1.5 km of evaporites, a mud volcano is observed with the mud source seemingly within the evaporite layer. At the eastern Cyprus Arc, the convergence zone of the African and the Anatolian plates, deep-rooted compression heavily deformed the base of the evaporites, whereas at the Eratosthenes Seamount mainly superficial compression affecting the Post-Messinian sediments and the top of the evaporites is observed. 相似文献
18.
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
19.
G. Jané A. Maestro G. Ercilla J. López-Martínez J.R. De Andrés D. Casas D. González-Aller M. Catalán-Morollón 《Marine and Petroleum Geology》2010
A total of 445 pockmarks were observed on the upper continental slope of the northwest corner of the Iberian Peninsula (the Ortegal Spur area) by swath bathymetric and ultrahigh resolution seismic data. The pockmarks are U-, V- and W-shaped and have terraces or indentations in cross-section, and are dish-shaped (circular to oval) in plan view. They occur on the surface of the seabed and buried within the Plio-Quaternary and Neogene sediments. Four types of pockmarks were identified and mapped on the basis of their plan-view and cross-section morphology: regular, irregular, asymmetric and composite. The concentration of pockmarks is attributed to seepage of fluids migrating up-dip from deeper parts of the sedimentary basin. A linear high-density concentration with a NNW to N, NE and ESE trend of pockmarks is observed above inferred basement faults that do not affect the Quaternary succession. These pockmarks are thus caused by seepage of thermogenic gas and/or other pore fluids from deeper Late Cretaceous units, and their distribution may help to improve our understanding of the fluid system and migration regime in this part of the Galicia continental margin. 相似文献
20.
Two distinct series of slumps deform the upper part of the sedimentary sequence along the continental margin of the Levant.
One series is found along the base of the continental slope, where it overlies the disrupted eastern edge of the Messinian
evaporites. The second series of slumps transects the continental margin from the shelf break to the Levant Basin. It seemed
that the two series were triggered by two unrelated, though contemporaneous, processes. The shore-parallel slumps were initiated
by basinwards flow of the Messinian salt, that carried along the overlying Plio-Quaternary sediments. Seawater that percolated
along the detachment faults dissolved the underlying salt to form distinctly disrupted structures. The slope-normal slumps
are located on top of large canyons that cut into the pre-Messinian sedimentary rocks. A layer of salt is found in the canyons,
and the Plio-Quaternary sediments were deposited on that layer. The slumps are bounded by large, NW-trending faults where
post-Messinian faulted offset was measured. We presume that the flow of the salt in the canyons also drives the slope-normal
slumps. Thus thin-skinned halokynetic processes generated the composite post-Tortonian structural patterns of the Levant margin.
The Phoenician Structures are a prime example of the collapse of a distal continental margin due to the dissolution of a massive
salt layer. 相似文献