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1.
New classification system for mass transport complexes in offshore Trinidad   总被引：3，自引：1，他引：2  
This paper delineates our use of 10 708 km2 of three‐dimensional (3D) seismic data from the continental margin of Trinidad and Tobago West Indies to describe a series of mass transport complexes (MTCs) that were deposited during the Plio‐Pleistocene. This area, situated along the obliquely converging boundary of the Caribbean/South American plates and proximal to the Orinoco Delta, is characterized by catastrophic shelf‐margin processes, intrusive/extrusive mobile shales and active tectonism. Extensive mapping of different stratigraphic intervals of the 3D seismic survey reveals several MTCs that range in area from 11.3 to 2017 km2. Three types of MTCs are identified: (1) shelf‐attached systems that were fed by shelf‐edge deltas whose sediment input is controlled by sea‐level fluctuations and sedimentation rates; (2) slope‐attached systems, which occur when upper‐slope sediments catastrophically fail owing to gas‐hydrate disruptions and/or earthquakes and (3) locally detached systems, formed when local instabilities in the seafloor trigger relatively small collapses. Such classification of the relationship between slope mass failures and sourcing regions enables a better understanding of the nature of initiation, length of development history and petrography of such MTCs. 3D seismic enables more accurate calculation of deposit volumes, improves deposit imaging, and, thus, increases the accuracy of physical and computer simulations of mass failure processes.  相似文献   

2.
The Quaternary to late Pliocene sedimentary succession along the margin of the South Caspian Basin contains numerous kilometre‐scale submarine slope failures, which were sourced along the basin slope and from the inclined flanks of contemporaneous anticlines. This study uses three‐dimensional (3D) seismic reflection data to visualise the internal structure of 27 mass transport deposits and catalogues the syndepositional structures contained within them. These are used to interpret emplacement processes occurring during submarine slope failure. The deposits consist of three linked structural domains: extensional, translational and compressive, each containing characteristic structures. Novel features are present within the mass transport deposits: (1) a diverging retrogression of the headwall scarp; (2) the absence of a conventional headwall scarp around growth stratal pinch outs; (3) restraining bends in the lateral margin; (4) a downslope increase in the throw of thrust faults. The results of this study shed light on the deformation that occurred during submarine slope failure, and highlight an important geological process in the evolution of the South Caspian Basin margin.  相似文献   

3.
《Basin Research》2018,30(5):942-964
Mass wasting is triggered on many continental slopes by a number of mechanisms, including seismic shaking, high sedimentation rates, the presence of weak geological units and gas hydrate dissociation. In this study, the morphology of a Late Miocene–Early Pliocene mass‐transport complex (MTC) on the Utgard High is unravelled and discussed in relation to possible trigger mechanisms. The approach used here includes 3D seismic interpretation and the analysis of variance attribute maps. The interpreted MTC is located on the crest and flanks of the Utgard High and is composed of three mass‐transport deposits with seismic characters varying from transparent and chaotic seismic facies at the base to slightly deformed layers composed of mounds and rafted blocks in the middle and chaotic to transparent reflections at the top. Lithologically, the MTC consists predominantly of claystone with high gamma ray and low density and resistivity values, demonstrating that the associated mounds represent remobilized ooze sediments. A vertical stack of six magmatic sills emplaced from 55.6 to 56.3 Ma into the Upper Cretaceous shales is interpreted at depths of 3,000–5,500 ms two‐way travel time (TWTT). In association with these magmatic sills are several hydrothermal vent complexes that interacted with the top MTC horizon, signifying that episodic and secondary fluid‐venting events might be the principal mechanism facilitating mass wasting in the study area. In addition, the remobilization of ooze sediments into mounds is hypothesized to be dependent on fluids and clayey layers. As a corollary of this work, the importance of relict and recurrent episodes of fluid flow in the Vøring Basin and their influence on the geotechnical integrity of the overburden and later mass wasting is established.  相似文献   

4.
The sediments of the Upper Cretaceous to lower Palaeogene Chalk Group were deposited through a wide range of depositional processes. Chalk was originally formed by settlement of coccolithophorid skeletal remains from suspension in the water column, with bottom currents redistributing the sediment shortly after deposition. Locally, tilting of the sea‐floor resulted in mass‐movement of chalk at scales varying from decimetre‐thick turbidites to slumps and slide sheets that were up to hundreds of metres thick. Syn‐depositional tectonic activity, therefore, constituted an important control on chalk facies. To study this relation in more detail, a three‐dimensional (3D)‐seismic stratigraphical analysis was carried out, comparing two study areas that experienced contrasting syn‐depositional tectonic evolutions. The Vlieland offshore area, which underwent gradual subsidence and westward tilting during deposition of the Chalk Group, is characterised by parallel and continuous reflections thought to represent pelagic chalk deposits. In the Dutch Central Graben, which was tectonically inverted during the Late Cretaceous to early Palaeogene, discontinuous and irregular seismic reflections that indicate large‐scale reworking of sediment are found. The improved image quality of 3D‐ vs. 2D‐seismic data allowed us to study the detailed geometry of allochthonous chalk bodies and aided the identification and tracing of the often subtle intra‐Chalk Group unconformities, resulting in a subdivision of the Chalk Group into seven seismic sequences.  相似文献   

5.
《Basin Research》2018,30(Z1):210-227
Gas chimneys are common in offshore petroliferous basins, but little known on land where seismic columnar anomalies are often attributed as poor data quality or processing artefacts. This study utilizes high‐quality 3D seismic data to document a seismic columnar anomaly penetrating through the Miocene heterolithic submarine fan‐deltaic infill of the Carpathian Foredeep. The interpreted gas chimney exhibits vertically clustered velocity push‐down features throughout the attenuated amplitude column accompanied by gas shows in well tests, has its root in gas‐bearing Palaeozoic interval and culminates in an anomalous geochemical gas record at soil level. The chimney system, ca 2 km in height and 500‐m wide, begins above the flank of a rotational bedrock fault‐block and extends vertically along a fault‐controlled conduit. At shallower levels, it passes upwards into amplitude wipeout zones that spread laterally around and partly across thin, gas‐charged reservoirs showing bright spots associated with an AVO response. At shallow levels, gas pathways through muddy slope and deltaic clinoforms are not imaged in low‐fold regions of the seismic volume. The surface geochemical anomalies, in contrast to the microbial methane signature of the Miocene succession, show significant enrichment in higher alkanes and alkenes with C2H6/C3H8 ratios indicative of a deep‐sourced, thermogenic gas or gas condensate. These anomalies form a semi‐enclosed halo around the chimney. Despite the juxtaposition of biogenic and thermogenic methane, the chimney structure imaged on seismic data supports a causal link of gases derived from Palaeozoic source rocks ascending to the surface.  相似文献   

6.
A subsurface evacuation model for submarine slope failure   总被引：1，自引：0，他引：1  
Analysis of three-dimensional (3D) seismic reflection data from the Norwegian continental margin provides an insight into an unusual, buried submarine slope failure, which occurred adjacent to the later Holocene-age Storegga Slide. The identified failure, informally named the 'South Vøring Slide' (SVS), occurs in fine-grained hemipelagic and contourite sediments on a slope of 0.5°, and is characterised by a deformed seismic facies unit consisting of closely spaced pyramidal blocks and ridges bound by small normal faults striking perpendicular to the slope. The SVS contrasts with other previously described submarine slope failures in that it cannot be explained by a retrogressive model. The defining characteristic is the high relative volume loss. The area affected by sliding has thinned by some 40%, seen in combination with very modest extension in the translation direction, with line length balancing yielding an extension value of only 4.5%. The volume loss is explained by the mobilisation of an approximately 40 m thick interval at the lower part of the unit and its removal from beneath a thin overburden, which subsequently underwent extensional fragmentation. Evidence for the mobilisation of a thick fine-grained interval in the development of a submarine slope failure from a continental margin setting may have implications for the origins of other large-scale slope failures on the Norwegian margin and other glacially influenced margins worldwide.  相似文献   

7.
At high‐latitude continental margins, large‐scale submarine sliding has been an important process for deep‐sea sediment transfer during glacial and interglacial periods. Little is, however, known about the importance of this process prior to the arrival of the ice sheet on the continental shelf. Based on new two‐dimensional seismic data from the NW Barents Sea continental margin, this study documents the presence of thick and regionally extensive submarine slides formed between 2.7 and 2.1 Ma, before shelf‐edge glaciation. The largest submarine slide, located in the northern part of the Storfjorden Trough Mouth Fan (TMF), left a scar and is characterized by an at least 870‐m‐thick interval of chaotic to reflection‐free seismic facies interpreted as debrites. The full extent of this slide debrite 1 is yet unknown but it has a mapped areal distribution of at least 10.7 × 103 km2 and it involved >4.1 × 103 km3 of sediments. It remobilized a larger sediment volume than one of the largest exposed submarine slides in the world – the Storegga Slide in the Norwegian Sea. In the southern part of the Storfjorden TMF and along the Kveithola TMF, the seismic data reveal at least four large‐scale slide debrites, characterized by seismic facies similar to the slide debrite 1. Each of them is ca. 295‐m thick, covers an area of at least 7.04 × 103 km2 and involved 1.1 × 103 km3 of sediments. These five submarine slide debrites represent approximately one quarter of the total volume of sediments deposited during the time 2.7–1.5 Ma along the NW Barents Sea. The preconditioning factors for submarine sliding in this area probably included deposition at high sedimentation rate, some of which may have occurred in periods of low eustatic sea‐level. Intervals of weak contouritic sediments might also have contributed to the instability of part of the slope succession as these deposits are known from other parts of the Norwegian margin and elsewhere to have the potential to act as weak layers. Triggering was probably caused by seismicity associated with the nearby and active Knipovich spreading ridge and/or the old tectonic lineaments within the Spitsbergen Shear Zone. This seismicity is inferred to be the main influence of the large‐scale sliding in this area as this and previous studies have documented that sliding have occurred independently of climatic variations, i.e. both before and during the period of ice sheets repeatedly covering the continental shelf.  相似文献   

8.
This paper presents a three‐dimensional (3D) seismic analysis of sediment remobilization and fluid migration in a 2000‐km2 area above the Gjallar Ridge located in the Vøring Basin, offshore Norway. Three distinct types of mounded structures have been identified as resulting from focused fluid/gas migration and associated mud remobilization and intrusion. Type A structures are gently mounded, and we infer that these structures formed because of in situ remobilization of Middle Eocene to Lower–Middle Oligocene fine‐grained sediments in response to fluid and minor sediment injection via deep‐seated normal faults. Type B structures comprise relatively steep‐sided mounds and are restricted to the pre‐Miocene interval. They are often located above narrow zones of discontinuous low‐amplitude reflections resembling gas chimneys. Some of the Type B structures are associated with stacked amplitude anomalies and possible mud volcanoes at the base Pleistocene indicating their long‐term significance as vertical fluid conduits. Type C structures comprise discrete mound features that seem to jack up the Top Palaeocene (Top Brygge) horizon. These are similar to hydrothermal mounds found elsewhere on the Norwegian Margin and associated with igneous sill intrusion during North Atlantic breakup. This study highlights the utility of 3D seismic data for mapping of fluid and sediment mobilization through time over large basinal areas.  相似文献   

9.
《Basin Research》2017,29(2):149-179
Integrated analysis of high‐quality three‐dimensional (3D) seismic, seabed geochemistry, and satellite‐based surface slick data from the deep‐water Kwanza Basin documents the widespread occurrence of past and present fluid flow associated with dewatering processes and hydrocarbon migration. Seismic scale fluid flow phenomena are defined by seep‐related seafloor features including pockmarks, mud or asphalt volcanoes, gas hydrate pingoes, as well as shallow subsurface features such as palaeo‐pockmarks, direct hydrocarbon indicators (DHIs), pipes and bottom‐simulating reflections (BSRs). BSR‐derived shallow geothermal gradients show elevated temperatures attributed to fluid advection along inclined stratigraphic carrier beds around salt structures in addition to elevated shallow thermal anomalies above highly conductive salt bodies. Seabed evidences of migrated thermogenic hydrocarbons and surface slicks are used to differentiate thermogenic hydrocarbon migration from fluid flow processes such as dewatering and biogenic gas migration. The analysis constrains the fluid plumbing system defined by the three‐dimensional distribution of stratigraphic carriers and seal bypass systems through time. Detailed integration and iterative interpretation have confirmed the presence of mature source rock and effective migration pathways with significant implications for petroleum prospectivity in the post‐salt interval. Integration of seismic, seabed geochemistry and satellite data represents a robust method to document and interpret fluid flow phenomena along continental margins, and highlights the importance of integrated fluid flow studies with regard to petroleum exploration, submarine geohazards, marine ecosystems and climate change.  相似文献   

10.
A new polygonal fault system has been identified in the Lower Congo Basin. This highly faulted interval (HFI), 700±50 m thick, is characterized by small extensional faults displaying a polygonal pattern in plan view. This kind of fracturing is attributed to volumetric contraction of sediments during early stages of compaction at shallow burial depth. 3‐D seismic data permitted the visualization of the progressive deformation of furrows during burial, leading to real fractures, visible on seismic sections at about 78 m below seafloor. We propose a new geometrical model for volumetrical contraction of mud‐dominated sediments. Compaction starts at the water–sediment interface by horizontal contraction, creating furrows perpendicular to the present day slope. During burial, continued shrinkage evolves to radial contraction, generating hexagonal cells of dewatering at 21 m below seafloor. With increasing contraction, several faults generations are progressively initiated from 78 to 700 m burial depth. Numerous faults of the HFI act as highly permeable pathways for deeper fluids. We point out that pockmarks, which represent the imprint of gas, oil or pore water escape on the seafloor, are consistently located at the triple‐junction of three neighbouring hexagonal cells. This is highly relevant for predictive models of the occurrence of seepage structures on the seafloor and for the sealing capacity of sedimentary cover over deeper petroleum reservoirs.  相似文献   

11.
Evolution of the Himalayan foreland basin, NW India   总被引：3，自引：0，他引：3  
This paper provides new information on the evolution of the Himalayan foreland basin in the under‐reported region of the Kangra and Subathu sub‐basins, NW India. Comparisons are made with the better documented co‐eval sediments of Nepal and Pakistan to build up a broader picture of basin development. In the Subathu sub‐basin, shallow marine sediments of the Palaeocene–lower Lutetian Subathu Formation are unconformably overlain by the continental alluvial Dagshai and Kasauli Formations and Siwalik Group. The start of continental deposition is now dated at younger than 31 Ma from detrital zircon fission track data, thereby defining the duration of this major unconformity, which runs basin‐wide along strike. Final exhumation of these basin sediments, as thrusting propagated into the basin, occurred by 5 Ma constrained from detrital apatite fission track data. In the Kangra sub‐basin, the Subathu Formation is not exposed and the pre‐Siwalik sediments consist of the Dharamsala Group, interpreted as the deposits of transverse‐draining rivers. In this area, there is no evidence of westerly axial drainage as documented for coeval facies in Nepal. Similar to data reported along strike, facies analysis indicates that the sediments in NW India represent the filled/overfilled stages of the classic foreland basin evolutionary model, and the underfilled stage is not represented anywhere along the length of the basin studied to date.  相似文献   

12.
《Basin Research》2018,30(Z1):424-436
Industry 2D and 3D seismic data across the North Taranaki Basin displays two listric normal faults that formed during Pliocene shelf edge clinoform progradation. The faults die out in the down‐transport direction with no evidence for contractional structures, except for two small thrust faults in one narrow zone. When active, the detachments lay at depths of about 1000 m below the seafloor. The overlying section had high initial porosities (30–60%). It is estimated that loss of about 17–20% pore volume by lateral compaction, and fluid expulsion over a distance of about 4–6 km in the transport direction occurred in place of folding and thrusting. Seismic and well evidence for abnormally highly compacted shales suggests there is about 6% less porosity than expected for in the prekinematic section, which possibly represents a residual of the porosity anomaly caused by lateral compaction. The observations indicate significant shortening (~20%) by lateral compaction and probably some layer parallel thickening are important deformation mechanisms in near‐surface deepwater sediments that needs to be incorporated into shortening estimates and ‘balanced’ cross‐sections. A key factor in listric fault initiation near the base of slope is inferred to be transient, increased pore fluid pressure due to lateral expulsion of fluids from beneath the prograding Giant Foresets Formation.  相似文献   

13.
The movement of magma through the shallow crust and the impact of subsurface sill complexes on the hydrocarbon systems of prospective sedimentary basins has long been an area of interest and debate. Based on 3D seismic reflection and well data, we present a regional analysis of the emplacement and magmatic plumbing system of the Palaeogene Faroe‐Shetland Sill Complex (FSSC), which is intruded into the Mesozoic and Cenozoic sequences of the Faroe‐Shetland Basin (FSB). Identification of magma flow directions through detailed seismic interpretation of approximately 100 sills indicates that the main magma input zones into the FSB were controlled primarily by the NE–SW basin structure that compartmentalise the FSB into its constituent sub‐basins. An analysis of well data shows that potentially up to 88% of sills in the FSSC are <40 m in thickness, and thus below the vertical resolution limit of seismic data at depths at which most sills occur. This resolution limitation suggests that caution needs to be exercised when interpreting magmatic systems from seismic data alone, as a large amount of intrusive material could potentially be missed. The interaction of the FSSC with the petroleum systems of the FSB is not well understood. Given the close association between the FSSC and potential petroleum migration routes into some of the oil/gas fields (e.g. Tormore), the role the intrusions may have played in compartmentalisation of basin fill needs to be taken fully into account to further unlock the future petroleum potential of the FSB.  相似文献   

14.
This case study of growth faults and associated deltaic sedimentation in the shallow‐offshore Niger Delta uses an integrated analysis of three‐dimensional (3D)‐seismic coherence facies and wireline data that supports an evaluation of the sedimentary response to delta tectonics. The study area comprises four fault blocks bounded by a set of kilometre‐scale, basinward‐dipping, synsedimentary normal faults. Correlation of highly variable growth stratigraphy across faults was achieved by a systematic visualization and interpretation of series of coherence horizon‐slices: the detection and matching of erosive and depositional patterns (e.g. channels) across faults allowed the establishment of sedimentology‐controlled links between diverse footwall and hanging‐wall growth successions. At the same time, this interpretation approach helped to visualize seismic‐sedimentological and seismic‐geomorphological features survey‐wide at all depth levels. The integration of this extensive 3D database with lithology information from wireline logs provides a powerful tool for subsurface sedimentology interpretation. Synoptic analysis of the 3D‐seismic sedimentology interpretation with stratigraphy based fault‐kinematic analysis using throw vs. depth plots (Th–Z plots) enabled a discussion of the relation between delta tectonics and sedimentary‐system development, and the evaluation of the Th–Z method for subsurface‐lithology prediction. The interpretation results document that both motion analysis of synsedimentary deltaic faults and Th–Z‐based lithology prediction are only feasible when supported by detailed 3D information on palaeoenvironment and palaeotopography at and around studied fault systems. We therefore recommend the use of fast‐track fault‐kinematic and subsurface‐lithology predictions based on Th–Z plots only when supported by comprehensive 3D seismic‐sedimentological interpretations.  相似文献   

15.
We use three‐dimensional (3D) seismic reflection and magnetic data to interpret and describe the 3D geometry of igneous dykes in the southern North Sea. The dykes were emplaced into Paleozoic and Mesozoic sediments and have a common upper termination in Early Tertiary sediments. We interpret the dykes to be part of the British Tertiary volcanic province and estimate the age of the dykes to be 58 Ma. The dykes are characterized by a narrow 0.5–2 km wide vertical disturbance of seismic reflections that have linear plan view geometry. Negative magnetic anomalies directly align with the vertical seismic disturbance zones and indicate the presence of igneous material. Linear coalesced collapse craters are found above the dykes. The collapse craters have been defined and visualized in 3D. Collapse craters have formed above the dyke due to the release of volatiles at the dyke tip and resulting volume loss. Larger craters have potentially formed due to explosive phreatomagmatic interaction between magma and pore water. The collapse craters are a new Earth analogue to Martian pit chain craters.  相似文献   

16.
3D seismic technology: the geological 'Hubble'   总被引：3，自引：0，他引：3  
The proliferation of three‐dimensional (3D) seismic technology is one of the most exciting developments in the Earth Sciences over the past century. 3D reflection seismic data provide interpreters with the ability to map structures and stratigraphic features in 3D detail to a resolution of a few tens of metres over thousands of square kilometres. It is a geological ‘Hubble’, whose resolving power has already yielded some fascinating (and surprising) insights and will continue to provide a major stimulus for research into geological processes and products for many decades to come. Academic and other research institutions have a major role to play in the use of this data by exploiting the enormous volume of geological information contained in 3D seismic surveys. This paper reviews some of the recent advances in basin analysis made using the medium of 3D seismic data, focusing on the fields of structural and sedimentary geology, fluid–rock interactions and igneous geology. It is noted that the increased resolution of the 3D seismic method provided the essential catalyst necessary to stimulate novel observations and discover new geological structures such as mud diapir feeders, km‐long gas blow‐out pipes, giant pockmarks and sandstone intrusions, and to capture the spatial variability of diagenetic fronts. The UKs first impact crater was also discovered using 3D seismic data. The potential for future developments in this field of geophysical interpretation is considerable, and we anticipate that new discoveries will be made in many years to come.  相似文献   

17.
An efficient high‐resolution (HR) three‐dimensional (3D) seismic reflection system for small‐scale targets in lacustrine settings was developed. In Lake Geneva, near the city of Lausanne, Switzerland, the offshore extension of a complex fault zone well mapped on land was chosen for testing our system. A preliminary two‐dimensional seismic survey indicated structures that include a thin (<40 m) layer of subhorizontal Quaternary sediments that unconformably overlie south‐east‐dipping Tertiary Molasse beds and a major fault zone (Paudèze Fault Zone) that separates Plateau and Subalpine Molasse (SM) units. A 3D survey was conducted over this test site using a newly developed three‐streamer system. It provided high‐quality data with a penetration to depths of 300 m below the water bottom of non‐aliased signal for dips up to 30° and with a maximum vertical resolution of 1.1 m. The data were subjected to a conventional 3D processing sequence that included post‐stack time migration. Tests with 3D pre‐stack depth migration showed that such techniques can be applied to HR seismic surveys. Delineation of several horizons and fault surfaces reveals the potential for small‐scale geologic and tectonic interpretation in three dimensions. Five major seismic facies and their detailed 3D geometries can be distinguished. Three fault surfaces and the top of a molasse surface were mapped in 3D. Analysis of the geometry of these surfaces and their relative orientation suggests that pre‐existing structures within the Plateau Molasse (PM) unit influenced later faulting between the Plateau and SM. In particular, a change in strike of the PM bed dip may indicate a fold formed by a regional stress regime, the orientation of which was different from the one responsible for the creation of the Paudèze Fault Zone. This structure might have later influenced the local stress regime and caused the curved shape of the Paudèze Fault in our surveyed area.  相似文献   

18.
This paper uses three‐dimensional (3D) seismic data from the continental margin of Israel (Eastern Mediterranean) to describe a series of slump deposits within the Pliocene and Holocene succession. These slumps are linked to the dynamics of subsidence and deformation of the transform margin of the eastern Mediterranean. Repeated slope failure occurred during the post‐Messinian, when a clay‐dominated progradational succession was forming. This resulted in large‐scale slump deposits accumulating in the mid‐lower slope region of the basin at different stratigraphic levels. It is probable that the slumps were triggered by a combination of slope oversteepening, seismic activity and gas migration. The high spatial resolution provided by the 3D seismic data has been used to define a spectrum of internal and external geometries within slump deposits. Importantly, we recognise two main zones for many of the slumps on this margin: a depletion zone and an accumulation zone. The former is characterised by extension and translation, and the latter by complex imbricate thrusts and fold systems. Volume‐based seismic attribute analysis reveals transport directions within the slump deposits, which are predominately downslope, but with subtle variations particularly at the lateral margins. Basal shear surfaces are observed to ramp both up and down stratigraphy. Slump evolution occurs both by retrogressive upslope failure, and by downslope propagation (out‐of‐sequence) failure. Slump anatomy and the combination of factors responsible for slump failure and transport are relatively poorly understood, mainly because of the limited 3D of outcrop control; hence, this subsurface study is an example of how improved understanding of the mechanisms and products can be obtained using this 3D seismic methodology in unstable margin areas.  相似文献   

19.
The Matakaoa Debris Flow (MDF) is a 200‐km‐long mass‐transport deposit resulting from the failure of the Matakaoa continental margin, northeast New Zealand, ca. 38–100 ky ago. In this study, high‐quality bathymetric and seismic reflection data are used to identify the morpho‐structural characters that reflect the kinematics of the MDF, as well as its interactions with basin sediments. We demonstrate how the transport energy, together with the local topography led to the present geometry and complex structure of the MDF deposits. The remarkable transport energy of the MDF is demonstrated by its dynamic impact on adjacent sedimentary series, including erosion of the substratum, shearing and compressional deformation. In the proximal zone of transport, momentous substratum erosion, demonstrated by giant tool marks and truncated sediments at the base of the debrite, triggered the excavation of a large volume (>200 km3) of basin sediments. The size of transported blocks (up to 3‐km long) is used to estimate the matrix yield strength in an early stage of transport. In the distal zone of transport, 100 km north of the source, seismic profiles show the propagation of thrust structures from the MDF into adjacent basin sediments. This study highlights that the remarkable volume of 2000 km3 of deposits partly resulted from the propagation of compressive structures within the basin sedimentary series to the front of the debrite.  相似文献   

20.
High‐resolution seismic imaging and coring in Lago Fagnano, located along a plate boundary in Tierra del Fuego, have revealed a dated sequence of Holocene mass‐wasting events. These structures are interpreted as sediment mobilizations resulting from loading of the slope‐adjacent lake floor during mass‐flow deposition. More than 19 mass‐flow deposits have been identified, combining results from 800 km of gridded seismic profiles used to site sediment cores. Successions of up to 6‐m thick mass‐flow deposits, pond atop the basin floor and spread eastward and westward following the main axis of the eastern sub‐basin of Lago Fagnano. We developed an age model, on the basis of information from previous studies and from new AMS‐14C ages on cored sediments, which allows us to establish a well‐constrained chronologic mass‐wasting event‐catalogue covering the last ～12 000 years. Simultaneously triggered, basin‐wide lateral slope failure and the formation of multiple debris flow and postulated megaturbidite deposits are interpreted as the fingerprint of paleo‐seismic activity along the Magallanes‐Fagnano transform fault that runs along the entire lake basin. The slope failures and megaturbidites are interpreted as recording large earthquakes occurring along the transform fault since the early Holocene. The results from this study provide new data about the frequency and possible magnitude of Holocene earthquakes in Tierra del Fuego, which can be applied in the context of seismic hazard assessment in southernmost Patagonia.  相似文献   

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