首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 78 毫秒
1.
The northeastern high-latitude North Atlantic is characterised by the Bellsund and Isfjorden fans on the continental slope off west Svalbard, the asymmetrical ultraslow Knipovich spreading ridge and a 1,000 m deep rift valley. Recently collected multichannel seismic profiles and bathymetric records now provide a more complete picture of sedimentary processes and depositional environments within this region. Both downslope and alongslope sedimentary processes are identified in the study area. Turbidity currents and deposition of glacigenic debris flows are the dominating downslope processes, whereas mass failures, which are a common process on glaciated margins, appear to have been less significant. The slide debrite observed on the Bellsund Fan is most likely related to a 2.5–1.7 Ma old failure on the northwestern Barents Sea margin. The seismic records further reveal that alongslope current processes played a major role in shaping the sediment packages in the study area. Within the Knipovich rift valley and at the western rift flank accumulations as thick as 950–1,000 m are deposited. We note that oceanic basement is locally exposed within the rift valley, and that seismostratigraphic relationships indicate that fault activity along the eastern rift flank lasted until at least as recently as 1.5 Ma. A purely hemipelagic origin of the sediments in the rift valley and on the western rift flank is unlikely. We suggest that these sediments, partly, have been sourced from the western Svalbard—northwestern Barents Sea margin and into the Knipovich Ridge rift valley before continuous spreading and tectonic activity caused the sediments to be transported out of the valley and westward.  相似文献   

2.
Approximately 1000 km of high resolution sleeve-gun array transects on the North Sea Fan, located at the mouth of the Norwegian Channel, reveal three dominant styles of sedimentation within a thick (> 900 m) Quaternary sediment wedge comprising numerous sequences. These are interpreted as: terrigenous hemipelagic sedimentation, large scale translational slides, and aprons of glaciogenic debris flow deposits contributing to considerable fan construction. Four large, buried translational slides involved sediment volumes upwards of 3000 km3 each and preceded the similarly dimensioned “first” Storegga Slide on the NE fan flank. Several thick (> 100 m) terrigenous hemipelagic deposits apparently represent long-lived (150–200 kyr) periods of sedimentation whose distribution indicates fan input via the Norwegian Channel. The upper sequences are each made upper sequences are each made up of one or several thick (> 100 m) aprons comprising stacked lensoid and/or lobate forms which range from 2 to 40 km in width and 15 to 60 m in thickness. They characterize debris flows attributed to periodic input from several phases of a Norwegian Channel ice stream reaching the shelf edge. Subsidence in the outer Norwegian Channel allowed preservation of several glaciation cycles represented by sheet erosion-bounded tills and progradational units. Much of the shelf/slope transition has been preserved, allowing a preliminary chronology of the fan sequences through correlation with borehole sediments in the Norwegian Channel. Debris flows, which signal the initial shelf-edge glaciation, are not recognized from the initial glaciation in the Channel (> 1.1 Myr) but are associated with a Middle Pleistocene and all following glacial erosion surfaces (GES) in the outer Norwegian Channel. This was followed by six further sequences, probably totalling over 13,000 km3 of sediment. At least four of these were shelf-edge ice-maximum events the last of which was Late Weichselian age (14C AMS). Considering earlier glaciation-related hemipelagic sedimentation, material since removed by the large slides, and extensive unmapped areas, total Quaternary fan sedimentation was in the vicinity of 20,000 km3.  相似文献   

3.
A Late Pleistocene submarine slide on the Bear Island Trough Mouth Fan   总被引：5，自引：2，他引：5  
A large submarine slide on the southern flank of the Bear Island Trough Mouth Fan, southwestern Barents Sea continental slope, has a run-out distance of about 400 km, a total volume of about 1100 km3, and is younger than 330 ka. Three seismic units, comprising mainly hemipelagic sediments has partly filled the slide scar. An increased sedimentation rate on the Bear Island Trough Mouth Fan from Late Pliocene time, probably in combination with abundant earthquakes, is the most likely cause of the slide. Based on these and previous studies, we suggest that large-scale slides were important sediment transport processes during Plio-Pleistocene.  相似文献   

4.
A giant three-stage submarine slide off Norway   总被引：8，自引：0，他引：8  
One of the largest submarine slides known, The Storegga Slide, is located on the Norwegian continental margin. The slide is up to 450 m thick and has a total volume of about 5,600 km3. The headwall of the slide scar is 290 km long and the total run-out distance is about 800 km. The slide involved sediments of Quaternary to Early Tertiary age and occurred in three stages. Earthquakes combined with decomposition of gas hydrates are believed to be the main triggering agents for the slides. The first slide event is tentatively dated to be about 30,000 to 50,000 years B.P. and the two last major events are dated to be at 6,000 to 8,000 years B.P.  相似文献   

5.
This study documents the fractal characteristics of submarine mass movement statistics and morphology within the Storegga Slide. Geomorphometric mapping is used to identify one hundred and fifteen mass movements from within the Storegga Slide scar and to extract morphological information about their headwalls. Analyses of this morphological information reveal the occurrence of spatial scale invariance within the Storegga Slide. Non-cumulative frequency-area distribution of mass movements within the Storegga Slide satisfies an inverse power law with an exponent of 1.52. The headwalls exhibit geometric similarity at a wide range of scales and the lengths of headwalls scale with mass movement areas. Composite headwalls are self-similar.One of the explanations of the observed spatial scale invariance is that the Storegga Slide is a geomorphological system that may exhibit self-organized criticality. In such a system, the input of sediment is in the form of hemipelagic sedimentation and glacial sediment deposition, and the output is represented by mass movements that are spatially scale invariant. In comparison to subaerial mass movements, the aggregate behavior of the Storegga Slide mass movements is more comparable to that of the theoretical ‘sandpile’ model. The origin of spatial scale invariance may also be linked to the retrogressive nature of the Storegga Slide. The geometric similarity in headwall morphology implies that the slope failure processes are active on a range of scales, and that modeling of slope failures and geohazard assessment can extrapolate the properties of small landslides to those of larger landslides, within the limits of power law behavior. The results also have implications for the morphological classification of submarine mass movements, because headwall shape can be used as a proxy for the type of mass movement, which can otherwise only be detected with very high resolution acoustic data that are not commonly available.  相似文献   

6.
Travel-time inversion of wide-angle ocean-bottom seismic (OBS) data results in detailed P-wave velocity models of the shallow sub-seabed beneath the Nyegga pockmark field. The area lies on the northern flank of the Storegga Slide on the mid-Norwegian margin. Velocity anomalies indicate two low P-wave velocity zones (LVZs) providing evidence for the presence of gas-rich fluids in the subsurface at Nyegga. Integrating the velocity results with 2D and 3D reflection seismic data demonstrates that LVZs coincide with zones of high-amplitude reflections that allow mapping the extent of the fluids in the subsurface. The upper fluid accumulation zone corresponds to a velocity inversion of ∼250 m/s and occurs at a depth of about 250 mbsf. The lateral extent is documented in two distinct areas. The westward area is up to 40 m thick where gas-rich fluids beneath a bottom-simulating reflection indicate that fluids may be trapped by gas hydrates. The eastward zone is up to 60 m thick and comprises a contourite deposit infilling a paleo-slide scar. On top, glacigenic debris flow deposits provide a locally effective seal for fluids. The second velocity inversion of ∼260 m/s extends laterally at about 450 mbsf with decreasing thickness in westward direction. Based on effective-medium theory the gas saturation of pore space in both layers is estimated to be between 0.5 and <1% assuming a homogeneous distribution of gas. Fluids probably originate from deeper strata approximately at the location of the top of the Helland-Hansen Arch. Fluids migrate into the second LVZ and are distributed laterally. Fluids migrate into shallower strata or are expelled at the seabed through the formation of vertical fluid migration features (VFMFs), so-called chimneys. The distribution of the chimneys is clearly linked to the two fluid accumulation zones in the subsurface. A conceptual model draws on the major controlling factors for fluid migrations at specific locations within Nyegga. Fluid migrations vary according to their actual position with respect to the prograding Plio–Pleistocene sedimentary wedge.  相似文献   

7.
Based on studies of sediment accumulations deposited from-and erode by-alongslope flowing ocean currents on the European continental margin from Porcupine (Ireland) to Lofoten (Norway), the evolution of the Cenozoic paleocirculation was reconstructed as part of the STRATAGEM project. There is evidence of ocean current-controlled erosion and deposition in the Rockall Trough, in the Faeroe-Shetland Channel and on the Vøring Plateau since the late Eocene, although the circulation pattern remains ambiguous. The late Palaeogene flow in the Rockall Trough was almost probably driven by southerly-derived Tethyan Outflow Water. The extent and strength of any northerly-derived flow is uncertain. From the early Neogene (early-mid-Miocene), there was a massive regional expansion of contourite drift development both in the North Atlantic and in the Norwegian-Greenland Sea. This was most probably related to the development of the Faroe Conduit, the opening of the Fram Strait and the general subsidence of the Greenland-Scotland Ridge. These may have combined to cause a considerable acceleration in the exchange and overflow of deep waters between the Arctic and Atlantic Oceans. An early late Neogene (late early Pliocene) regional erosional event has been ascribed to a vigorous pulse of bottom-current activity, most probably the result of a global reorganisation of ocean currents associated with the closure of the Central American Seaway. During the late Neogene, contourites and sediment drifts developed in deep-water basins, between units of glacigenic sediments as well as infill of several paleo-slide scars. These sediments were derived from areas of bottom-current erosion as well as from the development of Plio-Pleistocene prograding sediment wedges, incorporating the extensive sediment supply derived from shelf-wide ice sheets. Presently a profound winnowing prevails along the shelf and upper slope due to the inflowing currents of Atlantic water. Depocentres of sediments derived from the winnowing are located (locally) in lower slope embayments and in slide scars.  相似文献   

8.
Multichannel seismic reflection data from the Cosmonaut Sea margin of East Antarctica have been interpreted in terms of depositional processes in the continental slope and rise area. A major sediment lens is present below the upper continental rise along the entire Cosmonaut Sea margin. The lens probably consists of sediments supplied from the shelf and slope, being constantly reworked by westward flowing bottom currents, which redeposited the sediments into a large scale drift deposit prior to the main glaciogenic input along the margin. High-relief semicircular or elongated depositional structures are also found on the upper continental rise stratigraphically above the regional sediment lens, and were deposited by the combined influence of downslope and alongslope sediment transport. On the lower continental rise, large-scale sediment bodies extend perpendicular to the continental margin and were deposited as a result of downslope turbidity transport and westward flowing bottom currents after initiation of glacigenic input to the slope and rise. We compare the seismostratigraphic signatures along the continental margin segments of the adjacent Riiser Larsen Sea, the Weddell Sea and the Prydz Bay/Cooperation Sea, focussing on indications that may be interpreted as a preglacial-glaciomarine transition in the depositional environment. We suggest that earliest glaciogenic input to the continental slope and rise occurred in the Prydz Bay and possibly in the Weddell Sea. At a later stage, an intensification of the oceanic circulation pattern occurred, resulting in the deposition of the regional plastered drift deposit along the Cosmonaut Sea margin, as well as the initiation of large drift deposits in the Cooperation Sea. At an even later stage, possibly in the middle Miocene, glacial advances across the continental shelf were initiated along the Cosmonaut Sea and the Riiser Larsen Sea continental margins.  相似文献   

9.
Seafloor pockmarks and subsurface chimney structures are common on the Norwegian continental margin north of the Storegga Slide scar. Such features are generally inferred to be associated with fluid expulsion, and imply overpressures in the subsurface. Six long gravity and piston cores taken from the interior of three pockmarks were compared with four other cores taken from the same area but outside the pockmarks, in order to elucidate the origins and stratigraphy of these features and their possible association with the Storegga Slide event. Sulfate gradients in cores from within pockmarks are less steep than those in cores from outside the pockmarks, which indicates that the flux of methane to the seafloor is presently smaller within the pockmarks than in the adjacent undisturbed sediments. This suggests that these subsurface chimneys are not fluid flow conduits lined with gas hydrate. Methane-derived authigenic carbonates and Bathymodiolus shells obtained from a pockmark at >6.3 m below the seafloor indicate that methane was previously available to support a chemosynthetic community within the pockmark. AMS 14C measurements of planktonic Foraminifera overlying and interlayered with the shell-bearing sediment indicate that methane was present on the seafloor within the pockmark prior to 14 ka 14C years b.p., i.e., well before the last major Storegga Slide event (7.2 ka 14C years b.p., or 8.2 ka calendar years b.p.). These observations provide evidence that overpressured fluids existed within the continental margin sediments off Norway during the last major advance of Pleistocene glaciation.  相似文献   

10.
The Baiyun submarine slide complex (BSSC) along the Pearl River Canyon of the northern South China Sea has been imaged by multibeam bathymetry and 2D/3D seismic data. By means of maximum likelihood classification with slope aspect and gradient as inputs, the BSSC is subdivided into four domains, denoted as slide area I, II, III and IV. Slide area I is surrounded by cliffs on three sides and has been intensely reshaped by turbidity currents generated by other kinds of mass movement outside the area; slide area II incorporates a shield volcano with a diameter of approximately 10 km and unconfined slides possibly resulting from the toe collapse of inter-canyon ridges; slide area III is dominated by repeated slides that mainly originated from cliffs constituting the eastern boundary of the BSSC; slide area IV is distinguished by a conical seamount with a diameter of 6.5 km and a height of 375 m, and two slides probably having a common source that are separated from each other by a suite of residual strata. The BSSC is interpreted to be composed of numerous slide events, which occurred in the period from 10.5 to 5.5 Ma BP. Six specific factors may have contributed to the development of the BSSC, i.e., gas hydrate dissociation, gas-bearing sediments, submarine volcanic activity, seismicity, sedimentation rate and seafloor geomorphology. A 2D conceptual geological model combining these factors is proposed as a plausible mechanism explaining the formation of the BSSC. However, the BSSC may also have been affected by the Dongsha event (10 Ma BP) as an overriding factor.  相似文献   

11.
The Baraza Slide is located in the northwestern Alboran Sea, western Mediterranean region, between 590 and 830?m water depth, and its morphology, seismic facies and sedimentary structure are analyzed based on multibeam bathymetry and very high to medium resolution single-channel seismic records. During the Pleistocene and Late Quaternary this landslide has undergone repeated slope failures characterized by a succession of two main types of mass movement, the first of the mass-flow type and the second of the slide type. This study also reveals that the western sector of this landslide could still be active. The relatively high slope gradients, a sedimentary column characterized by the presence of under consolidated layers and earthquake shaking related to tectonic activity on the margin are the factors governing the genesis and post-mobility behavior of the Baraza mass movement. The recognition and analysis of these factors suggest that the Baraza Slide should be considered as a geo-hazard in the tectonically active Alboran Sea.  相似文献   

12.
Storegga Silide has been studied intensively due to the development of the big Ormen Lange gas field. Both marine and glacial deposits were involved in this slide, and marine layers were the sliding planes. Data from different wireline logs in the Storegga Slide area are analyzed using principal components and cluster statistical methods to characterize the two different kinds of sediments. The results show that the marine layer with high water content, high clay content and low strength can be differentiated from the glacial deposits. Moreover, the analysis from log response are compared with the physical parameters from the geotechnical boreholes, a good correlation exists in the dataset.  相似文献   

13.
Based on classification tests, oedometer tests, fall-cone tests and triaxial tests, physical and mechanical properties of sediments in the Storegga Slide region were analysed to assess parameter interrelationships. The data show good relationships between a number of physical and mechanical parameters. Goodness of fit between compression index and various physical parameters can be improved by multiple regression analysis. The interclay void ratio and liquidity index correlate well with the undrained shear strength of clay. Sediments with higher water content, liquid limit, activity, interclay void ratio, plasticity index and liquidity index showed higher compression index and/or lower undrained shear strength. Some relationships between parameters were tested by using data from two other sites south of the Storegga Slide. A better understanding of properties of sediments in regions such as that of the Storegga Slide can be obtained through this approach.  相似文献   

14.
Large craters associated with mounds of remobilised sediment have been recently mapped on the mid Norway margin in the Møre Basin. These craters and mounds may be linked to the long term migration of fluids upwards from the lower levels of the Møre Basin which exploit hydrothermal vent complexes emplaced in the late Paleocene and early Eocene. All of the craters are located on a regionally correlative seismic surface that is correlated with the basal shear plane of Slide W, a slide located at the base of the Plio-Pleistocene Naust Formation. The Craters are positioned in the western area of the Møre Basin at the foot of the continental slope on the crests and flanks of Miocene domes, where Oligocene biosiliceous ooze subcrops on the basal shear surface of Slide W. Not all of the craters are filled by Slide W. Mounds are emplaced above those craters which are filled by Slide W on the top surface of Slide W. Stratal relationships show that the mounds were emplaced on the paleo-seabed. We present and discuss two models that illustrate processes that may have been involved in the formation of craters and remobilisation of sediments. In one model, an eruption of fluid from beneath remobilises ooze into ooze mounds in a single event triggering slope failure, whereas in the other model the emplacement of Slide W and later slides loads low density ooze causing it to undergo liquefaction, a process which may have been facilitated by the trapping of continuous long term fluid migrating from beneath, causing the ooze to remobilise into ooze mounds in two or more events.  相似文献   

15.
The submarine Hinlopen Slide, located along the Arctic Ocean margin, is one of the largest known mass movements on Earth. The slide scar has several unusual morphometric characteristics, including headwalls up to 1,500 m high and spectacularly large, steep-sided rafted megablocks. The slide processes and continental margin properties that produced these features are not well known. A new high-resolution TOBI (towed ocean bottom instrument) side-scan sonar dataset reveals information about the detailed seafloor morphology and, therefore, slide dynamics during the final stages of sliding. First, the headwall area was efficiently and almost completely evacuated of slide debris, which is unusual for large submarine slides. Second, features relating to the propagation of extension to the shelf behind the headwall are absent, suggesting “strong” cohesive shelf material here or that a very stable shelf configuration was reached, possibly defined by NE-SW-trending faults. Third, there is little evidence for the translation of shelf material, again uncommon for submarine slides. Taken together with the occurrence of massive megablocks in the slide debris, Hinlopen Slide is distinct because of the juxtaposition of apparently “stronger” shelf material that has remained intact (headwalls, megablocks), and “weaker” shelf material that disaggregated fully during slope failure. Nevertheless, there is sonograph evidence of variable post-slide disintegration of the megablocks. Contrary to previous interpretations, this suggests that the blocks comprise sedimentary lithologies that are prone to failure, a key aspect awaiting confirmation.  相似文献   

16.
Pleistocene glacial history of the NW European continental margin   总被引：3，自引：3，他引：3  
In this paper new and previously published data on the Pleistocene glacial impact on the NW European margin from Ireland to Svalbard (between c. 48°N–80°N) are compiled. The morphology of the glaciated part of the European margin strongly reflects repeated occurrence of fast-moving ice streams, creating numerous glacial troughs/channels that are separated by shallow bank areas. End-moraines have been identified at several locations on the shelf, suggesting shelf-edge glaciation along the major part of the margin during the Last Glacial Maximum. Deposition of stacked units of glacigenic debris flows on the continental slope form fans at a number of locations from 55°N and northwards, whereas the margin to the south of this is characterised by the presence of submarine canyons. Glaciation curves, based primarily on information from the glacial fed fan systems, that depict the Pleistocene trends in extent of glaciations along the margin have been compiled. These curves suggest that extensive shelf glaciations started around Svalbard at 1.6–1.3 Ma, while repeated periods of shelf-edge glaciations on the UK margin started with MIS 12 (c. 0.45 Ma). The available evidence for MIS 2 suggest that shelf-edge glaciation for the whole margin was reached between c. 28 and 22 14C ka BP and maximum positions after this were more limited in some regions (North Sea and Lofoten). The last glacial advance on the margin has been dated to 15–13.5 14C ka BP, and by c. 13 14C ka BP the shelf areas were completely deglaciated. The Younger Dryas (Loch Lomond) advance reached the coastal areas in only a few regions.  相似文献   

17.
In this paper we present an overview of the major triggering mechanisms and preconditions for slope failure on the European continental margins, a vast area in which the dominant factors on sedimentation and erosional processes vary both spatially and temporally. Therefore, we have collated and integrated new as well as published data for both the formerly glaciated and non-glaciated areas of this highly dynamic margin for a time period mainly from the Last Glacial Maximum (LGM) to the present. Mass transport type is predominantly translational sliding on the high-latitude continental margins (north of 52°N), whereas turbidites dominate on lower latitudes. This is partly related to the average slope of the respective continental margin segments and differences in both sediment types and soil properties. Additionally, on low latitudes, submarine slope failures mainly occurred during glacial conditions with low sea level, whereas on high latitudes, they occur during the relatively fast transition from glacial to interglacial conditions (i.e. during periods of sea level rise). The largest submarine slides (e.g. Storegga, Trænadjupet, Andøya) on the glaciated Norwegian margin occurred during the Holocene, a time of rapid ice sheet decay, continental uplift and increased seismic activity, one of the most important triggering mechanisms for large failures during deglaciation processes. Preconditioning factors such as weak layers related to contourite drifts and rapid loading by glacial sediments may enhance strain localization and creep processes on the slope.  相似文献   

18.
The Cenozoic seismic stratigraphy and geological development of the south Vøring margin are analyzed to understand their relation to fluid flow and margin stability. The regional stratigraphy and palaeomorphology of the Møre and Vøring basins indicate gradual changes in depositional environment and tectonic compression between 55 Ma to 2.8 Ma during Brygge and Kai periods, and abrupt changes associated with glacial/interglacial cycles from last 2.8 Ma during Naust period. These changes resulted in deposition of various types of sediments and led to processes such as polygonal faulting and dewatering, inter-fingering of contouritic, stratified and glacigenic sediments, and margin progradation.A gas hydrate related bottom simulating reflector (BSR) occurs at Nyegga and within the central Vøring Basin while pockmarks are observed at Nyegga only. Diagentic reflectors due to Opal A - Opal CT conversion (DBSRs) occur along a wider area beyond the shelf edge. The DBSRs are located in oozes within the Kai and late Brygge Formations. The gas hydrate BSR occurrence is concentrated above Eocene depocenters in hemipelagic and contouritic sediments deposited during Late Plio-Pleistocene. The BSR overlies polygonal faults and DBSRs but are confined to the slope of anticlines indicating its formation being related to fluid pathways from methanogenic rocks through focused fluid flow. Microbial gas production in Kai, Brygge and deeper formations may have supplied the gas for gas hydrate formation. Fluid expulsion due to DBSR formation and polygonal faulting in oozes may have created overpressure development in permeable layers belonging to the overlying Naust Formation. Slide headwalls are also located close to the anticlines in the study area, implying that over pressured oozes and focussed fluid flow may have been important in creating weak surfaces in the overlying Naust sediments, promoting conditions for failures to occur.  相似文献   

19.
The Storegga Slide complex is a multi-stage slope failure on the Norwegian continental margin where the most recent major event occurred 8.1 ka b.p. (calendar years before present). Its northern flank contains pockmark features that are commonly inferred to be related to the historical and modern venting of methane-bearing fluids. Three jumbo piston cores (JPC), one from a pockmark and two background cores at variable distances from this site (proximal, 5 km, and distal, 15 km) on the northern flank of the slide (806–1,524 m water depths), were sampled at 10 cm resolution to assess the geologic record of methane venting in the Nyegga pockmark field. Six down-core radiocarbon measurements on mixed planktonic foraminifer species reveal ages of 9.4–16.4 ka b.p. Bathymodiolus mussel shell horizons, indicators of methane-rich environments, have been dated at 15.8–17.6 and ~22 ka b.p. in the pockmark core. Stable isotope analyses on planktonic (Neogloboquadrina pachyderma sinistral) and benthic (Islandiella norcrossi, Melonis barleeanum) Foraminifera reveal δ18O values indicative of a clear glacial/deglacial transition (−1.5‰ shift in planktonic species). Both planktonic and benthic δ13C signatures record multiple excursions, interpreted to reflect the influence of methane in the environment; these δ13C excursions occur in the pockmark core and also in the distal background core. While authigenic calcite formation on the seafloor may play an important role in producing such excursions, these data together suggest the influence of methane seepage within the pockmark field over the past 25 ka, whereby seepage was particularly active between 13 and 15 ka. This is consistent with previously inferred regional increases in porewater pressure associated with glacial loading and higher sedimentation rates, which can cause gas hydrate and slope instability.  相似文献   

20.
Late Cenozoic seismic stratigraphy of the Vøring continental margin has been studied in detail, with emphasis on the geological development of the Naust Formation deposited during the last 3 million years. The Kai Formation (15–3 Ma) comprises mainly biogenic ooze deposited in the Møre and Vøring Basins. In Naust time, there was a marked increase in supply of sediments from the inner shelf areas and the western part of the Scandinavian mountain range, and glaciers expanded to the shelf and reached the shelf edge several times during the last 1.5–2 million years. During early to mid Naust time the shelf was widened by westerly prograding sediment units, but for a long period the shallowest part of the Helland-Hansen Arch (HHA) formed a barrier preventing glacially derived debris from being distributed farther west. West of the HHA, mainly stratified marine and glacimarine sediments were deposited. A substantial part of these sediments were transported by the north-flowing Norwegian Atlantic Current, which redistributed suspended particles from ice streams, rivers, coastal erosion and seabed winnowing. After burial of the crest of the HHA at c. 0.5 Ma, glacial debris and slide deposits were also deposited west of this high. In the north, massive units of glacial debris were distributed beyond the crest of the HHA, also in mid Naust time, thinning westwards and interfingering with fine-grained sediments on the lower slope. The Sklinnadjupet Slide, inferred to be c. 250,000 years old, corresponds in age with an earlier huge slide in the Storegga area. An elongated area of uneven seabed topography previously interpreted as diapirs (Vigrid diapirs) on the slope west of the HHA is shown to be formed by ooze eruption from the crest of the arch and submarine sliding.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

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