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 609 毫秒
1.
An extensive refraction profiling program was carried out during the FRAM II experiment (March–May, 1980) in the eastern Arctic Ocean. Two structural areas were covered: north of the ice camp (86°N, 24°W) into the basin of the Pole Abyssal Plain and south onto the flanks of the Morris Jesup Rise. Digital multichannel data on an 800 by 800 m, 24 channel hydrophone array and a single 2-component ocean bottom seismometer (OBS) were recorded for offsets from 2.5 to 100 km. Arrival times, amplitudes and phase velocities of the seismic signals recieved on the hydrophone array were determined using high resolution array processing. From these measurements and the OBS data, preliminary velocity structural models of the crust have been derived. For the purposes of this paper, 2 refraction lines have been analyzed, a 40 km line on a flat region of the Pole Abyssal Plain and an 86 km line on a slightly dipping region taken as the drifting ice camp shoaled on the Morris Jesup Rise. These preliminary analyses yield a sedimentary layer with a gradually increasing velocity 1.5–2 km thick. This cover overlays a crust with a thin layer 2 (< 1 km) and yields a total ocean bottom to mantle thickness of 4–7 km.  相似文献   

2.
During an early phase of the Last Ice Age (Weichselian, Valdaian), about 90 000 yr ago, an ice sheet formed over the shallow Barents and Kara seas. The ice front advanced on to mainland Russia and blocked the north‐flowing rivers (Yenissei, Ob, Pechora, Dvina and others) that supply most of the freshwater to the Arctic Ocean. The result was that large ice‐dammed lakes were formed between the ice sheet in the north and the continental water divides to the south. Here we present reconstructions and calculations of the areas and volumes of these lakes. The lake on the West Siberian Plain was nearly twice as large as the largest lake on Earth today. The well‐mapped Lake Komi in northeast Europe and a postulated lake in the White Sea Basin would also rank before the present‐day third largest lake. The lakes overflowed towards the south and thus the drainage of much of the Eurasian continent was reversed. The result was a major change in the water balance on the continent, decreased freshwater supply to the Arctic Ocean, and increased freshwater flow to the Aral, Caspian, Black and Baltic seas. A sudden outburst of the lakes' water to the Arctic Ocean when the ice sheet thinned is postulated. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

3.
A numerical ice-sheet model was used to reconstruct the Late Weichselian glaciation of the Eurasian High Arctic, between Franz Josef Land and Severnaya Zemlya. An ice sheet was developed over the entire Eurasian High Arctic so that ice flow from the central Barents and Kara seas toward the northern Russian Arctic could be accounted for. An inverse approach to modeling was utilized, where ice-sheet results were forced to be compatible with geological information indicating ice-free conditions over the Taymyr Peninsula during the Late Weichselian. The model indicates complete glaciation of the Barents and Kara seas and predicts a “maximum-sized” ice sheet for the Late Weichselian Russian High Arctic. In this scenario, full-glacial conditions are characterized by a 1500-m-thick ice mass over the Barents Sea, from which ice flowed to the north and west within several bathymetric troughs as large ice streams. In contrast to this reconstruction, a “minimum” model of glaciation involves restricted glaciation in the Kara Sea, where the ice thickness is only 300 m in the south and which is free of ice in the north across Severnaya Zemlya. Our maximum reconstruction is compatible with geological information that indicates complete glaciation of the Barents Sea. However, geological data from Severnaya Zemlya suggest our minimum model is more relevant further east. This, in turn, implies a strong paleoclimatic gradient to colder and drier conditions eastward across the Eurasian Arctic during the Late Weichselian.  相似文献   

4.
Comparison of a new compilation of available Arctic bathymetric data north of 85° N latitude with previously published charts shows large discrepancies in the position and morphology of several major Arctic sea-floor features. Near the North Pole the Lomonosov Ridge pinches to a width of about 20 km with very steep slopes. The crest of the Ridge at this location is displaced dextrally by about 80 km. Also, the crest of this ridge curves towards Ellesmere Island and does not continue towards Greenland. The Marvin Spur is actually a series of knolls or sea mounts with relief varying from 500 to over 1300 m. The 600 km wide arch known as the Alpha Cordillera consists of closed, wide (10–40 km) elongated (180–260 km) troughs and ridges with relief of over 1000 m. Circular sea mounts and deeps are also noted along this Cordillera. The Arctic Mid-Oceanic Cordillera is a rather flat 200 km wide feature that tilts gently upward by about 500 m from the Pole Abyssal Plain to the Barents Abyssal Plain. It is characterized by a series of narrow ridges and troughs usually less than 20 km wide with a central deep trough over 5100 m deep and shallow ridges rising to heights of 2600 m. These features generally parallel the Lomonosov Ridge. This cordillera appears to be abruptly truncated along the Greenwich meridian. The Morris Jesup Plateau is a single pronged northeast trending feature with relatively shallow westward slopes and steeply dipping eastward slopes.  相似文献   

5.
It is summarized based on previous studies that warm and salty Atlantic Water (AW) brings huge amount of heat into Arctic Ocean and influences oceanic heat distribution and climate. Both heat transportation and heat release of AW are key factors affecting the thermal process in Eurasian Basin. The Arctic circumpolar boundary current is the carrier of AW, whose flow velocity varies to influence the efficiency of the warm advection. Because the depth of AW in Eurasian Basin is much shallower than that in Canadian Basin, the upward heat release of AW is an important heat source to supply sea ice melting. Turbulent mixing, winter convention and double-diffusion convention constitute the main physical mechanism for AW upward heat release, which results in the decrease of the Atlantic water core temperature during its spreading along the boundary current. St. Anna Trough, a relatively narrow and long trough in northern continental shelf of Kara Sea, plays a key role in remodeling temperature and salinity characteristics of AW, in which the AW from Fram Strait enters the trough and mixes with the AW from Barents Sea. Since the 21st Century, AW in the Arctic Ocean has experienced obvious warming and had the influence on the physical processes in downstream Canada Basin, which is attributed to the anomalous warming events of AW inflowing from the Fram Strait. It is inferred that the warming AW is dominated by a long-term warming trend superimposed on low frequency oscillation occurring in the Nordic Seas and North Atlantic Ocean. As the Arctic Ocean is experiencing sea ice decline and Arctic amplification, the role of AW heat release in response to the rapid change needs further investigation.  相似文献   

6.
《Quaternary Science Reviews》2004,23(11-13):1273-1283
Geological investigations undertaken through the Quaternary Environments of the Eurasian North programme established ice-sheet limits for the Eurasian Arctic at the Last Glacial Maximum (LGM), sedimentary records of palaeo-ice streams and uplift information relating to ice-sheet configuration and the pattern of deglaciation. Ice-sheet numerical modelling was used to reconstruct a history of the Eurasian Ice Sheet compatible with these geological datasets. The result was a quantitative assessment of the time-dependent behaviour of the ice sheet, its mass balance and climate, and predictions of glaciological products including sediments, icebergs and meltwater. At the LGM, ice cover was continuous from Scandinavia to the Arctic Ocean margin of the Barents Sea to the north, and the Kara Sea to the east. In the west, along the continental margin between the Norwegian Channel and Svalbard, the ice sheet was characterised by fast flowing ice streams occupying bathymetric troughs, which fed large volumes of sediment to the continental margin that were deposited as a series of trough mouth fans. Ice streams may also have been present in bathymetric troughs to the north between Svalbard and Franz Josef Land. Further east, however, the ice sheet was thinner. Across the Kara Sea, the ice thickness was predicted to be less than 300 m, while on Severnaya Zemlya the ice cover may have been thinner at the LGM than at present. It is likely that the Taymyr Peninsula was mainly free of ice at the LGM. In the south, the ice margin was located close to the shoreline of the Russian mainland. The climate associated with this ice sheet is maritime to the west and, in stark contrast, desert-like in the east. Atmospheric General Circulation Modelling has revealed that such a contrast is possible under relatively warm north Atlantic conditions because a circulation system develops across the Kara Sea, isolating it from the moisture-laden westerlies, which are diverted to the south. Ice-sheet decay began through enhanced iceberg calving in the deepest regions of the Barents Sea, which caused a significant ice embayment within the Bear Island Trough. By about 12,000 years ago, further iceberg calving reduced ice extent to the northern archipelagos and their surrounding shallow seas. Ice decay was complete by about 10,000 years ago.  相似文献   

7.
A considerable portion of Northern Eurasia, and particularly its continental shelf, was glaciated by inland ice during late Weichsel time. This was first inferred from such evidence as glacial striae, submarine troughs, sea-bed diamictons, boulder trains on adjacent land, and patterns of glacioisostatic crustal movements. Subsequently, the inference was confirmed by data on the occurrence and geographic position of late Weichselian end moraines and proglacial lacustrine deposits.The south-facing outer moraines in the northeastern Russian Plain, northern West Siberia, and on Taimyr Peninsula are underlain by sediments containing wood and peat, the radiocarbon dating of which yielded ages of 22,000 to 45,000 yr B.P. The youngest late-glacial moraines are of Holocene age: the double Markhida moraine in the lower Pechora River basin, presumably associated with “degradational” surges of the Barents Ice Dome, is underlain by sediments with wood and peat dated at 9000 to 9900 yr B.P.: this suggests that deglaciation of the Arctic continental shelf of Eurasia was not completed until after 9000 yr B.P.The reconstructed ice-front lines lead to the conclusion that the late Weichselian ice sheet of Northern Eurasia (proposed name: the Eurasian Ice Sheet) extended without interruptions from southwestern Ireland to the northeastern end of Taimyr Peninsula, a distance of 6000 km: it covered an area of 8,370,000 km2, half of which lay on the present-day continental shelves and a quarter on lowlands that were depressed isostatically below sea level. Hence, the ice sheet was predominantly marine-based.A contour map of the ice sheet based both on the dependence of the heights of ice domes upon their radii and on factual data concerning the impact of bedrock topography upon ice relief has been constructed. The major features of the ice sheet were the British, Scandinavian, Barents, and Kara Ice Domes that had altitudes of 1.9 to 3.3 km and were separated from one another by ice saddles about 1.5 km high. At the late Weichselian glacial maximum, all the main ice-dispersion centers were on continental shelves and coastal lowlands, whereas mountain centers, such as the Polar Urals and Byrranga Range, played only a local role.The portions of the ice sheet that were grounded on continental shelves some 700 to 900 m below sea level were inherently unstable and could exist only in conjunction with confined and pinned floating ice shelves that covered the Arctic Ocean and the Greenland and Norwegian Seas.The Eurasian Ice Sheet impounded the Severnaya Dvina, Mezen, Pechora, Ob, Irtysh, and Yneisei Rivers, and caused the formation of ice-dammed lakes on the northern Russian Plain and in West Siberia. Until about 13,500 yr B.P. the proglacial system of lakes and spillways had a radial pattern; it included large West Siberian lakes, the Caspian and Black Seas, and ended in the Mediterranian Sea. Later, the system became marginal and discharged proglacial water mainly into the Norwegian Sea.  相似文献   

8.
Satellite altimetry data, Bouguer anomalies, anomalous magnetic field, bottom topography, and Love wave tomography for the deepwater part of the Arctic Ocean Basin and East Siberian Sea have made it possible to detect several new regional tectonic elements. The basin area, 700 km wide and 1800 km long, extending from the Laptev Sea to the Chukchi Borderland is a dextral strike-slip zone with structural elements typical of shearing. The destruction of the Eurasian margin surrounding the Amerasia Basin occurs within this zone. The opening of the Amerasia Basin is characterized by intense plume magmatism superimposed on normal slow spreading in several areas of the paleospreading axis. Magma was supplied through three conduits with minor offsets, the activity of which waned partly or completely by the end of basin formation. The main central conduit formed the structure of the Alpha Ridge. The dextral strike-slip system, which displaces the Gakkel Ridge and structural elements in the basement of the Makarov Basin, most likely extends to the northern termination of the Chukchi Borderland.  相似文献   

9.
We propose that prior to the Younger Dryas period, the Arctic Ocean supported extremely thick multi-year fast ice overlain by superimposed ice and firn. We re-introduce the historical term paleocrystic ice to describe this. The ice was independent of continental (glacier) ice and formed a massive floating body trapped within the almost closed Arctic Basin, when sea-level was lower during the last glacial maximum. As sea-level rose and the Barents Sea Shelf became deglaciated, the volume of warm Atlantic water entering the Arctic Ocean increased, as did the corresponding egress, driving the paleocrystic ice towards Fram Strait. New evidence shows that Bering Strait was resubmerged around the same time, providing further dynamical forcing of the ice as the Transpolar Drift became established. Additional freshwater entered the Arctic Basin from Siberia and North America, from proglacial lakes and meltwater derived from the Laurentide Ice Sheet. Collectively, these forces drove large volumes of thick paleocrystic ice and relatively fresh water from the Arctic Ocean into the Greenland Sea, shutting down deepwater formation and creating conditions conducive for extensive sea-ice to form and persist as far south as 60°N. We propose that the forcing responsible for the Younger Dryas cold episode was thus the result of extremely thick sea-ice being driven from the Arctic Ocean, dampening or shutting off the thermohaline circulation, as sea-level rose and Atlantic and Pacific waters entered the Arctic Basin. This hypothesis focuses attention on the potential role of Arctic sea-ice in causing the Younger Dryas episode, but does not preclude other factors that may also have played a role.  相似文献   

10.
Recent observations on postglacial emergence and past glacier extent for one of the least accessible areas in the Arctic, northern Novaya Zemlya are here united. The postglacial marine limit formed 5 to 6 ka is registered on the east and west coasts of the north island at 10 ± 1 and 18 ± 2 m aht, respectively. This modest and late isostatic response along with deglacial ages of >9.2 ka on adjacent marine cores from the northern Barents Sea indicate either early (>13 ka) deglaciation or modest ice sheet loading (<1500 m thick ice sheet) of Novaya Zemlya. Older and higher (up to 50 m aht) raised beaches were identified beneath a discontinuous glacial drift. Shells from the drift and underlying sublittoral sediments yield minimum limiting 14C ages of 26 to 30 ka on an earlier deglacial event(s). The only moraines identified are within 4 km of present glacier margins and reflect at least three neoglacial advances in the past 2.4 ka.  相似文献   

11.
Clay-mineral distributions in the Arctic Ocean and the adjacent Eurasian shelf areas are discussed to identify source areas and transport pathways of terrigenous material in the Arctic Ocean. The main clay minerals in Eurasian Arctic Ocean sediments are illite and chlorite. Smectite and kaolinite occur in minor amounts in these sediments, but show strong variations in the shelf areas. These two minerals are therefore reliable in reconstructions of source areas of sediments from the Eurasian Arctic. The Kara Sea and the western part of the Laptev Sea are enriched in smectite, with highest values of up to 70% in the deltas of the Ob and Yenisey rivers. Illite is the dominant clay mineral in all the investigated sediments except for parts of the Kara Sea. The highest concentrations with more than 70% illite occur in the East Siberian Sea and around Svalbard. Chlorite represents the clay mineral with lowest concentration changes in the Eastern Arctic, ranging between 10 and 25%. The main source areas for kaolinite in the Eurasian Arctic are Mesozoic sedimentary rocks on Franz-Josef Land islands. Based on clay-mineral data, transport of the clay fraction via sea ice is of minor importance for the modern sedimentary budget in the Arctic basins.  相似文献   

12.
ABSTRACT The Moroccan Turbidite System (MTS) on the north‐west African margin extends 1500 km from the head of the Agadir Canyon to the Madeira Abyssal Plain, making it one of the longest turbidite systems in the world. The MTS consists of three interconnected deep‐water basins, the Seine Abyssal Plain (SAP), the Agadir Basin and the Madeira Abyssal Plain (MAP), connected by a network of distributary channels. Excellent core control has enabled individual turbidites to be correlated between all three basins, giving a detailed insight into the turbidite depositional architecture of a system with multiple source areas and complex morphology. Large‐volume (> 100 km3) turbidites, sourced from the Morocco Shelf, show a relatively simple architecture in the Madeira and Seine Abyssal Plains. Sandy bases form distinct lobes or wedges that thin rapidly away from the basin margin and are overlain by ponded basin‐wide muds. However, in the Agadir Basin, the turbidite fill is more complex owing to a combination of multiple source areas and large variations in turbidite volume. A single, very large turbidity current (200–300 km3 of sediment) deposited most of its sandy load within the Agadir Basin, but still had sufficient energy to carry most of the mud fraction 500 km further downslope to the MAP. Large turbidity currents (100–150 km3 of sediment) deposit most of their sand and mud fraction within the Agadir Basin, but also transport some of their load westwards to the MAP. Small turbidity currents (< 35 km3 of sediment) are wholly confined within the Agadir Basin, and their deposits pinch out on the basin floor. Turbidity currents flowing beyond the Agadir Basin pass through a large distributary channel system. Individual turbidites correlated across this channel system show major variations in the mineralogy of the sand fraction, whereas the geochemistry and micropalaeontology of the mud fraction remain very similar. This is interpreted as evidence for separation of the flow, with a sand‐rich, erosive, basal layer confined within the channel system, overlain by an unconfined layer of suspended mud. Large‐volume turbidites within the MTS were deposited at oxygen isotope stage boundaries, during periods of rapid sea‐level change and do not appear to be specifically connected to sea‐level lowstands or highstands. This contrasts with the classic fan model, which suggests that most turbidites are deposited during lowstands of sea level. In addition, the three largest turbidites on the MAP were deposited during the largest fluctuations in sea level, suggesting a link between the volume of sediment input and the magnitude of sea‐level change.  相似文献   

13.
A section, almost 20 km long and up to 80 m high, through alternating layers of diamict and sorted sediments is superbly exposed on the north coast of the Kanin Peninsula, northwestern Russia. The diamicts represent multiple glacial advances by the Barents Sea and the Kara Sea ice sheets during the Weichselian. The diamicts and stratigraphically older lacustrine, fluvial and shallow marine sediments have been thrust as nappes by the Barents Sea and Kara Sea ice sheets. Based on stratigraphic position, OSL dating, sea level information and pollen, it is evident that the sorted sediments were deposited in the Late Eemian-Early Weichselian. Sedimentation started in lake basins and continued in shallow marine embayments when the lakes opened to the sea. The observed transition from lacustrine to shallow marine sedimentation could represent coastal retreat during stable or rising sea level.  相似文献   

14.
Surface samples from the eastern Barents and south-western Kara seas have been analysed for clay mineralogy. Transport paths, the role of regional sources and local bedrock outcrops and the influence of hydrodynamic and glacigenous processes for clay distribution on the shelves are discussed in relation to central Arctic Ocean deep sea and sea ice sediments. Franz Josef Land and Novaya Zemlya show significantly different clay mineral associations. Although smectite concentrations are fairly high, Franz Josef Land can be excluded as a source for central Arctic sea ice sediments, which are relatively rich in smectite. In the Kara Sea, smectite concentrations in coastal sediments surpass even the Franz Josef Land concentrations. The large cyclonic gyre in the eastern Barents Sea between Novaya Zemlya and Franz Josef Land, which serves as a mixing zone between Arctic and North Atlantic water, is apparently reflected within the smectite distribution pattern. With the exception of Franz Josef Land, the area of investigation is typically low in kaolinite. In particular, coastal areas and areas north of Novaya Zemlya, influenced by the inflow of Arctic waters, show the lowest kaolinite concentrations. A high kaolinite occurrence within the Nansen Basin is most probably related to Franz Josef Land and emphasizes the importance of long-range downslope transport of sediments across the continental slope. The surface water circulation pattern in close interaction with local outcrops onshore Novaya Zemlya and locally restricted occurrences within the eastern Barents Sea significantly alter the illite dispersal pattern. Illite concentrations are lowest around Franz Josef Land. Chlorite is generally low in the area of investigation. Submarine outcrops and important chlorite occurrences onshore Novaya Zemlya bias its distribution pattern.  相似文献   

15.
Multichannel seismic reflection data acquired by Marine Arctic Geological Expedition (MAGE) of Murmansk, Russia in 1990 provide the first view of the geological structure of the Arctic region between 77–80°N and 115–133°E, where the Eurasia Basin of the Arctic Ocean adjoins the passive-transform continental margin of the Laptev Sea. South of 80°N, the oceanic basement of the Eurasia Basin and continental basement of the Laptev Sea outer margin are covered by 1.5 to 8 km of sediments. Two structural sequences are distinguished in the sedimentary cover within the Laptev Sea outer margin and at the continent/ocean crust transition: the lower rift sequence, including mostly Upper Cretaceous to Lower Paleocene deposits, and the upper post-rift sequence, consisting of Cenozoic sediments. In the adjoining Eurasia Basin of the Arctic Ocean, the Cenozoic post-rift sequence consists of a few sedimentary successions deposited by several submarine fans. Based on the multichannel seismic reflection data, the structural pattern was determined and an isopach map of the sedimentary cover and tectonic zoning map were constructed. A location of the continent/ocean crust transition is tentatively defined. A buried continuation of the mid-ocean Gakkel Ridge is also detected. This study suggests that south of 78.5°N there was the cessation in the tectonic activity of the Gakkel Ridge Rift from 33–30 until 3–1 Ma and there was no sea-floor spreading in the southernmost part of the Eurasia Basin during the last 30–33 m.y. South of 78.5°N all oceanic crust of the Eurasia Basin near the continental margin of the Laptev Sea was formed from 56 to 33–30 Ma.  相似文献   

16.
During the Late Palaeozoic and the Mesozoic, the development and evolution of the North West Shelf of Australia have been mostly driven by rifting phases associated with the break-up of Gondwana. These extensional episodes, which culminated in the opening of the Neotethys Ocean during the Permo-Carboniferous and a series of abyssal plains during the Jurassic-Cretaceous, are characterised by different stress regimes and modes of extension, and therefore had distinctive effects on the margin, and particularly on the Northern Carnarvon Basin.Interpretation of 3D and 2D seismic data enables a structural and stratigraphic analysis of the Late Palaeozoic sediments deposited in the proximal part of the Dampier Sub-basin (Mermaid Nose). Based on their seismic characters, stratigraphic relationship, internal patterns, lateral continuity, and architecture, these units are associated here with the Pennsylvanian?–Early Sakmarian glaciogenic Lyons Group and the Sakmarian–Artinskian Callytharra Formation. The former were deposited in a half-graben whose development is associated with the onset of the Neotethys rifting, and the latter is characterised by restricted deposition, inversion of prograding patterns, and uplift.The integration of seismo-stratigraphic characterisation of the Late Palaeozoic sequences and Mesozoic data from one exploration well (Roebuck-1) enables the construction of subsidence curves for the Mermaid Nose and the interpretation of its geohistory.The tectonic subsidence curves show a striking Permo-Carboniferous rifting phase related to the Neotethys rifting and a discrete Late Jurassic–Early Cretaceous event coeval with the opening and the spreading of the Argo Abyssal Plain.This result points out the predominance of the effects of the Permo-Carboniferous Neotethys episode, whereas the extension related to the Argo Abyssal Plain rifting that occurred later and closer to the studied area, had only limited effects on the subsidence of the proximal Dampier Sub-basin. Therefore, it supports a tectonic model with two distinct modes of extension for the Late Palaeozoic (widespread) and the Mesozoic (localised) rifting phases.  相似文献   

17.
Seismic refraction surveys conducted in 1976 and 1979 over the broken ice surface of the Arctic Ocean, reveal distinctly different crustal structures for the Fram, Makarov and Canada basins. The Canada Basin, characterized by a 2–4 km thick sedimentary layer and a distinct oceanic layer 3B of 7.5 km/s velocity has the thickest crust and is undoubtedly the oldest of the three. The crust of the Makarov Basin has a thin sedimentary layer of less than 1 km and is about 9 km in total thickness. The Fram Basin has a similarly thin sedimentary layer but is 3–4 km thicker than the Makarov as it approaches the Lomonosov Ridge near the North Pole. The ridge itself is cored by material with a velocity of 6.6 km/s and may be a metagabbro similar to oceanic layer 3A. This ridge root material extends to a depth of about 27 km, where a change occurs to upper-mantle material with a velocity of 8.3 km/s. The core is overlain by up to 6 km of material with a velocity of about 4.7 km/s which could be oceanic layer 2A basalts or continental crystalline rocks with some sedimentary material.The Fram Basin probably began to open contemporaneously with the North Atlantic about 70 m.y. ago, by spreading along the Nansen-Gakkel Ridge. Although not yet dated, the Makarov Basin is probably no older than the initiation of the Fram Basin and may be much younger. The Alpha Ridge may once have been part of the Lomonosov Ridge, splitting off to form the Makarov Basin between 70 and 25 m.y. ago and possibly contributing to the Eurekan Orogeny of 25 m.y. ago, evident on Ellesmere Island. In contrast, the likely age of the Canada Basin lies in the 125–190 m.y. range and may have been formed by the counter-clockwise rotation of Alaska and the Northwind Ridge away from the Canadian Arctic Islands. The Lomonosov Ridge emerges from this scenario as a block resulting from a strike-slip shear zone on the European continental shelf, related to the opening of the Canada basin (180-120 my) and then becomes an entity broken from this shelf by the opening of the Eurasia Basin (70-0 m.y.).  相似文献   

18.
A combined analysis of the recently collected aeromagnetic data from the Eurasian Basin with the magnetic data from the Labrador Sea, the Norwegian-Greenland Sea and the North Atlantic yields a plate kinematic solution for the Eurasian Basin which is consistent with the solution for the North Atlantic as a whole. It shows that the Eurasian Basin and Norwegian-Greenland Sea started to evolve at about anomaly 25 time, though active seafloor spreading did not start in either of these regions until anomaly 24 time. It further shows that the spreading in the Eurasian Basin has been a result of motion only between the North American and Eurasian plates since the beginning, with the Lomonosov Ridge remaining attached to the North American plate. The relative motion among the North American, Greenland and Eurasian plates as obtained from the plate kinematics of the North Atlantic shows that from Late Cretaceous to Late Paleocene (anomaly 34 to 25) Greenland moved obliquely to Ellesmere Island. It is suggested that most of this motion was taken up within the Canadian Arctic Islands resulting in little or no motion along Nares Strait between Greenland and Ellesmere Island. From Late Paleocene to mid-Eocene (anomaly 25-21) Greenland continued to move obliquely, resulting in a displacement of 125 km along and of 90 km normal to the Nares Strait. From mid-Eocene to early Oligocene another 100 km of motion took place normal to the Strait, which correlates well with the Eurekan Orogeny in the Canadian Arctic Island. During these times the relative motion between Greenland and Svalbard (Eurasian plate) was mainly strike-slip with a small component of compression. The implication of the resulting motion between the North American and the Eurasian plates onto the Siberian platform are discussed.  相似文献   

19.
A multiproxy analysis of Hole 911A (Ocean Drilling Program (ODP) Leg 151) drilled on the Yermak Plateau (eastern Arctic Ocean) is used to investigate the behaviour of the Svalbard/Barents Sea ice sheet (SBIS) during late Pliocene and early Pleistocene (~3.0-1.7 Ma) climate changes. Contemporary with the 'Mid-Pliocene (~3 Ma) global warmth' (MPGW), a warmer period lasting ~300 kyr with seasonally ice-free conditions in the marginal eastern Arctic Ocean is assumed to be an important regional moisture source, and possibly one decisive trigger for intensification of the Northern Hemisphere glaciation in the Svalbard/Barents Sea area at ~2.7 Ma. An abrupt pulse of ice-rafted debris (IRD) to the Yermak Plateau at ~2.7 Ma reflects distinct melting of sediment-laden icebergs derived from the SBIS and may indicate the protruding advance of the ice sheet onto the outer shelf. Spectral analysis of the total organic carbon (TOC) record being predominantly of terrigenous/fossil-reworked origin indicates SBIS and possibly Scandinavian Ice Sheet response to incoming solar radiation at obliquity and precession periodicities. The strong variance in frequencies near the 41 kyr obliquity cycle between 2.7 and 1.7 Ma indicates, for the first time in the Arctic Ocean, a close relationship of SBIS growth and decay patterns to the Earth's orbital obliquity amplitudes, which dominated global ice volume variations during late Pliocene/early Pleistocene climate changes.  相似文献   

20.
《Quaternary Science Reviews》2004,23(11-13):1435-1454
Numerous short sediment cores have been retrieved from the central Arctic Ocean, many of which have been assigned sedimentation rates on the order of mm/ka implying that the Arctic Basin was starved of sediments during Plio–Pleistocene times. A review of both shorter-term sedimentation rates, through analysis of available sediment core data, and longer-term sedimentation rates, through estimates of total sediment thickness and bedrock age, suggests that cm/ka-scale rates are pervasive in the central Arctic Ocean. This is not surprising considering the physiographic setting of the Arctic Ocean, being a small land-locked basin since its initial opening during Early Cretaceous times. We thus conclude that the central Arctic Ocean has not been a sediment starved basin, either during Plio–Pleistocene times or during pre-Pliocene times. Rigorous chronstratigraphic analysis permits correlation of sediment cores over a distance of ∼2600 km, from the northwestern Amerasia Basin to the northwestern Eurasia Basin via the Lomonosov Ridge, using paleomagnetic, biostratigraphic, and cyclostratigraphic data.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

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