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1.
Ice-rafted debris (IRD) (>2 mm), input in eight sediment cores along the Eurasian continental margin (Arctic Ocean), have been studied over the last two glacial/interglacial cycles. Together with the revised chronologies and new micropaleontological data of two cores from the northern Barents Sea (PS2138) and northeastern Kara Sea (PS2741) spanning Marine Isotope Stages (MIS) 6 to 1, the IRD data give new insights into the glacial history of northern Eurasian ice-sheets over the last 150 ka. The chronologies of the cores are based on stable isotope records, AMS 14C datings, paleomagnetic and biostratigraphic data.Extensive episodes of northern Barents Sea ice-sheet growth, probably to the shelf edge, occurred during the late Weichselian (MIS 2) and the Saalian (MIS 6). Major IRD discharge at the MIS 4/3-transition hints to another severe glaciation, probably onto the outer shelf, during MIS 4. IRD-based instabilities of the marine-based ice margin along the northern Barents Sea between MIS 4 and 2 are similar in timing with North Atlantic Heinrich events and Nordic Seas IRD events, suggesting similar atmospheric cooling over a broad region or linkage of ice-sheet fluctuations through small sea-level events.In the relatively low-precipitation areas of eastern Eurasia, IRD peak values during Termination II and MIS 4/3-transition suggest a Kara Sea ice-sheet advance onto the outer shelf, probably to the shelf edge, during glacial MIS 6 and 4. This suggests that during the initial cooling following the interglacials MIS 5, and possibly MIS 7, the combined effect of sustained inflow of Atlantic water into the Arctic Ocean and penetration of moisture-bearing cyclones into easterly direction supported major ice build-up during Saalian (MIS 6) and Mid-Weichselian (MIS 4) glaciation. IRD peak values in MIS 5 indicate at least two advances of the Severnaya Semlya ice-sheet to the coast line during the Early Weichselian. In contrast, a distinct Kara Sea ice advance during the Late Weichselian (MIS 2) is not documented by the IRD records along the northeastern Kara Sea margin.  相似文献   

2.
Towards a 4D topographic view of the Norwegian sea margin   总被引：1，自引：1，他引：0  
The present-day topography/bathymetry of the Norwegian mainland and passive margin is a product of complex interactions between large-scale tectonomagmatic and climatic processes that can be traced back in time to the Late Silurian Caledonian Orogeny. The isostatic balance of the crust and lithosphere was clearly influenced by orogenic thickening during the Caledonian Orogeny, but was soon affected by post-orogenic collapse including overprinting of the mountain root, and was subsequently affected by a number of discrete extensional events eventually leading to continental break-up in Early Eocene time. In the mid-Jurassic the land areas experienced deep erosion in the warm and humid climate, forming a regional paleic surface. Rift episodes in the Late Jurassic and Early Cretaceous, with differential uplift along major fault zones, led to more pronounced topographic contrasts during the Cretaceous, and thick sequences of clastic sediments accumulated in the subsiding basins on the shelf. Following renewed extension in the Late Cretaceous, a new paleic surface developed in the Paleocene. Following break-up the margin has largely subsided thermally, but several Cenozoic shortening events have generated positive contraction structures. On the western side of the on-shore drainage divide, deeper erosion took place along pre-existing weakness zones, creating the template of the present day valleys and fjords. In the Neogene the mainland and large portions of the Barents Sea were uplifted. It appears that this uplift permitted ice caps to nucleate and accumulate during the Late Pliocene northern hemisphere climatic deterioration. The Late Pliocene to Pleistocene glacial erosion caused huge sediment aprons to be shed on to the Norwegian Sea and Barents Sea margins. Upon removal of the ice load the landmass adjusted isostatically, and this still continues today.  相似文献   

3.
Seven regionally correlatable reflectors, named R7 (oldest) to R1, have been identified in the Upper Cenozoic sedimentary succession along the western continental margin of Svalbard and the Barents Sea. Regional seismic profiles have been used to correlate between submarine fans that comprise major depocentres in this region. Glacial sediment thicknesses reach up to 3 seconds two-way time, corresponding to 3.5–4 km. Despite limited chronostratigraphic control, ages have been assigned to the major sequence boundaries based on ties both to exploration wells and to shallow boreholes, and by paleoenvironmental interpretations and correlations with other regions. Lateral and vertical variations in seismic facies, between stratified and chaotic with slump structures, have major implications for the interpretation of the depositional regime along the margin. The main phases of erosion and deposition at different segments of the margin are discussed in the paper, which also provides a regional seismic stratigraphic framework for two complementary papers in the present volume. Reflector R7 marks the onset of extensive continental shelf glaciations, but whereas the outer Svalbard shelf has been heavily and frequently glaciated since R7 time, this did not occur, or occurred to a much less extent, until R5 time in the southern Barents Sea. The present study provides the background for a quantification of the late Cenozoic glacial erosion of Svalbard and the Barents Sea. The rates of erosion and deposition exhibit large temporal and spatial variations reflecting the importance of glacial processes in the Late Cenozoic development of this nearly 1000 km long margin.  相似文献   

4.
The land surface of what is now the Barents Sea region may have been eroded to a sub-aerial platform prior to the Quaternary, due to both tectonic uplift-induced and sea-level lowering-induced erosion processes. The Barents Sea was then further eroded into its present form by the subsequent action of ice sheets. Two bedrock configurations, representing the pre-Quaternary sub-aerial Barents Shelf topography and the largely submarine morphology of the present day, were used as input to a glaciological ice sheet model so that the dynamic evolution of the maximum-sized ice sheets, caused solely by a change in bedrock elevation, could be identified. The ice-sheet model was run under constant glacial environmental conditions, until mass balance stability was reached, over both bedrock configurations. The simple parabolic ice sheet surface, which formed on a flat sub-aerial bedrock platform, was found to be significantly different in dynamic character compared with an ice sheet developed on the present submarine bedrock topography. In this latter situation, the central ice dome is drained by ice streams in Bjørnøyrenna, Storfjordrenna and smaller outlet glaciers in the north of the ice sheet.  相似文献   

5.
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6.
Paleoceanographic changes since the Late Weichselian have been studied in three sediment cores raised from shelf depressions along a north–south transect across the central Barents Sea. AMS radiocarbon dating offers a resolution of several hundred years for the Holocene. The results of lithological and micropaleontological study reveal the response of the Barents Sea to global climatic changes and Atlantic water inflow. Four evolutionary stages were distinguished. The older sediments are moraine deposits. The destruction of the Barents Sea ice sheet during the beginning of the deglaciation in response to climate warming and sea level rise resulted in proximal glaciomarine sedimentation. Then, the retreat of the glacier front to archipelagoes during the main phase of deglaciation caused meltwater discharge and restricted iceberg calving. Fine-grained distal glaciomarine sediments were deposited from periodic near-bottom nepheloid flows and the area was almost permanently covered with sea ice. The dramatic change in paleoenvironment occurred near the Pleistocene/Holocene boundary when normal marine conditions ultimately established resulting in a sharp increase of biological productivity. This event was diachronous and started prior to 10 14C ka BP in the southern and about 9.2 14C ka in the northern Barents Sea. Variations in sediment supply, paleoproductivity, sea-ice conditions, and Atlantic water inflow controlled paleoenvironmental changes during the Holocene.  相似文献   

7.
We present a mass balance model for Eurasia which is based on the calculation of accumulation from a moisture balance concept. The model is forced with 500 hPa temperatures from GCM time slices at LGM and present day. The model simulates key characteristics, such as control on the size of ice sheets through the advection of moisture, asymmetric ice sheets due to advection of moisture and orography, and the drying of ice sheets when they grow. A simulation of the Eurasian Ice Sheet through a full glacial cycle shows that the model reproduces realistic ice sheets that compare well with geomorphological data. During the Middle Weichselian and the Late Weichselian, the model picks up the trend that the Scandinavian part of the ice grows towards the south and east whilst the ice sheet covering the Barents and Kara Seas remains relatively stable. However, the model seriously underestimates the observed ice extent in the Baltic area. Uncertainties in the temperature and the wind field limit the reliability of regional modelling results.  相似文献   

8.
Recent studies in the Arkhangelsk region, northwest Russia, have identified at least three consecutive tills all associated with the last Valdaian (Weichselian) glaciation. The Scandinavian ice sheet deposited a Late Valdaian till (ca. 17 ka BP), whereas two tills were deposited in the Early–Middle Valdaian by the Barents/Kara Sea ice sheet (ca. 45–60 ka BP) and an older ice sheet with an eastern centre (ca. 74 ka BP). This article expands on previous stratigraphical work on the discrimination of regional till units by a combination of compositional characteristics and directional properties. Tills associated with the Scandinavian ice sheet were deposited by a glacier advancing from west or northwest, transporting predominantly material from the Fennoscandian shield and the White Sea area. The Barents/Kara Sea ice sheet moved from the north and northeast, whereas the oldest ice advance came from the east–southeast. Although, the two oldest tills both contain material with an eastern provenance, the Viryuga Till is dominated more by local carbonate-rich material. This study demonstrates that detailed investigation of till units facilitate the distinction of glacial events imperative for the reconstructing of the last glaciation in northern Russia.  相似文献   

9.
The western Barents Sea continental margin, between 74° and 77°N, comprises 7–8 km post-Paleocene sediments. The margin sediments have been divided into four seismic sequences dated by seismic correlation to adjacent areas. This chronostratigraphy shows that the uppermost three sequences are of glacial origin, deposited during the last 2.3 m.y. A huge sedimentary wedge, the Storfjorden Fan, was deposited in front of the Storfjorden Trough between 2.3 and 0.44 Ma, whereas during the last 0.44 m.y. a more evenly distribution pattern is observed. The outbuilding of the fan is related to the onset of the northern hemisphere glaciations causing intense glacial erosion of predominantly consolidated rocks. Seismic facies interpretations indicates that the fan outbuilding was connected to large-scale mass movements. Within the uppermost part of the glacial sequence parallel and continuous reflectors and locally disturbed pattern on the upper slope are associated with downslope change in facies. Volumetric calculations, based on velocity studies and isopach maps, have been used to quantify Cenozoic erosion, sediment yield, sedimentation and erosion rates. Approximately 3300 m of post-Paleocene erosion is calculated within the drainage area of the Storfjorden Fan, of which about 1700 m was eroded in late Pliocene-Pleistocene times giving an average denudation rate of 0.63 mm/yr.  相似文献   

10.
The evolution of a submarine fan, the Bear Island Trough Mouth Fan, is outlined using high-resolution seismic data. Eight seismic units are identified. The identified units comprise sediments of Middle and Late Pleistocene age. They were probably deposited during eight glacial advances of the Barents Sea Ice Sheet to the shelf break. The units are dominated by a chaotic seismic signature on the upper fan and a mounded seismic facies further downslope. The mounded signature is inferred to reflect large submarine debris flow deposits, probably generated by oversteepening of the upper slope. Unlike many other passive margin fans, glacigenic sediments derived from an ice sheet at the shelf break were the primary sediment input. During interstadials and interglacials the sedimentation rate was reduced markedly. Three large sliding events also influenced the Middle and Late Pleistocene fan growth.  相似文献   

11.
Beach and shoreface sediments deposited in the more than 800-km long ice-dammed Lake Komi in northern European Russia have been investigated and dated. The lake flooded the lowland areas between the Barents–Kara Ice Sheet in the north and the continental drainage divide in the south. Shoreline facies have been dated by 18 optical stimulated luminescence (OSL) dates, most of which are closely grouped in the range 80–100 ka, with a mean of 88±3 ka. This implies that that the Barents–Kara Ice Sheet had its Late Pleistocene maximum extension during the Early Weichselian, probably in the cold interval (Rederstall) between the Brørup and Odderade interstadials of western Europe, correlated with marine isotope stage 5b. This is in strong contrast to the Scandinavian and North American ice sheets, which had their maxima in isotope stage 2, about 20 ka. Field and air photo interpretations suggest that Lake Komi was dammed by the ice advance, which formed the Harbei–Harmon–Sopkay Moraines. These has earlier been correlated with the Markhida moraine across the Pechora River Valley and its western extension. However, OSL dates on fluvial sediments below the Markhida moraine have yielded ages as young as 60 ka. This suggests that the Russian mainland was inundated by two major ice sheet advances from the Barents–Kara seas after the last interglacial: one during the Early Weichselian (about 90 ka) that dammed Lake Komi and one during the Middle Weichselian (about 60 ka). Normal fluvial drainage prevailed during the Late Weichselian, when the ice front was located offshore.  相似文献   

12.
The Pyoza River area in the Arkhangelsk district exposes sedimentary sequences suitable for study of the interaction between consecutive Valdaian ice sheets in Northern Russia. Lithostratigraphic investigations combined with luminescence dating have revealed new evidence on the Late Pleistocene history of the area. Overlying glacigenic deposits of the Moscowian (Saalian) glaciation marine deposits previously confined to three separate transgression phases have all been connected to the Mikulinian (Eemian) interglacial. Early Valdaian (E. Weichselian) proglacial, lacustrine and fluvial deposits indicate glaciation to the east or north and consequently glacier damming and meltwater run-off in the Pyoza area around 90–110 ka BP. Interstadial conditions with forest-steppe tundra vegetation and lacustrine and fluvial deposition prevailed at the end of the Early Valdaian around 75–95 ka BP. A terrestrial-based glaciation from easterly uplands reached the Pyoza area at the Early to Middle Valdaian transition around 65–75 ka BP and deposited glaciofluvial strata and subglacial till (Yolkino Till). During deglaciation, laterally extensive glaciolacustrine sediments were deposited in ice-dammed lakes in the early Middle Valdaian around 55–75 ka BP. The Barents–Kara Sea ice sheet deposited the Viryuga Till on the lower Pyoza from northerly directions. The ice sheet formed the Pyoza marginal moraines, which can be correlated with the Markhida moraines further east, and proglacial lacustrine deposition persisted in the area during the first part of the Middle Valdaian. Glacio-isostatic uplift caused erosion followed by pedogenesis and the formation of a deflation horizon in the Middle Valdaian. Widely dispersed periglacial river plains were formed during the Late Valdaian around 10–20 ka BP. Thus, the evidence of a terrestrial-based ice sheet from easterly uplands in the Pyoza area suggests that local piedmont glaciers situated in highlands such as the Timan Ridge or the Urals could have developed into larger, regionally confined ice sheets. Two phases of ice damming and development of proglacial lakes occurred during the Early and Middle Valdaian. The region did not experience glaciation during the Late Valdaian.  相似文献   

13.
Glaciations had a profound impact on the global sea-level and particularly on the Arctic environments. One of the key questions related to this topic is, how did the discharge of the Siberian Ob and Yenisei rivers interact with a proximal ice sheet? In order to answer this question high-resolution (1–12 kHz), shallow-penetration seismic profiles were collected on the passive continental margin of the Kara Sea Shelf to study the paleo-drainage pattern of the Ob and Yenisei rivers. Both rivers incised into the recent shelf, leaving filled and unfilled river channels and river canyons/valleys connecting to a complex paleo-drainage network.These channels have been subaerially formed during a regressive phase of the global sea-level during the Last Glacial Maximum. Beyond recent shelf depths of 120 m particle transport is manifested in submarine channel–levee complexes acting as conveyor for fluvial-derived fines. In the NE area, uniform draping sediments are observed. Major morphology determining factors are (1) sea-level fluctuations and (2) LGM ice sheet influence. Most individual channels show geometries typical for meandering rivers and appear to be an order of magnitude larger than recent channel profiles of gauge stations on land.The Yenisei paleo-channels have larger dimensions than the Ob examples and could be originated by additional water release during the melt of LGM Putoran ice masses.Asymmetrical submarine channel–levee complexes with channel depths of 60 m and more developed, in some places bordered by glacially dominated morphology, implying deflection by the LGM ice masses. A total of more than 12,000 km of acoustic profiles reveal no evidence for an ice-dammed lake of greater areal extent postulated by several workers. Furthermore, the existence of the channel–levee complexes is indicative of unhindered sediment flow to the north. Channels situated on the shelf above 120-m water depth exhibit no phases of ponding and or infill during sea-level lowstand. These findings denote the non-existence of an ice sheet on large areas of the Kara Sea shelf.  相似文献   

14.
The North Taymyr ice-marginal zone (NTZ) is a complex of glacial, glaciofluvial and glaciolacustrine deposits, laid down on the northwestern Taymyr Peninsula in northernmost Siberia, along the front of ice sheets primarily originating on the Kara Sea shelf. It was originally recognised from satellite radar images by Russian scientists; however, before the present study, it had not been investigated in any detail. The ice sheets have mainly inundated Taymyr from the northwest, and the NTZ can be followed for 700–750 km between 75°N and 77°N, mostly 80–100 km inland from the present Kara Sea coast.The ice-marginal zone is best developed in its central parts, ca. 100 km on each side of the Lower Taymyr River, and has there been studied by us in four areas. In two of these, the ice sheet ended on land, whereas in the two others, it mainly terminated into ice-dammed lakes. The base of the NTZ is a series of up to 100-m-high and 2-km-wide ridges, usually consisting of redeposited marine silts. These ridges are still to a large extent ice-cored; however, the present active layer rarely penetrates to the ice surface. Upon these main ridges, smaller ridges of till and glaciofluvial material are superimposed. Related to these are deltas corresponding to two generations of ice-dammed lakes, with shore levels at 120–140 m and ca. 80 m a.s.l. These glacial lakes drained southwards, opposite to the present-day pattern, via the Taymyr River valley into the Taymyr Lake basin and, from there, most probably westwards to the southern Kara Sea shelf.The basal parts of the NTZ have not been dated; however, OSL dates of glaciolacustrine deltas indicate an Early–Middle Weichselian age for at least the superimposed ridges. The youngest parts of the NTZ are derived from a thin ice sheet (less than 300 m thick near the present coast) inundating the lowlands adjacent to the lower reaches of the Taymyr River. The glacial ice from this youngest advance is buried under only ca. 0.5 m of melt-out till and is exposed by hundreds of shallow slides. This final glaciation is predated by glacially redeposited marine shells aged ca. 20,000 BP (14C) and postdated by terrestrial plant material from ca. 11,775 and 9500 BP (14C)–giving it a last global glacial maximum (LGM; Late Weichselian) age.  相似文献   

15.
Seismic data combined with core analysis of the northwesternmost exploration well on the Norwegian continental margin, well 7316/5-1, has been used to map and discuss the genesis of three well-defined sand ridges. The sand ridges have a NE-SW to N-S orientation and are of Late Pliocene age. The dimensions of the ridges are: height 40 m, length 2–4 km and width 0.5–1 km.In relation to the glaciation models of the Barents Sea, the position of well 7316/5-1, and especially information from a core that penetrated one of the sand ridges, provide important information. The ridges are not, in themselves, diagnostic for grounded glaciers at the margin of the Barents Sea shelf during the Late Pliocene, although the presence of pebbles in a cored section of the ridges may represent ice-dropped material. Whether the possible influx of glaciogenic material is related to local or regional glaciations on the Barents Shelf remains to be evaluated.  相似文献   

16.
The last post-glacial transgression and present highstand of sea level were accompanied by a reduction in the terrigenous flux to the deep ocean bordering the active convergent margin off the eastern North Island of New Zealand. Although in accord with long-established models of highstand shelf deposition, new data from giant piston core MD97 2121 (2314 m depth) reveal that the flux also varied with terrigenous supply and palaeocirculation. Between 15 and 9.5 ka, the flux reduced from 33 to 20 g/cm2/ka as supply declined with an expanding vegetation cover, and mud depocentres became established on the continental shelf. An increase from 20 to 27 g/cm2/ka during 9.5–3.5 ka coincided with a strengthened East Cape Current which probably introduced sediment from fluvial and shelf sources in the north. The flux profile shows no immediate response to the establishment of modern sea level 7 ka. However, accumulation decreased from 3.5 to 1 ka as more sediments were retained on the shelf, possibly under wind-strengthened, along-shelf currents. Over the last 1 ka, the flux decline halted under increased terrigenous supply during anthropogenic development of the land.Despite the proximity of the North Island's Central Volcanic Region, major eruptions caused only brief increases (centuries duration) in the terrigenous flux through direct deposition of airfall and possibly fluvial redistribution of onshore volcanic deposits. Frequent earthquakes also had little short-term effect on accumulation although such events, along with volcanism, probably contribute to the long-term high flux of the region.The other measured flux component, biogenic carbonate, reached maxima of 6 g/cm2/ka between 11 and 8.5 ka when nutrient-bearing waters of the East Cape Current dominated the palaeoceanography. After these peaks, carbonate accumulation declined gradually to modern levels of 3 g/cm2/ka.  相似文献   

17.
Based on a grid of high resolution, single channel seismic lines, this paper addresses the Late Cenozoic evolution of the western Svalbard continental shelf. The seismic structure of the shelf includes at least 16 erosional unconformities, each representing a glacial advance. The evolution during the last approximately one million years has been divided into six main erosional and depositional phases. Differential margin subsidence around a hinge zone is an important controlling mechanism for the accumulation of the sedimentary wedge at the outer shelf. The most significant depositional change appears to be related to a general climatic shift, globally recorded to be centred around 1 Ma. At this level, corresponding to the Upper Regional Unconformity (URU) on the shelf, the depositional regime changed from net erosion to net deposition and shelf aggradation. Of major significance is probably a shift from thick, eroding glaciers with steep ice profiles, to low profile fast flowing ice streams maintained by an increased amount of interglacial and interstadial sediments. The relationship between climatic fluctuations, glacial dynamics and depositional regime is discussed.  相似文献   

18.
Abstract— Organic geochemistry applied to samples of bedrock and surface sediment from the Haughton impact structure detects a range of signatures representing the impact event and the transfer of organic matter from the crater bedrock to its erosion products. The bedrock dolomite contains hydrocarbon‐bearing fluid inclusions which were incorporated before the impact event. Comparison of biomarker data from the hydrocarbons in samples inside and outside of the crater show the thermal signature of an impact. The occurrence of hydrocarbon inclusions in hydrothermal mineral samples shows that organic matter was mobilized and migrated in the immediate aftermath of the impact. The hydrocarbon signature was then transferred from bedrock to the crater‐fill lacustrine deposits and present‐day sediments in the crater, including wind‐blown detritus in snow/ice. Separate signatures are detected from modern microbial life in crater rock and sediment samples. Signatures in Haughton crater samples are readily detectable because they include hydrocarbons generated by the burial of organic matter. This type of organic matter is not expected in crater samples on other planets, but the Haughton data show that, using very high resolution detection of organic compounds, any signature of primitive life in the crater rocks could be transferred to surface detritus and so extend the sampling medium.  相似文献   

19.
A complex history of Cenozoic vertical movements in the Faroe region has been revealed from interpretation of geophysical and geological data, mainly offshore reflection seismic data, side-scan images, shallow cores, and onshore mapping. The history comprises several phases of tectonic disturbances observed at different scales. On the eastern margin of the Faroe Platform a late Eocene–early Oligocene phase of doming of the Faroe Platform has caused a postdepositional tilting of Eocene strata along the southern margin of the platform; a mid-Miocene phase of compressional tectonics is evidenced on seismic transects as gentle anticlines and associated reverse faults; and possible Pliocene uplift of the Faroe Islands is indicated by a progradational wedge of sediments deposited on the eastern Faroe Platform. At the continental margin/slope north of the Faroe Platform, reflection seismic data imaging the postbasalt sedimentary strata indicate three distinct tectonic events phases in the Eocene–Oligocene, Miocene and Pliocene, respectively. In contrast to the Faroe Platform the Faroe–Shetland Channel was characterised by more or less continuous subsidence dominated throughout the Cenozoic. During the Eocene, sediments deposited in the Faroe–Shetland Channel was mostly derived from a source area on the British shelf.  相似文献   

20.
Growth of mid-latitude ice sheets during the glacial cycles of the Quaternary repeatedly reorganises the pattern of groundwater flow on a continent-wide scale. Relatively small scale non-glacial catchments are replaced by catchments which are integrated on the scale of continental ice sheets. Simulations are presented of the response to glaciation of a large part of the western European groundwater system during the last two (Saalian, Weichselian) glacial cycles. A two-dimensional model along an ice sheet flowline from western Sweden to The Netherlands illustrates the impact of glaciation on flow in the vertical plane, and a vertically integrated model illustrates its impact on areal patterns of flow.Hydraulics heads, hydraulic gradients and flow velocities are increased far above their modern values, and relatively shallow aquifers are completely flushed out during glacial periods. There are significant implications for groundwater chemistry and geological structures. Large seepage pressures generated near to ice sheet margins and major impacts on the distribution of effective pressures will produce structures such as hydrofractures, sediment dykes, sediment volcanoes, loading structures etc. The model can be readily applied to hydrocarbon resorvoirs.  相似文献   

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