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101.
102.
Testing the sensitivity of the East Antarctic Ice Sheet to Southern Ocean dynamics: past changes and future implications 下载免费PDF全文
103.
NICOLAJ KROG LARSEN KAREN LUISE KNUDSEN CHARLOTTE FOG KROHN CHRISTIAN KRONBORG REW S. MURRAY OLE BJØRSLEV NIELSEN 《Boreas: An International Journal of Quaternary Research》2009,38(4):732-761
Based on a large number of new boreholes in northern Denmark, and on the existing data, a revised event‐stratigraphy is presented for southwestern Scandinavia. Five significant Late Saalian to Late Weichselian glacial events, each separated by periods of interglacial or interstadial marine or glaciolacustrine conditions, are identified in northern Denmark. The first glacial event is attributed to the Late Saalian c. 160–140 kyr BP, when the Warthe Ice Sheet advanced from easterly and southeasterly directions through the Baltic depression into Germany and Denmark. This Baltic ice extended as far as northern Denmark, where it probably merged with the Norwegian Channel Ice Stream (NCIS) and contributed to a large discharge of icebergs into the Norwegian Sea. Following the break up, marine conditions were established that persisted from the Late Saalian until the end of the Early Weichselian. The next glaciation occurred c. 65–60 kyr BP, when the Sundsøre ice advanced from the north into Denmark and the North Sea, where the Scandinavian and British Ice Sheets merged. During the subsequent deglaciation, large ice‐dammed lakes formed before the ice disintegrated in the Norwegian Channel, and marine conditions were re‐established. The following Ristinge advance from the Baltic, initiated c. 55 kyr BP, also reached northern Denmark, where it probably merged with the NCIS. The deglaciation, c. 50 kyr BP, was followed by a long period of marine arctic conditions. Around 30 kyr BP, the Scandinavian Ice Sheet expanded from the north into the Norwegian Channel, where it dammed the Kattegat ice lake. Shortly after, c. 29 kyr BP, the Kattegat advance began, and once again the Scandinavian and British Ice Sheets merged in the North Sea. The subsequent retreat to the Norwegian Channel led to the formation of Ribjerg ice lake, which persisted from 27 to 23 kyr BP. The expansion of the last ice sheet started c. 23 kyr BP, when the main advance occurred from north–northeasterly directions into Denmark. An ice‐dammed lake was formed during deglaciation, while the NCIS was still active. During a re‐advance and subsequent retreat c. 19 kyr BP, a number of tunnel‐valley systems were formed in association with ice‐marginal positions. The NCIS finally began to break up in the Norwegian Sea 18.8 kyr BP, and the Younger Yoldia Sea inundated northern Denmark around 18 kyr BP. The extensive amount of new and existing data applied to this synthesis has provided a better understanding of the timing and dynamics of the Scandinavian Ice Sheet (SIS) during the last c. 160 kyr. Furthermore, our model contributes to the understanding of the timing of the occasional release of large quantities of meltwater from the southwestern part of the SIS that are likely to enter the North Atlantic and possibly affect the thermohaline circulation. 相似文献
104.
CHRISTIAN CHRISTIANSEN HELMAR KUNZENDORF KAY-CHRISTIAN EMEIS RUDOLF ENDLER ULRICH STRUCK THOMAS NEUMANN VADIM SIVKOV 《Boreas: An International Journal of Quaternary Research》2002,31(1):65-74
The present study examines sedimentation rates in the eastern Gotland Basin using a variety of methods that reveal considerable heterogeneity in the rates, both spatially and temporally. High-resolution seismic recordings and correlation with long sediment cores indicate increased thickness of strata and higher sedimentation rates (0.75 mm a -1 ) in the eastern part of the basin than in the western part (0.23 mm a -1 ) since the Littorina transgression some 8000 14 C years BP. This difference is apparently a consequence of a counterclockwise near-bottom circulation in the basin with periodically high current speeds that cause winnowing on the steep SE slope of the basin and differential settling of sediments in areas of low current speeds. On shorter time scales, recent sediment accumulation rates based on radiometric dating ( 210 Pb) are in general twice as high as those observed 25 years ago using the same method. The higher modern rates, compared to those of the 1970s, may partly be due to increased eutrophication, as more carbon is buried in the sediment, and partly due to increased erosion in shallow water areas. However, strong lateral variations are evident. The average sediment accumulation rates vary between 119 and 340 g m -2 a -1 (corresponding to sedimentation rates of 2.1-2.5 mm a -1 ) in the deepest part of the basin. Very high rates (6100 g m -2 a -1 , corresponding to sedimentation rates of 30 mm a -1 ) are observed on an intraslope basin site (offshore Latvia) at a water depth of only 70 m. The radiometrically determined sediment accumulation rates are up to three times higher than those estimated from average water column concentrations of suspended matter and from sediment trap flux rates. The discrepancy suggests that sedimentation in the deep basin may have a substantial contribution from near-bottom lateral transport. 相似文献
105.
CHRISTIAN KOEBERL WOLF UWE REIMOLD STEVEN B. SHIREY 《Meteoritics & planetary science》1998,33(3):513-517
Abstract— The impact origin of small craters in sedimentary rocks is often difficult to confirm because of the lack of characteristic shock metamorphic features. A case in point is the 3.1 Ma Aouelloul crater (Mauritania), 390 m in diameter, which is exposed in an area of Ordovician Oujeft and Zli sandstone. We studied several fractured sandstone samples from the crater rim for the possible presence of shock metamorphic effects. In thin section, a large fraction of the quartz grains show abundant subplanar and planar fractures. Many of the fractures are healed and are evident only as fluid inclusion trails. A few grains showed sets of narrow and densely spaced fluid inclusions trails in one (rarely two) orientations per grain, which could be possible remnants of planar deformation features (PDFs), although such an interpretation is not unambiguous. In contrast, an impact origin of the crater is confirmed by Re-Os isotope studies of the target sandstone and glass found around the crater rim, which show the presence of a distinct extraterrestrial component in the glass. 相似文献
106.
107.
In the Aare River Valley between Berne and Thoune a mud till unit occurs together with lacustrine sediments in a complex relationship. The high content of fine material in the mud till is due to incorporation of lake sediments by the advancing Aare glacier probably during the most extensive glaciation of the Swiss Alps. Special attention is given to the evolution of the grain size parameters in vertical sequences in sections at Raintalwald and Räbli. The trend of vertical variation of the parameters reflects the origin of the mud till. Ground moraine and mud till may both be lodgement till but are texturally quite distinct, and the incorporation of pre-existing sediments in the mud till is clearly demonstrated by the use of the grain size parameters. 相似文献
108.
109.
The Quaternary of the Kattegat area, Scandinavia: a review 总被引:1,自引:0,他引:1
HOLGER LYKKE-ANDERSEN KAREN LUISE KNUDSEN CHRISTIAN CHRISTIANSEN 《Boreas: An International Journal of Quaternary Research》1993,22(4):269-281
The Quaternary sedimentary history and its relations to the pre-Quaternary in the Kattegat region are reviewed. The Quaternary in the area is restricted to relatively young sediments, including scattered findings of Saalian deposits and more continuous occurrences from the Eemian, the Weichselian and the Holocene. Glacial and interglacial palaeoenvironmental reconstructions, including Holocene changes in oceanographic circulation, are reviewed, and the recent sedimentary processes and the present hydrographic regime are outlined. Furthermore, Quaternary and present tectonic activity in connection with some of the pre-Quaternary fault zones is discussed. 相似文献
110.
OTTO SALVIGSEN LENA ADRIELSSON CHRISTIAN HJORT MICHAEL KELLY JON Y. LANDVIK LARS RONNERT 《Polar research》1995,14(2):141-152
Glacial striae and other ice movement indicators such as roche moutonées, glacial erratics, till fabric and glaciotectonic deformation have been used to reconstruct the Late Weichselian ice movements in the region of eastern Svalbard and the northern Barents Sea. The ice movement pattern may be divided into three main phases: (1) a maximum phase when ice flowed out of a centre east or southeast of Kong Karls Land. At this time the southern part of Spitsbergen was overrun by glacial ice from the Barents Sea; (2) the phase of deglaciation of the Barents Sea Ice Sheet, when an ice cap was centred between Kong Karls Land and Nordaustlandet. At the same time ice flowed southwards along Storfjorden; and (3) the last phase of the Late Weichselian glaciation in eastern Svalbard is represented by local ice caps on Spitsbergen, Nordaustlandet, Barentsoya and Edgeøya.
The reconstructed ice flow pattern during maximum glaciation is compatible with a centre of uplift in the northern Barents Sea as shown by isobase reconstructions and suggested by isostatic modelling. 相似文献
The reconstructed ice flow pattern during maximum glaciation is compatible with a centre of uplift in the northern Barents Sea as shown by isobase reconstructions and suggested by isostatic modelling. 相似文献