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1.
Late Weichselian glaciation history of the northern North Sea   总被引：8，自引：1，他引：8  
Based on new data from the Fladen, Sleipner and Troll areas, combined with earlier published results, a glaciation curve for the Late Weichselian in the northern North Sea is constructed. The youngest date on marine sedimentation prior to the late Weichselian maximum ice extent is 29.4 ka BP. At this time the North Sea and probably large parts of southern Norway were deglaciated (corresponding to the Alesund interstadial in western Norway). In a period between 29.4 and c. 22 ka BP, the northern North Sea experienced its maximum Weichselian glaciation with a coalescing British and Scandinavian ice sheet. The first recorded marine inundation is found in the Fladen area where marine sedimentation started close to 22 ka BP. After this the ice fronts receded both to the east and west. The North Sea Plateau, and possibly parts of the Norwegian Trench, were ice-free close to 19.0 ka, and after this a short readvance occurred in this area. This event is correlated with the advance recorded at Dimlington, Yorkshire, and the corresponding climatostratigraphic unit is denoted the Dimlington Stadial (18.5 ka to 15.1 ka). The Norwegian Trench was deglaciated at 15.1 ka in the Troll area. The data from the North Sea, together with the results from Andwa, northern Norway (Vorren et al . 1988; Møller et al . 1992), suggest that the maximum extent of the last glaciation along the NW-European seaboard from the British Isles to northern Norway was prior to c . 22 ka BP.  相似文献   
2.
High resolution environmental records with a refined chronology are essential to understand, reconstruct and model the climate dynamics of the last glacial-interglacial transition. Sediments from Lake Torfadalsvatn in northern Iceland contain at least four primary volcanic tephras that belong to ash zone I in the North Atlantic deep-sea cores. We chemically define these basaltic/rhyolitic tephras and the high resolution allows us to date them to about 10,800, 10,600, 9300 and 8900 BP. This detailed tephrostratigraphy will act as a refined dating and correlation tool in the North Atlantic region and enable calibration between different absolute chronologies. The pollen stratigraphy of the sediments suggests that by 10,400 14C years BP plant colonization of coastal north Iceland had begun. The pollen stratigraphy shows a succession of pioneer plants, from open tundra vegetation towards birch-juniper woodland, which probably also reflects a transition from a cool climate at 10,400 BP to conditions similar to today's sub-polar oceanic climate around 9200 BP. Diatom data largely concur with the climatic information from pollen, indicating gradually increasing productivity in the lake.  相似文献   
3.
A composite stratigraphical sequence, the Fnjóskadalur Sequence, reveals ten cycles of glacier advances and formation of ice-dammed lakes in Fnjóskadalur in central North Iceland. Chemical analyses of the Skógar Tephra, with its type locality in this valley, have enabled a correlation with Ash zone I in deep sea sediments of the North Atlantic and with the Vedde Ash Bed on land in western Norway, where it is dated to 10,600 BP. The Skógar Tephra is composed of two layers, a basaltic tephra (STP-1) and a rhyolitic tephra (STP-2) erupted almost simultaneously from two different Icelandic volcanoes. The STP-1 tephra originates from the Katla volcano in South Iceland, and the öræfajökull volcano in Southeast Iceland is considered a plausible source of the STP-2 tephra. This new dating of the Skógar Tephra puts the three youngest glacier advances of the Fnjóskadalur Sequence within a 1000 year period between 10,600 and 9650 BP. The redated Late Weichselian glacial history now extracted from the Fnjóskadalur Sequence shows that glaciers in North Iceland were more extended in Younger Dryas and Preboreal times than previously assumed. This fits with the revised deglaciation pattern which has evolved in recent years.  相似文献   
4.
Rundgren, M., Ingólfsson, Ó., Björck, S., Jiang, H. & Haflioason, H. 1997 (September): Dynamic sea-level change during the last deglaciation of northern Iceland. Boreas , Vol. 26, pp. 201–215. Oslo. ISSN 0300–9483.
A detailed reconstruction of deglacial relative sea-level changes at the northern coast of Iceland, based on the litho- and biostratigraphy of lake basins, indicates an overall fall in relative sea level of about 45 m between 11300 and 9100 BP, corresponding to an isostatic rebound of 77 m. The overall regression was interrupted by two minor transgressions during the late Younger Dryas and in early Preboreal, and these were probably caused by a combination of expansions of local ice caps and readvances of the Icelandic inland ice-sheet margin. Maximum absolute uplift rates are recorded during the regressional phase between the two transgressions (10000–9850 BP), with a mean value of c . 15 cm 14C yr-1 or 11–12 cm cal. yr-1. Mean absolute uplift during the regressional phase following the second transgression (9700–9100 BP) was around 6 cm 14C yr-1, corresponding to c . 3 cm cal. yr-1, and relative sea level dropped below present-day sea level at 9000 BP.  相似文献   
5.
Thirteen samples from three cores and boreholes are examined using micromorphology to test existing interpretations of Late Quaternary sedimentary sequences from the Norwegian Channel, North Sea Fan and the North Sea Plateau. Previous studies have interpreted these sediments using arbitrary parameters as reflecting Late Weichselian subglacial and glacimarine conditions associated with the Scandinavian Ice Sheet and Norwegian Channel ice stream. This study develops existing micromorphological criteria to interpret the samples as reflecting specific processes of subglacial deformation and proximal and distal glacimarine sedimentation during and subsequent to the Last Glacial Maximum. The study concludes by outlining diagnostic criteria for the identification of these sediment types from core and borehole samples of other Quaternary sediments.  相似文献   
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7.
Abundant dinocysts in a high-resolution core from Voldafjorden, western Norway, reflect changes in sea surface-water conditions during the last c. 11 300 BP. The period from c. 11 300 to 10 800 BP (Late Allerφd) was characterized by cool temperate surface-waters, high annual temperature variation and relatively strong stratification of the water column, which is characteristic of fjord environments. Due to the stratification of the surface waters, the uppermost layer may have warmed considerably. This generated a principal difference in temperature conditions between land and sea, with slightly higher temperatures in the marine environments. The period from c. 10 800 to 10 000 BP is characterized by very harsh conditions, with sea surface-water temperatures close to freezing and long lasting seasonal sea-ice cover. Similar temperature changes at the beginning and end of the Younger Dryas are characteristic for NW Europe, but those in Voldafjorden differ from those in the open sea and in the Norwegian Channel by being significantly larger. The stratification of the water column during the Late Allerφd was probably broken down because of incipient inflow of temperate normal saline waters, which caused a marked sea surface-water warming, at c. 10 000 BP. Surface-water conditions close to those of today were gradually established between c. 10000 and 9500 BP. However, these interglacial conditions were abruptly interrupted by a significant drop in winter sea surface-water temperature and salinity occurring around 9700 BP. From c. 9500 to 7000 BP the influence of temperate normal saline water masses increased stepwise until full interglacial conditions were established around c. 7000 BP. The change in the dinocyst assemblage around 7000 BP in Voldafjorden was probably related to the onset of the modern Norwegian Coastal Current, previously documented in cores from the Skagerrak and the Mid-Norwegian Continental Shelf. The last c. 7000 BP is characterized by relatively stable surface-water conditions, possibly interrupted by periods of cooling or decreased inflow of temperate normal saline water. Like several other dinoflagellate cyst records from the Norwegian-Greenland Sea, O. centrocarpum peak values are between 4000 and 5000 BP, suggesting a regional-scale oceanographic change.  相似文献   
8.
In connection with a new deglaciation concept for Iceland, implying an extensive glaciation during the Younger Dryas and the decay of the Icelandic inland ice sheet during the Preboreal, the history of relative sea-level changes on Iceland has been re-evaluated. New field data from the Reykjavik area, in Faxaflói Bay southwestern Iceland, were obtained in order to construct the first stratigraphically controlled curve of relative sea-level displacements for Iceland. The curve is constructed on the basis of radiocarbon-dated shells in raised marine deposits and on tephrostratigraphically controlled and radiocarbon-dated, submerged peat deposits. The curve suggests that a post-glacial relative sea-level change of about 45 m, from + 43 m a.s.1. to — 2 m a.s.l, occurred over a period of 900 14C-years in the Reykjavik area between 10 300 BP and 9400 BP. The sea-level curve shows a shoreline displacement of c . 5 cm 14Cyr-1 for that period. The mean absolute uplift rate is calculated to be 6.9 cm 14C yr-1, which is about double the fastest rate reported from any other coastal North Atlantic site. Although this rapid uplift can probably be partly explained by a 14C plateau around the termination of the Pleistocene, it is more than likely controlled by rapid Preboreal deglaciation, together with low asthenosphere viscosities below Iceland and the release of hydroisostatic stresses in connection with the deglaciation.  相似文献   
9.
Deposits within the floor of the Norwegian Basin were sampled to characterize the deposition from the Storegga Slide, the largest known Holocene‐aged continental margin slope failure complex. A 29 to 67 cm thick veneer of variable‐coloured, finely layered Holocene sediment caps a homogeneous, extremely well‐sorted, poorly consolidated, very fine‐grained, grey‐coloured sediment section that is >20 m thick on the basin floor. This homogeneous unit is interpreted to represent the uppermost deposits generated by a gravity flow associated with the last major Storegga Slide event. Sediments analogous to the inferred source material of the slide deposits were collected from upslope on the Norwegian Margin. Sediments sampled within the basin are distinguishable from the purported source sediments, suggesting that size sorting has significantly altered this material along its flow path. Moreover, the very fine grain size (3·1 ± 0·3 μm) suggests that the >20 m thick homogeneous unit which was sampled settled from suspension after the turbulent flow was over. Although the turbulent phase of the gravity flow that moved material out into the basin may have been brief (days), significantly more time (years) is required for turbid sediments to settle and dewater and for the new sea floor to be colonized with a normal benthonic fauna. Pore water sulphate concentrations within the uppermost 20 m of the event deposit are higher than those normally found in sea water. Apparently the impact of microbial sulphate reduction over the last ca 8·1 cal ka bp since the re‐deposition of these sediments has not been adequate to regenerate a typical sulphate gradient of decreasing concentration with sub‐bottom depth. This observation suggests low rates of microbial reactions, which may be attributed to the refractory carbon composition in these re‐deposited sediments.  相似文献   
10.
Analysis of 2D and 3D seismic records from the continental shelf off western Norway, in combination with chronological constraints from 14C dates, has led to a model for the glacial development in these shelf areas between c. 15 and 13 14C ka BP. On the shallow Måløy Plateau adjacent to the Norwegian Channel, iceberg scours are preserved below a prominent moraine ridge, which by correlation to the Norwegian Channel indicate ice retreat at c. 15 14C ka BP. Subsequently, the ice advanced across the scoured surface and deposited a till sheet before stabilizing to deposit a prominent moraine, termed the Bremanger Moraine. Based on location on the shelf, seismic stratigraphy, morphology and C dates the Bremanger Moraine is correlated with a significant moraine on the continental shelf off Trøndelag. We suggest that these features are products of a regional glacial event, the Bremanger Event, dated to <15–13.3 14C ka BP. The Bremanger Event is probably a result of the deteriorating climatic conditions in the NE Atlantic during Heinrich event 1.  相似文献   
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