摘要:

Shallow seismic, sedimentological and macrofossil data and AMS radiocarbon dates on terrestrial plant remains from submarine deposits in Fakse Bugt in the southwestern part of the Baltic Sea are presented. The sediments were deposited near the shore of the Baltic Ice Lake, mostly in barrier‐lagoon environments, during two highstand episodes dated to around 12.5–12.214C ka BP and 10.6–10.3 ka BP. Coastal sediments from the highstands indicate maximum water levels of 13–15 m and 13 m below present sea level, respectively. During the first episodeSalix polariswas widespread in the land area, and during the second episodeDryas octopetalaandBetula nanawere the most common woody plants. During the lowstand episodeBetula pubescenswoods dominated. The flora and fauna of the Baltic Ice Lake were rather diverse, reflecting the long and increasing distance to the margin of the Fennoscandian Ice Sheet. Calcium‐carbonate‐rich, mesotrophic water characterized the Baltic Ice Lake in

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00772.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

To a varying degree the Middle and Late Pleistocene ice sheets in northern Eurasia redirected the drainage of major catchments in Europe and western Siberia from the North Sea and Arctic Ocean south to the Caspian, Black Sea, and ultimately the Mediterranean. During the Late Weichselian, glacial meltwater reached the Mediterranean through the Dniepr and Don catchments and to a minor extent through the Danube. During the Warthe Substage of the Saalian, meltwater from the Volga was most likely added. During the Drenthe Substagc of the Saalian the watershed shifted Par to the east, and meltwater reached the Mediterranean also from the Oh. Irtysh, Yenisei, and Tunguska catchments in Siberia. Depending on the extent of the ice sheets, the increase in freshwater supply during deglaciations resulted in reductions of Mediterranean overflow into the North Atlantic. Such overflow reductions may have reduced vapour transport to the ice sheets and thus accelerated wastage.

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00773.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

A numerical ice‐sheet model was run in order to produce reconstructions of the Late Weichselian ice coverage of Franz Josef Land, Russian High Arctic. The model grid covers the archipelago and surrounding shelf, but does not include the whole Barents‐Kara region or the extensive ice cover that may have built up there. One experiment, where rates of iceberg calving at the grounded margin were curtailed because of the assumed presence of permanent thick sea ice, yielded a single I.8 km‐thick ice dome which covered the entire archipelago and surrounding sea. If, however, iceberg calving were included in the model's environmental input, the extent of the ice sheet would be limited to the periphery of the archipelago. If a large ice sheet existed over Franz Josef Land, the deglaciation of the islands may have been linked to the decay of the adjacent Barents‐Kara Sea Ice Sheet, permitting iceberg calving (enhanced by relative sea‐level rise) to occur. The introduction of a water‐depth‐related iceberg calving function at 15 000 yr ago forced an initial rapid rate of ice‐sheet decay of 30 000 km31000 yr'. However, as the ice sheet thinned, and isostatic rebound began, the calculated rate of iceberg calving was reduced such that ice remained over the archipelago at 8000 yr ago. The model's failure to simulate complete ice‐sheet decay by 8000 yr ago is at variance with radiocarbon‐dated raised terraces on Franz Josef Land, which indicates the complete deglaciation of the i

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00774.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

A millimetre‐thick bed of highly vesiculated pumiceous clasts was found in two peat bogs in Pomerania (NW Poland). Their phonolitic composition confirms the correlation with the Laacher See Tephra (LST). Based on the various CaO‐Na2O‐K2O content, most of these clasts can be linked with the Lower Laacher See Tephra (LLST), and some with the Middle Laacher See Tephra B (MLST‐B).14C dates obtained on peat samples are in agreement with an Allered stratigraphic position of that tephra. In several localities in NW Poland, it was found that there was no occurrence of tephra in peat bogs. Thus the presence of the LST is restricted to the northwestern fringes of Po

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00775.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Known changes in ice‐flow direction during a 100‐year interval have been used to evaluate how well ice‐flow indicators record complex deglaciation events. At Burroughs Glacier, nunataks emerging from a thinning Neoglacial ice mass and differential ice‐surface lowering caused by calving ice margins have produced major changes in ice‐flow direction sincc 1892. Cross‐cutting striae with angles of divergence of up to 105′ reflect the past range of flow directions in the area. Striae from the oldest flow events are deepest, and striae from some late‐stage flow events are missing. This may be caused by overprinting during late‐stage reversals in the direction of ice movement. The orientation of flutes and surficial bullet boulders reflects the final ice‐flow direction, but boulder orientations are less clustered than flute orientations. Surficial till pebble fabrics are weakly to moderately developed, but till fabrics vary with depth and record ice‐flow direct

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00776.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

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 90014C‐years in the Reykjavik area between 10 300 BP and 9400 BP. The sea‐level curve shows a shoreline displacement ofc. 5 cm14Cyr‐1for that period. The mean absolute uplift rate is calculated to be 6.9 cm14C 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 a14C 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 connecti

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00777.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Changes in lake status, a measure of relative water depth or lake level, have been reconstructed from geological and biological evidence for 87 sites in northern Europe. During the early Holocene. the lakes show conditions similar to or drier than present in a broad band across southern Britain, southern Scandinavia and into the eastern Baltic and wetter conditions along the west coast and in central Europe. This pattern is consistent with the effects of a glacial anticyclone over the Scandinavian Ice Sheet, namely enhanced southwesterly flow along the west coast and strengthened easterlies south of the ice. Afterc, 8000 BP a different lake status pattern was established. with conditions drier than present over much of northern Europe. Lakes higher than today were confined to the far north, the west coast, eastern Finland and western Russia. This pattern gradually attenuated after 4000 BP. Differences in lake status during the mid‐ to late Holocene are consistent with a strengthening of the blocking anticyclone over the Baltic Sea in summer. resulting in more meridional circulation than today. This strengthening of the blocking anticyclone during the mid‐Holocene is interpreted as a consequence of insolation changes, enhanced by the fact that the Baltic Sea was larger than pres

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00778.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Involutions in the early Anglian Barham Soil at Newney Green, Essex, and Badwell Ash, Suffolk, in eastern England, are attributed to soft‐sediment deformation during an episode of regional thermokarst development. The involutions show a striking resemblance in morphology and size to thermokarst involutions within a palaeo‐thaw layer at Crumbling Point, western arctic Canada. By analogy with the thermokarst involutions, the involutions in the Barham Soil are reinterpreted to have formed by loading during the melting of an ice‐rich layer at the top of Anglian permafrost. This period of thermokarst development may have coincided with an episode of intra‐Anglian climatic amelioration. Reinterpretation of the Barham Soil involutions implies that many other Pleistocene involutions in Britain may have formed during periods of thermokarst development rather than by active‐layer cryo

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00779.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY