摘要:

Morphological, seismic and lithostratigraphic investigations of a moraine deposit at Bleik (the Bleik moraine), northern Andøya, show short‐distance transported till overlying long‐distance transported predominantly glaciofluvial ice‐marginal deposits. Consolidated glaciomarine sediments from a core at present sea‐level,c. 400 m distally to the moraine complex, contain 31 species of foraminifera, among whichCassidulina reniforme, Islandiella helenaeandTrifarina fluensdominate, and fragments of the molluscsMya truncataandAstartesp. and the echinoidStrongylocentrotussp. Amino acid analyses of the foraminiferaCibicides lobatulusand the molluscMya truncataindicate ages between 22,000 and 16,000 BP. Radiocarbon dating of fragments ofMya truncatafrom the upper part of the core gave an age of 17,940 ± 245 BP, while a dating of unidentified shell fragments from the lower part gave an infinite age (>40,000 BP). The sediment was probably disturbed by icebergs beyond the end moraine zone, and the radiocarbon and amino acid dating ofMya truncatatherefore represent a maximum age for this process. This new evidence indicates two phases with a higher relative sea‐level than at present at Bleik,c. 18,000 and>40,000 BP. The Bleik moraine probably represents the early Late Weichselian glacial maximum (c. 22,000 BP), while the underlying deglaciation deposit and associated beach‐ridge (Bruvollen) is of pre‐Late Weichselian age. Moraine ridges 3–4 km to the south of Bleik probably indicate advances of local glaciers between 22,

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1992.tb00007.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Book reviewed in this article:Bradley, R. S. (ed.) 1991: Global Changes of the Past. 514 pp. Office for Interdisciplinary Earth Studies, Boulder, Colorado

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1992.tb00008.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

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 10,40014C 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 t

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1992.tb00009.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

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 evol

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1992.tb00010.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Book reviewed in this article:Maizels, Judith K.&Caseldine, Chris (eds.) 1991:Environmental Change in Iceland: Past and Present.

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1992.tb00011.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Equilibrium‐line‐altitude (ELA) reconstructions using the toe‐to‐headwall‐altitude ratio method for paleoglaciers in the Cordilleras Blanca and Oriental, northern Peruvian Andes (7–10°S; 77°20′–77°35'W), indicate that ELAs during the last glacial maximum (LGM; marine isotope stage 2) werec. 4300 m in the Cordillera Blanca,c. 3900–3600 m on the west side of the Cordillera Oriental, andc. 3200 m on the east (Amazon Basin) side of the Cordillera Oriental. Comparison with estimated modern ELAs and glaciation thresholds indicate that ELA depression ranged fromc. 700 m in the Cordillera Blanca toc. 1200 m on the east side of the Cordillera Oriental. This augments data from many mountain ranges in middle‐ and low‐latitude regions that indicate that ELAs during the LGM were depressed byc. 1000 m. Published palynological evidence for drier conditions during the LGM in the tropical Andes suggests that ELA depression of this amount involved a temperature reduction (>5–6°C) that greatly exceeded the tropical sea‐surface temperature depression estimates of CLIMAP (<2°C). The west to east increase in ELA depression during the LGM indicates that the steep modern precipitation gradients may have be

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1992.tb00012.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

A brief review of the genesis of blanket peats is presented, together with detailed analyses of basal peats from northern Scotland. Particular attention is paid to local factors affecting peat growth and the problems of sampling and interpretation arising from them. Macrofossil and loss‐on‐ignition analyses of four peat‐mineral interfaces solve many of the terminological problems of such profiles and indicate that interpretations based on field stratigraphy alone are uncertain. Pollen analyses of two profiles from contrasting microtopographic situations show well‐defined vegetational change associated with early peat development. Fully organic ombrotrophic peat is present from 6805 ± 50 BP at one site, following anthropogenic burning fromc. 7500 BP and partial recovery of the open birch woodland. A change from birch woodland toCallunaheath occurs at approximately the same time on a more freely drained site with much later peat development, following further burning from 4890 ± 65 BP. Anthropogenic activity is clearly associated with changes in soil and vegetation preceding peat formation, and the role of climatic factors remains

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1992.tb00013.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Structural, stratigraphic, and lithologic data from a section 69 m long of Catfish Creek drift (north shore of Lake Erie) tell a complex story of two competing glacial lobes. Stone surface features and orientations indicate that stones rotated in viscously deforming, fine‐medium textured subglacial till prior to final emplacement. Fractures, shears, and attenuated sediment lenses in tills reveal that they experienced some brittle shear superposed on ductile shear during till dewatering and stiffening. The Huron‐Georgian Bay lobe advanced first from the northwest, deforming interstadial sediments and depositing subglacial till. Next, southward confluent flow of the Huron, Georgian Bay, and Erie lobes carved subglacial troughs into sediments and deposited (then deformed) bouldery deformation till by squeeze flow. The northwest flowing Erie lobe then prevailed, depositing deformation till, subglacial aquatic sediments, and mudflows. Finally, a pavement‐bearing, hybrid deformation‐lodgement till covered the section. Till formation was mainly by subglacial viscous flow with minor lodgement superposed as water content decreased and some fines were probably winnowed. This implies that till deformation probably accounted for much of the glacier movement. Therefore, rapid ice flow could have occurred over the section, along the southern margin of the Laurentide Ic

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1992.tb00014.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

While working with the revision of the Swedish Time Scale, based on clay‐varve chronology, mollusc shells ofPortlandia (Yoldia) arcticawere found in the clay at Ekensberg, Stockholm, Sweden, deposited at the beginning of the Finiglacial epoch. The clay‐varves have been connected with the revised Swedish Time Scale and the time for deposition is 10,370 clay‐varve years cal BP. Shells of bivalves, shell fragments and periostracum have been AMS radiocarbon‐dated at the The Svedberg Laboratory in Uppsala. The 11 radiometric datings are grouped in two assemblages, one between 10,500 and 11,600 BP (shell carbonate) and one between 8200 and 9100 BP (periostracum). These results are compared with the radiocarbon age obtained for a fish skeleton (Salmo alpinus) found in varved clay close to Ekensberg during the geological mapping of the area. The age of the fish is 8600 BP, which is in agreement with the periostracum datings. Reservoir effects and calibration of the radiocarbon ages (BP) to sidereal years (cal BP) are di

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1992.tb00015.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1992.tb00016.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY