摘要:

Till‐covered sand and silt sediments with organic material from Boliden, northern Sweden, have been resampled and reinvestigated. Texture and petrographic analyses demonstrated one till bed overlying, and one underlying the sandy sediments. Low frequencies of diatoms were noted, representing freshwater, halophilous and brackish water taxa. The diatoms may be allochthonous or autochthonous, or redeposited from older deposits. Pollen analysis revealed a new picture of the composition of the vegetation, as compared with earlier investigations. The flora consisted of an arctic‐subarctic treeless shrub and herb vegetation dominated bySalix, Betula nana, Gramineae and Cyperaceae.Artemisiaand several arctic‐alpine herbs were important elements. The identification ofSalixwood as well as fruits and fruit scales ofBetula nanaandBetulacf.humilisis in agreement with the pollen‐analytical results, as is the occurrence of Nordicboreal species of Coleoptera. Two radiocarbon datings resulted in an age ofc.45,000 B. P. and>40,000 B.P. The Boliden till‐covered sediments were most probably deposited during an Early or Middle Weichselian interstadial, but the initial or final stage of an interglacial (Eemian) is also

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1988.tb00118.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Current views on the internal structure of many glacial landforms need further definition. For example, drumlinized Halton till plain near the Scarborough Bluffs, Ontario would traditionally be. viewed as a lodgement till sheet, but it was found to consist of complex sedimentary assemblages including sediment flows, melt‐out, deformation and lodgement tills. These facies vary spatially depending on whether deposition occurred beneath grounded ice or within subglacial cavities. Proglacial sediments bury portions of the till plain. Surface Rutings and drumlins clearly indicate the action of subglacial processes on the surface of Halton drift. Sedimentary structures at the contact between stratified sediments and diamictons within the Late Wisconsinan Halton drift are similar to those in older beds exposed at Scarborough Bluffs. The demonstration of the role of grounded ice in Halton drift and the similarity of sedimentary structures to those of the underlying Thorncliffe and Sunnybrook sediments suggests that the action of grounded ice cannot be ruled out in the case of the lower beds, as has been done by Eyles&Eyles (Geology 11, 146–152, 1983). Thus, surface Halton drift may be a model for recognition of similar environments of deposition in older beds beneath Halton. This analysis indicates flaws in a recent re‐evaluation of Scarborough Bluffs sediment interpreted as solely lacustrine and not directly affected by gla

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1988.tb00119.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The carbon (δ13C) and oxygen (δ18O) isotopic composistion in mollusc shells in mainly determined by the isotopic composition of water and dissolved bicarbonate. The δ18O values of water show a good correlation with the salinity of the Baltic. This correlation served as a basis for reconstructing palaeosalinity and for stratifying the marine sediments according to the δ18O values of the carbonate skeletons of subfossil shells. The δ13C values in shells are mainly determined by the isotopic composition of land‐originating bicarbonate, especially in the carbonate skeleton ofLymnaea balthica, which inhabits the immediate coastal zone. According to the δ18O data, salinity in the investigated area (the coastal area of W and NW Estonia) was highest (about 9–11%) during the Littorina stage. The Limnae a stage had, in general, a salinity similar to the contemporary one, but during some phases possibly exceeding i

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1988.tb00120.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1988.tb00121.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Post‐depositional structures in late Quaternary subaqueous outwash near St. Lazare, Québec resemble icewedge casts but are interpreted as water escape fissures. Cryogenic origin is discounted because, in contrast with ice‐wedge casts, the fissures have a higher depth to width ratio, do not form an intersecting network, and do not exhibit adjacent upward turning of strata. In addition, their truncation by the sub‐littoral unconformitydemonstrates formation before regression of the post‐glacial Champlain Sea, under conditions in which ground ice development was highly unlikely. The fissures probably formed in response to elevated pore pressures caused by melting of remnant glacier ice or by liquefaction of deeper units. Excess pore water pressure initiated upward flow of dilute sediment‐water mixtures that became concentrated in planar zones (fissures) along which they entrained and removed sediment. Slumping of the fissure walls followed, either during or after water escape. Minor faulting over cavities created by melting ice or water escape along fractures in underlying strata may have controlled the morphology of th

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1988.tb00122.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Cores representing a 5.5m long sequence recovered from lake Æråsvatnet have been investigated for lithostratigraphy, micro‐ and macrofossils and radiocarbon chronology. For the first time in Fennoscandia the maximum Weichselian advance has been closely bracketed with radiocarbon datings (19,000–18,500 B.P.). A continuous stratigraphy from 18,500 B.P. and onwards, partly marine and partly lacustrine, discloses the local shoreline displacement, the palaeovegetation, the palaeoclimate and, together with other data, the deglaciation history. Two phases with a prevailing High Arctic climate have occurred: 18,000 to 16,000 B.P. and 13,700 to 12,800 B.P. Important climatic amelioration accelerating the deglacial recession occurred 16,000, 12,800 and 12,000 B.P. The continental ice sheet was situated close to its maximum position until about 16,000 B.P. The following deglaciation was interrupted by (a minor ?) readvance/halt about 15,000 B.P. (the Flesen event), 13,700‐13,000 B.P. (the D‐event), 12,500 B.P. (the Skarpnes event) and 11,000–10,000 B.P. (the TromsØ‐Lyngen event). The deglaciation chronology and pattern can be correlated with the suggested deep‐sea‐stratigraphy‐based stepwise pattern relying on the old age alternativ

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1988.tb00123.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1988.tb00124.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The Holocene chronology of gelifluction events in a snow‐patch environment of the Richmond Gulf area, eastern Hudson Bay Coast (northern Québec), has been constructed using sixty radiocarbon‐dated buried organic horizons. The samples were recovered from nine soil trenches located along an altitudinal gradient associated with a chronosequence as determined by the regional land emersion curve. The most significant gelifluction activity occurred after c. 2,800 B. P. Gelifluction events occurred around 5,600, 5,000, 4,500, 3,150, 2,500, 1,550, 1,200 and 450 B.P., and at present. According to the frequency of14C dates. gelifluction has been particularly active between 2,800‐2,300, 1,700–900 and 600‐300 B.P., and at present. Gelifluction occurrence seems to be closely related to well‐bracketed cold episodes in northern Québec. The increase in frequency of14C dates associated with burial of organic matter through gelifluction after c. 2,800 B. P. substantiates the colling trend depicted elsewhere, both in northern Québec and in the north

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1988.tb00125.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Macrofossil analyses, pollen analyses, and14C datings were carried out on profiles from a bog complex in southern Sweden. The development started with aCarexfen c. 6,000 B. P. which transformed to bog c. 1,000 years later. The bog has developed through three stages separated by highly humified peat layers, recurrence surfaces, 3 and 2m below the present bog surface, and formed c. 2,500 and 1,200 B. P., respectively. The fen formation and the initiation of the last two bog stages were contemporaneous with high water levels in lakes of the region. The transition to bog and the formation of the two highly humified peat layers may be related to low water levels in lakes. It is probable that changes in the development of the mire were caused by the climate, since varying water levels are thought to be dependent on variations in the climate.

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1988.tb00126.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1988.tb00127.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY