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1.
An inter-till organic sediment, probably a paleosol, was found in a ridge in the Setesdal Valley. A radiocarbon date on the fraction soluble in NaOH gave a finite age of 35,850 B.P., which is probably a minimum age as contamination of younger carbon might have occurred. Pollen analysis indicates that the sediment has originated above the tree-limit. Compared with different interglacial and interstadial deposits in Scandinavia, the sediment is interpreted as representing an interstadial period, tentatively named the Vatnedal interstadial, of Early or Middle Weichselian age.  相似文献   

2.
From a study of molluscan assemblages it is suggested that sea temperatures, particularly in the period 12,500 to 12,000 B.P., were 3°C lower than they are today for all but surface waters, implying that the interstadial North Atlantic Drift was weaker than the present Drift where it extends into the Norwegian Sea. An early interstadial 'warm' event may relate to a period when temperatures in the Bay of Biscay exceeded those of the present day. A later 'warm' episode may correlate with the warmest part of the interstadial deduced from the deep sea succession west of Ireland.  相似文献   

3.
Two eustatic high sea stands during the last glacial period are recognised at Pantai Remis. These highstands, lower than present-day sea-level, are tropical manifestations of the ameliorating interstadial climate during the Weichselian/Devensian/Wisconsin glaciation in the Northern Hemisphere. The earlier highstand corresponds to a sea-level of 14.6 m below mean sea-level (MSL). It is interpreted as synchronous with Oyxgen Isotope Stage 5a and is correlated with other known sea-level curves in other parts of the world. The younger high sea stand, dated 55810 ± 1140 to 53870 ± 1400 yr BP, indicates sea-level of 4.3 m below MSL. It represents an interstadial equivalent that lasted for at least 2000 yr, whereas the earlier interstadial period indicates a minimum duration of twice this amount or very likely even longer, as reflected from the thickness of the accumulated deposits. The palynological records indicate that during interstadial times, climatic stability in the tropics is attained and was sufficiently long for vegetation to thrive and develop. The palynofloral constituents of the earlier interstadial phase at Pantai Remis showed the establishment of vegetation in a coastal setting, initiated by Pandanus swamp forests. Simultaneously, mangrove swamp flourished in the lower lying parts of the area, hence the presence of direct tidal influence is evident. Both the Pandanus and mangrove swamps were succeeded by mixed freshwater swamp forests of a Campnosperma–Calophyllum assemblage. Subsequently a slightly open and somewhat drier mixed swamp forest prevailed, marked by the increase in fern spore representation. The later interstadial phase showed shorter vegetation successions, which commenced on the landward edge of a mangrove swamp forest. The mangrove was successively replaced by strand forest, as indicated by domination of Casuarina equisetifolia. The palynological assemblages in both the interstadial periods indicate similarity to the present-day coastal vegetation. This implies that during the interstadials the climate in the lowlands of Peninsular Malaysia and presumably throughout the equatorial region, was as that prevailing today. © 1997 John Wiley & Sons, Ltd.  相似文献   

4.
Till beds and waterlain sediments from at least 3 stadials and 2 interstadials during the Weichsel glaciation are recorded on Finnmarksvidda. The oldest, possibly Weichselian, ice-free period recorded on Finnmarksvidda is represented in one river section and is preliminary named the Vuolgamasjåkka thermomer. Its initiation is TL-dated to about 120 ka, which indicates a pre-Weichselian, possibly Eemian age. The interstadial which follows the subsequent and assumed oldest Weichsel stadial on Finnmarksvidda, the Eiravarri interstaeial, has previously been tentatively correlated lithostratigtrahically with the Peräpohojola interstadial ( sensu stricto ) in North Finland. The youngest interstadial, the Sargejåk internatiodial , is in this paper suggested to correlate with the Tärändö interstadial in North Sweden. The initial Weichselian ice movement across Finnmarksvidda is so far unknown, but locally N of Kautokeino in the W the initial (recorded) ice movement was directed towards NW-N. The regional ice movements for the two subsequent stadials on Finnmarksvidda were initially directed towards NE-ene and NNW, respectively.  相似文献   

5.
A glacial chronology for northern East Greenland   总被引：3，自引：1，他引：3  
In East Greenland between 75 and 76N three different glacial episodes can be identified: (1) An early period with more or less total ice cover and in which the ice reached out onto the continental shelf - the Kap Mackenzie stadial; (2) a period with glaciation of intermediate extent, when nunataks and a few ice-free lowland areas existed - the Muschelbjerg stadial; and (3) a final period with glacial advance, when the glaciers were mainly restricted to fjords and larger valleys - the Nanok stadial. Each of these stadials was followed by a period with general deglaciation, from which marine shell-bearing sediments have been found; the Hochstetter Forland interstadial, the Peters Bugt interstadial and the Flandrian interglacial, respectively. The marine limit sank with each of these ice-free periods; probably an isostatic effect of the decreasing amplitude of the glacial advances. The deglaciation after the Nanok stadial began about 9500 B.P. It is not known for certain when this glacial advance started, but 13,000 B.P. or earlier is suggested. According to 14C datings the Peters Bugt interstadial dates from at least 45,000 B.P. and the Hochstetter Forland interstadial from at least 49,000 B.P. However, amino acid analyses indicate a distinct age difference between these two interstadial, and Th/U datings give age estimates of 70,000–115,000 B.P. for the Hochstetter Forland interstadial, which therefore seems to be of Early Weichselian age although a pre-Weichselian age cannot be excluded. The same applies to the preceding Kap Mackenzie stadial. The correspondence between the present glacial chronology and similar tripartite ones on Bafffin Island, Ellesmere Island and Svalbard seems reasonably good  相似文献   

6.
Diatoms and plant macrofossils in Devensian Lateglacial lacustrine sediments in Shetland suggest that the earliest response to interstadial warming was from benthic aquatic communities that could develop under lake ice. Further warming permitted longer ice-free summers and plankton growth. The terrestrial vegetation communities responded more slowly. Pollen of land plants was then partly derived from long distance input. Macrofossils support a reconstruction of terrestrial vegetation of sparse Salix herbacea and mosses in the early interstadial, increasing to grass tundra with tall herbs and Empetrum locally present, and with patches of disturbed ground. The occurrence of Betula and Juniperus remains questionable because of a lack of macrofossils, despite the presence of their pollen. Rumex pollen peaks suggest significant local presence at the stadial/interstadial transitions. Overall, the palaeoenvironmental reconstruction at this isolated oceanic site depends on several proxy indicators, of which pollen is less reliable than diatoms and plant macrofossils.  相似文献   

7.
中国南方石笋氧同位素记录的重要意义   总被引：44，自引：15，他引：29       下载免费PDF全文
中国南部石笋氧同位素记录记载了重要的气候变化信息。应用石笋氧同位素记录时首先需要考虑检验石笋的平衡结晶生长,特别是重复性检验,以排除可能的偶然性或地方因素。中国南部重复性很好的南京葫芦洞和贵州董歌洞石笋氧同位素记录主要代表了当时的降水氧同位素信息。两洞的记录都显示,在冰期或冰段时期降水的氧同位素比间冰期或间冰段时期明显偏重。受夏季风强弱变化的控制,与目前亚洲季风降水氧同位素的季节变化相对应,在间冰期或间冰段时,ITCZ偏北,降水以夏季风的大规模大气环流下的对流降水为主,其氧同位素较轻;相反地,在冰期或冰段时,ITCZ偏南,降水以夏季风爆发前的锋面降水为主,其氧同位素较重。虽然尚有其他许多影响因素,亚洲季风的变化应是影响中国南部石笋氧同位素在冰期/间冰期或冰段/间冰段的尺度上变化的主导因素。但在更小的尺度上(例如小冰期),石笋氧同位素记录的解释则需要谨慎。虽然下最终结论为时尚早,但作为亚洲季风的两个组成部分的东亚季风和印度季风很可能是同步的,至少在冰期/间冰期或冰段/间冰段的尺度上是如此。基于上述研究,进一步提出亚洲夏季风强段/弱段的概念(AsianSummerMonsoonInterstadial/stadial,或ASMI/ASMS),其在上个冰期中与格陵兰冰芯间冰段/冰段一一对应  相似文献   

8.
Mutual climatic range (MCR) analysis was applied to 15 North American beetle assemblages spanning the interval from > 52 000 to 17 200 yr BP, bracketing a Mid-Wisconsin interstadial interval. The analyses yielded estimates of mean July (TMAX) and mean January (TMIN) temperatures. The oldest assemblage (> 52 ka) yielded TMAX values 7.5–8°C lower than present and TMIN values 15–18°C lower than present. A Mid-Wisconsin interstadial warming dating from 43.5–39 ka was rapid and intense. At the peak of the warming event, about 42 ka, TMAX values were only 1–2°C lower than modern. This level of amelioration apparently lasted only about 2000–3000 yr. By 23.7 ka, TMAX values declined to 11.5–10°C lower than modern, but another, small-scale amelioration is indicated by assemblages dating from 20.5 to 19.7 ka. The interstadial event recorded from the site at Titusville, Pennsylvania closely matches the timing and intensity of the climate change estimated from British beetle faunas in the Upton Warren interstadial. Another warm interval (ca. 31–32.5 ka) has been documented from fossil beetle assemblages in Europe and North America. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

9.
Pollen data from two sections from a coastal cliff on the western Yamal Peninsula (69°43.27′N, 66°48.80′E) document the environmental history during the Karginsky (Middle Weichselian) interstadial. Low pollen concentrations, high amounts of redeposited pollen, and relatively high presence of Artemisia pollen characterize sediments deposited at about 33,000 14C yr B.P. Grass-sedge plant associations with few other herbs occupied the area during the late Karginsky interstadial. Artemisia pollen may indicate rather xerophytic vegetation and disturbed soils in the area. The dominance of redeposited pollen reflects scarce (disturbed) vegetation cover and low pollen productivity. The climate was relatively cold and dry. Sediments dated to 32,400 14C yr B.P. contain fewer redeposited pollen and concentration of non-redeposited pollen is significantly higher. Pollen contents indicate the dominance of tundra-like grass-sedge vegetation and more humid conditions. Pollen records dated between 30,100 and 25,100 14C yr B.P. also reflect scarce tundra-like vegetation during this interval. The presence of Betula nana and Salix pollen may reflect limited presence of shrub communities. This suggests that the climate was somewhat warmer during the latter part of the interstadial. However, generally the pollen records show that harsh environmental conditions prevailed on the Yamal Peninsula during the Karginsky interstadial.  相似文献   

10.
Eemian—Weichselian sequences, located outside the maximum limit of the Late Weichselian ice sheet, provide excellent opportunities for the discovery of continuous sedimentary records encompassing the whole Last Interglacial/Glacial cycle. Such a sequence is recorded in a borehole (117P) through the succession in a small kettlehole lake located at Medininkai, eastern Lithuania. The succession consists of peat, gyttja and silt deposited on top of a Saalian till. Pollen and plant macrofossil analysis, lithological analysis, U/Th dating and mineral magnetic measurements on the sediments have allowed 19 lithostratigraphic units and 16 local pollen assemblage zones (LPAZ) to be identified. The palaeocarpological record reveals a clear transition from the Saalian Glacial to the Weichselian stadial and interstadial phases. The mineral magnetic parameters suggest a good correlation between the concentration of magnetic minerals and stadial and interstadial periods. The Merkine (Eemian) Interglacial and two Early Weichselian Interstadials, Jonionys 1 (Brörup) and Jonionys 2 (Odderade), separated by cryomers, are identified. Intervals interpreted as analogous to the Middle Weichselian Denekamp and Hengelo interstadials are also recognized on the basis of pollen assemblages. The results show alternating periglacial and interstadial palaeoenvironments in Lithuania during the Early and Middle Weichselian and are of importance for Late Pleistocene palaeoenvironmental reconstruction of the Baltic area as a whole.  相似文献   

11.
Pollen analysis of a section of lake sediments at Grassy Lake Reservoir indicates a vegetational sequence changing from tundra, to spruce-fir-pine forest, to pine forest, to tundra at the top. Pollen analysis of a section of lake sediments on Beaverdam Creek indicates a tundra vegetation at the base, followed by a brief episode of spruce-fir forest and a return to a tundra vegetation at the top. The analyses of both sections suggest a cold to cool to cold climatic sequence, interpreted as interstadial in character. However, differences suggest that they represent separate interstadials. Pinedale Till disconformably overlies the lake deposits at Grassy Lake Reservoir. The upper sediments contain wood 14C dated at >42,000 yr; the lowermost interfinger with till shown to be more than about 70,000 yr old. The deposits at Beaverdam Creek grade upward into proglacial Pinedale deposits, contain an ash that is probably about 70,000 yr old near their base, and rest comformably on gravel that grades down into lake sediments containing wood debris suggestive of an older climatic amelioration. We conclude that the warmest part of the interstadial at Grassy Lake Reservoir is probably more than 70,000 yr old, and that the warmest part of the interstadial analyzed at Beaverdam Creek is slightly younger than 70,000 yr old.  相似文献   

12.
The Saalian sequence of Belchatów, central Poland, is exceptionally thick and complete. Five tills, two from the older Saalian (Odranian, Drenthe) and three from the younger Saalian (Wartanian, Warthe), which are separated by the fluvial Chojny Formation, have been identified. The Saalian sequence at Be?chatów is underlain by Holsteinian and overlain by Eemian sequences, both palaeobotanically analysed. The Chojny Formation contains deposits of meandering (lower member) and braided (upper member) rivers, with occasional aeolian deposits. The lower member of the formation contains numerous organic layers. Pollen analysis indicates temperate (sub-boreal) to cold (sub-arctic) climatic conditions, with coniferous to mixed forests in the optimum phase of the interstadial. The interstadial floras of the Chojny Formation are interpreted as representing the intra-Saalian Pilica Interstadial. Profiles from Belchatów are designated as the stratotype profiles of this substage. The data from Be?chatów show clearly that reforestation occurred between the major advances of the Saalian ice sheet, although only interstadial rank, not interglacial, may be inferred from the pollen data.  相似文献   

13.
Twelve palaeogeographical reconstructions illustrate environmental changes at the southwest rim of the Scandinavian Ice Sheet 40–15 kyr BP. Synchronised land, sea and glacier configurations are based on the lithostratigraphy of tills and intertill sediments. Dating is provided by optically stimulated luminescence and calibrated accelerator mass spectrometry radiocarbon. An interstadial sequence ca. 40–30 kyr BP with boreo‐arctic proglacial fjords and subarctic flora and occasional glaciation in the Baltic was succeeded by a Last Glacial Maximum sequence ca. 30–20 kyr BP, with the closure of fjords and subsequent ice streams in glacial lake basins in Kattegat and the Baltic. Steadily flowing ice from Sweden bordered the Norwegian Channel Ice Stream. A deglaciation sequence ca. 20–15 kyr BP indicates the transgression of arctic waters, retreat of the Swedish ice and advance of Baltic ice streams succeeded by a return to interstadial conditions. When ameliorated ice‐free conditions prevailed in maritime regions, glaciers advanced through the Baltic and when interstadial regimes dominated the Baltic, glaciers expanded off the Norwegian coast. The largest glacier extent was reached in the North Sea around 29 kyr BP, about 22 kyr BP in Denmark and ca. 18 kyr BP in the Baltic. Our model provides new data for future numerical and qualitative landform‐based models. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

14.
This is the first of a series of articles presenting the results of a multi-proxy investigation aimed at reconstructing changes in the ecosystem and climate of Whitrig Bog, SE Scotland, during the last glacial-inter-glacial transition (Devensian Lateglacial, c . 14–10 ka BP). We present here the results from sediment lithology, chemistry, pollen, and plant macrofossil analyses. These data are used to infer the nature of the local catchment soils and both local and regional terrestrial vegetation. The interstadial period ( c . 13–11 ka BP) is characterized by a successional sequence developing from a landscape with bare, poorly developed minerogenic soils supporting a sparse herbaceous flora into open birch woodland with juniper scrub and stable organic soils. At c . 11 ka BP the Younger Dryas climatic cooling event caused an abrupt reversion to an open herbaceous arctic/alpine flora (e.g. macrofossil evidence of Silene furcata and Oxyria digyna ) and high levels of minerogenic erosion into the basin, indicating environmental response to a cold Arctic climate. In addition to this Younger Dryas climatic reversal, two lesser reversion episodes occurred earlier during the interstadial. The more pronounced of the two, late in the intersladial, is characterized by high levels of erosion and a change from birch/juniper woodland to an open herbaceous flora. The older oscillation occurs approximately mid-way through the interstadial sequence and is marked by similar pollen changes, albeit shorter lived and more subtle.  相似文献   

15.
A 22 m long sediment core from Lake Yamozero on the Timan Ridge in northern Russia has provided evidence of intriguing climatic shifts during the last glacial cycle. An overall shallowing of the lake is reflected in the lower part of the cores, where pollen indicates a transition from glacial steppe vegetation to interstadial shrub-tundra. These beds are capped by a well-defined layer of compact clay deposited in relatively deep water, where pollen shows surrounding spruce forests and warmer-than-present summer temperatures. The most conservative interpretation is that this unit represents the last interglacial period. However, a series of Optical Stimulated Luminescence (OSL) dates suggests that it corresponds with the Early Weichselian Odderade interstadial (MIS 5a). This would imply that the Odderade interstadial was just as warm as a normal interglacial in this continental part of northern Europe. If correct, then pollen analysis, as a correlation tool, is less straightforward and the definition of an interglacial is more complex than previously thought. We discuss the validity and possible systematic errors of the OSL dates on which this age model is based, but conclude they really indicate a MIS 5a age for the warm period. Above the clay is an unconformity, most likely reflecting a period of subaerial exposure implying dry conditions. Deposition of silt under fluctuating cold climates in the Middle Weichselian continued until a second gap in the record at c . 40 kyr BP. The lake basin started to fill up again around 18 kyr BP.  相似文献   

16.
Previously only three terrestrial interglacial periods were known from southern Scandinavia, all of which could be relatively easily correlated within the central European stratigraphical framework. Here, we present a new interglacial–interstadial pollen, plant macrofossil and charcoal record from Trelde Klint, Denmark, and analyse its biostratigraphy, correlation with other European records, vegetation development, fire dynamics and absolute dating. Except for a slight truncation of the early part of the record, the pollen stratigraphy exhibits a full interglacial succession, including temperate trees (Quercus, Ulmus and Tilia) during its mesocratic stage. Macrofossil analysis allowed identification to species level for Quercus robur, Picea abies and two mosses. Conifers (Pinus and Picea) dominate the pollen record of the interglacial sequence, and the occurrence of Larix pollen in the top part of the interglacial record as well as in the interstadial sediments is especially indicative of this interglacial. The overall diversity of tree genera is rather low. These biostratigraphical features suggest that Trelde Klint is unique among Danish records, but it is similar to records from northern Germany. Numerical analyses (REVEALS and DCA) indicate that forests during the temperate stage were dense and that vegetation openness increased only towards the end of the interglacial, accompanied by increased fire occurrence. A short interstadial sequence with a dominance of Pinus and Betula and the presence of Larix is present above the interglacial deposit. We argue that lack of attention to differences in fire regimes may hamper understanding of between‐site correlations of interglacial pollen records. OSL dating, using a novel feldspar technique, yields an average age of 350±20 ka for the sandy sediments above the interglacial layers at Trelde Klint, suggesting that the whole interglacial–interstadial succession belongs to Marine Isotope Stage 11.  相似文献   

17.
The Bølling–Allerød interstadial is the closest warm time period to the Holocene. The study of the climate variability during this most recent warm scenario provides a natural record of potential environmental changes related with global temperature variations. Little is known about this interstadial in the Southern Iberian Peninsula. Therefore, the exceptional climatic record of the Otiñar paleo-lake (ca. 14.5–14.0 cal ka BP), provides environmental information about the first part of this interstadial (Bølling) in this key region. Although the studied high-resolution isotopic record point to almost invariant hydrological conditions in the paleo-lake, with little change in the carbon budget and important limestone dissolution, the pollen record shows an increase in forest species that can be interpreted as a warming trend and an increase in humidity during the Bølling in the area. This record is one of the few continental archives that show this climatic trend in Southern Iberia, agreeing with many other regional records from the western Mediterranean. This does not agree with higher latitude records that show an opposite trend. This opposite pattern in precipitation between the western Mediterranean and more northern latitudes could be explained by a persistent and increasing negative NAO mode during the Bølling in this area.  相似文献   

18.
Márton Pécsi 《GeoJournal》1995,36(2-3):117-131
In the process of loessification, the development of loess fabric, the role of zonal, regional and partly of local environmental factors is regarded decisive. In the loess sequences various genetic types of loess pockets and paleosols occur and reflect different climatic and paleogeographical conditions.As a consequence, even within a single profile the colour, grain size and mineral composition, CaCO3 content, degree of weathering and fabric of loess may vary. Zonal, regional or even local variations in such loess properties may equally derive from syngenetic or postgenetic processes. For similar reasons, spatially and temporally different forms, types and subtypes of paleosol also developed.This way, loess and soil formation resulted in various spatial types in the same glacial, interstadial or interglacial phase in the various geographical zones and regions. Although there exist major loess regions where the interglacial soils (eg brown forest soils) are markedly distinct from interstadial steppe soils or from other types of humic soils, continental loess areas can also be observed where the paleosols developed under interglacial and interstadial conditions (eg steppe or forest steppe soils) cannot be referred into different genetic types. In such cases the changes in paleoenvironments are difficult and uncertain to reconstruct.The interregional correlation of paleosols is occasionally hindered by the various terminologies applied to denote them. In addition, there are uncertainties concerning the dating and identification of paleoenvironments of polygenetic soils and of soil complexes consisting of paleosol units: how many soil formation phases they represent and how long erosional gaps can be reckoned with between these phases.  相似文献   

19.
Subfossil bryophyte remains from Jameson Land, central East Greenland reveal diverse moss floras from the Langelandselv interglacial and the Hugin Sø interstadial. Around 30 species are reported as new subfossils from Greenland, indicating our insufficient knowledge of earlier bryophyte floras in the area. Among the species found from the Langelandselv interglacial. Several are southern and do not reach as far north as Jameson Land today, thus indicating a slightly warmer climate than at present in the area. The climate indications for the Hugin Sø interstadial are less clear, and further studies are necessary before delinitivc conclusions can he drawn. A large proportion of the found taxa indicate mineral-rich or intermediately mineral-rich conditions. Several wetland species indicate moving water, and a few sometimes or exclusively ( Sanionia nivalis ) occur in connection with late snow beds or meltwater brooks. Abundant material or the Polytrichaceae and of Racomitrum indicates that more or less unstable soil. with sparse vascular plant cover, was relatively abundant.  相似文献   

20.
Knudsen, Karen Luise: The Lundergard Clay and its Foraminifera, a new formation in the marine Quaternary of Denmark. Boreas, Vol. 1, pp. 289–297. Oslo, 1st December, 1972.
Samples from marine Quaternary clay deposits at Lundergård in Vendsyssel have been analysed for their content of Foraminifera. The clay, which is called the Lundergård Clay, contains a typical arctic foraminifer fauna with Quinqueloculina stalkeri and Elphidium ustulatum as characteristic species. To attempt an age determination of the Lundergård Clay, the fauna is compared with foraminifer assemblages from other marine Quaternary deposits of Vendsyssel and adjacent areas. The deposit may represent a hitherto unknown facies of the Older Yoldia Clay of Vendsyssel, which is supposed to be of Weichselian interstadial age, or it may be older and can perhaps be correlated with the Holderness Basement Till of Saale interstadial age.  相似文献   

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