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1.
Six successive zones with distinctive marginal moraines are recognized. Based on radiocarbon dates the ages of the three oldest zones are believed to be: older than 11,100 years B.P. (Vasdal event), about 10,900 B.P. (Glomfjord-Straumöy events), and between 10,400 and 9500 B.P. (Skjerstad event). The three youngest zones are Preboreal. Corresponding marine sediments, shorelines, glaciation limits and other glacial features are described.  相似文献   

2.
The deglaciation of Norway after 10,000 B.P.   总被引：1，自引：0，他引：1  
Several distinctive marginal moraines of Preboreal age have been observed in Norway. They are grouped into three major morainal zones that are radiocarbon dated at about 9900±100, 9600±100 and 9300±100 B.P. respectively. The following deglaciation of central Norway was rapid and most likely completed about 8500 B.P. Evidence of glacier fluctuations up to recent time is discussed. The results are based partly on observations by the field parties of the I.G.C.P. project 'Quaternary Glaciations in the Northern Hemisphere'.  相似文献   

3.
A clay varve chronology has been established for the Late Weichselian ice recession east of Mt. Billingen in Västergötland, Sweden. In this area the Middle-Swedish end moraine zone was built up as a consequence of cold climate during the Younger Dryas stadial. A change-over from rapid to slow retreat as a result of climatic deterioration at the Alleröd/Younger Dryas transition cannot be traced with certainty in the varve sequences, but it seems to have taken place just before 11,600 varve years BP. The following deglaciation was very slow for about 700 years — within the Middle-Swedish end moraine zone the annual ice-front retreat was only c . 10 m on average. A considerable time-lag is to be expected between the Younger Dryas climatic event and this period of slow retreat. The 700 years of slow retreat were succeeded by 200 years of more rapid recession, about 50–75 m annually, and then by a mainly rapid and uncomplicated retreat of the ice-front by 100–200 m/year or more, characterizing the next 1500 years of deglaciation in south and central Sweden. The change from about 50–75 m to 100–200 m of annual ice-front retreat may reflect the Younger Dryas/Preboreal transition. Clay-stratigraph-ically defined, the transition is dated at c . 10,740 varve years BP, with an error of +100 to -250 years. In the countings of ice layers in Greenland ice cores (GRIP and GISP-2) the end of the Younger Dryas climatic event is 800–900 years older. However, a climatic amelioration after the cold part of the Younger Dryas and in early Preboreal should rapidly be reflected by for example chemical components and dust in Greenland ice cores, and by increasing δ13C content in tree rings. On the other hand, the start of a rapid retreat of the inland ice margin can be delayed by several centuries. This can explain at least a part of the discrepancy between the time-scales.  相似文献   

4.
Shoreline displacement data from the Trondheimsfjord area have been collected and a synthesis of the Late Weichselian and Holocene relative uplift is presented. The isobase direction is N 30–35°E during the whole period. The gradients of the shorelines are 1.7? m/km at 11,800 years B.P., 1.3 m/km at 10,000 years B.P., gradually decreasing towards the present with a value of 0.2 m/km at 5,000 years B.P. Some irregularities in the shoreline gradient curve in the Late Weichselian and Preboreal chronozones may be ascribed to crustal readjustments by faults. An interpolation of the 9,500 years B.P. shoreline to the Ångermanland and Baltic area shows a relative uplift at 11,800 years B.P. of 400–450 m in the central area of glaciation. The island of Hitra was probably deglaciated at about 12,000 years B.P. and Ørlandet/Bjugn somewhat later. The Younger Dryas ice marginal deposits at Tautra have been deposited early in this chronozone, and deposits proximal to this at Hoklingen and Levanger were probably deposited in the late part of the same chronozone.  相似文献   

5.
At several times during the Quaternary, a major eastward-flowing outlet glacier of the former Patagonian Ice Sheet occupied the Lago San Martin Valley in Argentina (49°S, 72°W). We present a glacial chronology for the valley based on geomorphological mapping and cosmogenic nuclide (10Be) exposure ages (n = 10) of boulders on moraines and lake shorelines. There are five prominent moraine belts in the Lago San Martin Valley, associated with extensive sandar (glaciofluvial outwash plains) and former lake shorelines. Cosmogenic nuclide exposure ages for boulders on these moraines indicate that they formed at 14.3 ± 1.7 ka, 22.4 ± 2.3 ka, 34.4 ± 3.4 ka to 37.6 ± 3.4 ka (and possibly 60 ± 3.5 ka), and 99 ± 11 ka (1σ). These dated glacier advances differ from published chronologies from the Lago San Martin Valley based on 14C age determinations from organic sediments and molluscs in meltwater channels directly in front of moraines or in kettleholes within end moraine ridges. The moraine boulder ages also point to possible pre-LGM glacial advances during the last glacial cycle and a key observation from our data is that the LGM glaciers were probably less extensive in the Lago San Martin Valley than previously thought.  相似文献   

6.
The glacial hydrology of the meltwaters of the ice sheet during deglaciation in a large river basin has been reconstructed on the basis of heights of thresholds and saddles of bedrock topography, glaciofluvial accumulation forms (eskers, deltas and plains of sorted material) and erosional landforms (drainage channels and shorelines) as well as a few terminal moraines. The water level of glacial lake dropped in several stages. The lake existed and deglaciation took place before 9740±280 years B.P. The deglaciation took place at a much faster rate in the studied region than later in western Lapland.  相似文献   

7.
During the Late Weichselian, large marginal moraines were deposited in the Norwegian fjords. In Troms County these features are termed the Skarpnes and Tromsø-Lyngen moraines, respectively, and have been mapped from land into the marine environment where they were formed as ice-contact submarine fans. High-resolution seismic data from several fjords have been studied and reveal a typical sediment thickness of 150–320 m for these ice-contact systems. All of the ice-contact submarine fans were formed under similar climatic conditions, but display wide variation in geometry, architecture and seismic pattern. This variation is related to differences in sediment supply, the nature of the subsurface of the fan (e.g. position of thresholds), basin geometry and basin depth. Based on interpretation of the different seismic facies and the architecture of the fans, former ice-front positions have been suggested and a model has been presented for the formation of different types of ice-contact submarine fans dependent upon variation in local basin condition.  相似文献   

8.
The boundary between the last two geological epochs, the Pleistocene and the Holocene, is placed at 'the date 10,000 B.P., measured in radiocarbon years'. In the European chronostratigraphy, this corresponds to the Younger Dryas/Preboreal boundary, the pollen zone III/IV boundary and the Late Glacial/Postglacial boundary. The stratal sequence in the Botanical Garden of Gothenburg is proposed as a suitable boundary-stratotype of the Pleistocene/Holocene that fulfils the stratigraphical rules of marine environment and accessibility. A core, labelled B 873, has been analyzed for multiple parameters by various authors. The suggested Pleistocene/Holocene boundary in Core B 873 is indicated by a lithologic boundary, a palynological change tentatively correlated with the pollen zone III/IV boundary, and a distinct palaeomagnetic intensity maximum, the 'Gålön Magnetic Intensity Maximum', identified in numerous other cores at the Younger Dryas/Preboreal boundary and at the drainage of the Baltic Ice Lake in varved clay sequences (with the peak dated at the drainage ±4 varves). This boundary is closely radiocarbon dated at 10,000 B.P. (10,000–9950 B.P.) in terrestrial-lacustrine sequences within the proposed type area in Gothenburg and in Southern Sweden, the established type region for the Pleistocene/Holocene boundary. The corresponding varve date is 9965 varves B.P. (De Geer's varve –1073). The various parameters directly and indirectly connected with the study of Core B 873 make global correlations possible. Because every region has its own local characteristics, however, it will be necessary to establish regional type sections, hypostratotypes.  相似文献   

9.
Abstract In the Su-Lu ultrahigh- P terrane, eastern China, many coesite-bearing eclogite pods and layers within biotite gneiss occur together with interlayered metasediments now represented by garnet-quartz-jadeite rock and kyanite quartzite. In addition to garnet + omphacite + rutile + coesite, other peak-stage minerals in some eclogites include kyanite, phengite, epidote, zoisite, talc, nyböite and high-Al titanite. The garnet-quartz-jadeite rock and kyanite quartzite contain jadeite + quartz + garnet + rutile ± zoisite ± apatite and quartz + kyanite + garnet + epidote + phengite + rutile ± omphacite assemblages, respectively. Coesite and quartz pseudomorphs after coesite occur as inclusions in garnet, omphacite, jadeite, kyanite and epidote from both eclogites and metasediments. Study of major elements indicates that the protolith of the garnet-quartz jadeite rock and the kyanite quartzite was supracrustal sediments. Most eclogites have basaltic composition; some have experienced variable 'crustal'contamination or metasomatism, and others may have had a basaltic tuff or pyroclastic rock protolith.
The Su-Lu ultrahigh- P rocks have been subjected to multi-stage recrystallization and exhibit a clockwise P-T path. Inclusion assemblages within garnet record a pre-eclogite epidote amphibolite facies metamorphic event. Ultrahigh- P peak metamorphism took place at 700–890° C and P >28 kbar at c . 210–230 Ma. The symplectitic assemblage plagioclase + hornblende ± epidote ± biotite + titanite implies amphibolite facies retrogressive metamorphism during exhumation at c . 180–200 Ma. Metasedimentary and metamafic lithologies have similar P-T paths. Several lines of evidence indicate that the supracrustal rocks were subducted to mantle depths and experienced in-situ ultrahigh- P metamorphism during the Triassic collision between the Sino-Korean and Yangtze cratons.  相似文献   

10.
In the west-central part of Lago Argentino, the Puerto Bandera moraines are clearly detached from longer, more prominent moraines of the last glaciation and from shorter and smaller Neoglacial moraines. Scientists have long speculated about the age of the Puerto Bandera moraines. Detailed geomorphologic studies in the western area of Lago Argentino, including stratigraphic profiles at Bahía del Quemado in the northern branch (Brazo Norte), indicate that the Puerto Bandera moraines were deposited by three pulses of ice. Each of the three pulses is represented by single moraine ridges and belts of tightly arranged ridges. The timing of the three glacier advances was established by radiocarbon dating, including data published by John Mercer. The oldest moraine system, formed during the Puerto Bandera I substade, was deposited ca. 13,000 14C yr B.P. Moraines of the Puerto Bandera II substade were deposited ca. 11,000 14C yr B.P. The youngest moraine system was deposited during a minor readvance, shortly before 10,390 C14 yr B.P., and thus appears to have occurred some time during the European Younger Dryas interval. After this third substade, the ice tongues retreated into the interior branches of Lago Argentino and have remained there since. Evidence found at Bahía del Quemado, together with data provided by other authors, attests to a significant climatic change by the middle Holocene, which we believe occurred during the Herminita advance, the first Holocene glacial readvance recognized within the area.  相似文献   

11.
This paper considers the controversial issue of the existence of pre-'Little Ice Age' Neoglacial moraines in southern Norway. Schmidt hammer rebound values are combined with measures of boulder roundness and weathering rind thickness in an attempt to isolate moraines that include weathered boulders. A critical approach is used in distinguishing sites where boulders have weathered in situ from those where previously weathered clasts have been incorporated into relatively young moraines. The results confirm that possible pre-'Little Ice Age' Neoglacial moraines seem to be restricted to small, high-altitude glaciers in eastern Jotunheimen. It is concluded that at these glaciers a particularly large response to a short-lived earlier Holocene climatic event is more likely to explain the survival of such moraines than a particularly subdued response to the climatic deterioration of the 'Little Ice Age'. More refined dating techniques are required to determine the age of formation of the anomalous moraines, but before the palaeoclimatic significance of such dates can be assessed, a critical test is required to establish whether the moraines mark former ice-front positions, and therefore reflect lowering of equilibrium line altitudes, or whether they have been displaced forwards by later and more extensive glacier advances.  相似文献   

12.
Deglaciation of western Central Norway   总被引：4，自引：0，他引：4  
The glacier movements and corresponding ice margins in Central Norway during Younger Dryas and Preboreal are reconstructed. Scattered, older marginal deposits are difficult to correlate. Raised beach features indicate that the deep fjords became ice-free at an early stage due to calving. In Møre og Romsdal county the glacier front lay at the fjord heads during Younger Dryas, with extensive local glaciation in the intervening mountain areas, and a limit of glaciation 500–600 m lower than the present. In certain places local moraines older than Younger Dryas have been preserved. Autochthonous block fields are widespread in the mountains of Møre og Romsdal. The lower limit of block fields lies at c. 500 m above sea level on the outermost coast and rises to c. 1500 m above sea level in the interior fjord country. No erratics, striation or lateral moraines from the inland ice have been found above this limit. Its gradient, which in outer fjord districts is about 1%, seems to indicate the ice surface at the last maximum of Weichsel glaciation.  相似文献   

13.
The name Mérida Glaciation is proposed to designate the alpine glaciation which affected the central Veneruelan Andes; during the Late Pleistrocenc. Two main morainie levels have been recognired: one between 2600 and 2700 m, and another between 3000 and 3500 m elevation. The snow line during the last glacial advance was lowered approximately 1200 m below the present snow line (3700 m). Rodiocarbon dating indicates that the moraines are older than 10,000 years B.P., and probahly older than 13,000 years B.P. The lower morainie level probably corresponds to the main Wisconsin glacial advance. The upper level probably represents the last glacial advance (Late Wisconsin).  相似文献   

14.
Late Weichselian deglaciation in the Oslofjord area, south Norway   总被引：2，自引：0，他引：2  
The older 'moraine lines' outside the Ra Moraine in the outer Oslofjord area have been correlated with events in Bohuslän, Sweden. Recent radiocarbon datings in the vicinity of the Ra Moraine and a radiocarbon dated sea-level curve for the Ski area show that the Ra Moraine was formed during the Early Younger Dryas, whereas the Ski Moraine was formed at the end of the Younger Dryas chronozone. An equidistant shoreline diagram together with a large number of marine limit observations have been used to establish the position of the glacier front during Late Younger Dryas and Early Preboreal chronozones. Reconnaissance mapping indicates a fairly regular recession with many short stops during the Bølling, Older Dryas and Allerød chronozones; at least two readvances to the Ra Moraine before 10,600 years B.P.; a rapid recession during the Middle Younger Dryas and a number of ice-front oscillations at the end of the Younger Dryas chronozone.  相似文献   

15.
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   

16.
Recent studies of lake-level fluctuations during the last deglaciation in eastern France (Jura Mountains and Pre-Alps) and on the Swiss Plateau show distinct phases of higher water level developing at the beginning and during the latter part of Greenland Stade 1 (i.e., Younger Dryas event) and punctuating the early Holocene period at 11,250-11,050, 10,300-10,000, 9550-9150, 8300-8050, and 7550-7250 cal yr B.P. The phases at 11,250-11,050 and 8300-8050 cal yr B.P. appear to be related to the cool Preboreal Oscillation and the 8200 yr event assumed to be associated with deglaciation events. A comparison of this mid-European lake-level record with the outbursts from proglacial Lake Agassiz in North America suggests that, between 13,000 and 8000 cal yr B.P., phases of positive water balance were the response in west-central Europe to climate cooling episodes, which were induced by perturbation of the thermohaline circulation due to sudden freshwater releases to oceans. This probably was in response to a southward migration of the Atlantic Westerly Jet and its associated cyclonic track. Moreover, it is hypothesized that, during the early Holocene, varying solar activity could have been a crucial factor by amplifying or reducing the possible effects of Lake Agassiz outbursts on the climate.  相似文献   

17.
美国中西部第四纪冰川与黄土研究的进展和问题   总被引：1，自引：0，他引：1       下载免费PDF全文
冯兆东 《第四纪研究》1994,14(4):362-368
本文对美国中西部和中国黄土高原０．５Ｍａ以来的气候序列进行了对比。０．５—０．１ＭａＢ．Ｐ．，美国中西部间冰期以干暖为特征，１０００００—３５０００ａＢ．Ｐ．，气候从干暖向温湿转化。本次冰进阶段，冰盖达到最大后，风尘堆积占优势，气候湿凉为主。全新世先从温凉转为温湿，继而干暖，后又转向湿凉。总之，０．５Ｍａ以来除末次冰期外，美国中西部与中国黄土高原温度变化的总趋势是一致的，但两地的湿度变化是相反的。  相似文献   

18.
全新世早期是太阳辐射加强、全球温度上升,并伴随着冰盖消融的重要时期,而其间发生的冷事件以及亚洲季风区的弱夏季风事件的成因一直是全新世早期研究的重点。对亚洲季风-海洋-极地联系研究有着重要的意义。通过分析湖南莲花洞LHD5石笋28个U/Th年龄和535个氧同位素数据重建了全新世亚洲季风演化特征,其中全新世早期分辨率达8年。LHD5石笋记录到YD结束时间为11748±30 a B.P.,全新世开始于11684±39 a B.P.,转换时间约为64年,与格陵兰gicc05记录在误差范围内一致。LHD5石笋记录到全新世早期6次弱夏季风事件,事件年龄中心点分别为11461±34 a B.P.、10354±36 a B.P.、9957±25 a B.P.、9062±36 a B.P.、8744±23 a B.P.、8144±24 a B.P.,其δ18O值的波动幅度分别为1.08‰、0.94‰、0.66‰、0.90‰、0.55‰、1.02‰,这些弱季风事件在亚洲季风区具有普遍的区域意义。除8.2 ka事件之外,10 ka B.P.之前的弱季风事件除了受到太阳活动的影响,还受到北大西洋IRD事件的影响,而之后更多地受到太阳活动和ITCZ南移的影响。  相似文献   

19.
The Late Quaternary ( c . 130,000–10,000 BP) glacial history of the central west coast of Jameson Land, East Greenland, is reconstructed through glacial stratigraphical studies. Seven major sedimentary units are described and defined. They represent two interglacial events (where one is the Holocene). one interstadial event and two glacial events. The older interglacial event comprises marine and fluvial sediments, and is correlated to the Langelandselv interglacial, corresponding to oxygen isotope sub-stage 5e. It is followed by an Early Weichselian major glaciation during the Aucellaelv stade, and subsequently by an Early Weichselian interstadial marine and deltaic event (the Hugin Sø interstade). Sediments relating to the Middle Weichselian have not been recognized in the area. The Hugin Sø interstade deposits have been overrun by a Late Weichselian ice advance, during the Flakkerhuk stade, when the glacier, which probably was a thin, low gradient fjord glacier in Scoresby Sund, draped older sediments and landforms with a thin till. Subsequent to the final deglaciation, some time before 10,000BP, the sea reached the marine limit around 70 m a.s.l., and early Holocene marine, fluvial and littoral sediments were deposited in the coastal areas.  相似文献   

20.
Three kinds of end moraines, depending most probably on climatic conditions affecting depositional environments, are characterized: (1) fluvioglacial end moraines - built of gravels and sands froming fans superimposed on one another, and accumulated by abundant melt water during intense melting of an ice front in a comparatively warm environment; (2) 'Glacial' end moraines - built of flow tills accumulated during slow melting in a comparatively cold environment; and (3) fluvioglacial-and-glacial end moraines, the most widespread ones in Polish lowlands – built of fluvioglacial stratified gravels and sands and of glacial 'flow' deposits; zones of considerable prevalence of glacial deposits over fluvioglacial ones may probably point to comparatively cold stages during deposition, and vice versa. The question of deposition of end moraines in distal and proximal direction, and their geological and geomorphological features is also briefly discussed.  相似文献   

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