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1.
The modern drainage system of central Poland developed during the Holsteinian, but it originated from the Elsterian glacial tunnel valleys and deglacial residual overflow lakes. In spite of occupation of this area by the Wartanian ice sheet and the following formation of the landscape during deglaciation, a similar river network was renewed during the Eemian. During the Weichselian the Middle Vistula valley was subjected to widespread ice-dam deposition. This resulted in rise of the base level of erosion and in westward deflection of the runoff, connected with development of the Central European spillways. The presented reconstruction of the Middle and Late Pleistocene fluvial network shows that the Holstein and Eemian sea levels were the driving force for river system development in central Poland. The Holstein and Eemian sea levels were very close to the present water level of the Baltic Sea. They made interglacial fluvial patterns roughly similar to the contemporary one, and therefore the main watersheds have been only slightly modified since that time. However, due to the considerable southward extension of the sea during the Eemian and presumably also during the Holsteinian, buried interglacial river deposits in central Poland occur at present well beneath the Holocene alluvia.  相似文献   

2.
Finnish Lapland is known as an area where numerous sites with sediments from Pleistocene glacial and interglacial periods occur. Recent sedimentological observations and dating call for reinterpretation of the record, which shows a complicated Mid‐Weichselian ice‐sheet evolution within the ice‐divide zone. Here, a large, previously unstudied section from a former Hannukainen iron mine was investigated sedimentologically and dated with optically stimulated luminescence (OSL). Ten sedimentary units were identified displaying a variety of depositional environments (glacial, glaciolacustrine, fluvial and aeolian). They are all – except for the lowermost, deeply weathered till – interpreted to be of Mid‐ or Late Weichselian/Holocene age. Five OSL samples from fluvial sediments give ages ranging from 55 to 35 ka, indicating two MIS 3 ice‐free intervals of unknown duration. The Mid‐Weichselian interstadial was interrupted by a re‐advance event, which occurred later than 35 ka and caused glaciotectonic deformation, folding and stacking of older sediments. This new evidence emphasizes the importance of the Kolari area when unravelling the complex Late Pleistocene glacial history of northern Finland and adjacent regions.  相似文献   

3.
The Rautuvaara section in northern Finnish Lapland has been widely considered as the stratotype for the northern Fennoscandian late Middle and Late Pleistocene. It exposes four till units interbedded with sorted sediments resting on Precambrian bedrock. In order to shed light on the Scandinavian Ice Sheet (SIS) history and palaeoenvironmental evolution in northern Fennoscandia through time, a chronostratigraphical study was carried out at the Rautuvaara site. The succession was studied using sedimentological methods and different sand‐rich units between till units were dated using the Optical Stimulated Luminescence (OSL) method. The results obtained indicate that the whole sediment succession at Rautuvaara was deposited during the Weichselian Stage and there is no indication of older deposits. The SIS advanced across Finnish Lapland to adjacent areas to the east at least once during the Early Weichselian, twice during the Middle Weichselian (～MIS 4 and MIS 3) and once during the Late Weichselian substages. Glaciolacustrine sediments interbedded between the till units indicate that a glacial lake repeatedly existed after each deglacial phase. The results also suggest that there were two ice‐free intervals in northern Fennoscandia during the Middle Weichselian close to the SIS glaciation centre.  相似文献   

4.
The Late Pleistocene stratigraphy from the Severnaya Dvina‐Vychegda region of northwestern Russia is revised based on investigations of new localities, revisiting earlier localities, introduction of about 110 new OSL dates and burial depth corrections of earlier published OSL dates, in addition to six new radiocarbon dates. Most of the OSL samples studied here are from fluvial and subaquaeous sediments, which we found to be well bleached. Six chronostratigraphical units and their sedimentary environment are described, with the oldest unit consisting of pre‐Eemian glacial beds. For the first time, Early Weichselian sediments are documented from the region and a fluvial environment with some vegetation and permafrost conditions is suggested to have persisted from the end of the Eemian until at least about 92 ka ago. The period in which a Middle Weichselian White Sea Lake could have existed is constrained to 67?62 ka, but as the lake level never reached the thresholds of the drainage basin, the lake probably existed only for a short interval within this time‐span. Blocking and reversal of fluvial drainage started again around 21?20 ka ago when the Fennoscandian Ice Sheet advanced into the area, reaching its maximum 17?15 ka ago. At that time, an ice‐dammed lake reached its maximum water level, which was around 135 m above present sea level. Drainage of the lake started shortly after 15 ka ago, and the lake was emptied within 700 years. Severe periglacial conditions, with permafrost and aeolian activity, prevailed in the area until about 10.7 ka.  相似文献   

5.
黄河源区第四纪地质研究的新进展   总被引：8，自引：1，他引：8  
通过对黄河源区的钻孔、自然露头的研究, 建立了黄河源区的第四纪地层层序。第四纪地层可划分为下更新统、中更新统、上更新统和全新统。下更新统为河湖相沉积; 中更新统主要有湖积物、冰碛物和冰水沉积物; 上更新统主要有湖积物、冰碛物、冰水沉积物、洪积物和河流沉积物; 全新统主要由河流沉积物、洪积物和湖积物构成。黄河源区的冰期可划分为3期, 即末次冰期、倒数第二次冰期、倒数第三次冰期, 末次冰期又可分为2个冰阶。黄河源区的湖泊演化可划分为早更新世、中更新世和晚更新世—全新世3个阶段: 早更新世的湖泊范围小; 中更新世的湖泊范围明显扩大, 在位置上也较早更新世的湖泊南移; 晚更新世的湖泊经历了两次的扩张—收缩变化, 到了全新世, 除现今还发育的几个湖泊外, 大多数地区的湖水已退出, 基本上转变为河流环境。在晚更新世末期到全新世初期, 封闭黄河源区的多石峡被切开, 湖水外泄, 现今的黄河形成了, 同时发生了袭夺长江水系的水流。  相似文献   

6.
柴达木盆地三湖地区第四系沉积相与生物气成藏   总被引：30，自引：3，他引：27       下载免费PDF全文
柴达木盆地三湖地区第四系蕴藏着巨大的生物气资源,目前已探明加控制天然气储量接近3×1011m3。更新世时期,柴达木盆地的湖相沉积主要分布在三湖(吉乃尔湖、涩聂湖和达布逊湖)地区,自山前至盆地中心依次发育了冲积扇、河流三角洲和湖相沉积,其中湖相沉积分布最为广泛。早更新世湖相沉积开始形成,中更新世湖相沉积扩张并且达到鼎盛,晚更新世湖相沉积开始萎缩并形成盐湖沉积。中、早更新世冰川的出现和青藏高原的崛起使柴达木盆地的古气候变得干旱寒冷,沉积水体温度较低,盐度较高。本区第四纪独特的沉积环境是形成大型生物气藏最重要的地质条件。高盐度的水体环境减缓了有机质的降解速度,长期的低温条件抑制了甲烷菌的活动,避免了沉积有机质在沉积浅埋阶段的过量消耗,推迟了生物产气的高峰期。而三湖地区巨厚的第四系暗色泥岩和频繁发育的砂岩提供了充足的气源条件和构成了良好的生储盖组合。  相似文献   

7.
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   

8.
The article discusses geological data on proglacial lakes and spillways in the West Siberian Plain, data on crucial features of the Late Pleistocene reorganization of the drainage pattern of northern Eurasia. The discussion focuses on Late Pleistocene sediments along the margin of the last ice sheet and south of it, including new data recently obtained by the Russian-Norwegian project PECHORA in Trans-Uralia. Based on these data, the margin of the last ice sheet in the western and central parts of West Siberia is localized well above the Arctic Circle, i.e. 150-250 km north of the previously suggested ice limit. The available geochronological evidence indicates that the last ice dam across West Siberia, which diverted the great Siberian rivers to the south, appeared at early stages of the last, Weichselian ice age. The normal, northbound, drainage was restored later, within the time-span accessible to radiocarbon dating, when two pre-Holocene river terraces with mammal fauna were formed. The Late Weichselian was the driest period with ubiquitous aeolian activity and an absence of large water bodies. Preceding ice-dammed lakes of West Siberia could only drain through the Turgai valley which leads southward into the Aral and Caspian seas. The sedimentary sequence of this passage consists of lacustrine clay, diamictic gravity flows and aeolian sediments younger than 29 kyr which infilled the former spillway mainly in the Late Weichselian. The basal sand and gravel mantling the bedrock floor, which descends from 55 m a.s.l. at 55°N to 30-40 m a.s.l. in the south, is the only signature of a southward drainage. This fluvial episode probably reflects overflow of a Siberian proglacial lake whose water level could reach 60 m a.s.l. prior to 29 kyr BP.  相似文献   

9.
As the majority of the data on Quaternary sediments from the North Sea Basin are seismostratigraphical, we analysed the Elsterian Swarte Bank Formation, the Late Saalian Fisher Formation and the Late Weichselian (Dimlington Stadial) Bolders Bank Formation in order to determine genesis and provenance. The Swarte Bank Formation is a subglacial till containing palynomorphs from the Moray Forth and the northeastern North Sea, and metamorphic heavy minerals from the Scottish Highlands. The Fisher Formation was sampled from the northern and central North Sea. In the north, it is interpreted as a subglacial till, with glaciomarine sediments cropping out further south. These sediments exhibit a provenance signature consistent with the Midland Valley of Scotland, the Eocene of the North Sea Basin, the Grampian Highlands and northeast Scotland. The Bolders Bank Formation is a subglacial till containing palynomorphs from the Midland Valley of Scotland, northern Britain, and a metamorphic heavy‐mineral suite indicative of the Grampian Highlands, Southern Uplands and northeast Scotland. These data demonstrate that there was repeated glaciation of the North Sea Basin during the Middle and Late Pleistocene, with ice sheets originating in northern Scotland. There was no evidence for a Scandinavian ice sheet in the western North Sea basin. Copyright © 2011 John Wiley & Sons, Ltd.  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.
The Hitura open pit exposes a sedimentary sequence up to 50 m thick representing Late Saalian to Holocene glacial and non-glacial sediments. The sequence was investigated using sedimentological methods, OSL-dating and pollen and diatom analyses to reconstruct the Middle Weichselian (MWG) glacial event in the central part of the Scandinavian Ice Sheet (SIS). The results indicate that the sediment succession represents two entire glacial advance and retreat cycles. The lowermost deposits are Late Saalian esker and delta sediments overlain by sediments that correlate with the early Eemian lacustrine phase. Remnants of the Eemian soil post-dating the lacustrine phase were also observed. The area was ice-free during the entire Early Weichselian (EWG). The first glacial advance recorded in the sediments is related to the MWG. It started 79 kyr ago, deformed underlying sediments and deposited an immature till, including large detached sediment pods containing remains of organic material, soils and fluvial sediments representing allochthonous material from EWG ice-free stadials and interstadials. The glacial deposits are conformably overlain by glaciolacustrine and littoral accumulations, indicating MWG deglaciation between 62 and 55 kyr ago. Based on the fabric measurements from the till unit overlying the MWG sediments, ice advance during the Late Weichselian (LWG) was initially from the west and later from a north-northwesterly direction. The Hitura strata provide the first dating of the MWG deglaciation (55 to 62 kyr ago) from central parts of the SIS. It can be considered as a key site for studying the growth and decay of SIS during the poorly known early parts of the glaciation.  相似文献   

12.
罗布泊东部阿奇克谷地第四纪古地理   总被引：5，自引：0，他引：5  
通过对罗布泊东部阿奇克谷地中部AK1孔及露头剖面第四纪沉积特征的综合研究,初步分析了阿奇克谷地第四纪以来的沉积环境与古地理演化。结果表明,阿奇克谷地第四纪古地理受上新世以来区域构造控制,谷地两侧北山及阿尔金山的隆升,一方面为其提供了丰富的物质来源,同时也控制了其沉积环境的演化。其中第四纪以来阿奇克谷地沉积环境有两次明显变化,早更新世中期谷地中开始出现湖相沉积;中更新世晚期湖相沉积范围扩大,为罗布泊湖的大发展期。晚更新世谷地两侧普遍出现砾石层,与中更新世呈不整合接触,表明构造抬升造成湖泊退缩。晚更新世以来湖泊沉积环境波动变化加快。  相似文献   

13.
The moraine plateau near BetchatÓw (central Poland) was incised at the beginning of the Middle Weichselian. Valleys 20–35 m deep were formed and then infilled with silts, sands, gravels, organic sediments and slope diamictons of the Piaski Formation, which is characterized by highly varying sedimentary environments. Initially - 40,000–30,000 BP - lacustrine sediments with an obvious colian supply (re-worked loess) and locally fluvial suites were deposited in depressions. Slope sediments were simultaneously deposited at the valley margins. The Middle Weichselian was relatively mild and dry, but the milder interstadial periods have not been precisely established. Semi-anastomosing, stable-channel, highly aggrading and ephemeral streams of a semi-arid climate (subpolar desert) formed c. 30,000–22,000 BP. Continuous permafrost is implied from cyclic sedimentary processes reflecting summer melting and from periglacial structures. This was succeeded by a highly aggrading, high-energy and ephemeral braided fluvial system in an arid climate (polar desert), reflecting a complete lack of vegetation and increased eolian activity. These braided rivers formed during a period which may be directly correlated with the time of the maximum extent of the last ice sheet (22,000–14,350 BP), characterized by the most severe climatic conditions with strong periglacial activity. Finally - (14,350-12,700 BP)- eolian sediments were deposited, reflecting milder climatic conditions at the time of the abrupt ice sheet decay.  相似文献   

14.
晋中盆地是位于汾渭地堑系中部的新生代陆内断陷沉积盆地,研究晋中盆地第四纪的沉积序列对于进一步认识该盆地区域构造和区域气候环境变化具有重要意义。为查明晋中盆地第四纪沉积序列结构、研究揭示晋中盆地第四纪沉积环境及演化,通过构造岩相学方法,对晋中盆地地表和钻孔内第四纪沉积物和沉积环境进行了研究。结果表明:晋中盆地清徐地区地表第四纪沉积序列结构为盆地内部沱阳组河床相和河漫滩相-盆地边缘汾河组河流相—盆山过渡带峙峪组河流相、汾河组冲积扇相及马兰组风积相-基岩山地（盆地外围）二叠系浅海相。钻孔岩芯内第四纪沉积序列结构为下更新统浅湖相和滨湖相—中更新统浅湖相和河流相—上更新统河流相和冲积扇相—全新统冲积扇相。研究认为晋中新生代陆内断陷盆地内沉积序列和演化结构为早更新世陆相湖盆沉积环境—中更新世萎缩湖泊环境—晚更新世强烈萎缩的湖泊和河流环境—全新世再度沉降的陆相湖盆;陆相湖盆从中心向山地沉积环境分带为湖泊沉积环境—河流和湖泊沉积环境—冲积扇沉积环境（盆地边缘出山口区）。盆山过渡带地区上更新世沉积物错位现象与同沉积活动断裂有关,断裂活动性揭示了晋中盆地阶梯式断陷成盆的动力学机制。这些研究成果为区域气候环境变化和晋中盆地区域构造研究提供了新证据,也为太原市城市群建设中工程场址的选择提了供参考。   相似文献   

15.
Foraminifera, pollen, lithology and radiocarbon dates from a core in the southern Kattegat provide a rare opportunity to obtain data relating to environmental conditions during the Middle Weichselian in the offshore Kattegat. This core is also correlated with an adjacent second core. Redeposited Eemian foraminifera and pollen occur in the Middle Weichselian sediments. This is interpreted as a result of reworking by an active Middle Weichselian ice present in, or advancing from, a northeasterly to easterly direction. During a second phase the Middle Weichselian sediments were compacted, probably a result of overriding by an ice from the northeast during the Middle Weichselian and/or the Late Weichselian Maximum. The Middle Weichselian sequence is overlain by a Holocene sequence which, in turn, is overlain by an admixture of Middle Weichselian and Holocene sediments. This mixing may be a result of tectonic activity some time between 7300 and 1000 BP. The core ends in Holocene fine sediments representing the last c. 1000 years.  相似文献   

16.
Core material obtained from three boreholes was studied from the Ruunaa area, Finnish northern Karelia, in order to reveal the Late Pleistocene environmental history of eastern Finland. Conventional litho- and biostratigraphical methods were used and suitable sediment samples were dated using quartz optically stimulated luminescence. The results indicate that two till units were deposited by two separate Weichselian ice advances into the area. The first advance took place prior to 52 kyr ago, most likely during the early Middle Weichselian, while the second is thought to have taken place during the Late Weichselian after 25 kyr ago. The sediment succession at Ruunaa therefore indicates a Middle Weichselian ice-free period around 50–25 kyr ago in the eastern part of Fennoscandia.  相似文献   

17.
罗布泊位于塔里木盆地东端,地处欧亚大陆深腹地,罗北凹地则是罗布泊东北部的一个次级凹地。通过对罗北凹地LDK01深孔沉积物粒度、磁化率和地球化学的分析,并结合沉积物的岩性、盐类矿物形态特征和和组合类型、构造背景,对罗布泊地区第四纪成钾环境的阶段性变化规律进行探讨。研究表明,罗布泊地区早更新世以来依次发育了河流相、三角洲相、湖泊相-风成相等沉积体系,并呈现出明显快速的湖相推进和退缩交替的频繁变化,指示盐湖演化是干湿气候周期变化和湖盆周围山区淡水周期补给共同作用结果。第四纪时期罗北凹地发展并最终形成塔里木"高山深盆"中最深的次级凹地地貌,这是青藏高原隆升导致的向北挤压的必然结果,大地构造和环境的变化直接控制了罗布泊盐湖的构造演化和沉积体系的转变。罗布泊盐湖的演化大致可分为三个阶段:第一阶段为断陷阶段,早更新世以来主要沉积淡水河流湖泊相陆源碎屑物;第二阶段为坳陷阶段,中更新世中期发育膏岩湖相,以石膏等硫酸盐析出为主要特征;第三阶段为萎缩阶段,进入晚更新世,大量盐湖相钙芒硝沉积至全新世时期石盐等氯化物析出;上述三个阶段构成一个完整蒸发沉积构造旋回并于最终阶段中形成了超大型的钾盐矿床。  相似文献   

18.
At Kap Herschell, in the outer fjord zone of central northeast Greenland, exposed sections in a Late Pleistocene ice-cored moraine revealed four major stratigraphic units deposited during the complex Kap Herschell Stade . All contain fragmented and redeposited marine shells that most likely belong to an Eemian or Early Weichselian marine episode. The oldest unit consists of buried ground ice with folded and sheared debris bands. Isotopic analyses show that the slope of the regression line for δ2H vs. δ18O of the ice is about 8.5. which suggests correlation with the Global Meteoric Water Line (GMWL). Data strongly suggest that the ground ice at Kap Herschell is a remnant of a Late Pleistocene glacier. It was probably generated at low altitudes (< 1000 m) in the inner fjord region or in the nunatak zone. The ground ice is unconformably overlain by all younger stratigraphic units, the oldest of which is a diamicton probably deposited as ablation till from the ice. A complex unit composed of mainly glaciolacustrine deposits and subordinate beds of fluvial and deltaic origin overlies the till and ground ice. Luminescence dating of the lacustrine sediments indicates maximum ages younger than 43 ka BP, suggesting deposition during isotope stages 3 or 2. The glaciolacustrine deposits suffered strongly from glaciotectonic deformation, caused by renewed glacier advance through the fjord. It reached the inner shelf and led to deposition of a discordant till at Kap Herschell, most probably during the Late Weichselian.  相似文献   

19.
Sedimentological analysis of the Weichselian deposits exposed in the coastal cliff section at Lønstrup Klint, northern Jutland, Denmark, demonstrates the presence of four sedimentary units comprising fine-grained lacustrine and fluvial deposits of the latest Middle Wcichselian. The Lønstrup Klint section also shows an interplay between glaciotectonics and sedimentation. The two lower sedimentary units are separated by an erosional unconformity of pretectonic origin, whereas the upper two units are syntectonic. The glaciotectonic processes reflect the Late Weichselian expansion of the Scandinavian ice cap into northern Jutland. The sedimentary structures indicate high rates of deposition. The area underwent dramatic palaeogeographic changes from deep lake to proglacial fluvial plain in a time-span of a few thousand years.  相似文献   

20.
A section, almost 20 km long and up to 80 m high, through alternating layers of diamict and sorted sediments is superbly exposed on the north coast of the Kanin Peninsula, northwestern Russia. The diamicts represent multiple glacial advances by the Barents Sea and the Kara Sea ice sheets during the Weichselian. The diamicts and stratigraphically older lacustrine, fluvial and shallow marine sediments have been thrust as nappes by the Barents Sea and Kara Sea ice sheets. Based on stratigraphic position, OSL dating, sea level information and pollen, it is evident that the sorted sediments were deposited in the Late Eemian-Early Weichselian. Sedimentation started in lake basins and continued in shallow marine embayments when the lakes opened to the sea. The observed transition from lacustrine to shallow marine sedimentation could represent coastal retreat during stable or rising sea level.  相似文献   

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