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1.
A coastal cliff facing the ocean at the west coast of Spitsbergen has been studied, and seven formations of Weichselian and Holocene age have been identified. A reconstruction of the palaeoenvironment and glacial history shows that most of the sediments cover isotope stage 5. From the base of the section, the formation 1 and 2 tills show a regional glaciation that reached the continental shelf shortly after the Eemian. Formation 3 consists of glacimarine to marine sediments dated to 105,000–90,000 BP. Amino acid diagenesis indicates that they were deposited during a c . 10,000-year period of continuous isostatic depression, which indicates contemporaneous glacial loading in the Barents Sea. Foraminifera and molluscs show influx of Atlantic water masses along the west coast of Svalbard at the same time. Local glaciers advanced during the latter part of this period, probably due to the penetration of moist air masses, and deposited formation 4. A widespread weathering horizon shows that the glacial retreat was succeeded by subaerial conditions during the Middle Weichselian. Formation 5 is a till deposited during the Late Weichselian glacial maximum in this area. The glaciation was dominated by ice streams from a dome over southern Spitsbergen, and the last deglaciation of the outer coast is dated to 13,000 BP. A correlation of the events with other areas on Svalbard is discussed, and at least two periods of glaciation in the Barents Sea during the Weichselian are suggested.  相似文献   

2.
Troitsky, Leonid, Punning, Jaan-Mati, HÜtt, Galina & Rajamäe, Raivo 1979 12 01: Pleistocene glaciation chronology of Spitsbergen. Boreas , Vol. 8, pp. 401–407. Oslo. ISSN 0300–9483.
Geomorphological and geochronological studies of Pleistocene deposits were carried out in sections along Billefjorden and Bellsund as well as on Bröggerhalvöya and Prins Karls Forland. For purposes of correlation and development of a time scale, radiocarbon (14C) and thermoluminescent (TL) dating methods were used. The dates obtained indicate the presence of older Pleistocene deposits on Spitsbergen and also provide information on the distribution of Middle Pleistocene glacial deposits. A correlation scheme of Pleistocene deposits of Spitsbergen with stratigraphic units of the Alps and northwestern Europe is presented.  相似文献   

3.
The record of Quaternary glaciations of coastal areas is frequently preserved as a raised deglacial-emergence sequence. Detailed radiocarbon dating of foraminifera and marine macrofossils from a representative deglacial sequence on west Spitsbergen document two periods of sedimentation at c . 11,400 BP and at 9500 BP that together span < 500 years. The incompleteness of this record (< 25%), the highly episodic nature of sedimentation, the dominance of local glacial and environmental effects and the presence of allochthonous foraminifera inhibits ascertaining the relation between deglaciation of Svalbard/Barents Sea and changes in thermohaline circulation in the Norwegian Sea. The Late Weichselian and older deglacial sequences on west Spitsbergen have a similar sedimentologic succession. Thus, one possibility is that older raised-marine deglacial sequences on Svalbard and other Arctic areas may represent similar brief intervals, potentially confounding correlations across the Arctic and with well established events (i.e. the Eemian Interglacial) at lower latitudes.  相似文献   

4.
A sedimentological study of Quaternary sediments from the northwestern part of the Barents Sea shows that their composition is controlled by the underlying Mesozoic bedrock and that very little sediment has been supplied from outside sources. The Quaternary sediments consist of Pleistocene glacial clays (moraines) and Holocene gravel, sand and mud, derived by erosion of the clay-rich moraines, which again have been derived from underlying Mesozoic rocks. On the shallow Spitsbergen Bank (30-100 m depth) we find a high energy facies of bioclastic carbonate sand and gravel and lag deposits of Mesozoic rock fragments from the underlying moraine. 14C-datings of the bioclastic carbonates (Molluscs and Barnacles) suggest that soft bottom conditions with Mya truncata prevailed in early Holocene time, succeeded by a hard bottom high energy environment with Barnacles in the last 2000-3000 years. This may be due to a southward movement of the oceanic polar front into the Spitsbergen Bank due to colder climate in Late Holocene (subatlantic) time, which at present day produces strong bottom currents down to 100 m depth. On the Spitsbergen Bank carbonate sedimentation has succeeded glacial sedimentation as a result of withdrawal of clastic sediment supply in Holocene time and high organic productivity because of upwelling. A similar mechanism may have been operating during earlier glaciations, i.e. in Late Precambrian time to produce an association of glacial and carbonate sediments although the biological precipitation was different at that time. In Late Precambrian time precipitation or carbonate by algaes may have occurred in colder water on the shelves due to higher saturation of carbonate in the sea water.  相似文献   

5.
Sejrup, Hans Petter 1987 03 01: Molluscan and foraminiferal biostratigraphy of an Eemian-Early Weichselian section on Karmøy, southwestern Norway. Boreas , Vol. 16, pp. 27–42. Oslo. ISSN 0300–9483.
At Karmøy, southwestern Norway, a section with marine sediments from the last interglacial (the Avaldsnes Interglacial) and from two ice-free periods (the Torvastad and Bø Interstadial) in the Weichselian have been examined for molluscs and foraminifera. The following conclusions concerning the depositional environments of these sediments can be drawn: (1) The Avaldsnes Interglacial was a high-energy environment with a sea level 20 to 50 m higher than at present, regressing towards the end of the interglacial. Sea temperatures were as in the area today or slightly warmer. (2) During the Torvastad Interstadial (71–85 ka) the sea level was between 0 and c . 20 m higher than at present, and sea temperatures were as between Svalbard and northern Norway today. (3) The Bø Interstadial (40–64 ka) shows a complete interstadial cycle, with changing sea level and temperatures. Its optimum was close to the conditions prevailing in North Norway today or slightly colder. By comparison with other sites, a total of at least four interstadial episodes through the Weichselian in southwestern Norway is proposed. These date to c . 30 ka, 40–64 ka, 71–85 ka and 87–101 ka. The episodes and the glacial advances between them do not directly correlate with published interpretations of changes in surface circulation in the Norwegian Sea through the Weichselian. It is suggested that the nourishment of the southern part of the Scandinavian ice sheet might be more related to sea surface conditions in the North Atlantic than to those of the Norwegian Sea.  相似文献   

6.
Direct evidence for Late Weichselian grounded glacier ice over extensive areas of the Barents Sea is based largely on indirect observations, including elevations of old shorelines on Svalbard and arguments of isostatic rebound. Such isostatic models are discussed here for two cases representing maximum and minimum ice-sheet reconstructions. In the former model the ice extends over the Kara Sea, whereas in the latter the ice is limited to the Barents Sea and island archipelagos. Comparisons of predictions with observations from a number of areas, including Spitsbergen, Nordaustlandet, Edgeøya, Kong Karls Land, Franz Josef Land, Novaya Zemlya and Finnmark, support arguments for the existence of a large ice sheet over the region at the time of the last glacial maximum. This ice sheet is likely to have had the following characteristics, conclusions that are independent of assumptions made about the Earth's rheological parameters. (i) The maximum thickness of this ice was about 1500–2000 m with the centre of the load occurring to the south and east of Kong Karls Land. (ii) The ice sheet extended out to the western edge of the continental shelf and its maximum thickness over western Spitsbergen was about 800 m. (iii) To the north of Svalberg and Frans Josef Land the ice sheet extended out to the northern shelf edge. (iv) Retreat of the grounded ice across the southern Barents Sea occurred relatively early such that this region was largely ice free by about 15,000 BP. (v) By 12,000 BP the grounded ice had retreated to the northern archipelagos and was largely gone by 10,000 BP. (vi) The ice sheet may have extended to the Kara Sea but ice thicknesses were only a fraction of those proposed in those reconstructions where the maximum ice thickness is centered on Novaya Zemlya. Models for the palaeobathymetry for the Barents Sea at the time of the last glacial maximum indicate that large parts of the Barents Sea were either very shallow or above sea level, providing the opportunity for ice growth on the emerged plateaux, as well as on the islands, but only towards the end of the period of Fennoscandian ice sheet build-up.  相似文献   

7.
A proposal for the classification of accumulations formed at the foot of mountain slopes and glacier snouts is presented for South Spitsbergen. Simple (talus cones) and complex (protalus ramparts, protalus rock glaciers, moraine rock glaciers) landforms are distinguished. The homogeneity of the features deposited at the foot of mountain slopes on a bedrock as well as on a glacial ice is noted, although the latter are more easily destructed due to melting of the buried ice. A significance of the ice core (interstitial or glacial ice) for a development of protalus rock glaciers and moraine rock glaciers is emphasized.  相似文献   

8.
Changes in paleoenvironments over the last 17,500 yr have been documented by a high-resolution clay mineralogy and grain–size records of Core KNG5 from the northern slope of the South China Sea. Our results indicate that clay minerals are mainly from the Pearl River from 17,500 to12,500 cal yr BP, and the South China Sea modern current system began to form since 12,500 cal yr BP, as a result, Taiwan turns to be the major contributor of clay minerals after 12,500 cal yr BP. Two grain-size populations with high variability through time were identified in the 13–28 μm and 1–2.2 μm grain-size intervals. The 1–2.2 μm grain-size population are mainly controlled by provenance supply and current transport. The 13–28 μm grain-size fraction could be controlled mainly by the sea-level change. The 1–2.2 μm grain-size population record demonstrates that East Asian Summer Monsoon intensity generally follows changes in insolation and that the response is similar for a large area of China and other northern low-latitude records, implying the globality of the monsoon evolution since Holocene. The anomalous environmental conditions in the northern South China Sea may imply intensified ENSO activity during the late Holocene.  相似文献   

9.
Geochemical characteristics of marine sediment from the southern Drake Passage were analyzed to reconstruct variations in sediment provenance and transport paths during the late Quaternary. The 5.95 m gravity core used in this study records paleoenvironmental changes during the last approximately 600 ka. Down-core variations in trace element, rare earth element, and Nd and Sr isotopic compositions reveal that sediment provenance varied according to glacial cycles. During glacial periods, detrital sediments in the southern Drake Passage were mostly derived from the nearby South Shetland Islands and shelf sediments. In contrast, interglacial sediments are composed of mixed sediments, derived from both West Antarctica and East Antarctica. The East Antarctic provenance of the interglacial sediments was inferred to be the Weddell Sea region. Sediment input from the Weddell Sea was reduced during glacial periods by extensive ice sheets and weakened current from the Weddell Sea. Sediment supply from the Weddell Sea increased during interglacial periods, especially those with higher warmth such as MIS 5, 9, and 11. This suggests that the influence of deep water from the Weddell Sea increases during interglacial periods and decreases during glacial periods, with the degree of influence increasing as interglacial intensity increases.  相似文献   

10.
郑范  李前裕  陈木宏 《地球科学》2006,31(6):780-786
南海北部ODP1144站中更新世气候转型时期的浮游有孔虫在千年尺度上以高频率变化为主要特征.冰期旋回主要周期在0.9Ma由41ka转变为100ka, 浮游有孔虫组合也随冰期旋回出现大量的冷水种.据转换函数得出的表层水降温高达10℃发生在0.9~0.6Ma间的转型过渡期, 跨越MIS22、20、18、16四大冰期.同时, 温跃层深度呈阶梯式变浅, 在MIS20上升至65m左右.所以, 南海北部上层水体环境在中更新世气候转型期出现比末次冰期更重的δ18O值, 温跃层变浅, 深水种含量降低或消失, 突出了边缘海区南北气候梯度反差和冬季风在冰期增强的讯号.南海南北部的环境差异与东西太平洋的差异, 共同表明低纬过程在气候变化中的重要性.   相似文献   

11.
曲华祥  黄宝琦 《地学前缘》2019,26(3):236-242
海洋沉积物中的某些主微量元素与沉积物源区有着密切的联系,它们之间的比值变化受到源区化学风化强度的影响,因此这些元素的比值变化可以反映出海洋沉积物源区古气候的变化。本文研究了南海北部陆坡MD12-3432站位深海氧同位素6期和5期(MIS6/5) 沉积物的主微量元素,发现其表现出良好的气候控制变化特征,K/Ti、Mg/Ti、Al/Ti、Fe/Ti、Co/Ti、Zn/Ti和V/Ti等比值在MIS 5期时较高,而在MIS6期时较低。南海北部的碎屑物质主要来自中国华南地区,沉积物中元素比值的变化表明间冰期时(MIS5)华南地区陆壳化学风化增强,说明该时期华南陆地气候环境温暖湿润,这可能是间冰期时东亚夏季风加强的结果;而冰期时南海北部沉积物源区化学风化减弱,则与此时东亚冬季风较强,华南地区气候干燥寒冷相关。同时,与表层海水生产力相关的Ba/Ti比值在间冰期较高而冰期较低,反映出南海北部在间冰期时表层生产力较高而冰期时相对较低,这可能是由于东亚夏季风增强带来更多降雨,陆地化学风化作用加强,大量营养成分随河流进入南海,导致南海北部表层海水生产力增加。  相似文献   

12.
Quantitative analyses of planktic foraminifera, sea‐surface temperatures (SSTs), oxygen isotope and radiocarbon dating from a deep‐sea core recovered in the South Adriatic Sea have been used to reconstruct a subcentennial climatic and biochronological record since the late glacial (the last 24 cal. ka BP). The identification and relative abundance of 25 species of planktic foraminifera along the core have provided a continuous record of the faunal changes over this time interval. These results have permitted the establishment of 10 biozones in the South Adriatic Sea based on the appearance and/or disappearance of the main specific taxa, from peaks of abundance and/or by modification in marine conditions. The robust chronology of the South Adriatic core allowed correlation of SST estimates to the GISP2 ice core record, indicating that the main climate changes recorded in Greenland ice cores over the last 24 ka are recorded and globally synchronous with those observed in the South Adriatic Sea. This finding further allows comparison of the planktic foraminifera record with the event stratigraphic scheme proposed by the INTIMATE group in order to better identify the relationship between past climatic changes and the response of microfaunal assemblages in the South Adriatic. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

13.
Significant changes in moisture have occurred in the subtropical Andes over the last 20,000 years as evidenced by shorelines of high lake stands and extensive glacial moraines. Lakes with sediment records that reflect these moisture changes are present in some valleys where headwalls are below the snowline elevation reached during the latest Pleistocene glacial culmination (14,000–12,000 BP). One such lake, Laguna Kollpa Kkota, which is located on the western slope of the eastern cordillera in Bolivia, has basal radiocarbon dates of about 20,000 BP. The snowline reconstruction for this site confirms earlier work in the region that suggests late Pleistocene snowline depression was less than 500 m, or half the amount generally considered for low-latitude regions during the last glacial maximum. The sediment stratigraphy from Laguna Kollpa Kkota indicates that sediment accumulation and organic carbon deposition increased significantly from 14,000 to 12,600 BP. This increase in sedimentation may have resulted from greater inwash to the lake and higher productivity In the lake itself as a result of higher lake levels. These changes could reflect the postulated late Pleistocene increase in precipitation that led to the formation of Lago Tauca on the Altiplano and to glacial advances in the surrounding cordillera.  相似文献   

14.
王汝建 Abelm.  A 《地球科学》2000,25(6):553-556
试图通过南海更新世以来3个柱状样中Botryocyrtis scutum (放射虫) 的研究, 探讨其地层和古海洋学意义. 根据南海更新世以来3个柱状样中Botryocyrtis scutum的丰度变化与氧同位素记录的对比研究发现, 氧同位素18期以来Botryocyrtis scutum丰度变化与氧同位素记录有较好的对应关系, 其丰度变化随冰期与间冰期旋回而波动.冰期丰度降低, 间冰期丰度增加.其丰度变化基本上与氧同位素记录一样, 反映了冰期与间冰期旋回, 并且可以作为地层划分和对比的工具.   相似文献   

15.
南海深水区晚更新世以来沉积速率、沉积通量与物质组成   总被引：6，自引：2，他引：6  
通过调查所获得柱样沉积物氧碳同位素测年资料及多学科综合分析表明,晚更新世以来南海沉积速率和沉积通量具有以下几个特征 :(1)总体上为间冰期沉积速率低、冰期沉积速率高,冰期沉积速率是间冰期沉积速率的 1.3～ 1.6倍;(2 )南海沉积速率趋势面分析表明,氧同位素 1期东北陆坡和西南陆坡沉积速率高,氧同位素 2、3期沉积速率分布特征相似,与 1期有所不同,东北陆坡沉积速率高于西南陆坡,表明氧同位素 2期之后,南海的沉积环境发生明显的改变,造成上述沉积速率分布的主要控制因素是南海周围的河流分布、季风、海流等;(3)南海东部沉积通量与物质组成分析表明,末次冰期以来沉积总通量北部陆坡区明显高于深海区,前者是后者 2～ 3倍,并有自北向南逐渐降低的趋势;(4)硅质生物沉积通量冰期明显高于间冰期,末次冰期以来东北部陆坡区的硅质生物沉积通量最高,末次冰期之前恰好相反,深海盆高于陆坡区;(5 )末次冰期以来,陆源沉积约占南海东部海域沉积的 4 4 %以上。  相似文献   

16.
Based on a revised chronostratigraphy, and compilation of borehole data from the Barents Sea continental margin, a coherent glaciation model is proposed for the Barents Sea ice sheet over the past 3.5 million years (Ma). Three phases of ice growth are suggested: (1) The initial build-up phase, covering mountainous regions and reaching the coastline/shelf edge in the northern Barents Sea during short-term glacial intensification, is concomitant with the onset of the Northern Hemisphere Glaciation (3.6–2.4 Ma). (2) A transitional growth phase (2.4–1.0 Ma), during which the ice sheet expanded towards the southern Barents Sea and reached the northwestern Kara Sea. This is inferred from step-wise decrease of Siberian river-supplied smectite-rich sediments, likely caused by ice sheet blockade and possibly reduced sea ice formation in the Kara Sea as well as glacigenic wedge growth along the northwestern Barents Sea margin hampering entrainment and transport of sea ice sediments to the Arctic–Atlantic gateway. (3) Finally, large-scale glaciation in the Barents Sea occurred after 1 Ma with repeated advances to the shelf edge. The timing is inferred from ice grounding on the Yermak Plateau at about 0.95 Ma, and higher frequencies of gravity-driven mass movements along the western Barents Sea margin associated with expansive glacial growth.  相似文献   

17.
The retreat of the Barents Sea Ice Sheet on the western Svalbard margin   总被引：1，自引：0，他引：1  
The deglaciation of the continental shelf to the west of Spitsbergen and the main fjord, Isfjorden. is discussed based on sub-bottom seismic records and scdirncnt cores. The sea lloor on the shelf to the west of Isfjorden is underlain by less than 2 m of glaciomarine sediments over a firm diamicton interpreted as till. In central Isfjordcn up to 10 m of deglaciation sediments were recorded, whereas in cores from the innermost tributary, Billefjorden, less than a meter of ice proximal sediments was recognized between the till and the 'normal' Holocene marine sediments. We conclude that the Barents Sea Ice Sheet terminated along the shelf break during the Late Weichselian glacial maximum. Radiocarbon dates from thc glaciomarine sediments above the till indicate a stepwise deglaciation. Apparently the ice front rctrcatcd from the outermost shelf around 14. 8 ka A dramatic increase in the flux of line-grained glaciomarine sediments around 13 ka is assumed to reflect increased melting and/or current activity due to a climatic warming. This second stage of deglaciation was intcrruptcd by a glacial readvance culminating on the mid-shelf area shortly after 12.4 ka. The glacial readvance, which is correlated with a simultaneous readvance of the Fennoscundian ice sheet along the western coast of Norway, is attributed to the so-called 'Older Dryas' cooling event in the North Atlantic region. Following this glacial readvance the outer part of Isljorden became rapidly deglaciated around 12.3 ka. During the Younger Dryas the inner fjord branches were occupied by large outlet glaciers and possibly the ice liont terminated far out in the main fjord. The remnants of the Harcnts Sea Ice Shcet melted quickly away as a response to the Holocene warming around 10 ka.  相似文献   

18.
通过对南海西部上升流区MD05-2899孔开展高分辨率碳酸盐地层学和XRF岩芯扫描元素地球化学分析,重建了晚第四纪54万来以来东亚夏季风的演化历史,探讨海平面升降对南海西部陆源碎屑供应量的影响。研究选用了ln(Ba/Al)作为该海区古生产力的指标,ln(Br/Al)作为有机物的指标,ln(Ti/Al)作为陆源碎屑供应量的指标。研究结果显示,东亚夏季风在过去54万年以来强度不断增强,具有明显的冰期—间冰期旋回特征,在间冰期强盛和冰期减弱,是控制该海区有机物含量变化的主要因素。东亚夏季风不断强盛可能直接导致了南海周边陆地降雨增强,河流径流量加大,使得南海西部上升流区域的陆源碎屑供应量在间冰期明显高于冰期。研究发现,当相对海平面低于-60 m的时候,大面积暴露的巽他陆架可能向南海西部深水区输入大量陆源碎屑物质,造成研究站位的陆源碎屑供应量在冰盛期出现高值。因此,晚第四纪的东亚夏季风演化和海平面升降共同控制了南海西部上升流区陆源碎屑物质供应量的变化。  相似文献   

19.
南海北部中更新世晚期以来古海岸变迁及其地质意义   总被引：2，自引：0，他引：2  
本文在研究南海北部陆架区ZQ2和ZQ4钻孔资料的基础上，对该区单道地震资料进行地震层序划分、地震-沉积相解释分析。根据钻孔地层、地震反射和海底地貌特征，对中更新世晚期、末次盛冰期以及冰后期这三个时期的古海岸位置进行了分析，并探讨了该区中更新世晚期以来的古海岸变迁，对进一步指导该区的第四纪环境研究具有重大意义。  相似文献   

20.
Using extensive data sets from three separate areas in the German North Sea sector, consisting of seismic grids, cores and in‐situ cone penetration tests (CPT), we have established a revised stratigraphical framework for the mid to late Quaternary deposits of the German North Sea sector. This framework consists of four regional unconformities and 15 other local unconformities derived from seismic profiles. Using these unconformities, along with lithological and geotechnical data, it was possible to define and correlate 14 major units and 21 subunits within the framework. The Quaternary cover in the area is characterized by a variety of environmental settings ranging from glacial terrestrial and fluvial to lacustrine as well as brackish and marine environments with associated erosion, reworking and deposition. The complexity of Quaternary deposits within the area is explained by its history of repeated ice advances interrupted by marine transgressions and exposed periglacial landscapes. Within the framework, eight buried tunnel valleys and two shallow buried river valleys are identified from seismic profiles with four phases of tunnel valley generation inferred. These phases of tunnel valley generation are associated with the Elsterian (three) and Saalian (one) glacial stages. Infill of these tunnel valleys consists of glaciofluvial sands, thick sequences of marine and lacustrine fine‐grained sediments and some reworked till remnants. Elsewhere, extensive tabular units have formed consisting of marine and fluvial sediments. We compare this new stratigraphy with previous stratigraphies for the German North Sea sector, attribute informal stratigraphical names and offer preliminary correlations with established stratigraphies from other sectors of the North Sea.  相似文献   

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