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91.
Eric A. Colhoun 《The Australian geographer》1993,24(1):3-11
Observational studies on Cainozoic environmental changes in both Tasmania and East Antarctica have led to important modifications in the accepted interpretation of the history of glaciation for each area. Many contributors have played an important role in the processes of investigation leading to the present state of knowledge. A crucial role has been played by the integration of the methods of glacial geomorphology, stratigraphy, sedimentology and dating methods. From studies based on combinations of these approaches, a model of multiple glaciations has been developed to explain observed features in Tasmania. This model is complemented by studies of vegetation history, largely through pollen analysis. A less complete picture of the history of ice‐sheet fluctuations in East Antarctica is beginning to emerge from similar applications of cross‐disciplinary studies. 相似文献
92.
Randy W. Dirszowsky William C. Mahaney Kyle R. Hodder Michael W. Milner Volli Kalm Maximiliano Bezada Roelf P. Beukens 《Journal of South American Earth Sciences》2005,19(4):525-536
At Pedregal, more than 40 m of sediments are exposed within a ‘fan complex’ formed between lateral moraines of the adjacent Mucuchache and El Caballo valleys. Early and late Mérida (Wisconsinan) glaciations are represented by till and till plus proglacial sediments, respectively. A middle Wisconsinan interstadial event, here termed the Pedregal interstade, began at the end of the Early Mérida glaciation at approximately 60 ka BP. Following the retreat of ice from the small Pedregal Basin, a lake formed when the local drainage was blocked due to movement of the Mesa de Caballo along the Boconó Fault. Shallow lake or no-lake phases lasted approximately a few hundred to, at most, 2000 years, and each lake phase was marked by peat accumulation. Four of seven peats identified formed during sufficiently long intervals for soil profiles (incipient to mature Spodosols) also to develop. The Spodosol with the strongest development (Eb/Bsb/Coxb/Cub horizons) is found adjacent to the lowest peat and reflects ongoing early Mérida stadial (MIS 3) conditions; the youngest peats, associated with weak podzolic soils (Eb/Bsb horizons), formed under slightly warmer interstadial conditions, presumably with less soil water. Cyclic lacustrine deposition is related to lake level and relative depth fluctuations, due in part to variable shoreline/delta progradation and shallowing as the lake deepened in general. Whereas final drainage of the lake is related to movement of the Boconó Fault and breach of the moraines that form the Mesa de Caballo, earlier lake level fluctuations appear related to climate change. Radiocarbon dating of the peats suggests they are related to warmer periods and may tentatively correlate with small ‘interstadials’ or ‘D-O events’ detected in the oxygen-isotope record of Greenland ice cores and North Atlantic marine sediments. 相似文献
93.
Ian S. Evans 《Geografiska Annaler: Series A, Physical Geography》2006,88(2):115-133
Mass balance of glaciers in mountain areas varies not only with altitude and regional position but also with aspect, gradient, glacier size, glacier type and detailed topographic position. These factors are combined here in models of how glacier altitude varies, tested with data for the Alps edited from the World Glacier Inventory. An overall northward tendency in glacier numbers (toward 005 ± 4°) and lower altitudes (013 ± 5°) is maintained across a range of glacier sizes, types, altitudes and the major divisions of the Alps. Variation with aspect of glacier altitude (and, by implication, of glacier balance) in the Alps is essentially unimodal, and north‐facing glaciers average 220 m lower in middle altitude than south‐facing: 148 m in the Western Alps, 232 m in the West‐central, 252 m in the East‐central, and 268 m in the Eastern Alps. For smaller subdivisions, confidence intervals on estimates are broader and many differences lack statistical significance. Contrasts are greater in the higher massifs, with greater relief, and lower in cloudy, windward areas. There are small windrelated tendencies east of north along the northern and western fringes, but trends across space are weak: position is thus treated by subdivision into districts and groups. Mid‐altitude averages 2891 m overall and varies from 2552 to 3127 m for 27 glacier districts, and from 2124 to 3209 m for 103 glacier groups. Glacier mid‐altitude varies also with glacier form, nourishment, height range and area, which account for over two‐thirds of variance in combined models. 相似文献
94.
STEPHAN HARRISON E. ANDERSON D. PATEL 《Geografiska Annaler: Series A, Physical Geography》2006,88(3):199-207
ABSTRACT. Geomorphological and sedimentological evidence of former glaciation in the Bizzle valley in the Cheviot Hills of northern England and southern Scotland was used to reconstruct the dimensions of a small topographically constrained glacier with an equilibrium line altitude (ELA) of 535 m. This was interpreted as having formed during Younger Dryas cooling; this is the only glacier to have been described from the area and is the most easterly site of Younger Dryas glaciation in the British Isles. Whilst glaciation at this time was extensive in the Lake District to the southwest, the restricted nature of Cheviot ice cover suggests that a steep west–east precipitation gradient existed in this region during the Younger Dryas. 相似文献
95.
It is generally considered that four-times ice age happened during the Quaternary epoch on the Tibetan Plateau. However, the
research on the chronology of the four-times ice age is far from enough. The Shaluli Mountain on the Southeastern Tibetan
Plateau is an ideal place for plaeo-glacier study, because there are abundant Quaternary glacial remains there. This paper
discusses the ages of the Quaternary glaciations, based on the exposure dating of roche moutonnée, moraines and glacial erosion
surfaces using in situ cosmogenic isotopes 10Be. It is found that the exposure age of the roche moutonnée at Tuershan is 15 ka, corresponding to Stage 2 of the deep-sea
oxygen isotope, suggesting that the roche moutonnée at Tuershan is formed in the last glacial maximum. The exposure age of
glacial erosion surface at Laolinkou is 130–160 ka, corresponding to Stage 6 of the deep-sea oxygen isotope. The oldest end
moraine at Kuzhaori may form at 421–766 kaBP, corresponding to Stages 12–18 of the deep-sea oxygen isotope. In accordance
with the climate characteristic of stages 12, 14, 16 and 18 reflected by the deep-sea oxygen isotope, polar ice cores and
loess sequence, the oldest end moraine at Kuzhaori may form at stage 12 or stage 16, the latter is more possible. 相似文献
96.
第四纪中期青藏高原冰冻圈的演化及其与全球变化的联系 总被引:56,自引:13,他引:43
文章给出了冰冻圈的含义与组成,新生代42Ma前南极冰盖出现至中更新世,是地球上冰冰圈发展的漫长过程,青藏高原在早更新世只在个别高峰有冰川作用,直到1.1~0.6MaBP的昆(仑)黄(河)运动,将高原面抬升至3500m左右高度的降温作用和同时期地球接受日射的轨道转型*(由4.1万年周期的轨道倾斜率过渡为10万年周期的轨道偏心率控制)及相伴的降温作用相耦合。形成了测年数据在0.6~0.8MaBP间的倒 相似文献
97.
北美东部威斯康星中、晚期古环境与气候变化的甲虫化石证据 总被引:1,自引:0,他引:1
北美Laurentide冰盖于末次冰期的大部分时间在北美东北部一直存在,冰盖的活动对北美东部冰期时的环境和气候有很大的影响。甲虫分析表明,北美东部中纬度地区在威斯康星中、晚期的气候以寒冷为主,中间分别在42000aB.P.,34000aB.P.和28000aB.P.出现3次明显的气候变暖。此区威斯康星中期气候冷暖波动的幅度和出现的时间可以与同期的格陵兰冰芯记录及北大西洋Heinrich事件对比。 相似文献
98.
西伯利亚含盐地位于西伯利亚地台。含钾盐系属下寒武统安加拉组,岩盐层总厚600余米,钾盐层厚70-150m,共有钾石盐岩和钾石盐-光卤石岩6层。钾石盐层中KCl含量达35%-45%,MgCl2和水下溶物含量均小于1%,含盐盆地四周以堡礁带和陆岛与广海相隔,含钾坳陷处于地台上坳陷最深部位。 相似文献
99.
庐山东南麓冰川作用表皮构造特征及其意义 总被引:4,自引:1,他引:4
庐山东南麓第六阶地基座上,发现了早更新世冰川作用表皮构造。按其形态与成因可分为巨砾压入基岩、小型倒转构造与不协调褶皱、逆冲-贯入构造、大型片麻岩包裹体等四种类型。早更新世初期之庐山,确实多次发生过山麓冰川作用。 相似文献
100.
Warren D Sharp Kenneth R LudwigOliver A Chadwick Ronald AmundsonLaura L Glaser 《Quaternary Research》2003,59(2):139-150
Reliable and precise ages of Quaternary pedogenic carbonate can be obtained with 230Th/U dating by thermal ionization mass spectrometry applied to carefully selected milligram-size samples. Datable carbonate can form within a few thousand years of surface stabilization allowing ages of Quaternary deposits and surfaces to be closely estimated. Pedogenic carbonate clast-rinds from gravels of glacio-fluvial terraces in the Wind River Basin have median concentrations of 14 ppm U and 0.07 ppm 232Th, with median (230Th/232Th) = 270, making them well suited for 230Th/U dating. Horizons as thin as 0.5 mm were sampled from polished slabs to reduce averaging of long (≥105 yr), and sometimes visibly discontinuous, depositional histories. Dense, translucent samples with finite 230Th/U ages preserve within-rind stratigraphic order in all cases. Ages for terraces WR4 (167,000 ± 6,400 yr) and WR2 (55,000 ± 8600 yr) indicate a mean incision rate of 0.26 ± 0.05 m per thousand years for the Wind River over the past glacial cycle, slower than inferred from cosmogenic-nuclide dating. Terrace WR3, which formed penecontemporaneously with the final maximum glacial advance of the penultimate Rocky Mountain (Bull Lake) glaciation, has an age of 150,000 ± 8300 yr indicating that it is broadly synchronous with the penultimate global ice volume maximum. 相似文献