Geomorphological evidence from the Lleyn Peninsula constraining models of the magnitude and rate of isostatic rebound during deglaciation of the Irish Sea Basin     

Danny McCarroll 《Geological Journal》1995,30(2):157-163

A stepped series of sand and gravel terraces on the Lleyn peninsula of North Wales is used to test the magnitude and rate of isostatic depression required by the recently proposed glacimarine model of deglaciation of the Irish Sea Basin. A relative sea-level fall of 70 m is required while the ice remained pinned at the north Lleyn coast. Even taking the maximum known rate of isostatic uplift, the margin would have to remain stationary for 1400 years. It seems more reasonable to interpret the Lleyn terraces, and similar features around the Irish Sea Basin, as glacifluvial and glacilacustrine.  相似文献   

末次冰盛期以来日本海浮游植物生产力和群落结构变化   总被引：2，自引：0，他引：2  

赵美训  张荣平  邢磊  张海龙  刘焱光 《中国海洋大学学报(自然科学版)》2009,39(5)

生物标志物法已经被广泛应用于重建海洋浮游植物生产力和群落结构变化。本文利用这种方法重建了日本海末次冰盛期以来浮游植物生产力和群落结构变化。结果显示,生物标志物含量在末次冰期最盛期21～19 ka和14～4 ka时有高值,而在19～14 ka、4～0 ka有低值。末次冰期最盛期时生物标志物的高含量是由于分层导致的底层水缺氧,生物标志物得到较好保存的结果,而此时日本海盐度很低,使颗石藻相对含量很低;19～14 ka陆源输入减少,日本海生产力水平较低,不断增加的盐度使浮游植物群落结构由硅藻、甲藻占优转变为颗石藻占优;14～4 ka对马暖流流量的加大提高了日本海的初级生产力,同时高营养盐利于硅藻、甲藻的生长,使颗石藻的相对比例减小;4 ka以后随冬季风的增强和黑潮减弱,对马暖流减弱,供应的营养盐减少,日本海生产力水平降低,使颗石藻的相对比例增大,硅藻、甲藻的相对比例减小。  相似文献   

Middle Wisconsinan marine shells near Repulse Bay,Nunavut, Canada: implications for Marine Isotope Stage 3 ice‐free conditions and Laurentide Ice Sheet dynamics in north‐west Hudson Bay     

Isabelle McMartin  Janet E. Campbell  Lynda A. Dredge 《第四纪科学杂志》2019,34(1):64-75

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Last glaciation and maximum glaciation in the Qinghai-Xizang (Tibet) Plateau: A controversy to M. Kuhle’s ice sheet hypothesis     

Yafeng Shi  Benxing Zheng  Shijie Li 《中国地理科学(英文版)》1992,2(4):293-311

Since the late 1950’s, many Chinese scientists have explored the remains of the Quaternary glaciation in the Qinghai-Xizang (Tibet) Plateau and its surrounding mountains. In the main, 3–4 glaciations have been recognized. The largest one occurred in the Late Middle Pleistocene with piedmont glaciers, ice caps and trellis valley glaciers in many high peak regions. But here is no evidence of a unified ice sheet covering the whole plateau as described by M. Kuhle. Due to the further uplifting of the Himalayas and Qinghai-Xizang Plateau the climate became progressively driver, diminishing the extension of glaciers during the Late Pleistocene. The elevation of the snow line during the Last Glaciation was about 4,000 m on the south, east and northeast edges of the plateau and ascended to 5500 m on the hinder northwest of the plateau. The thermal effect of the big plateau massif, the sharp increase of aridity from the southeast rim to the northwest inland area and the abrupt decrease of precipitation during the Ice Age largely account for the distribution of the Quaternary glaciers in the Qinghai-Xizang Plateau. The neglect of Chinese literature may be one of the causes accounting for M. Kuhle’s misinterpretation on the environment of the Quaternary glaciations in the Qinghai-Xizang Plateau.  相似文献   

宜阳罗圈组的发育特征和成因探讨     

汪明洲  杨铁汾 《地球科学与环境学报》1996,(2)

本文根据河南宜阳罗圈组发育特征和分布规律，结合华北地台西南缘罗圈组发育和分布概况，论述了其成因和成因类型，提出了罗圈组时代的归属，认为罗圈组应是大陆高原冰川活动产物。其时代应属早震旦世晚期，大体相当于南沱组。  相似文献   

The last glaciation of Germania Land and adjacent areas,northeast Greenland     

Jon Y. Landvik 《第四纪科学杂志》1994,9(1):81-92

A profile across the unglaciated coast of northeast Greenland at 77°N was studied with regard to the Quaternary stratigraphy and glacial history. The Germania Land peninsula is characterised by till-covered lower ground which contrasts sharply with the blockfields and extensive gelifluction deposits of its higher altitudes. Two glaciations are distinguished. The older one extended over the entire area and had its margin on the continental shelf. The younger one, of Late Weichselian age, reached the present coastline and several mountains and high plateaus on western Germania Land formed nunataks. The Late Weichselian glaciation was more extensive and occurred later on the Germania Land peninsula than on the coast further south. Radiocarbon dates suggest that the glacier margin rested to the east of the present coastline until ca. 10 000 yr BP. This correlates with the Late Weichselian Milne Land Stage, which is found as a late glacial readvance along the coast of East Greenland. A series of recessional moraines formed during the deglaciation were probably caused by glacier dynamics, as opposed to being of climatic origin.  相似文献   

网纹红土的成因及其研究意义   总被引：26，自引：0，他引：26  

朱景郊 《地理研究》1988,7(4):12-20

本文阐述我国网纹红土的分布和特征,着重讨论网纹红土的形成原因,指出网纹红土可表征我国南方中更新世以来新构造运动的幅度和性质,并可作为我国东部是否存在古冰川作用的佐证.  相似文献   

Quaternary glaciation of the Bale Mountains,Ethiopia     

Henry A. Osmaston  Wishart A. Mitchell  J. A. Nigel Osmaston 《第四纪科学杂志》2005,20(6):593-606

Central Ethiopia comprises a high plateau at 2000–3000 m, formed from Tertiary lava flows and bisected by the Eastern African Rift. Ten volcanic mountains rise to altitudes of just over 4000 m, but on only three has Quaternary glaciation been substantiated by published field observations. On the Bale Mountains (4400 m), a previous report based on limited evidence proposed an ice‐cap extending to 600 km². Based on aerial photographs and ground surveys, this paper reports evidence of a more complex situation. A wide spread of large erratic boulders on the plateau records a central ice cap of 30 km², though ice probably extended for a further 40 km². Further north two groups of deeply incised and clearly glaciated valleys contain moraines and roches moutonnées (60 km²). On interfluves between them and on the open north slopes are moraines from an earlier stage of the same glaciation or from a distinct older event. Altogether about 180 km² may have been glaciated. Cores dated by ¹⁴C from inside and outside the glaciated area suggest that at least the northern valley glaciers may date from the Last Glacial Maximum. Estimated equilibrium line altitudes for these glaciers and the ice‐cap are 3750–4230 m. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Geomorphological and Pedological Investigations on the Glacial History of the Kali Gandaki (Nepal Himalaya)     

Markus Wagner 《GeoJournal》2005,62(3-4):91-113

In semi-arid orographic left tributaries of the Kali Gandaki at the northern and western flank of the Nilgiri Himal, glacio-geomorphological and pedological investigations were carried out on prehistoric moraines. Geomorphological relief analysis was derived from other literature and the own fieldwork of the author. The resulting glacial chronology was used as benchmark to explore the limits of different pedological dating methods regarding the degree of soil development. These methods are based on iron fractionation, total element contents and particle size distribution. In general the different glacial stages are mirrored correctly in the relative graduation of soil development. The ratio of well crystallised pedogenic iron-oxides to the total iron content and the ratio fine clay to total clay are most suitable, because they are almost independent from existing changes in the lithological composition. The total element based weathering indices are less suitable, because they react highly sensitive to the geology dependent shift to higher carbonate contents. Most of the grain size based weathering indices are inapplicable because of the typically high textural variability within till deposits.  相似文献   

Pleistocene glacial relief of the central part of Mt. Prokletije (Albanian Alps)     

Milovan Milivojevi&#x;  Ljubomir Menkovi&#x;  Jelena &#x;ali&#x; 《Quaternary International》2008,190(1):112

The central and highest area of Mt. Prokletije (Albanian Alps) is situated in northern Albania and eastern Montenegro (at 42°30′N). The highest peak is Maja e Jezerces (2694 m). Detailed geomorphological mapping was used to reconstruct the positions of former glaciers. The longest Ropojana glacier had a length of 12.5 km and surface of 20 km²; others include Valbona Glacier (9.5 km, 10.5 km²), Grbaja Glacier (5 km, 6.7 km²) and Bogićevica Glacier (6 km, 6.9 km²). Three series of moraines can be distinguished: the lowest at an average altitude of 990 m (average ELA 1750 m), the middle series at 1350 m (ELA 1942 m), and the highest at 1900 m (ELA 2123 m). As no advanced dating methods have yet been used to provide a numerical chronological framework for these features, hypotheses are made based on the comparison with the advanced studies of other similar mountains in the Mediterranean region. The moraines of the first stage (lowest series) correspond to one of pre-LGM glaciations (Middle or even Early Würmian), the second stage moraines probably correspond to LGM, and the third stage could be attributed to Younger Dryas. The mapping included a number of inactive and active rock glaciers, as well as three small active glaciers (surface 5 ha and less), at 1980–2100 m altitude, in the area close to Maja e Jezerces.  相似文献