Extent Of Pleistocene Glaciations Research Articles

Late Quaternary evolution of the sedimentary environment in Modrejce near Most na Soči (Soča Valley, Julian Alps)

Geomorphological and geological mapping have long been used to study the glacial history of the Slovenian Alps, but many uncertainties remain regarding the time and extent of Pleistocene glaciations there. Glacial landforms and undisturbed glacial deposits are rare in the areas of the former glacier terminus, especially in the Soča Valley, where large discrepancies in the interpretation of the extent of the former Soča Glacier have been reported. Early studies proved inconclusive as to whether one or two glaciations extended into the Soča Valley as far as Most na Soči. In order to answer this question, the Quaternary sedimentary succession and landforms in the Modrejce Valley near Most na Soči were investigated. New geological and geomorphological field data allow the interpretation of the sedimentary environment and the stratigraphic relationships between different units. In response to glacial dynamics, the sedimentation developed from glaciofluvial and glaciolacustrine to fully glacial environments, followed by slope deposition. At higher altitudes lateral moraines are preserved, while the staircase-like slope below has been carved into older glacial, glaciofluvial and glaciolacustrine deposits by glacial and post-glacial processes, including fluvial erosion and slope dynamics. We conclude that the succession studied here was deposited over the course of two different glacial advances – LGM and pre-LGM. Our study thus suggests that the Soča Glacier extended as far as the area of Most na Soči twice over the course of the late Quaternary.

Record of glacial outburst floods in marginal zones and forelands of Scandinavian glaciations in Poland

In international literature, much attention has been paid to sedimentological and geomorphological evidence of extreme floods in the forelands of both contemporary and Pleistocene glaciers and ice sheets. Reports on this subject come from areas and periods of different glaciations. In Poland such events have been documented in more than ten works. This situation prompts us to establish whether or not the occurrence of such extreme events was more frequent and widespread in the area of Poland than it has been believed to date. The article reviews the existing research concerning within the extent of Pleistocene glaciations in Poland, which include the occurrence of high energy glacial outburst floods in the interpretation of sediments or landforms. Its objective is to determine the current state of knowledge and to indicate the direction of further research. The review also includes a study of palaeogeographic conditions of the previously documented jökulhlaup in Siedlątków, on the border of the Łask Heights. The analysis of works and the conducted comparisons lead to the conclusion that the state of knowledge about great glacial floods in the Polish Lowland is not satisfactory. It indicates the need to undertake intense studies on the record of such events and their reconstruction as their morphogenetic role e.g. in the formation of ice-marginal valleys and other elements of glacigenic landscape is underrated.

The evolutionary history of sharp- and blunt-snouted lenok (Brachymystax lenok (Pallas, 1773)) and its implications for the paleo-hydrological history of Siberia

BackgroundBroad-scale phylogeographic studies of freshwater organisms provide not only an invaluable framework for understanding the evolutionary history of species, but also a genetic imprint of the paleo-hydrological dynamics stemming from climatic change. Few such studies have been carried out in Siberia, a vast region over which the extent of Pleistocene glaciation is still disputed. Brachymystax lenok is a salmonid fish distributed throughout Siberia, exhibiting two forms hypothesized to have undergone extensive range expansion, genetic exchange, and multiple speciation. A comprehensive phylogeographic investigation should clarify these hypotheses as well as provide insights on Siberia's paleo-hydrological stability.ResultsMolecular-sequence (mtDNA) based phylogenetic and morphological analysis of Brachymystax throughout Siberia support that sharp- and blunt-snouted lenok are independent evolutionary lineages, with the majority of their variation distributed among major river basins. Their evolutionary independence was further supported through the analysis of 11 microsatellite loci in three areas of sympatry, which revealed little to no evidence of introgression. Phylogeographic structure reflects climatic limitations, especially for blunt-snouted lenok above 56° N during one or more glacial maxima. Presumed glacial refugia as well as interbasin exchange were not congruent for the two lineages, perhaps reflecting differing dispersal abilities and response to climatic change. Inferred demographic expansions were dated earlier than the Last Glacial Maximum (LGM). Evidence for repeated trans-basin exchange was especially clear between the Amur and Lena catchments. Divergence of sharp-snouted lenok in the Selenga-Baikal catchment may correspond to the isolation of Lake Baikal in the mid-Pleistocene, while older isolation events are apparent for blunt-snouted lenok in the extreme east and sharp-snouted lenok in the extreme west of their respective distributions.ConclusionSharp- and blunt-snouted lenok have apparently undergone a long, independent, and demographically dynamic evolutionary history in Siberia, supporting their recognition as two good biological species. Considering the timing and extent of expansions and trans-basin dispersal, it is doubtful that these historical dynamics could have been generated without major rearrangements in the paleo-hydrological network, stemming from the formation and melting of large-scale glacial complexes much older than the LGM.

Extent and spatial distribution of Pleistocene glaciations in eastern Tibet

As a contribution to the controversial discussion regarding the nature and extent of the Pleistocene glaciation on the Tibetan Plateau, additional observations and results were obtained during several Chinese-German joint expeditions. In the investigation area of the eastern and central Tibetan Plateau, it will be shown that the maximum extent of the last glaciation was limited to the glaciation of isolated mountain groups or smaller plateau glaciations. These glaciations are characterized by glacial erosional features such as U-shaped valleys in the inner mountain massifs and cirques in the higher summit areas. Accumulation forms, such as terminal and lateral moraines (less common than basal moraines) are marked by granitic and basaltic erratics. Using two examples from the eastern margin of the Tibetan Plateau (Nianbaoyeze Shan and northern Chola Shan), the extent of Pleistocene glaciations can be mapped by the distribution of terminal and lateral moraines and erratic granite boulders on the slopes of the surrounding schists. Two to three main Pleistocene glaciations can be separated using weathering criteria, paleosols, and the overlying stratum on the moraines and associated terrace sequences. Overlying stratum consist of aeolian sandy silt or solifluction debris. The younger moraines are found to be characterized by large erratics, were therefore named “Big-Boulder-Moraine”, and can be found over the investigated area. The ice free areas are characterized by Pleistocene terraces along the main rivers, loess deposits with sand and ice wedges at higher elevations (e.g. the basin of Zoige), and paleosols in the basins below 3500 m a.s.l. (e.g. Aba basin or Garze basin). The hypothesis of an extensive plateau glaciation could not be verified for this region. A rising snowline (equilibrium-line altitudes = ELAs) is revealed in two cross-sections during the Last Glacial Maximum (LGM) at the eastern and northern margin of the Tibetan Plateau. Snowlines migrated from about 4000 m in the east (Minshan), to 4300 m in the Nianbaoyeze, and to about 4700 m in the west (Bayan Har Shan). A rise was also recorded from about 3800 m in the north (central Qilian Shan), up to a range of 4300–4950 m (different exposures) in the Kunlun Shan, to approximately 5200 m in the Tanggula Shan in the center of the Tibetan Plateau. The general increase of modern and LGM snowlines (or ELAs) towards the plateau corresponds with a decrease of precipitation from east to west and from north to south respectively. Precipitation was more pronounced at the eastern margin during glacial times than compared to present.

An outline of physical geography including Pleistocene glacial landforms of Eastern Tibet (provinces Sichuan and Qinghai)

The relief of the expedition area in NW-Sichuan and SE-Qinghai can simply be separated into two main areas: the catchment area of the Yangtze with deeply incised rivers in narrow V-shaped valleys up to about 3,000 m and the plateau area with old peneplains in the Huang He catchment with meandering rivers up to more than 4,000 m. Precipitation and temperature decrease towards the NW. All zonal boundaries, eg the vegetation boundaries or the snowline, are ascending in elevation towards the interior of the plateau. The natural vegetation, especially the forests, are modified by anthropo-zoogenic influences. Within the zone of alpine meadows and the uppermost region of natural forest as well as in the Red Basin evidence of pasture and agriculture goes back by at least 2,000 years. During the last 20 years within the transition zone of the deeply incised valleys towards the plateau one third of the forests have been cut down. The main investigation area of Nianbaoyeze is built up by a granite-dome being about 500 to 800 m higher than the surrounding peneplains. The extent of Pleistocene glaciations can be mapped by the distribution of terminal and lateral moraines and erratic granite boulders on the slopes of the surrounding schists. The altitude of terminal moraines indicates a snowline of the last glaciation at about 4,300 m, which is about 800 m below the present snowline. Three main Pleistocene glaciations can be separated due to palaeosols, the overlying stratum being either aeolian sandy silt or solifluction debris. The ice free areas shows several Pleistocene terraces and in addition loess deposits with palaeosols in the deeper basins. In summary there is a rising of the snowline of the last glaciation at the E margin of the Tibetan Plateau from about 4,000 m in the E (Minshan) to 4,300 m at Nianbaoyeze and to about 4,700 m in the W (Bayan Har Shan). The hypothesis of an extensive plateau glaciation could not be verified for this region.

Quaternary glaciation of tibet: The geological evidence

The question of the number and extent of Pleistocene glaciations on the Qinghai-Xizang (Tibet) Plateau remains contentious. There has been considerable research activity in Tibet by Chinese scientists since the late 1950s and their principal findings, including data on glacial and periglacial geomorphology, sedimentology, tectonics, stratigraphy and lake history, have been used to reconstruct ice margins and palaeosnowlines. Three, and in places, four distinct glaciations have been recognised, the most extensive occurring in the later Middle Pleistocene. Valley and piedmont glacial systems, with some mountain ice caps and a small ice sheet on the upper reaches of the Huang He, have been recognised but there is no evidence of a single Tibetan ice sheet. As the Plateau and the Himalaya-Karakoram underwent accelerating uplift through the Quaternary, there occurred progressive desiccation in the interior as the influx of Indian Ocean moisture was constrained. Equilibrium line elevations in the last glacial maximum were 4000 m in the south, east and northeast Plateau margins, rising to 5500 m in the northwest interior. The heat island provided by the Plateau, the progressive reduction in precipitation most marked during the glacials, and the strong southeast to northwest precipitation gradients, produced a glacier distribution pattern dominated by the trans-Tibetan mountain ranges. Tectonics and periglacial (including aeolian) processes have played an equal role with glaciation in generating the Plateau's Quaternary sedimentary succession.

The impact of the Ice Age on the present form of the geoid

The shape of the geoid in North America and Fennoscandia shows a remarkable correlation with the extent of Pleistocene glaciation in these areas.