It has become clear that glacial records vary in time and extent across the Mediterranean, and it is not possible to compare glacial sequences over large areas without robust dating frames. In addition to differences in glacial expanses between glacial cycles, there is also evidence of complexity within ice ages, and this has been demonstrated for the late Pleistocene. In many regions, maximum glacier extent occurred at the end of the Pleistocene at the beginning of the last glacial cycle, before the Last Global Glacial Maximum (gLGM). Sometimes it was only a few thousand years ago (e.g. Greece, Italy), while sometimes it was tens of thousands of years earlier (Spain, Morocco). However, in most regions, the gLGM was not much smaller than the earlier larger glacial maximum, and in some places an earlier maximum is missing or difficult to see, particularly in Turkey (Akçar et al., 2017) and parts of Spain where it is evident but not dated or well preserved (Gómez-Ortiz et al., 2012). Extensive glaciations were unusual events in Earth`s history. There is rare evidence of glaciation during the long Archaic era, and only two significant episodes, the Huronian and the Cryogenics, at the beginning and the Cryogenics, respectively. End of the Proterozoic. The last 750 Ma of Earth`s history saw an increase in the frequency of glaciations, which included cryogenics, the Ediacaran and two large phanerozoic ice ages and several smaller ones (Fig. 2.1).
As for the great glaciations, surviving records suggest that there was one in the first three billion years and at least four in the last 750 million years. Simulations show that paleogeography, CO2 content and orbital forcing all contribute to Gondwana`s glaciation. Net radiative forcing is the predominant factor in initiating glaciation or deglaciation after glacial maximum; However, continental geography plays an even more important role than net radiative forcing in some special continental configurations. Meanwhile, the Milankovitch cycle probably causes an abrupt change in a certain level of CO2 and a continental geography like that of the Precambrian. The early glaciation of the Alps is still poorly understood. Part of the original deposits of the Günz glaciers of Penck and Brückner (1901/1909) are known to be magnetized upside down. They must therefore be dated to Matuyama Chron (i.e. before 0.78 Ma). The first ice ages were also reported in the French, Italian and Swiss parts of the range. However, in many cases, such as the Northern Alps-Danube deposits and the Beaver Stadium, much of the evidence is based on sediments of indirect glacial origin, and the number and extent of early alpine glaciations remains unknown.
Figure 3.3. Marine oxygen isotope stratigraphy from the global stack of 57 sediment cores from Lisiecki and Raymo (2005). The dotted line represents the moving average of 50 ka δ18O in the. The increasing trends towards 100 ka cycles across the Pleistocene are illustrated by larger amplitudes in the 50 ka moving average of δ18O values. The black vertical line in bold marks the phase change from the 100 ka amortized cycles to the 100 ka higher amplitude cycles from MIS 16. The last glacial cycle represents one of the largest and heaviest ice ages of the last million years. Glaciation, like volcanism, can cause rapid changes in the landscape over a period of hundreds to thousands of years. Glaciation is an extreme form of climate change.
We are referring here to areas that have been glacial. Climate change certainly has not affected glacial areas, but in the absence of tectonic stress, volcanism, glaciation, or changes in rock type or structural shape, climate change alone is unlikely to be strong enough to reincarnate the landscape. Non-glacial climate change is more likely to accelerate, slow down or rejuvenate the aging process. Examples of landscape reincarnation due to glaciation exist in the north-central United States, where continental glaciers, discussed in Chapter 12, flattened and buried pre-existing landscapes, completely altering the pre-existing drainage pattern. Erosion and glacial deposition have altered the mountainous areas of the Cordilleras, as well as the mountainous regions of New England and the Adirondacks. Numerous geological studies have revealed the three brief global cooling events in the Cretaceous, i.e. the Campanium-Maastricht boundary, the Middle Maastricht and the end of the Maastrichtian. The data indicated a possible complete glaciation of Antarctica. The simulation results support the idea of glaciation in this period of supergreenhouse conditions. About half the actual size of the modern Antarctic ice sheet has been reconstructed, corresponding to a change in sea level of 20 to 40 m, which is in good agreement with recent isotope discoveries. The end of the Sasaal Ice Age in northern Bohemia, the Rasnitz Ice Age, reached only the northernmost parts of the Frýdlant region.
It has certainly been detected near the villages of Horní Rasnice and Háj. At Háj, the chests of the Elster glaciotectonic were glaciotectonically deformed by the end of the Saale Ice Age and pushed onto the first glaciofluvian deposits. Although glaciations probably occurred in all major glacial cycles, direct evidence recorded by glacial landforms such as moraines is directly related to the decrease in size of successive glaciations. In other words, if the glaciation of the last glacial cycle (late Pleistocene) was the most extensive, then evidence of earlier glaciations will have been removed, or at least transformed, revised or buried under the deposits of later glacial advances. Nevertheless, even in these situations, glacier records are subject to fragmentation (Hughes and Gibbard, 2018), and in many regions that experienced extensive glaciation from the Late Pleistocene, it is the legacy of these ice ages that has shaped contemporary landscapes. This is particularly the case in the Iberian Peninsula, where Late Pleistocene glaciations were often almost as extensive or more extensive than previous ice ages (e.g. Cowton et al., 2009). This contrasts with other regions such as the Balkans, where glaciation in the Middle Pleistocene was much larger than glaciation in the Late Pleistocene (e.g., Hughes et al., 2006b, 2010, 2011). Recent studies have shown that the Permocarboniferous is characterized by three overlapping glacial episodes with ice-free gaps. The results of the simulation, based on the energy balance model with a simple empirical diagram of ice sheets, are presented to explain such hysteresis of glaciations. Gondwana reached its glacial maximum when the CO2 content was roughly equal to or slightly above the pre-industrial value.
While the CO2 content was three to four times higher than the pre-industrial value, glaciation was only distributed along the coasts of Gondwana. With a further increase in CO2, defrosting dominates and leads to an ice-free state. If CO2 fell to current levels, Gondwana would be glaciated again and begin a new cycle of glaciation and deglaciation. Changes in CO2 content provided an example of SICI and LICI on Gondwana in the Permocarboniferous. The simulation is consistent well with the latest geological discoveries. The glacial reliefs in the Mediterranean mountains are best preserved for the last glacial cycle (MIS 5d-2), but it is clear that the current landscape of the Iberian Peninsula and wider Mediterranean mountains is the product of several glacial episodes. This is certainly true for the last 700 ka since the Middle Pleistocene transition, when large glaciers were able to form in all major Mediterranean mountains in all glacial cycles. This is especially true for the mountains of the Iberian Peninsula, which today with Karen just below the glaciation threshold are only marginal to glaciation, especially in the Sierra Nevada, the Picos de Europa and the Pyrenees, which recently and still today contain ice sheets or small glaciers (Serrano et al., 2018).
In this context, the mountains of the Iberian Peninsula and the wider Mediterranean would be glacial longer than in the last hundred thousand years. This is important to understand when considering the glacial landscapes of the region. The glaciations of the Phanerozoic era were less extreme, did not reach the equator, and were not associated with postglacial carbonates. This apparently more balanced climate could be related to the formation of the metazoan biosphere in the late Proterozoic and early Phanerozoic and their influence on global geochemical cycles. Three main glaciations took place (Fig. 1(b)): a „Lower Paleozoic cooler“ of the late Ordovician and early Silurian (ca. 455 Ma–425 Ma, with an endordovician glacial maximum [47.48]); a long-lasting permocarboniferous glaciation (about 325 Ma–270 Ma [49]), with ice covering much of the Gondwana paleocontinent (with traces widespread in South America and Africa, then over the South Pole); and the current glaciation, which began in the Southern Hemisphere through the Eocene-Oligocene epoch boundary interval (about 34 Ma) with ice growing over Antarctica [50] and developing into a full-fledged bipolar glaciation towards the end of the Pliocene and the beginning of the Quaternary at about 2.6 Ma, with the significant expansion of ice in the Northern Hemisphere [51]. Glaciation in Australasia, with the exception of a few high volcanoes in Papua and Indonesia, occurred in Tasmania and New Zealand (see Eustatic changes in sea level since the Last Glacial Maximum) (Table 3). The first records on both islands date back to the Plio-Pleistocene (2.6 Ma: MIS 98-104), although it may be older in Tasmania. Barely younger is the oldest known glacial event in New Zealand (the Porika glaciation).
This is followed by a 1 My pause before the glacier recording continues in MIS 12, followed by MIS 6, 4 and 3.
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