engleski

A case study of Dinaric Pleistocene glaciation

Quaternary glaciation GCR Block ✓ Alpine network ✓ Adriatic Dinarides network ✓ Interior Dinarides network Quaternary glaciation GCR Block: Adriatic Dinarides network Early Quaternary was in Dinarides a period of extensive glaciation which lasted for most of Pleistocene, interrupted by warm and arid interglacials. During the glacial periods, valley glaciers descended from the high mountains and reached the modern eastern Adriatic coast and some of islands. The ice dynamics was controlled by orography and variations in supply/ablation ratio- The glaciers seem to have originated from small ice caps, instead of cirques, because the latter were not recognized so far, but instead the high coastal mountains have rather flat strongly karstified summits. However, glacial tongues descended from the ice caps following the inherited alluvial topography. Associated sea-level fall was accompanied by base-level lowering which had caused deep incision of lower reaches of alluvail streams, which eventually were flooded by the Holocene sea-level rise. Pleistocene hydrology provided abundant subglacial waters which were trapped under the ice caps on the high mountains and drained through numerous sinkholes, in adition to subglacial waters which were confined to subglacial tunnels and drained away at the glacier fronts. The subglacial water provided essential running water which reworked the glacial deposits providing glaciofluvial deposits which are locally still preserved. The periods of ice retreat provided additional large amount of meltwater which was ponded in proglacial lakes, some of which were quite extensive. The lakes were still in a direct contact with the calving ice, as indicated by numerous dropstones. The periods of climate deterioration are marked by formation of frozen ground, permafrost, as indicated by ice-wedge casts of various sizes and infill types. Episodes of renewed ice advance exerted high pressure on the underlying sediments, creating small-scale glaciotectonic features such as small thrust faults. During the maximal extent of glaciation, sometime in Middle Pleistocene, valley glaciers have reached the islands of Krk and Pag, providing the debris for construction of the kame-terraces. Abundant melt-waters released during the ice retreat flew in large rivers which meandered over, and reworked the underlying glacial deposits (eg. on the Krk island and in the Novigrad Sea). Deglaciation was not a steady process but was punctuated by several pulses of ice advance which are documented by De Geer moraines in the upper reaches of the Velika Paklenica Canyon. Characteristics of the block Pleistocene glaciation shaped the topography by widening of some valleys, depsition of vast amounts of sediments in some lakes and along the valley walls. A number of ice-diagnostic features can still be recognized, such as: U-shaped valleys, hanging valleys, moutonated rocks, medial moraine ridges, De Geer moraines, remnants of terminal moraines, kame-terraces, proglacial lake sediments with dropstones, drainage-basin missing meandering rivers, glacial outwash plains-sandur, eratic blocks, striated cobbles and boulders, cryoturbation in lacustrine sediments, glaciotectonics, and exotic debris drifts. The relief of the coastal Dinarides is characterized by relativelly flat summits which are commonly heavily pitted by inumerous dolines, steep mountain slopes which are dissected by steep steep-walled canyons, and locally developed closed mountain valleys which strike along the mountain chain. The lower part of the mountain foot is dissected by relativelly short, but deep and steep-walled gorges which are in their lower reaches flooded by the sea. Representative sites The documents of ice dynamics in the Adriatic Dinarides are to be found in several well-defined areas where a number of geological monuments can be identified. The representative areas are: A) Veliko Rujno valley and Velika Paklenica Canyon for the evidence of high-mountain valley glaciers and their dynamics, B) Novigrad Sea for the evidence of low altitude valley glaciers, their dynamics, and proglacial processes and environments, C) Krk Island for the evidence of distal ice wedge dynaimcs, valley glacier depositional bodies, and postglacial modification processes. The characteristics of the Quaternary deposits, their distribution and variability in the eastern Adriatic coastal mountains, along the shore and on the islands document the geological history of the Adriatic Dinarides during the last ca. 1.000.000 years. The ongoing research will undoubtedly provide many new data, and eventually new sites will be identified which will document the geological processes and unvail the course of geological events in the interior part of the Dinaric mountain range. Quaternary Glaciation of Adriatic Dinarides GCR Block ✓ pre-glacial marine network ✓ glacial network ✓ post-glacial network Pre-glacial marine network This network represents Early Pleistocene marine deposits with marine microorganisms which are preserved only in local erosional remnants on the Island of Krk. These sediments were deposited in shoreface setting with strong influence of storm surges and wave-action. Important characteristics of pre-glacial marine network are: * early Pleistocene foraminiferal fauna, which is rarely found onshore * shallow-marine deposits of middle shoreface Glacial network This network represents glacial-induced relief and glacial deposits of ? Middle Pleistocene age which are rarely preserved in Europe. The sediments and sedimentary bodies are exposed at a variety of altitudes above the modern sea-level, starting from the very coast up to the highest summits of the coastal Dinaric mountains. Here we have evidence of several ice-advance periods which were separated by warm and arid interglacial periods. The ice dynamics was not simple. so ice retreat was followed by episodes of reactivated ice advance , which all left evidence in the deposits. Important characteristics of glacial network are: * evidence of Middle and Late Pleistocene climate change * ice-contact deposits * proglacial and permafrost features * glacial and proglacial depsotional processes and sediments Post-glacial network This network represents post-glacial depsoits of interglacial stages which were deposited in a variety of climatic settings, ranging from temperate and humid to warm and arid. The sediments are represented by glacial outwash plain (sandur) constructed of gravelly braided river system, meandering river systems with well developed point bars, and red paleosols. Important characteristics of post-glacial network are: * sandur deposits * glaciofluvial deposits * drainage basin-missing meandering river deposits in karstifeid area * evidence of climate change and pedogenesis

Dinarides; glaciation; Pleistocene

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