Geological geomorphological features of the Baltic region and adjacent areas: imprint on glacial postglacial development
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- Sediment redistribution
- Uplift residuals and tectonic component
- Conclusions
Hydroisostasy:
Sediment redistribution: Plio-Pleistocene erosion and sedimentation significantly impact post-glacial uplift. For modeling purpose we determine the changes in surface load caused by glacial and post-glacial erosion and sedimentation over 1000 year time intervals utilizing a largely automated interpretation of regional geological and geomorphological observations that is constrained by plausible bounds on the rate of erosion of various lithologies and the known general pattern and behavior of glacial ice (ice boundaries over time, the dendritic pattern of ice movement, geometry of fast-flowing ice streams, plausible changes in frozen-bed conditions, etc) (Amantov et.al., 2011). Mass-balance between erosion and deposition is enforced at all times with account of remaining eroded material in the ice body. Fig. . Sample time slices of erosion – accumulation approximations involved in overall isostatic rebound modeling The first glaciations likely dominated in shaping the major bedrock landforms, although it is possible that in some areas the deepening was distributed evenly over all the cycles. Younger glaciations mainly removed sediments left by their predecessors and accumulated during interglacial time, locally incising and changing the dip of the bedrock surface. Degree of resulting lowering of the surface in zones of repeated erosion strongly depends on scenarios of interglacial sedimentation. Knowledge of bedrock topography, measure of its overdeepenings and its lowering from reconstructions of older relief facets serve as important validation steps in determination of the erosion magnitude. However, it cannot be used for judgment on erosional rates. In many cases glacially shaped topography, with elongated basins alternating with conformal ridges and riegels produced multiple local depocenters for interglacial (postglacial) sedimentation, with partial inheritance. For such areas erosion and posterior sedimentation could be compared with pendulum, when the nature “masked its wounds”. Local zones of deep erosion appeared as zones of profound sedimentation with maximum rates immediately after glacial retreat, but roles reversed again on the next advance. For example, strongly increased thickness of recent postglacial sediments on reduced Quaternary section represented by latest tills only in many cases may indicate zone of preceding intensive erosion of comparable amount. Late Pleistocene – Holocene uncompacted sediments that were accumulated after glacial retreat, like the varved clays were approximated in time-slices by separate automation module (Fig. ). Numerous local overdeepenings of the resulting heterogeneous late-glacial surface were shifted into correspondent local depocenters with relatively rapid accumulation after glacial retreat. As a result, a thick (tens meters over wide areas) veneer of sediments has been deposited. Huge landslides at the continental slope, like Storegga slide (Haflidason et. al., 2004) and others impacted rebound isobases locally. In erosion zones exhibited by lowlands and overdeepenings the rebound effect of sediment redistribution and of the hydroisostasy could often be linked, complicating resulting pattern in time. 
Fig. . Sample time slices of postglacial accumulation approximations involved in overall isostatic rebound modeling (cal. years BP). Storegga slide is simplified after Haflidason et. al., 2004. Uplift residuals and tectonic component: 
The Scandinavian (Norwegian) mountain range has its correspondent feature at the opposite side of the Atlantic ocean. That is called East Greenland mountain range (orogen) developed as linear high mountain range along the Greenland coast, from 70 to 82 degrees north latitude. It’s important to mark that both East Greenland and Norwegian modern ranges were precursed by the Caledonian belts. West-vergent Caledonian thrust sheets are known in the East Greenland, whereas east-vergent thrust sheets typify the Caledonian Orogen of Scandinavia. The Caledonian Orogen in East Greenland is exposed over a several hundred kilometer wide stretch of ice free land that extends for 1300 km between latitudes 70° and 82 °N (as the modern mountain range does!), being comprised by domains with 1) a partly exposed foreland in the west, 2) a western marginal thrust belt that exposes foreland windows in anticlinal culminations, and 3) an eastern thick-skinned thrust belt that incorporates major segments of Caledonian reworked Laurentian gneiss basement in major thrust sheets, as described by N. Henriksen and others. Post-Caledonian extension is exhibited by intermontane continental Middle to Upper Devonian basins, while Paleozoic - Mesozoic - Tertiary sedimentary sequences occur fragmentary onshore and at adjacent shelf area with rifting or quazi-rifting events at some stages, especially linked with history of Atlantic. Tertiary history is of special focus, when 4−5 × 105 km3 pile of tholeiitic basalts on the central east Greenland coast was erupted in latest Palaeocene and earliest Eocene time, with correspondent high-rate formation of effusive; marine horizons at the base and top of the pile show that its build-up was accompanied by concomitant crustal depression (Sopera et.al., 1976). Wide onshore distribution of Tertiary basalts and known prominent Tertiary faults of the “coastal flexure” could be referred as some specific feature of Greenlands side of Atlantic, while their equivalents along the Norwegian margin are distributed offshore. South of the greatest Scoresby Sund Fjord a major NE−trending dip−slip normal fault called the Muslingehjørnet fault is known. It downthrows to the east by more than 1000 m (Birkenmajer 2000), and also controls distribution of pre-basalt Tertiary sediments (Birkenmajer 2010). Lithomorphic component is clear in modern topography either. The hard plutonic rocks of Lilloise and Borgtindern have withstood further erosion better than the surrounding basalts and have formed spectacular Alpine-type peaks (Matthews, 1979). Brooks (1979) proposes that to the south and west of Skaergaard (which is approximately 100 km south west of Rosenborg Glacier), where the overall level of erosion is much deeper, there is evidence that the plutons and their roof rocks have, throughout their history, shown greater resistance to erosion than their surroundings. Alkaline lavas overly the main basalt pile at some highs (Gronau West Nunatak). Gunnbjørn Fjeld south of Scoresby Sund Fjord is highest mountain and also the highest mountain north of the Greenland and Arctic circle. It is located in the Watkins Range on the east coast, which contains several other summits above 3500 metres. However, if to assume melting of the present ice sheet, account uplift due to heavy erosion of the coastal areas and implicate it to reconstruction of Tertiary surfaces, than the major (“anomalous”) uplift of the East Greenland mountain range (orogen) would be displaced further north to the now-a-day zone of high subice mountain plateau. Conclusions: Baltic Sea lowland exhibits part of the super-regional structural-denudation form that was created with dominate role of Tertiary multiphase preglacial erosion and strong selective Pleistocene glacial – fluvioglacial denudation that mostly affected the Meso-Neoproterozoic early platform basins and soft post-Late Vendian sedimentary cover. Central sedimentary basins could be an important integral part of overall ice-age pattern Glacial erosion and sedimentation significantly impact the landscape evolution and total glacial rebound, but the pattern and rates of glacial erosion are strongly variable in time and space. More distinct radial pattern at the early stage with selective exhumation of relatively resistant formations caused developing stable topographic ice-streams in favorable zones at later stages. The observed post-glacial uplift in the Baltic area is the result of various processes, the most important being the glacio isostatic movements. High resolution modeling including glacial isostasy, hydro isostasy, sediment isostasy confirms earlier rheology model (Fjeldskaar & Cathles, 1991) of asthenosphere with a thickness less than 150 km and viscosity less than 7.0x1019 Pa s, mantle viscosity beneath the asthenosphere with viscosity 1021 Pa s, flexural rigidity of the lithosphere of 5x1023 Nm (effective elastic thickness of 30-40 km). Significant residuals in the present rate of uplift of the northern and southern Scandes Domes could be related to Atlantic transverse fault system and explained by viscosity variations from mantle temperatures. References: Amante, C. & Eakins, B. W., 2009. 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Stockholm Contrib. Geol., 40 (3), pp.83-168. Winterhalter, B., 1972. On the geology of the Bothnian Sea, an epeiric sea that has undergone Pleistocene glaciation. Geol. Surv.Finland, Bull. 258, 66 p. Directory: pub pub -> Project Scoring Template Pre-Construction Phase New Core/Branch Campus Projects pub -> Acm word Template for sig site pub -> The german unification, 1815-1870 pub -> Baltic Olympiads in Informatics: Challenges for Training Together pub -> Preparation of Papers for ieee transactions on medical imaging pub -> Forthcoming meetings and conferences pub -> Asilomar Conference on Circuits, Systems & Computers, Pacific Grove, ca, November 1978, pp. 55 58 pub -> Forthcoming meetings and conferences pub -> Harmonised compatibility and sharing conditions for video pmse in the 7 9 ghz frequency band, taking into account radar use Download 17.21 Mb. Share with your friends:
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