Profiles

Karin Ebert

Karin Ebert

Universitetslektor

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Arbetar vid Institutionen för naturgeografi
Telefon 08-16 47 79
E-post karin.ebert@natgeo.su.se
Besöksadress Svante Arrhenius väg 8
Rum T 412
Postadress Inst för naturgeografi 106 91 Stockholm

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Publikationer

I urval från Stockholms universitets publikationsdatabas
  • 2017. Andreas Ströberg (et al.). Environmental Monitoring & Assessment 189 (118)

    Industrially utilized river basins are frequently exposed to contaminants originating from polluting activities. However, the physical instability and probability of mass movement mobilization of contaminated soil into rivers have only received little attention. In this study, we present a GIS-based method to produce a regional overview of where and how contaminated areas are potentially exposed to slope instability. A landslide susceptibility-index was used to study the degree and distribution of overlap between contaminated sites and unstable ground. A contaminated area instability hazard classification was produced integrating slope instability and contamination risk classification. Our results indicate that mass movement can be tied mainly to a slope gradient ≥16°, a proximity to the river that is <500 m, a distance of <500 m from roads, concave surface curvature, and sand- and silt soils. Forty-six (22%) of all considered contaminated sites are located within areas with a non-negligible slope instability, of which a majority, 30 sites (14%) are situated on ground with a low or moderate instability. Three sites with a class 2 contamination risk (the 2nd highest class) are located on ground with a very high slope instability.

  • 2016. Karin Ebert, Karin Ekstedt, Jerker Jarsjö. Natural hazards and earth system sciences 16 (7), 1571-1582

    Future sea level rise as a consequence of global warming will affect the world's coastal regions. Even though the pace of sea level rise is not clear, the consequences will be severe and global. Commonly the effects of future sea level rise are investigated for relatively vulnerable development countries; however, a whole range of varying regions needs to be considered in order to improve the understanding of global consequences. In this paper we investigate consequences of future sea level rise along the coast of the Baltic Sea island of Gotland, Sweden, with the aim to fill knowledge gaps regarding comparatively well-suited areas in developed countries. We study both the quantity of the loss of features of infrastructure, cultural, and natural value in the case of a 2 m sea level rise of the Baltic Sea and the effects of climate change on seawater intrusion in coastal aquifers, which indirectly cause saltwater intrusion in wells. We conduct a multi-criteria risk analysis by using lidar data on land elevation and GIS-vulnerability mapping, which gives the application of distance and elevation parameters formerly unimaginable precision. We find that in case of a 2 m sea level rise, 3 % of the land area of Gotland, corresponding to 99 km(2), will be inundated. The features most strongly affected are items of touristic or nature value, including camping places, shore meadows, sea stack areas, and endangered plants and species habitats. In total, 231 out of 7354 wells will be directly inundated, and the number of wells in the high-risk zone for saltwater intrusion in wells will increase considerably. Some valuable features will be irreversibly lost due to, for example, inundation of sea stacks and the passing of tipping points for seawater intrusion into coastal aquifers; others might simply be moved further inland, but this requires considerable economic means and prioritization. With nature tourism being one of the main income sources of Gotland, monitoring and planning are required to meet the changes. Seeing Gotland in a global perspective, this island shows that holistic multi-feature studies of future consequences of sea level rise are required to identify overall consequences for individual regions.

  • 2015. Karin Ebert. Canadian journal of earth sciences (Print) 52 (11), 966-979

    The erosional impacts of former ice sheets on the low-relief bedrock surfaces of Northern Hemisphere shields are not well understood. This paper assesses the variable impacts of glacial erosion on a portion of Baffin Island, eastern Canadian Arctic, between 68 degrees and 72 degrees N and 66 degrees and 80 degrees W. This tilted shield block was covered repeatedly by the Laurentide Ice Sheet during the late Cenozoic. The impact of ice-sheet erosion is examined with GIS analyses using two geomorphic parameters: lake density and terrain ruggedness. The resulting patterns generally conform to published data from other remote sensing studies, geological observations, cosmogenic exposure ages, and the distribution of the chemical index of alteration for tills. Lake density and terrain ruggedness are thereby demonstrated to be useful quantitative indicators of variable ice-sheet erosional impacts across Baffin Island. Ice-sheet erosion was most effective in the lower western parts of the lowlands, in a west-east-oriented band at around 350-400 m a.s.l., and in fjord-onset zones in the uplifted eastern region. Above the 350-400 m a.s.l. band and between the fjord-onset zones, ice-sheet erosion was not sufficient to create extensive ice-roughened or streamlined bedrock surfaces. The exception-where lake density and terrain ruggedness indicate that ice-sheet erosion had a scouring effect all across the study area-was in an area from Foxe Basin to Home Bay with elevations <400 m a.s.l. These morphological contrasts link to former ice-sheet basal thermal regimes during the Pleistocene. The zone of low glacial erosion surrounding the cold-based Barnes Ice Cap probably represents the ice cap's greater extent during successive Pleistocene cold stages. Inter-fjord plateaus with few ice-sheet bedforms remained cold-based throughout multiple Pleistocene glaciations. In contrast, zones of high lake density and high terrain ruggedness are a result of the repeated development of fast-flowing, erosive ice in warm-based zones beneath the Laurentide Ice Sheet. These zones are linked to greater ice thickness over western lowland Baffin Island. However, adjacent lowland surfaces with similar elevations of non-eroded, weakly eroded, and ice-scoured shield bedrock indicate that-even in areas of high lake density and terrain ruggedness-the total depth of ice sheet erosion did not exceed 50 m.

  • 2015. Adrian M. Hall, Pertti Sarala, Karin Ebert. Geomorphology 246, 472-488

    The nature of the regolith that existed on the shields of the Northern Hemisphere at the onset of ice sheet glaciation is poorly constrained. In this paper, we provide the first detailed account of an exceptionally preserved, deeply weathered late Neogene landscape in the ice sheet divide zone in northern Finland. We mine data sets of drilling and pitting records gathered by the Geological Survey of Finland to reconstruct regional preglacial deep weathering patterns within a GIS framework. Using a large geochemical data set, we give standardised descriptions of saprolite geochemistry using a variant of the Weathering Index of Parker (WIP) as a proxy to assess the intensity of weathering. We also focus on mineral prospects and mines with dense pit and borehole data coverage in order to identify links between geology, topography, and weathering.

    Geology is closely linked to topography on the preglacial shield landscape of northern Finland and both factors influence weathering patterns. Upstanding, resistant granulite, granite, gabbro, metabasalt, and quartzite rocks were associated with fresh rock outcrops, including tors, or with thin (< 5 m) grusses. Plains developed across less resistant biotite gneisses, greenstones, and belts of alternating rock types were mainly weathered to thick (10–20 m) grusses with WIPfines values above 3000 and 4000. Beneath valley floors developed along mineralised shear and fracture zones, weathering penetrated locally to depths of > 50 m and included intensely weathered kaolinitic clays with WIPfines values below 1000.

    Late Neogene weathering profiles were varied in character. Tripartite clay–gruss–saprock profiles occur only in limited areas. Bipartite gruss–saprock profiles were widespread, with saprock thicknesses of > 10 m. Weathering profiles included two discontinuities in texture, materials and resistance to erosion, between saprolite and saprock and between saprock and rock. Limited core recovery when drilling below the soil base in mixed rocks of the Tana Belt indicates that weathering locally penetrated deep below upper fresh rock layers. Such deep-seated weathered bands in rock represent a third set of discontinuities. Incipient weathering and supergene mineralisation also extended to depths of > 100 m in mineralised fracture zones. The thin weathering crusts found extensively beneath till may represent types of early or middle Pleistocene palaeosols.

    We confirm that glacial erosion has been very limited (< 20 m) in northern Finland and has been widely restricted to the partial stripping of saprolith. The Fennoscandian Ice Sheet in this ice-divide zone remained cold-based and unerosive throughout the Pleistocene. The large-scale shield geomorphology developed before glaciation and is a product of differential weathering and erosion acting on diverse rock types and structures through the Neogene. The first ice sheets did not advance across planar, uniformly soft, deeply kaolinised beds as proposed in recent models of the Laurentide ice sheet. Instead, in northern Finland, the shield topography comprised broad plains and valleys with isolated hills and hill masses, with a relative relief of several hundred metres. Weathered rock was restricted in its distribution and thickness and provided diverse bed materials for ice sheets, including rock, broken saprock, permeable gruss, and linear zones of impermeable clay, with multiple discontinuities. Glacial erosion and local glacial transport led to widespread incorporation of this saprolith material into tills.

  • 2015. Karin Ebert, Leona Axelsson, Jon Harbor. Journal of Higher Education Policy and Management 37 (2), 252-262

    Because of the potential value of alumni involvement for student success, for connections to society and as a base for future philanthropy, there is growing interest in developing university alumni relations programmes in countries that do not have a long tradition in this area. This case study of Stockholm University describes the goals, strategies, barriers and successes of building an alumni programme in an environment that lacks a tradition of alumni relations and aims to provide perspectives and ideas that can help other universities worldwide with their work towards building alumni programmes that fit their cultural contexts and goals.

  • 2015. Karin Ebert (et al.). Geomorphology 233 (SI), 64-74

    Much previous work on Late Cenozoic glacial erosion patterns in bedrock has focussed on mountain areas. Here we identify varying impacts of ice sheet erosion on the low-relief bedrock surface of the Fennoscandian shield, and examine the geological, topographical and glaciological controls on these patterns.

    We combine GIS-mapping of topographical, hydrological and weathering data with field observations. We identify and investigate areas with similar geology and general low relief that show different degrees of ice sheet erosional impact, despite similar ice cover histories. On two transects with a total area of ~ 84 000 km2 across the northern Fennoscandian shield, we first establish patterns of glacial erosion and then examine why glacially streamlined areas exist adjacent to areas of negligible glacial erosion. The northern transect includes two areas of exceptional glacial preservation, the Parkajoki area in Sweden and the so-called ice divide zone in Finland, each of which preserve tors and deep saprolite covers. The southern transect, overlapping in the northern part with the first transect, includes areas of well developed glacial streamlining, with bedrock areas stripped of loose material and barely any weathering remnants.

    For both areas, we firstly present contrasting indicators for ice sheet erosional impact: streamlined and non-streamlined inselbergs; parallel and dendritic/rectangular drainage patterns; and the absence and presence of Neogene weathering remnants. This is followed by an investigation of factors that possibly influence ice sheet erosional impact: ice cover history, ice cover duration and thickness, bedrock type and structure, and topography.

    We find that the erosional impact of the Fennoscandian ice sheet has varied across the study area. Distinct zones of ice sheet erosion are identified in which indicators of either low or high erosion coexist in the same parts of the transects. No direct impact of rock type on glacial erosion patterns was found, but an indirect control appears clear. Bedrock geology and long-term differential weathering and tectonic evolution determined the topography of the pre-glacial landscape, and these topographic differences subsequently influenced ice sheet dynamics and thereby partly controlled patterns of ice sheet erosion. Ice cover duration and former ice thickness were not significant controls on glacial erosion patterns. Extensive preservation of pre-glacial relief through low glacial erosion is attributed to the maintenance throughout the Pleistocene of divergent flow and frozen-bed conditions in the Fennoscandian ice sheet. In contrast, glacial streamlining and strong glacial erosion were caused mainly by acceleration of flow around major obstacles and flow towards major depressions on the ice sheet bed. The relatively strong ice sheet erosion towards the Gulf of Bothnia is the result of a combination of favourable factors: bedrock structure and river valleys aligned sub-parallel to ice sheet flow and convergent ice flow towards the Baltic.

  • 2013. H. Albert Gilg, Adrian M. Hall, Karin Ebert. Palaeogeography, Palaeoclimatology, Palaeoecology 392, 454-462

    We use D/H and 18O/16O ratios to explore the age of kaolins on the Fennoscandian Shield. Sub-Cretaceous kaolins in southern Scandinavia have isotopic compositions indicative of weathering under warm mean annual temperatures (MATs) of > 15 °C. Deep kaolins on the shield surface in Finland previously also have been regarded as products of humid tropical weathering of Mesoproterozoic to Eocene age. New oxygen and hydrogen isotope ratios indicate, however, weathering by cool groundwater under MATs of 13–15 °C. Isotope ratios are also not consistent with deep (> 1 km) burial by cover rocks, indicating that a very old age for the weathering is unlikely. Palaeotemperatures are below Cretaceous MATs, yet substantially above Plio-Pleistocene MATs. Comparisons with palaeotemperatures in N Europe and around the Arctic Ocean indicate that the Finnish kaolins developed on the shield surface in the Palaeogene or, alternatively, Miocene. Deep weathering was selectively developed in highly fractured shield rocks and took place in response to latest Cretaceous and Palaeogene uplift and after stripping of Palaeozoic cover rocks. The cool kaolins in Finland indicate that previous routine attributions of kaolinitic weathering products in the geological record to humid tropical environments should be closely scrutinised.

  • 2013. Johan Kleman (et al.). Climate of the Past 9, 2365-2378

    We here reconstruct the paleotopography of Northern Hemisphere ice sheets during the glacial maxima of marine isotope stages (MIS) 5b and 4.We employ a combined approach, blending geologically based reconstruction and numerical modeling, to arrive at probable ice sheet extents and topographies for each of these two time slices. For a physically based 3-D calculation based on geologically derived 2-D constraints, we use the University of Maine Ice Sheet Model (UMISM) to calculate ice sheet thickness and topography. The approach and ice sheet modeling strategy is designed to provide robust data sets of sufficient resolution for atmospheric circulation experiments for these previously elusive time periods. Two tunable parameters, a temperature scaling function applied to a spliced Vostok–GRIP record, and spatial adjustment of the climatic pole position, were employed iteratively to achieve a good fit to geological constraints where such were available. The model credibly reproduces the first-order pattern of size and location of geologically indicated ice sheets during marine isotope stages (MIS) 5b (86.2 kyr model age) and 4 (64 kyr model age). From the interglacial state of two north–south obstacles to atmospheric circulation (Rocky Mountains and Greenland), by MIS 5b the emergence of combined Quebec–central Arctic and Scandinavian–Barents-Kara ice sheets had increased the number of such highland obstacles to four. The number of major ice sheets remained constant through MIS 4, but the merging of the Cordilleran and the proto-Laurentide Ice Sheet produced a single continent-wide North American ice sheet at the LGM.

  • 2013. Adrian Hall, Karin Ebert, Clas Hättestrand. Geografiska Annaler. Series A, Physical Geography 95 (1), 33-49

    We seek to quantify glacial erosion in a low relief shield landscape in northern Sweden. We use GIS analyses of digital elevation models and field mapping of glacial erosion indicators to explore the geomorphology of three granite areas with the same sets of landforms and of similar relative relief, but with different degrees of glacial streamlining. Area 1, the Parkajoki district, shows no streamlining and so is a type area for negligible glacial erosion. Parkajoki retains many delicate pre-glacial features, including tors and saprolites with exposure histories of over 1 Myr. Area 2 shows the onset of significant glacial erosion, with the development of glacially streamlined bedrock hills. Area 3 shows extensive glacial streamlining and the development of hill forms such as large crag and tails and roches moutonnées.

    Preservation of old landforms is almost complete in Area 1, due to repeated covers of cold-based, non-erosive ice. In Area 2, streamlined hills appear but sheet joint patterns indicate that the lateral erosion of granite domes needed to form flanking cliffs and to give a streamlined appearance is only of the order of a few tens of metres. The inheritance of large-scale, pre-glacial landforms, notably structurally controlled bedrock hills and low relief palaeosurfaces, remains evident even in Area 3, the zone of maximum glacial erosion. Glacial erosion here has been concentrated in valleys, leading to the dissection and loss of area of palaeosurfaces. Semi-quantitative estimates of glacial erosion on inselbergs and palaeosurfaces and in valleys provide mean totals for glacial erosion of 8 ± 8 m in Area 1 and 27 ± 11 m in Area 3. These estimates support previous views that glacial erosion depths and rates on shields can be low and that pre-glacial landforms can survive long periods of glaciation, including episodes of wet-based flow.

  • 2013. Adrian Hall (et al.). Geology 41 (12), 1203-1206

    Glaciated passive margins display dramatic fjord coasts, but also commonly retain plateau fragments inland. It has been proposed recently that such elevated, low-relief surfaces on the Norwegian margin are products of highly efficient and extensive glacial and periglacial erosion (the glacial buzzsaw) operating at equilibrium line altitudes (ELAs). We demonstrate here that glacial erosion has acted instead to dissect plateaus in western Norway. Low-relief surfaces are not generally spatially associated with cirques, and do not correlate regionally with modern and Last Glacial Maximum ELAs. Glacier dynamics require instead that glacial erosion is selective, with low-relief surfaces representing islands of limited Pleistocene erosion. Deep glacial erosion of the coast and inner shelf has provided huge volumes of sediment (70,000 km3), largely resolving apparent mismatches (65–100,000 km3) between fjord and valley volumes and Pliocene–Pleistocene sediment wedges offshore. Nonetheless, as Pleistocene glacial valleys and cirques are cut into preexisting mountain relief, tectonics rather than isostatic compensation for glacial erosion have been the main driver for late Cenozoic uplift on the Norwegian passive margin.

  • 2012. Karin Ebert (et al.). Quaternary Geochronology 12, 11-22

    We examine Be-10 concentration in two pit profiles in the Parkajoki area at similar to 67 degrees N on the northern Fennoscandian shield in northern Sweden. Due to repeated cover by cold-based, non-erosive ice sheets, the area retains many relict non-glacial features, including tors and saprolites. In the examined pit profiles, gruss-type saprolite developed from weathering of intermediate igneous rocks is overlain unconformably by Weichselian till.

    Our results show that Be-10 concentrations found in the till greatly exceed the levels of Be-10 that can have accumulated since deglaciation at similar to 11 ka and are comparable to those reported from Pliocene and Early Pleistocene tills in North America. Old tills with grussified boulders at depth were excavated in the Parkajoki area and correlations with neighbouring parts of Finland indicate a Middle Pleistocene or older age. Evidence from pit excavations and geochemistry shows that the underlying saprolites have been truncated by glacial erosion and that previously weathered material has been incorporated into the till sequence. Hence, Be-10 inventories in the tills are dominated by material recycled from Middle Pleistocene or older soils, near-surface sediments and saprolite, and cannot be used to date the periods of till deposition. The retention of relict Be-10 in the tills nonetheless confirms minimal glacial erosion.

    Concentrations of meteoric Be-10 in the saprolites are lower than any reported saprolite concentrations measured in other settings. Uncertainty in the pre-glaciation Be-10 concentrations in the saprolites makes age determinations difficult. One possibility is that that the saprolite had higher Be-10 concentrations in the past but that saprolite formation ended after glaciation and burial by till and that the Be-10 has substantially decayed. Modelling of the meteoric Be-10 depth profiles in this case suggests that the saprolites in the Parkajoki area were formed at a minimum of 2 Ma. Erosion of the saprolite allows an older age of up to similar to 5 Ma, with up to 250 cm of material removed and incorporated into later tills. A second possibility is that concentrations of meteoric Be-10 in the saprolite were originally lower, with formation of the saprolite in a period or periods of ice- and permafrost-free conditions before 0.8 Ma.

  • 2012. Karin Ebert, Adrian M Hall, Clas Hättestrand. Norsk Geologisk Tidsskrift 92 (1), 1-17

    We investigate the long-term geomorphological evolution of the inselberg plains on the glaciated northern Fennoscandian shield. The shield surface has been largely stripped of pre-Quaternary correlative sediments and saprolites by non-glacial and glacial erosion, which makes investigations of pre-Quaternary landscape development a challenge. The relief of the study area, covering 33,000 km3 in the centre of the shield in northern Sweden, includes an abundance of inselbergs that provide the basis for the study. We examine the relief of the inselberg plains, integrated with glacial-geomorphologic features, geology, and weathering remnants, by using GIS-analysis and fieldwork. Several key areas are used to demonstrate the impact of glaciations on the large scale relief, and the influence of geology, structure and deep weathering on relief formation.

    Glacial erosion had only a minor impact on the large-scale bedrock morphology of northern Sweden. Based on excavations and observations in the Parkajoki area, an area largely preserved under cold-based ice during Quaternary glaciations, we infer that grus weathering, resulting in saprolite covers of up to 10-20 m thickness, occurred in the Neogene. However, inselbergs are considerably higher than that, and must therefore be the result of older deep weathering and erosional events. Narrow fracture zones associated with deep kaolins found in northern Fennoscandia may represent the roots of older generations of deep weathering covers but their age and formation is yet unclear.  The geology of the area has greatly influenced the present surface relief. The positions and footprints of the inselbergs are often closely controlled by bedrock type and fracturing. Granite inselbergs generally have dome forms where dome shape and slopes are determined by joint patterns. Steps between palaeosurfaces locally coincide with lithological boundaries and major faults. These links indicate the fundamental importance of etch processes in shaping the relief through multiple cycles of deep weathering and stripping. Palaeosurfaces have been extended and lowered through time, with isolation of small inselbergs during erosion of higher palaeosurfaces. The timescales for relief generation remain uncertain and there is a pressing need to understand the significance of and to date the sediments, saprolites and weathered ore bodies that rest on the surface of the northern Fennoscandian shield.

  • 2010. Karin Ebert, Clas Hättestrand. Geomorphology 115 (1-2), 56-66

    We investigate the glacial modification of inselbergs (large, isolated bedrock hills) in northern Sweden. Inselbergs are generally regarded as products of deep weathering (etching) and stripping under warm and humid climates. Unlike inselbergs found in the tropics, the inselbergs in northern Sweden were exposed to ice sheet glaciation for long periods of the Quaternary. We used DEMs to examine 794 inselbergs in our study area and they were classified according to their degree of glacial modification. Bedrock structural control was assessed using GIS data on the regional geology. Clusters of inselbergs were mapped in the field for features indicative of glacial erosion, such as glacial cliffs and stripped bedrock surfaces, and for features indicative of limited erosion, such as tors and blockfields. The results of the study indicate that inselbergs in the area were mostly modified by Quaternary ice sheets only to a low or moderate extent and that the degree of glacial erosion is dependent on their relief and location. Inselbergs with a relative relief of < 100 m and in areas of lower absolute relief experienced the strongest glacial modification, where the strongest glacial modification can result in lateral erosion of the inselberg flanks. Inselberg summits often display signs of minimal glacial erosion, such as tor-like bedrock outcrops with signs of strong weathering. In summary, we argue that inselbergs in northern Sweden have largely retained their pre-Quaternary shape despite long periods of ice sheet cover.

  • 2009. Karin Ebert. Progress in physical geography 33 (2), 163-182

    In this paper the terminology used in long-term geomorphology is evaluated. Long-term geomorphology is the study of landforms that are of mostly pre-Quaternary, Cenozoic, Mesozoic or even Palaeozoic age. Many terms have been introduced to name the long-term large-scale landforms that persist to the present. The definitions of many of these terms are ambiguous, have changed over time, and their use and meaning is consequently often unclear. An attempt is made to clarify definitions, when possible, and to facilitate more concise usage of these terms. Long-term geomorphology deals in great parts with the lowering of a land surface to the base level (mostly sea level), leaving a new land surface. The largest group of terms concerns descriptions and genetic models for these kinds of new land surfaces collectively called “base level surfaces” here. Other terms discussed here relate to relict and preglacial landforms and regional terms for stepped surfaces. Terminology is discussed with particular reference to examples from and its use in Scandinavia. There is a long history of long-term geomorphology study in this region. Scandinavia is unique in the respect that pre-Quaternary landforms where repeatedly covered by Quaternary ice-sheets but often survived with different degrees of glacial modification. The usage of the terms in question is discussed from the view of long-term geomorphology in that area.

  • 2013. Adrian Hall, Karin Ebert. Palaeogeography, Palaeoclimatology, Palaeoecology 388, 1-14

    Allochthonous Cenozoic microfossils have been reported from Late Pleistocene lake and mire host sediments across an area of > 30,000 km2 in northern Finland. Two main groups of microfossils are recognised: Palaeogene marine diatoms, silicoflagellates and ebridians that include taxa from around the time of the Palaeocene–Eocene Thermal Maximum and Pliocene to early Pleistocene freshwater diatoms. The presence of these microfossils has been regarded as evidence that Eocene marine and late Neogene freshwater sediments formerly existed on the shield surface. Both groups have been referred to frequently in reconstructions of the sea level, tectonic and erosion history of the northern Fennoscandian shield. The questions raised by the presence of allochthonous Cenozoic microfossils in northern Finland are, however, strongly resonant of the debate over the biota, origin and age of the Pliocene Sirius Group in Antarctica where competing hypotheses have been put forward of local deposition and reworking versus distant wind transport of marine diatoms from the continental shelf.

    This review explores alternative origins for the allochthonous Cenozoic microfossils in northern Finland. Local reworking of Palaeogene marine sediments during Pleistocene glaciation is unlikely, as no source rocks of Palaeogene age are known from the shield surface or from surrounding sedimentary basins in the Baltic and White Sea. Moreover, at all sites except Akanvaara, the marine diatom taxa cover wide age ranges and occur only as minor components in diatom assemblages that are dominated by Quaternary freshwater taxa. Local reworking of Pliocene–Pleistocene freshwater diatoms is, however, compatible with the widespread survival of pre-Pleistocene deep weathering although no in situ or unmixed, ice-rafted Pliocene–Pleistocene lacustrine sediment has yet been found. An alternative origin for the marine Palaeogene microfossils by distant wind transport is proposed. In this hypothesis, Palaeogene diatomites on the Barents Sea shelf were exposed to deep glacial and fluvioglacial erosion during the Pliocene and Early Pleistocene and in low sea level stages of the Middle and Late Pleistocene. Intense wind action acting on comminuted mudstones on outwash plains carried dust including microfossils into northern Fennoscandia to be deposited by rain-out in lakes and wetlands. This material may have been later further recycled by glacial and meltwater transport and more localised wind action, processes that also may help to account for the distribution of Eemian marine diatoms well beyond Eemian shorelines. The distant wind transport hypothesis implies that the presence of marine Palaeogene diatoms on the shield surface in northern Finland cannot be regarded as vestiges of former marine sediments and so do not constrain the tectonic and geomorphic history of the northern Fennoscandian shield in the Cenozoic.

  • 2011. Karin Ebert (et al.). Geomorphology 132 (3-4), 339-350

    Stepped relief is a characteristic feature of many upland areas on Earth. In this study, we examine if stepped relief can be identified objectively by GIS-analysis of digital elevation models (DEMs). We specifically study the stepped relief landscapes of northern Sweden, comprising areas of contrasting topography in the mountainous northern Scandes and on the inselberg plains of the Precambrian basement east of the Caledonides.We mainly use hypsographic curves to examine the elevation distribution of the study areas and to identify palaeosurfaces. Peaks in the hypsographic curves are interpreted as palaeosurfaces, while hypsographic minima are interpreted as breaks in slope, separating these surfaces. In the northern Scandes, where only patchy remnants of palaeosurfaces remain, we use empirical cutoff values of slope angles to restrict palaeosurface areas to those identified in thefield and in air photos. In addition, air photo andfield mapping of glacially eroded areas is necessary to exclude glacially formed low relief surfaces, such as valley floors. These latter procedures introduce an unavoidable degree of subjectivity to the study. Our results indicate that in the northern Scandes, surfaces with an inclination of 11°, after glacially formed features are abstracted, correspond well with palaeosurface remnants. Breaks in slope separating the surface generations in themountains are centred around 860, 1320, and 1520 masl (above sea level), respectively. On the plains east of the northern Scandes, hypsographic data were filtered to remove inselbergs in order to analyse only the plains. Hypsographic curves of both the filtered and the unfiltered data of the inselberg plains show minima at elevations that correspond to steps separating multiple palaeosurfaces at elevations of 190, 250, and 400 masl. The steps separating the different palaeosurfaces are, in places, aligned with known geological discontinuities, but extensive remnants also transect structure. The presence of stepped relief is consistent with existing models of phased Cenozoic uplift and incision in northern Fennoscandia.

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Senast uppdaterad: 23 mars 2018

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