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Karna

Karna Lidmar-Bergström

Professor emerita i naturgeografi

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Arbetar vid Institutionen för naturgeografi
Telefon 08-16 47 90
E-post karna@natgeo.su.se
Besöksadress Svante Arrhenius väg 8
Rum T 227
Postadress Inst för naturgeografi 106 91 Stockholm

Publikationer

I urval från Stockholms universitets publikationsdatabas
  • 2017. Karna Lidmar-Bergström, Mats Olvmo, Johan M. Bonow. GFF 139 (4), 244-259

    The relationships between different denudation surfaces/peneplains formed across crystalline basement rocks give valuable information to the tectonic development of ancient shields. The denudation surfaces can be identified by the aid of their landforms, tilt and remnant weathering mantles in relation to cover rocks. Three types of denudation surfaces are identified across south Sweden (1) a tilted flat plain, (2) a tilted hilly surface with relative relief below 150 m and (3) stepped horizontal plains with residual hills. All three types of denudation surfaces are peneplains, denudation surfaces graded to specific base levels. The re-exposed parts of the inclined flat sub-Cambrian peneplain (SCP) extend as a landscape feature from below cover rocks in the north and east and reaches up on the highest summits of the South Swedish Uplands. The SCP (the exact unconformity) is encountered again below Cambrian covers outside the west coast. Thus south Sweden is a geological dome, the South Swedish Dome (SSD), in relation to the Cambrian cover. The southern and western low flanks of the exposed part of the dome are instead characterized by a hilly peneplain, the inclined sub-Cretaceous denudation surface, with remnants of thick, kaolinitic, clayey saprolites. This sub-Cretaceous peneplain is cut off at a distinct level in the south and west by the almost horizontal South Smaland Peneplain, a never covered, epigene, peneplain. The uplift history of the SSD aids to the understanding on the development of late Tertiary drainage systems of the Baltic Basin by the Eridano River.

  • 2013. Karna Lidmar-Bergström. Carlshamniana 28, 77-82
  • 2013. Karna Lidmar-Bergström, Johan M. Bonow, Peter Japsen. Global and Planetary Change 100, 153-171

    Stratigraphic Landscape Analysis (SLA) is based on a) the relationship between peneplains (low-relief denudation surfaces) in basement and their cover rocks of different age, b) the crosscutting relationships between such re-exposed peneplains and never covered (epigene) peneplains, and c) the occurrence of valleys incised below peneplains. Previous studies based on detailed SLA of the South Swedish Dome (SSD) have identified two major re-exposed peneplains, the flat sub-Cambrian peneplain and the sub-Jurassic/Cretaceous peneplain with undulating hilly relief. Both surfaces developed dose to former sea levels, were subsequently transgressed, and buried below sedimentary covers. The preservation of these peneplains documents that uplift of the land surface was followed by subsidence. Crosscutting relationships between these re-exposed and tilted peneplains and a third peneplain, an epigene and horizontal plain with residual hills, demonstrate that the latter is younger and thus of post-Cretaceous age. Three topographic highs characterize Scandinavia, the Northern Scandes (NS), the Southern Scandes (SS), and the low SSD. We show that the three relief types of the SSD can be identified across Scandinavia and that they demonstrate phases of uplift/denudation and subsidence/burial of Scandinavia during the Phanerozoic. In particular, we show that the epigene peneplains of the NS, the SS and the SSD are Cenozoic erosion surfaces and this also leads us to identify three major Cenozoic morphotectonic units. A result of our studies is that the paradigm of continuous uplift of steady state landscapes cannot be assumed as a universal model of landform evolution.

  • 2013. P. F. Green (et al.). Geological Survey of Denmark and Greenland Bulletin (30), 9-+

    The continental margin of West Greenland is similar in many respects to other elevated, passive continental margins (EPCMs) around the world. These margins are characterised by extensive regions of low relief at elevations of 1-2 kilometres above sea level sloping gently inland, with a much steeper, oceanward decline, often termed a 'Great Escarpment', terminating at a coastal plain. Recent studies, based on integration of geological, geomorphological and thermochronological evidence, have shown that the high topography of West Greenland was formed by differential uplift and dissection of an Oligo-Miocene peneplain since the late Miocene, many millions of years after continental break-up between Greenland and North America. In contrast, many studies of other EPCMs have proposed a different style of development in which the high plateaux and the steep, oceanward decline are regarded as a direct result of rifting and continental separation. Some studies assume that the elevated regions have remained high since break-up, with the high topography continuously renewed by isostasy. Others identify the elevated plains as remnants of pre-rift landscapes. Key to understanding the development of the West Greenland margin is a new approach to the study of landforms, stratigraphic landscape analysis, in which the low-relief, high-elevation plateaux at EPCMs are interpreted as uplifted peneplains: low-relief surfaces of large extent, cutting across bedrock of different age and resistance, and originally graded to sea level. Identification of different generations of peneplain (re-exposed and epigene) from regional mapping, combined with geological constraints and thermochronology, allows definition of the evolution leading to the formation of the modern-day topography. This approach is founded particularly on results from the South Swedish Dome, which document former sea levels as base levels for the formation of peneplains. These results support the view that peneplains grade towards base level, and that in the absence of other options (e.g. widespread resistant lithologies), the most likely base level is sea level. This is particularly so at continental margins due to their proximity to the adjacent ocean. Studies in which EPCMs are interpreted as related to rifting or break-up commonly favour histories involving continuous denudation of margins following rifting, and interpretation of thermochronology data in terms of monotonic cooling histories. However, in several regions, including southern Africa, south-east Australia and eastern Brazil, geological constraints demonstrate that such scenarios are inappropriate, and an episodic development involving post-breakup subsidence and burial followed later by uplift and denudation is more realistic. Such development is also indicated by the presence in sedimentary basins adjacent to many EPCMs of major erosional unconformities within the post-breakup sedimentary section which correlate with onshore denudation episodes. The nature of the processes responsible is not yet understood, but it seems likely that plate-scale forces are required in order to explain the regional extent of the effects involved. New geodynamic models are required to explain the episodic development of EPCMs, accommodating post-breakup subsidence and burial as well as subsequent uplift and denudation, long after break-up which created the characteristic, modern-day EPCM landscapes.

  • 2009. Peter Japsen (et al.). Earth Surface Processes and Landforms 34 (5), 683-699

    The usefulness of large-scale, low-relief, high-level landscapes as markers of uplift events has become a subject of disagreement among geomorphologists. We argue that the formation of low-relief surfaces over areas of large extent and cutting across bedrock of different age and resistance must have been guided by distinct base levels. In the absence of other options the most likely base level is sea level. We have analysed West Greenland landscapes in a recent study by combining the cooling history from apatite fission-track analysis (AFTA) data with the denudation history from landscape analysis and the stratigraphic record. An important difference between our approach and that of classical geomorphology is that we now have the ability to document when thick sections of rocks have been deposited and then removed. The present-day high-level plateau in West Greenland is the remnant of a planation surface that was formed by denudation that lasted 1 km of cover was removed after maximum burial at the Eocene–Oligocene transition. Here we present additional AFTA data to show that the planation surface is the end-product of Cenozoic denudation even in basement areas and argue that Phanerozoic sediments – most likely of Cretaceous–Palaeogene age – must have been present prior to denudation. The planation surface was offset by reactivated faults and uplifted to present-day altitudes of up to 2 km. The uplift occurred in two late Neogene phases that caused incision of valleys below the planation surface and their subsequent uplift. We therefore find that the elevated and deeply dissected plateau is evidence of episodic post-rift uplift that took place millions of years after cessation of sea-floor spreading west of Greenland. We suggest that other margins with similar morphology may also be characterized by episodic post-rift uplift unrelated to the processes of rifting and continental separation, rather than being permanently uplifted since the time of rifting, as is commonly assumed.

  • 2007. Johan M. Bonow (et al.). Geological Survey of Denmark and Greenland Bulletin: Review of Survey activities 2006 (13), 33-36

    The western margin of the Greenland craton has been much

    less stable in the Phanerozoic than previously thought. This

    new insight has come from close integration of independent

    data sets: geomorphological analysis of large-scale landscapes,

    apatite fission track analysis (AFTA), onshore and offshore

    stratigraphy and analysis of onshore fault and fracture sys -

    tems. Each data set records specific and unique parts of the

    event chronology and is equally important to establish a con-

    sistent model. A key area for understanding the Mesozoic-

    Cenozoic landscape evolution and into the present is the

    uplifted part of the Nuussuaq Basin, where remnants of pla-

    nation surfaces cut across the Cretaceous to Eocene sedimen-

    tary and volcanic rocks. Our integrated analysis concluded

    that the West Greenland mountains were formed by late

    Neogene tectonic uplift (Fig. 1) and also provided new

    insight into early Phanerozoic development. To understand

    our model, we present the different methods and the results

    that can be deduced from them.

  • 2009. Karna Lidmar-Bergström, Johan Mauritz Bonow. Journal of Geodynamics 48, 95-100
  • 2007. Karna Lidmar-Bergström (et al.). Norwegian Journal of Geology 87 (1 & 2), 181-196

    The geometry of major bedrock landforms in a central part of the Northern Scandes has been examined for interpretation of landforming events and their chronology. Analysis of palaeosurfaces and palaeovalleys was undertaken based on digital elevation data. Four major landscape generations, governed by different base levels, were reconstructed within the mountains. In the east the generations more or less merge and form plains with residual hills. The configuration of the landscape generations suggests an asymmetrical uplift with maximum uplift in the west caused by discrete events during the Cenozoic and guided by reactivated Mesozoic faults west of the study area. The style and amount of uplift differs from the Southern Scandes and a hinge line is defined in between. The landscape generations were also used for estimations of the amount of glacial/fluvial erosion since the beginning of the Late Cenozoic glaciations. Erosion amounted up to 200 - 400 m in the valleys that hosted the major outlet glaciers, while the eastern plateaux and the plains with residual hills have experienced no or limited glacial erosion.

  • 2006. Johan M. Bonow (et al.). Geomorphology 80 (3-4), 325-337

    Remnants of a high plateau have been identified on Nuussuaq and Disko, central West Greenland. We interpret the plateau as an erosion surface (the summit erosion surface) formed mainly by a fluvial system and graded close to its former base level and subsequently uplifted to its present elevation. It extends over 150 km east–west, being of low relative relief, broken along faults, tilted westwards in the west and eastwards in the east, and having a maximum elevation of ca. 2 km in central Nuussuaq and Disko. The summit erosion surface cuts across Precambrian basement rocks and Paleocene–Eocene lavas, constraining its age to being substantially younger than the last rift event in the Nuussuaq Basin, which took place during the late Maastrichtian and Danian. The geological record shows that the Nuussuaq Basin was subjected to subsidence of several kilometres during Paleocene–Eocene volcanism and was transgressed by the sea later during the Eocene. By comparing with results from apatite fission track analysis and vitrinite reflectance maturity data, it is suggested that formation of the erosion surface was probably triggered by an uplift and erosion event starting between 40 and 30 Ma. Surface formation was completed prior to an uplift event that started between 11 and 10 Ma and caused valley incision. This generation of valleys graded to the new base level and formed a lower erosion surface, at most 1 km below the summit erosion surface, thus indicating the magnitude of its uplift. Formation of this generation of valleys was interrupted by a third uplift event also with a magnitude of 1 km that lifted the landscape to near its present position. Correlation with the fission-track record suggests that this uplift event started between 7 and 2 Ma. Uplift must have been caused initially by tectonism. Isostatic compensation due to erosion and loading and unloading of ice sheets has added to the magnitude of uplift but have not significantly altered the configuration of the surface. It is concluded that the elevations of palaeosurfaces (surfaces not in accordance with present climate or tectonic conditions) on West Greenland's passive margin can be used to define the magnitude and lateral variations of Neogene uplift events. The striking similarity between the landforms in West Greenland and those on many other passive margins is also noted.

  • 2007. Johan M. Bonow (et al.). Norwegian Journal of Geology 87, 197-206

    Elevated erosion surfaces were used as an independant data set in an integrated study of the landscape development in central West Greenland. The study resulted in a time-constrained model describing multiple episodes of post-rift uplift, erosion and burial on a passive margin. The model is based on full integration of three data sets: analysis of large-scale landforms, apatite fission track analysis (AFTA) of samples from outcrops and deep boreholes, and the geological record. These data are equally important as they record specific an unique parts of the landscape history. The relative chronology obtained from the landform record is constrained by geology, which gives the maximum age of an erosin surface, and AFTA that records the cooling history of the subsurface rock. This combined approach validates the interpretation of erosion surface as having been goverened by different base levels in the past, and shows that erosion surfaces can be used to reconstruct tectonic events. Geomorphological key observations for the landscapes of southern Norway are presented and the similarities with landscapes in central West Greenland emphasised, especially the elevated plateaux and the Mesozoic etch surfaces. This similarity suggests that it may be possible to construct a time-constrained model for the landscape development of southern Norway based on our West Greenland approach.

  • 2003. Johan Mauritz Bonow, Karna Lidmar-Bergström, Jens-Ove Näslund. Norsk Geografisk Tidsskrift 57 (2), 83-101
  • 2006. Johan M. Bonow, Karna Lidmar-Bergström, Peter Japsen. Global and Planetary Change 50 (3-4), 161-183

    Landform analysis of basement rocks has been undertaken with the aid of digital elevation data, aerial photographs and field observations in central West Greenland (69°15′N–66°00′N). Palaeosurfaces have been identified, dated relatively to each other, used to quantify uplift and fault movements and also used to estimate differential erosion. Two types of palaeosurfaces were mapped across the Precambrian basement: a surface at low elevation with distinct hills (hilly relief), and two planation surfaces formed across different types of basement rocks. The hilly relief surface emerges as an inclined surface from Cretaceous cover rocks in Disko Bugt and is interpreted as a stripped late Mesozoic etch surface. This surface is cut off towards the south by a less inclined planation surface, which is younger and thus of Cenozoic age. It is similar to the post-Eocene (Miocene?) planation surfaces identified on Disko and Nuussuaq in other studies. The planation surface splits in two southwards towards high areas around Nordre Isortoq and Sukkertoppen Ice Cap. The upper planation surface forms near-summit areas of tectonic blocks dipping in different directions and with different tilts. The uplift centres define the crests of two mega blocks, separated by the ‘Sisimiut Line’ which coincides with the Precambrian Ikertôq thrust zone. A partially developed lower planation surface indicates a first uplift of maximum 500 m followed by a second uplift of maximum 1000 m. We infer that these uplift events occurred during the late Neogene based on correlation with similar surfaces on Nuussuaq and the timing of exhumational events estimated from apatite fission track analyses of samples from a deep borehole on Nuussuaq (reported elsewhere). The difference between a reconstruction of the upper planation surface across the entire area and the present topography was used as an estimate of erosion of basement rock since the formation of the upper planation surface. The erosion is unevenly distributed and varies from almost none on the well-preserved planation surfaces to 800–1300 m along valleys, and even more in the fjords. Erosion is less within areas of gneiss in granulite facies, than in areas of gneiss in amphibolite facies.

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Senast uppdaterad: 23 oktober 2018

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