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Palaeosurfaces and palaeovalleys on North Atlantic previously glaciated passive margins

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Palaeosurfaces and palaeovalleys on North Atlantic previously glaciated passive margins-

reference forms for conclusions on uplift and erosion

Johan Mauritz Bonow

Keywords: palaeosurface, palaeovalley, uplift, valley, incision, glacial erosion, weathering, Neogene, southern Norway, West Greenland

AbstractPalaeosurfaces and palaeovalleys are landforms under destruction in the present climate and/or tectonic regime, and thus mainly reflect processes not active today. Uplifted palaeo-surfaces exist along the formerly glaciated passive continental margins around the North Atlantic. Large-scale landform development has recently become a matter of interest also for geologists and geophysicists as the result of an increasing awareness that a thorough know-ledge of uplift, erosion, deposition and development of landforms along continental margins can only be accomplished by combined studies using independent data from different sci-entific disciplines. The present study focuses on one of these above data sets; the landform record. Two uplifted areas, southern Norway and central West Greenland, were selected for landform analysis of high resolution digital elevation models, aerial photographs, relation between landforms in basement and cover rocks, offshore seismic lines and X-ray diffraction of clay minerals in saprolites.

In southern Norway, analysis of slope angles within the range of pediment slopes was combined with analysis of main valley incision. This resulted in the identification of three main planation surfaces in a stepped sequence formed along the main valleys as a conse-quence of tectonic uplift events, maybe in the Palaeogene, (in total >1000 m). Two phases of late uplift (~900 m), probably in the Neogene, triggered incision of deep fluvial valleys, later reshaped by glacial erosion (up to 300 m).

In central West Greenland palaeosurfaces were analysed in relation to cover rock of dif-ferent age. An exhumed etch surface, characterized by a typical hilly relief, occurs on Disko and south of Disko Bugt, and are by the presence of cover rocks shown to be sub-Palaeocene in origin. To the north, a post-Eocene erosion surface on Nuussuaq, cuts across basement and basalt and was probably formed close to sea level. Uplift in two phases elevated this surface up to 2000 m above present sea level and broke it in differently tilted tectonic blocks. South of Disko Bugt, a planation surface, of probably the same age as the one on Nuussuaq, cuts the tilted etch surface, and also cuts across different bedrock types. The planation sur-face rises towards the south and splits in two surfaces, separated in altitude up to 300 m, within two highly elevated areas. The separation into two surfaces indicate two uplift events: A first minor event of a few hundred metres in the uplift centres resulted in incision of the lower planation surface. This event was later followed by a major uplift event amounting to >1000 m. Correlation with the offshore sedimentary record suggests that both uplift events occurred in the Neogene. The erosion pattern calculated from one reconstructed palaeosur-face to present topography shows large spatial variations. This is interpreted as an effect of differential bedrock resistance and local variations of glacial erosion (400–1300 m in low areas).

The results presented in this thesis demonstrate the usefulness of palaeosurfaces and pa-laeovalleys as tools for deciphering magnitude of uplift events, establishing relative event ch-ronologies and for calculation of erosion. Moreover integrated studies of palaeolandforms, offshore geology and thermal chronologies, are shown to be invaluable when used to solve the spatial and temporal patterns of uplift, erosion and deposition.

J. M. Bonow

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© 2004 Johan M. BonowISSN 1650–4992ISBN 91–7265–876–2Layout: Johan M. Bonow (exept Paper I)Front Cover: A well preseved planation surface south of Sukkertoppen Iskappe, West Greenland.

Detail from oblique aerial photograph 507B–S–51, 1948.©Kort & Matrikelstyrelsen, Denmark.

Printed in Sweden: Intellecta DocuSys AB, Sollentuna, 2004.

Doctoral Dissertation 2004Department of Physical Geography and Quaternary GeologyStockholm University


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Palaeosurfaces and palaeovalleys on North Atlantic previously glaciated passive margins-

reference forms for conclusions on uplift and erosion

Johan Mauritz Bonow

The doctoral thesis consists of this summary and the following four papers:

Paper I.Bonow, J.M., Lidmar-Bergström, K., Näslund, J-O., 2003. Palaeosurfaces and major valleys

in the area of Kjølen Mountains, southern Norway–consequences of uplift and climatic change. Norsk Geografisk TidsskriftNorsk Geografisk Tidsskrift–Norsk Geografisk Tidsskrift–Norsk Geografisk Tidsskrift Norwegian Journal of GeographyNorwegian Journal of Geography 57, 83–101.

Paper II.Bonow, J.M., Re-exposed basement landforms in the Disko region, West Greenland– basic data

for estimation of glacial erosion and uplift modelling. Submitted to Geomorphology.Submitted to Geomorphology.

Paper III.Bonow, J.M., Japsen, P., Lidmar-Bergström, K., Cenozoic uplift of Nuussuaq and Disko, West

Greenland – a preliminary interpretation of landforms. Submitted to Geomorphology.Submitted to Geomorphology.

Paper IV.Bonow, J.M., Lidmar-Bergström, K., Japsen, P., Palaeosurfaces in central West Greenland

as reference for identification of tectonic movements and estimations of glacial erosion. Submitted to Global and Planetary ChangeSubmitted to Global and Planetary Change.

In this summary the papers are referenced to by the above roman numbers.

Karna Lidmar-Bergström initiated the project described in paper I, while the mapping, ana-lysis of digital elevation data, interpretation of aerial photographs, fieldwork and majority of the writing of the manuscript was done by myself. Lidmar-Bergström assisted with the analysis and outlined parts of the paper, which were later developed and extended by me. Jens-Ove Näslund contributed with a regional map (Fig. 2).

The idea, the analysis, field work and the writing of paper II was done by me. Karna Lidmar-Bergström, Jens-Ove Näslund and Clas Hättestrand provided valuable comments to the manuscript.

The initial idea to paper III, initial writing and field work was equally shared between Peter Japsen and myself. I prepared the DEM, made the maps and topographical profiles and made the first landform analysis. Japsen compiled the geology in profiles and made aerial photographs available. Lidmar-Bergström made a more detailed landform analysis, iden-tified the palaeodrainage systems and together we formulated the final text. Näslund and Hättestrand provided valuable comments to the manuscript.

Paper IV was initiated by Lidmar-Bergström and myself. I prepared the DEM, prepared the initial maps and wrote the manuscript. Palaeosurface analysis was jointly initiated by Lidmar-Bergström and me. I finished the analysis of palaeosurfaces, interpreted aerial pho-tographs and constructed maps and profiles. Lidmar-Bergström assisted with structure of the paper and outlined parts of it. Peter Japsen contributed to the regional interpretation in the discussion. Näslund and Hättestrand provided valuable comments to the manuscript.

Söderstadion, April 2004Johan Bonow

J. M. Bonow

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IntroductionEvolution of large bedrock landforms along passive conti-nental margins has recently become an increasingly interes-ting topic for geologists and geophysicists as well as for geo-morphologists (Japsen and Chalmers, 2000; Summerfield, 2000; Doré et al., 2002). A wide spectrum of methods has previously been used to investigate uplift, erosion and de-position. Such methods include studies on e.g., geomor-phology, fission tracks, sediment supply and structural relations, although commonly carried out separately. An increasing awareness has emerged, realizing that a com-prehensive understanding of uplift, erosion, deposition and landform development can only be achieved by integrated studies. In addition, it is most important that these studies are based on independent data and analysed separately to avoid circular arguments. The present study use analysis of large landforms for conclusions on long-term landform development, uplift, valley incision and estimations of ero-sion. The aim of the thesis is to show the usefulness of land-form analysis in a geological and geophysical context.

Choice of study areas and topicsDuring the last 50 years a few Swedish theses have dealt with pre-Quaternary evolution of landforms. Rudberg (1954) and Ängeby (1955) mapped stepped erosion sur-faces in the mountains, Mattson (1962) and Lidmar-Bergström (1982) emphasized the importance of exhumed landscapes and palaeo-weathering for present landscapes, while Johansson (2000) focussed on the relations between palaeo-landforms, tectonics and glacial erosion. Two areas have been selected as study areas for the present investiga-tion, a part of central southern Norway and central West Greenland (Fig. 1).

Southern NorwayKarna Lidmar-Bergström had worked for a long time with large landforms in Sweden (e.g., Lidmar-Bergström, 1982, 1988, 1995, 1996; Lidmar-Bergström et al., 1997), but had shifted her interest to southern Norway with its ‘palaeo-surfaces’ at high elevation (Lidmar-Bergström et al., 2000; Fig. 2). The established opinion regarding large landforms in southern Norway was the view of Gjessing (1967). He regarded the high undulating plains, the paleic surface as one single surface developed by deep weathering, unrelated to a general base level. Gjessing described the high plains as hills and basins interconnected by passes. The slopes from the hilltops to the basins were described as consisting of a steep slope, followed by a sharp knick and ending with a pediment-like surface stretching towards the edge of the basin.

Lidmar-Bergström had used a generalized contour map over southern Norway to get an overview of the large land-forms (Lidmar-Bergström et al., 2000). The maps showed regularly spaced stepped surfaces, which were tentatively interpreted to have formed by fluvial processes in response to uplift. The exact appearance of surfaces and valley sys-tems were not known. A project for a MSc-degree was launched regarding the long term landform evolution in southern Norway. I studied bedrock surfaces and valleys along Gudbrandsdalen valley and made a relative chronol-ogy based on these landforms (Bonow, 1997). This initiated the PhD project, which first focused on how etch processes had affected the development of surfaces and how the rela-tive effect between fluvial incision and glacial erosion was

for the formation of valleys in the same area as I previously worked in. The project aimed at deciphering the develop-ment of the undulating, highly situated ‘palaeosurface’ and the deeply incised valleys. Was surface development mainly controlled by climate and caused by deep weathering and pedimentation, as suggested by Gjessing (1967), or was it a result of tectonic uplift and fluvial landform develop-ment (e.g., Reusch, 1901; Strøm, 1945; Holtedahl, 1960; Lidmar-Bergström et al., 2000)? The use of a Digital Eleva-tion Model (DEM) ought to give more objective descrip-tions of the landforms than early researchers could make. The chosen area has only been moderately affected by gla-cial erosion (Sollid and Sørbel, 1994) and thus the preser-vation of ‘palaeorelief’ was expected to be good compared to other areas of southern Norway.

The first part of the PhD project focused on the relative importance of different processes forming the landscape. The landform studies confirmed the conclusion by Lidmar-Bergström et al. (2000), that there is a regular appearance of stepped surfaces at high elevation, separated from deep-ly incised valleys. Furthermore that the large landforms in southern Norway were found to be mainly a result of fluvial landform development, induced by tectonic uplift events (Bonow, 2001).

West GreenlandThe focus of the thesis shifted during work to the use of ’pa-laeosurfaces’ as reference surfaces for calculations of uplift and erosion. Through my supervisor I also got the opportu-nity to take part in a project launched by GEUS (Geological Survey of Denmark and Greenland). The project “Neogene uplift, erosion and redeposition in West Greenland – Iden-tification of pre-glacial landforms and neotectonic activity” was under leadership of senior research geophysicist Dr Scient. Peter Japsen.

The development of large-scale landforms in West Greenland has largely been neglected. The landscape has only been described in the terms of differential glacial ero-sion (e.g., Sugden, 1972, 1974; Gordon, 1981; Sugden et al., 1987). The study area (Fig. 3) is characterised by high plateaus both in the north (Nuussuaq and Disko) and in the south around Angujaatorfiup Nunaa and the Sukkertop-pen Iskappe (ice cap). A basin area in-between these two high areas is occupied by Disko Bugt (bay). The highest areas are in the west with summits reaching above 2000 m a.s.l. on Nuussuaq. In the south there is a great escarpment along the coast with a narrow strandflat. Towards north, the topography drops in altitude and the escarpment fades away. The landscape immediately south of the Disko Bugt is dominated by an archipelago. The Jakobshavn Isbrae dis-charges 10% of the yearly iceberg production of the Green-land ice sheet into the Disko Bugt (Weidick, 2000). The present fjord has been the major drainage outlet for rivers of a watershed draining the major part of southern and central Greenland that has been functioning at least since the Cretaceous (Funder, 1989, 2000; Dam et al., 1998).

Neogene uplift of the North Atlantic margins– a short summary of ideasIn general the passive continental margins around the North Atlantic are characterized by high rims with steep coasts forming great escarpments (Jessen, 1948; Fig. 1). These characteristics are similar to passive continental mar-gins elsewhere: e.g., eastern Australia (Ollier, 1982; Bishop


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Pre-Quaternary Geology of theNorth Atlantic domain

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Fig. 1. The North Atlantic domain and the passive continental margins. Palaeogene sequences are truncated along the margins. After Japsen and Chalmers (2000).

et al., 1985; Seidl et al., 1996), western India (Gunnel and Fleitout, 2000), and southern Africa (King, 1976; Partridge and Maud, 1987; Cockburn et al., 2000; Van der Wateren and Dunai, 2001).

The passive continental margins around the North At-lantic have experienced uplift during the Neogene (Japsen and Chalmers, 2000; Doré et al., 2002, Fig. 1). In Norway, uplift was first recognized and described by geomorpholo-gists based on the observation of the distinct difference be-tween highly situated erosion surfaces and deeply incised valleys (Reusch, 1901; Wråk, 1908; Ahlmann, 1919; Fig. 2). Reusch named the elevated surface, the Palaeic surface (cf. Gjessing, 1967). Holtedahl (1953) compared southern Norway and Baffin Island (eastern Canada) and regarded both areas as tilted blocks. Geomorphologists continued to study the passive margins of the North Atlantic and based conclusions on uplift mainly on the appearance of land-forms (e.g., Bretz 1935; Ahlmann, 1941a, 1941b; Linton 1951; Godard, 1965; George, 1966; Brookes 1977, 1993; Brooks 1985).

Spjeldnæs (1975) studied the Tertiary sediments in Denmark and interpreted the influx of terrigenous mate-rial as a result of sharpened relief of Fennoscandia through the Miocene and the Pliocene. The sedimentary sequences, below the Plio-Pleistocene wedges, offshore southern and central Norway (Jensen and Schmidt, 1992, 1993; Stuevold et al., 1992; Stuevold and Eldholm, 1996) showed steep-ened dips and with the oldest sediments along the continen-tal margin (Fig. 1). This was interpreted as a consequence

of Neogene uplift of southern Norway. In several studies landforms were used together with the offshore record to decipher the geomorphological evolution (Peulvast, 1985, 1988; Le Coeur, 1988; Hall, 1991, Peulvast et al., 1996; Hall and Bishop, 2002; Lidmar-Bergström et al., 2000; Lidmar-Bergström and Näslund, 2002).

Along a traverse across northern Scandinavia, samples were taken for geothermochronological studies, which re-sulted in conclusions on a continuous tilt and uplift since the Cretaceous/Paleocene boundary (Hendriks, 2003). The uplifted margins around the North Atlantic have all been under influence of cold climates and glacial erosion, which further complicate the interpretation of the landform his-tory, compared to non-glaciated continental margins (cf. Lidmar-Bergström et al., 2000).

Mesozoic–Palaeogene tectonic developmentSouthern Norway consists of Precambrian and Palaeozoic rocks reworked during the Caledonian orogeny (Sigmond, 1992), while central West Greenland belongs to a Precam-brian shield (GGU, 1971; Henriksen et al., 2000) separated from North America by Mesozoic rifting and Early Tertiary commencement of sea floor spreading (Chalmers and Pul-vertaft, 2001). Southern Norway and central West Green-land are surrounded by tectonic basins, which are filled with Mesozoic and Tertiary sedimentary sequences, earlier covering larger areas.

J. M. Bonow

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Fig. 2. Topography of southern Norway. Deeply incised valleys are cut in the margins of the Palaeic relief.

Southern NorwayThe Caledonian basement of southern Norway has a posi-tion between intracratonic rift systems along the Oslo rift and in the North Sea, active during the Permian-Mesozoic (Ziegler, 1990) and the Møre-Trøndelag fault zone, reacti-vated during the Jurassic and Cretaceous (Doré et al., 1999). The bedrock is dominated by less reworked Precambrian rocks in the west while Caledonian nappes with Palaeozoic rocks, thrusted eastwards, dominate in the east (Sigmond, 1992). The Caledonian relief was completely removed after a Jurassic-Triassic erosional event (Rohrman et al., 1995). It is postulated that the end result of this erosion event was a low relief surface (Riis, 1996), which was transgressed during the Mesozoic to an unknown extent (Jensen and Schmidt, 1993; Riis, 1996). Southern Norway has mainly been above sea level since the Paleocene (Ziegler, 1990; Jordt et al, 1995). Mesozoic outliers are encountered along the Norwegian coast, but not in the study area of paper I.

West GreenlandWest Greenland consists of a crystalline Archaean craton, partly reworked during the early Proterozoic (Escher and Watt, 1976; Henriksen et al., 2000). The Precambrian ba-sement dips down beneath 1–2 km thick Cretaceous strata

in the Disko Bugt (Fig. 4). Cretaceous bedrock is also pre-sent on eastern Disko, on Nuussuaq and offshore north of Nuussuaq, with an eastern limit along the Cretaceous Boundary Fault System (Chalmers et al., 1999). The Pre-cambrian basement, onshore and offshore, is in certain places weathered beneath the Cretaceous and Palaeogene strata to a kaolinitic saprolite (Pulvertaft, 1979; Bate 1997; Paper II). On West Greenland, Cretaceous and Palaeogene rocks rest directly on basement in the northern parts of the study area.

Aims of the studyLandforms in general represent the net result of proces-ses acting over a certain time frame. Large landforms in basement rocks may represent present processes and cli-mate, but usually may have inherited forms from several different process systems of landform formation (Thornes and Brunsden 1977; Brunsden, 1993; Ahnert, 1994 1998, Godard et al., 2001a). The general aims of this thesis is to1) evaluate the relative importance of etch processes, fluvial

incision and glacial erosion for landform formation in different scales.


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DefinitionsThe identification of denudation surfaces of different kinds is crucial for studies of relative denudation chronologies. There are several terms used by different authors, some of them are just descriptive, while other terms denote a special origin of the surface. The terms have been used differently by different authors and there is much confusion. It is the-refore necessary to define how they are used. A review of the definitions and the terminology used within the field of large-scale landform development in Fennoscandia is in preparation by Ebert and Näslund (in prep.).

An erosion surface is a fairly flat surface formed by ero-sion. An erosion surface can be structurally controlled, cut across a resistant sedimentary layer, or it can be guided by some sort of base level; local, regional or the sea. Erosion surfaces can cut across both fresh and weathered rock. A true erosion surface is guided by some sort of base level.

Peneplain (almost level plain) (Davis, 1899) denotes a surface of low relief, the end result of the fluvial cycle of erosion. In the Davis’ model the entire landscape is affected simultaneously. Initial uplift is postulated and followed by valley incision and slope decline of valley sides. Twidale (1976) noted that the Davis model can not describe the de-velopment of multicyclic landscapes. Yet this model was used before 1960 to explain erosion surfaces in stepped se-quences (Belbin, 1985). Fairbridge and Finkl (1980) argued for the use of the word peneplain in Davis’ original defini-tion as “an almost featureless plain showing little sympathy to structure, and controlled by a close approach to base level”, but without any other aspects on the way slopes had developed. This latter meaning equals the use of the term true erosion surface.

In central Europe, surfaces in stepped sequences have long been identified. Penck (1924) considered their devel-opment to reflect accelerating tectonic uplift resulting in the formation of a series of surfaces, piedemonttreppen, along the margins of the uplifted primary surface. (King, 1951, 1953, 1967, 1976) used stepped surfaces in southern Africa and other parts of the world for reconstruction of tectonic events in relation to continental break up. In his model surfaces in stepped sequences are formed by valley incision and scarp retreat. King called the surface formed a pediplain, and the process pediplanation. The concept of slope retreat, in contrast to Davis’ slope decline is similar to the theories of Penck. This idea is currently maintained by Ahnert (1982, 1998), Demoulin (1995), Huguet (1996), and in this thesis (Paper I). The concept of base level is valid also for pediplain formation, but local base levels are often considered (e.g., Ahnert, 1982).

The word planation is sometimes used synonymous-ly with pediplanation (Mayhew, 1997), but the concept planation surface is often used to denote a level plain re-gardless of origin (Adams, 1975; Godard et al., 2001b).

An etch plain or etch surface is a surface across bedrock and saprolite (Wayland, 1933; Büdel, 1957; Thomas, 1966; Migon and Lidmar-Bergström, 2001). When the saprolite is stripped, occasionally over prolonged periods of inter-

mittent stripping and deep weathering, an irregular weath-ering front is exposed, a stripped etch surface, which can have considerable relative relief, up to several hundreds of metres (Thomas, 1966; Lidmar-Bergström, 1995). Erosion of the saprolite occurs by surface wash in semiarid areas (Büdel, 1957; Mensching, 1970; Young, 1972) and in con-nection with pedimentation at the foot of the inselbergs. Se-ries of pediment steps can be recognized on the flanks of in-selbergs (Büdel, 1970). If the saprolite has been successively stripped the combination of etching and stripping leads to a surface that is related to a pediplain (cf. Mabbutt, 1961), as it is the local base level that is decisive for its position. Much confusion emanates from the mixing between the terms etch plain and pediplain. Totally stripped etch sur-faces are only met with in formerly glaciated areas (Lidmar-

2) identify and map ‘palaeosurfaces’ and ‘palaeovalleys’ on two formerly glaciated continental margins, southern Norway and West Greenland.

3) reconstruct the geomorphological development with the aid of these landforms and establish a relative chronology of uplift and incision.

4) use the ‘palaeoforms’ as reference forms for calculations of erosion and uplift.

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Fig. 3. Topography of central West Greenland. A-Angujaa-torfiup Nunaa, D-Disko, Nu-Nuussuaq, S-Sisimiut, Sv-Svar-tenhuk, Fjords: N-Nassuttooq, K-Kangerlussuaq, NI-Nordre Isortoq.

J. M. Bonow

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Bergström et al., 1997; Olvmo et al., 1999; Johansson et al., 2001; Paper II).

Exhumed or re-exposed surfaces are common phe-nomena on oldlands (Demoulin, 1995; Lidmar-Bergström, 1995, 1996; Peulvast et al., 1996; Twidale, 1999; Hall and Bishop 2002). Oldlands are complex surfaces on Precam-brian shields and cratons (Twidale, 1999). Within the Baltic and Laurentian shields there are two different kinds of re-exposed surfaces. First, there are extremely flat surfaces exhumed from below Lower Paleozoic cover rocks, e.g., sub-Cambrian in Fennoscandia (Rudberg, 1954; Lidmar-Bergström, 1996) and sub-Ordovician in Canada (Ambrose, 1964; Bouchard and Jolicoeur, 2000). Second, there are sur-faces exhumed from Mesozoic cover rocks. These surfaces are characterized by remnants of thick kaolinitc saprolites and a hilly topography caused by deep weathering and sub-sequent stripping, an etch surface (Lidmar-Bergström 1982, 1989, 1995; Bouchard and Jolicoeur, 2000).

Palaeosurface is often used for a surface with saprolite remnants, and which is under destruction and not develop-ing under present conditions. Their former wider extent is often possible to reconstruct (cf. Widdowson, 1997). There are two criteria defining a palaeosurface: First, it is a sur-face in conflict with present climatic conditions. Second it has developed prior to a tectonic event. In the latter case the surface was either uplifted and has experienced both partial destruction and some further development or the surface is down faulted, buried, and later exhumed. Only one of the criteria is necessary for using the term palaeosurface, but often both criteria are involved. The palaeic (Reusch, 1901; Ahlmann, 1919) or paleic (Gjessing, 1967) surface in Norway is also a surface, which is not developing at present. The first two authors had the opinion that it had developed before an uplift, and thus the term primarily denotes a pre-uplift surface, while Gjessing stressed its formation in a warm climate by deep weathering and pedimentation.

Envelope surface is used to denote an imagined surface across summits. It is postulated to approximately denote remnants of a surface that is gone (Gjessing, 1967; Hall, 1991; Lidmar-Bergström et al., 2000). Even if it seems im-aginary it can be useful in general discussions.

In this thesis I have used the term denudation surface as a general term, embracing two types of surfaces across basement rocks: 1) a surface with hilly relief, interpreted as an etch surface and 2) surfaces with planar relief, planation surfaces. They are all palaeosurfaces and at present under destruction. I have also used the term envelope surface de-noting something more abstract, but still of value for the discussion of landform development. Erosion surface is also used as a general term for the uplifted palaeosurface on Nuussuaq and Disko.

MethodsLandform analysis has been based on the following met-hods:1) Construction of maps and profiles from high resolution

digital elevation data. 2) Mapping of lineaments and bedrock hills from aerial

photographs. 3) Analysis of the relation between landforms and bedrock

lithology and structure. 4) Interpretation of basement landforms in offshore seismic

lines.5) Field inventories of saprolites and bedrock forms.6) Analysis of clay minerals in saprolites.

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Fig. 4. Basement/cover rock in central West Greenland. Geol-ogy after Chalmers and Pulvertaft (2001) and Pulvertaft and Larsen (2002).

Digital elevation modelsIn the text it was stated that Digital Elevation Models (DEM) ought to give more objective description of land-forms than traditional methods using field observations and poor elevation data. Is this true? The interpretation of landforms is subjective, which may lead to different results depending on the interpreter. How data points are selected may also be highly subjective and the subsequent interpre-tation will be different depending on the quality and den-


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sity of the grid. The way interpolation and transformation of data are made also affect the results (e.g., change of pro-jection, moving DEM between different software’s etc).

In this study I have used Digital elevation models with grid sizes from 8 m to 1 km. In 8 m grids, minor errors are seen immediately, while in 1 km data sets valleys may com-pletely ‘disappear’. It is very important to use a grid size that fit the purpose with the analysis (e.g., Hall, 2002). For analysis of large-scale bedrock landforms I have found that moderate DEM resolutions are the most suitable, ranging from 100–250 m in detailed scale and up to 500 m in more general scale. Too densely spaced grids contain a lot of in-formation of no use for the analysis of large landforms, and may actually make the interpretation more difficult.

The main topics of the papers were to 1) map palaeosurfaces (Paper I, IV).2) examine the forms of major incised valleys (I).3) analyse the origin of palaeoforms (I, II, IV).4) establish relative chronologies for erosional events based

on landform analysis (I, II, III, IV).5) draw conclusions on tectonic movements from the

palaeoforms (I, III, IV).6) calculate erosion with palaeosurfaces as reference

(I, IV).7) evaluate glacial erosion from the reconstructed

palaeoforms (I, II, IV).

Presentation of papersI. Bonow, J.M., Lidmar-Bergström, K., Näslund, J-O.,

2003. Palaeosurfaces and major valleys in the area of Kjølen Mountains, southern Norway - consequences of uplift and climatic change. Norsk Geografisk Tidsskrift Norsk Geografisk Tidsskrift –Norwegian Journal of GeographyNorwegian Journal of Geography 57, 83-101.

In this paper we tested if the stepped surfaces mapped from overview maps by Lidmar-Bergström et al., (2000) could also be mapped in detail in an area along the Gudbrands-dalen valley in southern Norway (Figs 1; 2). The study area was selected because it had vast undissected plateau areas, and the area had been described by Sollid and Sørbel (1994) as one of the least affected areas of glacial erosion in Norway. The landforms were analysed by a digital eleva-tion model (DEM), profiles and aerial photographs. The landforms were checked against bedrock structures.

Stepped palaeosurfaces, separated by distinct slopes, were mapped from the DEM. The palaeosurfaces occur above 900 m a.s.l.. Their regular altitudinal appearance in-dicated that their formation was guided by a general base level, and weathering remnants show that they formed in a warmer climate than present. Thus pediplanation can be used as a term for their formation.

The fluvial incision of main valleys can be reconstruc-ted to have occurred in two phases. It was concluded that the study area consists of stepped surfaces resulting from mainly fluvial processes in response to older uplift events, maybe Palaeogene, and that the successive incision of main valleys was triggered by tectonic uplift, probably in the Neogene.

The identification of palaeosurfaces and palaeovalleys made it possible to calculate glacial erosion, which in pla-ces lowered the surfaces up to 100 metres. Glacial erosion has also widened the main valleys from their fluvial form up to 1500 metres and deepened them between 110 and 320 meters.

II. Bonow, J.M., Re-exposed basement landforms in the Disko region, West Greenland–Disko region, West Greenland–Disko region, West Greenland basic data for estimation of glacial erosion and uplift modelling. Submitted to Geomorphology.Geomorphology.

A basement surface on southern Disko, which is re-expo-sed from protective basalt of Paleocene age, is the focus of this study (Fig. 4). There had earlier been reports of weathered basement at the contact with the basalt (Clark and Pedersen, 1976, Møller-Nielsen, 1985). Hills in the basement were mapped together with lineaments from ae-rial photographs. A detailed DEM with 8 m resolution was used to create contour maps. Field work included inven-tory and sampling of saprolites, inventory of clefts, docu-mentation of weathering forms as well as documentation of glacial impact. XRD-analysis was conducted on the fine fraction of the saprolites. Basement hills were interpreted in offshore seismic lines.

The documentation of saprolites, corestones and clefts with weathered joints, shows the importance of weathering processes prior to the basalt flows in the Paleocene for the present forms. The glacial erosion has only affected rock surfaces in stoss side positions, but weathered forms are well preserved in protected positions. Glacial erosion has given the final shape of rock knobs, but joints and weather-ing along joints have been decisive for the shaping of indi-vidual forms.

At the landscape scale, the basement surface consists of hills up to 100 m high, which are limited by fracture zones. Hills of similar height were also identified offshore. Thus, the forms of the basement surface away from the basalt cover and the saprolite remnants, in spite of glacial erosion of the saprolite and some reshaping, is interpreted as a re-exposed etch surface, characterized by hilly relief, with an origin in pre-Paleocene time. It has characteristics which are similar to other stripped etch surfaces on the northern hemisphere shields.

III. Bonow, J.M., Japsen, P., Lidmar-Bergström, K., Cenozoic uplift of Nuussuaq and Disko, West Greenland – a preliminary interpretation of landforms. Submitted to Geomorphology.to Geomorphology.

Both Nuussuaq and Disko have high elevated summit plains, and on Nuussuaq the plain cut across Precambrian and Pa-laeogene volcanic rocks (Figs 3; 4; Japsen et al., 2002). A DEM was used to create contour maps, topographical pro-files and a map of flat surfaces. The profiles were combined with onshore and offshore geology. Oblique photographs were used to support the interpretation of profiles.

The study resulted in the identification of remnants of a vast erosion surface, at 500 metres above present sea level in the east and rising to over 2000 m a.s.l. in central Nuus-suaq. In the west the summit plain on both Nuussuaq and Disko dips towards the west. Remnants of a lower plateau were identified along the rims of the main valleys at 1000 m a.s.l. in the west and sloping to 500 m a.s.l in the east. A southeast heading palaeodrainage system could be con-nected to the lower plateau, and with a direction opposite to the present drainage. The interpretation of the palaeod-rainage was supported by the erosional pattern of the ba-salt cover.

A relative event chronology could be established. A post-Eocene erosion surface was developed and its final formation is suggested to be Oligocene or early Miocene by correlation with offshore data. A first uplift of the erosion

J. M. Bonow

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surface was in the order of 1000 metres in the area of maxi-mum uplift, and the surface was broken and tilted in dif-ferent directions. Uplift triggered incision of a SE-heading drainage system. A second uplift phase of almost the same magnitude combined with further tilting of tectonic blocks resulted in renewed fluvial valley incision, followed by gla-cial erosion resulting in the present relief, and re-arranging the drainage system to the west.

IV. Bonow, J.M., Lidmar-Bergström, K., Japsen, P., Palaeosurfaces in central West Greenland as reference for identification of tectonic movements and estimations of glacial erosion. Manuscript prepared for Global and Manuscript prepared for Global and Planetary Change.Planetary Change.

Four palaeosurfaces, i.e. denudation surfaces under de-struction in present climatic and tectonic conditions, have been identified in a landform study in Precambrian base-ment covering the area between Sukkertoppen Iskappe and Disko Bugt, central West Greenland (Fig. 3). A digital elevation model with a 250 metres grid was used to ana-lyse large landforms. The analysis was done in three steps: 1) a first preliminary study to identify different palaeosurfa-ces, 2) detailed mapping to confirm the palaeosurfaces and identify fault blocks, and 3) reconstruction of one specific palaeosurface for calculation of amount of erosion. The palaeosurfaces were mapped on a contour map by support of closely spaced crosscutting profiles, aerial photographs and field visits.

The mapping resulted in the identification of a sum-mit envelope surface, and below that an upper and a lower planation surface within two elevated areas. The palaeo-surfaces are formed across different bedrock types. In the north and east there is only one planation surface. In the northernmost coastal areas, the basement is characterized by structurally controlled hills, forming a hilly relief. The characteristics of the basement surface is typical for stripped etch surfaces found elsewhere. The formation of surfaces can be arranged in a relative chronology. It is possible that the envelope surface may be the last remnants of a sub-Ordovician peneplain. The hilly relief is interpreted to be a sub-Cretaceous or sub-Paleocene etch surface, exhumed from a Cretaceous–Paleocene cover. The planation surface cut the etch surface at low angle and regarded contempo-rary with a regional post-Eocene erosion surface, identified on Nuussuaq. Two uplifted and tilted tectonic mega-blocks are defined by the upper planation surface. They are sepa-rated by a major fault along the ‘Sisimiut Line’. This line coincides with a major Precambrian structure, which was reactivated during block tilting.

The uplifted and broken planation surfaces must each have developed at a low uniform level, probably with fi-nal formation in a semiarid climate. A first uplift in the order of a few hundred metres resulted in incision of the lower planation surface, followed by a major uplift event of more than 1000 metres in the uplift centres. Here up-lift triggered deep valley incision. Further north the uplift resulted in exhumation and stripping of the etch surface. Correlation with offshore data suggests the uplift to have occurred in the Neogene. The incision and development of the lower surface testifies that uplift, at least the first event, occurred prior to late Cenozoic glaciations. Total erosion since uplift was calculated by subtracting present topogra-phy from a reconstruction of the upper planation surface. Erosion amounts 800–1300 metres, and maybe up to 2000

metres in the valleys, close to the coast in-between areas of highest uplift. Erosion down to the lower planation surface level is considered as fluvial, while regarded as both flu-vial and glacial along the main valleys, and mainly glacial where palaeosurfaces are obliterated. Bedrock resistance is stressed as important since granulite gneiss areas preserve planation surfaces better than areas underlain by amphibo-lite gneisses.

The analysis has shown that palaeosurfaces are useful for identification of tectonic movements, for establishing relative uplift chronologies and for calculation of amount of erosion and uplift. The relative chronology suggested here may be correlated with the Cenozoic sedimentary suc-cession offshore and with tectonic episodes identified by analysis of thermal chronologies.

Interpretation of palaeosurfaces and palaeovalleys in previous studies

Modern cyclic modelsEver since the early geomorphologists used landforms for conclusions on uplift, the relevance of landforms as a data set has been questioned (Chorley, 1963). Still there is doubt (e.g., Brown et al., 2000), and an approach in which uplift and erosion is modelled connecting geothermal chronolo-gies with tectonic models is often favoured (Summerfield, 2000).

Despite this criticism, analysis of palaeosurfaces and palaeovalleys are a topic of increasing interest (Japsen and Chalmers, 2000; Doré et al., 2002). Analysis of palaeo-surfaces and palaeovalleys can be used for making conclu-sions of long-term landform development. Main valleys are regarded as persistent features (e.g., Brunsden, 1993; Ahnert, 1994, Hjartarson and Bonow, 2004) and drainage systems have been used as a tool for conclusions on palaeo-surface development and for conclusions on uplift events (e.g., Ollier, 1981; Ahnert, 1982). The strong connection between valleys and surfaces are stressed by several authors in studies. Ahnert (1982, 1998) explains stepped surfaces by multiple uplifts interrupted by long pauses. During each event a planation surface forms adjusted to the new base-level. Streams incise in the upper surface and create slopes down to a new valley bottom, which successively widens by slope retreat and pedimentation. At the river mouth interfluves are reduced and successively obliterated. The valleys are V-shaped in the upper reaches where they are incised in the upper surface. According to Ahnert (1998), two processes are important to explain stepped surfaces: pedimentation at the valley exits and scarp retreat at the valley heads. The planation surfaces hence expand at their upper edge, while they are reduced at their lower edge (see Ahnert, 1982).

Huguet (1996, 1998, 1999) described two generations of pediplain surfaces in the Ardennes, Belgium, and in the Hunrück, southwestern Germany. He showed that the up-per surface was bounded by a cyclic scarp and that the lower surface had formed by pediplanation after a dom-al upheaval. Further uplift in the Plio-Pleistocene created deeply incised valleys. Demoulin (1995, 2003) investigated the palaeosurfaces in the Ardenne-Eifel and interpreted the four youngest stepped surfaces as a result of uplift and tilt-ing. In central Spain seven stepped erosion surfaces, delim-ited by erosional scarps was regarded as formed by uplift


11

and erosion (Casas-Sainz and Cortés-Gracia, 2002). In Canada, United States and in East Greenland, pal-

aeosurfaces have been recognized and their high position today has been interpreted as a result of uplift or eustat-ic fall of sea level (see Brookes, 1977 for references). In Newfoundland summit plains with multiple denudation surfaces of early Cenozoic age are bordered by steep-sided tablelands. These stepped surfaces are interpreted as result of fluvial planation (Brookes, 1977; 1993).

Uplift and differential weatheringIn Scotland Le Coeur (1988) identified tilted lower pla-nation surfaces and concluded that this was a result of Late Neogene movements. Le Coeur discussed differential weathering as an important process in surface formation. Studies in Scotland by Hall (1991) and Hall and Bishop (2002) showed the importance of deep weathering for the present relief in warm and temperate climates in the Early Neogene and in the Mesozoic. Palaeosurfaces on different levels were found to be adjusted to lithology. Migón (1997) regarded palaeosurfaces in the Sudetes (SW Poland) as for-med by weathering and the present levels of the palaeosur-faces in the landscape were explained by faulting.

Peulvast et al., (1996) studied landforms in eastern Canada. Inland, the stepped planation surfaces were limited by escarpments, which were found to be controlled by lito-hology, faults or flexures. At low level, a sub-Carboniferous palaeosurface was recognized emerging from below Car-boniferous strata. It was concluded that the higher pal-aeosurfaces inland reflected late tectonic uplift. Peulvast (1991) looked upon East Greenland as a marginal bulge, with similarities to southern Norway. The surfaces were re-garded as formed by differential weathering. Peulvast iden-tified two uplift events, Eocene and Miocene or later and the morphology at the edge of the highland was regarded as closely connected to these events.

On Nuussuaq, West Greenland, palaeovalleys identified in sedimentary sequences have been used for conclusions on Palaeogene uplift events (Dam et al. 1998, 2002). A pre-viously not recognized younger palaeodrainage system was established by later uplift events, probably in the Neogene (Paper III). Steps in the palaeovalley development suggest two uplift events of c. 1 km each.

Discussion

Palaeovalleys in Norway and inWest GreenlandEarly observations in southern Norway were made of the successive shift of the water divide towards the east (Wråk, 1908; Vogt, 1914; Ahlmann, 1919). Later studies have used this observation for conclusions on uplift (e.g., Holtedahl, 1953; Peulvast, 1985). Valleys in formerly glaciated areas have usually been reshaped by glacial erosion. Papers descri-bing models for valley shape transformation, from V-shaped to U-shaped, are common (e.g., Harbor, 1992; Augustinus, 1995), but knowledge of the initial fluvial shape is often poor. Recently, a few geomorphologists discussed the ‘pre-glacial’ shape and uses geomorphological tools for the ana-lysis of valley development (e.g., Kirkbride and Mathews, 1997; Lidmar-Bergström et al., 2000; Montgomery, 2002). In paper I in this thesis, dealing with southern Norway, we show that a combined analysis of palaeodrainage pattern and valley shape can be used to gain knowledge concerning two specific issues. First, the fluvial incision pattern of a palaeovalley system in two steps could be identified; second the fluvial shape and depth of incision of that palaeovalley could be reconstructed.

Formation of palaeosurfaces in southern Norway and West GreenlandIn the study area in southern Norway three palaeosurfa-ces, separated by distinct slopes, appear regularly along the main incised valleys. The surfaces are therefore interpreted as the result of fluvial incision to successively lowered base level, initiated by uplift, and the surfaces thus initially for-med as valleys-in-valleys (Paper I). This view is different from Gjessing (1967) who regarded the forms to be the result of deep weathering and pedimentation, unrelated to any common base level. This is, however, not a contradic-tory statement as deep weathering during a long time of Palaeogene and Mesozoic exposure clearly has affected the Norwegian landscape. Saprolite remnants and pre-weathe-red material in glacial deposits indicate the importance of weathering (Gjems, 1963; Roaldset, 1972; Rosenqvist, 1975a, 1975b; Roaldset et al., 1982; Rea et al., 1996; Whalley et al., 1997).

Fjellanger and Etzelmüller (2003) showed how weath-ering-resistant rocks have guided the formation of steps between palaeosurfaces in southeastern Norway. Their in-terpretation is slightly different from Bonow et al., (2003) (Paper I), who regard the formation of surfaces tectonically initiated and controlled of a common base level, while the preservation of surfaces are dependant on bedrock resist-ance and lower steps have grown wider across easily erod-ible rocks.

Palaeosurfaces in West Greenland have not been de-scribed previously. Two types of surfaces were identified: exhumed etch surfaces (Paper II, IV) and planation surfaces (Paper III, IV). The surfaces can be correlated regionally and are used for conclusions on landscape development and up-lift. While palaeosurfaces in central southern Norway only tentatively can be correlated with offshore sedimentary records (Lidmar-Bergström et al., 2000), their age in West Greenland are better constrained by the cover rocks of dif-ferent age, which are in direct contact with basement. The West Greenland situation is similar to southern Sweden, where etch and planation surfaces can be dated both ab-solutely and relatively by aid of the cover rocks (Lidmar-Bergström, 1982, 1996).

Estimation of erosionValleysAn analysis of the relative effect of fluvial and glacial ero-sion was made only at the Norwegian study area. It was found that the depth of erosion by valley glaciers from the pre-glacial fluvial valley to the present valley floor was reflected by the surrounding topography. A high source area, i.e. Jotunheimen, have generated valley glaciers for much longer time periods than in areas lacking these high source areas. Similar conclusions were made by Kirkbride and Mathews (1997) in New Zealand and by Montgomery (2002) in northwestern USA.

J. M. Bonow

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SurfacesThe basement surfaces in West Greenland have similar characteristics as a re-exposed etch surfaces in southern Sweden. In southeast Sweden there are areas with preser-ved cover rocks through which basement hills protrude (Lidmar-Bergström, 1989). Outside these covers, deep kaolinitic saprolites locally occur, and a landscape with exhumed hills continues far away from the cover boun-dary. Along the Swedish west coast, further distant from the boundary to the Mesozoic cover rocks, a similar topo-graphy occurs, occasionally with kaolinitc saprolite rem-nants. This area is much more affected by glacial erosion, and the basement has been almost totally stripped from all preglacial saprolites. Glacial erosion has abraded hill tops and plucked the lee sides of the hills (Olvmo et al., 1999, Johansson et al., 2001). Yet the present topography here is best described as a totally stripped etch surface, where the deep weathering, which caused the etching, mainly emana-tes from the Mesozoic.

The summit surfaces in West Greenland are all more or less affected by glacial scouring (Sugden, 1974), and are thus visually similar in character. However, as concluded by Hall and Sugden (1987), not much erosion is needed to reshape a palaeosurface to a surface of glacial scour. By using the mapped palaeosurfaces on a general landscape level as reference, the effect of erosion of basement rocks was evaluated and calculated. The absolute amounts of erosion differed highly across the area. The palaeosurfaces were best preserved in certain rock types, while others had been more prone to erosion. In an area where the planated palaeosurface is located in a comparatively low position the glacial erosion is locally severe and had evacuated up to 400 metres of rock. A typical surface characterized by glacial scour, can thus have been affected very differently by glacial erosion.

Palaeosurfaces for estimation of uplift and tectonic eventsIn Norway several studies have tried to estimate amount of uplift using different techniques. Rohrman et al. (1995) used fission tracks and estimated maximum surface uplift to 1–1.5 km in south central Norway, while Riis (1996) es-timated it to 1000 metres based on correlation with offsho-re data. The palaeosurfaces in southern Norway identified in the present study indicate two main uplift events. First, the stepped relief indicate uplift in the order of 1000 metres in the study area, shown by the height difference within the stepped relief (between ~900–1883 m a.s.l.). This is a minimum value for uplift as outside the study area a higher palaeosurface level exists (Lidmar-Bergström et al., 2000). Second, a late uplift in two phases, indicated by valley ben-ches in Gudbrandsdalen, is in the order of 900 metres or slightly less, i.e. the height difference between the lowest level of the palaeosurface and the present sea level.

In West Greenland, Chalmers (2000) estimated uplift on Nuussuaq to at least 2600 metres, by geometric cor-relation between onshore and offshore strata. Mathiesen (1998) used fission track and maturity data and calculat-ed 2–3 km of erosion in the basalt section. The planation surface observed in the present study must have formed at a uniform base level. At present the surface is situated at c. 2 km above present-day sea level, broken in blocks and tilted in different directions. These observations strongly suggest a tectonic uplift of the palaeosurface.

In the Sukkertoppen Iskappe area the upper planation surface is at c. 1.5 km above present sea level in the uplift

centres, which gives an indication of the total amount of uplift. The height difference between the upper and lower planation surface, a few hundred metres, thus indicate the magnitude of a first uplift event here.

A model of passive continental margin evolutionA model for landform development on passive continental margins is presented in Fig. 5. The model is not intended to give a complete picture of all processes involved, but rather to give an overview of the main processes and features re-levant for the present study. The model summaries the con-ditions described in this study from southern Norway and central West Greenland. Two tectonic uplift events, during the Palaeocene and in the Neogene are thus in mind, with a sequence of stepped surfaces in southern Norway and block tilting in central West Greenland.

Figure (5a) shows the important link between base level and erosion, and that a planation surface forms towards the base level.

Uplift is the main cause for triggering valley incision (Fig. 5b). This critical event can be studied through differ-ent techniques: analysis of palaeosurfaces and palaeoval-leys give the magnitude, fission track studies provides the timing, and offshore records can confirm erosional volumes and constrain timing.

Surface development (through peneplain formation, Ahnert, 1982, 1998) by scarp retreat, widens the valley (Fig. 5c), but the valleys also extend longitudinally by head-ward erosion forming valley-in-valley systems, similar to the developmet suggested for southern Norway. Surfaces are thus oldest at their margins and younger at the valley head.

A new uplift phase trigger a new cycle of stepped sur-faces, and in costal areas new, fast developing and deeply incised valleys may form (Fig. 5d). By reconstructions of palaeosurfaces amount of uplift can be estimated as well as erosion since formation of a palaeosurface (Fig. 5e).

ConclusionsPalaeosurfaces are characteristic and common landscape features fundamental for analysis of long-term landscape development, tectonic development, uplift reconstructions, climate change and where applicable, the impact of late Cenozoic glaciations. Palaeosurfaces are preserved due to different causes. In the study areas, the two most impor-tant factors controlling preservation of palaeosurfaces are their occurrence in highly resistant rocks and the presence of protective cover rocks. During the late Cenozoic gla-ciations, palaeosurfaces survived at high positions also in weaker rocks, due to cold based and non-erosive ice sheets. Palaeosurfaces and palaeovalleys are particularly useful in deciphering tectonic events and their magnitude, especially in areas close or in contact with cover rocks of different age. Identified palaeosurfaces and palaeovalleys can also be used to reconstruct earlier landform configurations and are therefore a useful reference tool for calculation of erosion. In the present study I have shown the usefulness of palaeo-surfaces and palaeovalleys as tools for studies of long-term landform development and shown some of the possibilities for integrated studies of palaeolandforms, offshore geology and thermal chronologies for conclusions on uplift events, erosion, deposition and landscape development.


13

Sedimentation

Total uplift

22

11

Paleosurfaces

Samplepoint(fission track)

Samplepoint(fission track)

ePaleovalley

xx

UpliftUpliftUpliftUplift

Amount ofsecond uplift

Sedimentation22

Fluvial incision andvalley widening

Sedimen

tation

Sedimen

tation

Valleywidening

UpliftUplift

Planation surface

Shallow valley

Amountof uplift

UpliftUplift UpliftUplift

11

Amountof uplift

Sedimentation

Sedimentation

Fluvial valleyincision

Sea level

a

b

c

d

Sedimentati

onSedim

entation

Subsidence

FaultUplift

Basement

SandstoneMudstone

Conglomerate Parallel slope retreat,Sea level

Reconstruction

Amount of uplift

completedprojected

Suggestions for further studiesAn analysis of valley incision on central West Greenland should shed more light on the relative importance of gla-cial and fluvial erosion for valley development. Palaeodrai-nage towards the Disko Bugt was concluded in paper III, but was not investigated in the area south of Disko Bugt (Paper IV). Incision of valleys is triggered by uplift (Ahnert, 1970, Wakabayashi and Sawyer, 2001), and is thus a va-luable tool to decipherer tectonic uplift events. Can a pa-laeodrainage be reconstructed in this area, by aid of the identified palaeosurfaces and the tilt of tectonic blocks? Svartenhuk, north of the studied area is an interesting area for integrated studies of palaeosurfaces, deep weathering and late uplift. Here basalt covers an uplifted basement sur-

b: Differential uplift rises the planation surface, which becomes a tilted palaeosurface. The base level is lowered. Uplift may here be estimated as the height differences between the summit of the palaeosurface and base level, shown in the figure. Uplift triggers valley incision. This erosional event can be seen as onset of coo-ling in analysis of thermal chronologies, e.g., in fission track stu-dies. The incision also increases the sedimentation rate offshore, often with coarser sediment types.

Fig. 5. Schematic sketch of fluvial landform development and tectonic uplift at passive continental margins around the North Atlantic. The model may also be applicable on passive continen-tal margins elsewhere. In addition the figure shows the relation between geomorphological studies of landform development in basement areas, studies of sedimentary offshore records, and geothermal chronology. The sea level is regarded as fixed and the effect of isostatic compensation is not included.

a: Initial low planation surface with shallow valleys. Low offshore sedimentation rates.

c: If tectonic conditions then stabilize, valleys expand and form rock-floored terraces. The newly developed surface expands from the centre of the valleys by pedimentation and parallel scarp re-treat. In this process, fluvial valleys adapt to the new base level (Fig. b) and headward incision contributes to reduction of the pa-laeosurface. Offshore sedimentation rate decreases and finer sedi-ments are again deposited. Subsidence may occur offshore.

d: During and after a second tectonic uplift event, with further block tilting, the main valleys will incise more deeply, and a new valley cycle is initiated, adjusted to the again lowered base level. The valley system develops in a valley-in-valley manner, followed by development of a new surface generation. It is just the upper most surface that only is consumed (also Fig. c). Uplift may also initiate completely new valleys. Sediments offshore are uplifted and subsequently eroded, creating an unconformity. The oldest se-diments are onlapping the coastal areas while younger sediments are deposited in the basins further offshore forming a prograding shelf-margin wedge.

e: The total amount of tectonic uplift can be estimated (1+2). The amount of erosion associated with each uplift event can be esti-mated by reconstructing the palaeosurfaces. The erosion is here described as mainly fluvial, but where applicable it may also be partly glacial.

J. M. Bonow

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face (Pulvertaft and Larsen, 2002), which could be used to establish a relative event chronology. A similar task is pos-sible to perform south of Sukkertoppen Iskappe where vast planation surfaces occur and a hilly relief is present in the coastal areas around Nuuk.

In southern Norway, the main valleys can be remark-able different in appearance such as deep fjords (e.g., Sognefjord) and glacial valleys (Sunndalen), large, deeply incised mainly fluvial valleys (Lærdalen, Aurlandsdalen), glacially deepened paleovalleys (Gudbrandsdalen) and high situated shallow palaeovalleys (Veigdalen, Vermedalen). A study can give interesting results concerning different age of landscape features, and estimations of fluvial and glacial erosion. The changes of the drainage system in relation to uplift and tilting of palaeosurfaces in a long-term context are also of interest. There are also major differences between wide old V-shaped valleys (Lordalen, Nordheringslii), nar-row V-shaped valleys either hanging (Jönndalen) or incised down to glacially deepened valley bottoms (Svartdalen), and numerous of small V-shaped valleys connecting different palaeosurfaces (see Paper I for location). A more detailed mapping of different palaeosurfaces in general in southern Norway is also of interest. Integrated studies with correla-tion of palaeosurfaces with offshore sedimentary records and with thermal chronologies could better constrain the age of surfaces, and thus lead to conclusions when erosion on land occurred.

AcknowledgementsTo complete a thesis one need a lot of support from a great main supervisor, Karna Lidmar-Bergström, and unlimited understanding from the family. Karna, without all your efforts, discussions and the many hours you have spent reading the manuscripts over and over again colouring them in ink, I would never have finished this thesis. You have been very inspiring and enthusiastic and have always found time for discussions. I have enjoyed our various travels and excursions and I am very happy that I got the opportunity to get to know you. Thank you.

I am fortunate to have a large family. Madeleine, I know it has been hard, especially this last year. You have always encouraged me and made our home a place to rest. That has been very important for me. Lovisa and Gustav, at last daddy has finished his book and will now spend more time with you. I also want to thank the rest of the family, who has always been there whenever needed.

Supervisors Clas Hättestrand and Jens-Ove Näslund have been great for discussions, and their thoughtful and provoking comments have significantly improved the papers. Peter Japsen my friend, thank you for your unlimited support and your hospitality. You have a great family. I will always remember our walk-and-talk in West Greenland, which was the time when I really got to know you. I had also great help from Hans Linderholm, who talked and talked and talked forever during fieldwork on Disko. Hasse, thank you, I really enjoyed that trip, but I tell you, watch out for the icebergs….

Knud-Erik Klint, I have not forgotten your multiple invitations for dinner, you are a true chef. Annette Falsvig, thank you for the help with all practical issues, it is actually a true nightmare to order flight tickets to Greenland from Stockholm. I am thankful to Siv Olsson and Vibeke Ernstsen, who carried out XRD-analysis. Jan Sulebak was an excellent guide during a field visit in southern Norway. I have had long discussions with Jakob Fjellanger about palaeosurfaces in Norway, very fun because it is not often anyone can discuss the subject that enthusiastic.

Peter Jansson, the sportsman (it is time to convert to Bajen), Norwayfan and layout master, you have made me laugh many times, thanks. Krister Jansson, Björn Gunnarson, Hans Linderholm and Anders Törnqvist, thank you for big laughs at our numerous coffee breaks when we discussed everything. You all know how to look on the bright side of life. Stefan Ene and Ulf Jansson, thank you for your time assisting with my DEM:s during the project. Furthermore, James Chalmers, Krister Jansson, Peter Kuhry, Wibjörn Karlén, Chris Pulvertaft, Elen Roaldset, Bo Strömberg and Arjen Stroeven have given valuable feedback to various manuscripts.

I would also thank all persons at the Geovetenskapens hus for all the great company, encouragement and help during the years, especially Anna A, Johan Berg, Ingemar, Anders C, Sara, Lisa E, Ola F, Anders F, Håkan, Carina H, Ulf, Stig, Peter Kinlund, Per K, Cecilia, Jan Risberg, Lena R, Britta, Hanna, Klara, Richard P, Maria R, Lasse W, Ann-Charlotte Wistedt, Anders Y and Peter Östman.

This project has been financially supported by Svenska Sällskapet för Geografi och Antropologi (SSAG): Andréefonden and Vegafonden; Lillemor och Hans W:son Ahlmanns fond för geografisk forskning; Axel Lagrelius fond för geografisk forskning; Stiftelsen Carl Mannerfelts fond; Stiftelsen Margit Althins stipendiefond (KVA); Letterstedtska Föreningen Nordisk Tidskrift; C.F. Liljevalch J:ors stipendiefond; John Söderbergs stiftelse, and the Geological Survey of Denmark and Greenland (GEUS). The project has also been financed by grants to Karna Lidmar-Bergström for the project ‘palaeorelief, saprolites and uplift/denudation of cratons’ obtained from the Swedish Natural Science Research Council/The Swedish Research Council. Logistic support was provided by Arktisk Station–Disko, Københavns universitet.

ReferencesAdams, G.F., Planation surfaces, peneplains, pediplains and

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Paper I

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Dear Johan Bonow,

Re: Bonow, J.M., Lidmar-Bergström, K., Näslund, J.O., 2003. Palaeosurfaces and major valleys in the area of Kjølen Mountains, southern Norway -consequences of uplift and climatic change. Norsk Geografisk Tidsskrift-Norwegian Journal of Geography 57, 83-101

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Opposite side:Paper reprinted from Palaeosurfaces and major valleys in the area of Kjølen Mountains, southern Norway-consequences of uplift and climatic change by Bonow, J.M., Lidmar-Bergström, K., Näslund, J.O fromNorsk Geografisk Tidsskrift-Norwegian Journal of Geography, www.tandf.no/ngeog, 2003, 57, 83-101, by permission of Taylor & Francis AS.

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