Ngunr 350 Bulletin 50 Vorren.Pdf
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/ "< 4 < * NGU Norges geologiske undersøkelse Geological Survey of Norway Norges geologiske undersøkelse (Geological Survey of Norway), Leiv Eirikssons vei 39, Trondheim. Telephone: national (075) 15860, international + 47 75 15860. Postal address-' Box 3006, N-7001 Trondheim, Norway. Administrative Director: Dr. philos. Knut S. Heier Geological division: Director Dr. philos. Peter Padget Geophysical division: Director Inge Aalstad Chemical division: Director Aslak Kvalheim The publications of Norges geologiske undersøkelse are issued as consecutively numbered volumes, and are subdivided into two series, Bulletin and Skrifter. Bulletins comprise scientific contributions to the earth sciences of regional Norwegian, general, or specialist interest. Skrifter comprise papers and reports of specialist or public interest of regional, technical, economic, environmental, and other aspects of applied earth sciences, issued in Norwegian, and with an Abstract in English. EDITOR Førstestatsgeolog Dr. David Roberts, Norges geologiske undersøkelse, P.0.80x 3006, N-7001 Trondheim, Norway. PUBLISHER Universitetsforlaget, P.0.80x 7508, Skillebekk, Oslo 2, Norway. DISTRIBUTION OFFICES Norway: Universitetsforslaget, P.0.80x 2977, Tøyen, Oslo 6. United Kingdom: Global Book Resources Ltd., 109 Great Russell Street, London WC 1 B, 3ND. United States and Canada: Columbia University Press, 136 South Broadway, Irvin"ton-on- Hudson, New York 10533. EARLIER PUBLICATIONS AND MAPS The most recent list of NGU publications and maps, 'Publikasjoner og kart 1891 — 1977', appeared in 1977. Copies can be obtained from the Publisher. The most recent maps available from NGU are listed inside the back cover. MANUSCRIPTS Instructions to contributors to the NGU Series can be found in NGU Nr. 273, pp. 1-5. Offprints of these instructions can be obtained from the editor. Contributers are urged to prepare their manuscripts in accordance with these instructions. 2001 554.81eff NOR Norges geologiske under Bulletin 1- Vorren, T. O. 1979: Weichselian ice movements, sediments and stratigraphy on Hardangervidda, South Norway. Norges geol. Unders. 350, 1-117. Based on studies of glacial directional elements and on lithology, palynology and stratigraphy of the Quaternary sediments, the following climatostratigraphy and ice movement patterns are indicated; an early ice-free period, the Hovden thermomer, which is correlated with the Eemian; an early Weichselian glacial event, the Hovden kryomer, characterised by ice movements towards the east from a westerly situated ice divide (Phase I); an Early Weichselian ice-free event, the Fornes thermomer; a continuous glaciation period, the Fornes kryomer, which ended with the Holocene deglaciation. During the Fornes kryomer, the ice divide was situated far to the west in the earliest periods (Phase II). Later, the ice divide was located over eastern Hardangervidda (Phase III) and finally the ice movement diverged from a westerly situated ice divide and a dome located to the north (Phase IV). The environment during the thermomers is discussed as well as the temperature, relief and the reason for the changing ice movement patterns of the ice sheet during the kryomers. Textural and petrographical studies have been carried out on 485 sediment samples. Emphasis is laid upon ruling out the comminution and dilution of phyllite during glacial and glaciofluvial transport. T. O. Vorren, Institutt for biologi, og geologi, Universitetet i Tromsø, Box 790, N-9001 Tromsø CONTENTS ABSTRACT 1 INTRODUCTION 2 Bedrock 2 Bedrock morphology 5 Previous Quaternary geology studies 7 ICE MOVEMENTS 8 Directional elements - types and terms 8 Methods 9 Collection of data 10 Analysis of individual observations 10 Description of directional elements on Hardangervidda 13 Results and discussion 17 Phases I and II 19 Phase 111 22 Phase IV 24 Comparisons with earlier investigations 26 Some characteristics of the Weichselian ice sheet on Hardangervidda 27 General discussion 27 Phase I and II 29 Phase 11/111 transition 31 Phase 111 34 Phase IV 35 2 TORE O. VORREN SEDIMENTS 37 Methods 37 Mapping 37 Sampling 37 Laboratory processing 38 Till 39 Nomenclature and classification 39 Structures 42 Phyllite content 46 Heavy minerals 57 Coloured phyllosilicates 59 Grain-size distribution - regional variation 60 Origin of the till 62 Sorted sediments 64 Grain-size distribution 64 Grain-size distribution parameters 65 Petrography and grain-size distribution 68 Glaciofluvial transport 69 STRATIGRAPHY 71 Description of localities 72 The Mosvatn area 72 The Mår area 75 The Goyst area 83 Sterra 87 The Hansbu area 89 Holsbu 93 The Svinto area 93 Discussion 99 SUMMARY AND MAIN CONCLUSIONS 105 ACKNOWLEDGEMENTS 109 REFERENCES 109 Introduction The investigated area, shown in Fig. 1, is delimited by the 59° 45' N and 60°30' N parallels and the 6°35'45" E and 8°28'10" E meridians This 8623 km2 tract is covered by fifteen 1 : 50.000 topographical map sheets (Fig. 17). The field work was carried out during the five summers 1970-74. It goes without saying that five seasons field work was not sufficient to satisfactorily cover this extensive area. Within the two southeasternmost maps, Røldal and Haukeliseter, only scattered observations from aerial photographs were made, with no field control. Varying amounts of field work have been carried out within all the remaining maps, though least on the Ullensvang, Eidsfjord, Ringedalsvatn and Skurdalen sheets. Some results of this work have been published earlier (Vorren 1977 a, b, Vorren & Roaldset 1977). Bedrock The most important publications concerned with the regional bedrock geology of Hardangervidda are: Brøgger (1893), Reusch et al. (1902), Rekstad (1903), Kvale (1947), Dons (1960 a, b), Naterstad et al. (1973) and Andresen (1974 a, b, c). Other isolated observations are quoted in these studies. The greater part of Hardangervidda is Precambrian basement (Fig. 2) with predominantly granitic and granodioritic gneisses. WEICHSELIAN ICE MOVEMENTS, HARDANGERVIDDA 3 Fig. 1. Location map of the investigated area, hatched. The Telemark suite is represented by metasediments and metavolcanics. They mainly occur in the west near Sørfjorden (Kvale 1947), and in the easterly parts (Dons 1960 a, b, Holtedahl & Dons 1960). The Cambro-Ordovician rocks and those of the Holmasjø Formation (here referred to collectively as Cambro—Ordovician) form the main basis for my sediment petrography investigations and will therefore be described in some detail here. Based upon his own and earlier studies, Andresen (1974a) has proposed the following stratigraphy for the autochthonous Cambro-Ordovician sequence: grey schist (phyllite), greenschist with marble zones, marble, bluish quartzite, black shale (Alum shale), basal conglomerate. Naterstad et al. (1973, p. 8) consider that the greenschist is the uppermost member. This difference is probably due to Andresen assigning the Holmasjø Formation, consisting chiefly of quartz-rich phyllites (Naterstad et al. 1973, 4 TORE O. VORREN Fig. 2. Bedrock geology map of Hardangervidda based on mapping and publications cited in the text and Løberg (1973). WEICHSELIAN ICE MOVEMENTS, HARDANGERVIDDA 5 p. 8), to the autochthonous series as Brøgger (1893) and Reusch et al. (1902) had done. However, in the present context it is the geographical location and extent of the different outcrops which is significant. Southwest of a line from Sandflott to Kinso river the grey schists predominate and only local remnants of the other sedimentary rocks can be found (Andresen 1974a, p. 43). The bluish quartzite is bounded by this line, to the southwest and by a north-south line along Veigdalen which, south of Grananutane, turns east-wards and contin ues to Bjornesfjorden before heading south again (Rekstad 1903, p. 16). The marble occurs mainly within the same zone, while grey schists dominate once more in the northern and eastern areas. The allochthonous nappe rocks are restricted to the southern areas and to Hårteigen and Hardangerjøkulen. They consist mostly of different types of gneiss and meta-supracrustals (Naterstad et al. 1973). Bedrock Morphology Most of Hardangervidda lies between 1000 and 1400 m a.s.l. (Fig. 3). Areas exceeding 1400 m are found in the west, often coinciding with nappe rocks, and similarly in the north at Hardangerjøkulen. In addition, there are areas of Precambrian basement between Songevatn and Møsvatn which rise to over 1400 m a.s.l. The greatest relative relief on Hardangervidda is displayed by the cirques and hanging valleys in the westernmost parts. The cirque topography is especially well developed in the northwest. There are quite considerable altitude variations in the southeast too, but with somewhat gentler forms. Two surfaces are distinguishable here, the Møsvatn basin at about 900-1000 m a.s.l. and the surrounding areas lying at 1200-1500 m a.s.l. (Gjessing 1967, Fig. 16). Generally, though, Hardangervidda is typified by its low relief. The origin of this more or less undulating landscape which is part of Norway's Paleic Surface has been a matter for debate, cf. Gjessing (1967). Reusch (1901) regarded it as a fluvial denudation surface, O. Holtedahl (1960, p. 508) as an exhumed sub-Cambrian peneplain and Gjessing (1967) as the product of subaerial weathering and denudation during an arid or semi-arid pre- Quaternary period. The drainage routes from Hardangervidda's Paleic surface in the west and to a lesser degree in the southeastern areas, lead into deeply incised younger valleys and fjords. The valleys in