Crustal Structure and Development of the SW Barents Sea and The

DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. CONTENTS Preface Introduction Paper 1 Gudlaugsson, S.T., Faleide, J.I., Johansen, S.E. & Breivik, A.J., in press Late Palaeozoic structural development of the south-western Barents Sea, Mar. and Petr. Geol. Paper 2 Breivik, A.J., Gudlaugsson, S.T. & Faleide, J.I., 1995 Ottar Basin, 5W Barents Sea: a major Upper Palaeozoic rift basin containing large volumes of deeply buried salt, Bas. Res., 7, 299-312. Paper 3 Breivik, A.J., Faleide, J.I. & Gudlaugsson, S.T., in press SW Barents Sea margin: Late Mesozoic sedimentary basins and crustal extension, Tectonophysics. Paper 4 Breivik, A.J., Verhoef, J. & Faleide, J.I., submitted Properties of a young transform margin, Western Barents Sea: Gravity, isostasy and lithospheric thermal structure, J. Geophys. Res. Afterword PREFACE The work for this Dr. Sclent, thesis has been carried out at the Department of Geology at the University of Oslo during my four year position as research fellow (stipendiat). The thesis was supervised by professor Jan Inge Faleide, and I would in particular like to thank Jan Inge Faleide as well as my other coauthors, Steinar Thor Gudlaugsson and Jacob Verhoef, for their support and valuable insight at various stages of the Dr. Scient. project. Consisting of an introduction and four papers, the thesis originates from three different projects. Two of the projects have been partly funded by the oil industry, and results have also been presented in industrial reports and oral presentations. Investigation into the Late Paleozoic of the Barents Sea was funded by Statoil (contract no. T-171165), and the project on the Veslemdy High and S0rvestsnaget Basin area was initially funded by Enterprise Oil. The Barents Sea Margin project was partly funded by Norges Forskningsrad (the Research Council of Norway, grant no. 117610/431) and the Geological Survey of Canada (Atlantic). Oslo, 19 desember, 1997 / Asbj0m Breivik Introduction INTRODUCTION The western Barents Sea is located at the northwest ern comer of the Eurasian continent between the Norwegian and Russian mainland, and the Svalbard archipelago (Fig. 1). Because of the expected petro leum potential, the region has been extensively mapped and investigated, resulting in a good under standing of the geological development, though still far from complete. As expected, the deeper parts are more difficult to map, and therefore the early post- Caledonian tectonism and basin formation is not well described. This uncertainty applies also to the onset of the last major rift phase at the western mar gin, where the penetration of seismic data is poor. The development of the area is an important key to understanding the development of the North- Atlantic rift zone, leading through a long history of rifting up to passive margin formation. The western Barents Sea margin is also one of the world's major transform margins, representing an important exam ple of an end member of the development of crustal transform faults. © Figure 1. Position of the Barents Sea in a regional setting. EB: Eurasia Basin, CGFZ: Charlie-Gibbs Geological background Fracture Zone, NGS: Norwegian-Greenland Sea. In the southwestern part, large Mesozoic sedimen tary basins and upper Paleozoic evaporite deposits dominate, while the northern part is dominated by a la Hoek basement terrain shows varying metamor platform area (Fig. 2). The geological province con phic grades. However, the extent of the Caledonian stitutes an important part of the North-Atlantic rift tectonism in the Barents Sea is not well known. The system, as well as being part of an area affected by main problem here is determining the location of the the Caledonian orogeny (e.g., Dore, 1991, Ziegler, Caledonian front, and two different views exist. 1988). The area apparently has been influenced by at Ziegler (1988) proposes a northerly turn of the Cale least two different tectonic grains, and it is a key donian suture along Svalbard, while Dore (1991) area marking a change between the northwesterly argue a continuation northeast through the Barents trend of the North-Atlantic rift, and a north- Sea. Large sinistral strike-slip movements have also northwest trend represented by the tectonism present been a prominent model in which the collection of on Svalbard. This change in direction is also to some the present basement terrain is understood (e.g., extent reflected in a change of the direction of the Harland, 1967; Ziegler, 1988), where the Billefjor- passive continental margin of the North-Atlantic, den Fault lineament (Fig. 2) played an important where both trends can be seen competing on the role, though this model has not gained universal southwestern Barents Sea margin, to be dominated acceptance. by the north-northwest trend of the western Svalbard margin (e.g., Eldholm et al., 1987; Faleide et al., 1991). The geological development of the area from 2: The early post-Caledonian graben formation on mid-Paleozoic time and to the present can roughly the island of Spitsbergen created the Devonian Ba be divided into eight main phases: The Caledonian sin (e.g., Manby & Lyberis, 1992), possibly by orogeny, Devonian graben formation, mid-Carbon- extensional collapse of the Caledonian orogen. iferous rifting, Permian to Early Triassic tectonism Whether Devonian graben formation occurred in the in the western part, Permian and Triassic regional Barents Sea is a matter of debate, as no uncontro subsidence, Middle Jurassic to early Tertiary rifting vertible evidence for this has yet been presented, and basin formation in the southwest, early Tertiary though candidates exist. margin formation and onset of seafloor spreading, and late Tertiary uplift and erosion. 3: Carboniferous rifting has been recognized throughout the North-Atlantic rift zone (e.g., Hazel- 1: Theclosure of the Iapetus ocean caused suturing dine, 1984; Steel & Worsley, 1984; Dengo & R0ss- of western Europe and eastern North-Amer land, 1992). In the Barents Sea, this tectonic event ica/Greenland, and thereby causing the Caledonian resulted in the formation of several basins that col orogeny. Much of the present metamorphic base lected large volumes of evaporites during the Late ment of Norway and probably also the Barents Sea Carboniferous and Early Permian (e.g., Gerhard & was created during this event. On Svalbard, the Hek- Buhrig, 1990; Jensen & S0rensen, 1992). Subse- 10° 20° 30° Figure 2. Structural elements of the western Barents Sea, based on Faleide et al. (1993). The map has been updated with the new continent-ocean boundary from Paper 4, and salt deposits and the Ottar Basin from Paper 1 and 2.1: Bathymetry (m), 2: Magnetic anomalies, 3: Continent-ocean boundary, 4: Mesozoic-Ceno- zoic faults, 5: Late Paleozoic faults, 6: Salt diapirs and detached pillows, 7: Salt pillows and unmobilized salt, 8: Approximate extent of Vestbakken Volcanic Province, 9: Tertiary stretched continental crust. BB: Bj0m0ya Basin, BF: Billefjorden Fault, BP: Bjarmeland Platform, EP: Edge0ya Platform, FSB: Fingerdjupet Subbasin, FP: Finnmark Platform, GH: Gardbanken High, HB: Harstad Basin, HfB: Hammerfest Basin, HFZ: Hom- sund Fault Zone, LH: Loppa High, MB: Maud Basin, NB: Nordkapp Basin, NH: Norsel High, OB: Ottar Basin, SB: S0rvestsnaget Basin, SFZ: Senja Fault Zone, SH: Stappen High, SkB: S0rkapp Basin, SR: Senja Ridge, TB: Troms0 Basin, TKFZ: Trollfjord-Komagelv Fault Zone, VH: Veslem0y High, WP: Vestbakken Volcanic Province. u quent mobilization of these deposits has played an 7: During the Early Eocene, the Norwegian- Green important role in the Mesozoic development of land Sea started to open predominately by dextral some of the sedimentary basins. Dextral strike slip shear movement between Greenland and the Barents along the Trollfjord-Komagelv Fault Zone linea Sea/Svalbard. Two sheared margin segments with a ment has been proposed to form the Nordkapp Basin small, rifted margin segment in between have been (Jensen & S0rensen, 1992). An early model of a identified (e.g., Eldholm et al., 1987; Faleide et al. conjugate strike-slip system as the main mode of de 1991), However, there was an extensional compo formation within the Barents Sea (e.g., R0nnevik & nent to the opening, and high velocity oceanic base Jacobsen, 1984) has not been substantiated by later ment has been related to this early opening geometry observations. (Eldholm et al., 1987; Myhre & Eldholm, 1988). They relate the high gravity anomalies at the margin to anomalous oceanic crust emplaced during this 4: Permian to Early Tiiassic tectonism occurred at early phase of the margin formation. The southern the western part of the southwestern Barents Sea af margin gravity anomaly was originally used to de fecting the Loppa and Stappen Highs, (e.g., Brekke fine the Senja Fracture Zone (Taiwan! & Eldholm, & Riis, 1987; Gabrielsen et al., 1990). No major 1977). faulting is observed from this episode in the eastern parts. 8: During the Cenozoic large amounts of sediments derived from the Barents Sea shelf were deposited 5: By the Early Permian, the subsidence of the into the newly formed oceanic basin. Two depo southwestern Barents Sea had obtained a regional centers developed based on different drainage areas. character, (e.g., Gerhard & Buhrig, 1990) with The southern depocenter, called the Bj0m0ya Fan, evaporite and carbonate deposition, though the un has generally lower sedimentary velocities than the derlying Carboniferous rift system appears to deter northern, the Storfjorden Fan (Myhre & Eldholm, mine the location of the depocenters. This regime 1981; 1988; Fiedler & Faleide, 1996; Hjelstuen et was continued into the Triassic, with large, regional al., 1996). Neogene uplift and Pliocene-Pleistocene deposition of clastic marine sediments, apparently glaciations greatly increased the erosion rate, and not related to any tectonic event, while the eastern more than half of thesediments were deposited dur Barents Sea underwent formation of the large North- ing the last ~3 m.y.

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