Geology and palynology of the Triassic succession of Bjørnøya

Unspecified DOI: 10.1111/j.1751-8369.1990.tb00382.x Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: http://doi.org/10.5167/uzh-112675 Originally published at: Mørk, Atle; Vigran, Jorunn Os; Hochuli, Peter A (1990). Geology and palynology of the Triassic succession of Bjørnøya. Polar Research, 8(2):141-163. DOI: 10.1111/j.1751-8369.1990.tb00382.x Geology and palynology of the Triassic succession of B j@m@ya ATLE MBRK, JORUNN 0s VIGRAN AND PETER A. HOCHULI MIrk, A., Vigran, J . 0. & Hochuli, P. A. 1990: Geology and palynology of the Triassic succession of BjIrncaya. Polar Research 8, 141-163. The Triassic succession of Bjdrndya (200 m) comprises thc Lower Triassic Urd Formation (65 m) of the Sasscndalen Group, and the Middle and Upper Triassic Skuld Formation (135 m) of the Kapp Toscana Group. These units are separated by a condensed ?Middle Triassic sequencc represented by a phosphatic remaniC conglomerate (0.2 m). The Urd Formation consists of grey to dark grey shales with yellow weathering dolomitic beds and nodules. Palynology indicates the oldest beds to be Diencrian: ammonoid faunas in the middle and uppcr part of the formation arc of Smithian age. The organic content (c. 1%) includes kerogcn of land and marine origin. reflecting a shallow marine depositional environment. The Skuld Formation is dominated by grey shales with rcd weathering siderite nodules. There arc minor coarsening upwards sequences; the highest bed expobed is a 20 m thick, very fine-grained sandstone. Palynomorphs indicate a late Ladinian age for the lowcr part of the formation. and macrofossils and palynomorphs indicate Ladinian to Carnian ages for the upper part. Sedimentary structures, a sparse marine fauna and microplankton indicate deposition in a shallow marine environment. The organic residues contain dominantly terrestrially derived kerogen. Atle M ~ r k and Jorunn 0 s Vigran, Continental Shelf Institute ( IKU) , N-7034 Trondheim, Norway; Peter A. Hochuli, Esso Rep, 213 Cours Victor Hugo, B. P . 150,33321 Bgles, CEDEX, France; August 1989 (revised February 1990). Bjorn~ya, the southernmost island of the Svalbard Archipelago, is situated on the Stappen High close to the western margin of the Barents Shelf, midway between Spitsbergen and the mainland of Norway (Fig. 1). Despite its small size (178 km2), the island has an extensive geological succession of late Precambrian to early Mesozoic age that aids significantly the understanding and interpretation of the geology of the adjacent Barents Shelf area. Geological study of the island began at the end of the last century, the Triassic succession was described by Anderson (1900); his fossil collection was described by Bohm (1903). Detailed mapping (Horn & Orvin 1928, 1:50.000 geological map) gave little new information on the Triassic succession. Comments on the Triassic succession of the island were included in the regional studies of the Svalbard Archipelago by Buchan et al. (1965) and Tozer & Parker (1968). These studies were, however, hampered by lack of new field data. A new phase of investigation of the Triassic rocks, started by Soviet geologists (Pchelina 1972; Krasilshchikov & Livshits 1974), was continued by Norwegians (Mork et al. 1982; Bjor0y et al. 1983; Worsley et al. in press). Geological setting The sedimentary succession of Bj~rnoya comprises three main geological elements (Horn & Orvin 1928) (Fig. 1): -Triassic, c. 200 m of fine-grained clastics. -Upper Devonian to Permian, c. 1,200111 of clastics and carbonates. -Hecla Hoek basement, c. 1.200 m of metamorphosed clastics and carbonates. The Hecla Hoek basement forms the mountainous southern part of B j ~ r n ~ y a , nd clastics and carbonates of Devonian to Permian age are exposed over most of the remainder of the island. The uppermost Permian Miseryfjellet Formation (and partly the Hambergfjellet Formation) rests with angular unconformity on earlier Permian and pre-Permian units. The Triassic rocks are present only on the highest mountain of Bj0rn0ya. Miseryfjellet, where they rest disconformably on the Miseryfjellet Formation. This contact is marked by a topographic break in slope (Fig. 2) that reflects the great difference in hardness of the Permian limestones and the Triassic shales. The Devonian to Permian succession was briefly described by Worsley & Edwards (1976)