A new Triassic palynostratigraphy for the Norwegian Arctic area, with focus on the Early Triassic palynological turnovers

A new Triassic palynostratigraphy for the Norwegian Arctic area, with focus on the Early Triassic palynological turnovers Mangerud, G. 1 , Jorunn Os Vigran 2 , Atle Mork 2 and Peter Hochuli 3 1 Department of Earth Science, University of Bergen, Allegaten 41, N-5007 Bergen, Norway, 2 Sintef Petroleum Research, NO-7465 Trondheim, Norway, 3 Palaeontological Institute and Museum, University Zurich, Karl Scmid Str. 4, CH-8006 Zurich, Switzerland The Norwegian Barents Shelf with Svalbard forming its exposed north-western corner reveals an almost complete Triassic sedimentary record when combining outcrops with stratigraphic cores and explorations wells. Palynological studies from these sections have been carried out both in relation to needs from the petroleum industry to establish correlative tools and dating as well in connection with fundamental research to unravel the history of the Triassic Period in these areas. The present study is based on combining previous published palynological data with new studies form various section from Svalbard as well as from stratigraphic cores and explorations wells from the Barents Sea. The main aim was to establish a formal regional zonal scheme for the entire Triassic succession serving as a solid correlative tool for the vast area of the Norwegian Arctic. The present study has therefore to a great extent incorporated previously published schemes (Hochuli et al. 1989 and Vigran et al . 1989). 15 composite assemblage zones applicable as a regional tool covering this huge region have been defined, including 7 zones for the lower Triassic, 4 zones for the Middle Triassic and 4 zones for the Upper Triassic. Many of the zones are calibrated to other fossil groups and in one case also to Re-Os dating from the same section. The potential of establishing more local zonation schemes is definitely present and our study has clearly demonstrated the need for further detailed investigation of stratigraphic ranges as well as taxonomic issues. Distinct palynological turnovers are recorded. In t he Lower Triassic succession a major turnover is related to the transition from Permian palynofloras dominated by pollen to earliest Triassic palynofloras dominated by spores. Records of typical Permian species, also appearing relatively consistent in the lowermost part of the Griesbachian, are a typical feature of the Griesbachian Stage. A discourse exits as to whether these are in situ or reworked. The present study has concluded that these are in situ and consequences of this interpretation will be discussed. Further a marked change in the palynoflora composition is recorded at the Smithian-Spathian boundary where a pronounced shift from lycopod spore dominance to gymnosperm assemblages is recorded. This shift will be discussed and related to the major climatic shift suggested to take place at this time (Galfetti et al . 2007a, b). Galfetti T, Hochuli, P., Brayard A., Bucher H., Weissert H, Vigran, J.O.  (2007). Smithian-Spathian boundary event: Evidence for global climatic change in the wake of the end-Permian biotic crisis. Geology,  vol 35, no. 4; p. 291–294 Galfetti T, Bucher H., Ovtcharova, M., Schaltegger U., Brayard A., BruhwilerT., Goudemand, N.and Weissert H., Hochuli, P., Cordey, F., Guodun, K. (2007). Earth and Planetary Science Letters 258 593–604. Hochuli, P.A., Colin, J.P. & Vigran, J.O. 1989: Triassic biostratigraphy of the Barents Sea area. In Collinson, J.D. (ed.), Correlation in Hydrocarbon Exploration . Norwegian Petroleum Society/Graham & Trotman, 131-153 London. Vigran, J.O., Mangerud, G., Mork, A. & Bugge, T. & Weitschat, W. 1998: Biostratigraphy and sequence stratigraphy of the Lower and Middle Triassic deposits from the Svalis Dome, Central Barents Sea, Norway. Palynology 22 , 89-141.