Sedimentology of Polygonal Palaeoaplysina Buildup Complexes of Carboniferous-Permian Age on Spitsbergen: An Analogue to the Norwegian Barents Shelf

Jesper Nielsen

The frontier areas of the under-explored Norwegian Barents Sea received much attention during the 22nd licencing round as tens of petroleum companies applied for 72 blocks (NPD 05.12.2012). As there are only relatively few wells drilled into the Late Palaeozoic carbonates, this is one of the least investigated plays. In this study, we will present a new model for the Palaeoaplysina buildup complexes that for the first time are reported from Svalbard (Hanken & Nielsen, accepted). Field observations from central Spitsbergen show that Palaeoaplysina buildups mostly have the shape of tabular banks. However, the great lateral extent of these buildups of the Tyrrellfjellet Member (Upper Carboniferous-Lower Permian) strongly indicates that there must have been several growth centres of many small structures, resembling patch reefs, which amalgamated into large buildups. By a combination of vertical and lateral growth the incipient patch reefs coalesced to form wide, tabular buildups. The flat-topped tabular buildups can be viewed as the mature stage of buildup growth. With decreasing accommodation space continued vertical growth was hampered and lateral growth became dominant. The uppermost part of the buildups may contain Microcodium, indicating subaerial exposure and vegetation cover. The lateral interfingering between the bedded fusulinid dolostones along the buildup margins and the fossil barren dolostones containing gypsum further out in the lagoon may indicate an increasing salinity from the lagoon margin to the central part. The ring-shaped to polygonal buildup complexes encircle a lagoon which has a diameter of several kilometres. The buildups are commonly stacked; individual buildups sit directly on top of each other or are separated by thin sequences of inter-buildups sediments. The buildup complexes on central Spitsbergen are comparable both in size and geometry with those seismically recorded from the Norwegian Barents Sea. Palaeoaplysina buildups in Ural have a proven hydrocarbon potential. Wells penetrating Palaeoaplysina buildups in the Norwegian sector of the Barents Sea have shown oil staining or residual oil, but there have so far been no commercial discoveries. However, a better understanding of facies relationships and the 3D geometry of the buildup complexes is important in developing better play models in the future. References Hanken, N.-M. & Nielsen, J.K. (accepted). Upper Carboniferous to Lower Permian Palaeoaplysina buildups on Svalbard: the influence of climate, salinity and sea level. In: Gasiewicz, A. and Slowakiewicz, M. (eds), Late Palaeozoic Climate Cycles: Their Evolutionary, Sedimentological and Economic Impact. Geological Society of London, Special Publications.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013