Abstract
Abstract. A megaspore biozonation of the non-marine Åre Formation is proposed, based on a micropalaeontological analysis of key Haltenbanken area wells (Block 6608/11). The lower part of the Åre Formation is divisible into Banksisporites pinguis, Nathorstisporites hopliticus and Horstisporites areolatus zones, and subzones, occupying the Rhaetian–Hettangian interval. In the upper Åre Formation a marked turnover of megaspore assemblages is evident, with the appearance of several species of Trileites and the mesofossil Kuqaia quadrata. On this basis, the biozonation is extended into the Sinemurian–Pliensbachian, with the recognition of the Kuqaia quadrata Zone and subzones. Reference to selected wells in the Urd Field (Block 6608/10) and further south demonstrates that these biozones correlate across the northern Haltenbanken region. Biozonal boundaries are calibrated with miospore/microplankton markers where possible, to provide a robust bio-chronostratigraphical framework with which to evaluate the stratigraphy of the Åre Formation and its reservoir units. Comparison with published European biostratigraphical data shows that a similar megaspore succession exists through the Rhaeto-Liassic interval, with shifts in megaspore composition occurring within the same time intervals. On this evidence it is suggested that the megaspore biozones identified are regionally extensive and may reflect palaeoclimatic controls on the distribution of the megaspore-producing plants. It is concluded that megaspores are a stratigraphically important microfossil group, which should be utilized routinely in Upper Triassic–Jurassic oil field and regional biostratigraphical studies.
Highlights
Atlantic margin, Upper Triassic–Lower Jurassic sediments include reservoir units within the Åre Formation that form several major oil fields on the Heidrun–Norne trend (Fig. 1)
The present study demonstrates that by using standard micropalaeontological techniques, megaspore assemblages can be effectively extracted from non-marine sediments of the Åre Formation
The results obtained show that a distinct megaspore succession is present within the unit, which can be divided into several assemblage zones
Summary
Upper Triassic–Lower Jurassic sediments include reservoir units within the Åre Formation that form several major oil fields on the Heidrun–Norne trend (Fig. 1). Biostratigraphical evaluation of the Åre Formation in the Haltenbanken region was based primarily on palynological analysis, but the predominance of morphologically diverse, long-ranging miospores prevented reliable biozonation of reservoir units (see below). During such phases of evaluation, megaspores were generally excluded from palynological preparations because of their comparatively large size; they are usually removed along with plant debris through ‘swirling’ and filtering. The stratigraphical value of offshore, Upper Triassic–
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
