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Depositional Environments and (Bio-)stratigraphy of the Upper Triassic Kapp Toscana Group on Svalbard and the Barents Sea Shelf

Abstract

Triassic rocks are well exposed in Svalbard and continue southward in the subsurface below the Barents Sea Shelf to northern Norway where they serve as potential hydrocarbon reservoir sandstones. Also, Upper Triassic sandstone intervals are a potential storage unit for CO2 (e.g. UNIS CO2-storage project). However, the presence of several hiatuses makes correlation with the international standard zonation difficult due to the lack of useable marine index fossils. The aim of this project is to establish a palynostratigraphic scheme, and to correlate it with the equivalents in the Barents Sea and with their age equivalents of the Taylorsville Basin (Newark Supergroup, VA & MD, USA) at a later stage. Approximately 80 outcrop samples have been studied from four locations (Festningen, Dronbreen, Botneheia and Juvdalskampen) where Upper Triassic sediments are exposed. All samples were cleaned and about 10g from each sample was crushed and treated with HCl and HF following standard palynological processing procedures. Heavy mineral separation was done with ZnCl2. Samples were then mounted on slides for qualitative and quantitative analysis. The samples yield diverse and well preserved assemblages of terrestrial and marine palynomorphs of a deltaic depositional environment. The sedimentary organic matter is dominated by palynodebris, such as wood or cuticle phytoclasts, or by semi-transparent structureless amorphous material while palynomorph abundance is low. Palynomorph preservation is best in the lowermost and uppermost sections. The lowermost Tschermakfjellet Fm is characterized by terrestrially dominated assemblages with a large amount of bisaccate pollen. Further up the sequence, the De Geerdalen Fm is dominated by spores while the topmost Wilhelmoya and Knorringfjellet Fms contain mostly terrestrial forms with a higher content of aquatic taxa. Age indicative taxa allow integration into the international standard stratigraphic framework, and suggest a Carnian age for most of the De Geerdalen Fm with the Carnian/ Norian boundary located within the uppermost De Geerdalen/ lowermost Knorringfjellet Fm. A correlation with other sections on Spitsbergen and the Barents Sea is successfully applied. Sequence stratigraphy records a maximum flooding surface at the base followed by a highstand systems tract for most of the section. The sedimentology suggests a delta dominated depositional environment with mainly terrestrial palynomorphs and some aquatic taxa.