Investigations on the use of triaromatic dimethylcholesteroids as age-specific biomarkers in bitumens and oils from Arctic Norway

Abstract

Triaromatic dimethylcholesteroid (TA-DMC) and triaromatic dinosteroids (TA-dinosteroids) derive from dinoflagellates and are considered age-specific biomarkers that have some potential to distinguish between petroleum generated from Paleozoic vs Mesozoic strata. Still, some ambiguity remains concerning a gradational or abrupt Paleozoic vs Mesozoic phylogenetic change in the precursor bio-molecule for these biomarkers. Our examination of TA-DMC in a series of 112 sedimentary rock samples and oils from the Barents Sea, Svalbard, the Norwegian Sea and Novaya Zemlya ranging from the Silurian to the Cretaceous could shed light on these issues. TA-DMC together with TA-dinosteroids occur locally in Upper Permian source rocks of the Ørret Formation, while the Upper Permian Røye Formation did not reveal any occurrences. The abundance of both compound classes in Permian sediments might either suggest the presence of dinoflagellates in palaeo-niche environments during the Late Permian in the studied area, or hint towards the occurrence of related ancestors among acritarchs or non-calcifying haptophytes. TA-DMC and TA-dinosteroid were found in Lower Induan rocks from the Haltenbanken area, which implies the occurrence of TA-DMC and TA-dinosteroid producing organisms in the Early Triassic. However, the appearance of TA-DMC and TA-dinosteroids in Lower to Middle Triassic sediments from the Svalis Dome (SW Barents Sea) increases during the Anisian, while no TA-DMC have been found in Early Triassic Olenekian sequences, which is in accordance with global observations. Based on these results, it could be concluded that the 7324/8-1 Wisting Central oil discovery was generated from Olenekian intervals of the Lower Triassic Steinkobbe Formation.