LAUSR

Abstract The late Palaeozoic buried Finnmark platform, in the Norwegian Barents Sea, is a depositional system which developed under major modifications of palaeoclimatic and palaeoceanographic conditions, given by the northward drifting of the Arctic depositional domain beyond the tropical belt, the activity of the Gondwanan icecaps, and the gradual closure of the Eastern European seaway. In this study, detailed core/microfacies analysis from the explorations wells 7128/4-1 and 7128/6-1, combined with new 2D seismic sections and available dataset from previous studies in the eastern Finnmark area, have allowed a re-evaluation of the depositional scenarios associated with the Orn and Isbjorn/Polarrev Formations. The late Asselian–early Sakmarian depositional record of the Orn Formation, followed by the middle Sakmarian transition to the Isbjorn/Polarrev Formations, shows depth-related variations in sedimentation modes and a change of the platform morphology. In particular, a shift from Chloroforam to Bryonoderm sedimentation mode took place through a stratified water column during the deposition of the Orn Formation, over what we suggest was a distally steepened ramp. In the late Sakmarian, the deposition of the Isbjorn/Polarrev Formations, characterised by a full Bryonoderm sedimentation mode, took place through a cooler non stratified water column, leading to the gradual instauration of a homoclinal ramp profile. Among the other results, our integrated study suggests the development of subtidal heterozoan mounds associated with the Orn Formation, predating the formation of the larger, stacked and well-known heterozoan distal complexes of the Polarrev Formation. Given the good potential of the Orn Formation within the Finnmark depositional domain, our results may help to improve the assessment of future evaluations of reservoir properties in the area, which are closely associated with the depositional style and their post-depositional modifications.