Mesozoic extension versus Tertiary compression along the Billefjorden Fault Zone south of Isfjorden, central Spitsbergen

Abstract

AbstractThe Billefjorden Fault Zone displays a complex tectonic history going back into Precambrian times. Observed thickness variations within Mesozoic sequences across the fault zone have previously been related to Mesozoic extensional movements along the fault zone. Recent structural, stratigraphical and sedimentological investigations suggest that the thicknessvariation observed across the fault zone is due to Tertiary compressional tectonics, and that Mesozoic extensional movements are minor or nonexistent.Tertiary deformation is characterized by a combined thin-skinned/thick-skinned structural style. Thin-skinned thrusting is due to the development of décollement zones in the Jurassic/Cretaceous Janusfjellet Subgroup and in the Triassic Sassendalen Group. Thick-skinned faulting is related to reverse faulting along a steep, east-dipping fault rooted in the pre-Mesozoic basement. Interacting thin-skinned thrusting and thick-skinned faulting has resulted in out-of-sequence thrusting, and is responsible for the thinning of Mesozoic sequences across the fault zone.