Extensional tectonic history of the western Barents Sea

Abstract

Extensional tectonics was the dominant mode of deformation in the western Barents Sea beginning in Late Devonian-Early Carboniferous time and culminating with the break-up between Greenland and Norway in Paleocene time. This paper describes extensional tectonic elements that have been recently mapped, places them within a regional tectonic framework and, discusses the significance that this extensional deformation may have to petroleum exploration in the Barents Sea. The oldest tectonic event that can be mapped regionally in the western Barents Sea occurred in Late Devonian-Early Carboniferous time in response to the initial rifting between Greenland and Norway. This event established a fundamental basement architecture of half-grabens and intervening highs that influenced the location of younger basins and hydrocarbon traps, the deposition of source, reservoir and seal facies and the timing of hydrocarbon maturation and migration. Major basins that formed at that time are the Tromsø, Bjørnøya, Hammerfest and Nordkapp basins, as well as a newly identified basin named the Dia Graben. The Nordkapp and Bjørnøya basins are each sub-divided into two major half-grabens. Salt deposition in these basins marks the end of rifting and the beginning of thermal subsidence, in Late Carboniferous time. During Permian through Late Triassic, a time of relative tectonic quiescence, some basement-involved normal faults were reactivated, possibly in response to the Uralian Orogeny and loading by westward prograding clastic sediments. Fault reactivation is apparent along the eastern margin of the Dia Graben which provided a structural control for the position of the Early-Mid Triassic shelf edges. Basement-detached normal faults developed in association with salt withdrawal, mostly in the Dia Graben and Nordkapp basin. In Late Jurassic-Early Cretaceous times there was renewed crustal extension in the Barents Sea. However, only those basins west of the Loppa High underwent rapid tectonic subsidence. The Cretaceous Tromsø, Bjørnøya and south-western Hammerfest basins, and perhaps the Kvaløy and Harstad basins are interpreted as pull-apart basins that formed in response to oblique rifting between the Barents Sea and Greenland. Basement faults bounding the Troms-Finnmark Platform and southern Nordkapp Basin also were reactivated. Basement-detached normal faulting developed east of the Loppa High and west of the southern Nordkapp Basin. There was additional salt withdrawal in the Nordkapp basins, Dia Graben and possibly the Tromsø Basin. Northward-propagating rifting led to sea floor spreading in Late Paleocene time and the development of a passive margin along the western Barents Sea. Most of the observed deformation is west of the Senja Ridge; however, there was continued movement along basement-involved normal faults bounding the Harstad, Tromsø, Bjørnøya and southern Nordkapp basins, accompanied by additional salt withdrawal. Neogene contractional deformation, manifested primarily as basin inversion, is apparent along most of the passive margin, west of Loppa High.