Along-strike changes in fault array and rift basin geometry of the Carboniferous Billefjorden Trough, Svalbard, Norway

The Billefjorden fault zone (BFZ) of Svalbard, Norway, is a long-lived major tectonic lineament with significant influence on the structural style of the northwestern Barents Shelf. The fault zone can be traced for around 2–300 km in an N-S direction, where it is made up of three major fault strands, all dipping 50–70° to the east. Field and seismic data delineate gradual shifts in displacement between master faults (northern Odelfjellet, Balliolbreen, and southern Drønbreen faults) and suggest that two c. 20 km long, 2–3 km wide relay zones exist along strike. The western fault strand consistently has a pre-Carboniferous reverse character; placing basement on top of Devonian sedimentary units with a throw estimated at 10 km. Subsequent Carboniferous extensional reactivation of segments of the BFZ resulted in formation of the Billefjorden Trough, with a rift basin showing a fairly consistent polarity for its length. This suggests a profound control by the older, Devonian reverse faults on the extensional structural style.The Billefjorden Trough extends for a minimum of 110 km along strike, and is 20–30 km wide at the most. A gentle north plunge of the basin axis in the south is mirrored by an opposite plunge in the north, offering a depth/thickness of around 2000 m in the central realm, diminishing to 500 m in the south. Geometries of the trough suggest sedimentary response to fault-growth, with weak lithologies such as evaporites promoting fault-monocline formation and associated lenticular basin geometries. On the contrary, wedged shaped fill geometries toward major faults is consistent with significant fault movement and growth sequences. Subsequent mild Tertiary reactivation of fault segments of the BFZ is suggested by local reverse faults and deep-seated anticline-syncline pairs.

► Focus on the along-strike characteristics of the Billefjorden fault zone (BFZ) of Svalbard, Norway.
► BFZ is a long-lived major tectonic lineament with significant influence on the structural style of the northwestern Barents Shelf.
► Onshore–offshore approach to the study offers learning's into regional tectonics, basin geometry and fault-tip monocline development, and along-strike changes in basin signature as seen in seismics.
► Discuss the strong control by the inherited structural grain, contrary to other rift zones.