The geometric and temporal evolution of fault-related folds constrain normal fault growth patterns, Barents Sea, offshore Norway

Extensional growth folds form ahead of the tips of propagating normal faults. These folds can accommodate a considerable amount of extensional strain and they may control rift geometry. Fold-related surface deformation may also control the sedimentary evolution of syn-rift depositional systems. Thus, by examining the stratigraphic record, we can constrain the four-dimensional evolution of extensional growth folds, which in turn provides a record of fault growth and broader rift history. Here, we use high-quality 3D seismic reflection and borehole data from the SW Barents Sea, offshore northern Norway to determine the geometric and temporal evolution of extensional growth folds associated with a large, long-lived, basement-rooted fault. We show that the fault grew via the linkage of four segments, and that fault growth was associated with the formation of fault-parallel and fault-perpendicular folds that accommodated a substantial portion (10%-40%) of the total extensional strain. Several periods of fault-propagation folding occurred in response to the periodic burial of the fault, with individual folding events (ca. 25 and 32 Myr) lasting a considered part of the ca. 130 Myr rift period. Our study supports previous suggestions that continuous (i.e. folding) as well as discontinuous (i.e. faulting) deformation must be explicitly considered when assessing total strain in an extensional setting. We also show that changes in the architecture of growth strata record alternating periods of folding and faulting and that the margins of rift-related depocentres may be characterised by basinward-dipping monoclines as opposed to fault-bound scarps. Our findings have broader implications for our understanding of the structural, physiographic and tectonostratigraphic evolution of rift basins.