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, the stratigraphic record can constrain the four-dimensional evolution of extensional growth folds, which in term 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-involved fault. We show that the fault grew via 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. Fault-propagation folds formed at multiple times in response to periodic burial of the causal fault, with individual folding events (c. 25 Myr and 32 Myr) lasting a considered part of the total, c. 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 extensional setting. We also show changes in the architecture of growth strata record alternating periods of how folding and faulting, showing how rift margins 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.
Geometric and temporal evolution of extensional growth folds in the Barents Sea, offshore Norway: A tool to understand normal fault growth
