Abstract

Growth faults and deltaic coastlines are common features along basin margins with a high flux of sediment delivery. It has been observed in previous studies that wave-dominated deltas are the characteristic and long-lived coastline type in such growth-faulted, extensional basins. During deltaic progradation the structural and depositional systems migrate and adjust as sedimentation rates keep pace with fault displacement rates. A numerical model indicates that increased subsidence along growth faults slows the progradation rate of deltas as new accommodation is being created. The decrease in forward delta growth results in a longer period of wave reworking per unit of sediment due to the retention of large fetch and water depth. Since subsidence is maintained through time, sediments tend to accumulate on delta topsets, creating thick wave-dominated delta-front successions on the downthrown sides of faults. The proposed model may guide subsurface interpretations where it is difficult to assess the shoreline type without cores. It is proposed here to use values of expansion index derived from seismic reflection profiles or well-log correlations as a proxy for the likelihood of “wave dominance” on the delta shoreline.