David Hodgson

The bases of active submarine channels are marked by large erosional features, such as knickpoints and plunge pools. However, their presence in ancient channel-fills has rarely been documented, so their importance in submarine channel morphodynamics requires investigation. Using seismic reflection data calibrated by wells from a buried submarine channel-fill, we document erosional features hundreds of metres long and tens of metres deep, here interpreted as knickpoints and a plunge pool, and provide a mechanistic process for their transfer into the stratigraphic record. Channel incision patterns are interpreted to record a transient uplift in an otherwise subsiding depocentre. Local structural complexities in the channel slope formed zones of preferential scouring. A switch to a depositional regime preserved the irregular channel base, inhibiting both the upstream migration of scours and smoothing of the channel base. The formation and preservation of these scours record the responses to salt tectonics and provide a unique snapshot of the formative processes of an ancient submarine channel. The presence of these exceptional basal scours indicates that headward erosion processes did not operate rapidly, challenging the paradigm that knickpoint migration controls channel evolution. Our results show that the primary erosion of the main channel surface and long-term channel evolution are both dominated by far more gradual processes.