A salty snapshot: extreme variations in basal erosion patterns preserved in a submarine channel

Active submarine channel bases are marked by large erosional features, such as knickpoints and plunge pools. Their presence in ancient channel-fills has rarely been documented, meaning 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 100s m long and 10s m deep, here interpreted as knickpoints and a plunge pool, and provide a mechanistic process for their transfer into the stratigraphic record for the first time. 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 their upstream migration and smoothing of the channel base. Their formation and preservation record 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 dominated by far more gradual processes.