Bottom current controlled sedimentation on the Canterbury Margin since the Pliocene: seismic evidence for the development and migration of contourite drifts

The Pliocene to Recent succession of the Canterbury Basin (southeast New Zealand) records the long-term interaction between alongslope bottom currents and episodic downslope sediment delivery, expressed in a contourite-dominated mixed depositional system. A new regional seismic stratigraphic framework, built from 2D seismic reflection data tied to IODP/ODP drill sites, identifies four major seismic units bounded by regionally mappable discontinuities dated at ca. 4.3 Ma, 3.65 Ma, 2.4 Ma, and 1.1 Ma. These boundaries correspond to major shifts in tectonic, climatic, and oceanographic forcing, including reorganisations of the Subtropical Front (STF), variations in Subantarctic Mode Water (SAMW) / Antarctic Intermediate Water (AAIW), and modulation of the Southland Current.

Seismic facies, time-structure maps, and isochron analysis reveal systematic temporal and spatial changes in sediment thickness, reflection character, and depositional geometries across the shelf–slope–basin system. Key contourite morphological elements include plastered drifts, elongated mounded drifts, moats, slope terraces, and sediment-wave fields. Hybrid facies and mass-transport deposits demonstrate ongoing interaction between alongslope bottom currents and downslope gravity flows. Drift asymmetry, crest migration, and moat incision document the persistent role of bottom currents throughout the Pliocene–Quaternary.

Integration of these observations yields a multi-stage evolutionary model linking drift growth, moat migration, terrace development, and slope instability to variations in bottom-current strength, frontal position, and glacio-eustatic forcing. This work establishes the Canterbury margin as a high-latitude reference system for contourite sedimentation and mixed turbidite–contourite processes