Sedimentology and stratigraphy of syn-subduction Miocene fine-grained turbidites deposited in first stages of trench-slope basin development: Whakataki Formation, North Island, New Zealand

This study provides a detailed sedimentological, stratigraphic and depositional model for the lower Whakataki Formation. The fine-grained nature of the turbidite successions and common Tbcde successions suggests deposition associated with medial to distal submarine fan deposits. However, the textural and compositional immaturity, combined with a high carbonaceous and carbonate content of the clastic sediments indicates a proximal detrital input. In the examined section of the lower Whakataki Formation the sedimentology and facies associations identified that the turbidite successions were deposited as dilute low-density turbidity currents that transported sediment down-slope, overflowing or bypassing upper- and mid-trench-slope basins into a structurally confined lower trench-slope basin. Flows entering the structurally confined basin were deflected to the north-northeast, producing palaeo-flow along the axis of the basin and represent deposition in the early stages of trench-slope basin development. Here, we provide a depositional model for a lower (immature) trench-slope basin and highlight that the application of the ‘classical’ submarine-fan model to all fine-grained turbidite deposits is not always appropriate.