Variations in bottom water activity at the southern Argentine margin: indications from a seismic analysis of a continental slope terrace

Abstract

Continental slope terraces at the southern Argentine margin are part of a significant contourite depositional system composed of a variety of drifts, channels, and sediment waves. Here, a refined seismostratigraphic model for the sedimentary development of the Valentin Feilberg Terrace located in ~4.1 km water depth is presented. Analyzing multichannel seismic profiles across and along this terrace, significant changes in terrace morphology and seismic reflection character are identified and interpreted to reflect variations in deep water hydrography from Late Miocene to recent times, involving variable flow of Antarctic Bottom Water and Circumpolar Deep Water. A prominent basin-wide aggradational seismic unit is interpreted to represent the Mid-Miocene climatic optimum (~17–14 Ma). A major current reorganization can be inferred for the time ~14–12 Ma when the Valentin Feilberg Terrace started growing due to the deposition of sheeted and mounded drifts. After ~12 Ma, bottom water flow remained vigorous at both margins of the terrace. Another intensification of bottom flow occurred at ~5–6 Ma when a mounded drift, moats, and sediment waves developed on the terrace. This may have been caused by a general change in deep water mass organization following the closure of the Panamanian gateway, and a subsequent stronger southward flow of North Atlantic Deep Water.