Change in direction of the Pelorus River, Marlborough, New Zealand: Evidence from composition of Quaternary gravels

Abstract

Clasts in greenish subsurface gravels of presumed Quaternary age in the Kaituna valley comprise mainly metamorphosed and variably foliated volcanic litharenite of the Pelorus Group, but also contain some Dun Mountain Ophiolite Belt lithologies. These clast compositions are inconsistent with the gravel source being either the surrounding schist basement or the nearby Wairau River, but instead strongly suggest a source in the Pelorus River catchment. Thus, at some time in the Quaternary, the Pelorus River flowed south into the Wairau River instead of east and north into Pelorus Sound as it does now. The change in drainage direction since then was due either to non‐tectonic river capture and/or northward regional tilting.

Keywords:

• Marlborough
• gravels
• river terraces
• Quaternary
• Pelorus Group
• tectonics