Geomorphological evidence for a Pleistocene barrier at Matakana Island, Bay of Plenty, New Zealand

Abstract

New Zealand's largest barrier island, Matakana Island, consists of an elongate coastal sand barrier of Holocene age that encloses Tauranga Harbour and adjoins an area of Pleistocene terraces and terrace remnants. The lowest Pleistocene terrace is well preserved, with a degraded marine cliff, vestiges of shore‐parallel relict foredunes, and a parabolic dune. These hitherto unrecognised coastal landforms are analogous to those of the Holocene barrier and indicate that a prograded coastal plain underlies the terrace. The original landforms of the coastal plain are now mainly below sea level but survived the postglacial marine transgression because at least 12 m of tephra accumulated on the surface, preserving the topography, albeit in a subdued form. In a separate area of the island, the present morphology may reflect the former presence of large parabolic dunes of Pleistocene age. Morphological evidence indicates that coastal processes shaped the island during both Pleistocene and Holocene times, and that the Holocene barrier is welded to a Pleistocene “proto‐barrier”.