Late Quaternary geology of the Wairau Plain, Marlborough, New Zealand

Abstract

The late Quaternary deposits of Wairau Plain are subdivided on the basis of mapping, test drilling, radiocarbon dating, and macropaleontology (paleoecology). Otira (last) Glaciation fluvial gravel, sand, and clay deposits (cOlTelated with the Speargras1.i Formation of the upper Buller River valley) are capped by a surface which extended at least to the present-day coast and possibly into Cloudy Bay. Postglacial deposits overlying Speargrass Formation are grouped into 2 contemporaneous formations described in this paper. Dillons Point Formation (new name) consists of marine embayment and estuarine sediment and fauna, deposited over the land surface during the postglacial marine transgression and the subsequent regression. The maximum inland transgression occurred about 6000 to 7000 years ago before a barrier spit (Boulder Bank) was formed part of the way across Cloudy Bay. Progradation of the coast occurred outside the northern end of the Boulder Bank simultaneously with the infilling of the lagoons and estuaries behind the Boulder Bank. Rapaura Formation (new name), a postglacial fluvial gravel, sand, silt, and clay deposit, is derived mainly from erosion of the Speargrass Formation as a result of alternating aggradation and degradation by the Wairau River. Rapaura Formation lenses out against, and interfingers with, Dillons Point Formation. Macrofaunas from Dillons Point Formation (mainly drillhole samples) are detailed in an appendix and the paleoecology is discussed.