Quaternary deposits in the Porirua Area, New Zealand

Abstract

Quaternary deposits in nine sections in the Porirua area are correlated by means of red-weathering horizons, radiocarbon dates, altitude above sea level, lithologies, and erosion intervals. The red weathering of superficial deposits and greywacke—argillite bedrock is considered to have taken place in the Quaternary in a climate warmer than the present, and probably in three distinct episodes—a lengthy warm, humid period, followed later by two shorter warm, humid periods. Preceding the periods of red weathering there was at least one intense periglacial episode, indicated by red-stained solifluction deposits. The earlier period of red weathering possibly occurred during the Last Interglacial, more than 45,000 years ago, at a time when sea level stood some 60 ft above the present. During one of the later red-weathering phases sea level probably stood at 25 ft above the present. This latter period of warm, humid conditions was followed by a cooling 37,500 years ago, by warm, wet conditions about 25,000 years ago, and then by a period of periglaciation from 23,000 to 20,000 years ago. Before the Last Interglacial, there seems to have been a period of intense tectonic activity, but later earth movements have been spasmodic and on a small scale.