Late Quaternary geology of Whangaparaoa area, East Cape, New Zealand

Abstract

Upper Pleistocene coastal, river terraces and tephras in the north eastern corner of the North Island, New Zealand are examined, mapped and correlated. Six coastal terraces are established. They areclassified, in descending order of elevation, as Matakaoa, Otamaroa, Ruakokere, Te Papa, Orete and Urutana coastal Terraces formed during high sea-level maxima at c.200,000, c.120,000, c. 100,000, c.80,000, c.2000 and c.1000 years. By Tephrochronological and geomorphological means, the marine terraces in the study area can be correlated with East Cape region and around the Bay of Plenty. Three river terraces have been recognised in order of increasing age Waiotuma, Ngarue andWaipa Terraces. They are considered to have been formed during stadial periods at c.110,000, c.70,000 and c.5000 years. Three tephras in order of increasing age - Mangaone Lapilli, Rotoehu Ash and Hamilton Ashwere recognised. They have been recognised and named by other workers in areas outside the mapped area.In the Te Piki area, several tephra layers are found, which are likely tobe considerably older than Rotoehu Ash based on stratigraphic position. According to major element glass chemistry, three tephra layers can be confidently correlated to Matahina Ignimbrite. The height distribution of Otamaroa Terrace in the study area, suggests that two tectonicregions can be distinguished. Region A is characterized by strong uplift with northerly tilt and region B shows lower uplift and north westerly tilting which can be correlated asfar as Te Araroa area. The Uplift rate for Otamaroa Terrace (c.125,000 years) is higher at East Cape region than in the study area.