Aspects of Upper Quaternary stratigraphy of the Wanganui Basin

Abstract

Four sections apparently straddling the Castlecliffian Stage / Haweran Series boundary are studied between Wanganui and the Rangitikei River valley in the Wanganui Basin. These are situated within a presently rising landscape that has interacted with changes in sea level to produce flights of marine and river terraces. Detailed mineralogy, tephrostratigraphy and pollen analysis of the four sections allows a chronology to be developed which is compared with the chronologies of previous workers in the region. Comparison with tephrochronologies elsewhere in the North Island and the oxygen isotope record of Pacific core V28-239, (Shackleton and Opdyke 1976), is also attempted. It is concluded that Landguard Bluff records a double transgressive peak during oxygen isotope stage 7 and that the Landguard Formation and the Brunswick Formation, at Warrengate, were both deposited during oxygen isotope stage 9. At the Mingaroa section it is implied that the shellbed containing Pecten aotea was not deposited contemporaneously with the Landguard Formation, (also containing Pecten aotea) and that the marine sediments including and overlying the Mingaroa Fossil Bed are Haweran in age. Results from the Glencairn section are equivocal and the age of the shellbed containing Pecten aotea is uncertain at that site. Since the occurrence of Pecten aotea is apparently time transgressive across the Wanganui Basin its use as a chronostratigraphic marker is not recommended. The mineralogy of the sediments is used as a provenance indicator and shows the central North Island and Egmont volcanoes to have been active as far back as the antepenultimate interglacial, (oxygen isotope stage 9).