Geology of the Whangaparaoa area, eastern bay of plenty

Abstract

Abstract Sedimentary rocks within the Whangaparaoa area are divided into two groups. Of these, one group and three formations are newly established and one formation is redefined; another previously accepted formation is discarded. Poorly exposed, unfossiliferous Haumurian‐Teurian sediments are included within the Mangatu Group which is not further subdivided. Coarse lithologies which grade up the stratigraphic sequence into interbedded thin sandstones and grey mudstones containing basal Miocene microfaunas are included within the Whakai Formation. The Wharekahika Formation, which was erected by Ongley and MacPherson in 1928 and regarded as of probable Pliocene age, is discarded because it cannot now be readily identified and the fauna listed for it is likely to be a mixed one. Strata of the Runaway Group which crop out over large portions of the Whangaparaoa area comprise two formations—the Te Kahika Formation of Opoitian age and the Whangaparaoa Pumiceous Sandstone of Opoitian to ? Waipipian age. Fossiliferous Castlecliffian lithologies of two small, widely separated outcrops are included as separate members of the Waipaoa Formation. Within one member is the richly fossiliferous Te Piki Bed which contains an excellently preserved, diverse, Aotea zone fauna. Middle to Upper Pleistocene deposits underlying terraces at 63 m and 33 m, and other undifferentiated levels, constitute the Rukuhanga Formation. Igneous rocks of problematical Upper Mesozoic to Paleogene age are marginal to the area and are mapped as undifferentiated lithologies belonging to the Matakaoa Volcanic Group. The claim that a continuous graben exists from Cape Runaway to Hick's Bay, which mcludes the Whangaparaoa area, is examined and is partly rejected. In presenting a geological history of the area we correlate an unconformity spanning most of the Miocene with uplift in a nearby area considered by a previous worker to be the source region for a series of thrust slices.