Lithofacies, paleoenvironments and sequence stratigraphy of the Late Oligocene Aotea Formation (Te Kuiti Group), central-western North Island, New Zealand

Abstract

This report presents a comprehensive facies and sequence stratigraphic analysis of the Late Oligocene Aotea Formation within the Late Eocene – Earliest Miocene Te Kuiti Group in the Waikato-King Country Basin in central-western North Island, New Zealand. The Aotea Formation is a mixed carbonate-siliciclastic succession with four facies associations: limestone (Waimai Limestone Member), calcareous sandstone (Hauturu Sandstone Member, Kihi Sandstone Member), calcareous siltstone (Patikirau Siltstone Member) and chemogenic facies (upper parts of Kihi Sandstone Member, Patikirau Siltstone Member and Waimai Limestone Member). Theses facies are established from field descriptions supplemented by laboratory textural and petrographic data and are inferred to have accumulated in different sectors of a shelf environment. The Aotea Formation comprises one sequence for which key surfaces and systems tracts are described and interpreted. The lower sequence boundary is a wave-planed surface. It, together with the subsequent onlap deposits represent a marked basinward shift in the position of coastal onlap arising from basin inversion focussed along the western margin of the basin, followed by marked subsidence in the northern part of the basin.