Upper Jurassic stratigraphy, south Kawhia region, New Zealand

Abstract

Previously defined formations of the Upper Jurassic Murihiku Supergroup (Kirikiri, Ahuahu, and Owhiro Groups) based on the south Kawhia coast are mapped south to the Te Anga area. The Kirikiri Group consists dominantly of siltstones, mudstones, and fine to very fine sandstones. Siltstones and mudstones dominate, and medium‐coarse sandstones and conglomerates are common in northern exposures of the Ahuahu and Owhiro Groups. Most formations thicken southwards and fine southwards and eastwards. Calcareous concretions are intercalated in mudstones and siltstones throughout the sequence. These units lie within the Heterian, Ohauan, and Puaroan local stages of the Upper Jurassic sequence. From bio‐stratigraphic considerations, an earlier proposed three‐fold division of the Heterian is accepted and a tripartite division of the Ohauan Stage is introduced. Bivalves, ammonites, brachiopods, belemnites, and gastropods are dominant faunal elements in the lower part of the Upper Jurassic sequence, whereas the upper part is dominated by belemnites and ammonites with only rare bivalves. Stratigraphic ranges of important species in the type section are summarised. The Upper Jurassic sequence at Kawhia is entirely marine and was deposited in submarine fans supplied by turbidity currents including occasional high density flows. © 1995 The Royal Society of New Zealand.