Belemnite biostratigraphy of the New Zealand Late Jurassic Mangaoran (Early Puaroan) Substage and the Puaroan Stage revisited

Abstract

Hibolithes arkelli Stevens, H. marwicki Stevens, and H. mangaoraensis Stevens are common fossils with partly overlapping stratigraphic ranges in the Mangaoran Substage, of the Late Jurassic Puaroan Stage. Studies based on samples from known stratigraphic positions in the Kawhia Harbour sequence provide data for comparative purposes. The three species are similar in several measurable features. Mean values differ only slightly, and dispersions are partially concurrent. The specific identification of fragmentary specimens may be difficult, and that of pre‐adult fragments particularly so. The stratigraphic proximity of the morphologically similar Upper Ohauan Hibolithes kaimangoensis Challinor is a complicating factor. The stratigraphic succession of H. arkelli, H. marwicki, and H. mangaoraensis can be demonstrated in several sections in the Kawhia and Port Waikato regions. Hibolithes arkelli grantmackiei Challinor, currently used to define the base of the Puaroan Stage, is a composite taxon some members of which are here re‐identified as H. arkelli and H. mangaoraensis. The remainder are re‐described as Hibolithes sp A. Its morphology and stratigraphic range are poorly known and the species is unsuitable as a stage boundary marker. Hibolithes arkelli regularly appears near the base of the Puaroan Stage as presently defined and a formal re‐definition based on that taxon is proposed. Although this alters the faunal basis of the stage, the position of its base remains unchanged.