Dinoflagellate biostratigraphy of the Arowhanan Stage (upper Cenomanian-lower Turonian) in the East Coast Basin, New Zealand

A new dinoflagellate zonation scheme for the New Zealand Arowhanan Stage (upper Cenomanian-lower Turonian) is proposed based on a study of the dinoflagellate assemblage from four onshore East Coast Basin sections, including the boundary stratotype section for the Arowhanan Stage. The existing Endoceratium ludbrookiae Zone is emended; its top now coincides approximately with the base of the Arowhanan Stage, at the highest occurrence of Endoceratium turneri. Three new interval zones are proposed above it: Ascodinium serratum Zone, Cyclonephelium clathromarginatum Zone and Hapsocysta peridictya Zone. The three zones together cover all but the uppermost part of the Arowhanan Stage. The Cenomanian/Turonian (C/T) stage boundary is located above the top of the Hapsocysta peridictya Zone, below the Arowhanan/Mangaotanean stage boundary. The boundary between the inoceramid bivalve Magadiceramus rangatira haroldi Zone and Magadiceramus rangatira rangatira Zone, which informally subdivides the Arowhanan into lower and upper substages, is located in the upper part of the Cyclonephelium clathromarginatum Zone. The distribution pattern of key dinoflagellate taxa in the Mangaotane Stream section indicates that the C/T boundary interval may be condensed or missing from that section. The new dinoflagellate Pareodinia mangaotanensis, which is restricted to the Arowhanan Stage, is described from the sections.