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Abstract
Several new ammonite assemblages are described from the uppermost Temaikan and basal Heterian regional stages of New Zealand, Auckland Province, consisting mainly of the east Pacific Eurycephalitinae (Family Sphaeroceratidae). Four successive faunas are distinguished in the upper Awakino valley: all include the Andean genus Araucanites, here occurring with both sex‐morphs. Fauna 1 includes Araucanites awakino n. sp., Iniskinites cf. crassus Riccardi & Westermann, and Xenocephalites grantmackiei Westermann & Hudson ?/m × Lilloettia aff. steinmanni (Spath) ?/M—latest Bathonian; Fauna 2 includes Araucanites postawakino n. sp. and Xenocephalites cf. stipanicici Riccardi et al.—Early/earliest Callovian; Fauna 3 with Araucanites ponganui n. sp., Iniskinites gr. cepoides (Whiteaves), and Choffatia gr.furcula (Neumayr)—Early Callovian; Fauna 4 with Araucanites spellmani n. sp.—? Middle Callovian.
The Oraka Sandstone at Kawhia Harbour is now placed entirely in the uppermost Bathonian and Lower Callovian (i.e., with Faunas 1 and 2). Ammonites previously identified with Kimmeridgian taxa—that is, "Epimayaites”, “Epicephalites”, and "Subneumayria"—are now classified as microconchs of Araucanites and with macroconchs of Lilloettia and Iniskinites. The superjacent Ohineruru Formation contains a typically Indo‐Pacific fauna of Late Oxfordian to Early Kimmeridgian age, based on Sulaites heteriensis (Stevens) [ex Idoceras], a close relative of S. gerthi Oloriz & Westermann from New Guinea, and, above, Paraboliceras macnaughti (Stevens) [ex Kossmatia].
The interval Upper Callovian to Middle Oxfordian cannot be documented by ammonites in New Zealand, suggesting a hiatus between Oraka and Ohineruru Formations, marked by the Captain King's Shellbed.
Other useful index fossils are forms of the bivalve Retroceramus. The first occurrence of R. galoi (Boehm) defines the base of the Heterian regional stage, but its New Zealand occurrence is much earlier than in Indonesia (Middle Oxfordian). Furthermore, first occurrence is diachronous according to ammonite biostratigraphy even in Auckland Province, that is, between Faunas 3 and 4 in Awakino valley and in Fauna 2 at Kawhia Harbour. Regional and local facies control is indicated. On the other hand, Fauna 2 includes R. stehni Damborenea known from the Early/earliest Callovian of the Andes.