Martin Young

Dinoflagellate biostratigraphy of the vertebrate fossil-bearing Maungataniwha Sandstone, northwest Hawke's Bay, New Zealand

Abstract Fossil organic-walled dinoflagellate cysts (dinocysts) have been used to constrain the age of the Maungataniwha Sandstone and associated phosphatic and calcareous concretions from the Mangahouanga Stream, northwest Hawkes Bay, New Zealand. These concretions often contain dinosaur and marine reptile fossils, including the mosasaur Moanasaurus mangahouangae, first discovered within the study area in a calcareous concretion. The Maungataniwha Sandstone contains low to moderately diverse dinocyst assemblages corresponding to the Vozzhennikovia spinulosa – Isabelidinium pellucidum zonal interval (lower to upper Haumurian). Recovered dinocyst assemblages from in situ concretions are similar to those from the surrounding sediments, suggesting that the concretions have grown in place. Calcareous float concretions containing the mosasaur Moanasaurus mangahouangae, as well as the two phosphatic concretions (one of which also contained a mosasaur fossil), are all of a lower Haumurian age. Plesiosaur fossil-bearing calcareous concretions exhibit a range of ages from lower to upper Haumurian (early Campanian to early Maastrichtian), spanning the age range of the Maungataniwha Sandstone section within the study area. The two dinosaur fossil-bearing calcareous concretions can only be dated as no younger than the middle upper Haumurian (early Maastrichtian).