SHALLOW MARINE PALEOECOLOGY OF HALOBIA OF THE NORIAN (LATE TRIASSIC) IN OWAKA, NEW ZEALAND

The genus Halobia is a globally distributed biostratigraphic index fossil group confined to the Late Carnian and Early to Middle Norian (~235-208.5 Ma); the time ranges of Halobia species are largely well-defined.Halobia are known from deeper, dysoxic deposits, but in New Zealand they appear to have thrived in relatively normal shallow marine conditions, making up the base of the benthic community. Their paleoecology in shallower environments is not well understood. This study on the paleoecology and diversity of Halobia and other benthic taxa focuses on the Owaka region of New Zealand from the early and middle Norian (Oretian and Otamitan NZ substages).

Bulk samples were collected from across the Owaka area of New Zealand (southeastern South Island) in order to assess Halobia diversity and abundance through time and over a broad geographic region. Bulk sample ages were determined biostratigraphically using Halobiaand Manticula occurrences. Oretian assemblages exhibited relatively low biodiversity with high dominance by Halobia with other rare epifauna including brachiopods and gastropods. The persistent dominance of Halobia suggests that the success of Halobia is not controlled by depth but perhaps by ecological factors. Otamitan bulk samples largely have higher diversity but are still primarily composed of immobile epifauna, including Manticula and Hokonuia, and in younger samples, brachiopods. Thus, these assemblages are unique not only for their endemic fauna, but for the high degree of Halobia dominance in an apparently oxic shallow marine system.