Bryozoan fauna of the Kaipuke siltstone, northwest Nelson: A Miocene homologue of the modern Tasman Bay coralline bryozoan grounds

Abstract

The Kaipuke Siltstone Formation (Westhaven Group) near the Anatori River mouth, northwest Nelson, contains a reasonably well preserved bryozoan fauna of Otaian age. Analysis of this fauna has yielded six species of Cheilostomatida, mostly with an erect‐rigid colony form. One new species, Hippoporina miocenica, is described. F‐'our of the species appear conspecific with modern hryozoans, including the two species (Celleporaria agglutinans (Hutton) and Hippomenella vellicata (Hutton)) that dominate the modern Tasman Bay bryozoan grounds. From foraminiferal evidence and from what is known of the ecological requirements of the modern bryozoan species it is possible to infer the paleoenvironment of the Kaipuke Siltstone fauna, viz, an area of near‐oceanic salinity, water movements able to exceed 0.3 m/s, a seasonal temperature range probably c. 12.5–17°C, and with the possibility of terrigenous sediment accumulation. We conclude that this tauna is an early Miocene homologue of the present‐day, ecologically important “Tasman Bay coral” and that this biotope has persisted for at least 20–22 Ma.

Keywords:

• Kaipuke Siltstone
• northwest Nelson
• Otaian
• Altonian
• Miocene
• Bryozoa
• “Tasman Bay coral”
• paleoenvironment
• Celleporaria
• Hippomenella
• Hippoporina n. sp.