BRYOZOAN FAUNA OF THE KAIPUKE SILTSTONE, NORTHWEST NELSON - A MIOCENEHOMOLOG OF THE MODERN TASMAN BAY CORALLINE BRYOZOAN GROUNDS

The Kaipuke Siltstone Formation (Westhaven Group) near the Anatori Riv er mouth, northwest Nelson, contains a reasonably well preserved bryoz oan fauna of Otaian age. Analysis of this fauna has yielded six specie s of Cheilostomatida, mostly with an erect-rigid colony form. One new species, Hippoporina miocenica, is described. Four of the species appe ar conspecific with modern bryozoans, including the two species (Celle poraria agglutinans (Hutton) and Hippomenella vellicata (Hutton)) that dominate the modern Tasman Bay bryozoan grounds. From foraminiferal e vidence and from what is known of the ecological requirements of the m odern bryozoan species it is possible to infer the paleoenvironment of the Kaipuke Siltstone fauna, viz, an area of near-oceanic salinity, w ater movements able to exceed 0.3 m/s, a seasonal temperature range pr obably c. 12.5-17 degrees C, and with the possibility of terrigenous s ediment accumulation. We conclude that this fauna is an early Miocene homologue of the present-day, ecologically important ''Tasman Bay cora l'' and that this biotope has persisted for at least 20-22 Ma.