Geological setting and diverse fauna of a Late Oligocene rocky shore ecosystem, Cosy Dell, Southland

Abstract

A new fossil locality of Late Oligocene (Duntroonian) age at Cosy Dell farm, Waimumu, southern New Zealand has yielded a diverse array of exceptionally well-preserved fossils derived from rocky shore, sandy beach and estuarine habitats. A lag deposit of Jurassic Murihiku basement boulders and cobbles is overlain by richly fossiliferous, locally concretionary, pebbly shellbeds. The fauna is remarkable for its taxonomic diversity. It includes thick-shelled bivalves and large gastropods, an abundance of juveniles and micromolluscs, and species with nacreous shell and colour patterns preserved. More than 350 species of molluscs are present, including 10 chitons, 90 bivalves and 250 gastropods. Other notable components of the biota include > 125 ostracod species, barnacles, foraminifera, brachiopods, bryozoans, echinoderms, hermatypic corals, otoliths and penguin bones. Oyster-encrusted and pholad-bored boulders, and intertidal and estuarine species indicate proximity to a rocky coastline and estuary, confirming the presence of land in southern New Zealand during Late Oligocene times.