Middle Eocene echinoids from the western Eucla Basin, Western Australia

WA Museum Records and Supplements | Updated 3 years ago

ABSTRACT – The oldest carbonate sediments in the western Eucla Basin in south-western Australia are a series of cool-water bryozoan-dominated bioclastic grainstones, packstones and marls that represent deposition during the Tortachilla Transgression during the Bartonian (middle Eocene) planktonic foraminiferal zones 14–15. The two principal units are the Nanarup Limestone and a unit reported here for the first time and named, informally, the Manypeaks limestone. These units contain rich invertebrate faunas dominated by bryozoans, echinoids, bivalves and brachiopods. Herein we document fourteen echinoid species that occur in these limestones. They comprise one cidaroid, one camarodont, one salenioid, two cassiduloids, one echinolampadoid, one clypeasteroid and seven spatangoids. Four new species are described, the cassiduloid Eurhodia westaustraliae sp. nov., the clypeasteroid Fossulaster susae sp. nov., and the spatangoids Cyclaster jamiei sp. nov. and Gillechinus kaitae sp. nov. The species of Fossulaster represents the earliest known member of the Fossulasteridae and the earliest known record of a marsupiate echinoid in Australia. Analysis of the middle and late Eocene echinoids faunas of the western Eucla Basin establishes that the Nanarup Limestone echinoid fauna represents the cassiduloid biofacies, while the Manypeaks limestone is a mixed cassiduloid and spatangoid biofacies.