Barremian Foraminifera from the Muderong Shale, oldest marine sequence in the Cretaceous of the southern Carnarvon Basin, Western Australia

To clarify foraminiferal biogeographic affinities and the degree of differentiation of the inner shelf fauna from deeper water assemblages in the juvenile Indian Ocean, an assemblage of siliceous organic-cemented agglutinated foraminifera characteristic of the Ammobaculites Association described from the Southern Carnarvon Basin. The typical Muderong Shale assemblage is associated with the dinoflagellate Muderongia australis Zone, and is distinct from coeval foraminiferal assemblages known from Exmouth Plateau and the Argo Abyssal Plain. Lithofacies and biofacies suggest that the Muderong fauna inhabited dysaerobic sea-floor muds in the upper offshore zone (10-50 m water depth) in a sea with a very gentle sea-floor gradient deepening slightly toward the north. Faunal comparisons suggest that the Barremian ocean was well stratified on the mid-western Australian margin.