Palaeobathymetry of ostracod associations before and after the Chinaman Gully regression (‘Eocene/Oligocene boundary’) in South Australia

Abstract

The Chinaman Gully Formation in South Australia is a regressive non-marine to marginal marine unit previously correlated with the ‘Eocene/Oligocene boundary’ type 1 Sequence Boundary Ta 4.3/4.4. It is barren of ostracods. Cytherellid, krithiid, pontocypridid, paracypridid and trachyleberidid ostracods are abundant in the underlying Blanche Point Formation (BPF), whereas bairdiids, xestoleberidids, hemicytherids and loxoconchids are more abundant in the Port Willunga Formation (PWF) which overlies the Chinaman Gully Formation. A major contrast in trachyleberidid, loxoconchid and hemicytherid species composition is evident between the BPF and PWF. A bootstrap variety of correspondence analysis identified Paracypris, Kuiperiana, Krithe, Tasmanocypris?, Argilloecia, Trachyleberis, Cytherella and Bythocypris as significant genera (indicating a palaeodepth of 120–200 m) in the BPF and Quadracythere, Hornibrookella?, Loxoconcha, Microcytherura, bairdiids, Schizocythere, Cytheralison, Kangarina and Xestoleberis a...