ORDOVICIAN MICROFOSSILS FROM THE BALLAST FORMATION (GIRILAMBONE GROUP) OF NEW-SOUTH-WALES

The Ballast Formation (Girilambone Group) comprises quartzose sandston e turbidite and siltstone, and less common chert and mafic-intermediat e igneous rocks, that unconformably underlie Early Devonian strata in a wide tract of north central New South Wales. Conodonts and radiolari ans extracted by acid dissolution of cherty rocks, indicate that the u nit is of Llanvirn-early Caradoc (Darriwilian-Gisbornian) age. The Bal last Formation is a basinal sequence of cratonic derivation, but the l imits of its depositional realm are poorly established.