The Early Permian intracratonic Arckaringa Basin is composed of a central platform area of gently undulating shallow crystalline basement surrounded by peripheral depressions. It was established by downfaulting along the marginal depressions, principally the Boorthanna and Phillipson Troughs which contain up to 1,300 m of Permian sediments, underlain unconformably by 880 metres or more of unmetamorphosed Early Palaeozoic rocks or by Precambrian metasediments. Eromanga Basin sediments unconformably overlie the Permian sequence in most areas varying in thickness from zero to about 200 m in Area E.