A Lower and Middle Devonian radiolarian biozonation of the Gamilaroi terrane, New England Orogen, eastern Australia

Abstract

Seven distinctive radiolarian assemblages defined from the Gamilaroi terrane of eastern Australia form the basis of an uppermost Lower to Middle Devonian radiolarian biostratigraphy. In ascending order these are the: Stigmosphaerostylus horrida, Helenifore laticlavium, Circulaforma admissarius, Helenifore pilosidiscus n. sp., Protoholoeciscus hindea, Ceratoikiscum regalinodus, and Trilonche minax assemblages. Gamilaroi terrane sedimentation occurred during the interval Early (Pragian) to Late (Frasnian) Devonian in a volcanic island arc environment in which radiolarians were abundant but sedimentary facies were locally variable. Radiolarian assemblages can be used for terrane-wide correlation. Although assemblages are dominated by spumellarians they also include more distinctive ceratoikiscid forms. Two new ceratoikiscid taxa: Circulaforma davidi n. sp. and Helenifore pilosidiscus n. sp are described.