Marine Micropaleontology, 15 (1990) 365-378 365 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands Significance of Devonian-Carboniferous Radiolarians from Accretionary Terranes of the New England Orogen, Eastern Australia JONATHAN AITCHISON Department of Geology and Geophysics, University of New England, Armidale, NSW 2351 (Australia) (Received August, 1~88; revised and accepted March, 1989) Abstract Aitchison, J.C., 1990. Significance of Devonian-Carboniferous radiolarians from accretionary terranes of the New England orogen, eastern Australia. Mar. Micropaleontol., 15: 365-378. Radiolarians provide age constraints for many previously undated terranes in the New England Orogen (NEO), a tectonic collage developed along the eastern margin of Australia. Djungati terrane, the age range of which was previously unknown, contains two distinctive siliceous sedimentary lithofacies. The oldest is a thick sequence of red, ribbon-bedded cherts which probably accumulated in a deep ocean- floor setting far from land. Middle Silurian through Late Devonian radiolarians have been recovered from these cherts. Green tuffaceous cherts which contain a latest Devonian (Famennian) radiolarian fauna depositionaUy overlie the lower red ribbon-bedded chert sequence. These cherts are intercalated with volcaniclastic sediments and the fauna which they contain can be used to constrain the timing of accretion of older rocks into a subduction complex. Anaiwan terrane, which was also previously undated, contains thin ribbon-bedded cherts which are depositionally overlain by tuffaceous chert, siliceous siltstones and volcaniclastic sediments. Latest Devonian (?late Famennian) and Early Carboniferous radiolarians have been recovered from these cherts and tuffaceous siltstones. Radiolarians also occur in fine-grainedsiliceous sediments of the Yarrimie Formation, part of the Gamilaroi terrane. These radiolarians are of Late Devonian (Frasnian) affinity and their presence indicates that blocks of limestone, which contain Givetian conodonts and corals and were previously thought to indicate the age of the Yarrimie For- mation, are allochthonous. Introduction The geology of eastern Australia is domi- nated by a tectonic collage of terranes known locally as the New England Orogen (NEO). The detailed geology of the NEO is not well known due to structural complexity and poor expo- sure. Recent detailed work has shown the oro- gen to be a complex collage ofterranes (Fig. 1 ) which were accreted to the eastern margin of Australia at various times during the late Pa- leozoic (Flood and Aitchison, 1988a, b). Early plate tectonic models for this portion of eastern Australia assumed a relatively simple active plate margin during the Paleozoic (Leitch, 1974, 1975; Cawood, 1983; Harrington and Korsch, 1985; Murray et al., 1987). However, previous models for the tectonic development of the NEO are inconsistent with the available data (Flood, 1988) and the interrelationships of many of the terranes present are unknown. Although some terranes are moderately fossiliferous (e.g., Gamilaroi terrane), macrofossils are generally scarce and previous tectonic models have been based on assumed ages. Recent radiolarian 0377-8398/90/$03.50 © 1990 Elsevier Science Publishers B.V.