SIGNIFICANCE OF DEVONIAN-CARBONIFEROUS RADIOLARIANS FROM ACCRETIONARY TERRANES OF THE NEW-ENGLAND OROGEN, EASTERN AUSTRALIA

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 depositionally 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-grained siliceous 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 Formation, are allochthonous. © 1990 Elsevier Science Publishers B.V.