Permo‐carboniferous silicic volcanism and palaeogeography on the western edge of the New England Orogen, north‐eastern New South Wales

Abstract

Deposition of Late Carboniferous and Early Permian continental conglomeratic strata along the western edge of the New England Orogen was continuously accompanied by silicic volcanism. Disconformable relationships exist locally between the Early Permian Glossopteris‐bearing rocks and the Late Carboniferous Rhacopteris‐bearing rocks but have negligible stratigraphic significance since erosional surfaces are common within the older sequence and probably also occur in the younger sequence. The western volcanic terrain which had supplied ignimbrites, airfall deposits and volcanogenic detritus eastward during the Late Carboniferous still had some active centres in the Early Permian, though eruptions waned in scale and changed in style to include effusion of lavas. Proximal Early Permian volcanics comprised of lithic‐rich ignimbrites and lavas at Boggabri are the remnants of one such centre. After eruptions had ceased, denudation of this and other remaining centres contributed volcanogenic detritus, including ‘flint clay’ clasts, to coal measure sediments (Greta equivalent) accumulating in the flanking low‐lying areas of the incipient Gunnedah Basin. There is no evidence in support of easterly provenance for these Early Permian coal measures nor for movement on the Mooki Thrust at this time.