This renewed palynological study of the Mount Johnstone Formation, at Balickera in the Hunter Valley region of New South Wales (eastern Australia), discloses a considerably more diverse palynoflora – termed the Grandispora maculosa Assemblage – than was reported in 1968. Represented are some 51 species of palynomorphs, comprising 46 species of trilete spores (distributed among 27 genera), three species of monolete spores (three genera), one species of hilate spores, and a single algal-cyst species. The following species are newly instituted: Verrucosisporites adgeratus, V. johnstonense, V. pavimentatus, Anapiculatisporites robertsii, Convolutispora perplicata, Knoxisporites balickeraensis, Densoisporites argutus, Laevigatosporites demutabilis, and Latosporites durabilis. Quantitatively important and/or consistently represented species include Reticulatisporites magnidictyus (particularly), Punctatisporites spp., Verrucosisporites spp., Rattiganispora apiculata, Grandispora maculosa, Indotriradites kuttungensis, Velamisporites australiensis, Laevigatosporites demutabilis, and Psomospora detecta. The absence of marine palynomorphs supports the previously envisaged, predominantly fluvial deposition of the Mount Johnstone Formation. Key palynostratigraphic indices, in conjunction with absolute-age determinations obtained from sub- and suprajacent rocks, indicate that the G. maculosa palynoflora and its hosting Mount Johnstone strata are Mississippian – specifically middle–late Visean – in age. This dating also applies to similarly palyniferous deposits in the northern Perth and Carnarvon basins of Western Australia. Beyond Eastern Gondwana, equivalents of the G. maculosa association have been reported from Western Gondwana (Brazil and Argentina in particular) and, to a lesser extent, from Northern Gondwana, thus attesting to its wide distribution and chronostratigraphic significance within the supercontinent and its distinctiveness vis-à-vis Euramerican regions.

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