Intraspecific variation and palaeogeographic dispersal of the Mississippian miospore Reticulatisporites magnidictyus Playford & Helby, 1968

ABSTRACT

Renewed study of an Australian Mississippian-age palynoflora – the Grandispora maculosa zonal assemblage from the Mount Johnstone/Italia Road Formation (Hunter Valley, New South Wales) – reveals significant morphological variation in some of its key miospore components – in particular Reticulatisporites magnidictyus, the subject of the present account. Detailed microscopy of numerous topotypic specimens of this species, originally described in 1968, results in its formal emendation; this takes particular account of the hitherto unrecognised presence of a proximo-apical prominence about the confluence of the laesurae. The G. maculosa palynoflora, with its constituent R. magnidictyus, has been reported from within a ca. 30–45°S palaeolatitudinal belt, at numerous Western, Eastern, and Northern Gondwanan locations in strata of middle Visean–early Serpukhovian age, but with a possible extension into the Early Pennsylvanian (Bashkirian). Consequently, R. magnidictyus is one of a very limited group of distinctive miospore species that facilitate long-distance chronostratigraphic correlation within the supercontinent.

KEYWORDS:

• Reticulatisporites magnidictyus
• morphology
• Mount Johnstone Formation
• New South Wales
• Mississippian
• Gondwana

Acknowledgements

Sincere thanks are expressed to the following: Derek Hoy (School of Earth and Enviromental Sciences, The University of Queensland) for providing insights into the geology and tectonic evolution of the Southern New England Orogen and for drafting Figure 3; and to Professor Geoffrey Clayton (Trinity College Dublin) and Dr Jan Hennissen (British Geological Survey), whose comments on the original manuscript have proven very beneficial.

Disclosure statement

No potential conflict of interest was reported by the author.

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Notes on contributors

Geoffrey Playford

GEOFFREY PLAYFORD is a graduate of the Universities of Western Australia (BSc Hons I, DSc) and Cambridge (PhD) and is currently a professor emeritus in the School of Earth and Environmental Sciences, The University of Queensland (UQ). While an Honours student at the University of Western Australia (UWA), he was introduced to palynology by the inspirational Dr Basil Balme, then newly appointed to the university. Geoff's PhD research at Cambridge – supervised by Dr Norman Hughes – was undertaken during the tenure of a Robert & Maude Gledden Research Fellowship awarded by UWA. Subsequently, while a National Research Council of Canada Postdoctoral Fellow, he worked with the late Dr Peter Hacquebard and Sedley Barss at the Geological Survey of Canada (Ottawa), followed by a lectureship appointment at UQ. During periods of sabbatical leave from UQ, he has conducted collaborative research, notably with the late Dr Francine Martin (Belgium); Dr Colin McGregor (Canada); Prof. Reed Wicander and Merrell Miller (USA); Prof. Marco Tongiorgi (Italy); Drs Felipe González and Carmen Moreno (Spain); and, in Brazil, with Drs Rodolfo Dino and José Henrique Gonçalves de Melo, mainly at the Petrobras Research Center in Rio de Janeiro. Geoff has published extensively on a diverse range of Palaeozoic and Mesozoic palynomorphs, with main emphasis on their stratigraphic applications.