Mississippian palynoflora from the northern Perth Basin, Western Australia: systematics and stratigraphical and palaeogeographical significance.

Core material from an exploratory diamond drillhole (DDH CL5) in the Irwin Terrace, northern Perth Basin, Western Australia, contains a profuse and well-preserved palynofloral assemblage composed almost exclusively of trilete miospores. These comprise at least 32 species, distributed among 23 genera. Two species –Retusotriletes separatussp. nov. andApiculiretusispora tersasp. nov. – are new, andVelamisporites cortaderensis(Césari & Limarino, 1987) is proposed as a new binomial combination. The palynoflora essentially replicates compositionally theGrandispora maculosaAssemblage, first described in 1968 from New South Wales (Italia Road Formation of the Southern New England Orogen) with revised dating of late Visean. Particularly noteworthy in both local and regional biostratigraphical contexts is the combined presence ofG. maculosa,Reticulatisporites magnidictyus,Cordylosporites asperidictyus,Foveosporites pellucidus,Indotriradites kuttungensis,I. daemonii,Verrucosisporites aspratilis,V. gregatus,V. quasigobbettii,Raistrickia accinta,R. radiosa,Diatomozonotriletes daedalusandPsomospora detecta. Of these,V. quasigobbettiiandI. kuttungensisare predominant. Additionally, the assemblage contains some trilete species reported subsequently (in 1992) from a slightly younger (Pennsylvanian) succession of the Galilee Basin, southern Queensland; e.g.Cyclogranisporites firmus,Verrucosisporites basiliscutis,Dibolisporites disfacies,Diatomozonotriletes birkheadensis,Densoisporites truswelliae(syn. Densoisporitessp. of Jones & Truswell),Grandispora(Spelaeotriletes)queenslandensisandVelamisporites cortaderensis(syn.,inter alia,Reticulatisporites bifronsJones & Truswell). Significantly, however, the CL5 palynoflora is devoid of gymnospermous prepollen (indeed any pollen grains) that have been documented from the Galillee Basin deposits. Many components of theG. maculosasuite have been reported from elsewhere in Gondwana, particularly Brazil and Argentina, attesting to its stratigraphical significance across the supercontinent, and to the widespread dispersal of its pteridophytic parental flora in a relatively narrow time interval, bracketed within the late Visean through early Serpukhovian. The present assemblage, and indeed its representatives elsewhere in Gondwana, was likely deposited in non-marine, fluvial or lacustrine, interglacial environments that preceded the extensive icehouse conditions that prevailed during much of the Pennsylvanian. [ABSTRACT FROM AUTHOR]