The Baralaba Coal Measures and the succeeding red-bed sequence, the Rewan Formation, are lithological units of the Bowen Basin of central and southeast Queensland, which contains extensive, economically valuable deposits of coal. The Blair Athol sequence occupies a small basin adjacent to the western margin of the Bowen Basin.
Plant microfossils extracted mainly from core samples of these non-marine sequences are systematically documented in the present study. One hundred and seventy species of miospores and ten of acritarchs, distributed amongst 101 genera, are identified. Five genera are newly described. They comprise: two of acavate, trilete spores, Phidiaesporites (type species, P. fosteri sp. nov.) and Limatulaspovites (type species, L. limatulus (Playford) comb, nov.]; an alete spore, Rugaletes (type species, R. playfordii sp. nov.); and two of unknown affinities, Chordecystia (type species, C. chalasta sp. nov.) and Tessellaesphaera (type species, T. tessellata sp. nov.). The genus Interradispora Price is validly instituted and Indotriradites Tiwari 1954 is formally emended. Newly instituted species include: sixteen of trilete spores, Acanthotritetes superbus, Brevitritetes hennellyi, Catamospora? ubischii, Camptotriletes cretus, Concavissimisporites grumulus, Densoisporites holospongia, Gondisporites bharadwajii, Granulatisporites absonus, Indotriradites reidii, Interradispora daedala, Limbosporites balmei, Lundbladispora iphilegna, Microfoveotatispora explicita, Neoraistrickia gracilis, Punotatisporites dejerseyi, Raistriakia crenata; three of striatitid disaccate pollen, Protohaploxypinus bharadwajii, P. haigii, and P. hartii; and one of unknown affinities, Brazilea helbyi. Examples of protosaccate pollen grains are reported for the first time in Lower Gondwanan assemblages.
Miospore assemblages from each section are identified with previously established Australian palynofloral zones. The Blair Athol palynoflora is the oldest of the presently studied assemblages and is assigned to an informally designated zone, known as "upper stage 4a". Marine invertebrate faunas associated with this zone in the Bowen Basin are of Early Permian age (i.e. late Sakmarian - Baigendzinian). The Baralaba miospore floras belong, with one exception, to the upper part of the Duthuntyispora-Assemblage. Assemblages from the basal Rewan Formation belong to the Protohaploxypinus miorooorpus Assemblage-Zone. Key elements of the latter were identified in a transitional palynoflora from the upper part of the Baralaba succession. Comparisons with miospore floras from faunally dated sequences elsewhere in Gondwanaland indicate that the Baralaba Coal Measures and basal Rewan Formation were deposited during the Middle to ?Late Permian (i.e. late Chhidruan to ?early Griesbachian). Few of the recorded species are known in assemblages outside Gondwanaland, and the present study reinforces the concept of a Gondwanan floral province. The majority of shared taxa are striatitid disaccate pollen grains. However, the possible functional morphology of these grains suggests that their occurrence may be attributable to homoplasy rather than to cosmopolitan parents.
The relationship between the palynofloral succession and the Permian/Triassic boundary in Gondwanaland, and its implications, are discussed. In keeping with recent results from marine invertebrate faunal studies, the Griesbachian "Stage" is regarded as the youngest Permian biochronologic unit. The basal Rewan appears to be no younger than early Griesbachian, which refutes earlier claims that the upper limit of the Permian System in the Bowen Basin is coincident with the lithostratigraphic boundary between the Rewan and underlying coal measures.
Although correlation of individual seams of the Baralaba Coal Measures has been attempted, the overall stability of the miospore assemblage precludes recognition of a local palynostratigraphic zonation. Quantitative variations within the assemblage appear only to reflect contributions from local ecological niches. Palaeoecological inferences, based on the overall composition of each of the three assemblages studied, are discussed. It is most likely that the coals of both sequences are of hypautochthonous origin.