PALYNOLOGICAL ASSEMBLAGES FROM THE JK TRANSITION OF THE SURAT BASIN, AUSTRALIA: WHAT THEY TELL US ABOUT THE REGION'S FLORA

The Westbourne Formation to Mooga Sandstone interval of the Surat Basin contains the most complete record of deposition from Queensland from the time of the Jurassic–Cretaceous transition. As relatively few botanical macrofossils have been reported from this interval, and few of those have been well described, palynological studies, such as the one presented here, provide the best window into the region’s flora just before the arrival of the angiosperms. Palynological samples taken from three stratigraphic boreholes that intersected this interval produced a diverse, but relatively stable, microflora of 218 taxa. Fern spores are the most abundant component of assemblages, averaging 51 percent of all samples, in particular those of the Osmundaceae and Matoniaceae. Spores produced by the Dicksoniaceae, Gleicheniaceae, Horsetails, Marattiaceae, Schizaeaceae, Pteridaceae and Polypodiaceae are also represented. Averaging 20 percent of all assemblages the spores of the lycopods were the second most abundant group and were the most taxonomically diverse. Conifer pollen averaged 17 percent of all assemblages with that produced by the Araucariaceae being the most common of these. Pollen from the Cheirolepidaceae, Podocarpaceae, Pinaceae and Taxodiaceae is also recorded in these samples. Pollen produced by the seed ferns averaged five percent of all samples, while spores produced by bryophytes averaged less than two percent and the monocolpate pollen that may have been produced by some combination of cycads, ginkgoes and gnetales less than one percent of all assemblages. While the link between palynofloral and macro-floral abundances is not a direct one, being influenced by sedimentological and taphonomic effects, some broad conclusions about the parent flora can be made. The Surat Basin flora of the mid-Tithonian to early Hauterivian was a diverse one, with a floodplain (from where these samples were taken) flora dominated by members of the Matoniaceae and Osmundaceae along with numerous other species of ferns, lycopods and bryophytes. The somewhat drier upland flora is represented by the Araucariacean conifers with the seed ferns and the Podocarpacean and Cheirolepidacean conifers producing much of the remaining upland palynofloral assemblage.