Palynological studies in the Lower Cretaceous of the Surat Basin, Australia

This study deals with palynological work in Aptian and lower to middle Albian sediments of marine and terrestrial origin in the Surat Basin of southeastern Queensland and northeastern New South Wales. It comprises stratigraphic coverage of (a) the spore and pollen sequence, which is subdivided into three intervals: the Osmundacidites dubius Zone of Aptian age, the Crybelosporites striatus Zone of early Albian age, and the Coptospora paradoxa Zone of mid-Albian age; and (b) the dinoflagellate sequence, in which a lower subdivision, the Odontochitina operculata Zone of Aptian age, and an upper subdivision, the Pseudoceratium turneri Zone of early to middle Albian age, are distinguished. Systematic study includes a discussion of problems concerning dinoflagellate classification, and outlining a system for Australian fossil dinoflagellate cysts, based on paratabulation, mode of archaeopyle formation, and ornamental structure. Description and documentation of the microfossils includes 38 genera and 72 species of spores, 18 genera and 21 species of pollen grains, and 35 genera and 60 species of dinoflagellates. Four new species of spores: Lycopodiacidites dettmannae, Lycopodiumsporites solidus, Osmundacidites dubius, Stereisporites pocockii; eight new species of fossil dinoflagellates: Cleistosphaeridium granulatum, Diconodinium paucigranulatum, Leptodinium simplex, Membranosphaera coninckii, M. norvickii, M. romaensis, Tenua aptiense, Trichodinium eisenackii; and one new variety: Canningia minor var. psi/ata are proposed. A total of 17 species and form groups ranked as species assigned to 7 genera of acritarchs and 'chlorophytes' are described and documented. One new acritarch species, Palaeostomocystis pergamentaceus, is proposed. The spore and pollen floras include a large proportion of pteridophyte and pteridosperm elements; gymnosperms form only a small minority. Angiosperm pollen grains first appear in the Albian sequence. Clavatipollenites hughesii and Asteropollis asteroids appear in the Crybelosporites striatus Zone, and other monosculate forms (Liliacidites) as well as tricolpate pollen grains (Trieolpites variabilis, Rousea georgensis) appear sporadically in the Coptospora paradoxa Zone. The dinoflagellate assemblages consist mainly of gonyaulacacean proximate cyst genera; chorate forms (Cleistosphaeridium, Hystrichosphaeridium) form a small minority in the Aptian, and slightly increase in the Albian. Acritarch assemblages are dominated throughout the record by the genera Leiosphaeridia and Micrhystridium. From analysis of proportional abundances of the groups of spores and pollen, dinoflagellates, and acritarchs in the total assemblage counts, and fluctuations of these abundances with time, a tentative approach is outlined towards reconstruction of past environments and palaeogeography in the Surat Basin. It is shown that statistical (numerical) records of individual fossils as abundance fractions of the group of which they are part (i.e. spores and pollen; dinoflagellates; acritarchs) may lead to preliminary conclusions on how these fossils behaved with changing conditions, and thus give some indications as to their ecological preferences.

Tags: AU-NSW, AU-QLD, Bulletin, Earth Sciences, GA Publication, Published_External
Organization: Geoscience Australia Data