LATE TRIASSIC PALYNOLOGY OF THE MUNGAROO AND BRIGADIER FORMATIONS, NORTHERN CARNARVON BASIN, NW AUSTRALIA

The palynofloras of the thick Carnian-Norian fluviodeltaic successions of the Mungaroo Formation and the overlying paralic to shallow marine Brigadier Formation have been studied in increasing detail since the mid-1980s and particularly in the last 15 years as successful oil and gas exploration has continued in the Northern Carnarvon Basin. The current study aims to review the regional palynology, particularly the rather enigmatic dinoflagellate cyst assemblages. The palynofloras are dominated by spore-pollen assemblages that until the early 2000s, proved difficult to consistently subdivide beyond the broadest zonal levels. Prolonged industry research have resulted in the recognition of up to eighteen spore-pollen subzones for the Ashmoripollis reducta, Minutosaccus crenulatus and Samaropollenites speciosus zones, often driven by regional palaeoenvironmental wet-dry shifts as much as traditional biostratigraphic events. Dinoflagellate cysts are well known from the uppermost of these zones, in the more strongly marine Rhaetian Brigadier Formation. There are new species and a few genera to still be formally described from the Rhaetogonyaulax rhaetica Zone at this level, however, it is the wider range (than previously known) of dinoflagellate cyst types and distribution in the underlying Norian-Carnian sequences that is of major interest and stratigraphic utility. The Rhaetogonyaulax wigginsii, Wanneria listeri and Hebecysta balmei zones are not restricted to only a few major marine flooding events with low diversity dinoflagellate assemblages, but rather can be used to identify a large number of minor marine influxes or even demonstrate moderately persistent marine influence in the more outboard Northern Carnarvon Basin wells. Up to 30 taxa, including many new species and several new genera are recognised from this interval, however many are small, thin walled, lacking obvious tabulation and are thus easily missed or lost without careful palynological preparations. New insights are also provided to the dapcodinioid, rhaetogonyaulacoid, and suessioid evolutionary lineages that have the potential to lead to enhanced stratigraphic resolution.