Palynological assemblages from the Middle-Late Triassic Mungaroo Formation, northwestern Australia: palaeobotanical affinities, depositional facies and preferred habitats

One hundred and twenty-six samples of Late Carnian-Early Norian age were col-lected from conventional cores in four deep wells in the Mungaroo Formation in the Northern Carnarvon Basin, Western Australia. Palynological assemblages examined enabling palaeobotanical, palaeoenvironmental and palaeobiogeographical inferences to be made. The assemblages are diverse, reflecting a wide range of palaeoenvironments. The most important palynofloral elements are Falcisporites australis-producers, ferns, freshwater-brackish algae, lycopsids, conifers and early gymnosperms, Cycadopites spp., and equisetopsids. Most assemblages are dominated by Falcisporites australis, a bisaccate pollen with probable corystosperm affinity. While Falcisporites-producers were capa-ble of colonizing a wide range of palaeoenvironments, their widespread distribution may also reflect enhanced wind transport. Ferns, the most common and diverse plant group overall, generally prefer wetter, fine-grained substrates on the floodplain, however there is significant variability between taxa: Marattiaceaen ferns are more common in sandier, better-drained substrates than those from most other groups. Cycadopites spp. and conifers are persistent but minor palynofloral elements in most samples. Although Cycadopites spp. prefer finer substrates, and conifers prefer better-drained substrates, both groups may have inhabited a wide range of palaeoenvironments indicating a degree of adaptability and tolerance to diverse edaphic conditions. Freshwater algae attest to the persistent wetness of the Mungaroo delta. Bartenia, the most common genus of algae, is found in nearly all depofacies, indicating the capacity to tolerate a range of water salinities and energy levels. Sporadic dinocyst abundance spikes indicate occasional marine incur-sions onto the low-relief Mungaroo delta plain. The assemblages belong to the Onslow Microfloral Province categorized by the presence (4% on average) of cosmopolitan taxa including Ashmoripollis, Aulisporites, Camerosporites, Enzonalasporites, Ephedripites, Lunatisporites, Minutosaccus, Ovalipollis, Rimaesporites and Samaropollenites.