New U-Pb zircon dates reveal a late Norian age for the upper part of the Red Cliff Coal Measures, New South Wales, Australia—implications for biostratigraphy

The upper part of the Red Cliff Coal Measures in northern New South Wales hosts a well-preserved Late Triassic flora that, previously, has not been dated precisely. New high-precision U-Pb zircon dating (U-Pb CA-ID-TIMS) from a bentonite immediately overlying the fossiliferous beds yields a maximum depositional age of 208.66 ± 0.33 Ma. This new chronological constraint demonstrates that at least the upper Red Cliff Coal Measures, and the correlative Blackstone Formation of the Ipswich Basin, are Norian in age rather than Carnian, as suggested previously. Palynological assemblages, although thermally altered and dominated by degraded phytoclasts, include spores and pollen assignable to the Craterisporites rotundus Oppel Zone of de Jersey (1975) and are representative of the high-latitude ‘Ipswich microflora’ phytoprovince. The macroflora is well preserved in the upper part of the Red Cliff Coal Measures and is dominated by the umkomasialean ‘seed fern’ Dicroidium odontopteroides but incorporates at least 11 other gymnosperm and two fern taxa typical of the well-documented Late Triassic Dicroidium-dominated floras of southeastern Gondwana. The fossil foliage is typically preserved in dense accumulations reminiscent of modern autumnal leaf mats. These leaves host a moderate array of herbivory and oviposition damage attesting to the presence of a varied insect fauna that is not represented by body fossils. The sedimentary facies associations, ranging from coarse-grained alluvial fan and fluvial channel deposits to finer lacustrine and peat-mire successions, together with numerous scour surfaces and lateral interdigitation of bedforms indicate deposition in a dynamic landscape typical of a small fault-bound continental basin. Collectively, these data refine the stratigraphic framework of the Red Cliff area and correlative components of the Ipswich Basin, and clarify the composition of the Late Triassic palaeovegetation and palaeoenvironments along the eastern margin of Gondwana. Stephen McLoughlin* [[e-mail]] and Vivi Vajda [[e-mail]], Department of Palaeobiology, Swedish Museum of Natural History, Stockholm, Sweden; James L. Crowley [[e-mail]] Isotope Geology Laboratory, Boise State University, Boise, ID, USA.