Earliest Triassic (Induan) spores and pollen from the Junggar Basin, Xinjiang, northwestern China

Abstract

Permian–Triassic boundary strata cropping out in the southern Junggar Basin contain a continuous and varied fossil record, making this fluvio-lacustrine succession a potential candidate for a non-marine boundary stratotype. Abundant, diverse and well preserved miospores are recorded and illustrated from the upper part of the Guodikeng Formation and the basal part of the Jiucaiyuan Formation, comprising 92 species and 48 genera, as well as some acritarchs. Seven new species ( Anapiculatisporites decorus Ouyang et Norris, sp. nov., Baculatisporites uniformis Ouyang et Norris, sp. nov., Kraeuselisporites varius Ouyang et Norris, sp. nov., Lapposisporites echinatus Ouyang et Norris, sp. nov., Klausipollenites angustus Shu et Norris, sp. nov., Alisporites exilis Ouyang et Norris, sp. nov., Pilasporites perreticulatus Ouyang et Norris, sp. nov.) and 8 new combinations are proposed. Pteridophytic spores and gymnospermous pollen are almost equally diverse, comprising 45 species in 20 genera, and 43 species in 25 genera, respectively. Pteridophytes are numerically more important, notably Limatulasporites, Kraeuselisporites, Lundbladispora, Anapiculatisporites and Verrucosisporites, but also prominent are bisaccate pollen of Falcisporites, Klausipollenites and Alisporites. Less abundant taeniate pollen are largely bisaccate. These palynofloras are grouped together as the Lundbladispora– Lunatisporites– Aratrisporites Assemblage, argued to be Early Triassic (early Induan), and comprising both newly evolved Mesozoic taxa (herbaceous and shrubby lycopsids, coniferous trees, pteridosperms) and relict Paleozoic taxa (sphenophyllids, cordaitaleans and possibly Paleozoic lycopods). The lower boundary of the Triassic in the section is redrawn somewhat lower than by previous authors. The transitional nature of the Permian–Triassic palynofloras and of the paleophytoprovinces is discussed; neither indicates a sudden catastrophic event affecting terrestrial floras at the P–T boundary on a global scale. The Early Triassic vegetation appears to have grown under humid sub-tropical conditions in lowland flood plains and marshes dominated by hydrophilous and mesophilous pteridophytes and pteridosperms, but with locally drier upland environments supporting xerophilous and mesophilous conifers and pteridosperms. The Induan vegetation is closely comparable to that of the Angara, especially the Subangara Province, although it contains some elements of the Euramerican Province in association with a few Gondwanan, Cathaysian and cosmopolitan taxa.