Bashkirian Taeniate Bisaccate Pollen-Dominated Palynological Assemblage from Northwestern Junggar Basin, Xinjiang Province, China

The Early Pennsylvanian land plant community is characterized by widespread forests consisting of lycopsids, ferns, and seeds fern in swampy wetlands. The contemporaneous palynological assemblages are mainly composed of spores of Lycospora spp., Densosporites spp., and Laevigatosporites spp. and monosaccate prepollen of Florinites spp. Taeniate bisaccate pollen appeared for the first time during the Early Pennsylvanian but never prevailed in the coeval palynological assemblages. Here, we report a taeniate bisaccate pollen-dominated palynological assemblage from the Jiamuhe Formation of Well Ke 85 in the Zhongguai Uplift, northwestern Junggar Basin, Xinjiang. Nineteen miospore species belonging to 14 genera were identified from the assemblage. Based on their relative abundance, one assemblage is nominated informally as Calamospora breviradiata-Lunatisporites tersus (BT) assemblage. SIMS U-Pb geochronological analysis of zircons from two volcanic ash beds from the basal and upper parts of the formation yields weighted mean 206Pb/238U dates of 316.3 ± 2.2 Ma (MSWD = 1.2, n = 19) and 316.5 ± 2.8 Ma (MSWD = 0.85, n = 20) in an ascending order. A Bashkirian age is thus assigned to the BT assemblage. Our combined palynological and geochronological investigations reveal an early stage of the rise of conifers in the Kazakhstan Plate and offer a rare glimpse into the Early Pennsylvanian land vegetation in the subtropical area at the northern hemisphere