New U-Pb zircon ages document Late Triassic Tianqiaoling flora of eastern Jinlin, NE China

Abstract

The Late Triassic Tianqiaoling flora is well-known in China, and its discovery has changed our understanding of Chinese Late Triassic phytogeographical divisions. More broadly, this flora has great significance for the study of phytogeography in East Asia during this time. However, the previous dating of this flora was only evidenced by plant fossils and stratigraphic correlation, and the accurate dating has still not been achieved. In this study, rhyolite samples were collected from the bottom of the Tianqiaoling Formation, which is conformally contacted the Tianqiaoling flora-bearing beds. The results of new U-Pb dating gave ages for the rhyolites of 212.8±2.5 Ma, indicating the end of Malugou Formation and initial Tianqiaoling Formation in deposition occurred in the late Norian (~227–208.5 Ma), which is contemporaneous with the peak of the Tianqiaoling flora in development. Our radiometric dating results are basically consistent with paleobiological evidence. The new age provides a key anchor point for regional stratigraphic correlation of the Tianqiaoling flora with its related Late Triassic floras, and contribute to a better understanding of the geology and phytogeography in the East Asia, particularly in the “triangle region” covering the eastern Jilin (China), South Primorye (Russia) and Southwest Japan, during the Late Triassic.