Age constraint for an earliest Famennian forest and its implications for Frasnian-Famennian boundary in West Junggar, Northwest China

Abstract

As one of the five major extinction events in Earth history, the Frasnian-Famennian boundary (FFB) crisis caused dramatic reductions in marine and terrestrial diversity. The effects of this event on terrestrial ecosystems are not well understood due to the limited preservation of terrestrial sedimentary rocks and the relative scarcity of plant fossils. This study generates a robust zircon UPb age (371.5 ± 0.9 Ma; earliest Famennian) for a new fossil assemblage containing Lycopsida, Archaeopteridales, and Cladoxylopsida from the upper Zhulumute Formation of the West Junggar Basin, NW China. These taxa are typical arborescent plants of the Late Devonian and represent the oldest-known forest in China, documenting afforestation in West Junggar coevally with or just after the Upper Kellwasser event (~372 Ma). The new UPb ages generated in this study refine the placement of the FFB in West Junggar to within the Zhulumute Formation, instead of the Hongguleleng Formation as previously thought.