Silurian–Devonian boundary in Northern Xinjiang, NW China

Abstract

During the Silurian–Devonian Boundary (SDB) interval, in contrast to the predominantly carbonate facies observed in Europe and North America, China was composed of several plates/terranes dominated by clastic and pyroclastic rocks. Continuous sections across the SDB have been only sporadically reported from the orogenic belts and southwestern margin of South China. In many regions or sections in China, the identification of the SDB is based solely on fossil assemblages or non-index fossils, which results in only a rough approximation of the position of the boundary. This study focuses on the Junggar area in the Central Asian Orogenic Belt, characterized by pyroclastic rocks and scarcity of fossils compared to regions with carbonate dominated successions. This paper summarizes previous research findings and discusses the SDB in northern Xinjiang, China, integrating new data on Devonian conodont Caudicriodus hesperius, the presence of benthic organisms represented by encrinurid trilobites and crinoids, and the occurrence of late Silurian graptolites, along with the first organic carbon isotope curve around the SDB for the Central Asian Orogenic Belt, and provided crucial evidence for the recognition of the SDB in the orogenic belt area of China, consindering the SDB in Northern Xinjiang is located within the Utubulag Formation in the western Junggar and the presence of the SDB in the Kaokesaiergai Formation of the eastern Junggar has also been confirmed. The age of the corresponding strata: Utubulag, Manger, Kaokesaiergai formations are revised, and a more detailed description of the classic sections of the SDB in northern Xinjiang is provided. The new fossil and geochemical data serve as basis for recognition of the Silurian–Devonian boundary in northern Xinjiang, and also contribute to a more comprehensive understanding of paleoenvironmental events at the Silurian–Devonian transition in the northern hemisphere and the orogenic belt areas.