Biostratigraphic and paleogeographic significance of a palynological assemblage from the Middle Devonian Ulusubasite Formation, eastern Junggar Basin, Xinjiang, China

Abstract

Abundant palynomorphs are here reported for the first time from tuffaceous siltstones of the Middle Devonian Ulusubasite Formation at the Zhifang Section, eastern Junggar Basin, Xinjiang, Northwest China. Thirty-four miospore species assigned to 23 genera (four established species, two cf., 19 sp., and nine spp.), 19 acritarch species assigned to 19 genera (10 established species, three cf., five sp., and one spp.), and scolecodonts are identified. The biostratigraphic ranges of the acritarchs and miospores indicate a Mid Devonian age, corroborating the age assignment previously based on associated corals, brachiopods, and plant fossils. Paleogeographic reconstruction for the Middle Devonian indicates that the eastern Junggar Basin was part of the Kazakhstan Plate and situated in the low-mid latitudes of the Northern hemisphere between the Euramerican landmass to the west, and the North and South China, and Gondwana landmasses to the east and south. Although there is some miospore compositional similarity between the eastern Junggar Basin and the landmasses of Euramerica, South and North China, and Gondwana, it is not particularly high, and is mainly at the generic level. The acritarch assemblage, however, consists mostly of cosmopolitan species and provides new evidence for extending the marine linkage between North America, Baltica, the Junggar Basin of Kazakhstan, and Gondwana. Paleontologic and lithologic evidence indicates that the Ulusubasite Formation was deposited in a near-shore marine environment.