A late Eocene palynological record from the Nangqian Basin, Tibetan Plateau: Implications for stratigraphy and paleoclimate

Abstract

With the uplifting, large-scale thrusting and striking of the Tibetan Plateau, several Paleogene intracontinental basins formed within the northern Tibetan Plateau (TP). Stratigraphical and paleoenvironmental studies of the sedimentary successions within these basins are critical for understanding Paleogene climatological changes in Eurasia. The Nangqian Basin, one of such basins, formed in the Yushu area of the northeastern Tibetan Plateau. A set of lacustrine sediments, dominated by red clasolite, marlite, and gypsum, developed in the Yang Ala section in this basin. Paleontological records from the Nangqian Basin remain poorly known. Here, we investigate the palynological assemblages of one sedimentary succession at the Yang Ala section that belongs to the Gongjue Formation, and their implications regarding the geological age and paleoclimate are discussed. The results reveal that the assemblages are dominated mainly by angiosperm pollen (tricolpates and tricolporate), including Nitrariadites (Pokrovskaja), Quercoidites, and Labitricolpites, followed by gymnosperm pollen taxa, such as Ephedripites and Taxodiaceaepollenites, and sparse pteridophyte spores produced by ferns. A late Eocene age is inferred based on palynostratigraphy and comparison with other pollen assemblages in the TP. A relatively dry climate with brief humid periods is indicated by the high abundance of xerophytic pollen taxa, such as Ephedripites and Nitrariadites, which are associated with broadleaved deciduous and evergreen plants. The characteristics of the pollen assemblages from the studied Yang Ala section are consistent with other Cenozoic palynofloras from the Mahalagou Formation in the Xining Basin and with those of the Yaxicuo Group in the Hoh Xil Basin. These results provide an improved stratigraphical scheme for parts of the Cenozoic and enrich the current knowledge of the vegetation history of the northeastern Tibetan Plateau.