Neogene palynological assemblages in Zanda Basin, southwestern Tibet

The Zanda Basin is a Neogene rifted basin in Ngari Prefecture, southwest Tibet. It was formed in Late Miocene, at about 9.2Ma. The Duojidong section is located about 4km south of Zanda County. It has a well-developed set of lacustrine sedimentary strata. Palaeo-current measurement and provenance analysis show that the age interval of the Tuolin Formation is about 9.2-2.6Ma, and the Xiangzi Formation is dated at about 2.6-1.7Ma. As the sporopllen data can directly reflect paleoclimate changes, sporopllen data have been always regarded as one of the best environmental indicators. Through the palynological analysis, 6 palynological assemblages and vegetable types were recognized, and 3 phases of paleoclimatic changes were revealed: ① from 9.2Ma to 5.6Ma, correlated with assemblages 1-2, the environment was cold shrub steppe at about 9Ma, and then became warm and humid subtropical-temperate deciduous coniferous and broad-leaved mixed forests; ② from 5.6Ma to 3.1Ma, correlated with assemblages 3-5, the environment was mild and humid evergreen-deciduous broad-leaved mixed forests, and changed to the warm and a little dry deciduous conifer mixed forest at about 3.6Ma. This stage had a climate fluctuation; ③ from 8Ma to 1.7Ma, correlatied with assemblage 6, the environment became cold and dry deciduous coniferous and broad-leaved mixed forests and subalpine coniferous forests.