Early Pliocene paleo-altimetry of the Zanda Basin indicated by a sporopollen record

•We obtained sporopollen results of lacustrine sediments at Zanda Basin.•We found the high percentages of coniferous trees pollen in the Zanda Basin.•It suggests the elevation at the early Pliocene was lower than it was at present.

Whether the uplift of the Tibetan Plateau (TP) led to the origin and development of the Indian monsoon is still in dispute. A helpful indicator would be greater knowledge about the chronological development of paleo-altimetry. The Zanda Basin, located on the SW margin of the TP, forms one of the most extensive Cenozoic sedimentary basins in Tibet. The modern climate of this area is controlled by the Indian Monsoon circulation system. It is thus an appropriate region for the study of paleo-altimetry, in addition to research into the relation between the TP and the Indian Monsoon. Sporopollen analyses of early Pliocene lacustrine strata in the Zanda Basin show that gymnosperm pollen is dominant (av. 77%) and mainly composed of Picea (av. 27.2%) and Abies (av. 24.2%); fern spores occupy a lesser proportion (av. 17.6%), while angiosperm pollen including temperate, sub-tropical broadleaved trees, shrubs and herbs, accounts for only a small proportion of the assemblage. This sporopollen assemblage suggests that sub-alpine dark coniferous forests were distributed around the basin and grow in a cool and wet climate, rather than in a modern alpine steppe environment. These characteristics indicate that the Zanda Basin's altitude throughout the early Pliocene was most probably lower than it is at present.