Abstract:
The global climate and vegetation systems have experienced remarkable changes during Cenozoic. The systematic study of the Cenozoic vegetation and climate in Yunnan will also provide some important evidence and information on the uplifting of the Tibetan Plateau in addition to the initiation and evolution of the Indian monsoon. Although the abundant palynological studies have been conducted in recent decades, the systematic and comprehensive researches have not been conducted through the sporopollen in Yunnan. This paper show the comprehensive reviews on the Cenozoic sporopollen records from Yunnan compiled through sporopollen records studied since last four decades and finally reconstructed a 65 Ma record of changing vegetation and climate spanning the whole Cenozoic except for Eocene. The following pollen zones are identified:
Ulmipollenites - Ephedripites - Schizaeoisporites zone (Paleocene), the vegetation was composed of mixed evergreen and deciduous broad-leaved forest dominated by deciduous broad-leaved forest, revealing a partial dry climate;
Quercoidites-Alnipollenites- Pinaceae-Polypodiaceae zone (Early-middle Oligocene), the vegetation was subtropical evergreen broad-leaved forest, reflecting a warm and wet climate condition;
Pinaceae- Quercoidites -Polypodiaceae zone (Late Oligocene-Early Miocene), increasing in coniferous pollen imply a more cooling climate; Fagaceae-
Alnus -Polypodiaceae-Pinaceae zone (Middle Miocene), thermophilic taxa percentages were high (Fagaceae, fern), corresponding to the Middle Miocene Climatic Optimum, showing a warm and wet climate condition; Fagaceae-Pinaceae-
Alnus -herbaceous pollen zone (Late Miocene-Early Pliocene), a warm and humid climate in early stage, but the expansion of coniferous forest and herbaceous in later stage revealing a cooling and drying trend;
Quercus -Pinaceae-Polypodiaceae zone (Middle Pliocene), the tropical and subtropical taxa and their percentages increased, reflecting a warm and wet climate condition; Pinaceae-
Quercus -herbaceous pollen zone (Late Pliocene), the expansion of coniferous forest and herbaceous, and the decreasing in the thermophilic percentages (
Quercus), implying a cooling and drying trend; Pinaceae-herbaceous pollen-
Quercus zone (Pleistocene), coniferous forest and herbaceous expanded more resulting from a further climate deterioration; Pinaceae-
Quercus zone (Holocene), the warmest and wettest climate occurred in middle Holocene, corresponding to the Holocene climatic optimum. The palynofloras of Cenozoic in Yunnan thus shows the palaeotemperature as a key factor in controlling long-term trend of vegetation, the cooling in the Late Oligocene-Early Miocene was linked with the uplift of Tibetan Plateau, whereas the cooling and drying since Late Miocene may be the consequence of both the global cooling and the uplift of Tibetan Plateau. However, some problems such as insufficient data on sporopollen records of Paleogene and controversies on the geological ages of some sedimentary formations have remained in Yunnan. Hence, further studies on chronstratigraphy and reconstruction of Paleogene sporopollen in Yunnan are important and required in the future.