Abstract:
In the present paper a preliminary result is reported of the study on leaf and pollen flora from the Pliocene Gantang Formation near the Wanpu Village of Yuanmou Basin, Yunnan Province, SW China. The leaf flora contains 35 species and 24 genera of 15 families. All leaf fossils are identified to angiosperm except one genus of Taxodiaceae(? Taiwania ). Ulmaceae, Betulaceae and Leguminosae are the predominant families of the leaf flora both in species diversity and specimen quantity. Other important families are Salicaceae, Aceraceae, Rosaceae. Present in small number are the families of Fagaceae, Lauraceae, Myricaceae, Rhamnaceae, Caprifoliaceae, Elaeagnaceae, Ericaceae, Typhaceae, Graminosae. Pollen and spores are rich in the Wanpu flora with 97 types of 72 genera belonging to 44 families. The most aboundant families are Ulmaceae, Gramineae, Pinaceae(generally 20% 30% of total spores and pollen for each family) and the monolete spores of Pylopdiaceae(5% 10%). Angiosperm pollen, most of them are of Ulmaceae and Graminosae(over 10% respectively), occupies 50% 60% of the total. Juglandaceae, Fagaceae, Hamamelidaceae and Pteridaceae are common families, amounting to 1% 10% individually. Some pollen types probably related to xerophyte shrubs, e.g. Elaeagnus , Chenopodiaceae, have also been found in different quantities. The pollen flora also contains a number of subtropical evergreen forest elements of southern China, e.g. Lithocarpus/Castanopsis, Cyclobalanopsis, Symplocos, Reveesia, Alangium, etc. Either leaf flora or pollen assemblage is a mixed group of elements from subtropical evergreen forest and semi humid parkland. The mixture characters of leaf and pollen floras suggest pliocene vegetation differentiation in the Yuanmou area. On the surrounding high lands of the basin developed a subtropical broad leaved evergreen forest containing Fagaceae, Lauraceae, Juglandaceae, Sterculiaceae, Hammaelidacaae and Ericaceae, etc. Probably Pinaceae woodland also developed locally. While in the basin, grass land with some shrubs and/or herbs of Leguminosae, Elaeagnaceae, Myricaceae, Rosaceae, Euphorbiaceae, Caprifoliaceae developed. Ulmaceae, Betulaceae and other trees may grow in some areas of the basin with suitable environment. The climate in the basin was of semi humid subtropical type(with seasonal drought), which is similar to that of today. Our plant fossil data indicate that dry and hot basins along the Jinsha River in the northerm Yunnan area probably have been already existed in the mid Pliocene. This conclusion is interesting in tracing the history of monsoon climate in China.
