A review of the Paleobotanical study of Jianglang site, central Tibetan Plateau, China and future direction
Résumé
The past diversity in the central Tibetan Plateau (TP), as revealed by macro and micro-fossil of plants, changed throughout the Cenozoic following the dynamics of climate and topography. However, the Cenozoic flora in the core area of TP is still poorly known. A new Eocene site from the TP containing plenty of well-preserved leaves, fruits and seeds was discovered recently. The Jianglang site is located in Bangor County, Lunpola Basin, central TP. which is at 4850 m in altitude and corresponds to the Niubao Formation with is radiometric dating as the middle Eocene ( ˜47.5 Ma). A preliminary analysis reveals ca. 42 leaf morphotypes and ca. 34 morphotypes of fruits and seeds. The taxonomic study focused on fruits and seeds show 21 species of 13 families including Apocynaceae, Buxaceae, Ceratophyllaceae, Fabaceae, Hernandiaceae, Malvaceae, Menispermaceae, Passifloraceae, Rhamnaceae, Sapindaceae, Simaroubaceae, Ulmaceae and Vitaceae. The overall biodiversity corresponds to a tropical to subtropical forest. In addition, the Jianglang leaf traits indicate a subtropical climate, mostly frost-free. All together the fossils show a strong floristic affinity with what we can find in the early-middle Eocene of the Green River Formation in USA and with modern floras in Asia (Southeast China and north of mainland Southeast Asia). This flora is compatible with a low elevation during the Eocene in the Tibetan area. Several new scientific directions were developed in order to give a specific view of the past biodiversity in the TP during the Eocene. The taxonomic study of new fruits and seeds and of the leaves will allow us using the coexistence approach method in order to estimate climate parameters and to confirm or revise previous results. The study of the insects (5% of the total specimens) as well as the plant-insect interaction will bring new light on the ecological process associated to the flora.