Palaeovegetation and palaeoclimate of tertiary sediments from Hongsa Coalfield, Xayabouly province, Lao PDR – Implication from palynofloras

Palynological contents of organic-rich Tertiary sediments of the Hongsa coalfield, Xayabouly Province, north-western Lao PDR, were investigated. Palynomorphs that were used to reconstruct the palaeovegetation and palaeoclimate, were extracted from a sediment drill core from the central part of the Hongsa coal mine. Three pollen zones from bottom to top (Hongsa I zone, Hongsa II zone, and Hongsa III zone) were divided based on the quantitative change of the palynological assemblages. They indicate the change of climate from subtropical to temperate during the deposition of the Hongsa coal. The Hongsa vegetation composes of subtropical to warm temperate broad-leaved forests. Quercus, Fagus, castanoids, Salix, Fabaceae, and Myrtaceae were the dominant trees and shrubs, and ferns were commonly found on the forest floor. The palynological assemblages from the Hongsa Basin are different from the Oligocene and Miocene from northern Thailand; however, they are similar to the middle to late Miocene of southwest China.