Thesis (M.Sc.)--Chulalongkorn University, 2007

Paleovegetation in Lower Central Plain of Thailand was deduced from pollen analysis. The site at Ong Kharak District, Nakhon Nayok Province, was chosen as a representative. The stratigraphy of sediment samples was divided into three units namely Pleistocene stiff clay, Holocene marine clay regarded to Bangkok clay, and recent floodplain deposit. However, it was only Bangkok clay unit from which pollen and spores as well as plant and animal remains were found and extracted. From [superscript14]C radiometric dating of plant and animal remains, it was dated to be the Holocene (7,620 +- 360 BP) in age at the lowest layer of Bangkok clay. Pollen and spore assemblages suggested that as many as three plant communities including mangrove, back mangrove, and lowland forest might occupy this area. From the first two communities, they suggested that this area was influenced by sea water and mainly covered by mangrove plants, members of the family Rhizophoraceae, Sonneratiaceae, and Avicenniaceae. In addition, the fluctuation of pollen assemblages in mangrove and back mangrove vegetations indicated that the sea level in lower central plain during the Holocene epoch was fluctuated before turning into the flood plain much later on.