Paleoenvironmental changes of the Miocene sedimentary basins in Thailand.
Date:2007/06/26 - 2007/07/12
The geological survey was conducted in the Mae Soi area (about 60km south of Chiang Mai) and in the Sop Mae Tham area (about 130km north to Chiang Mai). Although thick recent soil (some parts were calcified) covered the Miocene nonmarine deposits in both areas, we could observe the 130m and 40m thick Miocene strata in the Mae Soi and in the Sop Mae Tham, respectively. We clarified that both areas are composed of fluvial deposits associated with a floodplain environment. Several gastropods were obtained from the sandstone exposed at the hill, named Kew Hoi Tal, in the Mae Soi area. In Sop Mae Tham, numerous crocodile teeth and fish bones were collected from the calcrete and the upper horizon of the calcrete. We could not collect the mammalian fossils from the original bed, whereas it is likely that they would be contained in the sandstone in the Sop Mae Tham. The paleontological investigation was carried out in the Chiang Muan Mine (about 150km east of Chiang Mai) and in the Pong area (about 140km west to Chiang Mai). Several kinds of freshwater fish, including three families, were collected from the lignite beds in the Chiang Muan Mine. We also got vertebrae of a snake and an isolated upper tooth of a wild-boar from the mine. The Huai Siew, which is located several kilometers north of the town of the Pong, yielded a lower premolar of the large-sized artiodactyl.