Palaeontology of proboscidean fossils from Changw at Nakhon Ratchasima, Thailand

Abstract

Aims of the present research are to construct the stratigraphy of Paleo-Mun river sediment system by using sedimentological analysis such as lithology, sedimentary structures and occurrences of Proboscidean fossils, to describe Proboscidean fossils from sandpits in Changwat Nakhon Ratchasima and to reconstruct palaeoenvironments from sedimentological and paleontological analysis. Stratigraphic succession of study area can be classified into 4 units, A, B, C and D in ascending order by the character of stratigraphy and lithology. Unit A is Miocene Period, this unit lies at the bottom of the sand pit which is represented by repetition of coarsening upward cycle. This unit is overlaid unconformably under the clay supported conglomerate, clay supported. In this unit the ancient elephant teeth of Stegolophodon and Stegodon were found. It can be assumed that ancient alluvial fan sediment had once located in this area and paleoenvironment of this place had ever been the forest or swamp which close to water source. Unit B was represented by fining upward and followed by coarsening upward cycle and fining upward. The unit B lies unconformably underneath the conglomerate. This unit contain the elephant fossil tooth of Sinomastadon. Pleistocene to Pliocene was proposed to be an age of this unit in ancient alluvial fan deposits. The paleoenvironment of this unit was expected that might be forested areas or swamp. Unit C was represented by repetition of coarsening upward cycle of alluvial fan deposits and fining upward of fine grain of meandering river system. This unit is also overlaid unconformably by fine sand, reddish yellow. It can be assumed as rapidly continuous decreasing of sediment and slope of alluvial fan whichs were reflected to expand and fill on the plain and river. Pleistocene age was expected in unit C. From this unit, proboscidean fossils was not found, but Tektite were found. Unit D was represented by fining upward succession and numerous archaeological remains, shell and elephant tooth of Elephant maximus Linnaeus. This unit shows clearly geological process by overbank floodplain deposits that was occurred during Holocene to Recent. It assumed as paleoenvironment of this place had ever been the grassland. According to Paleontological studies of proboscidean fossils in 8 genera such as Protanancus, Gomphotherium, Prodeinotherium,, Sinomastodons, Tetralophodon, Stegolophodon., Stegodon, and Elephas. The occurrences of fossils are allochthonous. Molars and bones are scattered in the sediments. Some fossils are transported and some fossils are in situ. The surface of bones and molars are excellent, no breakage and abrasion. They are not belonged to the reworked fossil. Base on the relationship among stratigraphy, lithology, sedimentary structures and elephant fossils found in the sand pit, Changwat Nakhon Ratchasima, the dominance of depositional environment in this site is the fluviatile enviromnent, both of fan and fluvial deposits of meandering river system. This is due to the adjustment level of palaeo-lanscape from alluvial fan to floodplain. Besides, it showed adaptation to the palaeoenvironment in Mun river area that developed from forest to glassland area.