INCISED MEANDERING STREAMS AS INDICATOR OF TERTIARY-QUATERNARY REGIONAL UPLIFT IN NORTHWEST THAILAND

In northern Thailand’s Western Ranges, field and map observations show that many deeply incised streams are highly sinuous and meandering - typical of rivers that form in flat flood plains, not mountainous regions. These streams likely formed in early Tertiary paleobasins, of which few relicts remain in the mountainous areas, during a period of tectonic quiescence. The streams then incised directly downward during homogeneous, regional uplift during the late Tertiary to the present, in most cases retaining the meanders rather than diverting. Most standard techniques of tectonic geomorphology, such as dating of terraces, are ineffective in jungle regions with high rates of surface erosion. Results have been obtained using DEM- and GIS-derived geomorphology data, determining relationships between sinuosity, amount of incision, hypsometry, and longitudinal and cross-sectional elevation profiles. The tectonic activity suggested by these relationships is likely related to the India-Asia convergence zone. While that convergence is the primary driver of recent tectonic activity in Southeast Asia, little previous work has been done constraining this activity. These results suggest that previous tectonic models for Thailand and Southeast Asia may be missing periods of activity that have been obscured from more standard techniques, but which should be expected from the relatively constant effect the India-Asia convergence has on the region.