MEKONG RIVER FLOODPLAIN STRATIGRAPHY AND RADIOCARBON DATING BENEATH THE 14TH CENTURY CITY OF CHIANG SAEN, GOLDEN TRIANGLE OF NORTHERN THAILAND

The 14th Century moated city of Chiang Saen, in northernmostThailand was built upon a foundation of 6 to 11 m of floodplain silt over bedload gravels of a former course of the Mekong River. The Mekong River is now eroding its west bank exposing stratigraphy and brick foundations of a number of 14-16th Century Buddhist monuments at Chiang Saen Noi. We describe in detail the stratigraphy of the 10-meter-high river bank (exposed at low-stage, March, 2003) along a 1 km reach. Cobble gravels are overlain by silt drapes which are overlain by massive silt beds, some greater than one-meter thick. Fine sand partings and sand beds up to 20-cm thick occur but rarely constitute more than 20 percent of the section. At a depth of 5 meters below the brick foundations of a Buddhist temple is a hearth layer 4-cm thick and 2-m in diameter containing burnt bone fragments and abundant charcoal within massive silts. We will report on AMS radiocarbon dating (in progress) of the hearth. This age will help date the rate of floodplain sediment accretion and human occupation prior to the medieval kingdoms of Lanna. Our studies are intended to provide new information on early northern Thai civilizations and the legendary 5th Century AD kingdom of Yonok Nagabandu.