In northern Thailand there are over 40 Tertiary intra-cratonic depositional basin ranging from 30 to 2000 km2 in area. The basins are mainly N-S trending half graben and graben with sedimentary fills ranging in thickness from 500-3000 m. These sediments rest unconformably on Mesozoic and older rocks. The basins are rich in coal and oil shale deposits with one basin currently producing crude oil. This study aims to understand the basin evolution, provenance, lithofacies and depositional environment of these basins. Landsat TM digital data covering the whole of northern Thailand are currently being processed and interpreted to gain structural and tectonic information. From the preliminary interpretation, the small Tertiary basins are dominantly half graben structure and have distinct normal border faults. They are often cut by small strike-slip faults. The large basins have S-shape or curved margins, are commonly complex in structure and are cut by large strike-slip faults. From the Landsat image, it is not known whether these large basins are half graben or graben structure. Many strike directions of the Tertiary sequences in the basins are parallel or sub-parallel to the structural trends of the basement rocks. The orientation of the basins at the time of their formation may be different from the present day structure and some small basins may be a remnant of larger Tertiary basins.

Fieldwork carried out in the northern Thailand has included a reconnaissance of road-cut outcrops, detailed logging of lithologies and sedimentary structures and sampling of the Tertiary sequences in five coal fields. From these data, sedimentary logs have been produced and eighteen lithofacies classified. The Upper Oligocene sequences have more coarse-grained lithofacies than fine-grained, whilst the Miocene sequences are dominantly fine-grained lithofacies. Lithofacies associations are proposed and depositional environments are interpreted. The sedimentary palacoenvironment in most of these non-marine basins evolved from braided river plain, seen in lower units, to lacustrine, peat swamp and flood plains, in the middle units, and finally to fluvial and alluvial and alluvial plaints in upper units.

Tertiary sandstones collecting from six basins are now being studied for detailed petrographic and heavy mineral analysis to establish sediment provenance of each basin and to examine assemblage of Tertiary sandstone consists of zircon, tourmaline and rare garnet. There are some differences in zircon varieties. Those of Oligocene sandstones have variable colours and are small subhedral to anhedral grains whilst the Miocene-Pliocene sandstone contain of more colourless and euhedral large zircon grains. The preliminary results from this study show that the provenance of Oligocene sandstones of the Li Basin may be stable craton interiors whilst the provenance of Miocene-Pliocene sandstones of Chiang Mai basin may be orogenic uplift of sedimentary cover.