Thailand

Thailand presently lies in the interior of the tectonically quiet Sundaland core. It forms the stable core beneath the Thai-Malay Peninsula, southern Indochina, parts of Sumatra, Java and Borneo. It is surrounded on all sides by volcanic and seismic activity, including the subduction at the Sumatra-Java-Timor trench, and collision between Australia and eastern Indonesia.

It is clear from the geometry of the sedimentary basins in Northern Thailand that their evolution is closely linked to NE-SW trending sinistral strike-slip faults and NW-SE trending dextral strike slip faults. This forms a wedge between the Mai Ping fault system in the south and the Northern Thailand Fault System in the north, consistent with north-south compression and east-west extension. In contrast the area to the south of the Mai Ping Fault, including the Gulf of Thailand seems to be much more dominated by extensional processes. Here through-going strike slip faults are rare and offsets between graben and changes in their polarity can be explained by normal linkage of extensional fault systems.

Phumee Srisuwon’s detailed analysis of the Phrae basin shows that its evolution is closely linked to sinistral movements on the NE-SW trending Phrae-Thoen fault. Anongporn Intawong will investigate the interaction between the extensional tectonics of the Gulf of Thailand and strike-slip deformation associated with the Klong Mariu Fault which marks its western boundary.

Interestingly, MSc project work supported by Thai Shell suggests that small basins in the Andaman Sea may have formed at the opposite end of the Klong Mariu Fault associated with splays that would be indicative of sinistral strike-slip displacement on this fault.

While the Tertiary basins provide a record of the evolution of the area from the Late Oligocene/early Miocene, we know relatively little about the earlier Tertiary history of the area. In particular regional uplift is likely to have been an important precursor to basin formation.

Regional Tectonic Setting

Thailand preserves an important record of Cenozoic basin development, strike-slip tectonics, sediment dispersal, and landscape evolution within mainland Southeast Asia. The country contains numerous Tertiary basins, especially in the north and in the Gulf of Thailand, many of which are associated with major regional fault systems.

Research in Thailand has focused on the structural development of these basins, the controls of strike-slip and extensional tectonics on accommodation space, and the provenance of sediments derived from surrounding uplands. These studies are important for understanding both regional tectonic evolution and the development of coal-, oil shale-, and hydrocarbon-bearing basin fills.

Our Previous Research in Thailand Includes:

Sedimentary Provenance

Provenance studies in Thailand have examined both modern river sediments and basin fills to understand how sediment composition reflects source rocks, drainage patterns, and transport mechanisms.

Heavy mineral analysis of river sediments from southern Thailand has been used to characterise sediment sources and identify links between modern drainage systems and the geology of the peninsula. These studies show how mineral assemblages can provide valuable information on source lithologies, transport pathways, and sediment recycling.

More broadly, provenance work in northern Thailand has identified contrasting sediment source regions supplying the Tertiary basins. These include:

Palaeozoic metamorphic and sedimentary rocks and Triassic granites to the west
Mesozoic sedimentary rocks of a recycled orogenic belt to the east

Changes in heavy mineral assemblages through time also reflect climatic shifts, uplift of hinterland source areas, and increasing relief during basin evolution.

Tertiary Basins of Northern Thailand

Northern Thailand contains numerous small to medium-sized Tertiary intramontane basins, many of which are rich in coal and oil shale and some of which produce hydrocarbons.

Research has shown that these basins are structurally diverse, ranging from simple half-graben to more complex curved and fault-linked depocentres. Most are closely related to strike-slip tectonics, with basin formation controlled by movements on northwest-trending dextral faults and northeast-trending sinistral faults.

Sedimentological studies indicate a common pattern of basin evolution:

early deposition in alluvial fans, small rivers, and local lakes within initial half-graben
later rapid subsidence producing larger lakes, poorly drained floodplains, and swamp environments
final stages dominated by braided river systems and well-drained floodplains

These basins provide important records of changing tectonics, climate, and sediment supply during the Cenozoic.

Phrae Basin

The Phrae Basin is one of the most significant Tertiary basins in northern Thailand and provides a detailed case study of strike-slip influenced basin development.

It formed during the Late Oligocene to Early Miocene and was strongly controlled by movement on the Phrae-Thoen Fault. Seismic and Landsat data reveal that the basin is divided into three sub-basins separated by basement highs and transfer structures.

Studies of seismic stratigraphy show three main stages of basin evolution:

rift fill, including an early localised phase and a more extensive main rift sequence
inversion-related deposits, linked to folding and reverse faulting
post-rift deposits, which blanket much of the basin except where uplift later removed them

Borehole data show changing depositional environments through time, from alluvial fans and braided rivers to lacustrine, peat swamp, floodplain, and coal-forming settings. The Phrae Basin therefore records both subsidence and later tectonic inversion, reflecting the interaction of regional extension and strike-slip tectonics.

Chumphon Basin and the Gulf of Thailand

The Chumphon Basin and related basins in the Gulf of Thailand provide an important example of basin formation along major strike-slip fault systems.

Research has focused on the relationship between these basins and the Khlong Marui Fault, one of the major northeast-southwest trending structures of southern Thailand. Earlier models often explained Gulf of Thailand basin development as the product of dextral shear between northwest-southeast faults, but newer work shows a more complex history involving extension, inversion, and multiple phases of fault movement.

Studies integrating seismic data, satellite imagery, digital elevation models, and field observations indicate that:

an initial phase of rifting began in the Late Eocene and became widespread during the Oligocene
some eastern basins experienced inversion at the start of the Miocene
extension resumed in the Early Miocene and was followed by broader basin subsidence in the Middle Miocene
later extension and renewed inversion occurred again during the Late Miocene to Pliocene

The Khlong Marui Fault marks a major geological boundary and appears to have remained active until relatively recent times. Field evidence suggests that it records an early phase of ductile sinistral shear, later brittle sinistral movement linked to basin formation, and a subsequent phase of brittle dextral reactivation associated with basin inversion.

Strike-Slip Tectonics and Basin Formation

A recurring theme in Thailand research is the strong influence of strike-slip tectonics on basin geometry and sedimentary evolution.

Many Tertiary basins in northern Thailand and the Gulf of Thailand are not simple extensional basins, but developed in response to movement on major regional fault systems. These faults created accommodation space, transfer zones, and local inversion structures, and strongly controlled basin shape, thickness, and depositional environments.

This work has shown that basin development in Thailand was governed by a combination of:

regional extension
strike-slip faulting
later inversion and uplift
changing plate interactions across Southeast Asia

Understanding these controls is essential for reconstructing the tectonic evolution of mainland Southeast Asia and for interpreting the distribution of economic basin fills.

Climate, Relief, and Sediment Supply

Research in Thailand has also highlighted the importance of climate change and hinterland uplift in controlling sediment composition and basin fill.

A shift from tropical humid conditions during the Oligocene to Middle Miocene toward more temperate and semi-arid conditions in the Late Miocene to Pliocene appears to have influenced sediment supply and mineral assemblages. At the same time, increasing topographic relief, linked in part to uplift of metamorphic core complexes, led to greater delivery of unstable grains and heavy minerals into basin sandstones.

These observations demonstrate that basin evolution in Thailand reflects not only tectonic controls, but also major changes in climate and erosion.

Regional Significance

Research in Thailand provides important insights into:

the structural evolution of Tertiary basins in mainland Southeast Asia
the role of strike-slip faulting in basin formation and inversion
provenance and transport of sediments in both modern and ancient systems
interactions between tectonics, climate, and sediment supply
controls on coal, oil shale, and hydrocarbon-bearing basin successions

Because Thailand preserves a wide range of fault-controlled basins and sedimentary environments, it offers an important regional perspective on how continental Southeast Asia responded to Cenozoic tectonic reorganisation.