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Research Article
ScienceAsia 29 (2003): 221-233 |doi: 10.2306/scienceasia1513-1874.2003.29.221
Oligocene-Miocene Climatic Changes in
Northern Thailand Resulting from Extrusion
Tectonics of Southeast Asian Landmass
Wickanet Songthama,b,*, Benjavun Ratanasthiena, Dallas C. Mildenhallc,
Sampan Singharajwarapana and Wittaya Kandharosaa
ABSTRACT: Palynological research has been carried out on some Tertiary basins of northern Thailand including
Mae Moh, Li, Na Hong, Mae Lamao, and Chiang Muan basins. Two main palynological assemblages are
recognised, namely warm temperate and tropical. Warm temperate elements include common to abundant
pollen of conifers such as Pinus, Picea, Tsuga, Taxodium, and Sequoia with rare occurrences of Podocarpaceae.
Angiosperm pollen includes Alnus, Betula, Carya, Engelhardia, Fagus, Ilex, Juglans, Liquidambar, Lonicera,
Pterocarya, and Quercus. These warm temperate elements are Oligocene to Early Miocene in age and
resemble present pollen from trees growing in temperate, high latitude, northern hemisphere climates.
Tropical elements include Calophyllum cf. C. inophyllum, Crudia, Dipterocarpaceae, Lagerstroemia, and
Radermachera. These tropical pollen assemblages are of Middle Miocene and probably also Early Miocene
age. These two assemblages, at two stratigraphic positions, suggest that climate in Thailand changed from
temperate to tropical during Oligocene to Miocene time. The climatic change is postulated to have been
caused by the southward to southeastward movement of the Southeast Asian landmass resulting from
extrusion tectonics induced by the collision between the Indian and Eurasian continents beginning about 40
to 50 Ma years ago. The movement of the Southeast Asian landmass from temperate latitude to tropical
latitude eventually led to the change of the vegetational patterns from temperate to tropical forests.
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a Department of Geological Sciences, Faculty of Science, Chiang Mai University, Huay Kaew Road, Chiang Mai 50200, Thailand.
b Bureau of Geological Survey, Department of Geological Resources, Rama VI Road, Ratchathevee, Bangkok 10400, Thailand.
c Institute of Geological and Nuclear Sciences, P.O. Box 30-368, Lower Hutt, New Zealand.
* Corresponding author, Email: wickanet@dmr.go.th
Received 20 Nov 2002, Accepted 31 Mar 2003
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