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Mae Long Formation

Mae Long Fm

Period:

Neogene

Age Interval:

late-Early through Middle Miocene (8)

Province:
NW Thailand – Inthanon Zone

Type Locality and Naming

Li Basin (NW Thailand, Inthanon Zone), Lamphun province. Type locality: Mae Long reservoir and extends into the Na Sai Coalfield (Ratanashien, 1990)

Synonym: หมวดหินแม่ลอง

[Figure: Map showing the Tertiary basins of Thailand, with Phetchabun basin highlighted. The solid black lines onshore are the principal rivers draining Northern and Central Thailand and the Khorat Plateau (Morley and Racey, 2011, page 224).]

Lithology and Thickness

Laminated shale, mudstone and coal seams. Including the ‘Upper Split’ coal horizon and the Na Sai paper shale. Coal seams are present in both the Ban Pa Kha Fm and the Mae Long Fm and may be up to 20 m thick, frequently with recognizable tree trunks; they are exploited at the Ban Pu and Ban Pa Kha mines…. The coal-bearing part of the Mae Long Fm varies in thickness from 30 to 250 m. It contains several layers of coal that can range up to 7 m thickness, interbedded with shale, claystone and fluvial sandstones and conglomeratic sandstones. The ‘Upper Split’ is an important seam which, as its name implies, splits laterally into a number of thinner seams that interfinger with marl and mudstone beds. … The paper shales comprise light grey mudstones, sandstones, conglomeratic sandstones and thin shales containing algae, carbonates and gypsum. (Morley and Racey, 2011).

Lithology Pattern:

Claystone

Relationships and Distribution

Lower contact

Overlies the Ban Pa Kha Fm

Upper contact

Unconformably overlain by the sandstone and conglomerates of the Mae Taeng Fm (unnamed in Li Basin, so name is projected from the northern en echelon Chiang Mai basin).

Regional extent

Lamphun and Chiang Mai provinces.

GeoJSON

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Fossils

The Mae Long Formation has yielded tropical species of pollen and the coal seams have an ash content of up to 42%. "Ginsburg et al. (1991) sifted 15 tons of sediment to find vertebrate fossils and a number of other studies … have found fish, bird, snake, rodent, turtle, primate and other mammal fossils. … Tree trunks are present within the coals. Fossils include otter, turtle, gastropods, crocodile, Cypriniforme and Siluriforme fish. Leaves are indicative of a warm, temperate climate." (Morley and Racey, 2011).

Age

upper Lower Miocene – Middle Miocene based on vertebrate fossils, leaves and palynology

Age Span:

Beginning stage:

Burdigalian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

20.45

Ending stage:

Tortonian

Fraction up in the ending stage:

0.0

Ending date (Ma):

11.63

Depositional setting

Lacustrine, swamp deposits. The pollen from the underlying Ban Pa Kha Fm is predominantly from warm temperate species, whereas the Mae Long Fm has yielded tropical species of pollen. This is thought to indicate a significant change in climate during the Early Miocene. (Morley and Racey, 2011).

Depositional pattern:

Additional Information

Compiler:

Wen Du - modified from Christopher K. Morley & Andrew Racey, 2011, Chapter 10 Tertiary stratigraphy in: Ridd, M.F., Barber, A.J., and Grow, M.J., editors, The Geology of Thailand, Geol. Soc. of London.; and Lexicon of Stratigraphic Names of Thailand of 2013.