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Yala Formation

Yala Fm

Period:

Paleogene, Neogene

Age Interval:

Upper Oligocene to Lower Miocene (1)

Province:
Andaman Sea: Mergui Basin

Type Locality and Naming

At the C-1 well in the southern part of the Mergui Basin, Named after the Yala province. References: Polachan (1988), Polachan and Racey (1994). Parent unit: Mergui Gr.

Synonym: หมวดหินยะลา

[Figure 1: Map of the Mergui Basin showing the main structural features including basin depocentres, based on an extensive grid of 2D seismic reﬂection data. (From C K Morley & A Racey, 2011)]

Lithology and Thickness

Mainly grey shales with minor sandstones in the lower part; white to light grey, fine grained, calcareous glauconitic sandstone in the upper part; abundant planktonic foraminifera and shell fragments; facies change with the Ranong and the overlying Trang formation. Thickness: 1,110 m at type locality, 2,085 m at the E-1 well.

[Figure 2: Stratigraphy and cross-section through the Mergui Basin, Andaman Sea, based on data in Polachan & Racey (1994) and Andreason et al. (1997). (a) Oligocene–Recent stratigraphy of the Mergui Basin; (b) stratigraphy of the syn-rift section (Oligocene–early Miocene) schematically illustrating the east–west variation in stratigraphy across the basin and the effect of rift-basin highs (e.g. Central High horst block) on large-scale distribution of sedimentary facies, modiﬁed from Andreason et al. (1997); (c) east–west cross-section through the Mergui Basin illustrating the typical half-graben geometries of the basin (modiﬁed from Polachan & Racey 1994). (From C K Morley & A Racey, 2011)]

Lithology Pattern:

Sandy_claystone

Relationships and Distribution

Lower contact

uncertain

Upper contact

Tai Fm (conformable), Kantang Fm (unconformable)

Regional extent

Andaman Sea: Mergui Basin. Correlation: Bampo Fm of North Sumatra Basin.

GeoJSON

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Fossils

Age

Upper Oligocene to Lower Miocene

Age Span:

Beginning stage:

Chattian

Fraction up in beginning stage:

Beginning date (Ma):

28.09

Ending stage:

Aquitanian

Fraction up in the ending stage:

Ending date (Ma):

23.04

Depositional setting

Deep sea, basin plain, changed upward to turbidite deposits.

Depositional pattern:

Additional Information

Compiler:

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