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Pattani Sequence III Formation

Pattani Sequence III Fm

Period:

Neogene

Age Interval:

Middle Miocene (7)

Province:
Gulf of Thailand

Type Locality and Naming

Pattani Basin (central Gulf of Thailand). 3^rd (upward) of the 5 sequences.

Sequence III is the primary hydrocarbon-producing and source-rock package in the Pattani Basin and is associated with a transgressive phase in the basin’s history.

Synonym: Upper Grey Beds

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

Lithology and Thickness

The sequence is dominated by varicoloured light-grey to brownish-grey claystones and muddy siltstones with inter-beds of sandstone and coals. The sandstones are clean to argillaceous, and fair- to well-sorted.

Lithology Pattern:

Claystone

Relationships and Distribution

Lower contact

Overlies Pattani Sequence IV Fm

Upper contact

On seismic data the top of the sequence may be conformably or disconformably overlain by Sequence IV. This boundary marks the Middle Miocene unconformity which may be erosional but tends, on seismic data, to be of low-amplitude expression and a subtle feature.

Regional extent

Pattani Basin (central Gulf of Thailand); but the succession is similar to adjacent basins (Fig. 10.16 in Morley and Racey, 2011). In the southern Pattani Basin this unit is thin, and thickens northwards into the central Pattani Basin.

GeoJSON

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Fossils

Age

lower-Middle Miocene (Fig. 10.16 of Morley and Racey, 2011)

Age Span:

Beginning stage:

Langhian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

15.99

Ending stage:

Langhian

Fraction up in the ending stage:

0.75

Ending date (Ma):

14.36

Depositional setting

Transgressive phase. n the central Pattani Basin the depositional environment is fluvial/deltaic with more occasional marginal marine deposits. The southern Pattani Basin shows a strong continental influence due to surrounding local sediment source areas.

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.