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Pattani Sequence IV Formation

Pattani Sequence IV Fm

Period:

Neogene

Age Interval:

late-Middle to Late Miocene (7)

Province:
Gulf of Thailand

Type Locality and Naming

Pattani Basin (central Gulf of Thailand). 4^th upward) of the 5 sequences

Synonym: Upper Red-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 unit comprises variegated dark-brown to reddish-brown claystones, grey to pale yellow sandstones and a few coals. It also contains important reservoir sandstone units for hydrocarbons.

Lithology Pattern:

Sandy claystone

Relationships and Distribution

Lower contact

On seismic data the base of the sequence may be conformably or disconformably overly Pattani Sequence III Fm. 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.

Upper contact

Overlain by Pattani Sequence V Fm

Regional extent

Pattani Basin (central Gulf of Thailand); but the succession is similar to adjacent basins (Fig. 10.16 in Morley and Racey, 2011)

GeoJSON

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Fossils

Age

upper-Middle Miocene (Fig. 10.16 of Morley and Racey, 2011). [To schematically show the mid-Miocene unconformity, the latest Langhian is shown as a gap.]

Age Span:

Beginning stage:

Langhian

Fraction up in beginning stage:

1.0

Beginning date (Ma):

13.82

Ending stage:

Tortonian

Fraction up in the ending stage:

0.0

Ending date (Ma):

11.63

Depositional setting

"Fluvial-deltaic, with sands accumulating in point bars and channels. The sequence was deposited during a regression; hence, deposition occurred primarily in a fluvial floodplain environment." (Morley & 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.