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Pha Huat Formation

Pha Huat Fm

Period:

Permian

Age Interval:

Middle Permian (11)

Province:
Sukhothai Fold Belt

Type Locality and Naming

Its type section is at Pha Huat about 20 km WSW of Ngao, Ngao district, Lampang province. Parent unit: middle formation in Ngao Gr.

Synonym: หมวดหินผาหวด

[Figure: Geological map of Ngao Group in Northern Thailand (data from Baum & Hahn 1977 and Charoenpravat et al. 1994). (from Ueno & Charoentitirat, 2011)]

Lithology and Thickness

The lower part, less than 100 m thick, is thin-bedded arkosic sandstone, probably partly volcanogenic, while the upper part (ca. 500 m) is massive and moderately recrystallized limestone with nodular or bedded chert layers and bedded limestone horizons at the base.. Thickness: 400-500 m (Piyasin, 1972), type section 600 m (Bunopas, 1981)

Lithology Pattern:

Sandy limestone

Relationships and Distribution

Lower contact

In the Lampang – Ngao area, the Pha Huat Fm conformably overlies the Kiu Lom Fm.

Upper contact

Huai Thak Fm (conformable)

Regional extent

Northern Region: Lampang and Phrae provinces. The limestone forms karstified hills in the Permo-Triassic greater Lampang Basin.

GeoJSON

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Fossils

Fusuline Neoschwagerina sp., brachiopods Martinia sp. and Dielasma sp. and bryozoans Polypora sp. and Fenestella sp.; fauna consisting of Neogondolella bitteri, Diplognathodus n. sp. and Hindeodus sp., and Iranognathus sosioensis. This Pha Huat conodont fauna is typical of a palaeobiogeographically warm-water setting similar to South China and is referable to the late Wuchiapingian which suggests the Pha Huat Formation extends up to the lower part of the Upper Permian. (Ueno & Charoentitirat, 2011).

Age

Middle Permian, and extends up to the lower part of the Upper Permian (Wuchiapingian). [Conformable over the Asselian-Sakmarian Kiu Lom Fm implies it extends downward through the Artinskian-Kungurian? Base-Kungurian used here.]

Age Span:

Beginning stage:

Kungurian

Fraction up in beginning stage:

Beginning date (Ma):

282.00

Ending stage:

Changhsingian

Fraction up in the ending stage:

Ending date (Ma):

254.20

Depositional setting

Shallow marine, neritic zone

Depositional pattern:

Additional Information

Remarks: This formation was previously mapped as part of the Ratburi Gr (Piyasin, 1972).

Compiler:

Wen Du -modified from Lexicon of Stratigraphic Names of Thailand (2013); and Katsumi Ueno & Thasinee Charoentitirat, 2011, Chapter5 Carboniferous and Permian in: Ridd, M.F., Barber, A.J., and Grow, M.J., editors, The Geology of Thailand, Geol. Soc. of London.