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Huai Thak Formation

Huai Thak Fm

Period:

Permian

Age Interval:

Latest Permian (11)

Province:
Sukhothai Fold Belt

Type Locality and Naming

Small creek next to mountain called Pha Phlung and Pha Huat, Ngao district, Lampang province; named after a small creek called “Huai Thak”.. Parent unit: uppermost formation in Ngao Gr.

Synonym: หมวดหินห้วยทาก

[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

Consists mainly of sandstone and shale. Dark grey to greyish- brown sandstone and shale, conglomerate, limestone, fossiliferous shale and thin-bedded, calcareous sandstone. Thickness: 762 m at type section (Piyasin, 1972), 750-1500 m (Bunopas, 1981)

Lithology Pattern:

Clayey sandstone

Relationships and Distribution

Lower contact

Pha Huat Fm (conformable)

Upper contact

Phra That Fm of the Lampang Gr (Early Triassic) (Unconformable)

Regional extent

Lampang-Phrae basin, west part of the Northern Region of Sukhothai Fold Belt. Widely distributed in the Lampang–Ngao–Wang Nua area (The geology of Thailand, 2011).

GeoJSON

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Fossils

Brachiopods includes Leptodus sp., Orthotetes sp. and Paramarginifera sp. Bivalve includes Aviculopecten sp.; Palaeofusulina-Colaniella fauna. An early Changhsingian lyttoniid brachiopod fauna and Gallowayinella-bearing fusuline fauna from the lower part of the Huai Thak Formation, both faunas having close similarities to those from South China. Late Changhsingian ammonoids including Pseudogastrioceras aff. szechuanense, Tapashanites yaowalakae and Paratirolites nakornsrii from shale of the upper part of the Huai Thak Fm, together with the Early Triassic ammonoid Ophiceras sakuntala from sandy shale in the basal part of the overlying Phra That Fm of the Lampang Gr (The geology of Thailand, 2011).

Age

Upper Permian (Kungurian-Kazanian) (p45 ); "These lines of evidence indicate that the Huai Thak Formation is latest Permian (Changhsingian)" (Geology of Thailand, 2011).

Age Span:

Beginning stage:

Changhsingian

Fraction up in beginning stage:

Beginning date (Ma):

254.20

Ending stage:

Induan

Fraction up in the ending stage:

Ending date (Ma):

251.90

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.