Ngao Gr

Cenozoic

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

Devonian

Early Paleozoic

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Ngao Gr

Period:

Permian

Age Interval:

Permian (11)

Province:
Sukhothai Fold Belt

Type Locality and Naming

Ngao district, Lampang province. A thick Permian succession with a north–south trending distri- bution in the Lampang–Ngao area, This group formerly mapped as Ratburi Gr by Piyasin (1972), and later changed the name to Ngao Group by Bunopas (1981). Subdivisions: Three formations, in ascending order (Piyasin, 1972): Kiu Lom Fm, Pha Huat Fm, Huai Thak Fm

Synonym: กลุม่หินงาว; Ratburi Gr; Uttaradit Gr (replacement name for Phrae Gr) is used for Permian strata in the region east of Phrae to NW of Sukhothai.

[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

Sandstone, shale, calcareous shale and thin-bedded limestone with fusulinids; massive to well bedded, recrystallized limestone; fossiliferous, shale and thin-intercalations intraformational conglomerate. See component Kiu Lom Fm, Pha Huat Fm, Huai Thak Fm. Total thickness: 1,960 m (600 + 600 + 760)

Lithology Pattern:

Clayey sandstone

Relationships and Distribution

Lower contact

"The basal contact is not known in the type area, but Piyasin (1972) reported that, east of Chiang Mai, a relatively thin succession (20–30 m thick) of his Kiu Lom Formation unconformably overlies the Mae Tha Gr. However, those rocks are in the Inthanon Zone and we (Ueno & Charoentitirat, 2011) exclude them from the Kiu Lom Fm." Therefore, the next older regional units are the Khanu Chert Fm, or the top of the Dan Lan Hoi Gr (Khao Khi Ma Fm).

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.: Lampang and Phrae provinces. Correlation: Ratburi Group (?). "This Permian is known to extend further northwards with a narrowing outcrop belt to around Chiang Rai and probably to the Thailand – Myanmar border. The Permian to the east and SE of Chiang Rai should probably also be included in this lithostratigraphic unit." (Ueno & Charoentitirat, 2011)

GeoJSON

null

Fossils

See component Kiu Lom Fm, Pha Huat Fm, Huai Thak Fm.

Age

Spans most of the Permian (late Asselian through Changhsingian)

Age Span:

Beginning stage:

Asselian

Fraction up in beginning stage:

Beginning date (Ma):

298.88

Ending stage:

Induan

Fraction up in the ending stage:

Ending date (Ma):

251.90

Depositional setting

Carbonate shelf, shallow marine shelf

Depositional pattern:

Additional Information

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.