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Mae Sariang Formation

Mae Sariang Fm

Period:

Triassic

Age Interval:

Middle to Upper Triassic (5)

Province:
Sibumasu: Western Region

Type Locality and Naming

Type section: Km post 5 to 10 on the highway from Mae Sariang to Mae Hong Son. Bunopas (1981) proposed the name Mae Sariang Gr for the Triassic sandstones, shales, cherts and limestones of the Mae Sariang – Mae Hong Son; but Chonglakmani (2011) preferred a formation rank (used here).

Synonym: หมวดหินแม่สะเรียง , Mae Sariang Gr

[Figure 1 : Generalized distribution of different Triassic sedimentary environments and some of the more important lithostratigraphic units, and their relations to the terranes. (The geology of Thailand, 2011) page 146]

Lithology and Thickness

Gray shale with chert and thin-bedded filament limestones; overlain by interbedded siltstone, and fine-grained sandstone; terminating in a conglomerate which contains pebbles of reworked radiolarite from which Carboniferous through mid-Triassic ages have been obtained. Thickness: 850 m

Lithology Pattern:

Chert

Relationships and Distribution

Lower contact

Not given. [Note: In the Mae Sot area, unnamed red-beds consist of unfossiliferous red to grey shale and sandstone about 270 m thick which disconformably overlie Permian mudstone, chert and limestone, and are overlain by gray shale and sandstone of late Ladinian to Carnian age. Therefore, regionally, the next older unit might be redbed facies (unnamed)?]

Upper contact

"At Kamawkala gorge a section more than 900 m thick of greenish-grey shale and sandstone forms the lowest clastic unit of the Mae Sariang Fm and contains Halobia sp. Posidonia sp. and ammonites. This fauna corresponds with the Halobia styriaca zone of the Mae Sariang area. Conformably overlying the clastics is the Kamawkala Limestone." (Chonglakmani, 2011).

Regional extent

Mae Sariang–Kanchanaburi Basin, including Mae Sot area.

[Figure 2 : Generalized distribution of marine Triassic sedimentary rocks in Thailand (in purple) (modiﬁed after Mantajit 1999). (The geology of Thailand, 2011) page 138]

GeoJSON

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Fossils

The lower chert unit is uncertain, with the ribbon cherts reported to have yielded Early Carboniferous, Late Permian and Middle-Late Triassic radiolarians. The bedded cherts contain radiolarians and locally abundant Carnian halobiids on the bedding planes (Chonglakmani & Grant-Mackie 1993). Kamata et al. (2002) confirmed an Early Carnian age for part of this chert sequence, but additionally they noted ?Early Triassic (Spathian) and Middle (Anisian and Ladinian) Triassic radiolarians in their study. The reported Middle Triassic (Ladinian) assemblage comprises Oertlispongus inaequispinosus, Baumgartneria retrospina and Paroertlispongus multispinosus. The Late Triassic (Early Carnian) assemblage includes Palaeosaturnalis triassicus, Praehe- liostaurus levis, Dumitricasphaera planustyla and Vinassaspongus subsphaericus." (Chonglakmani, 2011)

"Baum et al. (1970) reported finding Daonella cf. D. sumatrensis Volz, D. aff. D. lommeli (Wissmann) and Halobia styriaca Mojs in a sequence of shale, sandstone and conglomerate. This fauna corresponds with the Halobia styriaca zone of Carnian in the Lampang-Phrae Basin" [Sikhothai Tectonic Zone] ." (Chonglakmani, 2011).

Age

Basal age is quite uncertain; but Anisian-early Carnian range for the chert deposition and to mid-Late Carnian for the overlying clastics?

Age Span:

Beginning stage:

Anisian

Fraction up in beginning stage:

0.5

Beginning date (Ma):

244.15

Ending stage:

Carnian

Fraction up in the ending stage:

0.7

Ending date (Ma):

231.02

Depositional setting

Deep-sea for lower part, then shallowing upward. "The cherts and associated thin-bedded filament limestones are interpreted to have been deposited in a deep marine basin by Fon- taine & Suteethorn (1988) and in a continental slope environment by Saesaengseerung et al. (2007, 2008). The siliciclastic sediments which overlie the pelagic limestone and shale were described as a synorogenic flysch sequence by Tofke et al. (1993)." (Chonglakmani, 2011)

Depositional pattern:

Additional Information

Srinak and others (2007) subdivided their Mae Sariang Gr into 3 units, in ascending order: Kong Som, Pratru Muang, and Mae Laeb units.

Compiler:

Wen Du - modified from- Chonglakmani, C.P., 2011, Chapter 6 Triassic in Ridd, M.F., Barber, A.J., and Grow, M.J., editors, The Geology of Thailand, Geol. Soc. of London.；Lexicon of Stratigraphic Names of Thailand of 2013.