Cenozoic

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Devonian

Early Paleozoic

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Pak Chom Formation

Pak Chom Fm

Period:

Devonian

Age Interval:

Silurian-Devonian (?); Upper Devonian (14, no strat column)

Province:
Indochina Block: Loei Fold Belt

Type Locality and Naming

Pak Chom district, Loei

[Figure: Map of Thailand showing the distribution of the Devonian and closely associated Silurian and Carboniferous rocks. The belt of crystalline ‘basement’ rocks is mentioned in the text; they were previously thought to be Precambrian but radiometric dating shows them to be younger (Hansen & Wemmer 2011; Wongwanich & Boucot, 2011).]

Synonym: หมวดหินปากชม; Pak Chom chert (หมวดหินเชิรต์ปากชม)

Lithology and Thickness

The Pak Chom Formation was subdivided into two members: the Silurian–Devonian Ban Nong Shale at the base and the Devonian Pak Chom Chert above. The Ban Nong Shale consists of light brown shale, thick-bedded, light to dark grey limestone with Devonian corals at Nom Som (Bunopas 1988). The Pak Chom Chert consists of grey thin-bedded chert, volcanic tuff and limestone with Middle Devonian corals (Fontaine & Tantiwanit 1987) (Wongwanich and Boucot, 2011). Thickness: not mentioned

[Figure: Polished slab of Devonian tuffaceous shale. Road cutting on Pak Chom-Chiang Khan highway (Route 211), Loei Province (photograph courtesy of D. Saesaengseerung) (Wongwanich & Boucot, 2011).]

Lithology Pattern:

Siliceous limestone

Relationships and Distribution

Lower contact

unknown

Upper contact

Nong Dok Bua Fm (conformable)

Regional extent

Loei-Phetchabun Ranges and northwest of the Khorat Plateau.

[Geo-JSON omitted – would overlap other set.]

GeoJSON

null

Fossils

corals

Age

Age Span:

Beginning stage:

Lochkovian

Fraction up in beginning stage:

Beginning date (Ma):

419.20

Ending stage:

Frasnian

Fraction up in the ending stage:

Ending date (Ma):

382.69

Depositional setting

Marine

Depositional pattern:

Additional Information

Remarks: Bunopas (1988) divided the Lower to Upper Palaeozoic above the Na Mo Fm metamorphics into two formations: the Silurian–Devonian Pak Chom Fm and the Carboniferous Wang Saphung Fm.

Correlation: Based on the radiolarian assemblages, Sashida & Igo (1999) correlated the Pak Chom Chert with Fang Chert in the North. The Pak Chom Chert can also be compared to the Ban Khok Phai Fm of Fontaine (1990).

Compiler:

Wen Du -modified from Wongwanich T. & Boucot A. J., 2011, Chapter 4 Devonian, 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