Khorat Gr

Cenozoic

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

Devonian

Early Paleozoic

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Khorat Gr

Period:

Triassic, Jurassic, Cretaceous

Age Interval:

Upper Triassic to Late Cretaceous, possibly extending into the Cenozoic. (13, 14, 15)

Province:
Indochina Block: Khorat Plateau, Indochina Block: Loei Fold Belt

Type Locality and Naming

Khorat Plateau (eastern Thailand). Subdivisions: Consists of: Lower Nam Phong Fm, Upper Nam Phong Fm, Phu Kradung Fm, Phra Wihan Fm, Sao Khua Fm, Phu Phan Fm, Khok Kruat Fm, Maha Sarakham Fm and Phu Thok Fm (DMR, 2007; Jin-Geng and Meesook, 2013). [The Nam Phong Fm is widely accepted as the basal unit.]

Synonym: กลุ่มหินโคราช; Khorat Series

[Figure: NE and SE Thailand, showing distribution of Cretaceous outcrops. (Meesook, 2011. Page 170). At least some of the Pre-Cretaceous sedimentary rocks on the map may be Jurassic and the position of the Jurassic-Cretaceous boundary is discussed in Meesook (2011).]

Lithology and Thickness

Sandstone, siltstone, claystone, shale and conglomerate. Red clastic sedimentary rocks, sandstone, siltstone, claystone, shale and conglomerate. Thickness: 5,000 m.

[Figure: Composite stratigraphic column of the Mesozoic rocks of the Khorat Plateau, NE Thailand (Meesook, 2011).]

Lithology Pattern:

Sandstone

Relationships and Distribution

Lower contact

conformably on Huai Hin Lat Fm (but some diagrams include Huai Hin Lat Fm in this group; therefore below (unconformable)is the Saraburi Gr (its Sap Bon Fm).

Upper contact

in Loei-Phetchabun Range - Wichian Buri Gr (unconformable); in Khorat Plateau - Unnamed Quaternary (unconformable). [GeoJSON omitted here to avoid duplication of individual formations.]

Regional extent

The Khorat Plateau & Loei-Phetchabun Range of Indochina block.

GeoJSON

null

Fossils

See details in each individual formation.

Age

Latest Triassic (the Nam Phong Fm) through Late Cretaceous (the Phu Thok Fm) in age although possibly extending into the Cenozoic. (Chapter 8: Cretaceous in Geology of Thailand, 2011, page 169-174)

Age Span:

Beginning stage:

Rhaetian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

209.56

Ending stage:

Danian

Fraction up in the ending stage:

Ending date (Ma):

66.04

Depositional setting

Continental deposits

Depositional pattern:

Additional Information

Alternatively, it consists of 6 formations: Upper Nam Phong Fm, Phu Kradung Fm, Phra Wihan Fm, Sao Khua Fm, Phu Phan Fm, Khok Kruat Fm (Sattayarak and others, 1989; Booth and Sattayarak, 2011; Racey, 2011), based mainly on unconformities from seismic evidence.

Remarks: This Group was formerly named as the Khorat series (Brown and others, 1951, 1953). Mouret (1994) raised the Khorat Group to Khorat supergroup, but this name is informal, according to the International Stratigraphic Guide.

The International Stratigraphic Guide states that “local or minor hiatuses, disconformities or unconformities within a sequence of similar lithologic composition should not be considered reason for recognition of more than one lithostratigraphic unit” (Murphy and Salvador, 1999).

Compiler:

Wen Du - modified from- Booth, J. & Sattayarak N., 2011, Chapter 9 Subsurface Carboniferous-Cretaceous geology of NE Thailand 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.

Meesook A., 2011, Chapter 8 Subsurface Cretaceous 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.