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Khao Lak Formation

Khao Lak Fm

Period:

Jurassic

Age Interval:

Toarcian-Bajocian (4)

Province:
Sibumasu: Upper Peninsula

Type Locality and Naming

A small creek on the southern flank of Khao Lak, on the provincial boundary of Chumphon and Prachuap Khiri Khan provinces, by Meesook and Grant-Mackie (1996). But Meesook and Saengsrichan (2011) apply the name Khlong Min Fm from the nearby Nakhon Si Thammarat basin, although age span is quite different.

Synonym: หมวดหินเขาหลัก, Khlong Min Fm (depending upon usage).

Lithology and Thickness

Mainly mudstone and sandstone; bivalves and ammonites are common. Thickness: 190 m.

Lithology Pattern:

Fine-grained sandstone

Relationships and Distribution

Lower contact

Maybe Sai Bon Fm (unconformable) of Triassic; but that is in the middle of the South Peninsula (Trang Province).

Upper contact

Chumphon Redbeds Fm (unconformable) -- uncertain

Regional extent

Upper Peninsula: Chumphon province. Correlation: Hua Fai Gr, Khlong Min Fm

GeoJSON

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Fossils

At the original type section; ammonite and bivalve fauna were collected, the ammonites Eutmetoceras sp. and Docidoceras sp. indicating an Early Bajocian age. "The Chumphon Basin contains one of the richest Jurassic non-marine to marine faunal assemblages in Thailand. Brackish assemblages dominate over marine and include the bivalves Protocardia sp., Actinostreon sp., Praemytilus sp., Modiolus sp., Myrene sp., ostracods and plant remains. Marine forms, for example, Parvamussium sp. and Trigonia sp., are found locally but are not common. In the upper part of the formation, non-marine vertebrates and plant remains are the main fossils. … The fossil assemblages indicate a Middle Jurassic age." (Meesook and Saengsrichan, 2011)

Age

Fig. 7.3 of Meesook and Saengsrichan (2011) implies a possible mid-Toarcian to mid-Bajocian age for the Khlng Min Fm (their replacement name for the Khal Lak Fm) in the Chumphon Basin.

Age Span:

Beginning stage:

Toarcian

Fraction up in beginning stage:

0.5

Beginning date (Ma):

178.92

Ending stage:

Bajocian

Fraction up in the ending stage:

0.5

Ending date (Ma):

169.29

Depositional setting

Shallow marine

Depositional pattern:

Additional Information

Compiler:

Wen Du - modified from Lexicon of Stratigraphic Names of Thailand of 2013; Assanee Meesook & Wirote Saengsrichan, 2011, Chapter 7 Jurassic in Ridd, M.F., Barber, A.J., and Grow, M.J., editors, The Geology of Thailand, Geol. Soc. of London; Assanee Meesook, 2011, Chapter 8 Cretaceous in Ridd, M.F., Barber, A.J., and Grow, M.J., editors, The Geology of Thailand, Geol. Soc. of London.