Ket Hay Fm

Period:

Ordovician

Age Interval:

Late Ordovician-Early Silurian, (9)

Province:
West Bac Bo

Type Locality and Naming

Reference section is along the Pa No Stream. Named by Le ThanhHuu and Vu Xuan Luc (2005).

Synonym:

Lithology and Thickness

Pa No Stream section is 230 m thick: (1) Thin-bedded cherty shale; 90 m. (2) Cherty shale interbedded with black-grey thin-bedded shale and siltstone; 70 m. (3) Quartz-sericite-chlorite schist, grey thin-bedded calcaro-cherty shale; 70 m.

Lithology Pattern:

Chert

Relationships and Distribution

Lower contact

Tectonic contacts; therefore uncertain. Next older regional unit is the Dong Son Fm of early Ordovician.

Upper contact

Tectonic contacts; therefore uncertain. Next younger regional unit is the Ta Khoa Fm of early Devonian.

Regional extent

Occurs in a narrow band in the SW of the Son La Province – extending from Tram Co Pass through Xa Kenh to Ban Khuong areas. There are also discontinuous exposures in the west of the Son La – Tuan Giao area.

GeoJSON

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Fossils

Graptholites: Rostrites sp. (Late Ordovician), and Early Silurian taxa of Demirastrites triangulates, Hetrograptus cf. rectangularis, Diplograptus cf. modestus.

[Figure: Ket Hay Fm (O₃-S₁ kh): Ordovician: Graptolites Demirastrites triangulatus (images courtesy of Prof. Ta Hoa Phuong, Vietnam Natl. Univ. Hanoi)]

[Figure: Ket Hay Fm (O₃-S₁ kh): Ordovician: Graptolites Diplograptus cf. modestus (pair of images courtesy of Prof. Ta Hoa Phuong, Vietnam Natl. Univ. Hanoi)]

Age

Late Ordovician-Early Siluria on the basis of the collected fossils and stratigraphic correlation

Age Span:

Beginning stage:

Sandbian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

458.18

Ending stage:

Telychian

Fraction up in the ending stage:

1.0

Ending date (Ma):

432.93

Depositional setting

Depositional pattern:

Additional Information

Compiler:

Tran Van Tri and Vu Khuc (Editors; Geology and Earth Resources of Viet Nam, General Dept. of Geology and Minerals of Viet Nam; completed in Dec., 2011), with additional details from Tong-Dzuy Thanh and Vu Khuc (Editors; Stratigraphic Units of Viet Nam, 2^nd edition; 2011; English edited by A. Boucot).