Pac Ma Fm
Type Locality and Naming
The type section is located on the left side o f the Song Da River, near Pac Ma Village, Quynh Nhai District, Lai Chau Province (N= 21°56’; E= 103°50’).
Synonym: Hệ tầng Pác Ma: Vũ Khúc (in Vũ Khúc et al.) 2000 ịCarni); Vũ Khúc et al 2002. - Calcaire rouge de Pa-m a: Mansuy H. 1912 (Calovi)\ Saurín E. 1956 {Nori hạ). - Đá vôi đó Pác M a: Vũ Khúc 1967 (Carnì-Nori), 1984 (Carni), (in Tống Duy Thanh et al. 1995 - Carni). - Hệ tầng Suối Bàng (part.): Dovjikov A.E. et al.) 1965. - Tầng đá vói ám liêu màu đỏ: Phan Cự Tiến et al. ] 977 (Carni-Norí). - Bậc Carni (part.): Vũ Khúc, Trịnh Thọ (in Trần Văn Tri et al -) 1977, (in Dương Xuân Hào et al.) 1980. - Diệp Nậm Mu (part.): VQ Khúc, Bùi Phú Mỹ et al.) 1990.
Lithology and Thickness
Reef limestone, marl and siltstone; Characteristic section on the Da River bank is Reddish, thick-bedded coral reef limestone (80 m) grading upwards into greenish-grey, thin-bedded marl and siltstone (20 m), containing poorly preserved bivalves. In the north of Yen Chau Townlet, the Pac Ma Fm reaches up to 220 m in thickness.
Relationships and Distribution
Lower contact
Conformably lies upon clayey shale of the Nam Mu Fm containing the Camian bivalve Zittelihalobia cf. rugosa.
Upper contact
Not clear. Regionally, next younger regional unit is the Nam Po Fm of early Jurassic.
Regional extent
Pac Ma area near the Quyuh Nhai Coal Mine (Lai Chau Province) and as a narrow band extending from the Tat Heo Village (previoius Pho Village) eastwards to the Muong Lum Coal Mine (Son La Province). [NOTE: Lexicon user map-interface is slightly misleading here, because it would be ca. mid-way between columns 7 and 9; on level with 8).
GeoJSON
Fossils
Corals Thecosmilia sp. and Isastrea sp, and Brachiopods Rhaelina bamaensis, R. cf. complanata, Aulacothyropsis bisinuata, snd Holcorhynchia vietnamica, the Bivalve Halobia pacmaensis at the base.
Age
Depositional setting
Marks the end of the sea regression at the end of the Carnian in the Song Da-Tu Le Basin.
Additional Information