Da Nieng Fm
Type Locality and Naming
Upper formation of the Trang Khang Gr in West Bac Bo. Holostratotype: The Ban Cai - Phu Da Nieng section, Tan Lang Commune, Phu Yen District, Son La Province (N= 21° 830"； E= 104° 45'), chosen by Nguyen Xuan Bao ei al (1969). Hypostraiotype: Upstream of the Song Mua River, Muong Bang Commune, Phu Yen District, Son La Province (N= 21°12'; E= 104°44J). The formation is named after Da Nieng Mount (Phu Da Nieng) south of Ban Cai Village (Phu Yen District, Son La Province), where it was first described by Nguyen Xuan Bao et al, (1969). The BanjCai - Phu Da Nieng section is not continuously exposed and has a reverse dip, so it does not reflect the real stratigraphic sequence of the formation; therefore the section upstream of the Song Mua River has been proposed as the hypostratotype of the Da Nieng Formation.
Synonym: -Diep Da Nieng: Nguy£n Xuan Bao e( at. 1969 (D2gv. D3fr dn)\ Nguyen Vmh et al. 1972 (D^gv - D3); Durong Xuan H^o in TrSn V3n Trj el a!. 1977 - D2 gv-Dj fr; Duofng Xuan Hao ei aL 1975 (D3); Do^n Nh§t Truang in T6ng Day Thanh et al. 1995 (C|t). -Diep Ban Cdi (part.); Phan Cu Ti6n et al. 1977 (D2gv - D3 be); T6ng Duy Thanh 1979 (Djfr-fm - H§ t§ng); Duong Xuan Jiao et al. 1980 (D3 - CO; Doan Nhqt Truong 1980, 1984 (D3 - Ctt); Nguyin Cong Lirgmg el al. 1995 (Dj-Qt). -Cac tram tick Givei - Devon (ren: Nguyin Vinh 1977.
Lithology and Thickness
In the Song Mua River upstream section the formation sequence (130 m total) is as follows. (1). Grccnish-grcy, yellow-brown weathering, thin-bedded (3-5 cm) cherty-clay shale and cherty shale, 10 m thick. (2). Black-grey, medium-bedded, fine-grained limestone containing loaf-form calcareous chert and cryptocrystallinc chert, with some interbeds containing black carbonaceous materials, 120 m thick.
Relationships and Distribution
Lower contact
Conformable on banded limestone of the underlying Ban Cai Fm (Toe Tat Fm in new conception). Direct contact of the Da Nicng upon the Toe Tat Fm was not observed, because chcrty shale and chert of the lowermost the Da Nieng Fm is usually folded and strongly weathered. The conformable boundary between two formations has been inferred from their stable position in the observed sections and the gradual change of lithological composition from the Ban Pap Fm to the Da Nieng Fm.
Upper contact
Conformable below the grey to light grey, thick-bedded limestone of the overlying Da Mai Fm (= Bac Son Fm). The conformable relation between the Da Nieng Fm and the overlying Da Mai Fm has been based on the gradual change of lithological composition from each other. The common boundary of the two formations has been delineated between the dark grey limestone containing chert loaves of the Da Nieng Fm and the slightly grey limestone of the Da Mai Fm (= Bac Son Fm).
Regional extent
The distribution of the Da Nieng Fm is limited in the Ban Nguon and Ban Cai anticlines (Phu Yen District, Son La Province), and in the Lung Lo Pass area (along the car road N°.37), and in most of its distribution areas the lithology of the formation is stable.
GeoJSON
Fossils
Foraminifera and conodonts are abundant in the section, the lower part of member 2 contains the foraminifera Parathurammina suleimanovi, Septabrunsiina kingirica, S. primaeva, Palaeo- spiroplectammina ichernyshinensis, P. cf. sinensis, Glomospira glomerosa, Chernyshinella tumulosa, Latiendothyra parakosvensis, Planoendothyra rotayi; and conodonts: Pseudopolygnathus sp., Siphonodella sp., Hindeodella sp.. In its upper part there are Late Tournaisian and Toumaisian-Visean boundary fossils, such as the foraminifera Spinoendothyra ukrainica, Tuberoendothyra and the conodonts Siphonodella cooperi, S. isosticha, S. duplicata, S, crenulata, Scaliognathus anchoralis, Mestognathus beckmanu Polygnathus purus, etc..
The following faunal zones and assemblages have been established in the Da Nieng Fm dating their host rocks as Tournaisian - Early Visean. Conodonts: 1) Siphonodella duplicate 2) Siphonodella isosticha^ 3) Siphonodella crenulatay 4) Mestognathodus beckmani -Siphonodella anchoralis\ Foraminifera: 1) Chernyshinella-Palaeospiroplectamminay 2) Dainella - Eoparastaffella
[Figure: Đa Niêng Fm: Foraminifera fossils (images courtesy of Prof. Ta Hoa Phuong, Vietnam Natl. Univ. Hanoi)]
[Figure: Đa Niêng Fm: Conodont fossils (images courtesy of Prof. Ta Hoa Phuong, Vietnam Natl. Univ. Hanoi)]
Age
Depositional setting
The Da Nieng Fm took shape from the Late Devonian to the Visean when the basin was differentiated in intra-shelf troughs in a carbonate shelf. After that, the basin became homogeneous as is expressed by the widespread light grey limestone of the Da Mai Fm (= Bac Son Fm) on Viet Nam territory.
Additional Information