DSpace at VNU: Silurian and Devonian in Vietnam—Stratigraphy and facies

Journal of Geodynamics 69 (2013) 165–185

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Silurian and Devonian in Vietnam—Stratigraphy and facies
˜ Hùng c ,
Toˆ´ ng Duy Thanh a,∗ , Ta. Hoàng Phuong a , Philippe Janvier b , Nguye˜ˆ n Huu
Nguye˜ˆ n Thi. Thu Cúc a , Nguye˜ˆ n Thùy Duong a
a
b
c

Laboratory of Historical Geology, Vietnam National University, 334 Nguyen Trai Str., Thanh Xuan District, Hanoi, Viet Nam
UMR7207 du CNRS, Muséum National d’Histoire Naturelle, 8 rue Buffon, 75005 Paris, France
Institute of Geosciences and Mineral Resources, Thanh Xuan District, Hanoi, Viet Nam

a r t i c l e

i n f o

Article history:
Received 6 August 2010
Accepted 10 October 2011
Available online 17 October 2011
Keywords:
Silurian
Devonian
Stratigraphy
Facies

Viet Nam

a b s t r a c t
Silurian and Devonian deposits in Viet Nam are present in several zones and regions, including Quang
Ninh, East Bac Bo, and West Bac Bo Zones of the Bac Bo Region, the Dien Bien-Nghe An and Binh Tri Thien
Zones of the Viet-Lao Region, and the South Trung Bo, and Western Nam Bo Zones of the South Viet Nam
Region (Fig. 1). The main lithological features and faunal composition of the Silurian and Devonian Units
in all these zones are briefly described.
The Silurian consists of deep-water deposits of the upper parts of the Co To and Tan Mai Formations in
the Quang Ninh Zone, the upper parts of the Phu Ngu Formation in the East Bac Bo Zone and the upper
parts of the Long Dai and Song Ca Formations in the Viet-Lao Region. Shallow water facies Silurian units
containing benthic faunas are more widely distributed, including the upper part of the Sinh Vinh and Bo
Hieng Formations in the West Bac Bo Zone, the Kien An Formation in the Quang Ninh Zone, and, in the
Viet-Lao Region, the Dai Giang Formation and the upper part of the Tay Trang Formation.
No Lower and Middle Devonian deposits indicate deep water facies, but they are characterized by
different shallow water facies. Continental to near shore, deltaic facies characterize the Lower Devonian
Song Cau Group in the East Bac Bo Zone, the Van Canh Formation in the Quang Ninh Zone, and the A Choc
Formation in the Binh Tri Thien Zone. Similar facies also occur in the Givetian Do Son Formation of the
Quang Ninh Zone, and the Tan Lap Formation in the East Bac Bo Zone, and consist of coarse terrigenous
deposits—cross-bedded conglomerates, sandstone, etc. Most Devonian units are characterized by shallow
marine shelf facies. Carbonate and terrigenous-carbonate facies dominate, and terrigenous facies occur
in the Lower and Middle Devonian sections in some areas only.
The deep-water-like facies is characteriztic for some Upper Devonian formations in the Bac Bo (Bang
Ca and Toc Tat Formations) and Viet-Lao Regions (Thien Nhan and Xom Nha Formations). These formations contain cherty shale or siliceous limestone, and fossils consist of conodonts, but there are also
brachiopods and other benthos. They were possibly deposited in a deep water environment on the slope
of the continental shelf.
Most Devonian units distributed in the North and the Central Viet Nam consist of self shallow water
sediments, and apparently they were deposited in a passive marginal marine environment. The coarse
clastic continental or subcontinental deposits are distributed only in some areas of the East Bac Bo and
of the Quang Ninh zones of the Bac Bo Region, and in the south of the Binh Tri Thien Zone. This situation

suggests the influence of the Caledonian movement at the end of the Silurian period that called the
Guangxi movement in South China.
© 2011 Elsevier Ltd. All rights reserved.

1. Introduction
The Silurian and Devonian deposits of Viet Nam were first
discovered and described by French geologists of the Geological
Survey of Indochina (Saurin, 1956). Later, they have been systematically studied by Dovjikov et al. (1965), Tong-Dzuy Thanh (1993),

∗ Corresponding author. Tel.: +84 1696456546; fax: +84 438583061.
E-mail address: (T.D. Thanh).
0264-3707/$ – see front matter © 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jog.2011.10.001

Tong-Dzuy Thanh et al. (1988), Vu Khuc and Bui Phu My (1990),
and Tong-Dzuy Thanh and Vu Khuc (2006). Major contributions in
the description of Silurian and Devonian units have been made by
geologists from the Geological Mapping Division, during the last
decades of the 20th century (1:200,000 geological maps). Stratigraphic units have been well established and their correlations are
based on abundant faunas. Their study shows that Silurian and
Devonian deposits are widespread in the North and the Central
parts of the country, whereas in the South there are only terrigenous deposits of suspected Devonian age. New data on the Silurian


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Fig. 1. Zonal distribution of the Silurian and Devonian deposits of Viet Nam. 1. Bac Bo Region: 1a. Quang Ninh Zone; 1b. East Bac Bo Zone; 1c. West Bac Bo Zone. 2. Viet-Lao
Region: 2a. Dien Bien-Nghe An Zone; 2b. Binh Tri Thien Zone. 3. South Viet Nam Region: 3a. Trung Bo Zone; 3b. West Nam Bo Zone. Regional and zonal boundaries: I. Song

Chay Fault; II. Dien Bien-Lai Chau Fault; III. Song Ma Fault; IV. Rao Nay Fault; V. Tam Ky-Phuoc Son Fault.

and Devonian stratigraphy have also been obtained recently, and
contribute to processing the sequence of some sections and completing their distribution areas based on new discoveries.
The Silurian is characterized by marine deposits only, with deep
water facies in some regions and areas and shallow-water facies in
others. In contrast, the Devonian mainly comprises continental and
shallow-water marine deposits, and deep-water like facies of the
Upper Devonian in some areas. The difference between the various
sedimentary components and facies of the deposits depends on the
distribution areas that reflect the paleoenvironment conditions of
their sedimentary deposition processes. On the basis of the lithological components and facies, the distribution of the Silurian and
Devonian deposits can be differentiated into regions and zones as
follows (Fig. 1):
1. The Bac Bo Region (Northern Region) extends over almost all the
Northern part of the country (the Tonkin of older publications).
It is limited in the West by the Song Ma and Dien Bien-Lai Chau
faults and includes three zones:
1a. The Quang Ninh Zone includes the northeast coastal area of
Bac Bo, including the islands of the Ha Long Bay;
1b. The Eastern Bac Bo Zone extends eastward from the Song
Chay fault and is limited by the Quang Ninh Zone in the East;
1c. The Western Bac Bo Zone is located between the Song Chay
Fault in the East, the Dien Bien-Lai Chau Fault in the West,
and Song Ma Fault in the Southwest.

2. The Viet-Lao Region, which is located between the Song Ma and
Dien Bien – Lai Chau Fault in the Northwest and the Tam Ky –
Phuoc Son Fault in the South, is divided into two zones – the Dien
Bien – Nghe An and Binh Tri Thien zones, respectively.

2a. The Dien Bien-Nghe An Zone extends from the Dien Bien-Lai
Chau and Song Ma Faults in the Northern and Eastern sides
and the Rao Nay Fault in the South.
2b. The Binh Tri Thien Zone is located between the Rao Nay Fault
in the North and the Tam Ky-Phuoc Son one in the South.
3. The South Viet Nam Region, which extends southward from the
Tam Ky-Phuoc. Son Fault, includes two zones that are separated
by a presumed boundary.
3a. The South Trung Bo Zone (Southern part of the Central Viet
Nam) extends from the Tam Ky-Phuoc Son Fault to the East
Nam Bo area.
3b. The Western Nam Bo Zone includes the territory of Kien
Giang Province and the Vietnamese part of the Gulf of
Thailand.
The stratigraphic units will be presented below for each region
and its respective zone.
2. Stratigraphic units
2.1. Silurian
See (Fig. 2).


T.D. Thanh et al. / Journal of Geodynamics 69 (2013) 165–185

167

Fig. 2. The distribution in regions and zones of the Silurian and Devonian Units of Viet Nam.

2.1.1. Bac Bo region
2.1.1.1. Quang Ninh Zone. In the Quang Ninh Zone, the most
important Silurian deposits are distinguished by deep-water facies

containing graptolite faunas and form the upper part of the
Ordovician-Silurian formations in the northeastern coastal area and
in the Co To archipelago. The shallow-water deposits containing
benthic fauna are exposed in a small area of the Kien An District, in
the vicinity of Hai Phong City.
The Tan Mai Formation (O-S tm) is characterized by rhythmic
and banded structures, including terrigenous sediments. It is about
7 km broad an extends discontinuously for hundreds of kilometers along the southeast side of the NE-SW trending Yen Tu–Tien
Yen–Tan Mai Fault, and crops out in the Cai Chien and Vinh Thuc
islands.
The stratotype of the formation extends along the road from
Mong Cai Town through Tan Mai to Than Pun villages. It has been
subdivided into two parts: the lower one is 1000–1200 m thick and
comprises grey, greenish-grey, fine- to medium-grained quartzitic
micaceous sandstone with flattened pebbles interbedded with
micaschist, micaceous siltstone, and phyllite. The latter gradually
increases upwards in the section. In the upper part (about 1000 m
thick) occur green-grey mica schist, micaceous phyllite with
some interbeds of micaceous sandstone. Graptolites (Bohemograptus tenuis, Lobograptus cf. crinitus, Neoculograptus inexpectatus,
Pristiograptus pseudodubius) occur in the siltstone of the upper part
along with sporomorphs (Acanthotriletes sp., Lophozonotriletes sp.,
Simozonotriletes sp., Stenozonotriletes sp., and Punctatisporites sp.),
notably in the Nam Ha–Truong Thu section. Silurian fossils have
also been found in the upper part of the formation. Yet the Ordovician age of this part is only inferred from the thickness of beds
that underlie the Silurian fossiliferous layers (Nguyen Cong Luong,
2001a,b).
The Co To Formation (O-S ct) is mainly characterized by polymictic, cross-bedded sandstone bearing fragments of felsic effusives,

claystone with banded and rhythmic structure, and tuffaceous
interbeds and gritstone. It is therefore readily distinguished from

the Tan Mai and Phu Ngu formations of the same age. The total
thickness of the Co To Formation reaches over 1000 m (Fig. 3).
The Co To Formation occurs on over 40 islands and islets of Co To
Archipelago, situated in the extreme northeast of Bac Bo (Tonkin)
Gulf. It extends along a NE–SW trend, from Lo Chuc San, through
Thanh Lan to Co To Islands.
The 710 m thick Thanh Lan Section is composed of two parts:
the lower part is composed of mixed deep marine sediments intercalated with shallow marine facies, and the upper part, made up by
fine-grained, banded sediments that indicate deep marine facies.
Early Silurian graptolites (Streptograptus exiguus, Monograptus priodon) have been collected from the silty claystone of the uppermost
levels of the lower part. Apart from these species, other graptolites
were also reported from Co To Island (Spirograptus cf. minor, S. cf.
turriculatus, S. cf. regularis, Oktavites aff. O. planus, Campograptus
communis, Demirastites sp., Climacograptus sp., Monograptus ex gr.
pandus, Streptograptus sp. (Tran Van Tri et al., 1972, 1975, 1977).
Con Ngua Island also yielded Pristiograptus cyphus, Pristiograptus
sp., Pseudoclimacograptus sp. (in Nui Nhon Islet), and Demirastrites
triangularis (Nguyen Huy Mac and Pham The Hien, 1972), and Lo
Chuc San Island yielded Streptograptus exiguous and Monoclimacis
linarsoni. All these graptolites indicate an Early Silurian age and
are located in the lower beds of the upper part of the formation.
The unfossiliferous lower part is rather thick, consisting of deep
marine sediments and possibly corresponds to a relatively long
period; therefore, the Co To Formation is approximately considered as Ordovician–Early Silurian in age (Tong-Dzuy Thanh and Vu
Khuc (2006).
The Kien An Formation (S4 kn) crops out in several hills in the Kien
An District, near Hai Phong City (Fig. 4). According to Tong-Dzuy
Thanh et al. (2001) the tripartite sequence of the Kien An Formation consist of a 120 m thick lower part of blue-grey marl, mudstone

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Fig. 3. Correlation of the Silurian deposits in the Bac Bo Region. (A) West Bac Bo Zone: 1–3. Sinh Vinh Formation (O3 -S sv); 4. Bo Hieng Formation (S4 bh); (B) East Bac Bo Zone:
1–5. Phu Ngu Formation (O-S pn); (C) Quang Ninh Zone: 1–4. Co To Formation (O-S ct) (The legends in this figure are for Fig. 6 and Fig. 9 also).

and yellowish-grey sandstone containing Nikiforovaena cf. ferganensis and indeterminate rugosans, and a 320 m. thick middle part
composed of grey, quartzitic sandstone with dark purplish-red
mudstone interbeds which yields Retziella weberi, Nikiforovaena
ferganensis and Howellella sp. The upper part of the section, on
the north slope of Xuan Son Mountain, consists of about 100 m of
thick-bedded dark grey limestone with shale and marl interbeds
in the uppermost layers, which yield an abundant Retziella weberi
assemblage. At the same level, but on the north slope of Tien Hoi
Mountain, the brachiopods Retziella weberi, Nikiforovaena ferganensis, Howellella bragensis, Howellella sp. (Vu Khuc and Bui Phu My,
1990) were recorded, along with abundant corals, notably Favosites
admirabilis, Xiphelasma sp., Nipponophyllum sp., and Mesofavosites
sp.
No lower boundary of the Kien An Formation has ever been
observed, and its relations with the Co To and Tan Mai Formation
are unknown. It possibly unconformably underlies the Lower Devonian Van Canh Formation. The Kien An Formation is referred to the
Late Silurian, (Late Ludlow or Pridolian) (Tong-Dzuy Thanh et al.,
2001).
2.1.1.2. Eastern Bac Bo Zone. In Eastern Bac Bo Zone, the Silurian
deposits are represented by deep-water facies containing graptolite
faunas which occur in the central area of the zone. They make up
the upper part of the Ordovician-Silurian Phu Ngu Formation.
The Phu Ngu Formation (O-S pn) is characterized by banded,
mainly fine-grained rhythmic terrigenous sediments interbedded

with effusives of mafic to felsic and alkaline composition (Fig. 3).
The Formation occurs in two bands, the first of which extends from
Dai Tu (Thai Nguyen Province) to Cho Ra (Bac Can Province). The
second band extends from Luong Mt through Ngoi Nac, Vinh Tuy
to Huong Son areas (Ha Giang Province).
With a thickness of 2300–2400 m, the Phu Ngu stratotype is
composed of two distinct parts. The 1100 m thick lower part
includes argillaceous shale, cherty-argillaceous shale rhythmically
interbedded with silty sandstone, locally with lenses of limestone and mafic effusives. The 1200 m thick upper part comprises
silty sandstone interbedded with argillaceous shale and chertyargillaceous shale, locally with lenses of limestone and felsic
effusives. Graptolites (e.g., Climacograptus sp., Glyptograptus sp.,
Monoclimacis sp.) have been collected from the uppermost levels of the lower part, along with poorly preserved trilobites and
brachiopods (Fig. 3).
In Na Ri area (Bac Can Province), the formation occurs in small
exposures with a thickness of about 250 m, including grey silty
sandstone, greenish-grey marl, black, thin-banded argillaceous
shale containing the graptolites Diplograptus sp., Climacograptus
latus, Climacograptus cf. C. scolaris, Ptilograptus sp., Glyptograptus
sp., the trilobites Agnostus perrugatus, Remopleurides aff. R. salteri,
and the bryozoan Fenestella sp.
All these fossils are of Ordovician to Early Silurian age, but occur
in a fairly low position in the sections, but the part the section that
overlies the fossil-bearing beds is rather thick and characterized
by deep marine facies, therefore the formation can reasonably be


T.D. Thanh et al. / Journal of Geodynamics 69 (2013) 165–185

169

Fig. 4. Distributed area (A) and stratigraphic sequence (B) of the Upper Silurian Kien An Formation (S4 kn) in Kien An District (Hai Phong City).

dated as Ordovician-Silurian (Pham Dinh Long, 2001; Nguyen Kinh
Quoc, 2001; Tong-Dzuy Thanh and Vu Khuc, 2006).
2.1.1.3. Western Bac Bo Zone. In the Western Bac Bo Zone the Silurian deposits include the upper parts of the Ordovician-Silurian
Sinh Vinh Formation, and the Upper Silurian Bo Hieng Formations.
They mainly consist of shallow-water facies deposits, and deepwater deposits are limited to the west of Son La Province (Ket Hay
Formation).
The Sinh Vinh Formation (O3 —S sv) (Fig. 3) is mainly characterized by light grey, thickly bedded dolomitic limestone, exposed
in the lower section of the Song Da River in discontinuous narrow bands. In the Sinh Vinh Section, along the Song Da River, the
Formation is clearly distinguished by the three following parts:
(1) The 40 m thick lower part, made up by conglomerate, whose
quartzite pebbles are derived from the underlying Ben Khe Formation; (2) The 400 m thick middle part, made up by calcareous
sandstone and mudstone, dolomite, sandy limestone and marl
bearing the corals Reuschia sp., Plasmoporella kiaeri, Favositella alveolata; (3) The 350 m thick upper part, which consists of light grey,
thickly bedded dolomitic limestone and calcareous shale interbeds
bearing the corals Favosites sp., F. aff. F. forsbesi, F. ex gr. F. gothlandica, F. cf. F. hisingeri, F. cf. F. coreaniformis, Mesofavosites sp.,
Squameofavosites sp., and Parastriatopora sp. The total thickness of
this section is 800 m, but in other sections its thickness reaches
1000–1200 m.

Apart from the above mentioned fauna, some other fossils have
been collected, such as the corals Reuschia sp., Favositella alveolata,
and Favosites sp., F. aff. F. forbesi var. similis, F. ex gr. F. gothlandicus,
F. cf. F. hisingeri, F. cf. F. coreaniformis, Squameofavosites sp., Mesofavosites sp., Parastriatopora sp., Multisolenia ex gr. M. tortuosa, and
the crinoid Bistrowicrinus quinquelobatus.
The Bo Hieng Formation (S4 bh) is distributed in the limited area
of the lower section of the Song Da River basin, and it conformably
rests upon the Sinh Vinh Formation and under the Lower Devonian

Song Mua Formation (Fig. 3).
The 400 m thick Bo Hieng Formation, mainly consists of
dark green marly shale interbedded with black-grey limestone
and, in its lower part, some banded argillaceous shale containing brachiopods (Retziella weberi, Orbiculoidea tonkinensis), and
bivalves (Modiomorpha brevis, M. sp., Cymatonota cf. C. yunnanensis, Dysodonta sp., Actinopteria sp.). The upper part is composed of
black, thin- to medium-bedded limestone and marl in the upper
part, containing Retziella weberi, Tadschikia xuanbaoi, Howellella
sp., Scoliopora sp., and Favosites kunjakensis (Ta Hoa Phuong and
Le Van Manh, 1996).
In the Nui Tau Mt Section (Yen Lap, Phu Tho Province), the
black-grey limestone interbedded with argillaceous shale yielded
corals (Palaeofavosites aff. balticus, Favosites kernihoensis, Aphyllum aff. sociale) and brachiopods (Retziella weberi, Ferganella aff.
Turkestanica) (Nguyen Huu Hung et al., 1988), which indicate a Late
Silurian age of the formation (Tong-Dzuy Thanh et al., 2001). The


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T.D. Thanh et al. / Journal of Geodynamics 69 (2013) 165–185

Fig. 5. Distributed area and stratigraphic sequence of the Silurian Dai Giang Formation in Quang Tri Province.

lithology and fauna of the Bo Hieng Formation is similar to that of
the Kien An Formation described above.
The Ket Hay Formation (S1-2 kh) occurs in a narrow band in the
Southwestern area of Son La Province and discontinuous exposures
northwestward from Son La to Tuan Giao, all of them being probably in close relation to the Song Ca Formation (see below—Viet-Lao
Region). The 230 m thick Ket Hay Formation consists of thinbedded siliceous shale, interbedded with siliceous siltstone, shale,
sericite-chlorite schist, and calcareous-siliceous schist. Most of the
graptolites it has yielded (Demirastrites triangulates, Hedrograptus

cf. H. rectangulatus, Diplograptus cf. D. modestus) are Early Silurian
˜
in age (Le Thanh Huu and Vu Xuan Luc, 2005; Tran Van Tri and Vu
Khuc, 2009).

2.1.2. Viet-Lao Region
The Silurian deposits in the Viet-Lao region include the upper
part of the Ordovician-Silurian Song Ca Formation, and the Tay
Trang Formation of Late Silurian-Early Devonian age in the Dien
Bien-Nghe An Zone. In the Binh Tri Thien Zone, they are composed

of the upper part of the Ordovician-Silurian Long Dai Formation,
and the Upper Silurian Dai Giang Formation.
2.1.2.1. Dien Bien-Nghe An Zone. The Song Ca Formation (O3 -S2 sc)
crops out along two main strips, the first of which extends from
Muong Xen and Tuong Duong to Quy Chau, Nghe An Province,
south of the Song Ca River. The second strip extends from the
Vietnam-Laos border through Nghe An to Ky Anh, Ha Tinh Province.
The formation is about 2100–2300 m thick and mainly consists
of argillaceous shale, sandstone, and some beds of black, and
bedded limestone. The graptolites Monoclimacis vomerinus and
Pristiograptus kweichihensis occur in the argillaceous shale of its
upper part, and indicate an Early Silurian age. Besides, some Silurian spores also occur in this formation, such as Zonosphaeridium
sp. and Leiotrichoides sp. Since the Early Silurian graptolites occur
in the upper part of the formation, its lower part may therefore
tentitavely be referred to the Upper Ordovician (Tong-Dzuy Thanh
and Vu Khuc, 2006).
The Tay Trang Formation (S3 -D2 e tt) is distributed in Lai Chau and
Dien Bien areas, Northwest Bac Bo, extending to the West of Nghe

T.D. Thanh et al. / Journal of Geodynamics 69 (2013) 165–185

An Province (North Trung Bo), so it includes all the components
of the Tay Trang Formation introduced by Dovjikov et al. (1965)
and the Huoi Nhi Formation erected by Nguyen Van Hoanh (Le
Duy Bach and Nguyen Van Hoanh, 1995); therefore, the Tay Trang
name has priority.
The 800 m thick Tay Trang Formation consists of: (1) 540 m thick
grey, fine- to middle-grained sandstone, interbedded with ash grey
to dark grey, thin-bedded siltstone, and dark grey clay shale; (2)
260 m thick, dark grey, thin bedded clay shale, dark grey siltstone
with some dark grey, and fine-grained, thin bedded sandstone. The
formation yields fossils that indicate an age ranging from the Ludlow (Silurian) to the Eifelian (Middle Devonian). They include, in
the West of Nghe An Province, graptolites (Bohemograptus bohemicus, Monograptus thomasi, M. yukonensis, M. uniformis) (Nguyen Van
Phuc, 1998), and dacryoconarids (Nowakia cancellata, N. holynensis,
Homoctenus sp.), and, in the Tay Trang area (Dien Bien Province,
Western Bac Bo Zone), cephalopods (Erbenoceras sp., Anetoceras
sp.), the dacryoconarid Nowakia sp. (cf. N. acuaria), and the brachiopod Chonetes ex gr. tenuicostata. The Tay Trang Formation (=
Huoi Nhi Fm.) rests unconformably upon the Song Ca Formation
(O-S sc) and conformably under the Huoi Loi Formation (D1-2 hl)
(Tong-Dzuy Thanh and Vu Khuc, 2006).
2.1.2.2. Binh Tri Thien Zone. The Long Dai Formation (O2 -S2 ld) comprises terrigenous sediments of rhythmic structure, interbedded
with acidic to intermediate effusive, exposed in the south of the Rao
Nay Fault. In the Ban Ho–Vit Thu Lu stratotype, the formation is up
to 1250 m thick, and its lower part (about 1000 m thick) consists
of rhythmic intercalation of sandstone, siltstone and argillaceous
shale, clay-cherty shale with some interbeds of andesite, which
yield the Late Ordovician trilobites Cyclopyge sp., Microparia (?)
sagaviaformis, Ogygiocaris sp., Nileus sp., and the graptolite Diplograptus sp. Its upper part is composed of black argillaceous shale,

clay-chlorite shale with some interbeds of sandstone and gritstone
containing the Late Silurian graptolites Neodiversograptus nilssoni,
Monograptus sp., and Pristiograptus sp. The Le Ky section, which
reaches 1930 m in thickness, displays the same lithological components, but begins with 90 m thick conglomerate beds, and is
distinguished by the tuffaceous sandstone in its middle part, and
the lack of andesite interbeds. Llandovery graptolites (Demirastrites
convolutus, Monograptus halli, Oktavites spiralis) have been collected
from the middle part of the section, whereas its upper part yields
Bohemograptus bohemicus, Monoclimacis sp. (Nguyen Xuan Duong,
1996; Tong-Dzuy Thanh and Vu Khuc, 2006).
The Dai Giang Formation (S3-4 dg) is exposed in the Quang
Binh and Quang Tri Provinces, with thickness of about 1100 m
(Fig. 5), and its sequence begins with gritstone and coarse-grained
sandstone, unconformably overlying the Long Dai Formation. The
formation consists essentially of sandstone, siltstone and calcareous sandstone, with limestone and marl beds in its upper part.
A benthic fauna has been collected mainly from the middle and
the upper parts of the formation, and includes trilobites (Cromus beaumonti, Metacalymene sp., Praedechenella aff. vietnamica,
Encrinurus cf. sinicus), brachiopods (Retziella weberi, R. altaica,
Nikiforovaena vietnamica, “Howellella” cf. lynxoides), corals (Multisolenia cf. formosa, Nipponophyllum anmaense), bivalves (Schizodus?
myducensis, Sphenotus antecedens, Modiomorpha paracrypta, Goniophora dianensi), and fish remains referred to the placoderm
Myducosteus anmaensis and an indeterminate acanthodian (Nguyen
Xuan Duong, 1996; Tong-Dzuy Thanh and Vu Khuc, 2006).
2.2. Devonian
See (Fig. 2; Fig. 6).
Devonian deposits are widespread in Viet Nam, but their lithology and sequences, especially in the Lower Devonian, are different

171

in the Bac Bo, Viet-Lao, and South Viet Nam regions. The most complete Devonian sections are observed in the Bac Bo region, whereas
separate, discontinuous sections are met with only in some areas of

the South Viet Nam region (Tong-Dzuy Thanh and Vu Khuc, 2006).
In the Bac Bo region, the resemblances between the Devonian
sections is conspicuous and well characterized, both lithologically
and faunally, thereby indicating that they were formed in a single,
large basin. In the Quang Ninh, Eastern Bac Bo and Western Bac
Bo zones, the Devonian sections are composed of two conspicuous
parts, the lower one mainly consisting of terrigenous sediments,
and the upper one of carbonate. However, detailed differences
between these sections can be noticed. Notably, in the Eastern the
Bac Bo Zone, the Lower Devonian is characterized by Red Beds that
unconformably overly the Lower Paleozoic, while in the Western
Bac Bo there is a conformity between the Upper Silurian Bo Hieng
Formation and the Lower Devonian Song Mua Formation (Fig. 6).
2.2.1. Bac Bo Region
2.2.1.1. Quang Ninh Zone. In the Quang Ninh Zone, the Devonian
deposits consist of the Van Canh, Duong Dong, Do Son, and Trang
Kenh Formations, successively. The uppermost of the Devonian
sequences in this zone displays the lowermost part of the Upper
Devonian-Lower Carboniferous Con Voi and Pho Han formations.
The Van Canh Formation (D1 vc) is the lowermost formation of
the Devonian sequence in the Quang Ninh Zone, and crops out in
the Van Canh islet, Tra Ban, Ngoc Vung, and other islands in the Bai
Tu Long (Fai Si Lung) Bay, and on the Do Son Peninsula (Nguyen Huu
Hung et al., 2007). In the Van Canh type section, the formation consists of a 200 m thick series of alternating sandstone and mudstone
beds, which contains plant remains (Tainiocrada? sp. cf. T. decheniana, and Psilophytites? sp.). In this section, the Van Canh Formation
conformably underlies the Duong Dong Formation, which yields
the brachiopod Tulynetes nonpoensis.
On the Do Son Peninsula, the Van Canh Formation unconformably underlies the Do Son Formation. In previous works,
the Ngoc Xuyen mudstone and sandstone that has yielded the
eurypterids Rhinocarcinosoma dosonensis and Hughmilleria sp., isolated placoderm fish plates (referred to a primitive antiarch and a

“Wangolepis”-like placoderm) (Brady et al., 2002), and Lower Devonian sporomorphs, were considered as the lower part of the Do
Son Formation (Tong-Dzuy Thanh and Vu Khuc, 2006). They are
now referred to the Van Canh Formation (Nguyen Huu Hung et al.,
2007), but their eurypterid and vertebrate fauna seems more suggestive of the Uppermost Silurian (Brady et al., 2002; Janvier et al.,
2003).
The Duong Dong Formation (D1 –D2 e dd) is exposed in Kinh Mon
(Hai Duong Province), Duong Dong (Trang Kenh, Hai Phong City)
and Dong Trieu (Quang Ninh Province), and in Chau Dop, Tra Ban,
and Ngoc Vung islands (Ha Long Bay).
The new data provided by Nguyen Huu Hung et al. (2007) show
that the crossbedded quartzitic sandstone, siltstone and shale of the
upper part of the Duong Dong Formation described in the previous
works (Tong-Dzuy Thanh and Vu Khuc, 2006) should be referred
to the overlying Do Son Formation, and that the brachiopod- and
coral-bearing limestone lenses of its uppermost beds belong in
fact to the Trang Kenh Formation. This accords with the original description of the formation by Nguyen Quang Hap (1967).
According to Nguyen Huu Hung et al. (2007), the Duong Dong Formation in the Lo Son area consists of: (1). 50 m thick clay shale
and mudstone containing brachiopods; (2) 70 m thick fine-grained
sandstone and interbeds of shale containing brachiopods, and (3)
80 m thick fine-grained sandstone, mudstone interbeds containing poorly preserved brachiopods. The fossils from the Duong
Dong Formation are mainly brachiopods, and have been collected
from many localities, such as the Lo Son, Duong Dong and Hiep
Son (Kinh Mon) areas, and on Ngoc Vung and Van Canh islands


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T.D. Thanh et al. / Journal of Geodynamics 69 (2013) 165–185

Fig. 6. Correlation of the Devonian deposits in the Bac Bo Region. (A) West Bac Bo Region: 1. Upper Silurian Bo Hieng Formation (S4 bh); 2. Song Mua Formation (D1 sm); 3.

Ban Nguon Formation (D1 bn); 4. Ban Pap Formation (D1 p-D3 fr bp); 5. Bang Ca Formation (D2 gv-D3 fr bc); 6. Toc Tat Formation (D3 fm-C1 t tt). (B) East Bac Bo Zone: 1. Ordovician
Lutxia Formation unconformably is underlying the Si Ka Formation; 2. Si Ka Formation (D1 sk)—Red beds containing vertebrate remains; 3. Bac Bun Formation (D1 bb); 4. Mia
Le Formation (D1 ml) containing abundant Pragian benthos of the Euryspirifer tonkinensis assemblage; 5. Ban Pap Formation (D1 p-D3 fr bp); 6. Bang Ca Formation (D2 gv-D3 fr
bc); 7. Toc Tat Formation (D3 fm-C1 t tt). (C) Quang Ninh Zone: 1. Upper Silurian Kien An Formation (S4 kn); 2. Van Canh Formation (D1 vc); 3. Duong Dong Formation (D1 -D2 e dd);
4. Do Son Formation (D2 gv-?D3 fr ds); 5. Trang Kenh Formation (D2 gv-D3 tk.

(Bai Tu Long Bay). The brachiopods are referred to Euryspirifer cf.
tonkinensis, Indospirifer kwangsiensis, Schellwienella cf. S. lantenoisi,
Stropheodonta cf. S. interstrialis, Athyris concentric, Atrypa ex gr.
reticularis, Bacbochonetes sp., Retichonetes sp., Bacbochonetes janvieri, Perichonetes mutabilis, and occur along with the bivalves
Pterinopecten sp. Carinatina cf. C. arimaspa, Desquamatia sp. The
Duong Dong Formation conformably overlies the Van Canh Formation, and unconformably underlies the Do Son Formation. It is
referred to the Lower Devonian—Eifelian.
The Do Son Formation (D2 gv-?D3 fr ds) crops out in the Do Son
Peninsula and some islands of Bai Tu Long Bay. On the mainland of
the Quang Ninh Zone, it is usually exposed along with the Duong
Dong Formation and has sometimes been incorrectly referred to
part of the latter. It was first described by Lantenois (1907) as
the “Do Son Sandstone” (Grès de Do-Son), which occurs along the
beaches of Do Son Peninsula (Hai Phong City). Later, it has been
described as a tripartite formation (Tong-Dzuy Thanh and Vu Khuc,
2006). Our new investigations show that the Do Son Formation
includes two parts which correspond to Lantenois’s “Do Son Sandstone”, and a lower part of the “tripartite formation”, which is now
referred to the Van Canh Formation. The sequence of the formation
is thus as follows:
- 150–200 m thick, thick-bedded, locally cross-bedded quartz
gravelstone at the base, overlain by quartzitic sandstone, coarsegrained sandstone, sometimes with interbeds of chocolatecoloured siltstone. This member is most clearly exposed at the
back of the Do Son Market and along the road towards Beach
2, particularly around the Van Huong Quay. Some bivalves, such
as: Schizodus (?) sp., Ptychopteria (Actinopteria) hunanensis and

Goniophora sp. were collected on the mountain slope situated in
the back of the hamlet lying between the Do Son Market and the

main office of the Do Son Townlet. Vertebrate remains (Vietnamaspis trii, Briagalepis sp., Bothriolepis cf. B. gigantea) have been
found along with the lycophyte Bergeria or Knorria (cf. Lepidodendropsis sp.) on the shore of the Van Huong Quay area (Janvier and
Tong-Dzuy Thanh, 1998; Long et al., 1990; Tong-Dzuy Thanh and
Cai Chong-yang, 1995).
- 200 m thick, brown, medium-bedded, locally cross-bedded sandstone, dark chocolate-coloured siltstone interbedded with grey,
greenish-grey, yellow-brown weathering clay shale,. This barren
member is clearly visible on the road towards the Casino building, from near the “Bao Dai Villa” to the southernmost end of the
peninsula.
The sedimentology and fossils of the Do Son Formation indicate
a deltaic to coastal facies. However, the outcrops of this formation
are scattered over a large area and display a great diversity of facies
that is characteriztic for deltaic environments. Therefore it deserves
investigation.
The unconformity between the Do Son Formation and the
underlying Duong Dong Formation is only suggested by the presence of gravelstone beds at the base of the former formation, but is
conformably underlying the carbonate Trang Kenh Formation.
The Trang Kenh Formation (D2 gv-D3 tk) is largely distributed in
the Quang Ninh Zone, including islands of Ha Long Bay, and consists of limestone containing abundant corals, stromatoporoids and
some brachiopods. In previous works, the Trang Kenh Formation
was described as a tripartite unit, which is composed of two limestone parts, and a middle cherty part. Its total thickness varies
from 250 m to 300 m. The new study by Nguyen Huu Hung et al.
(2007) shows that this formation only consists of limestone, the
cherty part belonging in fact to the Pho Han Formation of Upper
Devonian-Lower Carboniferous age. The Trang Kenh Formation


T.D. Thanh et al. / Journal of Geodynamics 69 (2013) 165–185

yields Amphipora ramosa, A. rudis, Crassialveolites crassus, Scoliopora
denticulata, Caliapora battersbyi, Alveolites admirabilis, and the brachiopod Stringocephalus burtini, which all suggest a Givetian age.
However, the upper part of the formation yields stromatoporoids
and corals (Amphipora laxeperforata, A. pervesiculata, Stachyodes
costulata, S. fasciculate, which indicate a Givetian-Frasnian age. In
the Phuc Son–Nui Han area, Famennian conodonts (Palmatolepis
subperlobata, P. triangularis, P. glabra glabra, P. subrecta, P. perlobata)
have been recorded from the uppermost beds of the Trang Kenh
Formation (Tong-Dzuy Thanh and Vu Khuc, 2006; Nguyen Huu
Hung et al., 2004). The Trang Kenh Formation conformably rests
between the underlying Do Son Formation, and the overlying Con
Voi and Pho Han Formations, which are described below.
The Con Voi Formation (D3 fm-C1 cv) mainly consists of limestone and some thin beds of siliceous limestone that occur in the Mt
Nui Con Voi Kien An and An Lao Districts, Hai Phong City. The Pho
Han Formation (D3 fm-C1 ph) includes limestone, siliceous limestone and chert in Cat Ba Island (Ha Long Bay), and is the coeval
with the Con Voi Formation. These two formations are thus distinguished by siliceous components: some thin beds in the Kien An
Formation, and more diffuse ones in the Pho Han Formation. The
fauna of the Con Voi Formation mainly consists of brachiopods,
corals, and some foraminifera, whereas that of the Pho Han Formation includes many conodonts and a rich benthic fauna, such as
corals (Fuchungopora sp., Syrigopora distans, Tetraporinus sp.) and
many brachiopods in the lower beds of the formation. Both formations were dated as Upper Famennian-Lower Carboniferous, but
most of them are Lower Carboniferous in age, their Famennian part
being negligible in the sections and may be referred to the Trang
Kenh Formation. It is possible that the Con Voi and Pho Han Formations represent different sections of a single formation that displays
a variable number of siliceous components (Tong-Dzuy Thanh and
Vu Khuc, 2006).
2.2.1.2. Eastern Bac Bo Zone. The Song Cau Group (D1 sc) includes the
Si Ka Formation (red, subcontinental facies) and the Bac Bun Formation (deltaic facies grading upwards into shallow marine facies).
The Si Ka Formation (D1 sk) is exposed in the Viet Nam–China

frontier areas of Ha Giang Province and in Lang Son Province,
whereas in the Cao Bang and Thai Nguyen Provinces, it is composed
of part of the sequences of the Song Cau Group. In its stratotype
(Fig. 3), the Si Ka Formation consists of greenish-grey siltstone
interbedded with clay shale, greenish marly shale, thin-bedded,
fine-grained limestone, and grey siltstone with interbeds of violet chocolate marly shale. The total thickness of the formation is
about 650 m. According to Hoang Xuan Tinh, the basal conglomerate beds are locally up to 5–10 m and met with in the frame of
the Geological Map (1:200,000) of the Bao Lac Map sheet (Hoang
Xuan Tinh, 2001). Its sections are also observed in Dong Mo (Lang
Son Province) and Trang Xa (Thai Nguyen Province), where the
red sandstone is an important component in the sequence. Early
publications on this formation briefly mentioned (e.g., the fishes
“Asterolepis” sp., “Homosteus” sp., and the plant “Bythotrephis aff.
antiquate” (Saurin, 1956). During the last two decades the vertebrates from the Si Ka Formation have been shown to belong to
the two major fish groups that also populate the Lower Davonian of southern China, namely the Galeaspida and the antiarchan
Placodermi, to which can be added various Sarcopterygii. Neither
Asterolepis, nor Homosteus have been confirmed in the fauna. To
date, the upper beds of the Si Ka Formation consisting of sandstone
in Thai Nguyen Province has yielded the galeaspid Bannhuanaspis
vukhuci and fragmentary remains of various Polybranchiaspis-like
species, along with various yunnanolepiform and procondylolepiform antiarchs (Procondylolepis sp., Yunnanolepis spinulosa), and
youngolepidid sarcopterygian remains (Janvier et al., 1993; TongDzuy Thanh et al., 1994; Janvier and Ta Hoa Phuong, 1999). The Si Ka

173

Fig. 7. Lower Devonian Si Ka Formation unconformably rests upon the Ordovician
Lutxia Formation (Left cliff on the road Dong Van-Lung Cu (Photo: Ta Hoa Phuong).

Formation unconformably rests upon different levels of the Lower
Paleozoic deposits (Fig. 7) and conformably underlies the Bac Bun

Formation.
The Bac Bun Formation (D1 bb) (Fig. 4) consists of grey, chocolate,
variegated weathered clay shale and marly shale, siltstone containing vertebrates in the stratotype (Dong Van District, Ha Giang
Province). West of Dong Mo (Lang Son Province), it comprises a
member of grey carbonate phosphate containing well-preserved
vertebrates, and the overlying clay shale and siltstone member contains abundant brachiopods. In Trang Xa (Thai Nguyen Province), it
consists of grey limestone and marly shale containing corals, brachiopods and vertebrates. The thickness of the formation varies
from some tens to 500 metres. The distribution areas of this formation are much the same as for the Si Ka Formation, i.e. in the Ha
Giang, Cao Bang, Lang Son, and Thai Nguyen Provinces.
Vertebrate-bearing faunas of the lower member of the
Bac Bun Formation include, in the stratotype, the galeaspids
Polybranchiaspis sp. cf. P. liaojaoshanensis, numerous antiarchs
(Yunnanolepis deprati, Y. bacboensis, Chuchinolepis dongmoensis,
Vanchienolepis langsonensis), the petalichthyid Tongdzuylepis vietnamensis and the sarcopterygian Youngolepis cf. Y. praecursor. The
Dong Mo section yields much the same vertebrate fauna with,
in addition, a still indetermined lungfish (Tong-Dzuy Thanh and
Janvier, 1990, 1994; Tong-Dzuy Thanh and Vu Khuc, 2006). The
upper member of the formation yields brachiopods (Howittia
wangi, Cyrtochonetes indosinensis, Parachonetes zeili) (Racheboeuf
and Tong-Dzuy Thanh, 2000). The lithology and faunal composition of the Bac Bun Formation indicate a littoral to deltaic facies
grading upwards into a shallow marine facies.
The Mia Le Formation (D1 ml) is widespread in the Eastern zone
of Bac Bo region and consists of greenish-grey siltstone interbedded
with clay shale and marl, with some thin interbeds of argillaceous
limestone, and grey limestone in its uppermost part (Figs. 6 and 8).
The thickness of the formation in the Lung Co–Mia Le stratotype
(Dong Van District, Ha Giang Province) reaches 500 m, but in other
sections, it can decrease to a few hundred metres, as in the Ha Lang
area (Cao Bang Province), where it is only about 200 m. This formation is the most fossiliferous unit in the Paleozoic of Viet Nam,
containing hundreds of species of corals, brachiopods, trilobites,

crinoids, and other groups, all indicating a Pragian age. They are
components of the well-known Euryspirifer tonkinensis Assemblage
(Tong-Dzuy Thanh and Ta Hoa Phuong, 1994), which is dominated by brachiopods (e.g., Euryspirifer tonkinensis, Undispirifer aff.
pseudoaculiatus, Elymospirifer kwangsiensis, Dicoelostrophia annamitica, Atrypa aff. reticularis, Schellwienella douvillei, S. lantenoisi,
Athyris? tiaomachiensis, Parachonetes zeili) and corals (e.g., Favosites


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T.D. Thanh et al. / Journal of Geodynamics 69 (2013) 165–185

Fig. 8. Stratigraphic sequence of the Lower Devonian Lung Cu-Ma Le section (Dong Van District, Ha Giang Province).

goldfussi, F. styriacus, F. pencolei, F. preplacenta, Squameofavosites
cechicus, Sqf. giganteus, Sqf. sokolovi, Sqf. delicatus, Emmonsia yenlacensis, Squameopora vukhuci, Echyropora grandiporosa, Coenites
bulvankerae, Heliolites praeporosus), but also includes the trilobite
Proetus sp. and bivalves (e.g., Pterinea mieleensis). The Mia Le Formation lies conformably between the Bac Bun (D1 bb) and Ban Pap
(D1-2 bp) formations (Tong-Dzuy Thanh and Vu Khuc, 2006).
The Khao Loc Formation (D1-2 kl) is characterized by its carbonate composition and is limited to the Khao Loc Structure
Westward to Ha Giang Province. It consists of 15 m thick dark grey,
yellow-grey, red-brown weathering marl and clay shale containing abundant vertebrates, and 800 m thick, black-grey limestone
interbedded with argillaceous limestone that yield corals and
Amphipora sp. The vertebrate fauna notably includes galeaspids
(Polybranchiaspis liaojaoshanensis, Laxaspis yulongsus), antiarchs
(Yunnanolepis sp., Minicrania lissa, Heteroyunnanolepis qujingensis),
the acanthothoracid placoderm Hagiangella goujeti, and the sarcopterygian Youngolepis praecursor (Janvier and Ta Hoa Phuong,
1999; Racheboeuf et al., 2005). The lowermost limestone beds
of the formation yield corals (e.g., Favosites stellaris, F. vilvaensis,
Squameofavosites enormis, S. vanchieni, S. baolacensis, S. spongiosus, Thamnopora beliakovi, Cladopora cf. C. yavorskyi, Parastriatopora
champungensis, Caliapora cf. C. primitive) and the brachiopods

Howittia wangi and Howellella ex gr. crispa. The middle part of the
section yields Striatopora sp., Thamnopora kolodaensis, T. cf. T. siavis,

Alveolitella cf. A. polenowi, Coenites sp., and Corolites haoi (TongDzuy Thanh et al., 1988; Tong-Dzuy Thanh and Vu Khuc, 2006).
The corals, brachiopods, and vertebrates from the base of the
formation are to be correlated with the Bac Bun and Mia Le formations (Lower Devonian), whereas the corals from its middle part
indicate a Middle Devonian age.
The Ban Pap Formation (D1 p-D3 fr bp) is characterized mainly by
grey, thin to medium bedded limestone, widely extending in both
Eastern and Western Bac Bo Zones, and will be presented hereinafter for all Bac Bo Region. The total thickness of the formation
reaches 1200 m, but in certain sections, it may only be 300–400 m
thick.
The lower part of the Ban Pap Formation mainly consists of
dark grey, thin- to medium-bedded, bituminous limestone containing Emsian stromatoporoids and corals, such as Amphipora acerba
alaiskiensis, A. agreste vojachia, Favosites styriacus, F. stellaris, F. regularissimus, Emmonsia yenlacensis, Cladopora yavorskyi.
The middle part of the Ban Pap Formation includes dark
grey, medium-bedded, fine-grained limestone, and its upper
part grey to light grey, thick-bedded to massive fine-grained
limestone. Although the boundary between the lower and the
upper parts is difficult to identify on the basis of the lithology,
their respective faunas are readily distinguished. Its middle part
yields characteriztic Eifelian fossils, such as the dacryoconarids
Nowakia sp., Viriatellina irregularis, V. dalejensis, and the corals


T.D. Thanh et al. / Journal of Geodynamics 69 (2013) 165–185

Favosites robustus, Squameofavosites cf. S.kulkovi, and Thamnopora
cf. T. micropora.
The upper part of the Ban Pap Formation consists of grey to

light grey, thick-bedded to massive fine-grained limestone, containing a Givetian fauna, such as the stromatoporoids Amphipora
ramose and Actinostroma clatratum, the corals Thamnopora polygonalis, T. nicholsoni, Trachypora dubatolovi, Caliapora battersbyi,
Crassialveolites crassiformis, Coenites quydatensis, Scoliopora denticulata, Dendrostella trigemme, Grypophyllum cf. G.carinatum, Macgea
ex gr. multizonata, and the brachiopods Stringocephalus burtini and
Atrypa (Desquamatia) sp. Moreover, Early Frasnian species of the
Stachyodes costulata Assemblage occur in some sections.
It is worth noting that in small areas of Dong Van (Ha Giang
Province) there are limestone, clayish limestone, marl, black shale
and chert interbeds, containing numerous pelagic fossils. In the
lower beds are Lower Devonian fossils (Nowakia acuaria, N. barrandei, conodonts from the Polygnathus excavatus-Pandorinellina
steinhornensis, P. nothoperbonus zones, and there are still the corals
Favosites regularissimus and Heliolites sp. In upper beds occur
Givetian species, such as Palmatolepis varcus and others. These
carbonate deposits containing pelagic fauna can correlate with
the lower and middle parts of the Ban Pap Formation, and were
described as the Si Phai Formation by Dang Tran Huyen (1979), but
they can reasonably be considered as components of a member –
the Si Phai Member – within the Ban Pap Formation.
The Ban Pap Formation conformably rests between the Mia Le
and Toc Tat Formations. Most of the fauna indicate an EmsianGivetian age, but in the top part of Dong Van (Ha Giang Province)
and Chi Lang (Lang Son Province) sections, there are Early Frasnian
fossils; so, the upper boundary of the formation is diachronic, and
the formation should be referred to the Emsian-Frasnian (TongDzuy Thanh and Vu Khuc, 2006).
Tan Lap Formation (D2 gv-D3 fr tl) extends over some areas of
the Chi Lang District, Lang Son Province, and is composed of
35–80 m thick conglomerate, arkosic gritstone, and arkosic sandstone interbedded with black siltstone. In the sandstone were
collected plant remains that resemble Bergeria or Knorria (i.e. “Lepidodendropsis” sp.), and are similar to those also recorded from
the Do Son Formation. The Tan Lap Formation is an insert in the
limestone of the Ban Pap Formation; its basal conglomerate rests
unconformably upon Givetian limestone, and conformably on its

limestone containing an Early Frasnian Stachyodes costulata Assemblage (Fig. 2) (Nguyen Huu Hung et al., 1991; Tong-Dzuy Thanh and
Vu Khuc, 2006).
The Bang Ca Formation (D2 gv-D3 fr bc) is characterized mainly
by cherty shale, calcareous cherty shale and clay shale, and reaches
a thickness of about 200–250 m. This formation occurs in the Ha
Lang area, West of the Cao Bang Province, and in the Dong Van
and Yen Minh areas of the Ha Giang Province, it is also exposed
in the Van Yen area, Son La Province, in the West of Bac Bo. The
Givetian age of the formation is based on the brachiopod Stringocephalus burtini, and by conodonts (Polygnathus xylus xylus, P. varcus
and P. linguiformis) collected in the Ban Cai area (West Bac Bo).
The Frasnian age is based on foraminifera (Eonodosaria evlanensis, Eogeinitziana aff. E. rara, Nanicella aff. N. uralica, and Tikhinella
multiformis) and conodonts of the Palmatolepis hassi and P. rhenana
Zones (Pham Dinh Long, 2001; Ta Hoa Phuong, 1998).
The Toc Tat Formation (D3 fm-C1 t tt) mainly consists of variegated
(red-violet, brown-red, greenish-grey) limestone, cherty-clay
shale and marl and argillaceous limestone. Calcareous cherty shale
interbeds are also frequent in the formation, especially on the
top of the sections. It is usually exposed in narrow bands, like
the uppermost part of the section in all the distribution areas of
the Devonian. In the East of Bac Bo, the Toc Tat Formation occurs
in the Trung Khanh District (Cao Bang Province), where its shale
contains manganese ore, and in some areas there are important

175

economic seams. In the Dong Van Plateau (Ha Giang Province),
and the West of Bac Bo, in the Van Yen area (Son La Province). The
total thickness of the formation varies from 260–280 m to 350 m.
The fossils collected in the Toc Tat Formation comprise bivalves,
brachiopods, foraminifera, and conodonts, most of them, especially

the conodonts (Palmatolepis minuta, P. glabra, P. marginifera, P.
gracilis, P. sigmoidalis), indicating a Famennian age. However, in the
uppermost part of the formation occurs a Tournaisian fauna, with
such conodonts as Siphonodella sinensis, S. duplicate, S. isosticha,
and such foraminifera as Chernyshinella glomifomis, C. triangularis,
C. uralica (Pham Dinh Long, 2001; Ta Hoa Phuong, 1998).
The Toc Tat Formation conformably rests upon the Bang Ca Formation, and is covered unconformably by the Lower Carboniferous
Lung Nam Formation.

2.2.1.3. Western Bac Bo Zone. Except for the lower part of the Lower
Devonian, the Western Bac Bo Zone shows Devonian units that are
similar to those of Eastern Bac Bo Zone. In other words, from the
upper part of the Lower Devonian, the lithology of the synchronous
deposits in two zones of the Bac Bo Region resembles each other.
Actually, as described hereinbefore, the Ban Pap, Bang Ca, and Toc
Tat Formations extend in both Eastern and Western zones of the
Bac Bo Region. Therefore, in this section about the Western Bac Bo
Zone we only describe the Devonian Song Mua, Ban Nguon, and
Nam Pia Formations.
The Song Mua Formation (D1 sm) is distributed in the lower section of the Song Da River and is characteriztically very thick (from
1500 m to 2300 m, depending on the areas), it mainly includes black
clay shale, and is thus clearly distinguished from other Devonian
units of Viet Nam (Nguyen Vinh, 1978; Tong-Dzuy Thanh and Vu
Khuc, 2006).
Based on its lithology and fauna, the Song Mua Formation
can be subdivided into three parts. The 600–1500 m thick lower
part consists of black, black-grey, thin-bedded calcareous clay
shale containing poorly preserved fossils. The 500 m thick middle
part is composed of grey to black marly shale containing brachiopods (Mesodouvillina aff. M. subinterstrialis, Iridistrophia aff. I.
praeumbracula, Howellella sp., Schellwienella sp., Camarotoechia sp.,

Platyorthis sp.) and bivalves (Pteria sp., Sphenotus? sp., Posidonia
sp.). The 600 m thick upper part of the formation includes black,
black-grey clay shale, and quartzitic sandstone containing numerous Howittia cf. wangi, Pugnacina sp., Lingula sp., Sphenotus? cf. S.
spatulata, Mytilarca? sp., Pteria (Actinopteria) sp.). The Song Mua
Formation rests conformably upon the Bo Hieng Formation, and
conformably underlies the Ban Nguon Formation.
The Ban Nguon Formation (D1 bn) occurs in the lower section of
Song Da River basin, where it is exposed side by side with the underlying Song Mua Formation. It is mainly composed of argillaceous
shale, quartzitic sandstone, and limestone.
In its stratotype, the formation consists of argillaceous shale and
quartzitic sandstone, and marly shale containing abundant brachiopods and bivalves. In the Hoa Binh-Tu Ly section, its thickness
reaches 750 m, and its carbonate components include corals and
stromatoporoids. The fauna of the formation belongs to the Pragian
Euryspirifer tonkinensis Assemblage. Its characteriztic species are
corals (Favosites goldfussi, Squameofavosites attenuatus, Caliapora
macroporosa, Heliolites vulgaris, H. barrandei, Pseudozonophyllum
aff. P. zmeinogorskiensis), stromatoporoids (Stromatoporella rara,
Tienodictyon sp., Trupetostroma sp., Salairella sp., Clathrocoilona sp.)
and brachiopods (Dicoelostrophia annamitica, Euryspirifer tonkinensis, Nervostrophia rzonsnickajae, etc.). The Ban Nguon Formation
rests conformably upon the Song Mua and beneath the Ban Pap
formation. By its stratigraphic relations and faunal composition,
the Ban Nguon Fm. can be regarded as synchronous with the Mia
Le Fm. of the Eastern Bac Bo Zone, but differs from the latter by


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its lithological components (Nguyen Xuan Bao, 1978; Tong-Dzuy

Thanh and Vu Khuc, 2006).
The Nam Pia Formation (D1 np) is widespread in West Bac Bo,
from the upper course of the Da River (Lai Chau Province), following
the eastern margin of the Song Ma Structure to the West and East
of Thanh Hoa Province.
With a thickness of about 350 m, the Nam Pia Formation consists
of two parts. The lower part includes puddingstone, conglomerate
and gritstone, and coarse-grained quartzite, with some interbeds
of clay shale in the top. The upper part is composed of black-grey
clay shale interbedded with marl and quartzite, marl and limestone lenses in the top. Their faunas are distinguished by two
assemblages corresponding to the two levels, respectively. The
former one includes brachiopods belonging to the Iridistrophia
praeumbracula Assemblage of the lowermost level of the Devonian. The latter one contains corals and brachiopods belonging to
the Pragian Euryspirifer tonkinensis Assemblage. The most characteriztic of them are the corals Favosites brusnitzini, F. stellaris,
F. alpina, F. sublatus, F. ottiliae, Squameofavosites cechicus, S. baolacensis, Emmonsia yenlacensis, Cladopora rectilineata, Lecomptia
ramose, and the brachiopods Euryspirifer tonkinensis, Schellwienella
lantenoisi, Dicoelostrophia annamitica, Nervostrophia rzonsniskajae,
etc. The Nam Pia Formation rests in “pseudo-conformity” upon
sandstone of the Dong Son Formation (O1 ds) and conformably
underlies the Ban Pap Formation (Bui Phu My, 1978; Tong-Dzuy
Thanh and Vu Khuc, 2006).
The Ta Khoa Formation (D1 tk) is composed of two parts. The
lower part consists of grey, thin-bedded sandstone and quartzitic
sandstone intercalated with grey sericite schist and sericite-biotite
schist, and the upper part consists of sericitized black schist. Brachiopods (Stropheodonta annamitica, Spirifer sp., Atrypa reticularis,
Orthis sp., Leptaena sp. indet., Chonetes sp. indet.) (Le Thac Xinh and

Hoang Tri Nghi, 1964) and phacopid trilobites have been collected
at Ban Mong Village in dark schist belonging to the upper part of the
formation (Phan Cu Tien et al., 1977). In addition, Nguyen Huu Hung

(in Tong-Dzuy Thanh and Vu Khuc, 2006) has reported Howellella
cf. H. crispa, Levenea cf. L. depressa, Fasculiptera sp., Howellella cf.
H. crispa, Howellella sp., Dicoelostrophia sp., Atrypa sp., the bivalves
Modiomorpha oblonga and Modiolopsis cf. M. wuxuanensis, the trilobites Ancanthopyge cf. A. yiminensis, the crinoids Hexacrinites (?)
trangxaensis, Hexacrinites sp., and the bryozoan Fenestella sp.
The thickness of the Ta Khoa Formation is variously assessed:
more than 3000 m, according to some geologists, or less than
2000 m according to others. The contact of the Ta Khoa with the
underlying formation has never been observed, and its relation to
the overlying formation is either conformable according to some
geologists, or uncomformable to others. The fauna that has been
collected from the upper part of the Ta Khoa Formation corresponds
to the Euryspirifer tonkinensis Assemblage, and can thus be correlated with the level of the Mia Le and Ban Nguon formations, of
Pragian age.
2.2.2. Viet-Lao Region (Fig. 9)
See Fig. 9.
2.2.2.1. Dien Bien-Nghe An Zone. The Huoi Loi Formation (D1-2 hl) is
distributed in some areas of the West of Nghe An Province, notably
in the Muong Xen area and as a slender wedge form in Cua Rao, and
it can be divided into two parts.
The lower part is about 300 m thick and composed of light grey,
medium bedded sandstone, and upwards in the sequence are reddish brown thin interbeds of sandstone and argillaceous shale.
The latter yields Howellella sp., Stropheodonta sp., Hexacrinites?
Humilicarinatus, Lissocrinus sp. The upper part consists of 200 m

Fig. 9. Correlation of the Devonian deposits in the Viet-Lao Region. (A) South of Binh Tri Thien Zone: 1. Upper Silurian Dai Giang Formation (S3-4 dg); 2. A Choc Formation (D1
ac)—Red beds containing inarticulate brachiopods; 3. Tan Lam Formation (D2 gv-C1 tl); 4. Phong Son Formation (D3 -C1 ps). (B) North of the Binh Tri Thien Zone: 1. Rao Chan
Formation (D1 rc); 2. Ban Giang Formation (D1 -D2 e bg); 3. Muc Bai Formation (D2 gv mb); 4. Dong Tho Formation (D2 gv-D3 fr dt); 5. Thien Nhan Formation (D3 tn); 6. Xom Nha
Formation (D3 xn). (C) Dien Bien-Nghe An Zone: 1. Ordovician-Silurian Song Ca Formation (O3 -S2 sc); 2. Tay Trang Formation (S3 -D2 e tt); 3. Huoi Loi Formation (D1-2 hl); 4. Nam
Can Formation (D2 gv-D3 nc).

T.D. Thanh et al. / Journal of Geodynamics 69 (2013) 165–185

thick sandstone interbedded with limestone lenses, and contains
bivalves (Glossites sp., Sphenotus sp., Archaeocardium sp.), stromatoporoids (Stromatopora concentrica, Amphipora ramose) and corals
(Thamnopora cf. T. polygonalis, Crassialveolites crassus, Temnophyllum sp.).
The relation of the Huoi Loi Formation to the underlying formation is not observed, and it conformably underlies the Nam Can
Formation. The fauna from its lower part indicates a Late Emsian
age, and that from its upper part suggests an Eifelian to Givetian age. In sum, the Huoi Loi Formation can be referred to the
Emsian–Givetian (Nguyen Van Hoanh, 1995).
The Thien Nhan Formation (D3 tn) occurs in a narrow NW-SE
trending band, extending from the northeast of Huong Son, the
southwest of Thanh Chuong, Nam Dan (Nghe An Province), Duc
Tho to Ky Anh districts (Ha Tinh Province). With the thickness of
about 800 m, it consists of dark grey siliceous shale and interbeds of
argillaceous-siliceous shale, fine-grained sandstone, and siltstone.
Fossils are rare and poorly preserved, consisting of the conodonts Ozarkodina (Spathognathodus) sp. and Palmatolepis sp., of
Late Devonian age, and entactiniid and albaillellid radiolarians that
indicate a Middle-Late Paleozoic age.
Similar deposits occur in the Tuyen Hoa and Minh Hoa Districts,
(Quang Binh Province), where black argillaceous shale, chert and
siltstone, siliceous siltstone, and thin manganese interbeds, are
used to describe the Ngoc Lam Formation. Here were found the
conodont Palmatolepis subrecta and the brachiopod Calvinaria cf.
megistanu.
The lower and upper boundaries of the Thien Nhan Formation
have not been observed, but the “Ngoc Lam Formation” conformably rests between the underlying sandstone of the Dong Tho
Formation (D2 gv-D3 fr dt), and the overlying banded limestone and
chert of the Xom Nha Formation (D3 xn) (Tong-Dzuy Thanh and Vu

Khuc, 2006).
The Nam Can Formation (D2 gv-D3 nc) is restricted to the western
Ky Son District (Nghe An Province) in a narrow, 20 km long band,
and possibly extends into the Xieng Khoang Province of Laos. Its
thickness reaches 600 m.
The Nam Can Formation comprises two parts. The lower part consists of grey, bedded limestone, siliceous limestone, thin interbeds
or lenses of chert, containing Amphipora sp., Trachypora sp., Stachyodes radiata, Amphipora ramosa minor, and the corals Thamnopora
polyforata and Thamnophyllum sp. The upper part includes mainly
dark grey limestone with many calcite veins, and interbeds
of argillaceous shale, containing Stachyodes radiata, Amphipora
ramosa minor, the corals Thamnopora polyforata and Thamnophyllum sp., late Frasnian conodonts (Palmatolepis gigas, P. foliacea,
P. cf. P.triangularis, Ancyrognathus triangularis, Polygnathus xylus,
Spathognathodus sp.), and Famennian conodonts (Nothognathella
sp., Palmatolepis glabra glabra, P. perlobata schindewolfi, P. trachytera) (Le Duy Bach and Nguyen Van Hoanh, 1995).
The Nam Can Formation has conformable relations to the underlying Huoi Loi Formation. Its upper boundary usually shows a
tectonic contact, but seems to be conformable with the overlying
Lower Carboniferous chert.
2.2.2.2. Binh Tri Thien Zone. The A Choc Formation (D1 ac) shows
a restricted distribution in Quang Tri Province, crops out from A
Choc to Ta Puong villages (Huong Hoa District), and in Tan Lam
area it is exposed along the Road № 9. It was termed Tan Lam
Formation in former Vietnamese publications (Dang Tran Huyen
et al., 1980), but the name Tan Lam was used earlier by Tran Thi
Chi Thuan and H. Fontaine (1968) for the Devonian Tan Lam Limestone (Calcaire de Tan Lam) distributed in the same Tan Lam area
(Quang Tri Province). The formation is composed of sandstone and
siltstone interbedded with some argillaceous shale of chocolate
colour, and its thickness does not exceed 100 m. The lowest beds

177

consist of sandstone, conglomerate and pebble-bearing sandstone,
with 3–5 cm large, more or less rounded pebbles made of quartz,
quartzite, sandstone, siltstone, chert and sericite schist. The Early
Devonian age of the formation is suggested by inarticulate brachiopods Lingula aff. L. loulaensis, L. cf. muongthensis, L. cf. L. cornea, L.
aff. L. hawkei, Lingula sp. The A Choc Formation rests unconformably
upon the Silurian Dai Giang Formation, but its upper boundary is
still unknown (Tong-Dzuy Thanh and Vu Khuc, 2006).
The Rao Chan Formation (D1 rc) is characterized by black shale,
calcareous shale and sandstone, and limestone lenses, which are
widespread in the West of Quang Binh and Ha Tinh Provinces. The
thickness of the formation reaches more than 2000 m.
The corals that have been collected in the limestone of the lower
part of the formation include Pachyfavosites cf. P. delicatus, Alveolites sp., Coenites cf. simakovi, Heliolites cf. H. insolens, Chaetetes
ninae. Desmidopora? sp., Dohmophyllum sp. The upper part of the
formation yields brachiopods (Desquamatia vijaica, Levenea aff. L.
transversa) and the crinoid Lissocrinus curtus. The Rao Chan Formation is referred to the Lower Devonian; it pseudoconformably
overlies the Dai Giang Formation (S3-4 dg), and conformably underlies the Ban Giang Formation (D1 -D2 e bg) (Tran Tinh, 1996).
The Ban Giang Formation (D1 -D2 e bg) is about 700 m thick and
crops out in the West of Quang Binh and Ha Tinh Provinces. It consists of sandstone, quartzitic sandstone, siltstone interbeds, and
some calcareous argillaceous shale, limestone lenses in its upper
part.
The fauna it yields comprises species ranging from the Lower
Devonian (Emsian) to the Middle Devonian. Emsian species from
the lower part of the formation include corals (Calceola sandalina,
Stringophyllum sp.), crinoids Hexacrinites biconcavus, H. humilicarinatus), brachiopods (Atrypa auriculata, Chonetes sp.), and trilobites
Dechenella (Basidechenella?) sp. The limestone of the upper part
of the formation yields Middle Devonian species, such as corals
(Gephuropora vietnamica, Thamnopora nicholsoni, Cladopora gracilis,
Crassialveolites cf. C. multiperforatus, Thamnophyllum khelopense,
Pseudogrypophyllum stenotabulatum, Heliolites pororus, Paraheliolites cf. P. hanusi) and strmatoporoids (e.g., Stromatopora hupschii).

The Ban Giang Formation conformably rests between the underlying Rao Chan Formation (D1 rc) and the overlying Muc Bai
Formation (D2 gv mb) (Tong-Dzuy Thanh and Vu Khuc, 2006).
The Muc Bai Formation (D2 gv mb) occurs mainly in NW–SE bands
in the west of Ha Tinh and Quang Binh Provinces and consists
of terrigenous-carbonate deposits containing an abundant benthic
fauna. With the thickness of about 800 m, the sequence of this formation is characterized by the intercalation of marly limestone,
calcareous shale, sandstone, siltstone, argillaceous shale, in which
the fauna is usually met with in calcareous host rocks. The conformable relation of the Muc Bai Formation with the underlying
Ban Giang Formation and the overlying Dong Tho Formation is well
observed.
Among the abundant fossils from the Muc Bai Formation,
the most characteriztic ones indicate a Givetian age, such as
the brachiopods (e.g., Stringocephalus burtini, Bornhardtina sp.,
Schizophoria striatula, Gypidula biplicata, Emanuella takwanensis)
and the corals (Thamnopora nicholsoni, Caliapora battersbyi, Scoliopora denticulata, Iowaphyllum chucaense, Dendrostella trigemme).
In addition, the formation yields numerous stromatoporoids (e.g.,
Amphipora ramosa minor, Amphipora minima, Hermatoporella porosum, Flexiostroma flexiosum, Stachyodes concent, Clathrostroma
actinostromoides) (Tran Tinh, 1996; Tong-Dzuy Thanh and Vu Khuc,
2006).
The Dong Tho Formation (D2 gv-D3 fr dt) is characterized by
coarse sediments with a thickness of about 400 m and clearly
divided into two parts (Dovjikov et al., 1965). The lower part (150 m
thick) consists of dark grey argillaceous shale, sometimes with
interbeds of marly shale and sandstone, and the upper part (250 m


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T.D. Thanh et al. / Journal of Geodynamics 69 (2013) 165–185

Fig. 10. Stratigraphic sequence of the Upper Devonian Xom Nha Formation.

thick) is composed of light grey, yellowish grey sandstone, sometimes with shale interbeds. The Dong Tho Formation conformably
overlies the Muc Bai Formation (D2 gv mb), and conformably underlies the “Ngoc Lam Formation”, the latter being an equivalent of
the Thien Nhan Formation (D3 tn) (Tong-Dzuy Thanh and Vu Khuc,
2006).
The Dong Tho Formation yields brachiopods (Atrypa reticularis, Spinulicosta spinulicosta, Stropheodonta sp., Megachonetes sp.,
Schizophoria cf. S. ivanovi, Adolfia sp.) and bryozoans Fenestella sp.)
In the Hoi Da Stream, near Minh Le Village, an abundant flora has
been found in the siltstone and shale. The macrofossils have been
referred to Lepidodendropsis sp. and Protolepidodendron sp., and
the sporomorphs to e.g., Apiculatisporites sp., Gymbosporites magnifica, Costazonotriletes latidentatus, Archaezonotriletes variabilis,
Tholisporites densus, Aneurospora goensis, Ancyrospora involucra,
and A. tenicaulis. From the sandstone of the Ly Hoa Pass there are
vertebrates Lyhoalepis duckhoai, and Vukhuclepis lyhoaensis (TongDzuy Thanh et al., 1994, 1997).

The Xom Nha Formation (D3 xn) is about 200 m thick, and characterized by dark grey, light grey stylolitic limestone containing
abundant corals, stromatoporoids and conodonts, and it crops out
in the West of Quang Binh Province, as well as in the Chuc A area,
Ha Tinh Province (Fig. 10).
The lower part of the formation contains Frasnian fossils, such
as stromatoporoids (Stachyodes costulata, S. angulata, S. paralleloporoides; corals Scoliopora denticulata, Thamnopora polyforata,
Temnophyllum isetense) and the conodont Palmatolepis gigas.
Fossils from the upper part include Famennian conodonts of the
Palmatolepis triangularis, P. marginifera and P. crepida Zones. The
Xom Nha Formation conformably rests upon the cherty shale and
carbonaceous shale of the “Ngoc Lam Formation” (= Thien Nhan
Formation-D3 tn), and shows an unconformity with the overlying
Lower Carboniferous La Khe Formation (Nguyen Huu Hung et al.,
1995).

The Tan Lam Formation (D2 gv-C1 tl) was termed Cu Bai Formation in former Vietnamese publications (Nguyen Xuan Duong,


T.D. Thanh et al. / Journal of Geodynamics 69 (2013) 165–185

1996), but the name Tan Lam Limestone was used earlier by Tran
Thi Chi Thuan and H. Fontaine (1968) for this limestone. The formation consists mainly of black-grey limestone, light-grey dolomitic
limestone occurring sporadically in the West of Quang Tri Province,
and in the Le Thuy, Phong Nha areas of Quang Binh Province.
The fauna collected from the Tan Lam, Cu Bai, and A Choc sections (Quang Tri Province) suggests for this formation has an age
that ranges from the Givetian to the Famennian. In the lower
part of the formation, it includes Givetian stromatoporoids (e.g.,
Amphipora ramosa, A. pinguis) and corals (Dendrostella trigemme,
Argutastrea lavali, Disphyllum sp.). The middle part of the formation
yields Frasnian foraminifera (Tournayella jubra, Eonodosaria sp.),
stromatoporoids (Stachyodes costulata, Amphipora laxeperforata),
and brachiopods (Uchtospirifer nalivkini). Famennian brachiopods
(Tenticospirifrer minor, Cyrtospirifer postarchiaci, Cyrtiopsis graciosa,
Uchtospirifer nalivkini, Yunnanellina sp.) occur in the upper part of
the formation (Tong-Dzuy Thanh and Vu Khuc, 2006).
The Le Thuy and Phong Nha areas (Quang Binh Province)
limestone, possibly belonging to the uppermost Tan Lam Formation, contains Famennian-Lower Carboniferous fossils, such
as foraminifera (e.g., Eoendothyra communis, Quasiendothyra
kobeitusana, Tournayella jubra, Parathurammina suleimanovi, Septatournayella pseudocamerata), the coral Pseudouralinia aff. P.
tangpakonensis and the brachiopod Crurithyris urii.
The thickness of the formation in Tan Lam area is about 150 m,
and the limestone corresponding to its uppermost part in Le Thuy
and Phong Nha areas reaches about 170–300 m, so the total thickness of the Tan Lam Formation reaches 500 m and more. The
Tan Lam Formation rests unconformably upon the Dai Giang Formation (S3-4 dg), the upper boundary of the formation is not
clear.

The Phong Son Formation (D3 -C1 ps) occurs only in Thua Thien
(Hue Province), with few natural exposures, but drilling information shows that it extends in NW-SE trending bands from the south
of Hue City. The formation consists of ash and dark grey limestone
regularly intercalated with black clay shale containing fossils of
Famennian age in its lower part and Lower Carboniferous ones
in its upper part. Famennian fossils from the lower part comprise
brachiopods (e.g., Yunnanella hsikwangshaensis, Yunnanellina cf. Y.
hanburyi, Uchtospirifer sp., Athyris concentrica, Tenticospirifer tenticulum). The upper part yields a Late Famennian–Early Carboniferous
fauna, with such foraminifera as Septabrunsiina cf. minuta, S. cf. S.
rauserae, Septabrunsiina cf. S. kazakhtanica, Septatournayella cf. S.
segmentata, or Chernyshnella sp., and the corals Syringopora sp. and
Pseudouralinia sp. (Tong-Dzuy Thanh and Vu Khuc, 2006).

2.2.3. South Viet Nam Region
2.2.3.1. South Trung Bo Zone (southern part of Viet Nam Central).
The Cu Brei Formation (D1 cb) consists of 400 m thick terrigenouscarbonate sediments, distributed only in a narrow (6 km long, 3 km
wide) strip in the Cu Brei Mountain area (Yaly Commune, Sa Thay
District of Kon Tum Province), i.e. in the western margin of the Kon
Tum Block.
The formation is divided into two parts: the lower part consists of conglomerate, gritstone and sandstone, argillaceous shale,
some argillaceous schist interbeds, the upper—green grey talc schist,
limestone, dolomitised limestone, marly shale containing the coral
Squameofavosites aff. S. spongiosus, stromatoporoids (Syringostroma
cf. S. densum, Amphipora cf. A. raris, A. cf. A. raritalis, Simplexodictyon cf. S. artyschtence, Stromatopora cf. S. boriarchinovi), and
other undeterminable algae and crinoids. The Cu Brei Formation
rests unconformably on the biotite-hornblende granitoid Dien Binh
(384 ± 17; 418 ± 12 Ma by K/Ar method), and the mentioned coral,
stromatoporoid assemblage indicates the Early Devonian age of the
formation (Tong-Dzuy Thanh et al., 2007).

179

2.2.3.2. Western Nam Bo Zone. The Hon Heo Formation (D? hh)
mainly consists of sandstone, clay shale, occurring scatteredly in
the Kien Giang Province, in coastal areas and in some islands of the
Gulf of Thailand, such as Hon Trem, Hon Chong, Hon Heo, Bai Ot,
Hon Mot, Ba Lua Islands, etc. Fossils are rare and represented by
pooly preserved plant remains referred to, e.g., Taeniocrada? sp.,
Psilophyton sp. (Tong-Dzuy Thanh and Vu Khuc, 2006).
Since the formation is scattered over the islands, its stratigraphic
relations to the adjacent formations are unknown. The Hon Heo
Formation is supposedly referred to the Devonian on the basis of
the mentioned plant remains, but the study of Paleozoic spores in
Viet Nam is inadequate, so the age of this formation is still a matter
of controversy.
3. Facies distribution
3.1. Facies of the Silurian deposits
Silurian deposits in Viet Nam are differentiated into deep-water
facies containing graptolites and shallow water shelf facies. The
deep-water facies are characterized for the upper parts of the
Ordovician-Silurian formations, for instance, Co To and Tan Mai
formations in the Quang Ninh Zone, Phu Ngu Formation in the East
Bac Bo Zone, and Long Dai Formation in the Binh Tri Thien Zone,
Song Ca Formation, and the lower part of the Tay Trang Formation
in the Viet-Lao Region. The shallow water shelf facies is widespread
for most Silurian formations, such as the Kien An Formation in the
Quang Ninh Zone, the Sinh Vinh and Bo Hieng Formations in the
West Bac Bo Zone, and the Dai Giang Formation in the Binh Tri
Thien Zone.
3.1.1. Deep water facies of Lower Silurian deposits in the Bac Bo

Region (Fig. 11)
In the Quang Ninh Zone, both the Co To and Tan Mai Formations have been dated as Ordovician-Silurian, but fossils collected
in their upper parts indicate the Early Silurian only. The deep-water
facies of these formations have been proved by their fine-grained
components, rhythmic structure in its sequence, and by graptolites
assemblages, such as Streptograptus exiguus, Monograptus priodon,
Spirograptus cf. minor, Oktavites aff. O. planus, Campograptus communis, Demirastrites sp., Climacograptus sp., Monograptus ex gr.
pandus, Pristiograptus cyphus, Pseudoclimacograptus sp., Demirastrites triangularis, and Monoclimacis linarsoni (Nguyen Cong Luong,
2001a,b).
In the Co To Formation, the sections are turbidite-like and
belong to a dissected island arc environment (Pham Thanh Binh
and Nguyen Cong Luong, 1999). The studies by Nguyen Xuan Khien
(2000) have shown that the clastic components of the Co To Formation were deposited in a forearc sedimentary basin, and originated
from a regenerated orogenic process. The Tan Mai Formation, also
shows tuffaceous materials and rhythmic structure in its sequence,
but these are different from those observed in the Co To Formation,
the fragments of felsic effusive being absent in the components
of sediments, and fine-grained rocks being less abundant than in
the Co To Formation. Thus, perhaps the Tan Mai formation was
attributed to the back-arc marine basin situated near an old continental margin (Nguyen Xuan Khien, 2000; Tong-Dzuy Thanh and
Vu Khuc, 2006).
In the East Bac Bo Zone, the Phu Ngu Formation reaches
a thickness of more than 2000 m, consisting of argillaceous
shale, cherty-argillaceous shale rhythmically interbedded with
silty sandstone, and felsic effusive. The formation was dated
as Ordovician-Silurian, but fossils from the sections indicate an
Ordovician-Early Silurian age. Most of these fossils are graptolites
such as Climacograptus sp., Glyptograptus sp., Monoclimacis sp., and
Diplograptus sp., Climacograptus latus, Climacograptus cf. C. scolaris,

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T.D. Thanh et al. / Journal of Geodynamics 69 (2013) 165–185

Fig. 11. Sketch of the facial profile of the Silurian and Devonian deposits of the Bac Bo Region in the present situation.

Ptilograptus sp., Glyptograptus sp., and the trilobite Agnostus perrugatus. All these lithological and faunal characteriztics indicate a
deep-water facies of the deposits in an island arc environment in
the sedimentary process of the Phu Ngu Formation (Pham Dinh
Long, 2002; Tong-Dzuy Thanh and Vu Khuc, 2006).
3.1.2. Deep water facies of Silurian deposits the Viet-Lao Region
(Fig. 12)
In the Dien Bien-Nghe An Zone, the deep-water facies of the
Silurian deposits are expressed in the the upper part of the
Ordovician-Silurian Song Ca Formation and perhaps in the lower
part of the Upper Silurian-Eifelian Tay Trang Formation.
The deep-water facies of the Song Ca Formation are evidenced
by its fine-grained deposits reaching more than 2000 m in thickness, and containing Early Silurian graptolites in the upper part,
such as Monoclimacis vomerinus and Pristiograptus kweichihensis.
The deep-water facies are also characterized for the lower part of
the Silurian-Eifelian Tay Trang Formation, which consists of thinbedded siltstone, dark grey clay shale, and fine -grained sandstone
containing the graptolites Bohemograptus bohemicus, M. thomasi,
and M. yukonensis. Thus, in the Dien Bien-Nghe An Zone the deepwater facies characterizing all Silurian deposits includes the Lower
Silurian of the upper part of the Song Ca Formation and the Upper
Silurian in the lower part of the Tay Trang Formation.
Incidentally, it is worth noting that the Lower Silurian Ket
Hay Formation (Le Thanh Huu and Vu Xuan Luc, 2005), distributed along the northeast side of the Song Ma structure of the
present limits of the West Bac Bo Zone, is also characterized by

deep-water facies. Originally, this formation was a Silurian component of the Song Ca Formation in the Dien Bien-Nghe An Zone,
but was displaced to the northeast edge of the Song Ma structure
and wedged into the bodies of the Neoproterozoic Nam Co Formation by an imbricate fault (personal communication from Prof.
Tran Van Tri).
In the Binh Tri Thien Zone, the deep-water facies is composed
of the upper part of the Ordovician-Lower Silurian Long Dai Formation, which consists of black argillaceous shale, clay-chlorite
shale with some interbeds of tuffaceous sandstone, and gritstone
containing Silurian graptolites Neodiversograptus nilssoni, Pristiograptus sp., Demirastrites convolutus, Monograptus halli, Oktavites
spiralis, Bohemograptus bohemicus, and Monoclimacis sp. (Nguyen
Xuan Duong, 1996).
In summary, the deep-water facies is observed in Lower Silurian
in the Quang Ninh and East Bac Bo Zones, where some tuffaceous
sediments or effusive beds are interbedded in the sequences and
possibly indicate the arc basin of the sedimentary environment. In
the Viet-Lao Region, the deep-water facies is characteriztic for all
Silurian deposits of the Dien Bien-Nghe An Zone, and the Lower
Silurian only in the Binh Tri Thien Zone. In the West Bac Bo Zone
there is no Silurian deep-water facies, all Silurian deposits in this
zone are characterized by shallow water facies.
3.1.3. Shallow water facies of the Silurian deposits in the Bac Bo
Region (Fig. 11)
In the Quang Ninh Zone, the shallow water facies of the Upper
Silurian includes the Kien An Formation, which occurs in a small


T.D. Thanh et al. / Journal of Geodynamics 69 (2013) 165–185

area near Hai Phong City. Silty sandstone, marly shale, and limestone containing abundant benthos fauna of the formation such
as corals and brachiopods indicate the shallow water facies of the
deposits. Among the recorded fossils the brachiopods of the Retziella weberi Assemblage play an important role; its components,

especially the index species, are widespread in Upper Silurian of
Asia and Australia (Tong-Dzuy Thanh et al., 2001).
In the West Bac Bo Zone, all Silurian deposits (upper part of the
Sinh Vinh Formation, and the Bo Hieng Formation) are composed
of carbonate deposits containing an abundant benthic fauna. The
upper part of the Sinh Vinh Formation consists of dolomitic limestone and limestone containing Late Silurian corals, e.g. Favosites
sp., F. aff. F. forsbesi, F. ex gr. gothlandica, F. cf. F. hisinger, F. cf. F.
coreaniformis, Mesofavosites sp., Squameofavosites sp., and Parastriatopora sp. The Upper Silurian Bo Hieng Formation consists of marly
shale, limestone and some banded argillaceous shale containing
corals, brachiopods, and bivalves. Among the corals there are also
tabulates, such as Palaeofavosites aff. P. balticus, Favosites kernihoensis, and the rugosan Aphyllum aff. A. sociale. Remarkable fossils in
this formation are representatives of the Retziella weberi Assemblage, and bivalves Modiomorpha brevis, M. sp., Cymatonota sp. (aff.
C. yunnanensis), Dysodonta sp., and Actinopteria sp. (Ta Hoa Phuong
and Le Van Manh, 1996; Tong-Dzuy Thanh and Vu Khuc, 2006).
Thus, carbonate sediments and abundant benthic fauna clearly
indicate the shallow water shelf facies of the Silurian deposits in
the West Bac Bo Zone.
In the East Bac Bo Zone, the Upper Silurian is either lacking or
failed to be identified in the sections, and the Lower Devonian Red
Beds unconformably overly the older Silurian deposits.

181

Deep-water facies in the Devonian deposits of Viet Nam are
rarely observed, and most Devonian units belong to different kinds
of shallow water facies.

conformably overlies the Upper Silurian Bo Hieng Formation. Both
the Bo Hieng and Song Mua formations belong to the shallow water
facies, although their sedimentary components differ. The former

consists of carbonate-terrigenous deposits that yield a benthic
fauna and belongs to the shallow water shelf facies. The latter, the
thick Song Mua Formation, includes shale and sandstone bearing
brachiopods in the upper part, and showing possible shallow water
facies of offshore environment. Other Silurian-Devonian continuous sections have been recorded in the Tay Trang Formation in the
Dien Bien-Nghe An Zone of the Viet-Lao Region. The lower part
of this formation consists of thin-bedded siltstone, clay shale, and
fine- to middle-grained sandstone containing deep-water Upper
Silurian fossils, such as graptolites (Bohemograptus bohemicus, M.
thomasi, M. yukonensis), and the dacryoconarids Nowakia cancellata and N. holynensis. The upper part of the formation mainly
consists of siltstone, and sandstone containing Lower Devonian
brachiopods and cephalopods that indicate a shallow water
facies.
Lower Devonian “Red Beds”: The lowermost part of the Lower
Devonian in the East Bac Bo Zone of the Bac Bo Region and in the
Binh Tri Thien Zone of the Viet-Lao Region begins by “Red Beds”,
which unconformably overly the older sediments.
In the Western areas of the East Bac Bo Zone (Fig. 11), the Si Ka
Formation consists of conglomerate, greenish siltstone, clay shale,
and marly shale, and chocolate marly shale containing vertebrate
remains (Hoang Xuan Tinh, 2001). Upwards, the lower part of the
Bac Bun Formation consists of grey, chocolate, variegated weathering clay shale and marly shale, siltstone containing abundant
remains of vertebrates (see above, in the description of the Si Ka
and Bac Bun Formations). The upper part of the Bac Bun Formation
consists of shale, marly shale and limestone containing abundant
shallow water benthos of the Howittia wangi Assemblage, such
as Howittia wangi, Cyrtochonetes indosinensis, Parachonetes zeili
(Racheboeuf and Tong-Dzuy Thanh, 2000). The lithological composition and fauna of the Si Ka and Bac Bun Formations (Song Cau
Group) show that they probably belong to a transitional environment, ranging from lagoonal, coastal and deltaic facies to onshore
shallow marine facies.

It is noteworthy that in a small area, northwestward of the East
Bac Bo Zone, where the Khao Loc Formation (D1-2 kl) extended,
the lower Devonian is distinguished from sections of the Song Cau
Formation described above. There, the “Red Beds” are absent, and
the lower parts of the Khao Loc Formation include marl and marly
shale containing vertebrates that can be correlated with those
of the lowermost beds of the Devonian of Yunnan (China), such
as Youngolepis praecursor, Polybranchiaspis liaojaoshanensis, Minicrania lissa, Laxaspis yulongsus, and Heteroyunnanolepis qujingensis
(Tong-Dzuy Thanh et al., 1995; Janvier and Ta Hoa Phuong, 1999).
Lower Devonian “Red Beds” are also present in the south of the
Binh Tri Thien Zone (Viet-Lao Region), which unconformably overly
the Upper Silurian Dai Giang Formation. Here, the A Choc Formation consists of gritstone, conglomerate and sandstone, siltstone of
chocolate colour containing brachiopods (Lingula aff. L. loulaensis,
L. cf. L. muongthensis, L. cf. L. cornea, L. aff. L. hawkei, Lingula sp). The
lithology and faunal composition suggests that the A Choc Formation was deposited in a continental or brackish water environment
(Tong-Dzuy Thanh and Vu Khuc, 2006).

3.2.1. Lower Devonian
The lowermost Devonian sections are distributed into two kinds.
The first one is represented by the sections that are continuous since
the Upper Silurian, and the second one by the Devonian sections
that are separated from older deposits by an unconformity.
In the areas where the sections are continuous since the Upper Silurian, there is no sudden vertical change in the facies of deposition.
In the west Bac Bo Zone, the Lower Devonian Song Mua Formation

3.2.2. Lower Devonian-Eifelian shallow water marine facies
From the upper Lower Devonian to the Eifelian most of Viet Nam
was covered by marine shallow water deposits, except in the uplift
zones, such as the Red River uplift and the Kontum Block. Terrigenous deposits extend on the territory of the Quang Ninh and Binh
Tri Thien Zones, whereas terrigenous-carbonates and carbonates

occur in the other zones (Fig. 11).

3.1.4. Shallow water facies of Silurian deposits in the the Viet-Lao
Region (Fig. 12)
In the Viet-Lao Region, the shallow water facies is characteriztic
for Upper Silurian deposits in the Binh Tri Thien Zone (Dai Giang
Formation), but this facies is lacking in the Silurian of the Dien BienNghe An Zone (Fig. 12).
The Dai Giang Formation (S3-4 dg) consists of gritstone and
coarse-grained sandstone at its base, which unconformably overlies the Long Dai Formation. The main composition of the formation
consists of terrigenous deposits, such as sandstone, and limestone, marl beds in its upper part. Its benthic fauna include
trilobites (Cromus beaumonti, Metacalymene sp., Praedechenella aff.
P. vietnamica, Encrinurus cf. E. sinicus), brachiopods of the Retziella
weberi Assemblage, and bivalves (Schizodus? myducensis, Sphenotus
antecedens, Modiomorpha paracrypta, Goniophora dianensi) (Nguyen
Xuan Duong, 1996). In addition the Dai Giang Formation yielded
placoderm (Myducosteus anmaensis) and acanthodian fish remains
(Tong-Dzuy Thanh et al., 1997; Janvier and Tong-Dzuy Thanh,
1998). The composition of the sediments and the benthic fauna
indicates that the Dai Giang Formation corresponds to a shallow
water facies deposited in a littoral environment.
3.2. Facies of the Devonian deposits


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T.D. Thanh et al. / Journal of Geodynamics 69 (2013) 165–185

Fig. 12. Sketch of the facial profile of the Silurian and Devonian deposits of the Viet-Lao Region in the present situation.

3.2.2.1. Terrigenous deposits of shallow water marine facies.. In the

Quang Ninh Zone (Fig. 11), the Duong Dong Formation (D1 -D2
e dd) includes mudstone, fine-grained quarzitic sandstone containing, e.g., brachiopods, bivalves of the Euryspirifer tonkinensis
Assemblage. In the Binh Tri Thien Zone, both the Rao Chan (D1
rc) and Ban Giang (D1 -D2 e bg) formations mainly consist of shale
and sandstone, carbonate components present in thin calcareous
argillaceous shale interbeds or limestone lenses only. All the fossils
recorded are benthic. For instance, those from the Rao Chan Formation are corals (Pachyfavosites cf. P. delicatus, Coenites cf. C. simakovi,
and Heliolites cf. H. insolens, Chaetetes ninae. Dohmophyllum sp.),
brachiopods (Desquamatia vijaica, Levenea aff. L. transversa) and the
crinoid Lissocrinus curtus. The fossils from the Ban Giang Formation
are more diverse, with brachiopods, trilobites, crinoids, and some
corals in the thin limestone lense.

3.2.2.2. Terrigenous-carbonate and carbonate deposits of shallow
water marine facies. Starting from the upper Lower Devonian, carbonate components predominate in the Devonian sections in the
Bac Bo Region, and are increasing upwardly, becoming the main
component of the Eifelian sections in most zones.
Devonian carbonate components appear earliest in the northeastern area of the East Bac Bo Zone, from the lowermost beds of
the Lower Devonian in the Khao Loc Formation, which in marly
argillaceous shale yield vertebrate remains (see above). Upwards,
from the Givetian level with corals of the Euryspirifer tonkinensis
Assemblage, the Khao Loc Formation only consists of carbonate
sediments.

The terrigenous-carbonate facies are widespread in upper
Lower Devonian of the Bac Bo Region, in the Mia Le Formation of
East Bac Bo, and the Ban Nguon and Nam Pia formations of West
Bac Bo (Fig. 11). The faunas are abundant, and there are more than
300 species of corals, brachiopods, bivalves, trilobites, and crinoids
belonging to the Euryspirifer tonkinensis Assemblage. This faunal

community is the most abundant and diversified among the Devonian faunas in the Bac Bo Region and in Viet Nam as a whole.
Judging from the lithological composition and faunal assemblage,
the upper Lower Devonian terrigenous-carbonate deposits in the
East Bac Bo, and West Bac Bo Zones were probably deposited in a
shallow marine shelf environment.
3.2.2.3. Middle Devonian carbonate facies. The Middle Devonian
carbonate deposits occur in almost all zones of the Bac Bo and
Viet-Lao Regions. In the East Bac Bo and West Bac Bo Zones, they
compose the Eifelian-Givetian parts of the Ban Pap Formation and
the Khao Loc Formation, containing an abundant fauna of, e.g., stromatoporoids, corals, and some brachiopods. The same also occurs
in the North of the Viet-Lao Region, i.e. in the Dien Bien-Nghe An
Zone, where limestone is the main component of the Huoi Loi and
Nam Can Formations, but here some terrigenous composition also
occurs as thin interbeds. Limestone appears later as the unique
component, in the Givetian of the Quang Ninh Zone (Trang Kenh
Formation) and in the Binh Tri Thien Zone, in the Tan Lam Formation. Further northward in this zone, limestone appears even later,
in the upper Givetian, as in the Muc Bai Formation (Fig. 12).
The faunal community in the Eifelian formations mainly
includes corals, such as, e.g., Favosites styriacus, F. stellaris, F.


T.D. Thanh et al. / Journal of Geodynamics 69 (2013) 165–185

regularissimus, Emmonsia yenlacensis, Squameofavosites bohemicus,
S. enormis, and S. vanchieni. The dominant taxa in the Givetian
collections are the representatives of the Caliapora batersbyi
Assemblage, such as, e.g., Amphipora ramosa, Actinostroma clatratum, Thamnopora polygonalis, T. nicholsoni, Caliapora battersbyi,
Scoliopora denticulata, and Dendrostella trigemme, and the brachiopod Stringocephalus burtini. The carbonate composition and coral
fauna demonstrate that the Devonian carbonate deposits in the
Bac Bo and Viet-Lao Region represent a shallow water shelf facies.

Exceptionally, in small areas of Dong Van (Ha Giang Province)
are limestone, clayey limestone, marl, black shale and chert
interbeds, containing an abundant pelagic fauna. In the lower beds
are Lower Devonian fossils of the Nowakia acuaria and N. barrandei zones, conodonts of the Polygnathus excavatus, Pandorinellina
steinhornensis, and Polygnathus. nothoperbonus zones, and still the
corals Favosites regularissimus and Heliolites sp. In the upper beds,
Givetian species have been found, such as, e.g., Palmatolepis varcus and others. The carbonate and siliceous composition and the
pelagic fauna suggests that the “Si Phai Member” of the Ban Pap
Formation was deposited in an environment corresponding to the
slope of the continental shelf.
Specific case of the Do Son and Tan Lap Formations (Fig. 11): The Do
Son Formation mainly consists of conglomerate at its base, crossbedded sandstone, and shale interbeds that occur in the Quang Ninh
Zone. The Tan Lap Formation is composed of conglomerate, arkosic
gritstone, and arkosic sandstone interbedded with black siltstone
that extend in small areas of the East Bac Bo Region (Bac Son area).
Both the Do Son and Tan Lap formations contain continental plant
remains (Lepidodendropsis), and in the Do Son Formation there still
are bivalves, and vertebrates Vietnamaspis trii, Briagalepis sp., Asterolepis sp. (Janvier et al., 1989; Long et al., 1990; Nguyen Huu Hung
et al., 1991, 2007; Janvier and Tong-Dzuy Thanh, 1998). The lithological composition and fauna indicate the continental and deltaic
facies of the Do Son and Tan Lap formations. Both the Do Son and
Tan Lap formations unconformably overly the older deposits, the
Do Son Formation upon the Eifelian deposits of the Duong Dong
Formation, and the Tan Lap Formation upon the Givetian limestone
of the Ban Pap Formation. These coarse sediments of the Tan Lap
and Do Son formations can be regarded as transgression molasses
deposited after a local elevation; a similar situation occurred in
South China (personal communication from Hou Hong-fei to TongDzuy Thanh).
The case of the adjoining Muc Bai and Dong Tho Formations
(Fig. 12): The Muc Bai and Dong Tho Formations contiguously
extend in the the Binh Tri Thien Zone, the former mainly consisting of carbonate deposits, and the latter of coarse sandstone and

argillaceous shale. Both formations contain a benthic fauna, but in
the Muc Bai Formation, apart from brachiopods, there is a large
number of coral colonies, while in the Dong Tho Formation there is
only a shelly fauna (brachiopods, bryozoans, etc.) and plant remains
(Lepidodendropsis sp., Protolepidodendron sp.) in some siltstone and
shale interbeds. One can therefore suggest that these formations
were deposited in a shallow water environment of the same basin,
the Dong Tho Formation representing a coastal facies, and the Muc
Bai Formation the onshore, shelf shallow water facies.

3.2.3. Facies of the Upper Devonian deposits
In the Upper Devonian, the shelf shallow water facies are characterized by a large number of carbonate formations in the Bac Bo
and Viet-Lao regions. In the Quang Ninh Zone (Figs. 11 and 12),
one can notice the upper part of the Trang Kenh Formation, in the
North of the Dien Bien-Nghe An Zone, the upper part of the Nam
Can Formation, and in the Binh Tri Thien Zone, the upper part of the
Tan Lam and Phong Son formations. At the same time, there appear
carbonate-siliceous deposits containing conodonts which indicate

183

a deep-water facies in some areas of both the Bac Bo and Viet-Lao
Regions.
The deep-water facies in the Bac Bo Region begin with the
Givetian-Frasnian Bang Ca Formation, which consists of cherty
shale, calcareous cherty shale clay shale, occurring in the Ha Lang
area of the East Bac Bo Region and in the lower section of the Da
River basin. The fauna consists of conodonts of the Palmatolepis
hassi and P. rhenana Zones, and Polygnathus xylus xylus, P. varcus, P.
linguiformis, and also the brachiopod Stringocephalus burtini.

The Toc Tat Formation (D3 fm-C1 t tt) that overlies the Bang
Ca Formation is also characterized by deep-water facies, which is
evidenced by its composition, consisting of variegated limestone,
cherty-clay shale, marl, argillaceous limestone, and frequent calcareous cherty shale interbeds. Fossils of this formation mainly
include conodonts, such as Palmatolepis minuta, P. glabra, P.
marginifera, P. gracilis, and P. sigmoidalis, but there are also bivalves,
brachiopods, and foraminifera.
A similar condition is found in the Binh Tri Thien Zone and
the southern area of the Dien Bien-Nghe An Zone, where the
Thien Nhan and the Xom Nha formations extend as small bands.
The Thien Nhan Formation consists of argillaceous-siliceous shale,
chert, fine-grained sandstone, and siltstone, in which were found
conodonts (Ozarkodina (Spathognathodus) sp., Palmatolepis sp.) and
brachiopods. Similar deposits occur in the Tuyen Hoa and Minh
Hoa Districts, (Quang Binh Province), where occur black argillaceous shale, chert and siltstone, siliceous siltstone, thin manganese
interbeds, which are used to characterize the Ngoc Lam Formation. Here have been found the conodont Palmatolepis subrecta
and the brachiopod Calvinaria cf. C. megistanu. The Xom Nha
Formation consists of dark grey, light grey stylolitic limestone
containing abundant corals (Scoliopora denticulata, Thamnopora
polyforata, Temnophyllum isetense), stromatoporoids (Stachyodes
costulata, S. angulata) and conodonts (Palmatolepis gigas, P. triangularis, P. marginifera).
Thus, in the above-mentioned Upper Devonian formations, the
benthic fauna and conodonts coexist in the carbonate sediments.
These carbonate formations were possibly deposited in a deep
water environment on the slope of the continental shelf.

3.2.4. Facies of the Devonian deposits in the South Viet Nam
Region
Devonian deposits rarely occur in the South Viet Nam Region,
except in isolated areas. Moreover, their stratigraphic relations

with the underlying and overlying deposits are unknown; therefore, they are scarcely studied. Fossiliferous Devonian sediments
only occur in a small area in the West of the Kon Tum Block, in
the southern part of Central Viet Nam. There, the Cu Brei Formation (D1 cb) consists of terrigenous sediments in its lower part, with
conglomerate, gritstone in the bottom, and carbonate deposits containing corals, stromatoporoids in its upper part (Tong-Dzuy Thanh
et al., 2007). Perhaps the terrigenous-carbonate of the Cu Brei Formation belongs to an onshore, shallow water facies that is similar
to the ones in Viet-Lao Region. The Hon Heo Formation in western
Nam Bo Zone (Kien Giang Province) mainly consists of sandstone.
It is supposedly referred to the Devonian and belongs to the subcontinental facies, based on the presence of plant remains referred
to Psilophyton sp. and Taeniocrada? sp.

4. Remarks
4.1 Due to the extensive investigations carried out in the last
decades, new achievements of the Silurian and Devonian
stratigraphy of Viet Nam are well ascertained. All Silurian and
Devonian units have been well described on the basis of the


184

4.2

4.3

4.4

4.5

T.D. Thanh et al. / Journal of Geodynamics 69 (2013) 165–185

study of the lithology, paleontology, facies of the sediments,

and of their stratigraphic sequences.
On the stratigraphic relations of the Silurian and Devonian units
of Viet Nam
- In all studied sections of Viet Nam there are no gaps or unconformities between the Ordovician and Silurian have been
observed. The conformable relation is obviously expressed
in the sequences of the Ordovician–Silurian formations, such
as the Co To (O-S ct) and Tan Mai (O-S tm) formations in the
Quang Ninh Zone, the Phu Ngu Formation (O-S pn) in the East
Bac Bo Zone, the Sinh Vinh Formation (O-S sv) in the West Bac
Bo Zone, and the Song Ca (O3 -S2 sc) and Long Dai (O2 -S2 ld)
formations in the Viet-Lao Region.
- In the East Bac Bo and the Quang Ninh zones of the Bac Bo
Region, and in the Binh Tri Thien Zone of the Viet-Lao Region
the lowermost units of the Devonian with the basal conglomerate are unconformable lying upon the Silurian units. While
in the West Bac Bo Zone and in the Dien Bien-Nghe An Zone of
the Viet-Lao Region the relation between Silurian and Devonian units seem to be conformable.
- There are no gaps or unconformable relations are expressed in
the sequence between the Devonian and Carboniferous units.
In the most cases the Silurian deposits consist of the sandstone,
shale and limestone containing benthos fauna, which confirm
the marine shallow water environment of the sedimentation
process of these units. The deep-water facies of the Silurian
deposits is characterized for the Co To and Tan Mai formations
in the Quang Ninh Zone, and the Phu Ngu Formation in the East
Bac Bo Zone only. Perhaps the Co To and Tan Mai formations in
the Quang Ninh Zone were taken shape, in a forearc sedimentary basin, and originated from a regenerated orogenic process
(Nguyen Xuan Khien, 2000). This situation is similar to the Silurian deposits in the adjacent area of the Southeast China (Wang
Hongzhen, 1985).
By the lithological and paleontological compositions the Devonian deposits of the Bac Bo Region, especially of the East Bac
Bo Zone, are similar to the ones of the Guangxi (South China).

This similarity is obviously expressed in the Si Ka, Bac Bun and
Mia Le formations of the Bac Bo Region and the Lianhuashan,
Nakaoling and Yukiang formations, respectively, of the South
China (Wu Yi et al., 1987; Yang Si-pu et al., 1981).
Most Devonian units distributed in the North and the Central Viet Nam consist of self shallow water sediments, and
apparently they were deposited in a passive marginal marine
environment. The coarse clastic continental or subcontinental
deposits are distributed only in some areas of the East Bac Bo
and of the Quang Ninh zones of the Bac Bo Region, and in the
south of the Binh Tri Thien Zone. This situation suggests the
influence of the Caledonian movement at the end of the Silurian
period that called the Guangxi movement in South China.

Acknowledgments
The authors are grateful to the National Foundation for Sciences and Technology Development of Viet Nam (NAFOSTED) for
the effective support to the Projects 105.01.79.09 and 105.06.60.09.
We are thankful to Prof. A.J. Boucot (Oregon State University, USA)
and Prof. Yu Chang-min (Institute of Palaeontology and Geology,
Nanking. China) for their valuable criticisms and recommendations. Nguyen Thi Thu Cuc and Nguyen Thuy Duong would like to
thank the TRIG A project of the Hanoi University of Science (Vietnam National University, Hanoi, Viet Nam) for the support to study
mission at the University of Greifswald, Germany. We are very
grateful to an anonymous reviewer for their valuable comments
and suggestions, which helped us to improve the final version of

this manuscript. Interesting discussions of Prof. Tran Van Tri (Geological Association of Viet Nam) in the preparation of the paper are
much appreciated.

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