DSpace at VNU: Discovery of the fossiliferous Cu Brei Formation (Lower Devonian) in the Kon Tum Block (South Viet Nam)

Discovery of the fossiliferous Cu Brei Formation Lower Devonianin the Kon Tum Block South Viet Nam a Laboratory of Historical Geology, Vietnam National University, Ha Noi, 334 Nguyen Tra

Discovery of the fossiliferous Cu Brei Formation (Lower Devonian)

in the Kon Tum Block (South Viet Nam)

a Laboratory of Historical Geology, Vietnam National University, Ha Noi, 334 Nguyen Trai Thanh Xuan Ha Noi, Viet Nam

b Geological Mapping Division of South Viet Nam, 200 Ly Chinh Thang, District 3, Ho Chi Minh City, Viet Nam

c

Laboratory of Paleontology and Stratigraphy, Research Institute of Geology and Mineral Resources, Thanh Xuan, Ha Noi, Viet Nam

Received 2 February 2006; accepted 23 February 2006

Abstract

Lower Devonian corals and stromatoporoids have recently been discovered in limestones among low grade metamorphic rocks on the western margin of the Kon Tum Block (South Viet Nam) This unit has been identified as the Cu Brei Formation Coral and stromatoporoid species have been described including Squameofavosites aff spongiosus, Parallelostroma cf multicolumnum, Amphipora

cf rasilis, A cf raritalis, Simplexodictyon cf artyschtense, Stromatopora cf boriarchinovi and Stromatopora sp indet The Cu Brei Formation is exposed in a small area 6 km in length and 3 km wide at the foot of Cu Brei Mountain (Sa Thay District, Kon Tum Province) As this formation is in marine shelf facies it is probable that further exposures of Lower Devonian sediments may

be discovered in the Kon Tum Block This discovery raises the question of the tectonic history of the metamorphic Kon Tum Block It is possible that the block was not an area of positive uplift from the beginning of Paleozoic as has been supposed, but was submerged in a marine environment, at least on its outer margins, in the Devonian, and possibly even earlier, in Early Paleozoic

 2006 Elsevier Ltd All rights reserved

Keywords: Kon Tum Block; Lower Devonian; Corals and stromatoporoids

1 Introduction

The Kon Tum Block consists mainly of metamorphic

rocks that have been dated as Precambrian, but recently

the Cu Brei Formation, containing a Devonian fauna,

has been discovered among low grade metamorphic rocks

on the western margin of the block (Than Duc Duyen,

2003) The Cu Brei area is located about 30 km

southwest of Kon Tum Town and 10 km east of the Yaly

Hydroelectric Dam (Gia Lai Province) In January 2004

fieldwork was carried out by Bui Phu My, Tong-Dzuy

Thanh, Than Duc Duyen and his collaborators to

collect additional fossils, with the aim of determining

the age of the Cu Brei Formation in more detail As a result, the stratigraphic sequence of the Cu Brei Forma-tion was clarified and abundant coral and stromatopor-oid specimens were collected from the limestone and marly shale beds of the formation Studies of the fauna

by Tong-Dzuy Thanh and Nguyen Huu Hung showed that the Cu Brei Formation contains similar species to those found in the Lower Devonian of North Viet Nam

At present the Cu Brei Formation has been discovered outcropping along an unnamed small stream in a zone

6 km long and 3 km wide at the foot of the mountain

of the same name in the Sa Thay District, Kon Tum Province (Fig 1A) The Cu Brei Formation occurs in

an area of metamorphic rocks dissected by complicated faults The formation consists of marine sediments, so it

is possible that its distribution is not limited to the area

1367-9120/$ - see front matter  2006 Elsevier Ltd All rights reserved.

doi:10.1016/j.jseaes.2006.02.006

*

Corresponding author Tel.: +84 4 8 572 246; fax: +84 4 8 583 061.

E-mail address: tongdzuy@vnn.vn ( Tong-Dzuy Thanh).

www.elsevier.com/locate/jaes

so far discovered, but could be more widespread in the

Kon Tum Block To establish the sequence and to

determine the age of the formation two sections are

described in detail in this paper, namely North Cu Brei and South Cu Brei sections, together with their included faunas

Fig 1 Locality of the Cu Brei Formation and its stratigraphic sequences: (A) sketch map showing the Cu Brei area (small black rectangle) in the Kon Tum Block (in grey on the map); (B) geological sketch of the Cu Brei area; (C) stratigraphic column of the North Cu Brei Section; (D) stratigraphic column of the South Cu Brei Section.

2 Stratigraphy

2.1 North Cu Brei section

The North Cu Brei section (Fig 1B) is exposed in a

NW–SE section along an unnamed small stream at the foot

of Cu Brei Mountain The sedimentary units may be

divid-ed into two parts – a lower and an upper

The Lower part of the succession is composed of

terrig-enous sediments 171 m thick resting unconformably on the

Dien Binh Granite Complex, which is dated as 384 ± 17;

398 and 418 ± 12 Ma by the K/Ar method (Tran Van Tri

et al., 1980) In upward order the lower part is

character-ized by the following sequence:

1 The basal unit consists of thick-bedded conglomerate,

gritstone and coarse-grained sandstone (11 m thick)

The pebbles in the conglomerate are well rounded

and are composed of vein quartz, aplitic granite,

gra-nitic gneiss and crystalline schist Thin beds of

yel-low-green sandstone and siltstone are interbedded in

these coarse sediments Coarse-grained sandstone is

composed of quartz (74%), chert (1–2%) and a cement

(24–25%) composed of biotite, sericite, and chlorite

2 The basal unit is followed by yellow-green, light

green, medium to coarse grained, thick-bedded

sandstone, interbedded with thin-bedded gritstone,

sometimes with scattered, rounded quartz pebbles

(41 m thick) Sandstone grains consist of quartz

(34–45%), plagioclase (2–15%), biotite (4–8%),

muscovite (1–3%), the matrix make up about

56–64% and consists mainly of clay, chert, quartz,

and chlorite

3 Dark grey, thin bedded, laminated argillaceous schist

and siltstone with some yellowish-grey thin sandstone

interbeds (119 m thick) The mineral composition is

mainly sericite (86–89%), chlorite (3–4%), quartz (8–

10%), a few carbonaceous mudstone clasts and iron

oxide

The Upper part of the North Cu Brei section (231 m

thick) includes intercalated terrigenous and

carbon-ate sediments and is characterized by the following

sequence:

4 The lowest unit consists of dark green, light grey,

thin-bedded, laminated talcshist (18 m thick), with a

mineral composition of talc (76–88%), sericite

(15–21%) and a few clasts of iron oxide

5 Opaque grey, massive dolomitised limestone with

cal-cite (14–15%), dolomite (85–86%), and some thin

inter-beds of dark grey argillaceous schist (29 m thick)

6a Dark grey, strongly schistose argillaceous shale

com-posed of quartz (8–10%), sericite mudstone (86–98%),

chlorite (3–4%) and siltstone, with some sericite schist

(51 m thick)

6b Dark grey, thick-bedded limestone (calcite 99–100%,

quartz 0–1%) containing algal and crinoid fragments

(51 m thick)

7 Black shale, with interbeds of marly shale containing indeterminable algal, crinoidal and coral remains (22 m thick) The marly shale is composed of micritic calcite (75-88%), sericite mudstone (28–32%) and quartz (10–15%)

8 Dark grey, thin bedded dolomitised limestone com-posed of calcite (50–52%), dolomite (36–40%), car-bonaceous mudstone (10–12%), thin (1–2 cm) interbeds of marly schist and sericite schist (23 m thick)

9 The uppermost unit is composed of light grey, thick-bedded dolomitised limestone with the composition

of MgO (17–21%), CaO (27-30%), undissolved resi-due (2.3–6.6%), lost matter in burning (42.5–44.5%), and thin (1–2 cm thick) interbeds of dark grey argilla-ceous schist, marly schist, and sericitic argillaargilla-ceous schist (37 m thick)

2.2 South Cu Brei section The South Cu Brei section (Fig 1C) with a total thick-ness of 209 m, is also exposed along an unnamed small stream in a NE–SW section on the southeastern slopes of

Cu Brei Mountain, and may be divided into lower and upper parts

The Lower part of the succession consists of terrigenous sediments 176 m thick, and characterized by the following succession:

1 The basal unit includes yellowish-green, thick-bedded, gritstone and coarse-grained sandstone with scattered rounded polymictic pebbles, of vein quartz, granitic gneiss, aplite granite and crystalline schist (26 m thick)

2 Yellowish-green, opaque, thick-bedded, medium- to fine-grained sandstone with thin interbeds of grey siltstone (54 m thick) The composition of the sandstone includes quartz (42–46%) and a cement (51–56%) of sericitic clay, chert, chlorite and iron oxide

3 Violet-yellow, thick-bedded gritstone and sandstone containing small white well-rounded pebbles of vein quartz (26 m thick) The sandstone includes clasts of quartzite (46–47%), quartz (8–12%), pla-gioclase (7–10%), calcite (3–4%) in a matrix of sericite, chert, calcite, muscovite and a few ore grains

4 Yellowish-green, thin-bedded, laminated, fine grained sandstone (12 m thick) with clasts of quartz (52–56%), alkaloid feldspar (7–10%) in a cement (38–44%) consisting of biotite, sericite, quartz, iron oxide and a few ore grains

5 Grey, yellowish-grey siltstone, argillaceous schist with thin interbeds of black schist with the composed of quartz (20–30%), plagioclase (0–8%) and a cement (62–98%) of sericitic clay, chlorite and chert (58 m thick)

The Upper part of the South Cu Brei section is

com-posed of intercalated terrigenous and carbonate

sedi-ments 33 m thick with the following succession

6 Dark green, grey talcschist composed of talc (83–

94%), quartz (5–8%), sericitic clay (1–4%), with

inter-calated light grey dolomite lenses (2 m thick)

7 Ash-grey, thin-bedded dolomitized limestone

com-posed of calcite (35–36%), dolomite (64–65%) and

ore grains (6 m thick)

8a Dark grey, thin-bedded marly shale composed of

cal-cite (34–35%), quartz (18–20%), serical-cite (44–45%), a

some biotite, carbonaceous clay and ore grains (2 m

thick)

8b Dark grey, thin-bedded limestone consisting of calcite

(97–98%), quartz (0–3%) and clay minerals (0–5%)

(8 m thick)

9 Grey, thin-bedded dolomitized limestone

consist-ing of calcite (85–86%), dolomite (14–15%), a

few sericitic clay minerals and ore grains (4 m

thick)

10 Dark grey, thick-bedded limestone consisting of

micritic calcite (99–100) and a few sericitic clay

min-erals, ore grains, with some interbeds of light grey,

thin-bedded limestone (11 m thick) This dark grey,

thick-bedded limestone forms the uppermost unit in

the South Cu Brei section, and contains abundant

tabulate corals and stromatoporoids Specimens

col-lected were identified as Squameofavosites aff

spong-iosus Dubatolov, Syringostroma cf densum

Nicholson, Amphipora cf raris Yavorsky, A cf

rari-talis Yavorsky, Simplexodictyon cf artyschtense

Yavorsky, Stromatopora cf boriarchinovi Yavorsky,

and Stromatopora sp indet Apart from corals and

stromatoporoids, a large number of indeterminable

crinoidal and algal remains were found

3 The Cu Brei Formation in the Devonian geology of Viet Nam

3.1 Background of Devonian sediments in Viet Nam Devonian sediments are widespread in the North and the northern part of Central Viet Nam and include units from Lower to Upper Devonian (Fig 2), almost all of them well dated by characteristic fossil assemblages In South Viet Nam Devonian sediments are rarely exposed, at present only two formations are known – the unfossiliferous Hon Heo Formation in the Gulf of Thailand and the terrigenous car-bonate Cu Brei Formation described in this paper (Fig 2) 3.1.1 Devonian in North Viet Nam

The basal unit of the Lower Devonian in North Viet Nam consists of the beds bearing vertebrates of the Yunnanolepiforme and Galeaspida groups in the Eastern region (Sika F.), while in the Western region it includes marine argillaceous shale bearing brachiopods of Iridistro-phia praeumbracula Assemblage of the Song Mua Forma-tion (Tong-Dzuy Thanh, 1993; Tong-Dzuy Thanh et al., 1988a) The following units consisting mainly of argilla-ceous shale, marly shale and thin limestone interbeds play

an additional role in the sections (Bac Bun Formation, the lower part of the Nam Pia Formation, the upper part of the Song Mua Formation) (Fig 2) The Howittia wangi Assem-blage of these units contains characteristic species such as the brachiopods: Howittia wangi and Tulynets hoabinhensis, corals: Favosites intricatus and Thamnopora incerta, verte-brates: Yunnanolepis deprati, Y baolacensis, Y parvus, Chuchinolepis dongmoensis, Vanchienolepis langsonensis, Yunnanolepis cf praecursor, Y meemannae, Y.sp., Chuchi-nolepis dongmoensis, Zeaspis sp., Langdenia campylogna-thus and Tongdzuylepis vietnamensis, etc

Fig 2 Simplified Devonian stratigraphic scheme for Viet Nam.

The Mia Le and Ban Nguon formations, the upper part

of the Nam Pia and the lower part of the Khao Loc

Forma-tion (Fig 2) are characterized by carbonate - terrigenous

facies, in which the abundant fauna belongs to the

Euryspi-rifer tonkinensis Assemblage This characteristic faunal

assemblage is the most diversified Devonian fauna not only

in Viet Nam, but also in South China Among the fossils

are the well-known Stromatoporoids: Plectostroma

cylindr-iformis, Atelodictyon strictum, Simplexodictyon

artysch-tense, S vietnamensis, Anostylostroma arvense, A laxum,

A praetenerum, Trupestroma bilamellosum, Parallelostroma

spongiosum, Stromatopora boiarschinovi, Syringostroma

densum, Syringostromella perfectum, Amphipora

alaiskien-sis, A raris and A raritalis; Corals: Favosites goldfussi,

F fedotovi, F styriacus, F pencolei, F preplacenta,

Squa-meofavosites cechicus, Sqf giganteus, Sqf sokolovi, Sqf

del-icatus, Sqf spongiosus, Emmonsia yenlacensis,

Squameopora vukhuci, Echyropora grandiporosa, Coenites

bulvankerae, Heliolites praeporosus and Zelolasma

dongvan-ensis; Brachiopods: Parachonetes zeili, Euryspirifer

tonkin-ensis, Glyptospirifer chui, Indospirifer kwangsiensis,

Megastrophia orientalis, Schellwienella lantenoisi,

Dicoelo-strophia annamitica, Laeptenopyxis bouei; Trilobites:

Pro-etus indosinensis, Praedechenella sp.; and the Bivalve

Pterinea (Tolmaia) lineata erecta

3.1.2 Emsian (Lower Devonian) to Upper Devonian

carbonate facies

The Devonian sequence in North Viet Nam from

Emsian (uppermost Lower Devonian) to Upper Devonian

includes the Ban Pap, Trang Kenh and Khao Loc

forma-tions and the Trung Khanh Group characterised by

car-bonate facies In the lower part of this sequence

corresponding to Emsian–Middle Devonian a benthic

fau-na is domifau-nant (corals, stromatoporoids and some

brachio-pods), while in the upper part, correlated with Upper

Devonian, the main fossils are conodonts and pelagic

foraminifers In the basal unit of this sequence, which

con-formably overlies the Mia Le Formation, characteristic

zones of dacryoconarids and conodonts have been found,

such as the Dacryoconarid zones of Nowakia acuaria,

N zlichovensis, N nana, N barrandei and the Conodont

zones of Polygnatus excavatus, P inversus, and P

nothop-erbonus The presence of these pelagic faunal zones

strengthens the Pragian age indicated by the macrofauna

of the Euryspirifer tonkinensis Assemblage, which

charac-terises the Mia Le Formation

3.1.3 Devonian in the northern part of Central Viet Nam

The Devonian sequence in the northern part of Central

Viet Nam (south of the Song Ma Fault) is distinguished

from that of North Viet Nam by the dominance of

terrig-enous sediments, with carbonate facies appearing mainly

from the Late Givetian The Lower Devonian and Eifelian

are composed mainly of sandstone and shale (the Rao

Chan, Ban Giang, Huoi Nhi and Huoi Loi formations)

Givetian units are characterised by terrigenous-carbonate

facies containing a benthic fauna (Muc Bai Formation and the lower part of the Nam Can Formation) (Fig 2) Upper Devonian units are composed of carbonate rocks

or limestones with interbeds of chert (Ngoc Lam, Xom Nha and Nam Can formations) (Fig 2) The Lower Devo-nian fauna of this region is distinguished from that of North Viet Nam, especially by the absence of the Euryspi-rifer tonkinensis Assemblage However, the similarity of fauna in these regions was restored from Givetian, where the main role belongs to polyprovincial species

3.2 Age of the Cu Brei Formation Although in indifferent preservation, the tabulate corals and stromatoporoids described from the Cu Brei Forma-tion can be correlated with those of the Mia Le FormaForma-tion and the lower part of the Khao Loc Formation of North Viet Nam The Pragian age of these formations with a Euryspirifer tonkinensis Assemblage has been established

by the work of Dzuy Thanh et al (1988a,b); Tong-Dzuy Thanh (1993); Tong-Tong-Dzuy Thanh et al (2005) Thus, the Cu Brei Formation, which contains similar fossils, is also of Early Devonian (Pragian) age Moreover, the low-ermost unit of the Cu Brei Formation is a basal conglom-erate, which overlies unconformably the Dien Binh gneissic biotite-hornblende granodiorite complex, with an isotopic date by the K/Ar method of 384 ± 17; 398 and 418 ± 12

Ma (Faure and Fontaine, 1969; Tran Van Tri et al., 1980) 3.3 Cu Brei Formation in the geological framework of Viet Nam

The fossiliferous Cu Brei Formation represents the first Paleozoic sediments discovered on the western margin of the Kon Tum Block Another Paleozoic fossiliferous for-mation, the Dak Lin Forfor-mation, on the southern margin

of the Kon Tum Block, containing the Foraminifers Schw-agerina sp., Pseudofusulina sp., Verbeekina sp and Paraf-usulina sp., Bradyina sp., has been described by Nguyen Kinh Quoc et al (1982) and Tran Tinh (1998)

At present exposures of Paleozoic fossiliferous sediments

in the Kon Tum Block are known only from small areas, the first is Cu Brei Formation (Lower Devonian) located near

Cu Brei Mountain (Sa Thay District, Kon Tum Province), the second is Dak Lin Formation (Upper Carboniferous– Lower Permian) on the southern margin of the Kon Tum Block, NW of Buon Ma Thuot Town Both formations are

of marine shelf facies, so if these marine sediments are autochthonous they should be more widespread on the Kon Tum Block than is presently known

With these discoveries of the fossiliferous sediments, it

is unlikely that the Kon Tum Block has been an uplifted positive element in the tectonic evolution of South Viet Nam since the beginning of the Palaeozoic as has previ-ously been supposed In the Early Devonian, if not

earli-er, the Kon Tum Block, at least along its margins, was submerged and covered by shallow water marine

sediments With the presence of marine fossiliferous

Devonian and Carboniferous–Permian rocks, it is

sup-posed that the metamorphism of the Kon Tum Block

took place after the Permian

4 Description of fossils

Phylum Porifera Grant, 1836

Class Stromatoporoidea Nicholson and Murie, 1878

Order SyringostromatidaBogoyavlenskaya, 1969

Family Coenostromatidae Waagen and Wentzel, 1887

Genus Parallelostroma Nestor, 1966

Parallelostroma cf multicolumnum Stock and Holmes,

1986

Material Nine thin sections from four samples: KT.1903/4 (three thin sections), KT.1904/1 (two thin sec-tions), KT.1904/2 (two thin secsec-tions), KT.1904/3 (two thin sections) (seeFigs 3A and B)

Description Fossil samples in the slightly metamor-phosed limestone are fragmentary, with fragments 40–50 mm in size Pillars are thin and closely spaced with 4–5/mm, anastomosic in cross section, mostly spindle-spaced in vertical section with diameters 0.035–0.20 mm Pseudozooidal tubules are circular in cross section, 0.05–0.15 mm in diameter Latilaminae are well developed, spaced 4–5/2 mm, 0.15–0.2 mm in thickness Astrorhizae 0.15–0.2 mm in diameter are well developed, with an axial canal, 0.2 mm in diameter and branching lateral canals

Fig 3 Stromatoporoids from Cu Brei Formation: (A and B) Parallelostroma cf multicolumnum Stock and Holmes; (A) longitudinal section, 10·; (B) transverse section, 10·; Sample KT.1903/4; Upper part of the Cu Brei Formation (C and D) Stromatopora cf boiarschinovi Yavorsky; (C) longitudinal section, 10·; (D) transverse section, 10·; sample KT.1903/2; Upper part of the Cu Brei Formation (E) Simplexodictyon cf artyschtense Yavorsky, longitudinal section, 10·; Sample KT.1902/1g; Upper part of the Cu Brei Formation (F–H) Amphipora cf rasilis Yavorsky, transverse sections (F and G), 10·; transverse and longitudinal section (H), 10·; sample KT.1902/1b; Upper part of the Cu Brei Formation (I and K) Amphipora cf raritalis Yavorsky; (I) longitudinal section, 10·; (K) transverse section, 10·; sample KT.1902/2; Upper part of the Cu Brei Formation.

Discussion Based on the skeletal structure of the

coe-nostea, in which the pillars in tangential section are either

anastomosic or irregularly circular, the samples examined

here are referred to the genus Parallelostroma Nestor, 1966

The skeletal structure of the coenostea, and the

dimen-sions of the skeletal elements are very close to the species

Parallelostroma multicolumnum (Stock and Holmes, 1986,

p 575, figs 7, 1-7,4) from the Keyser Formation (Upper

Silurian–Lower Devonian), USA

Occurrence Upper part of the Cu Brei Formation

(Low-er Devonian), Kon Tum Province, Central Viet Nam

Order Stromatoporida Stearn, 1980

Family Stromatoporoidae Winchell, 1867

Genus Stromatopora Goldfuss, 1826

Stromatopora cf boiarchinoviYavorsky, 1961

Material Fourteen thin sections made from six samples

– KT.1903/1 (three thin sections), KT.1903/2 (two thin

sec-tions), KT.1904/2 (two thin secsec-tions), KT.1903/5 (two thin

sections), KT.1903/1 (three thin sections), KT.1903/6

(three thin sections) (seeFigs 3C and D)

Description The specimens are small (40–50 mm) and

fragmented, so that it is not possible to figure the

coeno-steal morphology The laminae are discontinuous and

short (0.2–0.03 mm thick), irregularly connected with

pil-lars The pillars are continuous, 0.2–0.3 mm thick, with

5–6 pillars/2 mm The galleries are irregularly shaped,

0.1–0.2 mm in diameter, either anastomosic or irregularly

circular in tangential section The astrorhizal system is

not clearly observed, and the foraminate microstructure

of tissue is not conserved

Remarks Based on their skeletal structure such as pillars

and laminar, the specimens are referred to the

representa-tives of the genus Stromatopora Goldfuss The pillars are

well developed, continuous and irregularly connected, with

the laminae making meandric zigzag shapes in tangential

section According to the dimension of the skeletal

elements the specimens described here are very close to

Stromatopora boiarchinovi Yavorsky, 1961 from the

Middle Devonian of Russia (Yavorsky, 1961, p 42, pl

XXV, figs 3–5); and from the Lower Devonian of Viet

Nam (Tong-Dzuy Thanh et al., 1988b, p 24, pl X, fig 2)

Occurrence Upper part of the Cu Brei Formation

(Lower Devonian), Kon Tum Province, Central Viet Nam

Order Stromatoporellida Stearn, 1980

Family Stromatoporellidae Lecompte, 1951

Genus Simplexodictyon Bogoyavlenskya, 1965b

Simplexodictyon cf artyschtenseYavorsky, 1955

Material Two thin sections from sample KT.1902/1g

(seeFig 3E)

Description The single specimen is a very small

frag-ment of 25 mm in size so that it is not possible to figure

the coenosteal morphology Laminae are developed,

continuous and convex 0.05–0.1 mm thick and there are

8–10/2 mm The pillar is simple, commonly spindle-shaped and limited by one interlaminar space, 0.05–0.20 mm in diameter, spaced at 5–7/2 mm

Galleries are oval-shaped, 0.25–0.30 mm in height, the typical cyst-plates are absent in galleries, and astrorhizae are absent

Remarks Based on the mentioned characteristics of the skeletal elements, the specimens described are referred to representatives of the genus Simplexodictyon Bogoyavlenskya, 1965b and they can be compared with the species Simplexodictyon artyschtense (Yavorsky,

1955) from the Eifelian of Russia (Yavorsky, 1955,

p 99, pl LII, figs.7-8)

Occurrence Upper part of the Cu Brei Formation (Lower Devonian), Kon Tum Province, Central Viet Nam Family Amphiporidae Rukhin, 1938

Genus Amphipora Schulz, 1883 Amphipora cf rasilisYavorsky, 1955 Material Ten thin sections made from four samples – KT.1902/1 (four thin sections), KT.1902/1b (two thin sec-tions), KT.1902/1c (two thin secsec-tions), KT.1902/1f (two thin sections) (seeFigs 3F–H)

Description Stem is round in tangential section, 1.5–2.6 mm in diameter, and with a length of 6–10 mm The axial canal is 0.2 mm in diameter, the epitheca is thin 0.03–0.05 mm in thickness The marginal vesicles are oval

or round 0.15–0.3 mm in high The galleries are oval or ver-micular in shape, with a diameter of 0.2–0.3 mm The skel-etal network is composed of vertical and horizontal elements with the thickness of 0.10–0.15 mm; the fibrous microstructure is not conserved

Remarks With their coenostea characteristics, the described specimens are referred to the genus Amphipora Schulz, 1883 Among the representatives of this genus the specimens from the Cu Brei Formation are very close to the Amphipora rasilis (Yavorsky, 1955, pp 156–157, pl LXXXV, figs 18 and 19) from the Upper Silurian of Russia

Occurrence Upper part of the Cu Brei Formation

(Low-er Devonian), Kon Tum Province, Central Viet Nam Amphipora cf raritalis Yavorsky, 1955

Material Six thin sections made from three samples – KT.1902/2 (two thin sections), KT.1902/1a (two thin sec-tions), KT.1902/1e (two thin sections) (seeFigs 3I and K) Description The coenostea are twig-like, occasionally branching with 0.8–1.5 mm wide and 5–18 mm long The axial canal is poorly differentiated, epitheca is very thin (0.03–0.05 mm in thickness) Marginal vesicles are 0.2–0.3 mm in height, and they are connected to each other, making larger vesicles

The galleries are oval or meandric in tangential section, 0.1–0.15 mm in diameter The skeletal networks, or vertical and horizontal skeletal elements, are commonly

0.1–0.15 mm thick Fibrous microstructure of tissue is not

conserved

Remarks Though fibrous microstructure is not

con-served, but based on the described skeletal structure of

coe-nostea, the specimens can be referred to the genus

Amphipora Schulz, 1883 With the dimensions of stems

and skeletal network described and marginal vesicles the

specimens are related to Amphipora raritalis (Yavorsky,

1955, p 156, pl LXXXV, figs 2-8), which occurs in the

Upper Silurian of Russia, and in the Lower Devonian of

North Viet Nam (Lower part of the Ban Pap Formation)

Occurrence Upper part of the Cu Brei Formation

(Low-er Devonian), Kon Tum Province, Central Viet Nam

Due to the poor preservation of these fossils, all

spe-cies are described briefly, with their identifying

character-istics only In the description of Stromatoporids, apart

from publications strictly related to the identification of

species, the author (Nguyen Huu Hung) referred to the

important works on the classification of this group, by

Stearn (1997) and Stearn et al (1999), and the point of

view of these paleontologists has been adopted in this

work

Subclass Tabulata Milne – Edwards and Haime, 1850 Order Favositida Wedekind, 1937

Family Favositidae Dana, 1846 Genus Squameofavosites Chernyshev, 1941 Squameofavosites aff spongiosusDubatolov, 1963 Material One moderate conserved colony KT.2795/1, from which four transversal and longitudinal sections have been made (seeFigs 4A–D)

Description The coralla are massive, hemispherical

15 cm in diameter and 10 cm in height with prismatic cor-allites of polygonal (quadrilateral to hexagonal–octagonal) transverse section The diagonals of the small, quadrilateral sections are from 0.65 to 1.25 mm, and those of the hexag-onal–octagonal sections 1.5–1.75 mm, and sometimes up to 2.0 mm The corallite wall is 0.15–0.25 mm in thickness, the median suture, 0.05 mm thick, is clearly distinguished in some place of colony Pores are numerous, round 0.20–0.25 mm in diameter; arranged in 1–2 rows on the wall Tabulae are numerous, thin, horizontal, and there are 4–5 of them per 2 mm Septal apparata are poorly developed, and include short spines and squamulae

Fig 4 Tabulate coral from Cu Brei Formation: Squameofavosites aff spongiosus Dubatolov; (A) Part of colony, 0.8·; (B) transverse polished section of a part of colony 0.8·; (C) transverse section, 4·; (D) longitudinal section, 4·; (E) longitudinal section showing septal squamulae, 8· Sample KT.2795/1; Upper part of the Cu Brei Formation.

Remarks By the form and dimension of the corallites

and their wall characteristics, their squamulae structure,

the shape and dimension of the communication pores,

the specimens from the Cu Brei Formation are related to

Squameofavosites spongiosus Dubatolov (1963), which

was described from the Lower Devonian of the Kuzbas

(Russian), and from the lower part of the Khao Loc

For-mation (Pragian) in North Viet Nam The Cu Brei

speci-mens are also close to Squameofavosites baolacensis

described by Tong-Dzuy Thanh (1967) from the Mia Le

Formation (Lower Devonian, Pragian) of North Viet

Nam However, the above-described specimens are

distin-guished from Squameofavosites baolacensis by their more

developed septal squamulae and communication pores

Occurrence Upper part of the Cu Brei Formation

(Low-er Devonian), Kon Tum Province, Central Viet Nam

Acknowledgements

This paper was prepared in the framework of Research

Project 721 804 in the field of Natural Sciences The

authors are grateful to the Council of Natural Sciences

and its Earth Science Branch (Ministry of Sciences and

Technology) for the support of their researches The

authors express their deep thanks to the colleagues in the

Geological Mapping project at 1:50,000 of the Kon Tum

Sheet (Geological Mapping Division of South Viet Nam)

for their assistances in the field work A review by Prof

Dr Bernhard Hubman (Graz, Austria) and assistance in

the preparation of the paper, with improvement of the

English by Dr A.J Barber (Deputy Editor-in-Chief, JAES)

are much appreciated

References

Bogoyavlenskaya, O.V., 1969 On constructing a classification of the

stromatoporoids Paleontologicheskyi Zurnal (Journal of

Paleontolo-gy) 1969 (4), 12–27 (in Russian).

Dubatolov, V.N., 1963 Tabuliaty, Geliolitidy i Khaetetidy Silura i

Devona Kuznezhkogo basseina [Silurian and Devonian Tabulates,

Heliolithids and Chaetetids of the Kuzness Basin] 194 p., 29 plates.

Nauka Moscow (in Russian).

Faure, C., Fontaine, H., 1969 Ge´ochronologie du Vietnam me´ridional.

Archives Ge´ologique du Viet Nam 12, 213–222, Sai Gon.

Nguyen Kinh Quoc, Ta Hoang Tinh, Tran Ty, 1982 Ve thanh tao tram

tich phun trao trung tinh he tang Dak Lin (On the intermediate

volcano-sedimentary Dak Lin Formation) Tap chi Dia chat (Journal

of Geology) 156, 16–22, Ha Noi (in Vietnamese).

Stearn, C.W., 1997 Intraspecific variation, diversity, revised systematics and type of the Devonian stromatoporoid, Amphipora Paleontology

40 (3), 833–854.

Stearn, C.W., Webby, B.D., Nestor, H., Stock, C.W., 1999 Revised classification and terminology of Palaeozoic Stromatoporoids Acta Palaeontologica Polonica 44 (1), 1–70.

Stock, C.W., Holmes, A.E., 1986 Upper Silurian – Lower Devonian Stromatoporoidea from the Keyser Formation at Mustoe, Highland Country, West-Central Virginia Journal of Paleontology 60 (3), 555–

580, 7 figs.

Than Duc Duyen, 2003 Phat hien da voi tuoi Devon o Kon Tum [Discovery the Devonian limestone in Kon Tum, South Viet Nam] Tap chi Dia chat (Journal of Geology) A 287: 72 Ha Noi (in Vietnamese).

Tong-Dzuy Thanh, 1967 Les Coelente´re´s du De´vonien au Vietnam Part

1 Les coraux tabulatomorphes du De´vonien au Nord Vietnam Acta Scientiarum Vietnamicarum Section: Biology, Geology and Geogra-phy III, 304 p Hanoi.

Tong-Dzuy Thanh, 1993 Major features of Devonian stratigraphy in Viet Nam with remarks on paleobiogeography Journal of Geology (Geology Department Viet Nam) B/1–2(3), 18, Ha Noi.

Tong-Dzuy Thanh, Dang Tran Huyen, Nguyen Dinh Hong, Nguyen Duc Khoa, Nguyen Huu Hung, Nguyen The Dan, Ta Hoa Phuong, Pham Kim Ngan, Doan Nhat Truong, 1988a Stratigrafia i tselenteraty Devona Vietnama [Devonian stratigraphy and Coelenterata of Viet-nam] 1 Stratigrafia: 184 p Nauka Novosibirsk (in Russian) Tong-Dzuy Thanh, Nguyen Duc Khoa, Nguyen Huu Hung, Nguyen The Dan, Ta Hoa Phuong, 1988b Stratigrafia i tselenteraty Devona Vietnama [Devonian stratigraphy and Coelenterata of Vietnam] 2 Tselenteraty (Coelenterata) Nauka Novosibirsk: 248 p (in Russian) Tong-Dzuy Thanh, Vu Khuc, Dang Tran Huyen, Do Bat, Doan Nhat Truong, Nguyen Dich Dy, Nguyen Huu Hung, Pham Huy Thong, Pham Kim Ngan, Ta Hoa Phuong, Tran Huu Dan, Tran Van Tri, Tran Tat Thang, Trinh Van Long, 2005 Cac phan vi Dia tang Viet Nam (Stratigraphic units of Viet Nam) Ha Noi National University Publishing House 520 p (in Vietnamese).

Tran Tinh (Ed.), 1998 Ban Do Dia chat va khoang san Viet Nam 1: 200.000, loat to Kon Tum - Buon Ma Thuot [Geological Map at 1:

200 000 scale Kon Tum - Buon Ma Thuot Sheet Group] Department

of Geology and Mineral Resources Ha Noi (in Vietnamese) Tran Van Tri, Nguyen Dinh Uy, Hoang Huu Quy, Lam Thanh, 1980 Tai lieu moi ve tuoi cua mot so thanh tao magma va y nghia kien tao cua chung [New data on the age of some magmatic intrusions in South Viet Nam and their tectonic significance] Tap chi Cac Khoa hoc Trai Dat (Journal of Earth Sciences) 4(2), 31–32, Ha Noi (in Vietnamese) Yavorsky, V.I., 1955 Stromatoporoids of the Soviet Union, Part 1 Trudy Vsesouznogo Nauchno-Issledovatelskovo Geologiceskogo Instituta Novaia Seria 8, 1–186 (in Russian).

Yavorsky, V.I., 1961 Stromatoporoids of the Soviet Union Part 3 Trudy Vsesouznogo Nauchno-Issledovatelskovo Geologiceskogo Instituta Novaia Seria 44, 1–144 (in Russian).