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

Journal of Asian Earth Sciences 29 (2007) 127–135 www.elsevier.com/locate/jaes Discovery of the fossiliferous Cu Brei Formation (Lower Devonian) in the Kon Tum Block (South Viet Nam) Tong-Dzuy Thanh a,* , Than Duc Duyen b, Nguyen Huu Hung c, Bui Phu My b a c 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 Laboratory of Paleontology and Stratigraphy, Research Institute of Geology and Mineral Resources, Thanh Xuan, Ha Noi, Viet Nam Received 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 km in length and 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 Ó 2006 Elsevier Ltd All rights reserved Keywords: Kon Tum Block; Lower Devonian; Corals and stromatoporoids 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 * Corresponding author Tel.: +84 572 246; fax: +84 583 061 E-mail address: tongdzuy@vnn.vn ( Tong-Dzuy Thanh) 1367-9120/$ - see front matter Ó 2006 Elsevier Ltd All rights reserved doi:10.1016/j.jseaes.2006.02.006 the age of the Cu Brei Formation in more detail As a result, the stratigraphic sequence of the Cu Brei Formation was clarified and abundant coral and stromatoporoid 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 km long and 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 128 Tong-Dzuy Thanh et al / Journal of Asian Earth Sciences 29 (2007) 127–135 Fig 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 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 Tong-Dzuy Thanh et al / Journal of Asian Earth Sciences 29 (2007) 127–135 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 divided into two parts – a lower and an upper The Lower part of the succession is composed of terrigenous 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 characterized by the following sequence: 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, granitic gneiss and crystalline schist Thin beds of yellow-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 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 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 carbonate sediments and is characterized by the following sequence: 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 Opaque grey, massive dolomitised limestone with calcite (14–15%), dolomite (85–86%), and some thin interbeds of dark grey argillaceous schist (29 m thick) 6a Dark grey, strongly schistose argillaceous shale composed 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) 129 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%) Dark grey, thin bedded dolomitised limestone composed of calcite (50–52%), dolomite (36–40%), carbonaceous mudstone (10–12%), thin (1–2 cm) interbeds of marly schist and sericite schist (23 m thick) The uppermost unit is composed of light grey, thickbedded dolomitised limestone with the composition of MgO (17–21%), CaO (27-30%), undissolved residue (2.3–6.6%), lost matter in burning (42.5–44.5%), and thin (1–2 cm thick) interbeds of dark grey argillaceous schist, marly schist, and sericitic argillaceous schist (37 m thick) 2.2 South Cu Brei section The South Cu Brei section (Fig 1C) with a total thickness 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: The basal unit includes yellowish-green, thickbedded, gritstone and coarse-grained sandstone with scattered rounded polymictic pebbles, of vein quartz, granitic gneiss, aplite granite and crystalline schist (26 m thick) 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 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%), plagioclase (7–10%), calcite (3–4%) in a matrix of sericite, chert, calcite, muscovite and a few ore grains 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 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) 130 Tong-Dzuy Thanh et al / Journal of Asian Earth Sciences 29 (2007) 127–135 8a 8b 10 The Upper part of the South Cu Brei section is composed of intercalated terrigenous and carbonate sediments 33 m thick with the following succession Dark green, grey talcschist composed of talc (83– 94%), quartz (5–8%), sericitic clay (1–4%), with intercalated light grey dolomite lenses (2 m thick) Ash-grey, thin-bedded dolomitized limestone composed of calcite (35–36%), dolomite (64–65%) and ore grains (6 m thick) Dark grey, thin-bedded marly shale composed of calcite (34–35%), quartz (18–20%), sericite (44–45%), a some biotite, carbonaceous clay and ore grains (2 m thick) Dark grey, thin-bedded limestone consisting of calcite (97–98%), quartz (0–3%) and clay minerals (0–5%) (8 m thick) Grey, thin-bedded dolomitized limestone consisting of calcite (85–86%), dolomite (14–15%), a few sericitic clay minerals and ore grains (4 m thick) Dark grey, thick-bedded limestone consisting of micritic calcite (99–100) and a few sericitic clay minerals, 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 collected were identified as Squameofavosites aff spongiosus Dubatolov, Syringostroma cf densum Nicholson, Amphipora cf raris Yavorsky, A cf raritalis 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 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 carbonate 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 Iridistrophia praeumbracula Assemblage of the Song Mua Formation (Tong-Dzuy Thanh, 1993; Tong-Dzuy Thanh et al., 1988a) The following units consisting mainly of argillaceous 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 Assemblage of these units contains characteristic species such as the brachiopods: Howittia wangi and Tulynets hoabinhensis, corals: Favosites intricatus and Thamnopora incerta, vertebrates: Yunnanolepis deprati, Y baolacensis, Y parvus, Chuchinolepis dongmoensis, Vanchienolepis langsonensis, Yunnanolepis cf praecursor, Y meemannae, Y.sp., Chuchinolepis dongmoensis, Zeaspis sp., Langdenia campylognathus and Tongdzuylepis vietnamensis, etc Fig Simplified Devonian stratigraphic scheme for Viet Nam Tong-Dzuy Thanh et al / Journal of Asian Earth Sciences 29 (2007) 127–135 The Mia Le and Ban Nguon formations, the upper part of the Nam Pia and the lower part of the Khao Loc Formation (Fig 2) are characterized by carbonate - terrigenous facies, in which the abundant fauna belongs to the Euryspirifer 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 cylindriformis, Atelodictyon strictum, Simplexodictyon artyschtense, S vietnamensis, Anostylostroma arvense, A laxum, A praetenerum, Trupestroma bilamellosum, Parallelostroma spongiosum, Stromatopora boiarschinovi, Syringostroma densum, Syringostromella perfectum, Amphipora alaiskiensis, A raris and A raritalis; Corals: Favosites goldfussi, F fedotovi, F styriacus, F pencolei, F preplacenta, Squameofavosites cechicus, Sqf giganteus, Sqf sokolovi, Sqf delicatus, Sqf spongiosus, Emmonsia yenlacensis, Squameopora vukhuci, Echyropora grandiporosa, Coenites bulvankerae, Heliolites praeporosus and Zelolasma dongvanensis; Brachiopods: Parachonetes zeili, Euryspirifer tonkinensis, Glyptospirifer chui, Indospirifer kwangsiensis, Megastrophia orientalis, Schellwienella lantenoisi, Dicoelostrophia annamitica, Laeptenopyxis bouei; Trilobites: Proetus 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 formations and the Trung Khanh Group characterised by carbonate facies In the lower part of this sequence corresponding to Emsian–Middle Devonian a benthic fauna is dominant (corals, stromatoporoids and some brachiopods), 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 conformably 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 nothoperbonus The presence of these pelagic faunal zones strengthens the Pragian age indicated by the macrofauna of the Euryspirifer tonkinensis Assemblage, which characterises 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 terrigenous 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 131 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 Devonian fauna of this region is distinguished from that of North Viet Nam, especially by the absence of the Euryspirifer 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 Formation can be correlated with those of the Mia Le Formation 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 Tong-Dzuy Thanh et al (1988a,b); TongDzuy Thanh (1993); Tong-Dzuy Thanh et al (2005) Thus, the Cu Brei Formation, which contains similar fossils, is also of Early Devonian (Pragian) age Moreover, the lowermost unit of the Cu Brei Formation is a basal conglomerate, 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 formation, the Dak Lin Formation, on the southern margin of the Kon Tum Block, containing the Foraminifers Schwagerina sp., Pseudofusulina sp., Verbeekina sp and Parafusulina 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 previously been supposed In the Early Devonian, if not earlier, the Kon Tum Block, at least along its margins, was submerged and covered by shallow water marine 132 Tong-Dzuy Thanh et al / Journal of Asian Earth Sciences 29 (2007) 127–135 sediments With the presence of marine fossiliferous Devonian and Carboniferous–Permian rocks, it is supposed that the metamorphism of the Kon Tum Block took place after the Permian Description of fossils Phylum Porifera Grant, 1836 Class Stromatoporoidea Nicholson and Murie, 1878 Order Syringostromatida Bogoyavlenskaya, 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 sections), KT.1904/2 (two thin sections), KT.1904/3 (two thin sections) (see Figs 3A and B) Description Fossil samples in the slightly metamorphosed 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 spindlespaced 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 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 Tong-Dzuy Thanh et al / Journal of Asian Earth Sciences 29 (2007) 127–135 Discussion Based on the skeletal structure of the coenostea, 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 dimensions 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 (Lower Devonian), Kon Tum Province, Central Viet Nam Order Stromatoporida Stearn, 1980 Family Stromatoporoidae Winchell, 1867 Genus Stromatopora Goldfuss, 1826 Stromatopora cf boiarchinovi Yavorsky, 1961 Material Fourteen thin sections made from six samples – KT.1903/1 (three thin sections), KT.1903/2 (two thin sections), KT.1904/2 (two thin sections), KT.1903/5 (two thin sections), KT.1903/1 (three thin sections), KT.1903/6 (three thin sections) (see Figs 3C and D) Description The specimens are small (40–50 mm) and fragmented, so that it is not possible to figure the coenosteal morphology The laminae are discontinuous and short (0.2–0.03 mm thick), irregularly connected with pillars 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 representatives 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 artyschtense Yavorsky, 1955 Material Two thin sections from sample KT.1902/1g (see Fig 3E) Description The single specimen is a very small fragment 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 133 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 rasilis Yavorsky, 1955 Material Ten thin sections made from four samples – KT.1902/1 (four thin sections), KT.1902/1b (two thin sections), KT.1902/1c (two thin sections), KT.1902/1f (two thin sections) (see Figs 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 vermicular in shape, with a diameter of 0.2–0.3 mm The skeletal 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 (Lower 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 sections), KT.1902/1e (two thin sections) (see Figs 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 134 Tong-Dzuy Thanh et al / Journal of Asian Earth Sciences 29 (2007) 127–135 Fig 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 0.1–0.15 mm thick Fibrous microstructure of tissue is not conserved Remarks Though fibrous microstructure is not conserved, but based on the described skeletal structure of coenostea, 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 (Lower Devonian), Kon Tum Province, Central Viet Nam Due to the poor preservation of these fossils, all species are described briefly, with their identifying characteristics 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 spongiosus Dubatolov, 1963 Material One moderate conserved colony KT.2795/1, from which four transversal and longitudinal sections have been made (see Figs 4A–D) Description The coralla are massive, hemispherical 15 cm in diameter and 10 cm in height with prismatic corallites 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 hexagonal–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 mm Septal apparata are poorly developed, and include short spines and squamulae Tong-Dzuy Thanh et al / Journal of Asian Earth Sciences 29 (2007) 127–135 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 Formation (Pragian) in North Viet Nam The Cu Brei specimens 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 distinguished from Squameofavosites baolacensis by their more developed septal squamulae and communication pores Occurrence Upper part of the Cu Brei Formation (Lower 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 Paleontology) 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 tao tram tich phun trao trung tinh he tang Dak Lin (On the intermediate 135 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, 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 Les coraux tabulatomorphes du De´vonien au Nord Vietnam Acta Scientiarum Vietnamicarum Section: Biology, Geology and Geography 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 Vietnam] 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] 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 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 Trudy Vsesouznogo Nauchno-Issledovatelskovo Geologiceskogo Instituta Novaia Seria 8, 1–186 (in Russian) Yavorsky, V.I., 1961 Stromatoporoids of the Soviet Union Part Trudy Vsesouznogo Nauchno-Issledovatelskovo Geologiceskogo Instituta Novaia Seria 44, 1–144 (in Russian)  ... represents the first Paleozoic sediments discovered on the western margin of the Kon Tum Block Another Paleozoic fossiliferous formation, the Dak Lin Formation, on the southern margin of the Kon Tum Block, ... 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 (Lower Devonian), Kon Tum Province, Central Viet. .. 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 Formation