1993c major features of devonian stratigraphy in VN with remarks on paleobiogeography

Series В, № 1-2/1993 GEO LO GI CAL SURVEY OF VI Ệ T NAM Н Л NỎ Ỉ Journal of G EO LO G Y EDITORIAL OFFICE: Series B, N 1-2/1993 Thirty third year 6^ Phạ m Ngũ Láo Str.,H Nộ i Tel.(84)4352319 Fax (84)4254734 Editorial Board TRAN VAN TRJ (Editor-in-chief) M em bers: LẺ ĐỨ C AN, PHẠ M VAN AN, NGUYỄ N XUÂN BAO, NGUYEN GIAO, v ũ N(K)C HÀI (D eputy E ditor-in-chief), v ũ KHÚC (Deputv Editor -in- chief), NGUYEN n g h i ê m m i n h , t ă n g MƯ Ồ I, VỎ CỒ NG N G H IỆ P, NGUYỄ N TIÊN THÀNH (Secretary), TÒNG DUY THANH, TRẦ N M INH THẺ , PHAN TRƯ Ở NG THỊ PHAN c ự TIÉN LÊ VÃN TRÀO, NGUYẺ N KHẮ C VINH, NGUYẺ N TRỌ NG V tM CONTENTS Page E d ito ria l T Ố N G D U Y T H A N H M ajor f e a tu r e s o f D e v o n ia n s t r a t i g r a p h y in Việ t N a m w ith r e m a r k s on p aleob io geograp hy T R À N LẺ Đ Ô N G , P H Ạ M H U Y L O N G , N G Ô T H Ư Ò N G SAN Geological evolutio n h isto ry o f Cenozoic b a sin s in S o u th V iệ t N a m c o n tin e n ta l s h e lf 19 LÉ Đ ÌN H T H Á M S e d im e n ta r y cycles in C u L o n g b a sin a n d t h e r e la tio n w ith h y d ro c a rb o n 23 N G U Y Ễ N T R Ọ N G Y Ê M O n th e n e o te c to n ic ge o d y n a m ic s itu a tio n o f S o u th T r u n g Bộ (Việ t N a m ) 33 BÙI C Ò N G Q U Ế So m e c h a c te r is tic s o f th e d eep c r u s ta l s t r u c t u r e a n d th e g eo d y n a m ic s in th e te r r it o r y o f V iệ t N a m a n d n e ig h b o u rin g s e a a r e a 39 VÕ C Ò N G N G H IỆ P G e o th e r m a l re so u rc e s in V iệ t N a m a n d p e rsp e ctiv es o f th e ir u s e for en e r g y p u r p o s e s 51 PH A N T R Ư Ò N G T H Ị C o ru n d u m - a n d z ir c o n -b e arin g b a s a lts in S o u th e a s t Asia 57 F E D O R T C H U K v.p A n tim o n y m i n e liz a tio n in N o r t h V iệ t N a m 73 C H R O N IC L E I n t e r n a ti o n a l w o rk s h o p /sy m p o s iu m o n "Geology, E x p lo r a tio n a n d d e v e lo p m e n t p o te n tia l o f e n e r g y a n d m i n e r a l re so u rc e s o f V iệ t N a m a n d a d jio n in g regions" H Nộ i, V iệ t N a m , T h e C u ltu r a l P a la c e M ay - J u n e 2, 1994 81 Journal o f G E O L O G Y (GS V iệ t N am ), Series B ■ № 1-2/19 93, pp 3-18 M AJOR FEA TU R ES OF D EV O N IA N STR A T IG R A PH Y IN VIỆ T NAM WITH REM ARK S ON PA LA EO BIO G EO G R A PH Y T Ô N G -D Z U Y T H A N H * N ew advances in the stud y o f the Devonian slratigraph y o f Việ t N a m have been m ade in recent decades On the basis o f abundant bent hie faunas and the fir s t data on pelagic f aunas, a Strati graphic scheme fo r Devonian has been revised D iffe rin g stratitg raphic sequences, facies and faunal communities allow two separate regional developm ents lo be recognized, oite in the N orth and one in Central Việ t Nam In N orth Việ t N a m limestones are predom inant and the sequences have been well studied T he local Strati graphic units are combined into Regional Stage divisions, nam ely the S i Ka, Bắ c Bun, M ia L é and Pắ c N ậ m in the Lower Devonian T he lowest unit consists o f red sandstones yielding the Vertebrate fa u n a in the northestern area Its equivalent in the northweastern area com prises black marine shales The M iddle Devonian contains two regional stages, the N ậ m T át and H Lang T he T Ố c T át Regional Stage is Late Devonian in age (Table 1) Devonian deposits in Central Việ t N am fa ll into three groups o f sections nam ed Sông Cả , Rào Cả i and Cừ Bai, with terrigenous rocks predom inant in the sequences The lowermost unit o f the Lower Devonian consists o f red sandstones o f the T ân Lâm Formation Tixe paleontology o f the Lower Dexonian o f Central Việ t N a m is in su ffic ie n tl V studied The Upper Devonian is dated bv conodont fa u n a s in some sections Previous investigations o f the Devonian T A IN E (1967)and A E D O V JIK O V ei al (1-965) stratigraphy of Viêt Nam were carried out mainly by R e m a r k a b l e adv a nc e s in k n o w le d g e o f the French geologists from the "Service Géologique Devonian of the country have been achieved over de l’Indochine" and by other foreign researchers the past thirty years, when V ietnamese geologists The main data from these studies have been sum ­ th e m s e lv e s have b e e n invo lv ed in c re a s in g ly marised by E S A U R IN (1956,1958), H.FO N - *Department o f G eology, universitv o f H N ộ i However, at present these new data are still little al 1990) The thickness of the Sika Formation is known in international stratigraphie literature In over one hundred metres in the northernmost this paper the major features of the Devonian areas near the Việ t Nam - China state border stratigraphy in Việ t Nam are presented Detailed Some plant remains have been determined as data have been published in monographs in V iet­ Bytrotrephis aff antique!, Cooksonia sp and fossil namese and in Russian (Tong-Dzuy Thanh et al., fishes are referred to Yunnanolcpiformes and Poỉ ybranchiaspis cf.gracilis (Tong-D/.uy Thanh & 1986, 1988) T h e D e v o n ia n d e p o s i t s a r e e s p e c ia ll y J a n v i e r 1987) O n the b a s is of the facics, widespread in Việ t Nam According to facial and geographic distribution, as well as the presence of I'aunal analysis they must be recognized in two fishes, it is suggested that the Sika Formation regions - the North and Ihc Central Việ t Nam should be correlated with the Lianhuashan Fo r­ regions (Fig 1) In both regions various local mation and the lower part of the Cuifengshan stratigraphie units, from lowermost to uppermost Formation of South China (Tong-Dzuy Thanh, within the system, have been dcscribcd In cach 1980; Tong-D/.uy Thanh el al., 1988) It can be region Devonian deposits are distinguished by compared also with the Old Red Sandstone facies characteristic facies and faunal communities, and of Western Europe The Sika Formation could be stratigraphie sequences (Table 1) as old as Lochkovian (Gcdinnian) (Tabic I) The Iridistrophia praewnbraculum Beds are NORTH VIỆ T NAM (he lo w e rm o s t m a r in e s t r a ta o f the L o w er Devonian in the northwestern area of North Việ t Low erm ost Lower Devonian In North Việ t Nam the lowermost Devonian succession begins with red beds (Sika Formation) in the northeastern area and with marine deposits in the northwest ( / ridislrophia praeumbraculum Beds) In more general stratigraphie classification of Ihc Devonian in Việ t Nam, these units are grouped together as the Sika Regional Stage The S ika Form ation consists of red con­ glomerates, sandstones and shales, which overlie the C am b rian or O rdovician unconformably These rocks arc widespread in the northeastern area of North Việ t Nam They were first described by Dcprat ( 1915) as the "Série de Sika" The "Série dc Do Son'1(Saurin, 1956,1958) and the lower part of the Sông Cau Formation (Trầ n Văn Tri et al., 1976) were considered as equivalent to the Sika F o r m a tio n New p a le o n to lo g ic a l d a ta from Son Formation have given evidence for a Givetian-Frasnian age (Janvier et M ua F o r m a tio n (the thickness of the latter reachcs over 2000m) which also extends down into the Silurian So far the faunas collected from these beds are still poor They were obtained only from the middle m e m b e r which yielded: the coral P arastriatopora rzonsnickajae Du b a t., th e brachiopods Iridislrophia praeumbraculwn Kozl., (Table 1) sandstones in the ĐỒ Nam They consist of black shales in the lower m em ber (thickness over 700-80()m) of the Sông M esodouvillina aff subinterstrialis Kozl., Platyorth is c im e x K o z l , and th e crin o id Schyschcatocrinus astericus (Schcwts) In most stratigraphic section in North Việ t Nam, the Silurian/Devonian boundary falls within a hiatus The uniformis-2x>nc could be expcctcd to be present in the northwestern area only, in the interval between the Bó Hicng Formation yiel­ ding Retziella weberi (U pper Silurian) and the Parastriatopora rzonsnickajae layer of the lower m e m b e r o f th e Sông M u a F o r m a t io n The Irldistrophia praeumbraculum B e d s a r e c o n ­ sidered now as the lowermost unit of the Devonian L egends for figures 2-5 Shales j,i peiitic limestones siliceous limestone* H ããôô*- ôằ S I *ằằằ sandstones fossil occurences conglom erates ! ■ • o ;■ : y j ; j • abundant average ■ 'calcareous shales - — I maris lim estones I » rare faunal assemblages I Vertebrates (fig-2) and Iridisrophia praeumbraculum (fig.3) Howima wa/igt Euryspirifer icmkinensis Parasnaiopora champungensis-Nowatda zlichovensis Pachvfavosites polymorphus-Viriatellina dalejensis Caliapora battersbyi Palmatolepis o th er fossil in the northwestern area and can be assigned to the Lochkovian (Table 1) Bắ c Bun Regional sta g e M ia Lé Regional Stage T h e M ia Lé R e g io n a l S ta g e is th e b io s tr a tig r a p h ic a lly m o st c h a r a c te r is tic unit among the Devonian strata of Việ t Nam It com ­ The Bác Bun Regional Stage was established prises a combined unit embracing all fromations on the basis of the correlation of m arine deposits a n d b e d s c h a r a c t e r i z e d by the E u ry sp irife r yielding the H owittia wangi fauna (H ysterolites tonkinensis fauna The stratigraphic sections con­ wangi fauna in previous works) This un't com ­ sist of shales, fine-grained sandstones and marls, prises the Bác Bun Form ation in the northeastern sometimes with limestone interbeds (Mia Lé F o r­ area, the upper m em ber of the Sông M ua Fo rm a ­ mation, Yen Lạ c Beds, and others in the north­ tion and the middle part of the N ậ m Pia F o rm a ­ e a s t) In th e n o r t h w e s t e r n a r e a ( T a b i c 1) tion in the northwestern area The rocks of this terrigenous components increase in the sequences unit consist mainly of black muddy shales, some- (Bả n Nguồ n and Nậ m Pia Formations) The thick­ ti m e s w i t h i n t e r c a l a t i o n o f f i n e - g r a i n e d ness of the whole unit changcs from 200-300 to sandstones In some sections, particularly in the 500-600m (Fig 2, 3) upper part of the division marls are present (Fig The E u r y s p ir ife r tonkinensis f a u n a is 2) Its thickness is over 300-500m in the north­ wellknown not only in North Việ t Nam but also in eastern area and 700-800m in northwest It has South China It is the most diverse Devonian fauna y i e l d e d a b u n d a n t f o s s i l s , in p a r t i c u l a r o f V iệ t N a m w ith b r a c h i o p o d s a n d c o ls brachiopods The most characteristic species are predominant Over 300 species of various groups the follow ing: B c h io p o d s -H o w ittia wangi o f b e n th ic fauna have be e n d e te r m in e d and (Hou), Howellella mercuri (Goss.), Protathyris described (Dư ổ ng Xuân H ả o et al., 1980 - Tổ ng- sp., C vm ostrophia stephani Barr., Chonetes nian- Dzuy Thanh, 1980,1982,1988; Tong-Dzuy Thanh, suyi Pattc; Bivalves - M ytilarca (Plectom ytilus) Janvier, 1990) The most characteristic specics o vifo rm is (H all); Corals in the u pp e r beds - are: Brachiopods- E u ry sp irife r tonkinensis (Man- Favosites subnitelus (Dubat), Squam eofavosites suy), A c ro sp irife r prim aevus (Steininger), In- kolym ensis (Tchcrn.), T ham nopora incerta Reg- d o s p ir ife r kw angsiensis H o u , Dicoelostrophia nel Some fossil fishes have been described - annamitica (Mansuy), Chonetes lacroixi Mansuy, Polybranchiaspis sp., Szea sp is sp., Yunnanolepis Parachonetes zeili (Mansuy), L ep ta enopyxis bouei bacboensis, Yunnanolepis deprati, Chuchinolepis (Barr.), C ym ostrophia quadrata Wang, A try p a d o n g m o e n sis, V a n c h ie n o le p sis la n g so n e n sis, krekovskiensis Rzons etc Youngolepis sp., Dipnoi indet, (Tong-Dzuy & Corals- Fossopora yenlacensis (Tong-Dzuy), Janvier 1990) In the above-m entioned faunas Favosites styriacus Penecke, S q u a m e o f avosites some typical" Siegenian" and Pragian forms were cechicus Galle, n o tic c d su c h as C ym o stro p h ia stephani a n d sis T o n g - D z u y , E m m o n sia intricata ( P o c ta ) , s brusnitzini (Peetz), s baolacen- Howellella mercuri All the mentioned corals are E.yenlacensis Font., T ham no pora incerta Regnell, similar to forms from the Krekovski "Horizon" in T elegantula Tchud., E chyropora grandiporosa the Salair region of the Russia Thus, the Bắ c Bun T o n g - D z u y , R o em erip o bohem ica ( P o c t a ) , Stage yielding the H owittia wangi fauna is prob ab ­ ly of Pragian age Caliapora stelliform is (Chapman), Heliolites barrandei P e n e c k e , H p r a e p o ro su s K e t n , T r y plasm a altaica ( D y b o w ) , H o lm o p h yllu m Yen Lac - Ban Than Sông Mua Section Fig.3- Correlation from of the Devonian sections the northwestern area of North Việ t N am Iiolini W dkd, R h izo p h yllu m yenlacensis Tong- stones, Nà Quả n and Hạ Dzuy The last was described in former works as Formation etc The present author has combined Calceola sandalina with several varieties (Tong- them into the Bả n Páp Regional Supcrstage, con­ Dzuy et al., 1988) etc sisting of three successive Regional Stages named Trilobitcs - Duclina vietnamica Maximova, Plagiolaria (?) orientalis Maximova Bivalves - Palaeosolen chapm ani Williams & Lang Suites, Bả n Páp Pác Nậ m, Nậ m Tát and Hạ Lang In almost all of North Việ t Nam the rocks of these divisions are limestones, cxccpt in the littoral facies of the Brcgcr, Sphznotus (?) spatula Mans., Pieria (Ac- northeastern area In this latter the Dư õng Dộ ng lionpteria) subdecussata Hall, Pterinea (Tolmaia) Formation corresponding to the Mia Lc, Pắ c Nậ m lincata erecta (Dalm.) and others and N ậ m Tát units is form ed o f shales and It is relevant to draw a tte n tio n to some pccularities of the Eurys-pirifer tonkinensis fauna sandstones 4.1 Pắ c Nậ m Regional Stage characterizing the Mia Lc Regional Stage Apart from many Pragian spccics known from Czechos­ This division consists mainly of dark grey, lovakia and of the stratigraphic equivalents from bituminous, well stratified limestones lying con­ the Salair region (Russia), various older forms formably on the Mia Lc Regional Stage In several were discovered such as H o lm o p h vllw n hoi mi, sections, especially in the northeastern area, inter­ T ry plasm a altaica, Howellella mercuri and others calations of chcrt arc present The occurrencc of The pclagic faunas of the Mia Lc unit have this division is well documented everywhere, with been feebly studied, but conodofits of the perbonus its thickness rcachine about l()0m (Fig 2, 3) zone and dacryoconarids of the zlichovensis zone Strom atoporoids and corals arc the most have been determined in the lowermost bed of the abundant fossils, but dacryoconarids and con- overlying Pác Nậ m Regional Stage Newly, Prof odonts are also predominant From (he Đồ ng Văn Lardeux (Francc) and Tạ Hòa Phư ng have deter­ section (near the Việ t Nam - China border) the mined N owkia acuaria from the upper beds of Mia following spccics have been determined: Lc Formation in (he Đồ ng Văn section (near Viclnamesc-Chinesc state border) On the basis of these data, the M ia Lé D a c r v o c o n a r i d s - N ow akia zlichoviensis Bouc., N barrandei Bouc & Prantl., Viriatellina hercynica Bouc., V aff.pseudogeinitziana Bouc Regional staiỊ c can be c o rre la ted within the Conodonts - Polygnathus pcrbonus (Phil.), Pragian Stage and may he to Lower Emsian In Bellodella devonica (Stauf.), H indeodellaequiden- any ca se it is lo w e r th a n the perbonus a n d tata R h o d e s , O zarkodina denckm ani Z ie g le r, zlicliovensis zones and the dehicens zone can be Panderodus unicostatus ( B r a n s o n & M e h l ) , drawn within the division spathogiiathodussteihornensis Ziegler, S.optim us Mosk., Trichonodella svm m etrica (B ran son & Bả n Páp Regional S uperstage The Emisian-Givetian dark grey stratified Mehl) and others Among bcnthic faunas the c o m ­ mon specics arc - A m p h ip o acerba alaikiensis limestones of the Bả n Páp Regional Superstagc Y a v o r s k , A a g re sta v o ja c h ic a K h r o m y k h , arc especially widespread in North Việ t Nam F avositesgoldfussi Orb., F regularissimus Yanct, They were described in previous publications P a rastriatopora cham pungensis T o n g - D z u y , under various names as Eifelian-Givetian Lim e­ T ry plasm a aeqiiabilis Lonsd and others stones, M ó Tôm Limestones, A rnphipora Lim e­ T rachypora dubatolovi T o n g -D z u y , Caliapora 4.2 Nậ m Tát Regional sta g e baltersbyi (M E dw ard s & H a im c ), Scoliopora The Nậ m Tát Regional Stage was established by grouping together the upper part o í Nà Quả n Formation and its equivalents in the northeastern area, the middle m em ber of Bàn Páp Formation and also its equivalents in the northwestern area The Ihickncss of these strala reaches 250-400m denticulata (M Edward & Haime), G ry p o p h y llu m is a c tis (F reeh), D en d ro stella trigem e ( Q u e n s t ) ; B r a c h io p o d s - E m a n u e lla cicer (E ich w ), S tr in g o c e p h a lu s b u rtin i D c fr., S p inatrypa aspera Dalm (Tong-Dzuy Thanh et al., 1988) The division consists mainly of light grey lime­ stones; only in the successions along the coast and in some islands of the Bác Bộ gulf arc the sections charactcri/.cd by sandstones and shales of the upper member of the Durtni> Dộ ng Formation T h e fo llo w in g sp ccics a rc Pelagic faunas are incquately studied; few spccics were discovered: N ow akia aff otoniari Richt., Viriatellina multicostatus M u , P olyg­ nathus x y lu s x y lu s S t a u f , Panderodus s p , spalhognathodus sp n o tew o rth y , Dacyoconarids - Viriatellina dalejensis Bouc., 4.4 Age of Regional Stages V.irregularis Bouc., Now akia cancellata (Richt.), N.nii.richleri Bouc Cordh-Favosites crọ nigerus The discovery of conodonts (perbomis zone) Orb., F.robustus Lee., Pachvfavosites polvm or- and dacryoconarids (zlichovensis zone, barrandci phas (Goldf.), sp o n g o p h y llu m halisitoides Eth., zone) has provided cvidcncc correlation of íhe Pác Tabulaphvlhtni curtoseplqtum Bulvankcr Nậ m unit with the Zlichovian and U p p e r Emsian Dala from corals and stromaloporoids support 4.3 Hạ Lang Regional stag e The Hạ Lang Regional Stage is the upper­ most part of Bàn Páp Regional Supcrstagc Pre.viously its c o m po ne nts w ere decribed as the "Scries de Hạ Lang", "Calcaires de Mó Tơm", "Givcrtmn" ctc (Saurin, 1956) The unit consists of dark grey limestones Increasing number, of this dating A s y e t th e costatus partitus z o n e ( E m sian/Eifelian boundary) has not been identified in Việ t Nam On the basis of the faunal associations and on stratigraphic interrelation of the three components of the Bàn Páp Supcrstage, the Nậ m Tát Regional Stage can be referred to the Eifclian chcrls upwards and the abundance of A m p h ip o So far the Eifelian/Givetian boundary has not in the succession can he regarded characteristic.of been identified, but the C aliapora baltersbvi - the Hạ Lantí Regional Stage Its limestones arc Slringocephalus burtini iauna and the conodont the most widespread Devonian deposits in North association of Polygnathus xylus xylus (varcus 'Việ t Nam; thickncsscs rcach up to 400-5()0m (Fig zone) together give the basis for a Givetian age to 2, Table 1) the Hạ Lang unit The Givctian age of this division Corals and brachiopods arc the predominant is proved also by the discovery of N ow akia otomari com ponents of the Caliapora battersbyi fauna (Richt.) and the Chinese form Viriatellina m ulti­ characterizing (he Hạ Lang Regional Stage The costatus Mu common spccics arc: Tố c T át Regional stag e S lro m a to p o ro id s and Corals- A m p h ip o ramosa (Phill.), Actinostrom a clathratwn Nich., The Tổ c Tát division has been established by Strom atopora concentriea Goldf., Tham nopora incorporating the Tố c Tát and Bàn Cả i F o rm a ­ nicholsoni Frcch, T.polygoitalis ( M a n s ) , tions and their equivalents in the U pp e r Devonian ta Munst and others New discoveries of the in North Viet Nam, which reach 300 - 500m in a b o v e - m e n t i o n e d f o r m a n if e r a n d c o n o d o n t thickness They are striped cherts, siliceous shales faunas, including diagnostic zonal forms, provide and marls which overlie conformably the H a Lang evidence for a Frasnian-Famennian age for the Regional Stage Locally there are intercalations T ố c T t Stage T he G ivetian /F rasnian , Fras- of variegated red limestones The extent of this nian/F am ennian and D evon ian/C arbo niferou s division is considerably narrow er than that of boundaries have not yet been determined We are those underlying it looking forward to finding them in the near future Foraminifers and Conodonts are prominent CENTRAL VIỆ T NAM components of the fauna From different sections the following species have been collected in the lo w er part of the unit: F o r a m in if e r s - N anicella uralica Tchuv., SÒ N G CẢ SECTIO NS Lower Devonian Eogcinitziana devonica L i p , E onodosaria evlanensis L i p , T ikh in clla m u ltifo rm is ( L ip ) , T frin g a Byk., Tour ell a jubra Lip et Pron Connodonts - Palm atolepis gigas Miller & Young., Ancyrodella nodosa Ulrich & Bassler, Polygnathus normalis Miller & Young and other species belong to Polygnathus asymetricus, Ancyrognathus triangularis and Palm atole/xs gigas /ones Moreover, some stomatoporoids were deter­ mined- Amplupora laxe/xrforata Lcc.fSlromatopora dubia Lee.,Trupetostrom a pingue Lee In the upper part of the division the fauna appears to be more abundant: Foraminifers - Quansiendolhyra kobeitusana (R au s.), Q.communis communis ( R a u s ) , Septaglomospiranella kazakhstaiuca Reit., Paralhirammina clegans Pojaik., Uralinella bicamerata Byk., Conodonts - Palm atolepis glabra glabra U l ­ The H uổ i N h ị F orm ation (thickness 700900m), consisting of sandstones and shales, may be transitional between the U pp er Silurian and the Lower Devonian in the Sông Cả sections It is overlain by Middle Devonian rocks o f the Huổ i Lôi Formation (Fig.4, Table 1) G raptolite and plant remains of the U pp e r Silurian age have been disc o v ere d in its low er m e m b e r T he E a rly Devonian age of the upper m em ber is confirmed by the N ow akia acuaria - N barrandei fauna A similar formation, named the Tây Chang F o rm a ­ tion, is observed in the Northeast of Laos towards the northwestern border with Viộ t Nam, in the Đ iệ n B iô n P h ủ d istric t In a d d i t i o n to dacryoconarids, the Erbenoceras-Anetoceras fauna have been found also in the upper m em b er of the latter formation The Early Devonian age of the upper m em ber of the Huổ i Nhị Form ation is in­ rich & Bassler, P.minuta Branson & Mehl, P.mar- disputable H ow ever, b ecause of the lack of g inifera m arginifera Helms, P.gracilis gracilis biostratigraphic data, its subdivision in detail and Branson & Mehl, P.perlobata Ulrich & Bassler, its stage correlation remain to be worked out Polygnathus stiriacus Ziegler, P.granulosus Bran­ son & Mchi, Icriodus alternatus Branson & Mehl, M iddle and U pper Devonian H indcodellu brevis Branson & Mehl In addition, some brachiopods and bivalves have been deter­ mined, such as C y rto sp irife r chaoi (G rabau), Productella subaculeata (Murch.), Schizophoria striatula (Schloth.), Posidonia (K aradjalia) venus- H uổ i Lôi Form ation (thickness 600-800m) Sandstones and shales with intercalations of lim e­ stones (in the upper m em ber only) of the Huổ i Lôi Formation are observed in the V iệ tN am -Lào bor- ^ r—■ — ĩ - mn^M—>■ '"! " * Fig.4 Devonian deposits from the Sông Cả section type dcrland area (Mư òng Xcn district) and arc con­ Famennian Limestones Beds In the Sông Cả firmed towards the Xiengkhuang province of Laos sections Famennian deposits have been recently (Fig-1, T ab ic.1, Fig.4) discovered and briefly studied A few of light lime­ Some beds in its lower m em ber yielding Cal- stones yielding Famenian conodonts were ob ­ ceola sandalina- Hexacrinites (?) hwnilicarinatus served only in the west of Nghệ An province, near should perhaps be correlated with the same level the Việ t Nam-Laos border Some conodont as­ as the Pắ c Nậ m Stage in North Việ t Nam and se m b la g e s have b ee n d e t e r m in e d from this could be correlated with the top of the Lower locality - Palm atolepis glabra glabra Ulrich & Devonian B a s s l e r , p p e rlo b a ta s c h in d e w o lfi M i l l e r , Predominant parts of the Huổ i Lôi Form a­ p.rugosa trachyteza Ziegler, N othognathella sp tion arc dated as Eifelian-Givetian by the two f o l l o w i n g fo ssil a s s e m b l a g e s : Atelodictyon R À O CẢ I SECTIONS F avosites g o ld fu s s i O r b , The Rào Cả i and Cù Bai sections are situated H eliolites porosus ( G o ld f ) a n d Tham nopora in the very ccntral part of Central Việ t Nam polygonalis (Mans.), Caliapora ballersbvi (M Ed­ (Fig 1,5, Tabic 1) Apparently, the Devonian in wards & Haimc), N atalophyllum rarum Tchud these sections is represented only by its extremity guangxiensis L i, in the East of Laos In the Rào Cả i sections several and others N ậ m Cắ n Form ation (thickncss over 500m) marine formations of Devonian, from the lower­ The (Jark-grcy limestones of the Nậ m Cán Forma- most strata of the system to the Famennian, have lion, conformably ovcrlvini» the Huổ i Lôi F orm a­ been described tion, crop out in narrow bc'ts in the same area, where Ihc rocks of the Huổ i Lôi Formation occur Lower Devonian Corals and stromatoporoids from the lower The Rào Chan Form ation (thickncss over member belong to the Caliapora battersbyi as­ 2000m) consists mainly of shales and sandstone semblage- the wcllknown Givctian fauna of North lenses arc also observed It is a thick formation Việ lNam Noteworthy species arc A m phi pora which unconl’o rmably overlies the Đạ i G iane Fo r­ ramosa (Phil.), A rudis Lee., Actinostroma mation yielding Pridolian graptolites ex­ pansum (Hall & Witficld), Caliapora battersbyi (M.Edwards & Haimc), Scoliopora denticulata There arc only a few corals recorded from the (M.Edwards & Haimc) The Frasnian age of the lower member: D ohm ophvllum S]) Alveolites sp upper mem ber is confirmed by conodonts: Polyg- and from the upper m e m b e r - Brachiopods: nathus xvlus Stauf., Palm atolepis foliacea Young, D esquam atia vijaica ( K h o d ) Levenca a ff Ancyrngnathus triangularis Young, Palm atolepis Iransvesa H o u C r i n o i d s : Lissocrinites curtus giga.s Miller & Young, p triangularis Bischoff & (J D u b a t.), Hexacrinites Ziegler In addition to conodonts there arc also (Yelt.) Frasnian stromatoporoids: A m phipora laxeper- (?) hiumdicarinatus M iddle and U pper Devonian fn ta Lee., Slachvodes costulala Lee and others The Givctian-Frasnian age of the Nậ m Cắ n The Bả n Giàng Formation (thickness over Formation is confirmed bv the above-mentioned 600m) consists of sandstones and shale intcrbcds fauna, but the Givetian/Frasnian boundary (L.as- conformably overlying the Rào Chan Formation symetricus zone) is not substantiated yet and succeeded in turn by the Stringocephalus 11 Rao Chan Fig.5- Devonian deposits from the Rào Câi section type levels of the Mụ c Bãi Formation There are some Givctian corals and brachiopods such as Tiiam - thin limestone lenses within the formation The n o p o r a n ic h o lso n i (F reeh), T.polygonalis rocks are considerably widespread in the west of (M ans.), Alveolites admirabilis Tong- Dzuy, Strin- Hà Tĩ n h and Quả ng Bình provinces and probably g ophylhim isaclis (Frcch), D endrostella trigem m e in the n e ig h b o u r in g a re a s o f E a s te r n Laos ( Q u e n s t ) , S tr in g o c e p h a lu s burtini (Fig-1,5) Chonelipustula orientalis Z uong & Rzons and In its faunal assem blage the noteworthy spccies arc: D e fr., others The second consists of Givclian and Frasnian C o r a l s - F avosites m u ltifo rm is D u b a t , forms ■ jThc most characteristic Givetian species Paraslrialopora dobretzovi D u b a t , Crassial- arc Tham nopora nicholsoni (Frcch), Caliapora vẹ olites crassus Lee., Helioliles porosus (Goldf.), battersbyi ( M E d w a r d s C haeletipora sokolovi D u b a t ct T o n g -D zu y , gocephalus burtini Defr Besides, many Frasnian sp o n g o p h y llw n halisitoides Eth., spccies have been discovered - A m p h ip o m ini­ Brachiopods - Septalaria sp., Desquamatia kurbesekiana Rzons., D.lanccodes Rzons Most of these specics indicate an Eifclian age Sonic forms, however, from the lowermost levels of the formation compare with the components of the I'auna of the Pác Nậ m Region! Stage in North Việ t & H a i m c ) , Strin- m a Ermakova,Alveolites lemnicus Smith,Aulocvstis polonicus N ow insky, Schizophoria ivanovi T sc h e rn , D esquam atia zo n a ta e fo rm is A l e k , Em anuella ronensis (Mans.), E tum ida Ljasch (Tố ng-Dzuy Thanh, 1982, 1988; Vũ Khúc el at., 1984) Nam (U pper Emsian) These arc, for example, the Without the evidence of the pclagic fauna, the species of Favosites, Parastr'atopora, Septalaria M ụ c Bãi F o r m a t i o n c o u ld n g e fro m the thus, the Bả n Giàng Formation can be referred to Givctian to Frasnian However its Givetian age is the Eifelian and perhaps to the Late Emsian in its indisputable and the faunal composition indicates lowermost levels perhaps only an Early Frasnian age for the u pper­ Mụ c Bãi Form ation (thickncss 400-X00m) th e r o c k s o f th e M ụ c Bã/ F o r m a t i o n a re most levels of the formation Dộ ng Thờ Form ation consists mainly of widespread in the Rào Cài section This formation sandstones with shale interbeds and rare lens of consists of sandstones, shales and some intcrbcds marls Accordinu to the orthography of the name of marls and limestones Terrigenous rocks arc of the mountain, after which Ihe formation was predominant in the lower member, with lime­ named, the name of this formation is corrccted stones and marls increasing towards the upper here as Dộ ng Thị, instead o f Dơng Thợ member The Mụ c Bãi Formation is distinguished vious publications in p re ­ by the variable thickncss and composition of the It was considered as an unit overlying the Mụ c rocks in its sections and by abundant and various Bãi Formation and was dated as Frasnian (Dov- bcnthic faunal assemblages These appear to pro ­ jikovei al 1977; Vũ Khúc, Bùi Phú Mỹ -Edit 1988; vide the evidence г о Г littoral facies Tong-Dzuy Thanh el al 1988) Two faunal assemblages have been distin- New collected Givetian plant fossils from Hói liuished; that of Chonelipuslulạ orientalis charac­ Dá, near Minh Lỗ terises the lower member, and Emamiella ronensis p ro v in ce- - the upper one railway bridge, Quả ng Bình p rololepidodendron s p , Lepidodendropsis sp ( i d e n t i f i e d by P r o f C.Y.Cai) support the dating age of the Độ ng Thò T he first a s s e m b la g e consists m ainly of Form ation as Givetian-Frasnian According to 13 the the new observation of the present author, the rocks of this formation, in particular in the deposits in Việ t Nam and they display consider­ ably reduced successions area of Lý Hòa pass, belong to the nearshore neritic fades, like those of the ĐỒ Son Formation Lower Devonian in North Việ t Nam So, in this paper the Độ ng Thò The T â n L â m F orm ation (thickness 100- Formation is recognized as an equivalent in age of 150m), u n c o n fo rm a b ly overlying the U p p e r the Mụ c Bãi Formation and both formations were a p p a tc n tly d e p o site d in the s a m e ne a rsh o re Silurian rocks of the Đạ i Giang Formation, con­ sists of red conglomerates, sandstones and shales, palcobasin X ó m N h a Form ation L im estones of the the red colour of the rocks, variable thickness and Xóm Nha Formation (thickncss over 200m) which other properties of the formation arc rcminisccnt conformably overlie (he Mụ c Bãi Formation crop of continental deposits of the Sika Formation in out in some sections in Quả ng Bình province North Việ t Nam Contacts with Carboniferous deposits arc not A few samples of Lingula have been studied known in the area under study In th e lo w er m em ber, F rasn ian strom atop oroids and corals have been d e te r­ m i n e d : S ta ch yo d es costư lata leloporoides L ee., L e e , s.paral- T e m n o p h y llu m lantenoisi (Mans.) Conodonts from the middle member which, apart from endcmic spccics, resem ble European Lower Devonian forms These arc LinỊ Ị ula cornea Sow., L aff Iiawkei Roualt, L aff loulanenxis Mans, and Ljnuongthensis Mans M iddle and U pper Devonian belong to the Palm atolepis gigas and p.triangularis z o n e s , b o lh o f F r a s n i a n ag e in the European zonal scale The CÙ Bai Form ation (thickncss 450-500m) is considered to he approximately equivalent to the Mụ c Bãi Formation and is distinguished by the The main components of the characteristic prescncc of thick stratified limestones, instead of conodont zones of the Fam ennian have been dis­ the predominant terrigenous rocks in the latter covered in the upper m em ber - Palm atolepis mar- formation Neither contacts between the Tân Lâm ginifera H e lm s , p.distorta B n so n & Mehl, and Cù Bai Formations, nor intermediate deposits p.m inuta minula Branson & Mchl, p.quadran- have been discovered in the studied sections tinodosa Branson & Mehl ctc The fauna collectcd from the lower part is quite similar to the Em anuella ronensis fauna of Because of the lack o f eonodonts in the lop of this formation and sincc there arc no Lower C a r­ b o n i f e r o u s d e p o s i ts in th e s e s e c ti o n s , the Devonian/Carboniferous boundary has not been identified CỦ BAI SECTIONS The CÙ Bai scclions arc situated in Quả ng Trị and Thừ a Thicn provinces (Central Việ t Nam) (Fig 1, Tabic 1) On the basis of new data, these arc the southernmost occurrcnccs of Devonian the Mụ c Bãi Formation (Tong-Dzuy Thanh et al., 1988) Its main forms are: A m phi pora rudis Lee., Crassialveolites crassus Lee., Em anuella ronensis M an s., G v p id u la p la n is p in o s a G rab au , Schizophoria bistriata Tschcrn and others These fossils suggest a Givctian age The l'auna from the upper m em ber indicates a Frasnian age and the following specics arc noted: F o r a m i n i f c r s - E o n o d o sa ria rara L i p , Nanicella porrecta Byk., Parathurammina radiata 14 Table Devonian stratigrapilic units of Việ t N am 15 Anthr., Tikhinella frin g a Byk., Tournayella jubra great difference between the facies of the U p p e r Lip & Pron Devonian and the Lower Carboniferous laxeper- A continuous Devonian-Carboniferous sec­ fora ta Lee., A patokensis Riab., Stachyodes cos- tion may be expected somewhere in Northermost tulala Lee., s.angulata Khromykh, Tienodictyon Việ t Nam S t r o m a t o p o r o i d s - A m phi pora tschussovense (Yavors.), The Devonian deposits in Việ t Nam arc Corals - Alveolites suborbicularis Lam., Al- especially widespread in two regions, North Việ t veolitdla densa (Lee.), A laiophyllum ĩn co iptum Nam and Central Việ t Nam (Bắ c Bộ and Việ t-Lào (Hill & Jell), palacobasins) In each region they are charac­ Brachiopods - c v r to s p ir ife r sublimis Ljasch., U chtospirifer nalivkini Ljasch The above-menlioned fauna undoubtedly indicates a Givetian- terized by particular facies, faunal communities and the sequences of the stratigraphic sections The Devonian faunal assemblages of North Frasnian age lor the CÙ Bai Formation, the top of Việ t Nam arc very similar to those of South China which is hardly younger than that of the Mụ c Bãi This similarity is well expressed in the compositon Formation in spite of its Givetian-Frasnian age of the Lower Devonian faunal assemblages, in In addition to the above-described deposits, limestones beds yielding Yunnanellina have been particular in the E u ry sp irife r tonkinensis and Howitlia wangi assemblages found in the CÙ Bai sections The slratigraphic While limestones are p rcdom inent in the sequence of these limestones is still under study, D evonian sequences of N orth Việ t Nam ter­ b u t th e b r a c h i o p o d s Y unnanellina harburyi rigenous rocks occur largely in the Devonian sec­ ( D a v i d ) , Y.dK.iriplicala th e tions of Central Việ t Nam, particularly in the ioraminifders Septaglom ospiranella aff rauserae Lower Devonian It should be noted that the G rabau and Dain, Uralinnclla sp and others arc very similar Devonian in the latter area represents (he eastern to the fauna of the Hshikuangshan Formation extremity of the palaeogeological region, callcd (Famcnnian) of South China Việ t-Lào by the present author (1980, 1988) The Lower and Middle Devonian faunas of CO N CLU D IN G REMARKS 1- The sedimantary regime in Việ t Nam was modified strongly by the Caledonian orogeny This is well expressed in North Việ t Nam, in particular in the north-eastern area, where the "Red Sandstones" of the Lowermost Devonian overlie different Lower Palaeozoic rocks How­ ever, at that tim e th e re was a stra it in the northwestern area and in the north of Central Việ t Nam Continuous Silurian-Devonian sections are observed in the Lower Sông Dà River and in the Sông Cả basin Apparently an U p p e r Devonian regression took place in the territory of Việ t Nam, but it was p ro b a b ly not d ic a l e n o u g h to ch an g e the sedimentary regime of the region and there is no 16 V iệ t N am b elo n g to th e In d o sin ian p a la e o b io g c o g rap h ic a l province (D u bato lo v, Spasskyi 1970; D u b a to lo v 1970) w hich c o r ­ responds to the South China Region of the Old World Realm in the conception of W ang Yu and Boucot (W ang Yu, Boucot, Rong & Yang, 1984; Boucot, Johnson & Talent, 1969) A part from a great number of endemic forms, many species belong to the West E uị ppean Devonian faunas, and Barrandian species in particular are dis­ covered in North Việ t Nam This affinity is espe­ cially well expressed in the composition of coral and brachiopod assemlages The affinity with the Uralian and Siberian faunas is also rem arkable as was pointed out in 1967 by the present autlhor In addition, some Devonian species from Australia were also discovered in Việ t Nam, but this affinity r e g i o n s s e p t e n t r i o n a l e s du H a u t T o n k i n is less conspicuous Mémoires du Service géologique de l’Indochine, B io stra tig rap h ic a lly , the D ev o n ia n in IV, 176 pgs North Việ t Nam is better studied than that in Central Việ t Nam Consequently, the corrélation of ils deposits is well established and the scqucncc of Devonian units arc established The Lower Devonian seem s especially widespread rather than the Eiftiian suggested in former works D O V J I K O V A.E et al 1965-Gcologia Scvcrnogo V ’clnama (Geology of the North Việ t Nam, in Russian) Hanoi: Geological Survey, 668 pg DUBATOLOV V.N l 972-Zoogcografia At present the pclaạ ic faunas arc insufficient­ devonskikh m orci Evrazii (Z o o g e o g p h y of ly studied in Việ t Nam For discrimination of the D evonian seas of E u rasia) Moscow: Nauka, boundaries of Devonian international stages, it is 126pcs ncccssary to increase rcscarch in this field The Devonian in Central Việ t Nam is con­ sidered as the eastern continuation of that in the Easl of Laos Its detailed division and corrélation will he better resolved with the collaboration of D U B A T O L O V V.N., SPASSKYI N.Ya 1970-K.orally osnovnykh palcobiogcografichcskikh provintsyi (lcvona (C o ls o f the m ain palcobiogeographical provinces in Devonian) In "Zakonomcrnosti rasprostrancnia palco/oiskikh the geologists OĨ Laos korallov SSSR", pp 13 31 Moscow Nauka ACKNOW LEDGEM ENT T h is p a p e r has been completed thanks to the support of the Fun- D Ư Ô N G X U Ả N H Ẩ O et al 1980-Charac- damcnlal Research Program e in the fields of tcrisiic fossils in the North of Vietnam Hanoi: Natural Sciences of Việ t Nam (KT04), which Khoa họ c-Kỹ thuậ t, 600 pgs (in Vietnamese with crcaled the favourable opportunities lor collect- Enulish summary) iĨ 1li the supplementary data and for ameliorating F O N T A IN E H.1967-Le Dcvonicn du Cam- Ihc manuscript of (he paper The author is in­ bodiỉ C, dll Laos cl dll Vietnam International Sym­ debted to Proĩ D.L Dinelcy (University of Bris- posium on Devonian System Calỗarv Pctrology- lo l, U K ), D r Gcology, 2, pp.569-581 P h Ja n v ie r ( I n s t i t u t dc Paléontologie, Paris), Dr J Holland (Geological Magazine London) lor their help in prcparinii (he manuscript in English of this paper JA N V IE R P., B LIECK A., G E R R E N N E P., T O N G - D Z U Y T H A N H 1987- Faune cl flore de la Formation de Sika (Dcvonicn inférieur) (Jans la presqu'ỵle de Doson (Vietnam) Bulletin REFERENCES du Muséum National d’Histoire naturelle Paris, 4.9 (3), pp.291-301 B O U C O T A J„ JO H N S O N J.G., T A L E N T J.A 1%9 - Early Devonian hrachiopod zoot»eoizraphv Gcoloiỉ ical Socicty of America, Spécial paper, 119, 113 pi’s C H L U P A C V 1976-The Bohemian Lower Devonian stases and remarks on Ihc Lower-Mid­ dle Devonian boundary New sletter on Strati tiraphy, (2/3), pp 168-189 SA U R IN E 195f>-Lcxiquc stratig raphiqu e in tc r n a lio n a l 111-Asic a-In d o c h in c Paris: Centre National de la Recherche scientifique, 140pp SA U R IN E 1958-Le Dcvonic-n en Indochine, sa Stratigraphie cl corrélation Annale de Faculté des Sciences de Saigon, pp 193- 221 TẠ H Ò A P H Ư Ô N G , H L A R D E U X - L c s D E P R A T J 1915-Etudcs géologiques sur les 17 Tentaculites dévoniens dans la coupc de Dồ ng Giang) Đị a chấ t, 218-219 (9/12/1993), pp 1-9) (in Văn-Nho Q ue (Nord-Est du Viỗt Nam du Nord), Vietnamese with French summary) (in press) T R Ằ N VĂ N T R Ị et al 1976-Đị a chấ t Việ t T O N G -D Z U Y T H A N H , 1967-Les Coraux Nam Phàn mièn Bác (Geology of Vietnam North tabulatomorphes du Dévonicn au Nord Vietnam part) Hanoi: Khoa họ c Kỹ thuậ t, 354pgs (in V iet­ A cta Scientiarum V ic tn a m ic a ru m G eologia- namese) Gcographia, III, Hanoi, 304 pgs VŨ KHÚC T O N G - D Z U Y T H A N H , 1980-Stratigrafia et al 1984-Hóa thạ ch đặ c trư ng ỏ mièn Nam Việ t Nam (Characteristic fossils in devonskikh otlojeniy V ’ctnam a (Stratigraphy of South Việ t Nam) Khoa họ c Kỹ D e vo nia n d e p o sits o f V ie tn a m ) G e o lo g ia i 286pgs (in Vietnamese with English summary) Geophizika, Novosibirsk, pp.46-5