2002 new stratigraphic schema of paleozoic and mesozoic in bac bo (north vietnam)

ISSN 0866 - 7381 J o urn al o f GEOLOGY No 19-20 Series B 2002 DEPARTMENT OF GEOLOGY & MINERALS OF VIỆ T NAM HÀ NỘ I Journal o f G E O L O G Y Series B, No 19-20/2002 (Fourty second year)' EDITORI AL OFFICE 6, Phạ m Ngũ Lão Hà Nộ i 6, Nguyên Hồ ng, Đố ng Đa Hà Nộ i Tel: (048) 261 779, 352 319, 355 468 Fax 84 254 734 Email: tapchidc@ hn.vnn.vn EDITORIAL BOARD Editor-in-chief: NGUYEN THÀNH VẠ N Deputy Editor-in-chief: TRỊ NH DÁNH, TRỊ NH XUÂN BEN Secretary: BÙI ĐỨ C THẮ NG M em bers: DƯ Ơ NG ĐÚC KIÊM, ĐÀO ĐÌNH THỤ C ĐINH THÀNH, NGUYEN ĐỨ C ĐẠ I, NGUYỄ N KHẮ C VINH, NGUYẺ N HŨÍJ TÝ, NGUYEN TIÊN BÀO, NGUYEN x u â n BAO, PHAM NĂNG VŨ , PHAN TRƯ Ờ NG THỊ , T ố N G DUY THANH, TRAN m in h , TRẦ N MINH THẾ , TRẦ N TAT t h ắ n g , t r a n v ă n t r ị , v ũ k h ú c CONTENTS Page Tố ng Duy T hanh, Vũ Khúc New stratigraphic schem a of Paleozoic and Mesozoic in Bắ c Bộ (North Việ t Nam) Tạ Hòa Phư ng Devonian and Carboniferous conodont biostratigraphy of the Đồ ng Văn Section, Hà Giang Province 14 T rầ n Trọ ng Hòa Subdivision and correlation of Permian-Triassic basaltoid associations in the Sông Đà structure (NW Việ t N am ) 22 Bùi Phú Mỹ , T rầ n Hồ ng Lĩ n h, Khiế u Văn Giáp, Hồng Đình Khả m Red beds in the Thổ Chu Archipelago, Kiên Giang Province .31 T rầ n Văn Bạ n, B ountheung Phengthavongsa, Vũ Khúc , Vũ C hâu, Inpong Homsombath- The Mesozoic Nam Theun basin, Middle Laos: Stratigraphy and development history .35 T rầ n T uân Anh, T rầ n Trọ ng Hòa, Phạ m Thị Dung Granites of the Yê Yên Sun Complex and their significance in tectonic interpretation of the Early Cenozoic stage in West Bắ c Bộ 43 Cao Đình T riề u Some characteristic features of seismotectonic conditions and seismic regime of the Tuầ n Giáo earthquake a re a 54 Nguyễ n Thị Bích Thuỷ , Siebel w , Satir M, Bùi M inh Tâm Internal structure of zircons anci U-Pb geochronological evidence for the existence of a Precambrian basement in the Đà Lạ t Zone, South Việ t Nam 69 Nguyễ n Văn Vư ợ ng, Tạ T rọ ng T háng, Vũ Văn Tích A new kinematic model for the Cenozoic deformation along the Red River shear zone: implication for the Sông Hồ ng Basin form ation 79 10 Đặ ng Huy Rằ m Some results of Ẹ eomorphologic hazard study along the Đà Nang Quả ng Ngãi Coast (from Liên Chieu to Dung Quấ t) 90 11 Nguyễ n Kim Lạ p, Đỗ Chiế n Tháng, Bùi Việ t Dũ n g, Nguyễ n Lê Yêm Geophysical hazards in the East Việ t Nam Sea and preventive m easures 96 12 Nguyễ n Văn T hành, Ngô Phú An, Phùng Văn D uân, Phạ m Huy Họ c, Vư ng M nh Son New data on the Rb-Sr isotopic age of granitoids from the Sông Miệ n Complex 103 SCIENTIFIC COMMUNICATION 13 H erbert H Covert, T rinh Dzanh, Đỗ Đứ c Q uang, Lê Quố c T hanh, Nguyén M nh Phi New Mammalian fossils from Ninh Bình Province, Việ t Nam 109 Journal of GEOLOGY Series B No 19-20/2002 p.1-13 NEW STRATIGRAPHIC SCHEMA OF PALEOZOIC AND MESOZOIC IN BAC BỘ (NORTH VIỆ T NAM) TỐ NG DUY THANH', v ũ KHÚC2 1Department o f Geology Vietnam National University, Hà Nộ i 334, Nguyễ n Trãi, Hà Nộ i 2Paleontological Association Phạ m Ngũ Lão Hà Nộ i A b stra c t On basis o f the “Stratigraphic Code” the authors attempt to assess the Paleozoic arid Mesozoic stratigraphic units described in Bắ c Bộ (North Việ t Nam) All the valid units are presented in two tables o f this paper (tab and tab 2), the change o f unit names, the explanation o f assessing these units, and the description o f new units are introduced ill the text Paleozoic The Sông Chả y Group, established by Hoàng Thái Sơ n, was divided recently into the Thác Bà (Neoprotozoic) and the An Phú (Lower Cambrian) Formations Mỏ Đồ ng and Bổ ng Sơ n Formations are synonyms o f the Than Sa Formation, as fo r Cô Tô and Tấ n Mài Formations, they distinguish each from other by lithological properties and should be different formations Đạ i Thị , Pia Phư ng, Cố c Xô should be invalid names o f the Mia Lé Formation, in the similar situation - Nà Quả n, Phia Khao, Khe Lau, Mỏ Nhài, Si Phai Formations are synonyms o f the Bẩ n Páp Formation, white Tràng Kênh and Bả n Coỏ ng Formations are restored, which consist o f limestone o f shelf facies and Givetian - Famennian in age LTmg Nậ m, Đa Niêng, Phô'Hàn and Con Voi are synchronous Formations Early Carboniferous in age, among them only the Con Voi Formation is characterized b \ shelf facies, tile rests are limestone o f deep water facies, while Bằ ng Ca, Tố c Tát and Lũ n g Nậ m Formations shape the Trùng Khánh bipartite Group The Bắ c Sơ n fomiation name is young homonym o f a Quatemai-y unit, so the formation name is changed by the Đá Mài one, in which includes and limestone described as the upper part o f the Bả n Diệ t Formation Mesozoic The ‘Tân Lạ c Formation ” is actually considered the upper part o f the Cò Nòi Formation, lower boundai-y o f which is diachronous Consisting mainly o f felsic effusive compositions, Lũng Trâu, Bình Liêu, Tiên n, Pị Hèn and Làng c ổ ng Fonm tions are synonyms o f the Khơn Làng Formation, while the n Bình Formation is a valid unit The Điể m He Formation was established recently on the basis oflentifonn limestone at the base o f the Nà Khuấ t Formation, while synonyms o f the last are Sơ n Dư tig, Dư iig Him and Tm i Sim formation names, and Nậ m Thế p aììd Huổ i Xa are invalid names corresponding to the Nậ m Pô Formation The discovei-y o f Gigantopteris remains result in the excluding most parts o f terrigenous and limestone components from the “Văn Chấ n Complex" and the remaining felsic effusive rocks with some thin tuffaceous sandstone belong to reaì Văn Chấ n Formation With the presence o f mafic components, the Suố i Bé Fonnation distinguishes fi-om the Văn Chấ n one, as fo r Nậ m Qua, Tú Lệ , Ban Hát, and Mư ng Kim formation names, they are only irrationally used fo r different parts o f the Vân Chấ n Formation INTRODUCTION •_ D u r in g c e n tu r y p e rio d , s in c e th e tim e , 7_f r \ 7’ XT“I , , when the geology of việ t Nam’s teiritory has been regularly studied, nearly 8.000 Iu , Twwxt ™ research works on the geology or Viêt Nam iTi J T _ _ were published Important successes in r ^ , , ,•, , so-atigraphy have been ach eved wh ch play the key role n underetanding struc ure and geological history of country s entrails In the twentieth century over 500 stratigraphic unit names have been i T ,- u , \ J A < f ™ published or proposed, and a lot of them £ Vietnamese _ 1_ D f uĩ rn> geological language Before the 50 s J J r ,° , "■ ,■ decade of last century stratigraphic , “ J u E u „A researches were realized by French and Xhich worked j S ; styies of their countries At that time, a great number of stratigraphic units were described in different stratigraphic conceptions The stratigraphic terms have been rapidly increased at last time, when the geological mapping works (at 1/200 000 and 1/50 000) were developed Though a stratigraphic code has been approved and published [25] many junior geologists appear to prefer creating new stratigraphic terms, instead of the available ones Some junior geologists understood the lithological properties of the lithostratigraphic unit as a rigid character and usual describe new unit and give a new term, although there is only a facies change of an acquainted unit In result, the number of stratigraphic terms increases rapidly causing a complicated picture in geological information In this situation, an assessment on the validity of stratigraphic units of Việ t Nam becomes a pressing work, and the present authors try to give an initial revision of Paleozoic and Mesozoic units in North Việ t Nam (Bắ c Bộ ) It is difficult to realize the revision on stratigraphic units in lacking an official commission, so all results of assessing stratigraphic unit terms presented in this paper are only a first contribution to this field of North Việ t Nam Working in this aim, the present authors have based on the statutes of the “Stratigraphic Code” approved by Geological Department of Việ t Nam [25] By tradition, stratigraphy is studied in the frame of present structural schemas, and in each geological region, stratigraphic units from oldest to youngest will be described Stratigraphic units were formed in a determined sedimentary basin, so they must be studied in the relationship with the basin environment where they were formed, but the last could not be a stable element through geological times There are not any sedimentary basin fixed through all geological history, and the description of all stratigraphic units from oldest to youngest in the frame of a present structural unit seems to be irrational mode As a result in this paper geological regions, in which stratigraphic units will be presented, have not been identical in the schemes of Paleozoic and Mesozoic In each scheme (Tab.l, Tab.2) of this paper, valid stratigraphic units are introduced, as for the change of the unit name and the explanation of assessing these names, and the description of new units they will be presented in detail in the text Due to the lack of data, some questionable problems in the stratigraphic division and unit dating are not solved yet, but they are also showed in the paper for studying in the time to come PALEOZOIC UNITS Lower Paleozoic Sông Chả y Group and Thác Bà, An Phú Formations The Sông Chả y Formation was first described in Trầ n Văn Trị et al [32] in Hà Giang Province and characterized by two parts (in ascending order): 1) Two-mica schist, interbeds of quartzite, 2000 m thick; 2) marble, dolomitic marble, 50-200 m thick Recently Hoàng Thái Sơ n has rationally described these different lithological parts of the Sông Chả y Formation in Yên Bái Province as the Thác Bà Formation (Neoproterozoic) and the An Phú one (Lower Cambrian), which are two components of the Sông Chả y Group [55] Thầ n Sa, Formations Bồ ng Sơ n and Mỏ Đồ ng Cambrian deposits containing Planolites in Thái Nguyên and Bắ c Kạ n Provinces were first described by E Patte [16], latter Vasilevskaia E D has described them as the Mỏ Đồ ng Formation [5] The Mỏ Đồ ng Formation is characterized by sandstone, interbeds of red-brown clay shale and chocolate, variegated, stripped silty sandstone, calcareous sandstone Apart from Planolites remains, Middle Cambrian trilobite Ptychagnostus atavus was collected from the Thầ n Sa village Just after the mapping works of Vasilevskaia E D., Trầ n Văn Trị did the exploration in the same area and described the Thầ n Sa Formation, which is characterized by the same rock sequences, so Thầ n Sa and Mỏ Đồ ng Formation should be synonyms [35] The paper in which the Thầ n Sa Formation is described, had been rapidly published in the Đị a Chấ t Journal [31] a year before the publication of Mỏ Đồ ng Formation [3] In this real unexpected situation, the MỎ Đồ ng Formation became a junior synonym of the Thầ n Sa one Lithostratigraphically, the Thầ n Sa Formation is much similar to the Bồ ng Sơ n one, described by Bouư et R [7] as “Série de Bong-Son.” However, the Bồ ng Sơ n Formation seems include some layers belonging to the Sông Cầ u Group (Lower Devonian), so the Bồ ng Sơ n term has not the priority, and almost all its rock components belong to the Thầ n Sa Formation Cô Tô and Tấ n Mài Formations Zhamoida A I and Phạ m Văn Quang [3] have described the Cô Tô and the Tấ n Mài Formations in the Coastal Zone of Bắ c Bộ , and dated the first as Neogene, and the second as Cambrian - Ordovician Later the first formation was redescribed by Trầ n Văn Tri et al [55], and the second - by Nguyễ n Công Lư ợ ng [35], with discovered graptolites indicating Ordovician - Silurian age of both formations The Cô Tô Formation was considered as a synonym of the Tấ n Mài one [36], because of its age was dated as the same Ordovician Silurian However, Cô Tô and Tấ n Mài formations distinctly distinguish each from other by their lithological compositions; in the first tuffaceous sandstone and rhyolitic tuffs play important role, while these components are absent in the second formation Therefore, both formations are worthy considered as valid units in stratigraphic terms of Việ t Nam Devonian Mia Lé Formation and its equivalents - Pia Phư ng, Cố c Xô and Đạ i Thị Formations The Pia Phư ng Formation, described by Nguyễ n Kinh Quố c [9], consists mainly of sericite schist, marlaceous shale, interbeds of carbonaceous clayish limestone, dolomitic limestone, calcareous silty sandstone, limestone, interbeds of manganese-bearing silty sandstone Nguyễ n Kinh Quố c [9] has indicated the presence of tuffaceous sandstone, rhyolitic tuff components in this formation, but isotopic data show that these volcanic rocks seem to be younger in age The Đạ i Thị Formation, described by Phạ m Đình Long, Nguyễ n Kinh Quố c, Hoàng Xuân Tinh [55], consists of sericite - quartz schist, sericite schist, interbeds of recrystallized limestone, silty sandstone, interbeds of sericite quartz schist, lustrous phyllite and thin beds of quartzitic sandstone So, the lithological components of Pia Phư ng and Đạ i Thị Formations are similar to those of the Mia Lé Formation, their slight difference expresses only the higher metamorphism level of the two first formations Furthermore, in Pia Phư ng and Đạ i Thị Formations the collected fossils belong to the same Euryspirifer tonkinensis Assemblage that characterized the Mia Lé Formation Mentioned data show that Pia Phư ng and Đạ i Thị Formations are junior synonyms of the Mia Lé Formation Here could be included and the most parts of the In this paper, the Pia Phư ng term is understood in accordance with the meaning of the Nguyễ n Kinh Quố c s description (1977), but not with the description in Vũ Khúc & Bùi Phú Mỹ (ỉ 990) Cố c Xô Formation that are characterized by the same lithological and fauna compositions (see also Tố ng Duy Thanh, Trầ n Văn Trị , Tạ Hoà Phư ng, Nguyễ n Hữ u Hùng [23]) ' Bả n Páp, Nà Quả n, Phia Khao, Mỏ Nhài, Si Phai, Bả n Coỏ ng and Tràng Kênh Formations The Bả n Páp Formation was established by Nguyễ n Xuân Bao [14] in the Sông Đà basin, characterized by Devonian grey bedded limestone Later, Phạ m Đình Long [17] described the Nà Quả n Formation in Cao Bằ ng Province, which is characterized by the same rock properties as of the Bả n Páp one, and which Dư ng Xuân Hả o called as “Nà Quả n” without section description The Bả n Páp Formation was described five years sooner than the Nà Quả n Formation, so the priority belongs to the Bả n Páp name, and the Nà Quả n name should be a synonym of the Bả n Páp The Phia Khao Formation was established and dated as Silurian - Early Devonian by Nguyễ n Kinh Quố c [9] Later it was irrationally considered as a component of the Pia Phư ng Formation [36] It consists mainly of recrystallized limestone, which were described as “Eifelian - Givetian Stages” [5] and Khe Lau Formation [23], and by new observation and fossil study it should be correlated with the Bả n Páp Formation in the current conception [23] Đặ ng Trầ n Huyên [4] described the Si Phai (Chi Phai) Formation, which consists of limestone, marl, and chert interbeds, overlying the Mia Lé Formation, and occurring only in the Đồ ng Văn area It should be considered as a facies change of the Bả n Páp Formation, that in it apart from pelagic fossils, one of us collected recently Tabulates such as Heliolites sp and other indeterminable Corals Other synonym of the Bả n Páp Formation is the “Mỏ Nhài Formation” [S], which consists of Frasnian limestone containing abundant Stromatoporoids, siliceous limestone, and occurring only in the Bắ c Sơ n area It is worthy to note that Devonian limestone containing shallow water fossils is a distinguished character of the Bả n Páp Formation in Bắ c Bộ , so the Mỏ Nhài Formation must be considered as the upper part of the Bả n Páp one The Tràng Kênh Formation characterized by Devonian dark grey limestone was described by Nguyễ n Quang Hạ p [11] in the coastal zone “Duyên Hả i”; its junior synonym is the LỖ Seta Formation described by Phạ m Văn Quang (1969), which is characterized by the same limestone and occurred in the same area In previous works, Tong-Dzuy Thanh [26] has considered this formation as a component of the Bả n Páp Formation, but new data from investigations of Nguyễ n Hữ u Hùng, Đoàn Nhậ t Trư ng and Tạ Hoà Phư ng and of us prove that it distinguishes clearly from the Bả n Páp Formation First, the Tràng Kênh Formation distinguishes from the Bả n Páp one by the presence of a siliceous member in the middle part and of the light variegated limestone Famennian age in the top of its sections Second, if benthos and pelagic fossils indicate Early Devonian - Frasnian age of the Bả n Páp Formation, the Tràng Kênh Formation has diachronous boundaries - from Givetian or Frasnian of the lower boundary to Famennian of the upper one Vasilevskaia E D [3] has described the Bả n cỏ ng (Bả n Coỏ ng) Formation, which distinguishes from the Nà Quả n one by containing Frasnian, but not Middle Devonian fossils, and by light grey but not dark grey limestone Later, Givetian brachiopods and corals were discovered from limestone of the Bả n Coỏ ng Formation, therefore the Bả n cỏ ng Formation was considered as a synonym of the Nà Quả n [2, 21, 22] or Bằ ng Ca ones [17] Table Paleozoic stratigraphic Units in Bắ c Bộ (North Việ t Nam)* * Stratigraphic units of Mư ng Tè area will be shown in another chart New data of Nguyễ n Hữ u Hùng, Đoàn Nhậ t Trư ng and of us prove that the Bả n Coỏ ng Formation clearly distinguishes by its rock properties and age of its fossils First, the Bả n Coỏ ng Formation is dated as Upper Givetian - Famennian, so it could be correlated with the upper part of “Nà Quả n Formation” and Bằ ng Ca, TỐ C Tát Formations including Second, the Bả n Coỏ ng Formation is characterized by shelf facies, containing benthos fossils such as foraminifers, corals, and brachiopods that clearly distinguishes from the deep-water facies with conodont, dacryoconarid fossils of Bằ ng Ca and Tố c Tát Formations Third, the Bả n Coỏ ng is characterized by diachronous lower boundary, which overlies the upper level of the “Nà Quả n Formation,” or the Bằ ng Ca Formation, as for its upper boundary, it may correspond to the upper boundary of the Tố c Tát Formation Table Mesozoic stratigraphie Units in Bắ c Bộ Therefore, the Bả n Coỏ ng Formation could not bẹ considered as a synonym of “Nà Quả n Formation” or of Bằ ng Ca Formation and it is worthy to be a valid formation Lũng Nậ m, Đa Niêng, Phố Voi - Synchronous Units Hàn and Con In East Bắ c Bộ (Cao Bằ ng Province), the Lũng Nậ m Formation consists of ash grey limestone, and manganiferous cherty shale, which contain Toumaisian - Visean foraminifers and conodont fossils In West Bắ c Bộ (Sông Đà Basin) Nguyễ n Xuân Bao [14,15] established the Đa Niêng (North Việ t Nam) Formation and dated it as Givetian Frasnian, which consists also of ash grey thin-bedded limestone and siliceous interbeds On the basis of abundant foraminifer and conodont assemblages from its hypostratotype in the Sơng Mua upstream, Đồn Nhậ t Trư ng [24] has dated this formation as Toumaisian - Visean and correlated it with the Lũng Nậ m Formation in East Bắ c Bộ So the Lũng Nậ m Formation closely resembles the Đa Niêng one, and it rules out a possibility that the first is synonymous with the second Ngơ Quang Tồn [7] described the Phố Hàn Formation in the Cát Bà Island (Hạ Long Bay), which consists also of ash grey thin-bedded limestone and siliceous interbeds, and in which Toumaisian Visean Conodont and Foraminifer fossils were collected Describing Lower Carboniferous limestone at the “Núi Con Voi” mount, near Hả i Phòng City, Nguyễ n Quang Hạ p [11] has given the name the Con Voi Formation French geologists described this Lower Carboniferous limestone mountain as “Calcaires noires de la Montagne de l’Elephant” and had dated it as Visean [20] But there are two different limestone beds in the same Con Voi Limestone Mountain The first consists off ash grey limestone, containing Lower Carboniferous foraminifers and corals, which correspond to the Con Voi Formation The second is composed of underlying dark grey dolomite, and more or less recrystallized limestone containing Frasnian Amphipora and foraminifers that belong to the upper part of the Tràng Kênh Formation [24] Thus from four synchronous formations, the Con Voi one distinguished itself by limestone of shallow water, all the rests (Lũng Nậ m, Đa Niêng and Phố Hàn Formations) are characterized by chert aụ d limestone containing conodonts and foraminifers of deep-water facies Lũng Nậ m and Đa Niêng Formations arc characterized by the same rock properties - dark grey limestone, thin cherty shale interbeds, and both of them contain Toumaisian - VLsean conodonts and foraminifers, for that reason they are possible synonyms As for the Phố Hàn Formation, a thick member of mudstone and shale (90-115 m) is distinguished among its limestone and cherty shale components Moreover, foraminifers and brachiopods from its lower and middle beds show that this formation seems to be a little older than the Lũng Nậ m and Đa Niêng Formations, its lower boundary may fall into upper Devonian Therefore, the Phố Hàn Formation may be distinguished formation of Upper Devonian - Lower Carboniferous only in the Coastal Zone of Bắ c Bộ (Duyên Hả i) Trùng Khánh Group in Bắ c Bộ In East Bắ c Bộ (Cao Bằ ng Province) successive stratigraphic units - Bằ ng Ca, Tố c Tát and Lũng Nậ m Formations, which occur mainly in the Trà Lĩnh, Tố c Tát, Hạ Lang areas of the Trùng Khánh District, have common characteristics in their deposits and fossils First, all of them are composed of grey limestone, chert shale, and manganiferous calcaro-cherty shale, and second - collected foraminifers and conodonts show that they belong to the deep-water facies These common characteristics reflect a sedimentary cycle in deep water environment of the region, so three successive units - Bằ ng Ca, Tố c Tát, and Lũng Nậ m Formations occurring mainly in the Trùng Khánh District should shape a tripartite unit namely the Trùng Khánh Group Respectively, three formations Bằ ng Ca, Tố c Tát and Đa Niêng in West Bắ c Bộ should be considered as components of the Trùng Khánh Group, though there manganiferous elements are not observed yet Đá Mài or Bắ c Sơ n, and Formations Bả n Diệ t The Bắ c Sơ n Formation was first described by Nguyễ n Văn Liêm [12] for grouping all Lower Carboniferous (Visean) - Lower Permian limestone that is widespread in North Việ t Nam, and this term became largely in use in geological language of country However, since 1925 [6] the Bắ c Sơ n name (Bacsonien) has been in use and is well known not only in Việ t Nam, but and in the world as a Quaternary unit (Holocene) by its eminent prehistoric instruments Avoiding the confusion in geological naming, the name of Carboniferous Bắ c Sơ n Formation appeared later than the one of Quaternary Bắ c Sơ n (Bacsonien), so it must be replaced by other suitable name In West Bắ c Bộ Nguyễ n Xuân Bao [75] has described two upper Paleozoic formations - the Đá Mài Formation Carboniferous - Early Permian in age, and the overlying Bả n Diệ t one Middle Permian in age The first was named after the Đá Mài limestones (Calcaire de Da May) [20] and is characterized by light grey limestone containing Visean - Early Permian Foraminifers According to the description of Nguyễ n Xuân Bao [75], the overlying Bả n Diệ t Formation is composed of two parts - shale and sandstone, effusive rocks in lower part, and limestones in the upper Lithostratigraphically, the thick lower part (shale and sandstone, and effusive rocks - 210 - 500m thick) worthy composes a formation - the Bả n Diệ t one As for the limestone part in the top, it should belong to the Đá Mài Formation, and in this case the terrigenous-effusive Bả n Diệ t Formation is as only an intercalating unit in the Đá Mài limestone Formation From above mentioned data, the Đá Mài Formation is characterized by the same light grey limestone and of the same Early Carboniferous (Visean) - Early Permian age, which are characteristics of the Bắ c Sơ n Formation Considering that the Đá Mài Formation was sooner described than the Bắ c Sơ n one, the priority belongs to the Đá Mài name, and it is the suitable name for replacing the Bắ c Sơ n name MESOZOIC UNITS Triassic Lạ ng Sơ n and Bắ c Thủ y Formations In East Bắ c Bộ , the Lạ ng Sơ n Formation was first described in the monograph “Geology of North Việ t Nam” [5] It is characterized by terrigenous beds bearing the Claraia Fauna and dated as Induan Later, in its distributive area thick members of marl and calcareous sandstone bearing the Meekoceras Fauna were found, basing on this Vũ Khúc proposed to establish the Bắ c Thủ y Formation [J5] of Olenekian age However, in the recently published Geological Map of the Lạ ng Sơ n Sheet at 1:200,000 scale [5] Lower Triassic in the An Châu Depression was described as Lạ ng Sơ n Formation containing both above said faunal assemblages We consider as more reasonable to separate these two Stratigraphie bodies into two formations, because they lithologically and paleontologically distinguish clearly from one another, and this subdivision better serves the geological mapping at 1:50,000 scale Cò Nòi and Viên Nam, Tân Lạ c Formations In West Bắ c Bộ , the Cò Nòi Formation was described in the monograph "Geology of North Việ t Nam" [5] as the lowest unit in the Mesozoic section in the Ninh Bình and Sơ n La Zones of this region But later, it has been determined as located in the Sơ n La and Thanh Hóa Zones and dated as Early Triassic, while in the Ninh Bình and Sơng Đà Zones the Triassic section begins by mafic effusives described as Viên Nam Formation of Induan age, which grades upward into teư igeno-carbonate beds of the Tân Lạ c Formation of Olenekian age Recent studies have been showing that the Tân Lạ c Formation lithologically and paleontologically is similar to the upper part of the Cò Nòi Formation, and it is not necessary to establish it This means, in the Ninh Bình and Sơng Đà Zones the Lower Triassic begins by the Viên Nam Formation which grades upward into the upper part of the Cò Nòi Formation So, the Tân Lạ c Fonnation becomes an invalid unit Khôn Làng Formation and its synonyms Lũng Trâu, Bình Liêu, Tiên n, Pị Hèn and Làng Cổ ng Formations Felsic effusives in the An Châu Depression of East Bắ c Bộ were all referred to Jurassic on the Geological Map of North Việ t Nam at 1:500,000 scale {1963) Nguyễ n Kinh Quố c et al [10] first distinguished that they are composed of two formations: one conformably underlies the Middle Triassic Nà Khuấ t Formation; another unconformably overlies it The lower corresponds to the Lũ n g Trâu Formation previously, but insufficiently described by Trị nh Thọ [3S], therefore it was redescribed by these geologists as Khôn Làng Formation of Anisian age; the upper - described as Tam Lung Formation of Late Jurassic age In the south of this depression, felsic effusives, their tuffs and terrigenous interbeds distributed in the Bình Liêu - Tiên Yên area were assigned to the Sông Hiế n Formation in the Geological Map of Việ t Nam at 1:500,000 scale (1988) During the geological mapping at 1:50,000 scale of this area Trầ n Thanh Tuyề n et al [29] proposed to limit the distribution of the above formation in the Sông Hiế n Depression, and basing on newly found Anisian fauna described these volcanogenic beds as Bình Liêu Formation Later, Trầ n Thanh Tuyề n considered that effusives in the Bình Liêu area grade upward into subvolcanic rocks, therefore they must be assigned to a subvolcanic complex - the Bình Liêu Complex At the mean time, the section composed of an intercalation of effusives and tuffaceous beds was described by him as Tiên Yên Formation, and the teư igenous beds lying beneath the Bình Liêu Complex - as Pò Hèn Formation [50] At that time, a section similar to the Tiên Yên Formation distributed in the Ba Chẽ area was described by Lê Hùng et al [Geological Ai'chives] as Làng Cổ ng Formation In our opinions, the assignment of subvolcanic rocks distributed in the Bình Liêu area to the Bình Liêu Subvolcanic Complex is a reasonable thing But, after that the remaining part can be compared with the Khôn Làng Formation which is distributed in the same geological structure, of the same lithological and petrographical composition, of the same Anisian age, although in the one or another locality it differs by the quantity of interbeds of effusives that can be regarded as intraformational change Therefore, we propose to consider the Khôn Làng Formation as valid unit, and the others Lũng Trâu, Tiên Yên, Pò Hèn and Làng Cổ ng formations as its synonyms Yên Bình Formation In the uplifted Lô-Gâm Zone, there is a small area of terrigenous sediments bearing Middle Anisian ammonoids that was formerly assigned to different stratigraphic unit: either to the Nà Khuấ t Formation [5], or to the Sông Hiế n Formation [32] But, detailed studies have been showing that these assignments are not reasonable, because the studied sediments not contain calcareous interbeds and belong to lower stratigraphic level in comparing with the Nà Khuấ t Formation, and not contain volcanogenic interbeds and belong to higher stratigraphic level in comparing with the Sông Hiế n Formation Recently, they were described as an independent stratigraphic unit - the Yên Bình Formation [34] Điề m He Formation At the base of the Nà Khuấ t Formation there is a lentiform body of black-grey, medium-bedded limestone In the Điề m He - Lùng Pa area its thickness reaches the maximum of about 200 m Apart from it, in the Nà Khuấ t Formation there is not any other interbeds of limestone Therefore, recently Đặ ng Trầ n Huyên has been proposing to establish an independent formation for this limestone - the Điề m He Formation It is reasonable, and we include it in the stratigraphic scheme Nà Khuấ t Formation and its synonyms Sơ n Dư ng, Dư ng Hull and Trạ i SŨU formations The Nà Khuấ t Formation distributed in the An Châu Depression has a stable lithological composition - terrigenous sediments with calcareous siltstone, calcareous sandstone in the lower part of the formation However, in the Geological Map of the East Bắ c Bộ Coal Basin at 1:200,000 scale Phạ m Văn Quang et al [78] established some formations - the Sơ n Dư ng, Dư ng Hư u and Trạ i Sư u formations, having the same lithological characteristics as that of the Nà Khuấ t Formation Later, geological mapping work at 1:200,000 scales in this area did not use these units, and they have been considered as synonyms of the last formation Jurassic-Cretaceous Nậ m PÔ Formation and its synonyms Nậ m Thế p and Huổ i Xa formations In the Điệ n Biên Zone of West Bắ c Bộ the continental red beds unconformably resting upon the Norian-Rhaetian coalbearing Suố i Bàng Formation were mapped on the Geological Map of North Việ t Nam at 1:500,000 scale {1963) as Nậ m Pô Formation of Early Jurassic age Later, during the geological mapping at 1:200,000 scale of the Yên Bái and Điệ n Biên Sheets Nguyễ n Vĩnh et al [/J] and Phan Sơ n et al [19] found similar beds, but distributed in the Sông Đà and the Sông Mã zones, and conformably lying on the Suố i Bàng Formation, therefore described them as Nậ m Thế p and Huổ i Xa formations In recent studies in the Điệ n Biên Zone many geologists have been observing the gradual transition between the Nậ m Pô and the underlying Suố i Bàng formations, and the similarity in lithological composition between the Nậ m Pô, Nậ m Thế p and Huổ i Xa formations According to our observations, in different zones of Northwest Việ t Nam after Early Norian the tectonic framework had no important influence in the formation of sedimentary sequences Therefore the three above formations in fact is a same, and in accordance with the law of priority the Nậ m Thế p and Huổ i Xa formations fall into synonyms of the Nậ m Pô Formation 10 Suố i Bé, Formations Văn Chân and Ngòi Thia The felsic effusives, their tuffs, interbeds of black coaly shale, coaly siltstone and lenses of motley-coloured limestone distributed in the Tú Lệ Volcanic Depression of West Bắ c Bộ were firstly described by Nguyễ n Vĩn h et al [13] as “Văn Chấ n Complex” including the Nậ m Qua, Tú Lệ and Bả n Hát formations, and dated as Late Jurassic Early Cretaceous According to these geologists it is unconformably covered and, locally, penetrated by volcanic and subvolcanic rocks of the Ngòi Thia Complex In the monograph “Geology of Việ t Nam Vol Stratigraphy” [36] the “Văn Chấ n Complex” was described as Văn Chấ n Formation and its componential formations - as its parts, because volcanites of these “formations” consist of the same orthophyre, quartz orthophyre and sedimentary beds - the same blackgrey carbonaceous shale, carbonaceous siltstone, tuffaceous rocks and lenses of limestone It is to note that the Suố i Bé Formation described by Nguyễ n Xuân Bao in the Vạ n Yên Map sheet [14] was also included in the Văn Chấ n Formation as its uppermost part, although in the Suố i Bé there are interbeds of mafic effusives In recent studies in the framework of geological mapping at 1:50,000 scale Nguyễ n Đắ c Đồ ng found leaf imprints of the Gigantopteris Flora of Late Permian age in the beds of black-grey carbonaceous shale, carbonaceous siltstone of the studied formation (unpublished yet data) Based on this finding the main part of its sedimentary beds, including limestone lenses, has been considered as of the basement of the Tú Lệ Depression, among them the carbonaceous beds containing Permian flora belong to the Yên Duyệ t Formation, limestone lenses exposed in the east margin of the depression - to the Đồ ng Giao Formation, and those exposed in the west margin - to the Mư ng Trai Formation The remaining part including the members of effusives and tuffaceous sandstone, tuffaceous siltstone can be called as “Văn Chấ n Formation”, because: 1) under this name geologists always think about volcanogenic beds, and the exclusion of flora-bearing sediments does not influence the concept on the formation; 2) Văn Chấ n is a large district where there are many sections from which we can select a good lectostratotype for the formation Other proposals, such as ‘T ú Lệ ” and “Mư ng Kim”, not conform to the Stratigraphic Codex: 1) Tú Lệ was used in different cases It was used by Nguyễ n Vĩnh for a componential formation of the Văn Chấ n Complex, but by authors of the monograph [37] for a complex including the two Văn Chấ n and Ngòi Thia formations So, this name may cause confusion in the understanding of the content of the formation; 2) Mư ng Kim is a young synonym of the Văn Chấ n Formation The Suố i Bé Formation has another, more mafic petrographical composition Therefore, it must be kept as an independent formation According to recent studies in the framework of geological mapping at 1:50,000 scale and of thematic research its distribution is not limited in the Tú Lệ Depression and, locally, erroneously described as interbeds of the Ladinian Mư ng Trai Formation According to new data it has been referred to Upper Jurassic, and is covered unconformably by the Văn Chấ n Formation The former Ngòi Thia Formation was recently assigned to a subvỏ lcanic complex Nậ m Bay Formation The continental red beds distributed in the Điệ n Biên Zone was recently described as Nậ m Bay Formation It differs from the Yên Châu Formation by the absence of interbeds of evaporite minerals,, that, possibly, shows a younger age - Early Cretaceous At present it is supposedly reíeư ed to Undifferentiated Cretaceous This paper was completed in the frame of the project Acknowledgment “Assessing the validity of stratigraphic units of Việ t Nam” (721101), funded by the Ministry of Sciences and Technology, Việ t Nam The present authors express their deep thanks to the Commission of Natural Sciences and the Commission of Earth 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đề tài “Hoàn thiệ n thang đị a tầ ng Việ t Nam” (KT 01.05)! Trung tấ m Thông tin Khoa họ c & Công nghệ Bộ Khoa họ c & Công nghệ Hà Nộ i 31 Trầ n Văn Trị , Tạ Hoàng Tinh, Phan Sơ n, Lê Đứ c An 1964 ỹ kiế n trầ m tích Paleozoi hạ vùng Thầ n Sa, Thái Nguyên (On the Lower Paleozoic sediments in the Thầ n Sa area, Thái Nguyên) Đị a chấ t 37: 6-11 25 Tố ng Duy Thanh, Vũ Khúc, Phan Cự Tiế n 1994 Quy phạ m Đị a tầ ng Việ t Nam (Stratigraphic Code of Vietnam) Cụ c Đị a chấ t Việ t Nam: 76 trang Hà Nộ i 26 Tong-Dzuy Thanh, 1993 Major features of Devonian stratigraphy in Việ t Nam with remarks on paleobiogeography J Geology, B / 1-2: 3-18 27 T rầ n Đăng Tuyế t 1994 Kiế n trúc đị a chấ t Mư ng Tè Bả n đồ ĐC (Geological structure of the Mư ng Tè area) Bả n đồ ĐC, SỐ ĐB kỷ niệ m 35 năm chuyên ngành BĐ ĐC : 207-212 Liên đoàn BĐ ĐC, Hà Nộ i 28 Trầ n Đứ c Lư ng, Nguyễ n Xuân Bao (Edit.) 1988 Bả n đồ đị a chấ t Việ t Nam tỷ lệ 1:500.000, kèm theo thuyế t minh tóm tắ t 'Geological Map of Việ t Nam at 1:500.000, with a brief explanatory note) Tổ ng cụ c MĐC, Hà Nộ i 29 Trầ n Thanh Tuyề n 2001 Characteristic M iddle Triassic section of the An Châu Depression with new data from volcano - sedim entary beds in the Bình Liêu - Hà Quả ng area (Quả ng Ninh Province) TC Đị a chấ t, A/266 : 7-12 Hà Nộ i 30 Trầ n Thanh Tuyề n, Vũ Khúc, Lư u Lân 1992 Tài liệ u mớ i điệ p Sông Hiế n vùng Bình Liêu, Tiên n (New data on the Sơng Hiế n Suite in the Bình Liêu, 32 T rầ n Văn Trị (Edit.) 1977 Đị a chấ t Việ t Nam (Phầ n Miề n Bắ c) (Geology of Việ t Nam: the North part) Nxb Khoa họ c & Kỹ thuậ t, Hà Nộ i 354 tr 33 Trầ n Văn Trị , Nguyễ n Đình Uy, Trầ n Đình Nhân, Đỗ Tuyế t 1972 Tài liệ u mớ i cấ u tạ o đị a chấ t quầ n đả o Cô Tô (New data on geological structure of the Cô Tô archipelago) (New data on geological structure of the Cô Tô archipelago) Đị a chấ t, 105:1-4 34 Vũ Khúc, 1980 Stratigrafija Triasa Vietnama Geologija i poleznye iskopaemye stran Azii, Afriki i Lat Ameriki : 34-44 Univ ỉ m Lumumby, M osh’d 35 Vũ Khúc, Đào Đình Thụ c, Lé Duy Bách, Tố ng Duy Thanh, Trầ n Tấ t Thắ ng, Trầ n Văn Trị , Trị nh Dánh 2000 Sách tra u phân vị đị a chấ t Việ t Nam (Lexicon of Geological units of Việ t Nam) Cụ c Đị a chấ t & Khoáng sả n Việ t Nam: 430 tr Hà Nộ i 36 Vũ Khúc, Bùi Phú Mỹ (Edit.) 1990 Đị a chấ t Việ t Nam I Đị a tầ ng (Geology of Việ t Nam Vol : Stratigraphy) Tổ ng cụ c Mỏ - Đị a chấ t 378 tr Hà Nộ i 37 Vũ Khúc, Trị nh Thọ 1975 Nhữ ng tài liệ u cổ sinh đị a tầ ng Triat thu thậ p đư ợ c 10 năm gầ n (1963-1972) (New Triassic paleontological and stratigraphical data collected during last decade (1963-1972)) Tuyể n tậ p CTNC ĐT : 185-243 Nxb KHKT, Hà Nộ i 13 The Journal o f GEOLOGY was first issued in 1961, as the official periodical publication o f the General Department o f Geology, at present - Department o f Geology and Minerals o f Việ t Nam The Journal has the task o f publishing research works on geosciences and mineral exploration in Việ t Nam, at the same time o f introducing new findings in geological research o f other countries in the region and worldwide, as well as activities in the geological branch and related new research methodology Every year the Journal appears in issues in Vietnamese with abstracts in English, grouped in the series A In addition, from 1993 on the Journal o f GEOLOGY has been issued annually in English, as the series B, in order to introduce to foreign readers the results o f geological and mineral researches in Việ t Nam and neighbouring areas, and scientific activities in the field o f geology which have taken place and will take place in Việ t Nam and in the world The Editorial Board o f the Journal o f GEOLOGY would like to introduce it to the readers inside and outside Việ t Nam and should be very grateful if you could send your paper and / or recommendation to the Journal, so that the Journal o f GEOLOGY could becomes more and more intimate and meets the requirements o f the readers Jo u rn al of G EO LO G Y Copyright © b y Department o f Geology and Minerals o fV iệ t Nam, Phạ m Ngũ Lão St! Hà Nộ i Việ t Nam All riẹ ìit resen ed No parr o f this publication may be produced or transmitted in any form wit hour permission Printed at the Printing Enterprise N o.15, Nguyên Hồ ng Str., Đố ng Đa, Hà Nộ i Permission o f the Publishing Department No 17HGP - BVHTT Completed at December, 2002 Tạ p chí ĐỊ A CHẤ T cụ c ĐỊ A CHẤ T & KHOÁNG SẢ N Loạ t B, Số 19-20/2002 V i ệ t NAM MỤ C LỤ C Trang Tố ng Duy T hanh, Vũ K húc Sơ đồ mớ i đị a tầ ng Paleozoi Mesozoi Bắ c B ộ Tạ Hòa Phư ng Sinh đị a tầ ng Răng nón Devon-Carbon tạ i mặ t cắ t Đồ ng Văn (Hà Giang) ! 14 T rầ n T rọ ng Hòa Phân chia đố i sánh tổ hợ p basaltoid P-T Sông Đà 22 Bùi Phú Mỹ , Trầ n Hồ ng Lĩn h, Khiế u Văn Giáp, Hồng Đình Khả m Các trầ m tích mau đỏ quầ n đả o Thổ Chu, tỉ nh Kiên G iang .7 31 Trầ n Văn Bạ n, Bountheung Phengthavongsa, Vũ Khútí, Vũ Châu, Inpong H om som bath Bồ n Mesozoi Nậ m Theun, Trung Lào: Đị a tầ ng lị ch sử phát triể n .! 35 T rầ n T uấ n Anh, T rầ n Trọ ng Hòa, Phạ m Thị Dung Granit phứ c hệ Yê Yên Sun ứ ng dụ ng minh giả i kien tạ o Kainozoi sớ m Tay Bắ c Viẹ t N a m 43 Cao Đình T riề u Vài đặ c điể m củ a điề u kiệ n đị a chấ n - kiế n tạ o chế độ đị a chấ n vùng độ ng đấ t Tuầ n G iá o 54 Nguyễ n Thị Bích Thuỷ , Siebel w , Satir M, Bùi M inh Tâm Cấ u trúc củ a zircon ng đị a thờ i U-Pb củ a tồ n tạ i mộ t móng Tiề n Cambri đớ i Đà Lạ t, Nam Việ t N am 69 Nguyễ n V ăn Vư ợ ng, Tạ T rọ ng Tháng, Vũ Văn Tích Mộ t mơ hình độ ng họ c mớ i củ a biế n ng Kainozoi dọ c đớ i trư ợ t cắ t Sông H n g 79 10 Đặ ng H uy Rằ m Mộ t số kế t nghiên u tai biế n đị a mạ o vùng ven biể n Đà Nẵ ng - Quả ng Ngãi (từ Liên Chiể u đế n Dung Q uấ t) 90 11 Nguyễ n Kim Lạ p, Đỗ Chiế n Tháng, Bùi Việ t Dũ n g, N guyễ n Lê Yêm Tai biế n đị a vậ t lý Biể n Đông biệ n pháp phòng trá n h 96 12 Nguyễ n Văn Thành, Ngô Phú An, Phùng Văn Duân, Phạ m Huy Họ c, Vư ng M nh Sơ n Số liệ u mớ i tuổ i đồ ng VỊ Rb-Sr củ a đá granitoid phứ c hệ Sông M iệ n ,7 103 THÔNG BÁO KHOA HỌ C 13 Herbert H Covert, Trị nh Dánh, Đỗ Đứ c Quang, Lê Quố c Thanh, Nguyễ n M nh Phi Phát hiệ n mớ i hoá thạ ch độ ng vậ t có xư ng số ng Pleistocen thành tạ o lấ p đẩ y khe nứ t ỏ Ninh Bình, Việ t Nam 109 ... contain calcareous interbeds and belong to lower stratigraphic level in comparing with the Nà Khuấ t Formation, and not contain volcanogenic interbeds and belong to higher stratigraphic level in. .. geosciences and mineral exploration in Việ t Nam, at the same time o f introducing new findings in geological research o f other countries in the region and worldwide, as well as activities in the... valid stratigraphic units are introduced, as for the change of the unit name and the explanation of assessing these names, and the description of new units they will be presented in detail in the