HA NOI NATIONAL UNIVERSITY PUBLISHING HOUSE

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1 Stratigraphic Units of Viet Nam Authors 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 Tat Thang, Tran Van Tri, Trinh Van Long Edited by Tong-Dzuy Thanh, Vu Khuc HA NOI NATIONAL UNIVERSITY PUBLISHING HOUSE 517

2 PREFACE CONTENT Chapter 1. SEDIMENTARY BASINS IN THE GEOLOGICAL EVOLUTION OF VIET NAM [Tran Van Tri, Tong-Dzuy Thanh, Vu Khuc] Archean megacycle 5 Paleoproterozoic Early Neoproterozoic megacycle 6 Neoproterozoic Middle Paleozoic megacycle 7 Late Paleozoic Mesozoic megacycle 12 Late Mesozoic Cenozoic megacycle 15 page 3 5 Chapter 2. PRECAMBRIAN 26 BAC BO REGION (North Viet Nam) 26 Song Hong Group [Tran Tat Thang] 26 Nui Con Voi Formation (AR? nv ) 27 Ngoi Chi Formation (AR? nc) 29 Xuan Dai Group [Tran Tat Thang] 30 Suoi Chieng Formation (PP sc ) 30 Sin Quyen Formation (PP sq ) 31 Nam Su Lu Formation (MP nl) 33 Sa Pa Group [Tran Tat Thang] 34 Cha Pa Formation (NP cp) 34 Da Dinh Formation (NP dd) 35 Song Chay Group [Tran Tat Thang] 35 Thac Ba Formation (NP tb) 36 An Phu Formation (NP-ε 1? ah) 37 Nam Co Formation (NP nc) 37 NORTH TRUNG BO REGION (North Central Viet Nam) 39 Bu Khang Formation (NP bk) [Tran Tat Thang] 39 CENTRAL TRUNG BO REGION (Mid Central Viet Nam) 40 Kan Nack Group [Trinh Van Long] 40 Kon Cot Formation (NA-PP kc) 41 Xa Lam Co Formation (NA-PP xc) 43 Dak Lo Formation (NA-PP dl) 45 Kim Son Formation (NA-PP ks)

3 Song Re Group [Trinh Van Long] 48 Son Ky Formation (PP sk) 49 Ba Dien Formation (PP bd) 51 Dak Mi Formation (MP dm) 53 Po Co Group [Trinh Van Long] 55 Dak Long Formation (NP dl) 56 Chu Se Formation (NP-ε 1 cs) 56 Song Tranh Group [Trinh Van Long] 57 Tra Don Formation (NP td) 58 Tra Tap Formation (NP tt) 59 Nuoc Lah Formation (NP-ε 1 nh) 61 Nui Vu Group [Trinh Van Long] 62 Son Thanh Formation (NP st) 63 Nuoc Lay Formation (NP-ε 1 nl) 64 Chapter 3. LOWER PALEOZOIC 67 BAC BO REGION (North Viet Nam) 70 EAST BAC BO 70 CAMBRIAN 70 Ha Giang Formation (ε 2 hg) [Pham Kim Ngan] 70 Than Sa Formation (ε 3 ts) [Pham Kim Ngan, Tong-Dzuy Thanh] 72 Chang Pung Formation (ε 3 cp) [Pham Kim Ngan] 76 ORDOVICIAN 80 Lutxia Formation (O 1 lx) [Pham Kim Ngan] 80 Na Mo Formation (O 2-3 nm) [Pham Kim Ngan] 82 ORDOVICIAN - SILURIAN 83 Phu Ngu Formation (O-S pn) [Tran Huu Dan] 83 Co To Formation (O-S ct) [Tran Huu Dan] 86 Tan Mai Formation (O-S tm) [Tran Huu Dan] 88 SILURIAN 90 Kien An Formation (S 3 kn) [Ta Hoa Phuong, Tong-Dzuy Thanh] 90 WEST BAC BO 92 CAMBRIAN 92 Cam Duong Formation (ε 1 cd) [Tran Huu Dan] 92 Song Ma Formation (ε 2 sm) [Tran Huu Dan] 94 CAMBRIAN - ORDOVICIAN 97 Ham Rong Formation (ε 3 -O 1 hr) [Tran Huu Dan] 97 Ben Khe Formation (ε-o 1 bk) [Tran Huu Dan] 100 ORDOVICIAN 102 Dong Son Formation (O 1 ds) [Tran Huu Dan] 102 ORDOVICIAN - SILURIAN 104 Sinh Vinh Formation (O - S sv) [Tran Huu Dan, Tong-Dzuy Thanh]

4 Bo Hieng Formation (S 2 bh) [Ta Hoa Phuong) 106 VIET-LAOS REGION (Extreme West Bac Bo and North Trung Bo) 109 ORDOVICIAN-SILURIAN 109 Song Ca Formation (O 3 -S sc) [Pham Kim Ngan] 109 Long Dai Formation (O-S ld) [Tran Huu Dan] 111 Dai Giang Formation (S 2 dg) [Nguyen Huu Hung] 114 (Mid Central Viet Nam) 116 CAMBRIAN - SILURIAN 116 A Vuong Formation (ε 2 -O 1 av) [Tran Huu Dan] 116 Phong Hanh Formation (ε-s? ph) [Pham Huy Thong] 118 Chapter 4. MIDDLE PALEOZOIC 120 (Devonian Units) BAC BO REGION (North Viet Nam) 120 LOWER DEVONIAN 120 Song Cau Group (D 1 sc) [Tong-Dzuy Thanh, Ta Hoa Phuong] 121 Si Ka Formation (D 1 sk) 121 Bac Bun Formation (D 1 bb) 124 Ban Thang Formation (D 1? bt) [Ta Hoa Phuong] 126 Song Mua Formation (D 1 sm) [Tong-Dzuy Thanh, Ta Hoa Phuong] 127 Nam Pia Formation (D 1 np) [Tong-Dzuy Thanh] 129 Mia Le Formation (D 1 ml) [Tong-Dzuy Thanh] 131 Ban Nguon Formation (D 1 bn) [Tong-Dzuy Thanh] 134 Ta Khoa Formation (D 1 tk) [Tong-Dzuy Thanh] 136 LOWER-UPPER DEVONIAN 138 Khao Loc Formation (D 1 -D 2 kl ) [Ta Hoa Phuong] 138 Duong Dong Formation (D 1 - D 2 e dd) [Nguyen Huu Hung] 140 Ban Pap Formation (D 1 p-d 3 fr bp) [Tong-Dzuy Thanh, Ta Hoa Phuong] 142 Tan Lap Formation (D 2 g-d 3 fr? tl) [Nguyen Huu Hung] 150 Do Son Formation (D 2 gv -? D 3 fr ds) [Tong-Dzuy Thanh, Ta Hoa Phuong] 152 MIDDLE-UPPER DEVONIAN LOWER CARBONIFEROUS 156 Trung Khanh Group 154 Bang Ca Formation (D 2 gv-d 3 fr bc) [Ta Hoa Phuong, Tong-Dzuy Thanh] 155 Toc Tat Formation (D 3 fr-c 1 t tt) [Ta Hoa Phuong] 157 Lung Nam Formation (C 1 t-v ln) [Doan Nhat Truong] See Chapter 5, page 206 Da Nieng Formation (C 1 dn) [Doan Nhat Truong]. See Chapter 5, page 207 Trang Kenh Formation (D 2 gv-d 3 fm tk) [Nguyen Huu Hung] 161 VIET-LAOS REGION (Extreme West Bac Bo and North Central Viet Nam) 164 LOWER-MIDDLE PALEOZOIC 164 Nam Cuoi Complex (PZ 1-2 nc) [Nguyen Huu Hung] 164 LOWER-MIDDLE DEVONIAN 166 A Choc Formation (D 1 ah) [Nguyen Huu Hung]

5 Tay Trang Formation (D 1 - D 2? tt) [Tong-Dzuy Thanh, Pham Huy Thong] 167 Rao Chan Formation (D 1 rc) [Nguyen Huu Hung] 170 Ban Giang Formation (D 1 -D 2 e bg) [Nguyen Huu Hung] 172 Huoi Loi Formation (D 1-2 hl) [Nguyen Huu Hung] 173 Muc Bai Formation (D 2 gv mb) [Nguyen Huu Hung] 175 MIDDLE-UPPER DEVONIAN 178 Nam Can Formation (D 2 gv-d 3 nc) [Nguyen Huu Hung] 178 Dong Tho Formation (D 2 gv-d 3 fr dt) [Tong-Dzuy Thanh, Nguyen Huu Hung] 180 Thien Nhan Formation (D 3 tn) [Tran Van Tri] 183 Ngoc Lam Formation (D 3 fr nl) [Pham Huy Thong] 184 Xom Nha Formation (D 3 xn) [Nguyen Huu Hung] 184 MIDDLE DEVONIAN - LOWER CARBONIFEROUS 187 Tan Lam Formation (D 2 gv-c 1 tl) [Nguyen Huu Hung] 187 Phong Son Formation (D 3 -C 1 ps) [Nguyen Huu Hung] 192 Co Bi Formation (D? cb) [Nguyen Huu Hung] 195 CENTRAL TRUNG BO REGION (Mid Central Viet Nam) 196 Cu Brei Formation (D 1 cb) [Tong-Dzuy Thanh] 196 NAM BO REGION (South Viet Nam) 198 DEVONIAN 198 Hon Heo Formation (D? hh) [Nguyen Huu Hung] 198 Chapter 5. UPPER PALEOZOIC 201 BAC BO REGION (North Viet Nam) 201 UPPER DEVONIAN - LOWER CARBONIFEROUS 201 Con Voi Formation (D 3 fm-c 1 cv) [Doan Nhat Truong] 201 Pho Han Formation (D 3 fm-c 1 ph) [Doan Nhat Truong] 204 LOWER CARBONIFEROUS 206 Lung Nam Formation (C 1 t-v ln) [Doan Nhat Truong] 206 Da Nieng Formation (C 1 dn) [Doan Nhat Truong] 207 LOWER CARBONIFEROUS - PERMIAN 210 Da Mai Formation (C-P 2 dm) [Doan Nhat Truong, Tong-Dzuy Thanh] 210 PERMIAN 215 Dong Dang Formation (P 3 dd) [Doan Nhat Truong] 215 Ban Diet Formation (P 1 bd) [Doan Nhat Truong] 218 Cam Thuy Formation (P 3 ct) [Doan Nhat Truong] 220 Yen Duyet Formation (P 3 yd) [Doan Nhat Truong] 222 Vien Nam Formation (P 3 vn) [Tong Duy Thanh, Vu Khuc, Dang Tran Huyen] 224 Bai Chay Formation (P 3 bc) [Doan Nhat Truong] 226 VIET-LAOS REGION (Extreme West Bac Bo and North Trung Bo) 229 LOWER CARBONIFEROUS 229 La Khe Formation (C 1 lk) [Doan Nhat Truong]

6 LOWER CARBONIFEROUS - PERMIAN 232 Da Mai Formation (C-P 2 dm) [Doan Nhat Truong, Tong-Dzuy Thanh] 232 UPPER PERMIAN 233 Cam Lo Formation (P 3 cl) [Doan Nhat Truong] 233 PERMIAN-TRIASSIC 234 Song Da Complex (P-T 2 sd) [Doan Nhat Truong] 234 SOUTH TRUNG BO AND NAM BO REGIONS 236 UPPER CARBONIFEROUS - PERMIAN 236 Dak Lin Formation (C 3 -P 1 dl) [Pham Huy Thong] 236 PERMIAN 237 Ha Tien Formation (P 1-2 ht) [Doan Nhat Truong] 237 Ta Not Formation (P 3 tn) [Doan Nhat Truong] 240 Hon Quan Formation (P 3 hq) [Doan Nhat Truong] 241 Dat Do Formation (P 3 dd) [Nguyen Huu Hung] 241 PERMIAN - TRIASSIC 243 Chu Prong Formation (P 3 - T 1 cp) [Pham Huy Thong] 243 Chapter 6. MESOZOIC 245 PRE-NORIAN TRIASSIC 245 BAC BO REGION (North Viet Nam) 245 EAST BAC BO [Dang Tran Huyen] 245 LOWER TRIASSIC 246 Song Hien Formation (T 1 sh) 246 Hong Ngai Formation (T 1 hn) 248 Lang Son Formation (T 1 i ls) 251 Bac Thuy Formation (T 1 o bt) 253 MIDDLE TRIASSIC 257 Khon Lang Formation (T 2 a kl) 257 Lan Pang Formation (T 2 a lp) 260 Yen Binh Formation (T 2 a yb) 262 Diem He Formation (T 2 a dh) 261 Na Khuat Formation (T 2 nk) 264 UPPER TRIASSIC 267 Mau Son Formation (T 3 c ms) 267 WEST BAC BO 269 LOWER TRIASSIC [Vu Khuc] 270 Co Noi Formation (T 1 cn) 270 MIDDLE TRIASSIC 273 Dong Giao Formation (T 2 a dg) 273 Nam Tham Formation (T 2 l nt) 276 Muong Trai Formation (T 2 l mt) 277 MIDDLE-UPPER TRIASSIC

7 Song Boi Formation (T 2 l-t 3 c sb) 279 Lai Chau Formation (T 2 l-t 3 c lc) 281 UPPER TRIASSIC 282 Nam Mu Formation (T 3 c nm) 282 Pac Ma Formation (T 3 c pm) 283 TRUNG BO REGION (Central Viet Nam) [Dang Tran Huyen] 285 VIET-LAOS AREA (Extreme West Bac Bo and North Trung Bo) 285 MIDDLE TRIASSIC 286 Dong Trau Formation (T 2 a dt) 286 Hoang Mai Formation (T 2 a hm) 288 Quy Lang Formation (T 2 l ql) 290 CENTRAL TRUNG BO AND SOUTH TRUNG BO REGIONS 292 MIDDLE TRIASSIC 292 Mang Yang Formation (T 2 a my) [Vu Khuc] 292 NAM BO REGION 295 EAST NAM BO 295 LOWER TRIASSIC 295 Song Sai Gon Formation (T 1 sg) [Vu Khuc] 295 MIDDLE TRIASSIC 296 Chau Thoi Formation (T 2 a ct) [Vu Khuc] 296 WEST NAM BO AND GULF OF THAILAND 298 LOWER TRIASSIC 298 Hon Đuoc Formation (T 1? hd) [Dang Tran Huyen] 298 MIDDLE TRIASSIC [Dang Tran Huyen] 300 Hon Ngang Formation (T 2 a hn) 300 Minh Hoa Formation (T 2 a mh) 302 Tay Hon Nghe Formation (T 2 l tn) 303 NORIAN - MIDDLE JURASSIC 304 BAC BO REGION (North Viet Nam) 304 EAST BAC BO 304 NORIAN-RHAETIAN 304 Van Lang Formation (T 3 n-r vl) [Dang Tran Huyen] 304 Hon Gai Formation (T 3 n-r hg) [Dang Tran Huyen] 306 LOWER-MIDDLE JURASSIC 310 Ha Coi Formation (J 1-2 hc) [Vu Khuc] 310 WEST BAC BO 313 NORIAN-RHAETIAN 313 Suoi Bang Formation (T 3 n-r sb) [Vu Khuc] 313 LOWER JURASSIC 317 Nam Po Formation [Vu Khuc] 317 TRUNG BO REGION (Central Viet Nam) 319 VIET-LAOS AREA

8 NORIAN-RHAETIAN 319 Dong Do Formation (T 3 n-r dd) [Vu Khuc] 319 CENTRAL TRUNG BO AREA (Mid Central Viet Nam) 321 NORIAN-RHAETIAN 321 Nong Son Group (T 3 n-r ns) [Vu Khuc] 321 An Diem Formation (T 3 n ad) 322 Suon Giua Formation (T 3 r sg) 323 LOWER-MIDDLE JURASSIC 324 A Ngo Formation (J 1-2 ag) [Dang Tran Huyen] 324 Tho Lam Group (J 1-2 tl) [Vu Khuc] 326 Ban Co Formation (J 1 h bc) 326 Khe Ren Formation (J 1 s-t kr) 328 Huu Chanh Formation (J 2 hc) 329 Bai Dinh Formation (J 1-2 bd) [Vu Khuc] 330 Binh Son Formation (J 1-2 bs) [Vu Khuc] 331 SOUTH TRUNG BO AND EAST NAM BO REGIONS 332 LOWER-MIDDLE JURASSIC 332 Ban Don Group (J 1-2 bd) [Vu Khuc] 332 Dak Bung Formation (J 1 h db) 333 Dak Krong Formation (J 1 s-t dk) 335 Ma Da Formation (J 2 a-bj md) 338 Song Phan Formation (J 2 bj-bt sp) 340 Ea Sup Formation (J 2 es) [Vu Khuc] 340 WEST NAM BO AND GULF OF THAILAND REGIONS 342 LOWER-MIDDLE JURASSIC 342 Ta Pa Formation (J 1-2 tp) [Dang Tran Huyen] 342 UPPER JURASSIC - CRETACEOUS [Vu Khuc] 344 BAC BO REGION (North Viet Nam) 344 EAST BAC BO 345 UPPER JURASSIC 345 Tam Lung Formation (J 3 tl) 345 CRETACEOUS 346 Ban Hang Formation (K bh) 346 WEST BAC BO 348 UPPER JURASSIC - LOWER CRETACEOUS 348 Tu Le Formation (J 3 -K 1 tl) 348 CRETACEOUS 350 Yen Chau Formation (K 2 yc) 350 Nam Ma Formation (K nm) 351 TRUNG BO REGION (Central Viet Nam) 352 VIET-LAOS AREA 353 UPPER JURASSIC LOWER CRETACEOUS

9 Muong Hinh Formation (J 3 mh) 353 Mu Gia Formation (J 3 -K 1 mg) 354 SOUTH TRUNG BO AND EAST NAM BO REGIONS 356 JURASSIC 356 Deo Bao Loc Formation (J 3 dl) 356 CRETACEOUS 359 Dak Rium Formation (K 1 dr) 359 Don Duong Formation (K 2 dd) 360 Nha Trang Formation (K nt) 361 WEST NAM BO AND GULF OF THAILAND REGIONS 362 CRETACEOUS 363 Phu Quoc Formation (K pq) 363 Chapter 7. CENOZOIC 367 TERTIARY ON THE MAINLAND 369 BAC BO REGION (North Viet Nam) 369 EAST BAC BO 369 PALEOGENE 369 Dong Ho Formation (E 2 dh) [Tong-Dzuy Thanh, Nguyen Dich Dy] 369 Cao Lang Group (E 2 -E 2 3 cl) [Tong-Dzuy Thanh, Nguyen Dich Dy] 371 Cao Bang Formation (E 2 cb) 372 Na Duong Formation (E 1 3 nd) 374 Rinh Chua Formation (E 2 3 rc) 376 NEOGENE 378 Tieu Giao Formation (N tg) [Tong-Dzuy Thanh, Nguyen Dich Dy] 378 RED RIVER TROUGH 380 PALEOGENE 380 Van Yen Formation (E 2 vy) [Vu Khuc, Nguyen Dich Dy] 380 Co Phuc Formation (E 3 cp) [Vu Khuc, Nguyen Dich Dy] 381 NEOGENE 381 Au Lau Formation (N 1 al) [Vu Khuc, Nguyen Dich Dy] 381 HA NOI DEPRESSION (North of the Red River Basin) [Do Bat] 383 PALEOGENE 383 Phu Tien Formation (E 2 pt) 383 Dinh Cao Formation (E 3 dc) 384 NEOGENE 385 Phong Chau Formation (N 1 1 pch) 385 Phu Cu Formation (N 2 1 pc) 386 Tien Hung Formation (N 3 1 th) 388 Vinh Bao Formation (N 2 vb) 390 WEST BAC BO [Vu Khuc, Nguyen Dich Dy] 391 PALEOGENE

10 Pu Tra Formation (E 2 pt) 391 Nam Un Formation (E 3 nn) 392 Nam Bay Formation (E 3 nb) 393 PALEOGENE - NEOGENE 394 Hang Mon Formation (E 3 -N hm) 394 NORTH TRUNG BO REGION (N of Central Viet Nam) [Vu Khuc, Nguyen Dich Dy] 396 PALEOGENE - NEOGENE 396 Khe Bo Formation (E 3 - N kb) 396 NEOGENE 397 Dong Hoi Formation (N 3 1 dh) 397 Sam Son Formation (N 2 ss) 398 Thach Han Formation (N 2 th) 399 SOUTH TRUNG BO REGION (South Central Viet Nam) 400 TAY NGUYEN HIGHLAND AREA [Nguyen Dich Dy, Vu Khuc] 400 PALEOGENE 400 Song Ba Formation (E 3 sb) 400 Kon Tum Formation (N 1 kt) 401 LAM DONG AREA [Nguyen Dich Dy, Vu Khuc] 403 PALEOGENE - NEOGENE 403 Di Linh Formation (E 3 -N 1 dl) 403 COASTAL AREA [Vu Khuc, Nguyen Dich Dy] 404 NEOGENE 404 Song Luy Formation (N 2 sl) 404 EAST NAM BO REGION (E of South Viet Nam) [Vu Khuc, Nguyen Dich Dy] 405 NEOGENE 406 Binh Trung Formation (N 3 1 bt) 406 Nha Be Formation (N 1 2 nb) 406 Ba Mieu Formation (N 2 2 bm) 407 WEST NAM BO REGION (W of South Viet Nam) [Vu Khuc, Nguyen Dich Dy] 407 NEOGENE 408 Ben Tre Formation (N 2 1 bt) 408 Phung Hiep Formation (N 3 1 ph) 408 Can Tho Formation (N 1 2 ct) 410 Nam Can Formation (N 2 2 nc) 410 TERTIARY ON THE CONTINENTAL SHELF 412 NORTH OF THE BAC BO GULF 412 PALEOGENE 412 Bach Long Vi Formation (E 3 blv) [Vu Khuc, Nguyen Dich Dy] 412 HUE - QUANG NGAI DEPRESSION (South of Song Hong Basin) [Do Bat] 414 PALEOGENE 414 Bach Tri Formation (E 3 bt)

11 NEOGENE Song Huong Formation (N 1 sh) 415 Tri Ton Formation (N 2 1 tt) 416 Quang Ngai Formation (N 3 1 qn) 418 Bien Dong Formation (N 2 bd) 419 CUU LONG BASIN [Do Bat] 420 PALEOGENE 420 Ca Coi Formation (E 2 cc) 420 Tra Cu Formation (E 1 3 tc) Tra Tan Formation (E 3 tt) 423 NEOGENE 424 Bach Ho Formation (N 1 1 bh) 424 Con Son Formation (N 2 1 cs) Dong Nai Formation (N 1 dn) 428 Bien Dong Formation (N 2 bd) 429 SOUTH CON SON BASIN [Do Bat] 431 PALEOGENE 431 Cau Formation (E 3 c) 431 NEOGENE 434 Dua Formation (N 1 1 d) 434 Thong - Mang Cau Formation (N 2 1 tc) Nam Con Son Formation (N 1 ns) 438 Bien Dong Formation (N 2 bd) 439 MALAYA - THO CHU BASIN (SW Vietnamese continental shelf) [Do Bat] 441 PALEOGENE 441 Kim Long Formation (E 3 kl) 441 NEOGENE 443 Ngoc Hien Formation (N 1 1 nh) 443 Dam Doi Formation (N 2 1 dd) 444 Minh Hai Formation (N 3 1 mh) 445 Bien Dong Formation (N 2 bd) 446 REFERENCES 448 INDEX OF STRATIGRAPHIC UNITS 474 INDEX OF GEOGRAPHIC NAMES AND GEOLOGISTS 483 CONTENT

12 528 PREFACE The geology of Viet Nam s territory has been regularly studied for over a century, during which nearly research works on the geology of Viet Nam were published. Important successes in stratigraphy have been achieved, which play the key role in understanding the structure and geological history of the country s bedrock. In the twentieth century over 500 stratigraphic unit names have been published or proposed, and a lot of them became popular in the Vietnamese geological language. Before the 50 s of the last century stratigraphic research was carried out by French and other foreign geologists, who used different styles. At that time a great number of stratigraphic units were described using different stratigraphic conceptions. The stratigraphic terms have rapidly increased more recently, when geological mapping at 1/ and 1/ was carried out. Though the Stratigraphic Code of Viet Nam has been approved and published (1994) many junior Vietnamese geologists understood the lithological properties of the lithostratigraphic unit as rigid and usually describe a new unit and use a new term, although there is only a facies change of a previously defined unit. As a result, the number of stratigraphic terms increased rapidly resulting in an unduly complicated picture. In this situation, an assessment of the validity of Viet Nam s stratigraphic units becomes pressing, and a revision of Viet Nam s stratigraphic units, including those of the continental shelf and the subsurface on the mainland, is presented in this work. The Quaternary sediments are distinguished by their special characteristics, and many units were described, but there still are disagreements on the principles of their division in Viet Nam. They should be dealt with in another work. Therefore in the Stratigraphic units of Viet Nam the units from Precambrian to Neogene are dealt with, but Quaternary sediments will be described only in the Neogene - Quaternary units. According to the Stratigraphic Code of Viet Nam (1994) effusive bodies are not described as stratigraphic units if there are no sedimentary interbeds in their sequences. However, there are, in fact, bedded effusive bodies situated in clearly stratigraphic sequences, and having clear relations with the adjacent units. In following the regulation of the Stratigraphic Code of Viet Nam, they will be described as stratigraphic units in this work. In former works stratigraphic units from oldest to youngest were usually described in the frame of the regions determined in accord with present geological structure. The territory of Viet Nam includes the mainland and the vast marine shelf belonging to different geological structural units. In the historical development of regional geology the structural units have changed, and there are no stable units through all geological periods for tens and hundreds of millions of years. For this reason, in the Stratigraphic units of Viet Nam the regional division for the stratigraphic description is not fixed through all great stratigraphic intervals, but each has its own scheme. In general the scheme of

13 the regional division is based on the paleobasin analysis presented in chapter 3, but each scheme has its distinguishing features according to the characteristics of the units. At present there are many problems in the stratigraphy of the country that are debated in geological circles. For the main problems the editor has referred to the Stratigraphic Code of Viet Nam and resolved them on the basis of new materials gathered by other geologists. In some acute cases the editor and concerned colleagues carried out field investigations for finding the best resolution. Nevertheless many new problems are expected that will need detailed studies in the near future. For instance, the case of the Ta Khoa, Ngoc Lam formations, and Nam Cuoi Complex, as well as many effusive - sedimentary formations etc. Authors of this monograph are geologists from different research institutions of Viet Nam, and they are as follows. Chapter 1 (Sedimentary paleobasins) Tran Van Tri (TVT), Tong-Dzuy Thanh (TDT), and Vu Khuc (VK); Chapter 2 (Precambrian) Tran Tat Thang (TTT), Trinh Van Long (TVL); Chapter 3 (Lower Paleozoic) Pham Kim Ngan (PKN), Tran Huu Dan (THD), Ta Hoa Phuong (THP), Tong-Dzuy Thanh, Nguyen Huu Hung (NHH), and Pham Huy Thong (PHT); Chapter 4 (Devonian) Tong-Dzuy Thanh, Nguyen Huu Hung (NHH), Ta Hoa Phuong (THP), Pham Huy Thong (PHT), and Tran Van Tri (TVT); Chapter 5 (Upper Paleozoic) Doan Nhat Truong (DNT), Tong-Dzuy Thanh; Chapter 6 (Mesozoic) Vu Khuc, Dang Tran Huyen (DTH). Chapter 7 (Cenozoic) Tertiary Units on mainland and on the Bach Long Vi Island were described by Vu Khuc (VK), Tong-Dzuy Thanh (TDT) and Nguyen Dich Dy (NDD) based on materials of Trinh Danh, Tran Dinh Nhan, Nguyen Dich Dy, Pham Quang Trung and others, which have been published or stored in Archives (see References); Do Bat (DB) described Tertiary Units on continental shelf and subsurface units on mainland. The Content, Index of geographic and geologist names, and Index of stratigraphic names were compiled by Tong-Dzuy Thanh and Vu Khuc. The detailed author index of items in each chapter will be indicated in the Contents by the abbreviation of the author names as shown above. The monograph Stratigraphic units of Viet Nam is an improved work of the Research Project KT ( ) led by Tong-Dzuy Thanh. It includes materials of the authors carried out over many years in their research and that of colleagues published at home and abroad, and some materials conserved in the geological Archives are also referred to. The manuscript was accomplished in the framework of the Fundamental Research Program (Project Assessing the validity of stratigraphic units of Vietnam led by Tong-Dzuy Thanh). The realization of this Project and the accomplishment of the manuscript was supported by the Council for Natural Sciences, the Council of Earth Sciences, the College of Natural Sciences (Vietnam National University, Ha Noi), and the Department of Geology & Mineral Resources of Viet Nam. The authors are deeply grateful for the valuable support of the named organizations. Manuscript was written in Vietnamese and edited by Tong-Dzuy Thanh (Viet Nam National University, Ha Noi); Vu Khuc (Viet Nam Paleontological Association) edited the parts on Mesozoic and Cenozoic, the English version was translated by Vu Khuc, Tong-Dzuy Thanh, and Trinh Van Long. The authors express their deep acknowledgement to Prof. A. Boucot 529

14 (Oregon State University, USA) for his work editing the English text, to Boucot and Dr Janvier Ph. for their help in improving this monograph. Prof. Tong-Dzuy Thanh 530