Cretaceous Research (2000) 21, 23–33
doi:10.1006/cres.2000.0199, available online at http://www.idealibrary.com on
Cretaceous palaeogeography of Tibet and
adjacent areas (China): tectonic implications
K. J. Zhang
Department of Earth Sciences, Nanjing University, Nanjing 210093, China
Revised manuscript accepted 14 December 1999
During the Berriasian–Early Barremian, littoral facies were present only on the southern half of the Qiangtang block and the
central Lhasa block. In the Late Barremian–Albian, neritic deposits were preserved in the northern Lhasa block, and a littoral
environment dominated southern Qiangtang, southwesternmost Tarim, and southern Lhasa. In the Early Cretaceous, the
rest of Tibet, including Qaidam, the majority of Tarim and western Qiangtang, Songpan-Ganzi, and the Longmenshan
Mountains, may have been uplifted, because only coarse continental deposits are preserved in these areas. In the Late
Cretaceous, a littoral environment predominated in Tarim, southern Qaidam, westernmost and southern Qiangtang, the
western part of the Sichuan Basin, and Lhasa. Meanwhile, western Qiangtang and Songpan-Ganzi were elevated but the
latter not more than 1000 m in the Eocene. These facts indicate that during the Late Cretaceous the topographic relief of
Tibet, including the present Longmenshan Mountains and Songpan-Ganzi, may have been a rather low peneplain, close to
sea level, and that Tibet was intensively elevated after the end of the Cretaceous, its high topography only being the product
of the Indo-Asian collision. During the Cretaceous, Tibet and adjacent areas generally were under the influence of a gradual
transgression although in southern Tibet a major transgression took place during the Late Barremian–Albian. This fact, and
the presence of a thick, widespread, Upper Barremian–Albian inner shelf limestone in northern Lhasa, suggests that southern
Tibet underwent intensive back-arc extension deformation during the late Early Cretaceous.
2000 Academic Press
K W: Tibet; Cretaceous; sedimentary facies; palaeogeography; back-arc extension.
1. Introduction
Tibet has long been recognized as a locus of
continental collision and accretion since the early
Mesozoic (e.g., Allegre et al., 1984; Chang et al., 1986;
Dewey et al., 1988). The Cretaceous Period was an
important time in the tectonic evolution of Tibet and
in the development of the Tibetan plateau. During the
Early Cretaceous, the Qiangtang block (Figure 1)
is believed to have been colliding with the Lhasa
block (e.g., Murphy et al., 1997), and in the latest
Cretaceous, the Indian continental plate may have
begun to make contact with the Lhasa block (Beck
et al., 1995). It has been speculated that the Lhasa
block was elevated before its collision with India after
the Late Cretaceous (England & Searle, 1986; Dewey
et al., 1988). Furthermore, mainly on the basis of a
traverse through the central Lhasa block, Murphy
et al. (1997) even suggested that the southern Tibetan
plateau had attained an elevation of 3–4 km by
c. 99 Ma and maintained significant topography until
the onset of the Indo-Asian collision. They considered
this to be a result of the collision between the Lhasa
and Qiangtang blocks during the Early Cretaceous.
0195–6671/00/010023+11 $35.00/0
Previous studies have focused mainly on the
petrology of the volcanics and the deformation of
the sedimentary cover, and concentrated on areas near
the Qinghai-Xizang and Xinjiang-Xizang highways.
An alternative source of data lies in the sedimentary
sequences, which possess the singular advantage
that they contain a vertically stacked and relatively
undeformed record of erosion and sedimentation and
therefore form a vital approach to testing and refining
the models of tectonic evolution (Carroll et al., 1995;
Zhang, 1997; Zhang et al., 1998).
This study attempts to reconstruct the geography of
the region during the Cretaceous Period, and to
provide a basis for evaluating former hypotheses or
even evolving an alternative hypothesis, for the
tectonic evolution of Tibet. Data on Cretaceous
sedimentary strata west of 92E were accumulated
mainly during field mapping at a scale of 1:50 000
during the summers of 1993–1998 by hundreds of
Chinese workers sponsored by the General Oil and
Gas Corporation of China. The results of other
Chinese investigations of recent years are also incorporated here. Although preliminary in nature, the
2000 Academic Press
24
K. J. Zhang
Figure 1. Sketch tectonic map of eastern Asia, revised after Sengor (1990) and Zhang (1997, in press). Main sutures or
faults: a, Altyan fault zone; b, Banggonghu–Nujiang suture; j, Jinsajiang suture; k, Kunlun suture; l, Longmenshan fault
zone; qi, Qilian suture; qn, Qinling suture; t, Tanlu fault zone; ts, Tianshan suture; y, Yarlung Zangbo suture; ys,
Yinshan suture. The divide between Cathaysia and Gondwana follows CIGMR & SCGR (1992) and Zhang et al.
(1998). The dashed line represents the extent of the Tibetan plateau.
data presented provide a starting point for more
comprehensive future studies.
2. Tectonic framework of Tibet
The Tibetan plateau represents a major part of the
Tethyan orogenic collage (Sengor, 1990) (Figure 1).
The Yarlung Zangbo suture marks the boundary
between the Tibetan Himalayas of the Indian continental plate to the south and the Lhasa block to the
north. It is generally believed that the Lhasa block was
separated from Gondwana around Triassic/Jurassic
boundary times (e.g., Allegre et al., 1984; Searle et al.,
1987; Dewey et al., 1988). The Neo-Tethys formed
between the Lhasa block and the Indian plate, beginning with a rift-stage during the Triassic. During the
Jurassic and Cretaceous, a relatively wide passive
continental margin existed along the northern rim of
the Indian plate (Liu & Einsele, 1994). However,
Carboniferous calc-alkaline volcanic rocks near Lhasa
(Pearce & Mei, 1988) indicate that the Neo-Tethys
could have been active much earlier than is popularly
favoured. During the latest Cretaceous and earliest
Tertiary, the Indian plate collided with the amalgamated Eurasian plates. After the collision, northward
indentation of India since about 40 Ma caused about
2000 km of crustal shortening, giving rise to the
largest plateau on our planet (e.g., Allegre et al., 1984;
Chang et al., 1986; Dewey et al., 1988).
The Lhasa block is bounded to the north by the
Banggonghu–Nujiang suture and the Qiangtang block
(Figure 1). These two narrow, elongate blocks are
predominantly continental and now form parts of
the Eurasian plate, but during the Palaeozoic they
belonged to the Gondwanan supercontinent (Liu &
Einsele, 1994) because voluminous tillites and glaciomarine faunas and Glossopteris floras of late Palaeozoic
age have been reported from them (CIGMR &
SCGR, 1992; Zhang, 1998). The Tethys branch
between the Lhasa and Qiangtang blocks was open by
about the Late Triassic (Allegre et al., 1984; Dewey
et al., 1988) and closed along the Banggonghu–
Nujiang suture during the Late Jurassic (Girardeau
et al., 1984; Chang et al., 1986). However, the subduction polarity data are ambiguous (Allegre et al.,
1984; Dewey et al., 1988; Yu & Wang, 1990).
The Kunlun suture separates the Tarim and
Qaidam blocks from others to the south. These two
continental blocks are, in turn, divided by the Altyan
fault zone. The Tethys branch represented by the
Palaeogeography of Tibet and adjacent areas (China)
25
Figure 2. Sketch map of Berriasian–Lower Barremian facies distribution and palaeogeography in Tibet and adjacent areas,
China. Fault zones and sutures: BNS, Banggonghu–Nujiang suture; JSS, Jinsajiang suture; KLS, Kunlun suture; LMF,
Longmenshan fault zone; YRS, Yarlung Zangbo suture.
Kunlun suture is believed to have closed during the
Late Triassic (Chang et al., 1986; Dewey et al., 1988;
Liu et al., 1990). The Songpan-Ganzi terrane is
bounded to the east by the Longmenshan fault zone
and the South China block (Figure 1). Recent studies
show that the Songpan-Ganzi terrain is underlain by
Precambrian continental basement, and that the huge
quantity of Triassic flysch on the terrain has been
explained as allochthonous tectonic flakes (for details
see Zhang, in press).
3. Distribution of marine Cretaceous deposits
Tables 1–3 briefly summarize the Cretaceous
stratigraphy and distribution of rocks of this system
in Tibet north of the Yarlung Zangbo suture and
adjacent areas. Berriasian–Lower Barremian marine
sequences only cover the southern half of the
Qiangtang block and the middle of the Lhasa block. In
these areas, the succession is composed mainly of
coarse- to fine-grained clastic rocks that reflect deposition in a littoral environment (Figures 2, 5, Table 1;
Wang, 1983; Wu, 1985; CIGMR & SCGR, 1992;
XZBGM, 1993).
In contrast, Upper Barremian–Albian marine
sequences cover the southernmost rim of the Tarim
block, the southern half and the southern rim of the
western half of the Qiangtang block, and the entire
Lhasa block (Figure 3, Table 2). Over most of these
areas, the Upper Barremian–Albian consists mainly
of coarse clastic rocks reflecting a littoral environment. However, on the southernmost rim of the
western Qiangtang block and the northern half of the
Lhasa block, the succession is composed mainly of
monotonous carbonate sediments, up to 5–6 km
thick, that possibly represent deposition in an inner
shelf environment (Figures 3, 5, Table 2). In the
Sichuan Basin of the western South China block just
east of the Longmenshan Mountains, the Lower
Cretaceous is mainly composed of continental clastic
rocks that coarsen westwards (Li, 1987).
Marine Upper Cretaceous is spread over nearly
every tectonic unit of Tibet and its adjacent areas
(Figure 4, Table 3). Marine sediments cover the
Tarim block (Tang et al., 1992; Guo, 1995), the
southern half (YNBGM et al., 1986; CIGMR &
SCGR, 1992) and westernmost rim (Guo et al., 1991;
XZBGM, 1993) of the Qiangtang block, and majority
of the Lhasa block (XZBGM, 1993; Figure 4,
Table 3). In the Tarim Basin and on the southern half
of the Qiangtang block, the Upper Cretaceous is
characterized by fine-grained sediments, mostly finer
than those of the Lower Cretaceous. However,
in general, up to 4 km of coarse-grained clastic
rocks characterize the marine Upper Cretaceous of
the Lhasa block and the westernmost rim of the
Qiangtang block, reflecting deposition in a littoral
environment. In the Sichuan Basin, the marine intercalation has been found to cover an area of more than
25 000 km2, though continental fine-grained clastic
Sandstones, siltstones, shales, intercalated with coal,
chert, and limestones. >2386 m
Sandstones, shales. 5400 m
Sandstones, shales, intercalated with andesite. >5000 m
Sandstones, carbonaceous shales (coal), intercalated with
conglomerates. >150 m
Sandstones, carbonaceous shales, intercalated
conglomerates. >620 m
Sanstones, carbonaceous shales, conglomerates, rich in
plant fragments. >3100 m
Pebbly sandstones, sandstones, shales, intercalated with
andesite. 905 m
Sandstones, carbonaceous shales, intercalated with
andesite. 1300 m
Sandstones, shales, intercalated with andesite. >5000 m
Conglomerates, sandstones, siltstones, carbonaceous
shales, intercalated with coal. >795 m
Sandstones, siltstones, shales, intercalated with coal,
chert, and limestones. >3140 m
Purple conglomerates, sandstones, siltstones, shales,
intercalated with coal, chert, and limestones. >3140 m
2. 2528N 10041E
3. 3321N 7918E
4. 3230N 8057E
5. 3146N 8451E
9. 3110N 8925E
10. 3032N 9020E
11. 3015N 9122E
12. 3040N 9605E
13. 3000N 9706E
8. 3057N 8855E
7. 3133N 8652E
6. 3142N 8517E
Quartzose sandstones, siltstones, shales, intercalated with
limestones. 759 m
1. 2515N 10014E
References: A, Wu (1985); B, XZBGM (1993); C, CIGMR & SCGR (1992).
Lhasa
Qiangtang
Lithology
Location
Main fossils
Euthymiceras (Berr.-Valang.), Neocomites (Berr.-Valang.),
Triporopollenites
Cyprina teolluensis (Berr.-Alb.), Cyprimeria cf. quadrata
(Berr.-Alb.), Thurmanniceras sp. (Berr-Valang.),
Veneridea meritix (Berr.-Alb.), Zamiophyllum sp. (Valang.)
Neocomites sp. (Berr.-Valang.), Neohoploceras sp.
(Valang.), Thurmanniceras sp. (Berr.-Valang.),
Zamiophyllum sp. (Valang.)
Neocosmocera bristrofferi (Berr.), Thurmanniceras sp.
(Berr.-Valang.), Zamiophyllum sp. (Valang.)
Cladophlebis sp. (Valang.), Clobularia sp., Neocomites sp.
(Berr.-Valang.), Protocardia sp., Weichselia reticulata Ward
(Valang.), Zamiophyllum buchianum Nathorst (Valang.)
Cladophlebis sp. (Valang.), Klukia sp., Weichselia reticulata
Ward (Valang.), Zamiophyllum buchianum Nathorst
(Valang.)
Baxoitrigonia vhligi, Cladophlebis sp. (Valang.), Klukia sp.,
Weichselia reticulata Ward (Valang.), Zamiophyllum
buchianum Nathorst (Valang.)
Cypridea sp. (Haut.-Barr.), Damonella ovata Gou
(Valang.), Falcimytilus sp., Leptosolen simaoensis
(Berr.-Apt.), L. dupinianus (Berr.-Apt.), Monosulcocypris
(Haut.-Barr.), Nucula sp., Scittila minuta (Berr.-Apt.),
Tancredia sp., Zamiophyllum buchianum Nathorst
(Valang.)
Cypridea sp. (Haut.-Barr.), Falcimytilus sp., Leptosolen
simaoensis (Berr.-Apt.), L. dupinianus (Berr.-Apt.),
Monosulcocypris (Haut.-Barr.), Plicatounio naktongensis,
Scittila minuta (Berr.-Apt.), Tancredia sp.
Cladophlebis browniana (Valang.), Kilianella sp.
(Berr.-Valang.), Neocosmocera bristrofferi (Berr.)
Sarasinella sp. (Valang.), Zamiophyllum buchianum
Nathorst (Valang.)
Axosmilia sp., Cladophlebis browniana (Valang.),
Stylinaparvistella
Neocomites (Berr.-Valang.), Zamiophyllum sp. (Valang.)
Table 1. Brief descriptions of marine Berriasian–Lower Barremian deposits in Tibet; location numbers as for Figure 2.
C
C
B
A
26
K. J. Zhang
Palaeogeography of Tibet and adjacent areas (China)
27
Figure 3. Sketch map of Upper Barremian–Albian facies distribution and palaeogeography in Tibet and adjacent areas,
China; for abbreviations, see Figure 2.
Figure 4. Sketch map of Cenomanian–Maastrichtian facies distribution and palaeogeography in Tibet and adjacent areas,
China; for abbreviations, see Figure 2.
rocks still dominate (Li, 1987). On the southern rim
of the Qaidam block, an Upper Cretaceous marine
sequence, coarsening upwards from limestones to
conglomerates, has been found to cover an area of
more than 120 km2 (Zhu et al., 1985). This succession is up to 1120 m thick (Liu et al., 1992). Figure 4
and Table 3 show the locations of marine Upper
Cretaceous deposits in Tibet and adjacent areas.
4. Lithofacies and palaeogeographic
reconstruction
According to present knowledge, it is possible to
delineate roughly the extent of Cretaceous lithofacies
and to reconstruct the palaeogeography of Tibet and
the adjacent areas, as shown in Figures 2–4. During
the Albian, marine sedimentation began on the
Purple conglomerates, sandstones, intercalated coal.
>1238 m
Purple conglomerates, sandstones, and mudstone,
intercalated with coal. >1393 m
Thin-bedded limestones. 5400 m
Thin-bedded limestones. >5000 m
Thin-bedded limestones, intercalated with andesite.
6071 m
Limestones. Chert nodules replace carbonate layers
and bioclastics. >150 m
Limestones with layers 20–240 cm thick rich in
foraminifera, brachiopods, crinoids and corals.
Chert nodules replace carbonate layers and fossils.
>620 m
Limestones, with layers 15–200 cm thick rich in
foraminifera, brachiopods, crinoids and corals;
some hummocky bedding. >3100 m
Shales, sandstones, intercalated with coal seams
and conglomerates. >623 m
Pebbly sandstones, sandstones, shales, intercalated
with andesite. 905 m
Limestones, with layers, 14–235 cm thick; some
hummocky bedding. <1300 m
2. 3345N 8020E
3. 3250N 9012E
5. 2515N 10014E
6. 2528N 10041E
7. 3321N 7918E
8. 3230N 8057E
9. 3125N 8105E
Qiangtang
Limestones. >5000 m
Siltstones, mudstones, limestones. <335 m
Limestones, with layers 15–210 cm thick. >3100 m
16. 3032N 9020E
17. 3015N 9122E
18. 3040N 9230E
15. 3110N 8925E
14. 3057N 8855E
13. 2925N 8710E
12. 3133N 8652E
11. 3142N 8517E
10. 3146N 8551E
Cyprina teolluensis (Berr.-Alb.), Cyprimeria cf. quadrata (Berr.-Alb.),
Orbitolina textena (Apt.-Alb.), Veneridea meritix (Berr.-Alb.)
Mesorbitolina birmanica (Late Barr.-Apt.), Orbitolina sp. (Apt.-Alb.),
Palorbitolina lenticularis (Early Apt.), Praeorbitolina corrnyi (Early Apt.),
Thamnasteria sp.
Adiozoptyxis sp. (Apt.), Palorbitolina lenticularis (Apt.-Alb.),
Praeorbitolina corrnyi (Early Apt.)
Meyeria magna (Apt.-Alb.), Notopocorystes xizangensis (Apt.-Alb.),
Orbitolina prisca (Apt.-Alb.), O. tibetica (Apt.)
Orbitolina lenticularis (Apt.), O. tibetica (Apt.)
Orbitolina textena (Apt.-Alb.), Palorbitolina lenticularis (Early Apt.)
Orbitolina aperta (Alb.), O. lenticularis (Apt.), O. tibetica (Apt.),
Triporopollenites
Lamprotula sp., Nippononaia aff. wakinoensis (Apt.-Alb.),
Paranippononaia cf. paucisulcata (Apt.-Alb.), Trigonioides sp.
(Apt.-Alb.)
Falcimytilus sp., Leptosolen simaoensis (Berr.-Apt.), L. dupinianus
(Berr.-Apt.), Nucula sp., Scittila minuta (Berr.-Apt.), Tancredia sp.,
Trigonioides kodairia (Apt.-Alb.)
Falcimytilus sp., Leptosolen simaoensis (Berr.-Apt.), L. dupinianus
(Berr.-Apt.), Nucula sp., Plicatounio naktongensis, Scittila minuta
(Berr.-Apt.), Tancredia sp., Trigonioides kodairia (Apt.-Alb.)
Mesorbitolina birmanica (Late Barr.-Apt.), Praeorbitolina corrnyi Early
Apt.)
Adiozoptyxis sp. (Apt.), Mesorbitolina birmanica (Late Barr.-Apt.),
Palorbitolina lenticularis (Apt.-Alb.), Praeorbitolina corrnyi (Early Apt.)
Ampullina xainzaensis (Apt.), Glauconia trorreri (Apt.), Nerinea cf. pauli
(Apt.), Nerinella dayi (Apt.), Plesioptyxis aff. langshansis (Apt.)
Adiozoptyxis sp. (Apt.), Axosmilia sp., Montlivaltia sp. (Alb.),
Stylinaparvistella
Mesorbitolina birmanica (Late Barr.-Apt.), Palorbitolina lenticularis
(Apt.-Alb.), Praeorbitolina corrnyi (Early Apt.)
Astarte sp., Nerinea sp. (Apt.-Alb.), Pteria sp.
Hedbergella siqali (Barr.), Orbitolina birmanica sahni (Apt.-Alb.),
Orbitolina trochus (Apt.-Alb.), Textularia sp.
Nodosaria sp., Saccammina globosa (Alb.)
Main fossils
References: A, Guo (1995); B, Zhu & Pan (1987); C, Lin et al. (1989); D, Wu (1985); E, CIGMR & SCGR (1992); F, XZBGM (1993).
Lhasa
Interbedded sandstones and conglomerates.
1000–1300 m
Sandstones, mudstones. >500 m
Upper: grey medium-thick bedded breccias,
micritic limestones, intercalated with bioclastic and
oolitic limestones. 919 m
Lower: purple conglomerate. 290 m
Siltstones, calcareous siltstones, intercalated with
limestones. >560 m
1. 39 55N 7705E
Tarim
4. 3315N 9150E
Lithology
Location
Table 2. Brief descriptions of marine Upper Barremian–Albian deposits in Tibet; location numbers as for Figure 3.
F
F
D
F
D
E
D
E
B
C
A
Reef limestone
Reef limestone
Bioclastic limestone
Reef limestone
Bioclastic limestone
Bioclastic limestone
Reef limestone
Bioclastic limestone
9. 3158N 8607E
10. 3148N 8616E
11. 3201N 8705E
12. 2925N 8705E
13. 3155N 9000E
14. 3115N 9020E
15. 3050N 9005E
16. 3015N 9122E
Biradiolites boldjuanensis (Camp.), Braarudosphaera bigelowii (Turon.), Pediastrum
(Maastr.)
Anadara sp. (Cenom.), Gryphaea vesiculosa turkesiania (Bobkova), Neocarassina
gigantia Chen, Ostrea qinghaiensis Chen (Cenom.-Turon.), Ostreaonalla nachitaiensis
Chen
Biradiolites lumbricoides (Coniac.-Camp.), Gorjanovicia acuticostata (Coniac.-Camp.),
Pycondonte cf. costei (Coniac.-Camp.), Radiolites crassus (Coniac.-Camp.), R. angeiodes
(Coniac.-Camp.)
Bournonian sp. (Camp.-Maastr), Trigonioides (Diverstr.) bangongwenesis Gu
(Cenom.-Turon.), Trigonioides (Diverstr.) xizangensis (Cenom.-Turon.)
Gomphocythere sp., Pontocypris sp. (Maastr.).
Nerinea parahicoriensis (Cenom.), Orbitolina concava (Cenom.-Turon.)
Bournonia sp. (Camp.-Maastr.), Neoptyxis sp., Plesioptyxis huzitai, Plisiotygmatis cf.
pupoides, Praeradiolites sp. (Cenom.-Camp.)
Lepidorbitoides gangdisicus (Maastr.), L. minor (Maastr.), L. zhongbaensis (Maastr.),
Libycoceras (Maastr.), Pseudorbitoides yini (Maastr.), Sphendiscus (Late Camp.)
Orbitolina concava Lamarck (Cenom.-Turon.), Trigoniodes sinensis (Cenom.-Turon.)
Orbitolina concava Lamarck (Cenom.-Turon.), Trigoniodes sinensis (Cenom.-Turon.)
Plicatula placunen (Turon.-Maastr.), Plicatula cf. inflata (Turon.-Maastr.), Orbitolina
concava (Cenom.-Turon.)
Lepidorbitoides gangdisicus (Late Camp.), Libycoceras (Maastr.), Manambolites
(Maastr.), Pseudorbitoides yini (Maastr.), Sphenodiscus (Camp.)
Acicularia americana (Maastr.), A. antiqua (Maastr.), Bournonia sp. (Camp.-Maastr.),
Neithea sexcostatus (Cenom.-Sant.), Plicatula placunen (Turon.-Maastr.), Plicatula cf.
inflata (Turon.-Maastr.), Orbitolina concava (Cenom.-Turon.)
Cumopolia sp. (Maastr.), Natica, Orbitolina concava (Cenom.-Turon.), Tritonium
kanabense Stanton, Turritella Stephenson (Cenom.-Coniac.), T. whitei Stanton
(Cenom.-Coniac.), Trinocladus megacladus (Maastr.)
Acicularia antiqua (Maastr.), Bournonia sp. (Camp.-Maastr.), Neithea sexcostatus,
Plicatula placumen (Turon.-Maastr.), Plicatula cf. inflata (Turon.-Maastr.), Orbitolina
concava (Cenom.-Turon.)
Aetostreon zhongshanensis, Altanicypris aff. bispinoferus, Amphidonte ostracina (Turon.),
Cypridopsis aff. bugintsavicus, Korobkovitrigonia sp. (Sant.), Pterotrigonia (Cenom.),
Pycnodonte vesiculosa, Tenea sp. (Camp.)
Nonion cf. sichuanensis Li (Coniac.-Camp.)
Nonion cf. sichuanensis Li (Coniac.-Camp.), Nonion sp. (Cenom.-Camp.)
Nonion cf. sichuanensis Li (Coniac.-Camp.)
Nonion cf. sichuanensis Li (Coniac.-Camp.), Nonion sp. (Cenom.-Camp.)
Nonion sp. (Cenom.Camp.)
Nonion cf. sichuanensis Li (Coniac.-Camp.)
Key fossils
N, O
N
P
P
P
P
D, L
G, I, K
J
D, G, H, I
D, G
2
D
F
D, E
1, D, E
D
B, C
A
1, interbedded with andesites dated at 77.8 Ma (K-Ar); 2, interbedded with andesites dated at 69.2 Ma (K-Ar). References: A, Tang et al. (1992); B, Zhu et al. (1985); C, Liu et al. (1992);
D, XBGMR (1993); E, Guo et al. (1991); F, YNBGM et al. (1986); G, XGS (1986); H, Han et al. (1983); I, Lin et al. (1989); J, Liang & Xia (1983); K, Wang (1983); L, Gou (1985);
N, HNGR (1993); O, Li (1985); P, Li (1987).
limestone
limestone
limestone
limestone
limestone
limestone
Bioclastic limestone
8. 2950N 8410E
Bioclastic
Bioclastic
Bioclastic
Bioclastic
Bioclastic
Bioclastic
Bioclastic limestone
Bioclastic limestone
Reef limestone
5. 2320N 10110E
6. 3201N 8105E
7. 3200N 8335E
9415E
9540E
10404E
10303E
10212E
10212E
Reef limestone
4. 3345N 8020E
3055N
3120N
3041N
3000N
2755N
2640N
Bioclastic limestone
3. 3456N 8114E
Qiangtang
17.
18.
19.
20.
21.
22.
Bioclastic limestone,
>469.2 m
2. 3557N 9448E
Qaidam
Lhasa
Reef limestone
1. 3540N 8105E
Index lithology
Tarim
Location
Table 3. Brief descriptions of marine Cenomanian–Maastrichtian deposits in Tibet; location numbers as for Figure 4.
Palaeogeography of Tibet and adjacent areas (China)
29
30
K. J. Zhang
Figure 5. Schematic transgression–regression curves for three main blocks during the Cretaceous Period. The curve for the
Tarim block follows Tang et al. (1992). CB, Chuanba Group; DB, Dongba Formation; H, Hutoushi Formation; J,
Jinxing Formation; JZ, Jingzhushan Group; KK, Kukebai Formation; K, Kezilesu Formation; L, Lanshan Formation;
MG, Mangang Formation; MK, Mankuanghe Formation. Facies: 1, continental; 2, supralittoral and intertidal; 3,
subtidal and neritic. Thickness (‘thick’) in metres.
southern rim of the Tarim block (Table 2; Guo,
1995). However, the limited extent of the littoral
sediments preserved there suggests that initially the
transgression was weak, but that it strengthened in
the Late Cretaceous (Figure 5) and continued into the
late Tertiary (Tang et al., 1992; Guo, 1995), covering
the Tarim block and also involving the southern rim
of the Qaidam block. The fine-grained sediments on
the Tarim block accumulated in a littoral, partially
neritic, environment during the Late Cretaceous
(Figures 4, 5).
Through the entire Cretaceous Period, the sedimentary facies and palaeogeography of the Qiangtang
block changed continually. Most of the western half
became dry land whereas the southern half continued
to be an area of marine sedimentation (Figures 2, 5;
Table 1). On the southernmost rim of the western
half, Upper Barremian–Albian sediments accumulated predominantly in a neritic-subtidal environment,
but the Upper Barremian–Upper Cretaceous succession of the southern half of western Qiangtang was
deposited in a littoral environment (Zhu & Pan, 1987;
Lin et al., 1989; Guo et al., 1991). The Cretaceous
rocks of southern half of the Qiangtang block reflect a
littoral-neritic environment of deposition but there
were apparently more transgressive overlaps during
the Late Cretaceous than in the first half of the period
(Figure 5). The landmass in the western half of the
Qiangtang block would have been least extensive
during the Late Barremian–Albian (Figure 3).
Sediment deposition on the middle of the Lhasa
block during the Berriasian–Early Barremian was
mainly dominated by a littoral environment (Figures 2,
5; Wu, 1985). However, during the Late Barremian–
Albian, deposition on the northern half of the block
west of 91E took place mainly on a carbonate platform
(Figure 3). In the Late Cretaceous, the entire block
was again within a littoral environment (Figure 4).
In the western Sichuan Basin of the South China
block, coarse-grained Lower Cretaceous sediments
accumulated in a continental setting whereas deposition during the Late Cretaceous was often in the
littoral marine realm (Figure 4; Li, 1987). The
Longmenshan Mountains could, therefore, have
been uplifted in the Early Cretaceous but eroded
through the Late Cretaceous.
Palaeogeography of Tibet and adjacent areas (China)
In the Songpan-Ganzi terrain, many typical tropical
floras, including eucalyptus and palms, have been
found in Eocene sediments in the Candu (9710E,
3110N) and Litang (10010E, 2955N) areas
(e.g., Liu et al., 1990). In addition, in the southern
part of the terrain, marine Paleogene sediments cover
an area of at least 1000 km2 (Li et al., 1987). These
two facts indicate that this region was not more
than 1000 m high during the Eocene and could
not, therefore, have been higher during the Late
Cretaceous.
5. Tectonic implications
5.1. Late Barremian–Albian back-arc extension in
southern Tibet
In general, it is believed that the ocean represented
by the present Banggonghu–Nujiang suture was
closed during the Late Jurassic (Allegre et al., 1984;
Girardeau et al., 1984; Wang & Sun, 1985; Chang
et al., 1986; Dewey et al., 1988). The Berriasian–
Lower Barremian coarse littoral clastics in the northern part of the Lhasa block (Figure 2, Table 1)
represent a molasse association deposited in a compressional regime and indicate that the collision
between the Qiangtang and Lhasa blocks could have
extended into the Berriasian–Early Barremian.
However, the Upper Barremian–Albian pure innershelf limestones, which are up to 5 km thick (e.g.,
XZBGM, 1993) and stretch from the southernmost
rim of the western half of the Qiangtang block to
the northern half of the Lhasa block, covered a larger
area (compare Figures 2 and 3). Furthermore, the
entire Lhasa block as well as the western half of the
Qiangtang block, was apparently under the influence
of a marine transgression, unlike most of the rest
of Tibet (e.g., Tarim block, southern half of the
Qiangtang block), where there was a marine regression (Figure 5). This indicates that the widespread
Upper Barremian–Albian limestone in southern Tibet
was not a product of eustatic transgression but of
tectonic subsidence or extension deformation during
the late Early Cretaceous. The latter could have
resulted from the back-arc collapse of the Gangdese
arc in the southern part of the Lhasa block. The
Cenomanian foraminiferan Orbitolina concava has
been found at the top of the pure limestone in several
locations in the northern half of the Lhasa block
(e.g., Yin et al., 1988; Yu & Wang, 1990); hence
the extension, approximately commencing in the
Late Barremian, could have extended into the Early
Cenomanian, thus possibly lasting at least 20 m.y.
31
5.2. Southern Tibetan plateau not uplifted in Late
Cretaceous
The timing of the uplift of the Tibetan plateau keeps
open a question that is of key importance to the
models for its development. Various schools of geologists have argued for markedly contrasting timing of
the uplift: (1) not uplifted until the onset of the
Quaternary, mainly suggested by palaeoclimatic
studies (e.g., Xu, 1981; Pan et al., 1990); (2) the
Lhasa block elevated before its collision with India
after the Late Cretaceous, based on deformation
studies (England & Searle, 1986); and (3) the
southern Tibetan plateau elevated 3–4 km by c. 99 Ma
and maintained until the onset of the Indo-Asian
collision (Murphy et al., 1997).
This study of the Cretaceous palaeogeography
provides a significant constraint and test on previous
conclusions, at least on whether southern Tibet had
been elevated (3–4 km) prior to the Indo-Asian collision, because the Upper Cretaceous sediments of the
region should have been predominantly continental if
this were so. Our investigations (Zhang et al., 1998) as
well as those of many Chinese colleagues in this region
(e.g., Han et al., 1983; Liang & Xia, 1983; Wang,
1983; Gou, 1985; Li, 1985; Pan, 1985; Zhu et al.,
1985; XGS, 1986; Wan, 1987; Lin et al., 1989; Pan
et al., 1990; Guo et al., 1991; Li & Wu, 1991; Liu
et al., 1992; HNGR, 1993; XBGMR, 1993) show that
over most of Tibet, shallow marine sedimentation
continued into the Late Cretaceous (Pan et al., 1990;
Liu et al., 1992; Figure 4). This sedimentation is
indicated by various rock types including reef limestones and radiolarian chert, and its timing is well
constrained by abundant fossils and radiometric
dating of the interbedded volcanics (Table 3). In
addition, the backarc extension in southern Tibet
during the late Early Cretaceous (possibly also involving the earliest Late Cretaceous), as discussed above,
is in agreement with this conclusion. The collision
between the Qiangtang and Lhasa terrains could have
ceased during the Early Barremian, in which case
there was no mechanism to create (and there is no
palaeogeographic and facies evidence for) southern
Tibet being at an elevation of 3–4 km by the end of
the Early Cretaceous, contrary to the suggestion of
Murphy et al. (1997). Instead, Tibet could have been
a rather low and extensive peneplain, close to sea
level, during the Late Cretaceous, intensive elevation
having begun only after the end of the Cretaceous
Period. In fact, in the (1) Tarim Basin (Tang et al.,
1992; Guo, 1995), (2) southern (YNBGM et al.,
1986) and westernmost (Guo et al., 1991; XZBGM,
32
K. J. Zhang
1993) Qiangtang block; (3) southernmost SongpanGanzi block (Li et al., 1987); and (4) northwestern
and southern rims (Wan, 1987; Pan et al., 1990), and
even the centre (Lin et al., 1989) of the Lhasa block,
marine sedimentation did not cease until the end of
the Eocene (Pan et al., 1990; Zhang et al., 1998). It is
suggested, therefore, that the high topography of
the Tibetan plateau can only be the product of the
Indo-Asian collision.
Acknowledgements
Hundreds of Chinese geologists took part in the
fieldwork in Tibet, China. I am grateful to Prof. B. D.
Xia at the NJU for logistical help and Prof. G. T. Pan
at the Chendu Institute of Geology and Mineral
Resources for his kind offer of useful references.
The constructive and thoughtful reviews of Prof.
D. J. Batten and an anonymous referee are greatly
appreciated.
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