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Cretaceous paleogeography in China
Palaeogeography, Palaeoclimatology, Palaeoecology, 59 (1987): 49 56 Elsevier Science Publishers B.V., Amsterdam Printed in The Netherlands
49
CRETACEOUS PALEOGEOGRAPHY IN CHINA CHEN PEI-JI Nanjing Institute of Geology and Paleontology, Academia Sinica, Chi-Ming-Ssu, Nanjing (People's Republic of China)
(Received October 2, 1986)
Abstract Chen Pei-ji, 1987. Cretaceous paleogeography in China. Palaeogeogr., Palaeoclimatol., Palaeoecol., 59:49 56. The paleogeography of China is represented by four maps: the Neocomian, Aptian-Albian, Cenomanian Santonian, and the Campanian Maastrichtian. The continental interior of China was characterized by large lake systems in tectonic depressions and intermontane basins, with little or no marine influence. Shallow epicontinental Cretaceous seas were limited by the eastern margins and to the tectonic troughs of the southern and western Tibetan Plateau. In contrast to the detailed knowledge of the interior Cretaceous deposits of China, the record of the marine invasions is known only in a general way.
Introduction The C r e t a c e o u s deposits of t h e i n t e r i o r of C h i n a are u n i q u e in t h a t t h e y m a i n l y reflect n o n - m a r i n e d e p o s i t i o n a l systems, i n c l u d i n g facies w h i c h depict a n u m b e r of l a r g e r i v e r s and l a k e s t h a t p e r s i s t e d for long periods of C r e t a c e o u s and T e r t i a r y time. F o l l o w i n g a m a r i n e r e g r e s s i o n w h i c h influenced l a r g e portions of C h i n a d u r i n g the J u r a s s i c , c o n t i n u e d e u s t a t i c l o w e r i n g of sea level coupled w i t h w i d e s p r e a d t e c t o n i c e l e v a t i o n of C h i n a c a u s e d f u r t h e r r e g r e s s i o n of the T e t h y a n seas. Subseq u e n t m a r i n e i n v a s i o n d u r i n g the C r e t a c e o u s was r e s t r i c t e d to m a r g i n a l t e c t o n i c b a s i n s in Xizang (Tibet) and s o u t h w e s t e r n Xinjiang. T h e s e deposits a r e o n l y k n o w n in a g e n e r a l way, and are p r e s e n t l y u n d e r detailed investigation. T h e C r e t a c e o u s n o n - m a r i n e facies, h o w e v e r , h a v e b e e n well studied a n d p e r m i t p a l e o g e o g r a p h i c r e c o n s t r u c t i o n s of t h e inter i o r of China, e v e n t h o u g h it is difficult at p r e s e n t to c o r r e l a t e t h e s e deposits w i t h the 0031-0182/87/$03.50
s t a n d a r d E u r o p e a n s t a g e s identified m a i n l y by m a r i n e b i o t a s (Chen et al., 1982). T h e p a l e o g e o g r a p h y of C h i n a c a n be described in four places, r e p r e s e n t e d by a series of m a p s ( F i g s . l - 4 ) , as follows.
P a l e o g e o g r a p h y of the N e o c o m i a n interval D u r i n g the e a r l y L o w e r C r e t a c e o u s , the T e t h y s Sea r e g r e s s e d f r o m s o u t h e r n Q i n g h a i to the n o r t h e r n Xizang P l a t e a u , b u t m a i n t a i n e d a c o n n e c t i o n with the s e a w a y of the H i m a l a y a n region, e x t e n d i n g s o u t h e a s t w a r d t h r o u g h the Q a m d o region, and p e r i o d i c a l l y r e a c h i n g w e s t e r n Y u n n a n . This s e a w a y h a d p r o b a b l y w i t h d r a w n from n o r t h e a s t e r n C h i n a by Neoc o m i a n t i m e e v e n t h o u g h t h e r e is some e v i d e n c e w h i c h d e m o n s t r a t e s t h a t a m a r i n e a r m of the Pacific O c e a n r e a c h e d the W u s u l i G u l f of e a s t e r n H e i l o n j i a n g d u r i n g the L a t e J u r a s s i c , and t h a t the T a i w a n P r o v i n c e was p r o b a b l y still s u b m e r g e d b e n e a t h the Pacific at this time.
:~'~1987 Elsevier Science Publishers B.V.
50
Fig.1. Sketch map showing the early Early Cretaceous (Neocomian)paleogeography in China. 1=Tethys Sea. 2= Pacific Ocean. 3= Wusuli Gulf. 4= Shu Lake. 5 = Xichang Lake. 6 = Yunnan Lake. 7= Puer Lake. 8= Ba Lake. 9 = Qingyang Lake. 10= ancient Datong River. 11= Chao Lake. 12= Junggar Basin. 13= Turpan Basin. 14= Kuqa Basin. 15= unnamed River. 16= Kashi Gulf. 17= Songhua Lake. 18= Yunmeng Lake. 19= ancient Gan River. 20= ancient Fuchun River. 21 = active volcanic zones in the eastern coastal low land. There were four major paleogeographic divisions of the interior of China during the Neocomian (see Fig.l). The southwestern
lakes group
A group of large lakes associated with the old Yangtze River drainage existed in southwestern China during the Neocomian (Fig.l; Chen, 1979). The largest of these were Shu Lake and Yu n na n Lake; Xichang Lake lay between these larger lakes and, at times, connected them. These lakes were surrounded by the Yunnan-Guizhou Plateau, the Hengduan Mountains and the old Qinling Ranges. The drainage of these lakes probably con-
nected to the T e t h y a n Seaway through the Nanjian Straits. The Neocomian climate of this region was hot, as evidenced by abundant red-beds bearing an extremely rich fauna of freshwater ostracods, bivalves, and some conchostracans. The inland
water system of Qingyang
Lake
Qingyang Lake occupied the present regions of n o r t h e r n and central Shaanxi, eastern Gansu and eastern Ningxia, an area of about 130,000 km 2 (Fig.l). This represented the largest freshwater lake in China at t hat time. Geographically, this lake bordered on the old Qinling Ranges on the south, the Yinshan
51 Mountains on the north, and the North China Plateau on the east. To the west, the old Datong River drainage, with its broad low floodplain containing numerous smaller lakes, entered Qingyang Lake. The Minhe Lake and the Chao Lake were among the larger lakes of this floodplain, which was also characterized by a complex network of rivers. The climate of this region was hot to mild, as indicated by variegated strata containing abundant freshwater conchostracans, ostracods, bivalves, fish and plants. The northwestern intermontane basins
During the Neocomian, northwestern China was characterized by numerous mountain ranges separated by large intermontane basins. Among these, the Junggar Basin of Xinjiang was the biggest; this basin was subtriangular in outline, and filled with a large lake that was intermittently deep and shallow. Sediments from this lake contain fossils similar to those of the Qingyang Lake. A second large intermontane basin, the Turpan Basin, lay to the east of the old Tianshan Mountains, and a piedmont sag (also called the Kuqa Basin) lay to the south of Tianshan; both basins occupied a narrow belt within this region. In the west-most border area of Xinjiang, there existed a major river system (the Unnamed River) which flowed toward the Tethys Sea in Central Asia. Red-colored sediments characterize the floodplain deposits of the Unnamed River Valley. The active volcanic zones of the eastern coastal lowlands
The Eastern Plateau of China was formed during active motion along the Pacific Plate during the late Jurassic, and began to break up and subside during the Neocomian. This resulted in the widespread eruption of lava and the formation of the active volcanic zones along the coastal lowland. Large parts of Zhejiang, Fujian, southern Jiangxi and eastern Guangdong were covered with neutral and,
predominantly, acidic volcanic rocks in terrestrial facies. Between episodes of volcanic eruption numerous marshes, ponds and lakes formed in depressions between flows. Therefore, great thicknesses of volcanic rocks on the Eastern Plateau of China are characteristically intercalated with numerous layers of lacustrine and fluvial sedimentary strata in which fossils of conchostracans, ostracods, bivalves, gastropods, fishes, plants and insects occur in abundance. These fossils form a reliable basis for stratigraphic subdivision and correlation (Chen and Shen, 1982). During the Neocomian, volcanic activity progressively declined toward the landward side of the Eastern Coastal Lowland, while remaining active on the coast. As a result, many parts of this region were characterized by deposition of red-beds and variegated strata, without intercalated volcanic flows; examples are the Sunchiawan Formation in western Liaoning, the Hsiachuang Formation to the west of Beijing, the Tiekuling Formation in western Jiangxi, and even the Wenmingsze Formation in southern Hunan.
Paleogeography o f the Aptian to Albian interval There is conclusive evidence for the transgression of shallow marine seaways around the Taiwan-Penghu region during the Aptian. Fossils of bivalves and ammonites have been found in drilled cores during petroleum exploration in the Yunlin-Peikang region, including the biostratigraphically important species HolcophyUoceras caucasicum taiwanum Matsumoto, an element of the Aptian Caucasian Sea (Matsumoto, 1979). During this time, there were few changes in the paleogeographical configuration of western and southwestern China, mainly marine volcanic eruptions from somewhere in the present Xizang Plateau (Zhang et al., 1981). In the middle to late Early Cretaceous, regional uplift occurred in southeastern and northwestern China, causing a significant reduction in the area of all inland basins and
52
Fig.2. Sketch map showing the late Early Cretaceous (Aptian-Albian) paleogeography in China. For further explanation of symbols used see Fig.1.
the disappearance of some rivers. This uplift was especially significant in the volcanic lowlands along the southeastern coast of China and in the drainage basin of the Qingyang Lake (Fig.2). The early Lower Cretaceous Moshishan Formation of Zhejiang was deeply eroded and the late Lower Cretaceous Guantou Formation, another volcanic sedimentary rock sequence, is consequently in disconformable contact with the Moshishan Formation. The Guantou Formation itself has very limited geographic distribution. The only major exception to this Aptian-Albian tectonic trend occurred in the northeastern hinterland of China, where a major depression formed in the site of Songhua Lake and deposition of dark-colored rocks of the Dengluku Formation took place.
Paleogeography o f the C e n o m a n i a n Santonian interval By the end of the Albian a major phase of crustal tectonics occurred within China. This period of thrusting and uplift corresponds to the so-called Austrian Movement in Europe. In China, this episode is called the ZhejiangFujian movement in the southeastern coastal region, and the fourth phase of the Yenshan Movement elsewhere. Tectonism during this interval greatly changed the paleogeographical patterns throughout China. The Tethys Sea withdrew from the northern Xizang Plateau, to the south of Lhasa, and never again extended into eastern Xizang and western Yunnan. In most cases, the group of southwestern lakes became closed saline or
53 80
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Fig.3. Sketch map showing the early and middle Late Cretaceous (Cenomanian Santonian) paleogeography in China. For further explanation of symbols used see Fig.1.
brackish lakes, in which rock salt and gypsum were widely deposited within red-bed sequences. In some specific basins deposits of sylvite mineral suites were formed. Following the disappearance of the Northwestern Intermontane Basins, however, the marine Kashi Gulf transgressed from Central Asia along the north slope of the ancient Kunlun Mountains, through Yecheng, and reached the vicinity of Hotan in Southern Xinjiang. In this shallow-marine gulf, warm Tethyan climates are indicated by abundant large oysters and rudist bivalves, as well as abundant foraminifers. The inland drainage system of the Quinyang Lake in the Ordos Region entirely disappeared by this time, and was replaced by the newlyformed Yunmeng Marsh system in central China. This took the form of a huge lake,
occupying a large area of the present Nanyang region, J i a n g h a n Plain and Dongting Lake Valley, and was joined with the Hengyang Basin on the south. A major river system feeding this lake is called the ancient Gan River; its upper reaches in Zhejiang are called the ancient Fuchun River: this river system was fed by a number of intermontane streams and creeks from east to west. During the Cenomanian to Santonian interval this region lay within a tropical to subtropical arid climate belt, and was characterized physiographically by low hills, barren deserts, saline lakes, and a yearly rainfall probably below 100 300 mm (Wu et al., 1979). Paleobotanical facies characterizing the region contain Manica, Schizaioisporites and Ephedripites. During the early and middle Upper Cretaceous, the so-called "Songhua Lake" of north-
54 eastern China was actually a broad region characterized by numerous marshes and a complex network of rivers around the lower reaches of the ancient Heilongjian River system, comprising an area of about 240,000 km 2. Shallow environments characterized this region and freshwater crustacean faunas (ostracods, conchostracans) were especially well developed. This region became an important source of petroleum. Songhua Lake was linked to the ancient Pacific Ocean from the northeast by occasional incursions of marine waters. Evidence for this marine influence is found in the Nenjiang Formation and its related upper and lower horizons, where fossils such as Striarca, Mytilus, Brachidontes, Musculus, Sungarichthys, Jilinchthys and Hama have been recovered. In Songhua Lake, variegated deposits containing fossils of hadro-
saurids and Paralligator have been found, indicating that the climate at that time was probably warm and humid. During the C e n o m a n i a n - S a n t o n i a n interval, the ancient Pacific Ocean not only extended into the northeastern corner of Heilongjiang Province from the Wusuli Gulf, but possibly also covered the eastern half of Taiwan, where some Late Cretaceous corals (Elephantaria) have been found from the metamorphic rocks in the Bihou Group east of the Central Mountains.
Paleogeography of the CampanianMaastrichtian interval During the C a m p a n i a n - M a a s t r i c h t i a n interval, there were probably no significant changes in the position of marine transgressions into Taiwan, Xizang and the Kashi region of
Fig.4. Sketch map showing the latest Late Cretaceous (Campanian-Maastrichtian)paleogeographyin China. For further explanation of symbolsused see Fig.1.
55 Xinjiang, but the climate became more arid and much warmer, and the extent of gypsum and salts deposited in the Kashi region increased. However, in northeastern China, the area of Songhua Lake was greatly reduced due to regional uplift which caused the withdrawal of the Wusuli Gulf from the valley. The distribution of drainage systems in the Yunmeng Marsh region changed with the disappearance of the ancient Gan River and Fuchun Rivers, leaving a series of northeastward trending intermontane basins in which the well known Nanxiong Formation and equivalent red bed facies were deposited. These coarse-grained deposits comprise thickbedded red sandstones and conglomerates which commonly form steep cliffs, intercalated with red mudstones containing abundant dinosaur fossils and their eggs. The Yunmeng Marsh became a closed basin during the Campanian Maastrichtian interval and was filled by a brackish to saline lake more restricted in size than the preceding marsh. The southwestern groups of lakes in China persisted for more than one hundred million years during the Jurassic and Cretaceous, and were continuously linked by the ancient Yangtze River, flowing east to west into the Tethys Sea. During the latest Cretaceous, the lakes underwent an extensive change, breaking up, becoming isolated, and changing their form. By the Campanian and Maastrichtian, only scattered small basins remained, in which were mainly deposited red sandstones and mudstones such as the Zhaojiadian and Mankuanhe Formations in Yunnan and the Jiading Group in southern Sichuan. In contrast with the tectonically uplifted terrain of eastern China, some intermontane basins were developed in northwestern China during the Campanian and Maastrichtian. Around the south and north borders of the Junggar Basin, as well as in Turpan and Kuqa, there occur a small number of coarse-grained red beds yielding dinosaur fossils which represent sedimentation in these basins. The sedimentation in these areas was continuous into the overlying Tertiary system.
Conclusions The following are the principal conclusions that can be derived from this paleogeographic survey of China during the Cretaceous. (1) During the Cretaceous, the continental interior of China was characterized by large lake systems in tectonic depressions and intermontane basins, with little or no marine influence. (2) Shallow epicontinental Cretaceous seas were limited to the eastern margins and western boundary areas of China and to the tectonic troughs of the southern and western Tibet Plateau. (3) The changes in continental topography and in the size, shape, and duration of large inland lakes were linked to regional and platemargin tectonic episodes. Many large lakes were formed, disappeared, and were reformed as a result of regional tectonic pulses. (4) Many large lakes underwent major changes in depositional environment as a result of regional Cretaceous tectonic episodes. They were intermittently deep and shallow, fresh to saline, closed basins or dissected by extensive river systems, and in some cases reduced to large marshes or series of smaller lakes. (5) During the Cretaceous, most of southern China was characterized by very warm, dry climates, resulting in the deposition of extensive red beds, gypsum, and rock salt in large water-filled depressions and intermontane basins.
Acknowledgements I wish to t h a n k Professor Erle G. Kauffman, Department of Geological Sciences, University of Colorado, for critically reviewing this manuscript and assistance in developing the English text. I further thank Dr. Kauffman and Dr. William W. Hay of the University of Colorado, Boulder, and Dr. Eric Barron of the National Center for Atmospheric Research, Boulder, Colorado, for inviting me to develop and present this research at the Penrose Confer-
56
ence on Cretaceous Climates at Florissant, Colorado, October 3-8, 1983, and for financial support provided by the National Science Foundation, U.S.A. References Chen Pei-ji, 1979. An outline of paleogeography during the Jurassic and Cretaceous Periods of China - - with a discussion of the origin of the Yangtze River. Acta Sci. Nat. Univ. Pekin., 3:90 109. Chen Pei-ji and Shen Yan-bin, 1982. Late Mesozoic conchostracans from Zhejiang, Jiangsu and Anhui. Palaeontol. Sin. N. S. B, 17, 117 pp.
Chen Pei-ji, Li Wen-ben, Chen Jin-hua, Ye Chun-hui, Wang Zhen, Shen Yah-bin and Sun Dong-li, 1982. Sequence of fossil biotic groups and stratigraphical classification of Jurassic and Cretaceous in China. Sci. Sin. Ser. B, 25(9; 11): 1011-1020; 1227-1248. Matsumoto, T., 1979. Restudy of a phylloceratid ammonite from Peikang, Taiwan. Pet. Geol. Taiwan, 16: 51-57. Wu Ping, Yang Zhen-qiang et al., 1979. CretaceousTertiary Lithofacies and Palaeogeography of Central° southern China. Geological Publishing House, Beijing, 164 pp. Zhang Bing-gao, Sun Dong-li, Yang Sheng-qiu and Ye Chun-hui, 1981. New observations on the Cretaceous of Baingoin and Xainza areas, northern Xizang. J. Stratigr. 5(4): 313-315.
49
CRETACEOUS PALEOGEOGRAPHY IN CHINA CHEN PEI-JI Nanjing Institute of Geology and Paleontology, Academia Sinica, Chi-Ming-Ssu, Nanjing (People's Republic of China)
(Received October 2, 1986)
Abstract Chen Pei-ji, 1987. Cretaceous paleogeography in China. Palaeogeogr., Palaeoclimatol., Palaeoecol., 59:49 56. The paleogeography of China is represented by four maps: the Neocomian, Aptian-Albian, Cenomanian Santonian, and the Campanian Maastrichtian. The continental interior of China was characterized by large lake systems in tectonic depressions and intermontane basins, with little or no marine influence. Shallow epicontinental Cretaceous seas were limited by the eastern margins and to the tectonic troughs of the southern and western Tibetan Plateau. In contrast to the detailed knowledge of the interior Cretaceous deposits of China, the record of the marine invasions is known only in a general way.
Introduction The C r e t a c e o u s deposits of t h e i n t e r i o r of C h i n a are u n i q u e in t h a t t h e y m a i n l y reflect n o n - m a r i n e d e p o s i t i o n a l systems, i n c l u d i n g facies w h i c h depict a n u m b e r of l a r g e r i v e r s and l a k e s t h a t p e r s i s t e d for long periods of C r e t a c e o u s and T e r t i a r y time. F o l l o w i n g a m a r i n e r e g r e s s i o n w h i c h influenced l a r g e portions of C h i n a d u r i n g the J u r a s s i c , c o n t i n u e d e u s t a t i c l o w e r i n g of sea level coupled w i t h w i d e s p r e a d t e c t o n i c e l e v a t i o n of C h i n a c a u s e d f u r t h e r r e g r e s s i o n of the T e t h y a n seas. Subseq u e n t m a r i n e i n v a s i o n d u r i n g the C r e t a c e o u s was r e s t r i c t e d to m a r g i n a l t e c t o n i c b a s i n s in Xizang (Tibet) and s o u t h w e s t e r n Xinjiang. T h e s e deposits a r e o n l y k n o w n in a g e n e r a l way, and are p r e s e n t l y u n d e r detailed investigation. T h e C r e t a c e o u s n o n - m a r i n e facies, h o w e v e r , h a v e b e e n well studied a n d p e r m i t p a l e o g e o g r a p h i c r e c o n s t r u c t i o n s of t h e inter i o r of China, e v e n t h o u g h it is difficult at p r e s e n t to c o r r e l a t e t h e s e deposits w i t h the 0031-0182/87/$03.50
s t a n d a r d E u r o p e a n s t a g e s identified m a i n l y by m a r i n e b i o t a s (Chen et al., 1982). T h e p a l e o g e o g r a p h y of C h i n a c a n be described in four places, r e p r e s e n t e d by a series of m a p s ( F i g s . l - 4 ) , as follows.
P a l e o g e o g r a p h y of the N e o c o m i a n interval D u r i n g the e a r l y L o w e r C r e t a c e o u s , the T e t h y s Sea r e g r e s s e d f r o m s o u t h e r n Q i n g h a i to the n o r t h e r n Xizang P l a t e a u , b u t m a i n t a i n e d a c o n n e c t i o n with the s e a w a y of the H i m a l a y a n region, e x t e n d i n g s o u t h e a s t w a r d t h r o u g h the Q a m d o region, and p e r i o d i c a l l y r e a c h i n g w e s t e r n Y u n n a n . This s e a w a y h a d p r o b a b l y w i t h d r a w n from n o r t h e a s t e r n C h i n a by Neoc o m i a n t i m e e v e n t h o u g h t h e r e is some e v i d e n c e w h i c h d e m o n s t r a t e s t h a t a m a r i n e a r m of the Pacific O c e a n r e a c h e d the W u s u l i G u l f of e a s t e r n H e i l o n j i a n g d u r i n g the L a t e J u r a s s i c , and t h a t the T a i w a n P r o v i n c e was p r o b a b l y still s u b m e r g e d b e n e a t h the Pacific at this time.
:~'~1987 Elsevier Science Publishers B.V.
50
Fig.1. Sketch map showing the early Early Cretaceous (Neocomian)paleogeography in China. 1=Tethys Sea. 2= Pacific Ocean. 3= Wusuli Gulf. 4= Shu Lake. 5 = Xichang Lake. 6 = Yunnan Lake. 7= Puer Lake. 8= Ba Lake. 9 = Qingyang Lake. 10= ancient Datong River. 11= Chao Lake. 12= Junggar Basin. 13= Turpan Basin. 14= Kuqa Basin. 15= unnamed River. 16= Kashi Gulf. 17= Songhua Lake. 18= Yunmeng Lake. 19= ancient Gan River. 20= ancient Fuchun River. 21 = active volcanic zones in the eastern coastal low land. There were four major paleogeographic divisions of the interior of China during the Neocomian (see Fig.l). The southwestern
lakes group
A group of large lakes associated with the old Yangtze River drainage existed in southwestern China during the Neocomian (Fig.l; Chen, 1979). The largest of these were Shu Lake and Yu n na n Lake; Xichang Lake lay between these larger lakes and, at times, connected them. These lakes were surrounded by the Yunnan-Guizhou Plateau, the Hengduan Mountains and the old Qinling Ranges. The drainage of these lakes probably con-
nected to the T e t h y a n Seaway through the Nanjian Straits. The Neocomian climate of this region was hot, as evidenced by abundant red-beds bearing an extremely rich fauna of freshwater ostracods, bivalves, and some conchostracans. The inland
water system of Qingyang
Lake
Qingyang Lake occupied the present regions of n o r t h e r n and central Shaanxi, eastern Gansu and eastern Ningxia, an area of about 130,000 km 2 (Fig.l). This represented the largest freshwater lake in China at t hat time. Geographically, this lake bordered on the old Qinling Ranges on the south, the Yinshan
51 Mountains on the north, and the North China Plateau on the east. To the west, the old Datong River drainage, with its broad low floodplain containing numerous smaller lakes, entered Qingyang Lake. The Minhe Lake and the Chao Lake were among the larger lakes of this floodplain, which was also characterized by a complex network of rivers. The climate of this region was hot to mild, as indicated by variegated strata containing abundant freshwater conchostracans, ostracods, bivalves, fish and plants. The northwestern intermontane basins
During the Neocomian, northwestern China was characterized by numerous mountain ranges separated by large intermontane basins. Among these, the Junggar Basin of Xinjiang was the biggest; this basin was subtriangular in outline, and filled with a large lake that was intermittently deep and shallow. Sediments from this lake contain fossils similar to those of the Qingyang Lake. A second large intermontane basin, the Turpan Basin, lay to the east of the old Tianshan Mountains, and a piedmont sag (also called the Kuqa Basin) lay to the south of Tianshan; both basins occupied a narrow belt within this region. In the west-most border area of Xinjiang, there existed a major river system (the Unnamed River) which flowed toward the Tethys Sea in Central Asia. Red-colored sediments characterize the floodplain deposits of the Unnamed River Valley. The active volcanic zones of the eastern coastal lowlands
The Eastern Plateau of China was formed during active motion along the Pacific Plate during the late Jurassic, and began to break up and subside during the Neocomian. This resulted in the widespread eruption of lava and the formation of the active volcanic zones along the coastal lowland. Large parts of Zhejiang, Fujian, southern Jiangxi and eastern Guangdong were covered with neutral and,
predominantly, acidic volcanic rocks in terrestrial facies. Between episodes of volcanic eruption numerous marshes, ponds and lakes formed in depressions between flows. Therefore, great thicknesses of volcanic rocks on the Eastern Plateau of China are characteristically intercalated with numerous layers of lacustrine and fluvial sedimentary strata in which fossils of conchostracans, ostracods, bivalves, gastropods, fishes, plants and insects occur in abundance. These fossils form a reliable basis for stratigraphic subdivision and correlation (Chen and Shen, 1982). During the Neocomian, volcanic activity progressively declined toward the landward side of the Eastern Coastal Lowland, while remaining active on the coast. As a result, many parts of this region were characterized by deposition of red-beds and variegated strata, without intercalated volcanic flows; examples are the Sunchiawan Formation in western Liaoning, the Hsiachuang Formation to the west of Beijing, the Tiekuling Formation in western Jiangxi, and even the Wenmingsze Formation in southern Hunan.
Paleogeography o f the Aptian to Albian interval There is conclusive evidence for the transgression of shallow marine seaways around the Taiwan-Penghu region during the Aptian. Fossils of bivalves and ammonites have been found in drilled cores during petroleum exploration in the Yunlin-Peikang region, including the biostratigraphically important species HolcophyUoceras caucasicum taiwanum Matsumoto, an element of the Aptian Caucasian Sea (Matsumoto, 1979). During this time, there were few changes in the paleogeographical configuration of western and southwestern China, mainly marine volcanic eruptions from somewhere in the present Xizang Plateau (Zhang et al., 1981). In the middle to late Early Cretaceous, regional uplift occurred in southeastern and northwestern China, causing a significant reduction in the area of all inland basins and
52
Fig.2. Sketch map showing the late Early Cretaceous (Aptian-Albian) paleogeography in China. For further explanation of symbols used see Fig.1.
the disappearance of some rivers. This uplift was especially significant in the volcanic lowlands along the southeastern coast of China and in the drainage basin of the Qingyang Lake (Fig.2). The early Lower Cretaceous Moshishan Formation of Zhejiang was deeply eroded and the late Lower Cretaceous Guantou Formation, another volcanic sedimentary rock sequence, is consequently in disconformable contact with the Moshishan Formation. The Guantou Formation itself has very limited geographic distribution. The only major exception to this Aptian-Albian tectonic trend occurred in the northeastern hinterland of China, where a major depression formed in the site of Songhua Lake and deposition of dark-colored rocks of the Dengluku Formation took place.
Paleogeography o f the C e n o m a n i a n Santonian interval By the end of the Albian a major phase of crustal tectonics occurred within China. This period of thrusting and uplift corresponds to the so-called Austrian Movement in Europe. In China, this episode is called the ZhejiangFujian movement in the southeastern coastal region, and the fourth phase of the Yenshan Movement elsewhere. Tectonism during this interval greatly changed the paleogeographical patterns throughout China. The Tethys Sea withdrew from the northern Xizang Plateau, to the south of Lhasa, and never again extended into eastern Xizang and western Yunnan. In most cases, the group of southwestern lakes became closed saline or
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Fig.3. Sketch map showing the early and middle Late Cretaceous (Cenomanian Santonian) paleogeography in China. For further explanation of symbols used see Fig.1.
brackish lakes, in which rock salt and gypsum were widely deposited within red-bed sequences. In some specific basins deposits of sylvite mineral suites were formed. Following the disappearance of the Northwestern Intermontane Basins, however, the marine Kashi Gulf transgressed from Central Asia along the north slope of the ancient Kunlun Mountains, through Yecheng, and reached the vicinity of Hotan in Southern Xinjiang. In this shallow-marine gulf, warm Tethyan climates are indicated by abundant large oysters and rudist bivalves, as well as abundant foraminifers. The inland drainage system of the Quinyang Lake in the Ordos Region entirely disappeared by this time, and was replaced by the newlyformed Yunmeng Marsh system in central China. This took the form of a huge lake,
occupying a large area of the present Nanyang region, J i a n g h a n Plain and Dongting Lake Valley, and was joined with the Hengyang Basin on the south. A major river system feeding this lake is called the ancient Gan River; its upper reaches in Zhejiang are called the ancient Fuchun River: this river system was fed by a number of intermontane streams and creeks from east to west. During the Cenomanian to Santonian interval this region lay within a tropical to subtropical arid climate belt, and was characterized physiographically by low hills, barren deserts, saline lakes, and a yearly rainfall probably below 100 300 mm (Wu et al., 1979). Paleobotanical facies characterizing the region contain Manica, Schizaioisporites and Ephedripites. During the early and middle Upper Cretaceous, the so-called "Songhua Lake" of north-
54 eastern China was actually a broad region characterized by numerous marshes and a complex network of rivers around the lower reaches of the ancient Heilongjian River system, comprising an area of about 240,000 km 2. Shallow environments characterized this region and freshwater crustacean faunas (ostracods, conchostracans) were especially well developed. This region became an important source of petroleum. Songhua Lake was linked to the ancient Pacific Ocean from the northeast by occasional incursions of marine waters. Evidence for this marine influence is found in the Nenjiang Formation and its related upper and lower horizons, where fossils such as Striarca, Mytilus, Brachidontes, Musculus, Sungarichthys, Jilinchthys and Hama have been recovered. In Songhua Lake, variegated deposits containing fossils of hadro-
saurids and Paralligator have been found, indicating that the climate at that time was probably warm and humid. During the C e n o m a n i a n - S a n t o n i a n interval, the ancient Pacific Ocean not only extended into the northeastern corner of Heilongjiang Province from the Wusuli Gulf, but possibly also covered the eastern half of Taiwan, where some Late Cretaceous corals (Elephantaria) have been found from the metamorphic rocks in the Bihou Group east of the Central Mountains.
Paleogeography of the CampanianMaastrichtian interval During the C a m p a n i a n - M a a s t r i c h t i a n interval, there were probably no significant changes in the position of marine transgressions into Taiwan, Xizang and the Kashi region of
Fig.4. Sketch map showing the latest Late Cretaceous (Campanian-Maastrichtian)paleogeographyin China. For further explanation of symbolsused see Fig.1.
55 Xinjiang, but the climate became more arid and much warmer, and the extent of gypsum and salts deposited in the Kashi region increased. However, in northeastern China, the area of Songhua Lake was greatly reduced due to regional uplift which caused the withdrawal of the Wusuli Gulf from the valley. The distribution of drainage systems in the Yunmeng Marsh region changed with the disappearance of the ancient Gan River and Fuchun Rivers, leaving a series of northeastward trending intermontane basins in which the well known Nanxiong Formation and equivalent red bed facies were deposited. These coarse-grained deposits comprise thickbedded red sandstones and conglomerates which commonly form steep cliffs, intercalated with red mudstones containing abundant dinosaur fossils and their eggs. The Yunmeng Marsh became a closed basin during the Campanian Maastrichtian interval and was filled by a brackish to saline lake more restricted in size than the preceding marsh. The southwestern groups of lakes in China persisted for more than one hundred million years during the Jurassic and Cretaceous, and were continuously linked by the ancient Yangtze River, flowing east to west into the Tethys Sea. During the latest Cretaceous, the lakes underwent an extensive change, breaking up, becoming isolated, and changing their form. By the Campanian and Maastrichtian, only scattered small basins remained, in which were mainly deposited red sandstones and mudstones such as the Zhaojiadian and Mankuanhe Formations in Yunnan and the Jiading Group in southern Sichuan. In contrast with the tectonically uplifted terrain of eastern China, some intermontane basins were developed in northwestern China during the Campanian and Maastrichtian. Around the south and north borders of the Junggar Basin, as well as in Turpan and Kuqa, there occur a small number of coarse-grained red beds yielding dinosaur fossils which represent sedimentation in these basins. The sedimentation in these areas was continuous into the overlying Tertiary system.
Conclusions The following are the principal conclusions that can be derived from this paleogeographic survey of China during the Cretaceous. (1) During the Cretaceous, the continental interior of China was characterized by large lake systems in tectonic depressions and intermontane basins, with little or no marine influence. (2) Shallow epicontinental Cretaceous seas were limited to the eastern margins and western boundary areas of China and to the tectonic troughs of the southern and western Tibet Plateau. (3) The changes in continental topography and in the size, shape, and duration of large inland lakes were linked to regional and platemargin tectonic episodes. Many large lakes were formed, disappeared, and were reformed as a result of regional tectonic pulses. (4) Many large lakes underwent major changes in depositional environment as a result of regional Cretaceous tectonic episodes. They were intermittently deep and shallow, fresh to saline, closed basins or dissected by extensive river systems, and in some cases reduced to large marshes or series of smaller lakes. (5) During the Cretaceous, most of southern China was characterized by very warm, dry climates, resulting in the deposition of extensive red beds, gypsum, and rock salt in large water-filled depressions and intermontane basins.
Acknowledgements I wish to t h a n k Professor Erle G. Kauffman, Department of Geological Sciences, University of Colorado, for critically reviewing this manuscript and assistance in developing the English text. I further thank Dr. Kauffman and Dr. William W. Hay of the University of Colorado, Boulder, and Dr. Eric Barron of the National Center for Atmospheric Research, Boulder, Colorado, for inviting me to develop and present this research at the Penrose Confer-
56
ence on Cretaceous Climates at Florissant, Colorado, October 3-8, 1983, and for financial support provided by the National Science Foundation, U.S.A. References Chen Pei-ji, 1979. An outline of paleogeography during the Jurassic and Cretaceous Periods of China - - with a discussion of the origin of the Yangtze River. Acta Sci. Nat. Univ. Pekin., 3:90 109. Chen Pei-ji and Shen Yan-bin, 1982. Late Mesozoic conchostracans from Zhejiang, Jiangsu and Anhui. Palaeontol. Sin. N. S. B, 17, 117 pp.
Chen Pei-ji, Li Wen-ben, Chen Jin-hua, Ye Chun-hui, Wang Zhen, Shen Yah-bin and Sun Dong-li, 1982. Sequence of fossil biotic groups and stratigraphical classification of Jurassic and Cretaceous in China. Sci. Sin. Ser. B, 25(9; 11): 1011-1020; 1227-1248. Matsumoto, T., 1979. Restudy of a phylloceratid ammonite from Peikang, Taiwan. Pet. Geol. Taiwan, 16: 51-57. Wu Ping, Yang Zhen-qiang et al., 1979. CretaceousTertiary Lithofacies and Palaeogeography of Central° southern China. Geological Publishing House, Beijing, 164 pp. Zhang Bing-gao, Sun Dong-li, Yang Sheng-qiu and Ye Chun-hui, 1981. New observations on the Cretaceous of Baingoin and Xainza areas, northern Xizang. J. Stratigr. 5(4): 313-315.