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Palaeochannels on the North China Plain: relationships between their development and tectonics
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Geomorphology18 (1996) 27- 35
Palaeochannels on the North China Plain: relationships between their development and tectonics Xu Qinghai, Wu Chen, Yang Xiaolan, Zhang Ningjia Institute of Geography, Hebei Academy of Sciences, 2 West Street, Shijiazhuang, 050011, China
Received 1 November1993; accepted 15 September 1995
Abstract Geological structure plays an important role in the development of the palaeochannels in the North China Plain. Mountain uplift, subsidence of the plain, and tectonic movement of the basement since the Cenozoic, have interacted with the flashy fluvial regime involving high sediment loads and frequent channel changes. The structure of the basement controlled the scale of palaeochannel development, and tectonics have influenced the changes of the ancient river systems.
1. The structure of the basement of the North China Plain The North China Plain has been a fault-subsidence basin since the Cenozoic, to the west and north of which are rising fault block mountains. In response to activity of the four fault groups, trending NNE, NE, NW and EW, the basement is divided into sub-swell and sub-depression areas, making it a compound fault-subsidence basin. Within the basin, the swells and depressions alternate with one another. From west to east, they are: the central Hebei depression, the Cangzhou and Neihuang swells, the Huanghua and Linqing depressions, the Chengning swell, the Jiyang and the Kaifeng depressions, and the Zhacheng-Lankao swell (Fig. 1). Faulting and subsidence have continued through the Quaternary. The Quaternary sediment in the central Hebei depression, where the greatest subsidence has taken place, is 600 m thick, while that over the Cangzhou and Neihuang swells is only 200-350 m thick. The thickness of Quaternary sediment in the
Huanghua depression, in the Chengning swell and in the Jiyang depression is 450-550 m, 350-375 m, and 350-450 m respectively (Ye, 1989). Tectonic movement makes the North China Plain an earthquake-prone area. There have been earthquakes of magnitude 8.5 or more on the Richter scale, 6 times; magnitude 7-7.9, 14 times; magnitude 6-6.9, 55 times; magnitude 4.7-5.9, over 200 times since 4000 B.P. (Deng, 1980). During the last 30 years several strong earthquakes have occurred, such as the Xintai earthquake (magnitude 6.8) in 1966, the Bohai Gulf earthquake (magnitude 7.4) in 1969 and the Tangshan earthquake (magnitude 7.4) in 1976.
2. The influence of the basement structure on the development of the palaeochanneis As mentioned above, Quatemary deposition was controlled by the structure of the basement, with thick accumulations in the depressions and thin accumulations on the swells. The development of
0169-555X/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. SSDI 0169-555X(95)00149-2
28
Xu Qinghai et al. / Geomorphology 18 (1996) 27-35
palaeochannels within the uppermost 50 or 60 m of the fill is also dominated by the structure of the basement. The greatest densities of palaeochannels
/ / /I_,
~
(palaeochannel zones) occur mostly in the depressions of the basement, while low densities of palaeochannels (inter-palaeochannel zones) occur over the basement swells. This is the case not only
Beii
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m g s h"an /
/:..'
2.'." ,...~... ,'.'." •
131
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B o h a i (;ulf ..
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/ /
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--
~Handan
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Explanatio ~
boundary between and Plain river
mountain
m8
N'%
~
ooast ,ino
'~'~@* o /
main basement f a u l t s
~..,,.~-] infered faults
Kinxiang
v
v
~
0
,Lankao
?
~
8o
,2o k~
Kaifeng
Fig. 1. Basement structure of the North China Plain. (I) Yanshan swell: (I s) Yanshan folded zone, (I 2) Xishan folded zone; (II) Shanxi swell: (II 1) Wutaishan swell, (II 2) Taihangshan anticlinoria; (III) North China depression: (III 1) central Hebei depression, (III2) Cangzhou swell, (III 3) Huanghua depression, (IIl 4) Chengning swell, (II15) central Bohai Sea swell, (lII 6) Jiyang depression, (III 7) Linqing depression, (III8) Neihuang swell, (III9) Zhacheng-Lankao swell; (IV) western and central swell of Shandong Province; (V) Kaifeng depression.
29
Xu Qinghai et al. / Geomorphology 18 (1996) 27-35
for the shallow-buried palaeochannels of the late Pleistocene to the middle Holocene, but also for the late Holocene surface palaeochannels. The shallowburied and surface palaeochannel zones through Yuanyang-Puyang-Liaocheng-Yucheng-Shanghe-
Huiming exist in the Linqing and Jiyang depressions; those through Guanxian-Xiajin-Linxian-Mengcun of the shallow-buried palaeochannel zone and surface palaeochannel zone are both in the Linqing and Huanghua depressions; those through Linzhang-
/
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Q Tianjin
./ /
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/iZ~// i ,A.oQin g fen g,,,,,,~ •
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.o.--.. •
oi"~ " // Jixian i/Huaxian j j
/ :.A"~
// ••
//
~
~
Jining o
Xinxiang
Explanation uanyang
Zhengzhou
i o
Lankao
[--~
•
Kaifeng
flood break
]
~-~-'~aneient river course
AlL
A o Shangqiu
0
50
100km
/ - - - q fault River ~ p r e s e n t Yellow
Fig. 2, Locationsmain floodbreachesof the YellowRiver(revisedfrom Lin, 1988)•(I) Kaifengdepression;(II) Zhacheng-Lankaoswell; (lid Dongpudepression•
30
Xu Qinghai et al. / Geomolphology 18 (1996) 27 35
Present
river
~
I,owland with clay
[~7]
Fault
Ancient course
river
~
Highland sand
~
diversion point
Explanation
0
15
with
30 R m
Fig. 3. Downstream shift of diversion points of the Hutuo River.
Qiuxian-Nangong-Weixian- Xinhe, ShijiazhuangG a o c h e n g - A n p i n g - H e j i a n - R e n q i u and XinleAnguo-Raoyang-Hejian-Renqiu are all in the central Hebei depression (Figs. 7 and 8 in Wu et al., 1996). In depressions, the area occupied by palaeochannel sand bodies occupies 50% or more of the total area; the thickness of the river sand bodies also accounts for 50% or more of the total stratum thickness. The sand bodies are composed mostly of midfine sand, fine sand, and silt at the periphery. On the swells, there are generally single palaeochannels with fewer sand bodies. The river
sand bodies account for less than 50% both in area and in thickness, and are composed mostly of fine sand, silt and sandy clay. From the late Pleistocene to the middle Holocene (25,000-2,500 yr B.P.), the rivers, such as the Yellow River, the Zhang River, the Hutuo River, the Yongding River in front of the Taihang Mountain on the North China Plain all underwent avulsion, generally shifting their courses towards the north. Each was flowing on the north side of its alluvial fan by the end of the middle Holocene. During the late Holocene the trend has been to shift from the north to the south. From the Qing Dynasty (1644 A.D.)
Fig. 4. Locations of diversion points, convergence points and flood breaches of the Yongding River and the Caobai River (revised from Wet, 1988). (Fj) Babaoshan-Caoliying fault; (F2) Nanyuan-Tongxian fault; (F0 Yongding River fault; (Fa) Nankou-Tongxian fault; (Fs) Tanghekou-Tongxian fault; (F6) Tongxian-Tianjin fault; (F7) Yongding-Sanhe fault; (Fs) Liangxiang-Ma]uqiao fault; (F9) NankouMajuqiao fault; (I) western Beijing swell; (1I) Beijing depression: (II~) major subsident area, (II 2) minor subsident area; (lid Daxing swell.
Xu Qinghai et al. / Geomorphology 18 (1996) 27-35
Explanation: ~'-]
31
ecaocun(
diversion point
r ~ - - ] convergence point ~
present river '~-~ ancient river course
~
mountain area
~ ~
\\
Yanggezhuang
]mountain front fan alluvial fan I I
----~ fault
x,
[----~ flood break
\\ \\ iX
ing City o Yanjiao F~
' Daxin ~
I\
\
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\\
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J J
a.
\ \ "~ ~ " ~ ~., \
I/
~. °Caiv~ "
~ "~7
~ongnu
\ \ 9Fengheying "-~
"'~--'
"2" 0
~
10 km
32
Xu Qinghai et al. / Geomorphology 18 (1996) 27-35
these rivers began to move northward again, and each had located in its present course by 100-200 yr B.P. As to the rivers in front of the Yanshan Mountains, a regularity in direction of avulsion and course change is also apparent, i.e. westward in the middle Holocene and eastward in the late Holocene. The fact that in this huge area of the plain, river courses changed in the same direction during the same period of time, strongly implies the influence of basement structure over river system changes and palaeochannel development. It can also be inferred that subsidence movements in the North China Plain were weak in the south but strong in the north from the late Pleistocene to the middle Holocene, hence influencing the rivers to change their courses northward. This is further substantiated by the fact that, in the over 4000 years of history, the Yellow River flowed in the northern part of the North China Plain for 3326 years, but only for 611 years to the south of its present location (Ye, 1982). In the late Holocene, subsidence movements in the southern part of the plain strengthened, while in the last 200 years subsidence is again stronger in the northern part. It is clear that in the subsiding North China Plain since the late Pleistocene, the differential movement of the basement has continued, causing the rivers to gather into the depressions. The fact that surface palaeochannel zones frequently overlap the shallowburied palaeochannel zones, and that the palaeochannel development and ancient river course changes are highly consistent in direction, are all reflections of the geological structure.
3. The influence of basement tectonics on the locations of the diversion points, convergence points and flood breaches A diversion point means a place where a river frequently divides and avulsions take place. A convergence point is a place where two or more rivers flow together. A flood breach is a point where river banks were broken. The locations of diversion points and convergence points of the rivers on the North China Plain have fluctuated several times since the late Pleistocene. This could be in part related to sea-level changes, in addition to neotectonic movements of mountain up-
lift and plain subsidence. Because erosion was dominant from the late Pleistocene to the early Holocene, accumulation dominant in the middle Holocene and erosion dominant in the late Holocene, all major changes took place synchronously with sea-level changes, resulting in fluctuations of fiver base-levels. It is not clear whether neotectonic movement or sea-level fluctuation is the dominant factor. Nevertheless, the locations of diversion points are indeed influenced by basement tectonics. For example, during the late Pleistocene the diversion points of the Yellow River concentrated around Mengjin, from where palaeochannels present a radial arrangement. After that, as the area around Mengjin was uplifted, diversion points moved eastward. The earliest flood breaches recorded in history (after 4000 yr B.P.) took place during the East Zhou Dynasty (770-256 yr B.C.) at Jixian in northern Henan province (Fig. 2). From the period of the Chunqiu and Zhanguo states to the west Han Dynasty (475-23 yr B.C.), the flood breaches were located further downstream near Guantao, Puyang and Huaxian, along the border of Hebei and Shandong provinces. From the East Han to the Tang Dynasties (25-907 A.D.) flood breaches were located upstream, near Jixian and Huaxian. During the North Song Dynasty (960-1127 A.D.) the Yellow River burst at Yangwu (now Yuanyang county), 100 km upstream from where flood breaches had occurred for 1000 years (Lin, 1988). All of the above indicates that before the North Song Dynasty the flood breaches were located within the Dongpu depression, and after the North Song Dynasty were located within the Kaifeng depression, but did not occur in the Zhacheng-Lankao swell at all. During the late Pleistocene the diversion points of the Hutuo River were located around Huangbizhuang, forming the old mountain front fan. By the late Holocene the diversion points had moved downstream to Gaocheng, forming a new alluvial fan. These points around Gaocheng are along the NNE Anguo-Gaocheng-Shexian fault (Shao and Hart, 1984). The flood breaches of this fiver are all located within the central Hebei depression (Fig. 3). According to Wei (1988), palaeochannel development of the Yongding River is characterised by a gradual southward shift of the diversion points. Alluvial fans of different ages developed sequentially at Shijinshan, Lugouqiao and Jinmenzha. Fig. 4 is taken
33
Xu Qinghai et al. / Geomorphology 18 (1996) 27-35
from Wei's (1988) map of diversion and convergence points and palaeochannel distribution of the Yongding and Chaobai Rivers, with revisions based
on the work by Li (1982). The flood breaches in Fig. 4 are inferred from the palaeochannel map. The Yongding River (Fig. 4) has 4 diversion points, of
Explanation Diversion point Ancient river course ~
Present river
~/~
Mountain area
~
Alluvial fan and fan delta
~
Mountain front fan 0
5
lokm
Dapuh~
[/Tin~lih~/ \
[vj &
~ oLiuzan
//
\'C ~ '1 ~
"
'~ \\
.-~<. "b
Rohai
" " "'~ ""'"" "'"
Fig. 5. Locationsof diversionpoints of LuanRiver(revisedfromWei, 1988). (Fl) Ninghc-Tangshanfault;(F2) Baigezhuang-Lulongfault; (F3) Ninghc-Luannan-Changlifault;(F4) Baigezhuang-Letingfault;(Fs) LuanRiverfault; (F6) YeJituo-Fcnrunfault.
34
Xu Qinghai et al. / Geomorphology 18 11996) 27 33
which the Shijingshan point is the earliest, lormed during the late Pleistocene, relating to fault F~ (Fig. 4). The Majuqao point is the second, formed during the late Holocene, with the diversion point on its apex located on the fault F5 (Fig. 4). The Lugouqiao point is the third, formed by the 1 lth centuu A.D., located just on the fault F 3 (Fig. 4). Due to the influence of the subsidence of the Beijing depression, the latest diversion point is the Jinmenzha point, formed in the 16th century, probably affected by the fault F 2 (Fig. 4). Fig. 4 also indicates that the flood breaches and diversion points of the Yongding River in the historical period were mostly located within the Beijing depression. The Chaobai River system is another major river system in the North China Plain, consisting of the Cao River, the Bai River and other tributaries. At the end of the Pleistocene and during the early historical period, the Chao River and the Bai River entered the sea separately. Under the influence of intense subsidence during the historical period (since 4000 yr B.P.), the two rivers migrated towards the centre of the subsidence. The development of palaeochannels of the Chaobai River was characterised not by diversion points or flood breaches, but by convergence points. The first convergence point of the Chao and the Bai rivers was formed during the North Wei Dynasty (386-535 A.D.), and located at the intersection of the fault F 2 and fault F4 (Fig. 4). Later on, the convergence point gradually moved upstream to the north of Shunyi during the 9th and 10th century A.D. and to the Miyun county seat during the Ming
Dynasty (1368-1644 A.D.), where it is still located. The upstream movement of the convergence point is probably the result of intense subsidence of the Shunyi depression and to the east of the fault Fs. During the late Pleistocene the Luan River developed an alluvial fan radiating from the diversion point at Xiakou village, Qianxi county. In the early Holocene, it developed a diversion point at Zhua village of Qianan county, and later on formed an alluvial fan from the diversion point at Luanxian. In the late Holocene, its diversion points moved downstream to Macheng, then to Dingliuhe and Leting (Wei, 1988). The Zhua diversion point is located on fault F6, the Luanxian point is at the intersection of faults F2 and F5, the Macheng point is also on fault Fs, and the Dingliuhe and the Leting points are probably influenced by faults F 3 and F4 respectively (Fig. 5). These indicate that the diversion points, the flood breaches and convergence points of the rivers on the North China Plain were influenced by the basement tectonics.
4. The influence of basement tectonics on abrupt changes in direction of river-flow
The shallow-buried palaeochannel zone of the Hutuo River turns to the north on the western edge of the Cangzhou swell. The surface palaeochannel belt of the Yongdinghe River abruptly broadens to the west of Tianjin. Tongxian-Wuqing-Ninghe
Table 1 Estimation of sedimentation rates on the North China Plain in the past 25,000 years Tectonic unit
Place
Total depth (m) and rate (cm/yr) depth
rate
Depth (m) and rate (cm/yr) by period Q~-~-Q~
QJ
Q43
depth
rate
depth
rate
depth
rate
Linqing-Jiyangdepression
Shenxian Huiming
37.00 31.00
0.150 0.124
21.50 2t.90
0.150 0,151
12.14 7.05
0.24 0.10
3.36 2.11
0.13 0.08
Huanghuadepression
Mengcun Huanghua
32.40 31.30
0.139 0.125
11.40 11.80
0,080 0.081
12,80 14.80
0.25 0.29
5.80 4.70
0.23 0.19
Cangxian swell
Nangong
29.98
0.119
11.00
0.080
12.00
0.24
6.98
0.28
Central Hebeidepression
Suning Hejian
30.00 36.00
0.120 0.140
10.00 19.00
0.071 0.130
13.00 14.00
0.26 0.28
7.00 7.00
0.28 0.28
Xu Qinghai et al. / Geomorphology 18 (1996) 27-35
palaeochannel suddenly turns a right angle to the east. These direction changes all appear to be related to the continued rise of the Cangxian swell (Figs. 7 and 8 in Wu et al., 1996). The Luan River abruptly turns its direction at Lulong and Luanxian roughly paralleling fault F 2 and F5 (Fig. 5).
5. The influence of basement tectonics on sedimentation rates
The sedimentation rates in the North China Plain since the late Pleistocene have been estimated on the basis of various analyses and strata divisions of the boreholes drilled by the authors (see Table 1). Table 1 reveals several regularities: (1) Since the late Pleistocene, the total sediment depth and sedimentation rates are greater in depressions than over swells. This is also the case for the whole Quaternary period, and corresponds to the fact that palaeochannels developed mostly in depressions (Ye, 1989). (2) During the late Pleistocene and the early Holocene, the Linqing, the Jiyang depression and the central Hebei depression were where the sedimentation rates were higher; while in the middle Holocene, they were high in the Huanghua depression and the central Hebei depression. This is consistent with the fact that subsidence was stronger in the northern than in the southern part of the plain from the late Pleistocene to the middle Holocene. In the late Holocene. The sedimentation rate in the central Hebei depression and in the Cangxian swell was relatively high. (3) Since the late Pleistocene, the middle Holocene had the highest sedimentation rate, with an average of 0.23 c m / y r , the average rate in the late Holocene was lower, 0.21 cm/yr, and that from the late Pleistocene to the early Holocene was the lowest, with an average sedimentation rate only 0.10 cm/yr.
35
6. S u m m a r y
It is clear that besides the impact of topography, hydrology, climate, sediment load, vegetation, organisms and human activities, which interact with each other, the development of the palaeochannels on the North China Plain was constantly under the influence of the tectonics of the basement. The relationship between palaeochannels and basement tectonics has important implications for research and in the utilization of palaeochannels as groundwater reservoirs.
References Deng Qidong, 1980. Cenozoic and recent geotectonic characteristics of the North China fault block region. In: Formation and Development of the North China Fault Block Region. Sci. Press. Li Huazhang, 1982. Study on fault structures and their movement of the Beiing Plain. Unpubl. data. Lin Hengzhang, 1988. An approach to the background of the Huanghe River (Yellow River) course evolution caused by the neotectonic movement. In: Remote Sensing Analysis of Dynamic Changes of Water Area in the North China Plain. Sci. Press, pp. 15-25. Shao Shixiong and Han Shuhua, 1984. Analysis on the main characteristics of the neotectonic movement in the Hebei Plain. Mar. Geol. Quat. Geol., 4(4). Wei Chengjie, 1988. Remote sensing analysis of dynamic changes of rivers in Beijing-Tianjin-Tangshan plain area. In: Remote Sensing Analysis of Dynamic Changes of Water in the North China Plain, Sci. Press, pp. 26-35. Wu Chen, Xu Qinghai, Zhang Xiuqing, Ma Yonghong, 1996. Palaeochannels on the North China Plain: types and distributions. In: Wu Chen (Editor), Studies of the Palaeochannels on the North China Plain. Geomorphology, 18: 5-14, this issue. Ye Qingchao, 1982. Model of the formation of the Yellow River alluvial-pluvial fan and the evolution of its course in lower reaches. The People's Yellow River, No. 4. Ye Qingchao, 1989. Landform system of the great plain of North China and its tendency of environmental evolution. Geogr. Res., 8(3): 10-21.
Geomorphology18 (1996) 27- 35
Palaeochannels on the North China Plain: relationships between their development and tectonics Xu Qinghai, Wu Chen, Yang Xiaolan, Zhang Ningjia Institute of Geography, Hebei Academy of Sciences, 2 West Street, Shijiazhuang, 050011, China
Received 1 November1993; accepted 15 September 1995
Abstract Geological structure plays an important role in the development of the palaeochannels in the North China Plain. Mountain uplift, subsidence of the plain, and tectonic movement of the basement since the Cenozoic, have interacted with the flashy fluvial regime involving high sediment loads and frequent channel changes. The structure of the basement controlled the scale of palaeochannel development, and tectonics have influenced the changes of the ancient river systems.
1. The structure of the basement of the North China Plain The North China Plain has been a fault-subsidence basin since the Cenozoic, to the west and north of which are rising fault block mountains. In response to activity of the four fault groups, trending NNE, NE, NW and EW, the basement is divided into sub-swell and sub-depression areas, making it a compound fault-subsidence basin. Within the basin, the swells and depressions alternate with one another. From west to east, they are: the central Hebei depression, the Cangzhou and Neihuang swells, the Huanghua and Linqing depressions, the Chengning swell, the Jiyang and the Kaifeng depressions, and the Zhacheng-Lankao swell (Fig. 1). Faulting and subsidence have continued through the Quaternary. The Quaternary sediment in the central Hebei depression, where the greatest subsidence has taken place, is 600 m thick, while that over the Cangzhou and Neihuang swells is only 200-350 m thick. The thickness of Quaternary sediment in the
Huanghua depression, in the Chengning swell and in the Jiyang depression is 450-550 m, 350-375 m, and 350-450 m respectively (Ye, 1989). Tectonic movement makes the North China Plain an earthquake-prone area. There have been earthquakes of magnitude 8.5 or more on the Richter scale, 6 times; magnitude 7-7.9, 14 times; magnitude 6-6.9, 55 times; magnitude 4.7-5.9, over 200 times since 4000 B.P. (Deng, 1980). During the last 30 years several strong earthquakes have occurred, such as the Xintai earthquake (magnitude 6.8) in 1966, the Bohai Gulf earthquake (magnitude 7.4) in 1969 and the Tangshan earthquake (magnitude 7.4) in 1976.
2. The influence of the basement structure on the development of the palaeochanneis As mentioned above, Quatemary deposition was controlled by the structure of the basement, with thick accumulations in the depressions and thin accumulations on the swells. The development of
0169-555X/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. SSDI 0169-555X(95)00149-2
28
Xu Qinghai et al. / Geomorphology 18 (1996) 27-35
palaeochannels within the uppermost 50 or 60 m of the fill is also dominated by the structure of the basement. The greatest densities of palaeochannels
/ / /I_,
~
(palaeochannel zones) occur mostly in the depressions of the basement, while low densities of palaeochannels (inter-palaeochannel zones) occur over the basement swells. This is the case not only
Beii
~ --Y~n2an
Mt
]
m g s h"an /
/:..'
2.'." ,...~... ,'.'." •
131
oBaoding (o."
.',i
,,o
Shijia z h u a n g
B o h a i (;ulf ..
'j::..-. • .....
/ /
Dezh,
-
/
--
~Handan
/~"J "~ J"" inan
Explanatio ~
boundary between and Plain river
mountain
m8
N'%
~
ooast ,ino
'~'~@* o /
main basement f a u l t s
~..,,.~-] infered faults
Kinxiang
v
v
~
0
,Lankao
?
~
8o
,2o k~
Kaifeng
Fig. 1. Basement structure of the North China Plain. (I) Yanshan swell: (I s) Yanshan folded zone, (I 2) Xishan folded zone; (II) Shanxi swell: (II 1) Wutaishan swell, (II 2) Taihangshan anticlinoria; (III) North China depression: (III 1) central Hebei depression, (III2) Cangzhou swell, (III 3) Huanghua depression, (IIl 4) Chengning swell, (II15) central Bohai Sea swell, (lII 6) Jiyang depression, (III 7) Linqing depression, (III8) Neihuang swell, (III9) Zhacheng-Lankao swell; (IV) western and central swell of Shandong Province; (V) Kaifeng depression.
29
Xu Qinghai et al. / Geomorphology 18 (1996) 27-35
for the shallow-buried palaeochannels of the late Pleistocene to the middle Holocene, but also for the late Holocene surface palaeochannels. The shallowburied and surface palaeochannel zones through Yuanyang-Puyang-Liaocheng-Yucheng-Shanghe-
Huiming exist in the Linqing and Jiyang depressions; those through Guanxian-Xiajin-Linxian-Mengcun of the shallow-buried palaeochannel zone and surface palaeochannel zone are both in the Linqing and Huanghua depressions; those through Linzhang-
/
/ /
•~ Shijiazhuang ©
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Q Tianjin
./ /
J / i '' "~" / °Cangzh°u f/''//,/.~'~ ~"t'
/..-" . i . S ' i . . i
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.
./," i ,.'.<
•
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: ./o Oeznou
/i// _ _ ,/////
//
ti\
k-i
/
•
.
/
.7---
)/'Gu&ntao"
Handa
Z
/iZ~// i ,A.oQin g fen g,,,,,,~ •
Xunxian /
.o.--.. •
oi"~ " // Jixian i/Huaxian j j
/ :.A"~
// ••
//
~
~
Jining o
Xinxiang
Explanation uanyang
Zhengzhou
i o
Lankao
[--~
•
Kaifeng
flood break
]
~-~-'~aneient river course
AlL
A o Shangqiu
0
50
100km
/ - - - q fault River ~ p r e s e n t Yellow
Fig. 2, Locationsmain floodbreachesof the YellowRiver(revisedfrom Lin, 1988)•(I) Kaifengdepression;(II) Zhacheng-Lankaoswell; (lid Dongpudepression•
30
Xu Qinghai et al. / Geomolphology 18 (1996) 27 35
Present
river
~
I,owland with clay
[~7]
Fault
Ancient course
river
~
Highland sand
~
diversion point
Explanation
0
15
with
30 R m
Fig. 3. Downstream shift of diversion points of the Hutuo River.
Qiuxian-Nangong-Weixian- Xinhe, ShijiazhuangG a o c h e n g - A n p i n g - H e j i a n - R e n q i u and XinleAnguo-Raoyang-Hejian-Renqiu are all in the central Hebei depression (Figs. 7 and 8 in Wu et al., 1996). In depressions, the area occupied by palaeochannel sand bodies occupies 50% or more of the total area; the thickness of the river sand bodies also accounts for 50% or more of the total stratum thickness. The sand bodies are composed mostly of midfine sand, fine sand, and silt at the periphery. On the swells, there are generally single palaeochannels with fewer sand bodies. The river
sand bodies account for less than 50% both in area and in thickness, and are composed mostly of fine sand, silt and sandy clay. From the late Pleistocene to the middle Holocene (25,000-2,500 yr B.P.), the rivers, such as the Yellow River, the Zhang River, the Hutuo River, the Yongding River in front of the Taihang Mountain on the North China Plain all underwent avulsion, generally shifting their courses towards the north. Each was flowing on the north side of its alluvial fan by the end of the middle Holocene. During the late Holocene the trend has been to shift from the north to the south. From the Qing Dynasty (1644 A.D.)
Fig. 4. Locations of diversion points, convergence points and flood breaches of the Yongding River and the Caobai River (revised from Wet, 1988). (Fj) Babaoshan-Caoliying fault; (F2) Nanyuan-Tongxian fault; (F0 Yongding River fault; (Fa) Nankou-Tongxian fault; (Fs) Tanghekou-Tongxian fault; (F6) Tongxian-Tianjin fault; (F7) Yongding-Sanhe fault; (Fs) Liangxiang-Ma]uqiao fault; (F9) NankouMajuqiao fault; (I) western Beijing swell; (1I) Beijing depression: (II~) major subsident area, (II 2) minor subsident area; (lid Daxing swell.
Xu Qinghai et al. / Geomorphology 18 (1996) 27-35
Explanation: ~'-]
31
ecaocun(
diversion point
r ~ - - ] convergence point ~
present river '~-~ ancient river course
~
mountain area
~ ~
\\
Yanggezhuang
]mountain front fan alluvial fan I I
----~ fault
x,
[----~ flood break
\\ \\ iX
ing City o Yanjiao F~
' Daxin ~
I\
\
/ qlngyu'hdiano "- ~
\\
,~\'~,
~ I \"~
"b .'~ ~Lixi
\,I.
\
J J
a.
\ \ "~ ~ " ~ ~., \
I/
~. °Caiv~ "
~ "~7
~ongnu
\ \ 9Fengheying "-~
"'~--'
"2" 0
~
10 km
32
Xu Qinghai et al. / Geomorphology 18 (1996) 27-35
these rivers began to move northward again, and each had located in its present course by 100-200 yr B.P. As to the rivers in front of the Yanshan Mountains, a regularity in direction of avulsion and course change is also apparent, i.e. westward in the middle Holocene and eastward in the late Holocene. The fact that in this huge area of the plain, river courses changed in the same direction during the same period of time, strongly implies the influence of basement structure over river system changes and palaeochannel development. It can also be inferred that subsidence movements in the North China Plain were weak in the south but strong in the north from the late Pleistocene to the middle Holocene, hence influencing the rivers to change their courses northward. This is further substantiated by the fact that, in the over 4000 years of history, the Yellow River flowed in the northern part of the North China Plain for 3326 years, but only for 611 years to the south of its present location (Ye, 1982). In the late Holocene, subsidence movements in the southern part of the plain strengthened, while in the last 200 years subsidence is again stronger in the northern part. It is clear that in the subsiding North China Plain since the late Pleistocene, the differential movement of the basement has continued, causing the rivers to gather into the depressions. The fact that surface palaeochannel zones frequently overlap the shallowburied palaeochannel zones, and that the palaeochannel development and ancient river course changes are highly consistent in direction, are all reflections of the geological structure.
3. The influence of basement tectonics on the locations of the diversion points, convergence points and flood breaches A diversion point means a place where a river frequently divides and avulsions take place. A convergence point is a place where two or more rivers flow together. A flood breach is a point where river banks were broken. The locations of diversion points and convergence points of the rivers on the North China Plain have fluctuated several times since the late Pleistocene. This could be in part related to sea-level changes, in addition to neotectonic movements of mountain up-
lift and plain subsidence. Because erosion was dominant from the late Pleistocene to the early Holocene, accumulation dominant in the middle Holocene and erosion dominant in the late Holocene, all major changes took place synchronously with sea-level changes, resulting in fluctuations of fiver base-levels. It is not clear whether neotectonic movement or sea-level fluctuation is the dominant factor. Nevertheless, the locations of diversion points are indeed influenced by basement tectonics. For example, during the late Pleistocene the diversion points of the Yellow River concentrated around Mengjin, from where palaeochannels present a radial arrangement. After that, as the area around Mengjin was uplifted, diversion points moved eastward. The earliest flood breaches recorded in history (after 4000 yr B.P.) took place during the East Zhou Dynasty (770-256 yr B.C.) at Jixian in northern Henan province (Fig. 2). From the period of the Chunqiu and Zhanguo states to the west Han Dynasty (475-23 yr B.C.), the flood breaches were located further downstream near Guantao, Puyang and Huaxian, along the border of Hebei and Shandong provinces. From the East Han to the Tang Dynasties (25-907 A.D.) flood breaches were located upstream, near Jixian and Huaxian. During the North Song Dynasty (960-1127 A.D.) the Yellow River burst at Yangwu (now Yuanyang county), 100 km upstream from where flood breaches had occurred for 1000 years (Lin, 1988). All of the above indicates that before the North Song Dynasty the flood breaches were located within the Dongpu depression, and after the North Song Dynasty were located within the Kaifeng depression, but did not occur in the Zhacheng-Lankao swell at all. During the late Pleistocene the diversion points of the Hutuo River were located around Huangbizhuang, forming the old mountain front fan. By the late Holocene the diversion points had moved downstream to Gaocheng, forming a new alluvial fan. These points around Gaocheng are along the NNE Anguo-Gaocheng-Shexian fault (Shao and Hart, 1984). The flood breaches of this fiver are all located within the central Hebei depression (Fig. 3). According to Wei (1988), palaeochannel development of the Yongding River is characterised by a gradual southward shift of the diversion points. Alluvial fans of different ages developed sequentially at Shijinshan, Lugouqiao and Jinmenzha. Fig. 4 is taken
33
Xu Qinghai et al. / Geomorphology 18 (1996) 27-35
from Wei's (1988) map of diversion and convergence points and palaeochannel distribution of the Yongding and Chaobai Rivers, with revisions based
on the work by Li (1982). The flood breaches in Fig. 4 are inferred from the palaeochannel map. The Yongding River (Fig. 4) has 4 diversion points, of
Explanation Diversion point Ancient river course ~
Present river
~/~
Mountain area
~
Alluvial fan and fan delta
~
Mountain front fan 0
5
lokm
Dapuh~
[/Tin~lih~/ \
[vj &
~ oLiuzan
//
\'C ~ '1 ~
"
'~ \\
.-~<. "b
Rohai
" " "'~ ""'"" "'"
Fig. 5. Locationsof diversionpoints of LuanRiver(revisedfromWei, 1988). (Fl) Ninghc-Tangshanfault;(F2) Baigezhuang-Lulongfault; (F3) Ninghc-Luannan-Changlifault;(F4) Baigezhuang-Letingfault;(Fs) LuanRiverfault; (F6) YeJituo-Fcnrunfault.
34
Xu Qinghai et al. / Geomorphology 18 11996) 27 33
which the Shijingshan point is the earliest, lormed during the late Pleistocene, relating to fault F~ (Fig. 4). The Majuqao point is the second, formed during the late Holocene, with the diversion point on its apex located on the fault F5 (Fig. 4). The Lugouqiao point is the third, formed by the 1 lth centuu A.D., located just on the fault F 3 (Fig. 4). Due to the influence of the subsidence of the Beijing depression, the latest diversion point is the Jinmenzha point, formed in the 16th century, probably affected by the fault F 2 (Fig. 4). Fig. 4 also indicates that the flood breaches and diversion points of the Yongding River in the historical period were mostly located within the Beijing depression. The Chaobai River system is another major river system in the North China Plain, consisting of the Cao River, the Bai River and other tributaries. At the end of the Pleistocene and during the early historical period, the Chao River and the Bai River entered the sea separately. Under the influence of intense subsidence during the historical period (since 4000 yr B.P.), the two rivers migrated towards the centre of the subsidence. The development of palaeochannels of the Chaobai River was characterised not by diversion points or flood breaches, but by convergence points. The first convergence point of the Chao and the Bai rivers was formed during the North Wei Dynasty (386-535 A.D.), and located at the intersection of the fault F 2 and fault F4 (Fig. 4). Later on, the convergence point gradually moved upstream to the north of Shunyi during the 9th and 10th century A.D. and to the Miyun county seat during the Ming
Dynasty (1368-1644 A.D.), where it is still located. The upstream movement of the convergence point is probably the result of intense subsidence of the Shunyi depression and to the east of the fault Fs. During the late Pleistocene the Luan River developed an alluvial fan radiating from the diversion point at Xiakou village, Qianxi county. In the early Holocene, it developed a diversion point at Zhua village of Qianan county, and later on formed an alluvial fan from the diversion point at Luanxian. In the late Holocene, its diversion points moved downstream to Macheng, then to Dingliuhe and Leting (Wei, 1988). The Zhua diversion point is located on fault F6, the Luanxian point is at the intersection of faults F2 and F5, the Macheng point is also on fault Fs, and the Dingliuhe and the Leting points are probably influenced by faults F 3 and F4 respectively (Fig. 5). These indicate that the diversion points, the flood breaches and convergence points of the rivers on the North China Plain were influenced by the basement tectonics.
4. The influence of basement tectonics on abrupt changes in direction of river-flow
The shallow-buried palaeochannel zone of the Hutuo River turns to the north on the western edge of the Cangzhou swell. The surface palaeochannel belt of the Yongdinghe River abruptly broadens to the west of Tianjin. Tongxian-Wuqing-Ninghe
Table 1 Estimation of sedimentation rates on the North China Plain in the past 25,000 years Tectonic unit
Place
Total depth (m) and rate (cm/yr) depth
rate
Depth (m) and rate (cm/yr) by period Q~-~-Q~
QJ
Q43
depth
rate
depth
rate
depth
rate
Linqing-Jiyangdepression
Shenxian Huiming
37.00 31.00
0.150 0.124
21.50 2t.90
0.150 0,151
12.14 7.05
0.24 0.10
3.36 2.11
0.13 0.08
Huanghuadepression
Mengcun Huanghua
32.40 31.30
0.139 0.125
11.40 11.80
0,080 0.081
12,80 14.80
0.25 0.29
5.80 4.70
0.23 0.19
Cangxian swell
Nangong
29.98
0.119
11.00
0.080
12.00
0.24
6.98
0.28
Central Hebeidepression
Suning Hejian
30.00 36.00
0.120 0.140
10.00 19.00
0.071 0.130
13.00 14.00
0.26 0.28
7.00 7.00
0.28 0.28
Xu Qinghai et al. / Geomorphology 18 (1996) 27-35
palaeochannel suddenly turns a right angle to the east. These direction changes all appear to be related to the continued rise of the Cangxian swell (Figs. 7 and 8 in Wu et al., 1996). The Luan River abruptly turns its direction at Lulong and Luanxian roughly paralleling fault F 2 and F5 (Fig. 5).
5. The influence of basement tectonics on sedimentation rates
The sedimentation rates in the North China Plain since the late Pleistocene have been estimated on the basis of various analyses and strata divisions of the boreholes drilled by the authors (see Table 1). Table 1 reveals several regularities: (1) Since the late Pleistocene, the total sediment depth and sedimentation rates are greater in depressions than over swells. This is also the case for the whole Quaternary period, and corresponds to the fact that palaeochannels developed mostly in depressions (Ye, 1989). (2) During the late Pleistocene and the early Holocene, the Linqing, the Jiyang depression and the central Hebei depression were where the sedimentation rates were higher; while in the middle Holocene, they were high in the Huanghua depression and the central Hebei depression. This is consistent with the fact that subsidence was stronger in the northern than in the southern part of the plain from the late Pleistocene to the middle Holocene. In the late Holocene. The sedimentation rate in the central Hebei depression and in the Cangxian swell was relatively high. (3) Since the late Pleistocene, the middle Holocene had the highest sedimentation rate, with an average of 0.23 c m / y r , the average rate in the late Holocene was lower, 0.21 cm/yr, and that from the late Pleistocene to the early Holocene was the lowest, with an average sedimentation rate only 0.10 cm/yr.
35
6. S u m m a r y
It is clear that besides the impact of topography, hydrology, climate, sediment load, vegetation, organisms and human activities, which interact with each other, the development of the palaeochannels on the North China Plain was constantly under the influence of the tectonics of the basement. The relationship between palaeochannels and basement tectonics has important implications for research and in the utilization of palaeochannels as groundwater reservoirs.
References Deng Qidong, 1980. Cenozoic and recent geotectonic characteristics of the North China fault block region. In: Formation and Development of the North China Fault Block Region. Sci. Press. Li Huazhang, 1982. Study on fault structures and their movement of the Beiing Plain. Unpubl. data. Lin Hengzhang, 1988. An approach to the background of the Huanghe River (Yellow River) course evolution caused by the neotectonic movement. In: Remote Sensing Analysis of Dynamic Changes of Water Area in the North China Plain. Sci. Press, pp. 15-25. Shao Shixiong and Han Shuhua, 1984. Analysis on the main characteristics of the neotectonic movement in the Hebei Plain. Mar. Geol. Quat. Geol., 4(4). Wei Chengjie, 1988. Remote sensing analysis of dynamic changes of rivers in Beijing-Tianjin-Tangshan plain area. In: Remote Sensing Analysis of Dynamic Changes of Water in the North China Plain, Sci. Press, pp. 26-35. Wu Chen, Xu Qinghai, Zhang Xiuqing, Ma Yonghong, 1996. Palaeochannels on the North China Plain: types and distributions. In: Wu Chen (Editor), Studies of the Palaeochannels on the North China Plain. Geomorphology, 18: 5-14, this issue. Ye Qingchao, 1982. Model of the formation of the Yellow River alluvial-pluvial fan and the evolution of its course in lower reaches. The People's Yellow River, No. 4. Ye Qingchao, 1989. Landform system of the great plain of North China and its tendency of environmental evolution. Geogr. Res., 8(3): 10-21.