| 青藏古植被的演变与青藏高原的隆起 |
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| 引用本文： | 徐仁.青藏古植被的演变与青藏高原的隆起[J].中国科学院研究生院学报,1982,20(4):385-391. |
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| 作者姓名： | 徐仁 |
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| 作者单位： | (中国科学院植物研究所) |
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| 摘 要： | 西藏北部，在早石炭世晚期位于欧亚古陆的南缘，其植物群与当时印度次大
陆的不同。在晚二叠世，藏北属华夏植物区(即大羽羊齿植物区)；印度河-雅鲁
藏布江大断裂带以南的地区出现舌羊齿植物群， 因而属冈瓦纳古陆的一部分。
到晚三叠世藏北植物群的面貌与我国西南同时代的植物群相似，与印度的则迥
然不同，显示藏北晚三叠世的植物群与南半球植物群也没有直接联系。 柴达木
侏罗纪植物群和拉萨附近早白垩世植物群与北半球的植物群有密切的关系。日
喀则晚白垩世植物群和阿里早始新世植物群也是如此。他们与印度德干玄武岩
夹层中出现的古新世植物群和印度北部始新世植物群也没有联系。 当时，西藏
的北部和南部属于两个不同的古陆，欧亚古陆和冈瓦纳古陆。 两者之间应有一
个很宽阔的特提斯海。因而，青藏的植物化石强有力地支持了大陆漂移的观点，
印度地块在晚侏罗世—白垩纪时是由非洲东南隅分离向北漂移，到始新世才与
亚洲连接，成为现在的南亚次大陆。 欧亚大陆与印度地块的接合线或许就是印
度河－雅鲁藏布江大断裂带。
从晚石炭世到早始新世的植物群的性质上看，藏北地势多半低洼。
中新世时，西藏中部和北部的植被是以落叶阔叶林为主，虽然某些地区有一
些常绿树存在，反映在中新世以前西藏中部和北部的地面已经上升到一定的程
度。在上新世时，藏北的常绿阔叶林逐渐减缩。柴达木盆地的植被转变成落叶
阔叶林－针叶林，以后转变成草原和半荒漠或荒漠，显示西藏和青海的地面进一
步抬升。
到晚上新世，藏北和青海的植被再行演变。然而，喜马拉雅地区的植被仍然
具有常绿栎林和雪松林。可能那时喜马拉雅山不像现在那么高。印度洋的季风
可以吹过喜马拉雅山，没有高山的阻碍。
第四纪是青藏山系和青藏地面上升最剧烈的时期。此时藏北已无常绿阔叶
树的存在。 到第四纪后期西藏大部分地区的植被逐渐演变为高寒荒漠。 最后， 青藏高原变成现在的情况。
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The uplift of the Qinghai-Xizang (Tibet) Plateau in relation to the vegetational changes in the past |
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| Hsü Jen.The uplift of the Qinghai-Xizang (Tibet) Plateau in relation to the vegetational changes in the past[J].Journal of the Graduate School of the Chinese Academy of Sciences,1982,20(4):385-391. |
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| Authors: | Hsü Jen |
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| Institution: | ( Instituic of Botany, Academia Sinica) |
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| Abstract: | By late Carboniferous the flora of northern Xizang differs from that of the
northern India. During late Permian, the northern Xizang was inhabited by the
Gigantopteris flora, while in the southern Xizang was widespread the Glossopteris flora.
The upper Triassic flora of the northern Xizang is closely related to that of south-
western China and quite different from that of India. The Jurassic flora found in
Tsaidam of Chinghai and the early Cretaceous flora found in Lhasa of the northern
Xizang are closely related to these of the northern hemisphere, and show no relation-
ship with these of the southern hemisphere. The late Cretaceous flora of Rikaze and
the early Eocene flora of Ali region are also of northern hemisphere in affinity and
show no relationship with the Daccan Intertrappean and the Eocene floras of India.
Hence, the northern and the southern Xizang should have belonged to two different
continents, Eurasia and Gondwanaland. Between them, a very wide sea, the Tethys,
was situated. This strongly supports the view of continental drift that the India block
drifted in late Jurassic-Cretaceous from the south-eastern corner of Africa and later
on in Eocene joined up with Asia to become its subcontinent. The suture line be-
tween Eurasia and the India block perhaps lies in the belt of basic to ultrabasic rocks
along the Yalu-Tsangpo valleys.
Judging from the nature of the floras ranging from the late Carboniferous to
the early Eocene, the northern Xizang most probably was of lowland in topography
throughout these periods.
The Miocene floras of the central and the northern Xizang were mainly com-
posed of deciduous broad-leaved trees, though some evergreen trees existed somewhere
else. It reflects the land of the central and the northern Xizang had already uplifted
to some extant before Miocene. During the time of Pliocene, the evergreen broad-
leaved trees were gradually declining in their development in the northern Xizang.
The vegetation of the Chaidamu (=Tsaidam) Basin further changed into deciduous
broad-leaved to coniferous forests and then turned into grasslands and semi-deserts
or deserts. It shows by that time the land of Xizang and Chinghai further upheaved.
Up to the late Pliocene, the vegetation of the northern Xizang and Chinghai
further changed. But the vegetation of the Himalayan region was still dominated by
evergreen oaks and Cedrus forests. Most probably by that time the Himalayas was not
so high as present. There was no barrier to prevent the monsoon winds of the Indian
Ocean passing over the Himalayas.
The most active period of the uplift of the mountain ranges in Xizang and the
Qinghai-Xizang Plateau is the Quaternary. By that time no evergreen broad-leaved
trees could live in the northern Xizang. During the late Quaternary, the vegetation of
most parts of Xizang gradually changed into cold alpine desert. At last the Qinghai-Xizang Plateau turned into the present state. |
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