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The uplift of the Qinghai-Xizang (Tibet) Plateau in relation to the vegetational changes in the past

Hsü Jen   

  1. ( Instituic of Botany, Academia Sinica)
  • Received:1900-01-01 Revised:1900-01-01 Online:1982-11-18 Published:1982-11-18
  • Contact: Hsü Jen

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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