Arkell.1956.Jurassic..

TIBET AND NEPAL 413
TIBET AND NEPAL
The exotic blocks and klippen seem to provide a tantalizing glimpse of
a faunal province lying to the north, in the geologically unexplored regions
of Tibet. Uhlig (1910a, p. 50) was convinced that somewhere there must
be a Tibetan facies of the Upper Jurassic, corresponding to the Alpine
facies of the Lower Lias in the exotic blocks, and perhaps containing such
Alpine genera as Simoceras and Pygope. These genera have not yet been
found, nor any Upper Jurassic Tethyan ammonites, but Uhlig's forecast
has been to some extent fulfilled by the discovery of Calpionella alpina
on the klippen summits of the Kiogars.
Subsequent exploration of Tibet, however, has limited the field of
speculation. A very large region farther east is now known geologically,
a great deal of it consisting of Jurassic rocks. Instead of the expected
'Tibetan facies', normal Spiti Shales are everywhere developed. Practically
continuous outcrops of Jurassic sediments stretch from longitude
82 0
for at least 500 miles through northern Nepal, southern Tibet, Sikkim
and Bhutan, at least as far as Lhasa and longitude 92°E. (Geological
Survey map of India). From the main outcrop, which occupies the
valley of the River Tsangpo and the mountains on both sides, extensions
run northward into the central Tibetan plateau almost to latitude 32 0
N.
The outcrops cover a total area of many thousands of square miles.
Our knowledge of this vast region is still sketchy. The principal sources
are Hayden's excellent account (1907) and the travels of Sven Hedin
(1915-22; and see Hennig, 1915). Hayden's synthesis of widely-scattered
sections is as follows (1907, pp. 35-6):—
Upper and partly Middle Jurassic
/ Spiti Shales
\ Shale and quartzite
Lungma Limestone
f Slate, quartzite and conglomerate
1 Crinoid limestone
\ Slate and quartzite
I Brachiopod limestone
'This, however, is based on such imperfect data that it can be regarded
merely as a suggestion for a temporary working hypothesis' (Hayden).
Apart from the Spiti Shales, the only formation from which Hayden
was able to record identifiable ammonites was the Lungma Limestone, a
band about 15 m. thick which crops out near Kampadzong. It is a hard,
shelly, mottled, patchily ironshot limestone, full of well-preserved shells.
The determinable ammonites collected by Hayden are Sonninia cf.
dominans Buckman, Witchellia aff. platymorpha Buckman, W. tibetica
Arkell, Dorsetensia cf. romanoides (Douville), D. cf. regrediens (Haug),
D. haydeni Arkell and Emileia (Frogdenites) sp. This fauna proves that the
limestone is wholly Middle Bajocian and comprises condensed representatives
of the Sowerbyi and Sauzei Zones and perhaps also the
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