Arkell.1956.Jurassic..

368 RANGES OF SOUTH-WEST ASIA
of Jurassic does not favour comparison of the Elburz with the Pyrenees
as advocated by Schroeder (1944).
There have been two major orogenies since deposition of the Jurassic
rocks. The first and greatest involved overfolding and northward thrusting
in the late Cretaceous, or possibly post-Cretaceous, followed by erosion
and marine transgression by Eocene and Oligocene seas. Afterwards
there was late Tertiary refolding and faulting and outbreak of giant
Quaternary volcanoes: a history also similar to that of the Caucasus.
In general the Elburz Jurassic falls into two major lithological and
palaeontological divisions: (1) the carbonaceous facies of the Lias, up to
1200 m. thick, perhaps locally much more, which may follow on marine
Trias or may overstep on to Palaeozoic and even crystalline schists as
near Meshed, and which may contain dense fissile limestones; (2)
marine limestones, generally poor in identifiable fos?ils, but mainly
Upper Jurassic in age but extending from at least as early as Bathonian
to Tithonian, with thicknesses varying from 1000 m. near Teheran to
1500 m. farther east (Clapp, 1940). In the east the lower part of the
limestones and also some sandstones and shales below are Middle Jurassic
in age (Bajocian-Bathonian).
The most detailed stratigraphical work so far has been done in the
region NE. of Teheran. Where the Heras and Alarm Rivers cut by
gorges through the mountains near the giant Quarternary volcano of
Demavend (18,600 ft.) there are complete sections. The succession in
the Alarm valley is as follows (Bailey & others, 1948, p. 29):—
Cretaceous limestones above
Crumpled Upper Jurassic limestone . . . . . . . 400 m.
Blue limestone with Upper Oxfordian Perisphinctids as figured by Fischer
(1915) (ident. L. F. Spath) . . . . . . . 300 m.
Thin-bedded limestone, in part at least Middle Callovian with Reineckeia
tilli Fischer (ident. L. F. Spath) . . . . . . 300 m.
Shales and sandstones of the Lias
The downward succession is best known in the Jaji Rud gorge, about
14 miles ENE. of Teheran (Bailey & others, 1948, pp. 6, 10) (thicknesses
approximate):—-
Oligocene green beds . . . . . . . . . 3000 m.
Eocene marine limestone . . . . . . • . 10 m.
LIAS—
Shales and sandstones with Pleydellia aff. subcompta (Branco) Fischer,
Pseudogrammoceras aff. fallaciosum (Bayle), and Calliphylloceras
cf. nilssoni auct. (ident. L. F. Spath) (Jurense Zone, uppermost
Toarcian) . . . . . . . . . . 150 m.
Lias limestone, thin-bedded, fine-grained argillaceous (cementstone),
with abundant irregular concretions of pale chert. Unidentifiable
ammonites . . . . . . . . . . 50 m.
Basement conglomerate of limestone, local . . . . . 20 m.
Carboniferous Limestone . . . . . . . . 100 m.
Old Red Sandstone . . . . . . . . 150 m.
The following treatment attempts a summary of the palaeontological
succession on the lines of that for the Caucasus, but the documentation
is more meagre and many of the ammonites recorded have been figured
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