Arkell.1956.Jurassic..

OMAN 379
Kuhn (1929) was able to identify as approximately Upper Oxfordian to
Kimeridgian in age. They indicate a shallow sea of Central European
type extending southward from Persia, and unconnected with that of
Cutch. From marl beds in the upper part he also collected a small
assemblage of fossils (no ammonites) of Lower Cretaceous type, probably
Barremian. On the basis chiefly of Foraminifera, the Lower Musandam
Limestone is regarded now as ranging from Lias to Tithonian. Examination
of the Radiolaria of the Hawasina Series (Davis, 1950) gives an
approximate date Tithonian-Neocomian.
More detailed work on the northern peninsula of Oman, the Ruus al
Jibal, published while this book was in proof, has produced much new
information (Hudson, McGugan & Morton, 1954). Although there were
pre-Aptian and Upper Cretaceous movements, the main thrusting was
Neogene, and the structures are a continuation of the thrusts in the
normally folded zone of the Zagros. The stratigraphy is also found to
agree better with this zone than had been supposed, and it also shows
connexions with central Arabia, despite absence of ammonites in Oman.
THE PLATEAU OF CENTRAL PERSIA AND AFGHANISTAN
The series of high plateaux, separated by minor mountain ranges, which
form the inner core of Persia and Afghanistan and fall in great steps to
the Mekran coast of the Arabian Sea, have been referred to as a 'Zwischen-
Gebirge' or median mass, between the greater mountain arcs of the Elburz-
Hindu Kush on the north and the Zagros-Kirthar ranges on the south.
Although the surface consists mainly of desert plains in internal drainage
basins (graphically described and illustrated, for instance, by Harrison,
1943), the underground structure is complicated.
In the Persian part, in a triangle with 500-mile sides, its corners on the
towns of Kerman and Isfahan and a point about 150 miles north of Tabas,
Jurassic rocks play an important part, cropping out along the sides of
mountains which have Triassic and Palaeozoic cores, and buried by superficial
deposits under the plains. There are also outcrops in the Mekran
hinterland and not many miles from the coast at the Strait of Ormuz.
Over this large area the Jurassic rocks naturally vary a great deal, but
there is everywhere a marked difference from the surrounding mountain
chains of the Elburz and Zagros systems. In the first place the Jurassic
as a whole is relatively thin and predominantly of continental type, with
carbonaceous shaly beds much in evidence. Secondly the marine episodes
are earlier than in the mountain systems: in the south and centre there are
Sinemurian and Lower Bajocian marine phases instead of ? Domerian,
Toarcian and Upper Bajocian-Bathonian. Thirdly, the whole Upper
Jurassic is missing over large areas and in other places represented by a
carbonaceous series like the Elburz Lias. Fourthly, in the south there are
massive extrusions of lava interbedded in the Jurassic sediments.
As in the Elburz, the Lias occurs in two main facies, carbonaceous
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