Arkell.1956.Jurassic..

358 RANGES OF SOUTH-WEST ASIA
1000-3000 m. of Middle Bajocian sediments and volcanics are^followed by
650 m. of quartz porphyry assigned to the Upper Bajocian, and continuance
of intermittent volcanism is proved by pyroclastics interbedded in
all parts of the 2000 m. or so of overlying Bathonian, Callovian, Oxfordian
and Kimeridgian. Only the Tithonian limestone is free (Leontyev, 1950).
While these events were in progress in the west and south, uniform
sedimentation went on in Daghestan, resulting in an unbroken series of
dark shales with nodules, spanning all the stages from Toarcian to Middle
Callovian.
In late Kimeridgian times the Nevadan movements convulsed the
western region, producing isoclinal folds and profound erosion. Across
the eroded structures so formed the Tithonian sea spread unconformably,
as in the Crimea. Unfortunately, work on the Tithonian sediments
has not progressed to the point where it is possible to date the transgression
precisely; but the light-coloured coral and shell limestones, which form
so strong a contrast with the dark shales and sandstones of most of the
earlier Jurassics, contain some of the fauna both of the Stramberg
Tithonian and the Lower Volgian of the Moscow basin, with additional
elements of the Spiti Shales. In any case the transgression was progressive,
for in the southern Caucasus the Tithonian is completely overlapped by
the Valanginian.
The marine period initiated with the Tithonian transgression lasted
until the end of the Cretaceous. Then began the emergence of the
present Caucasus, which was thrown up by successive orogenies in the
early, middle and late Tertiary. The extent of these orogenies may be
gauged by the occurrence of Jurassic sediments thrust over Upper
Cretaceous, and by the elevation of Middle Tertiary deposits to heights
of over 2000 m. above the sea; and even Pliocene deposits have been
folded and elevated to over 1000 m. (Stahl, 1923, p. 54).
The Jurassics of the Caucasus and Crimea were deposited in a marginal
trough fringing the southern edge of the Russian platform and perhaps
separated by land from Anatolia (Wilser, 1928; Egeran, 1947, pi. 2).
Deposition and sedimentation were extremely active in the Lower Lias
period: a point of correspondence with the Elburz and not with Anatolia.
The Anatolian Lias agrees rather with that of the Central Iranian plateau,
and both are situated on ground that in the Tertiary orogeny developed
as 'median masses'. For elaborate palaeogeographical maps see
Mokrinskij (1939) and for a sketch of the tectonics, with many references,
Renngarten (1939).
TITHONIAN
Typical light-coloured Tithonian limestones and dolomites are well
developed in many parts of the Caucasus, especially in Daghestan. They
have locally a basal conglomerate and in the north Caucasus overstep
unconformably on to lower stages down to the crystallines. The facies is
often coralline, with iVmwea-limestone, especially in the upper part.
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