Arkell.1956.Jurassic..

NORTHERN ASIA
sea never linked up with the southern ocean through the depression north
of the Aral Lake, which Suess called the 'Straits of Turgay'. On the
eastern slopes of the southern Urals, between Cheliabinsk and Orsk, the
plant-bearing beds are 200-400 m. thick. They rest horizontally against
the planed-off Palaeozoic and pre-Cambrian rocks of the Ural folds, which
were elevated and peneplaned in the Trias, and westward they are overstepped
by the Upper Cretaceous (Senonian) until they wedge out
(Razumovskaya, 1937, p. 73). The continental Jurassics reappear on the
west slopes of the Urals also, and there interfinger towards the west and
south-west with the marine facies in the north Caspian depression (see
p. 487).
The marine Upper Jurassic is known chiefly on the Rivers Soswa and
Liapine (= Sygwa), which drain the northern Urals between latitudes 62 and
65 0
N. and when united continue, as the Soswa, to flow eastwards to join the
Ob (Ilovaisky, 1903,1906,1917). The oldest Jurassic ammonites from this
region are Amoeboceras ('Cardioceras alternans') which, in the absence of
figures, might be Upper Oxfordian or Lower Kimeridgian. This is also
the type area for Rasenia uralensis (d'Orbigny) (Rivers Tehol and Tolya,
about latitude 64° N.). Most conspicuous, however, is the Aulacostephanus
assemblage of the Pseudomutabilis Zone; but Aspidoceras has not been
found. The Lower Kimeridgian shales appear to overlap westward against
easterly-dipping Devonian and crystalline rocks of the Urals. Rasenia
cymodoce and Amoeboceras ovale are recorded (Sirin & Shmakova, 1937).
The higher Kimeridgian is richly represented by several faunas of
Pavlovia, Dorsoplanites and Stschurovskya. The succession still remains
to be worked out, and differences between the Liapine and Soswa Rivers
indicate that it may not be straightforward (Ilovaisky, 1906, p. 262).
The Liapine River is the type area for the genus Pavlovia (based on P.
iatriensis Ilovaisky, 1917). Ilovaisky's intended monograph on these
ammonites was unfortunately never completed.* At least the higher parts
of these beds—largely green sandstones—represent the lower part of the
Lower Volgian. Upper Volgian is also reported (Volkov & Jacjuk, 1937).
The highest Jurassic beds (12 m.) are unfossiliferous. They are overlain
by Berriasian green sandstones with Paracraspedites spasskensis of the
Upper Ryazan Beds, and this is succeeded by Valanginian Polyptychites
beds.
Basin of the Anabar River
According to the palaeogeographic maps of Archangelsky (1939, p. 300)
the Jurassic sea in the basin of the Ob was connected north-eastward
across the Yenesei estuary, by way of the valley of the Khata River and the
lower Khatanga River, with the Arctic Ocean at the mouth of the Lena,
cutting off the Taimyr Peninsula as an island. Obrutschew (1926, pi. 7)
showed the postulated Jurassics (entirely concealed under Quaternary
* Only Part 1 appears to have been published, in 1917 (see Obrutschew, 1926, p. 294),
and of this no copy is known to exist in Britain or America (Spath, 1936, Cape Leslie,
p. 26, note 5; and personal enquiries in the U.S.A.). D. Ilovaisky died in 1939.
http://jurassic.ru/