Oyasay Formation

Oyasay Fm

Period:

Permian

Age Interval:

Asselian, CK2

Province:
Chatkal-Kuramin Region

Type Locality and Naming

At the Oyasay River, Karzhantau Ridge. N.P. Vasilykovsky, 1941 (130, p. 56).

Synonym: Oyasay Suite, Оясайская св.

Lithology and Thickness

Tuffs, ignimbrites, less frequently rhyolite, trachyrhyolite, rhyodacite, trachyrhyodacite, dacite, trachydacite, less frequently trachyte and quartz trachyte, characterized by fluidal, spherulitic, and felsitic textures. Conglomerates, sandstones, and rarely carbonate rocks are sometimes observed at the base of the suite. Thickness ranges from 250 to 3150 m.

Lithology Pattern:

Volcanic_ash

Relationships and Distribution

Lower contact

It lies with erosion on the Nadak Fm and Karzhantau Fm

Upper contact

It is unconformably overlain by the Shurabsay Fm volcanites.

Regional extent

Karchantau Ridge, basins of the Alchaban, Oyasy, Aktam rivers; Chatkal Ridge, basins of the Shavaz, Bashkyzylsay, Karabau, Dukent rivers; Kuramin Ridge, basins of the Naugarzan, Lashkerek, Angren, Kamchik, Gava rivers.

GeoJSON

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Fossils

In the interfluve of the Gava-Koksarek rivers, foraminifers *Rugosofusulina splendida* Bensh, *Schwagerina glomerosa* Schellw., *S. asiatica* M.-Macl., *Paraschwagerina koksarecensis* Bensh, etc., were found in carbonate rocks,

Age

Foraminifers allowed F.P. Bensh (1970) to assign the suite to the upper part of the Asselian stage. Discovered plant remains (1970) also indicate an Early Permian age of the deposits. The average absolute age of the rocks of the suite from different regions is 280 pm 5 million years, corresponding to the Early Permian (1970). It is assigned to the Early Permian (1970; 1970; 1970; 1970). Previously, the age of the O. suite was dated to the Late Carboniferous (1970; 1970; 1970).

Age Span:

Beginning stage:

Asselian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

298.89

Ending stage:

Asselian

Fraction up in the ending stage:

1.0

Ending date (Ma):

293.52

Depositional setting

Depositional pattern:

Additional Information

Compiler:

T.A. Iskandarkhojaev, V.V. Mikhailov– In: GeoGPT translation of: “Abduazimova, Z.M. (Ed.), 2001. Stratigraphic Dictionary of Uzbekistan. IMR (Institute of Mineral Resources), Tashkent, 580 pp. (In Russian)”