Irtash Formation

Irtash Fm

Period:

Neogene

Age Interval:

Upper Miocene – Lower Pliocene (?), CK10

Province:
Chatkal-Kuramin Region

Type Locality and Naming

Along the Irtashsai, a left tributary of the Angren River, Prishchekent District. B.I. Pinhasov, 1985 (145, p.37). The stratotype is the Tashsai section on the Angren Plateau.

Synonym: Irtash Formation, Ирташская св.

Lithology and Thickness

Consists of hills (2-7m) of pale-pink nodular marls and concretionary limestones, representing ancient carbonate weathering crusts, interbedded with proluvial-deluvial red-brown debris siltstones, sandstones, and coarse-clastic rocks. Thickness up to 50 m.

Lithology Pattern:

Limestone

Relationships and Distribution

Lower contact

In depressions, the carbonate crust lies between red-colored Oligocene-Miocene and brown-colored Upper Pliocene molasses. In the marginal parts of depressions and watersheds, it lies on the leveled Paleozoic. L.D. Anpleeva (Koloyarov et al., 1977) included the carbonate weathering crust thickness, developed on the Angren Plateau, in the Middle Miocene Arashan Fm

Upper contact

With erosion, it is overlain by the Gidzhal Fm and Pskent Fm

Regional extent

Angren Plateau, Chirchik River valley, Prishchekent Depression. F.P. Korsakov (166) includes the nodular limestones in the upper part of the red-colored Chulin Fm of the Prishchekent District.

GeoJSON

null

Fossils

Age

The suite is conditionally attributed to the Upper Miocene-Pliocene, according to its position in the general section of Late Cenozoic orogenic molasses. It is paralleled with the Pliocene Middle Tien Shan series, which corresponds to the lake gray salt-gypsum formation with the richest remains of hipparion fauna in the intermountain depressions.

Age Span:

Beginning stage:

Messinian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

7.25

Ending stage:

Piacenzian

Fraction up in the ending stage:

1.0

Ending date (Ma):

2.58

Depositional setting

Depositional pattern:

Additional Information

Compiler:

B.I. Pinhasov – In: GeoGPT translation of: “Abduazimova, Z.M. (Ed.), 2001. Stratigraphic Dictionary of Uzbekistan. IMR (Institute of Mineral Resources), Tashkent, 580 pp. (In Russian)”