Kosbulak Formation

Kosbulak Fm

Period:

Silurian

Age Interval:

Gorstian, K5

Province:
Kyzylkum Region

Type Locality and Naming

By the Kosbulak collective farm, N. Tamdytau, Central Kyzylkumy. A.I. Kim et al. in 1969 (1974f.) The stratotype is a group of sections in the area of the Kosbulak quarry and in the middle course of the Dzhaksan River.

Synonym: Kosbulakskaya Suite, Косбулакская св.

Lithology and Thickness

Green, greenish-gray sandstones and siltstone (aleurolites), tuffaceous sandstones, tuffaceous siltstone (aleurolites), medium-composition tuffs, containing interlayers of slates, gravelite horizons, and conglomerates. Thickness 150-200m.

Lithology Pattern:

Fine-grained sandstone

Relationships and Distribution

Lower contact

According to A. (A.I. Kim et al., 1974), the lower boundary is normal with the upper Wenlock (Tyumenbaitau Fm)

Upper contact

Normal relationships are assumed with the overlying Koskuduk Fm.

Regional extent

Northern part of the Tamdytau Mountains.

GeoJSON

null

Fossils

In the lower part, graptolites of the Neodiversograptus nilssoni and Lobograptus scanicus zones, characteristic of the lower Ludlow (Gorstian) - Bohemograptus bohemicus (Barr.), Pseudograptus chimaera (Barr.), Neodiversograptus nilssoni (Lapw.) and others; chitinozoans - Eisenackitina bohemica (Eis.), Cingulochitina convexa (Lauf.) and others. In the upper part, graptolites of the upper Ludlow (Ludfordian) - Saetograptus leintwardinensis (Lapw.-Hopk.), Bohemograptus tenuis (Bouček.) and others; chitinozoans Eisenackitina rimata Umn., Cingulochitina ervensis Paris., Umochitina aff. urna (Eis.), Margachitina margoritana poculum (Coll. et Schw.) and others. In the pebbles of the conglomerates, stromatoporoids, tabulates, brachiopods of the Llandovery-Wenlock (165).

Age

Sh. Sabdyushov (392) referred to these deposits as the Koshkumbay Fm and attributed them to the late Silurian; on the State Geological Map-500 of Uzbekistan (460), they are included in the Koshkumbay Fm of the upper-lower Silurian.

Age Span:

Beginning stage:

Gorstian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

426.74

Ending stage:

Ludfordian

Fraction up in the ending stage:

1.0

Ending date (Ma):

422.73

Depositional setting

Depositional pattern:

Additional Information

Compiler:

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