Berdak Formation

Berdak Fm

Period:

Jurassic

Age Interval:

Upper Aalenian-Lower Bajocian, U3

Province:
Ustyurt-Sultanuzdag

Type Locality and Naming

Along the Berdak plateau, Takhtakair district, Southern Ustyurt. V.V. Kurbatov, V.N. Polyakov in 1996; 1998 (165, p.125). The stratotype corresponds to the former parastratotype of the undivided upper Tonaishinskaya sub-suite and Karadiyir Fm (Karadiyirskaya suite), recommended by the Samarkand conference as a typical section on the Z. Zap. Shakhpahyty. (383). Used in the legend of the Priaral (Pre-Aral) sub-series of sheets for geological maps of the 1:200000 scale.

Synonym: Berdak Formation, Бердакская св.

Lithology and Thickness

Interbedding of claystones, siltstone (aleurolites), sandstones, and thin layers of brown coals. In the section, greenish-gray, dark-gray, and black argillites predominate. Thickness in synclines 200-300m, in uplift zones 80-100m.

Lithology Pattern:

Sandy claystone

Relationships and Distribution

Lower contact

With visible conformity, it lies on the Takhatakair Fm (Tahtakair Fm) and transgressively

Upper contact

With visible conformity, covered by the Raushan Fm.

Regional extent

Wells. The suite is included in the Gurud Horizon (252) and is a facies analogue of the middle and upper sub-suites of the Gurud Fm. V.V. Kurbatov, V.I. Troitsky (165). Corresponds to the productive horizon A4 - Anchalak - 4. On the S. Ustyurt, it was previously distinguished as the undivided upper Tonaishin sub-suite and Karadiyir Fm (383, table 4, p.2). 1998.

GeoJSON

null

Fossils

Contains spores and pollen - Cyathidites minor Couper (4-45), C. junctus (K.-M.) (2-3), Lycopodiumsporites subrotundus (K.-M.) Vin. (0-24), Neoraistrickia rotundiforma (K.-M.) Tar. (0-8), Osmundacidites jurassicus (K.-M.) Kuz. (0-17), Heterotriletes incertus Bolch. (ed.), Tripartina variabilis Mal. (0-2), Toroisporis solufionis Kr. (ed.). Pollen consists of Disaceites sp. (2-30), Ginkgocycadophytus sp. (2-36), freshwater bivalve mollusks, large plant remains (446).

Age

The age of the suite is accepted as the upper Aalenian - early Bajocian.

Age Span:

Beginning stage:

Aalenian

Fraction up in beginning stage:

0.5

Beginning date (Ma):

172.80

Ending stage:

Bajocian

Fraction up in the ending stage:

0.5

Ending date (Ma):

169.54

Depositional setting

Depositional pattern:

Additional Information

Compiler:

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