Raushan Formation

Raushan Fm

Period:

Jurassic

Age Interval:

Upper Bajocian-middle Bathonian, U3

Province:
Ustyurt-Sultanuzdag

Type Locality and Naming

Along the Raushan plateau, Takhatakir district, Southern Ustyurt. V.V. Kurbatov, V.N. Polyakov in 1996 (165, p. 125).

Synonym: Raushan Suite, Раушанская св.

Lithology and Thickness

Clayey and siltstone rocks of gray and greenish-gray color. Fine interbedding of claystones and fine-grained siltstones is often observed. Concretions of yellowish-gray siderites are encountered. The rocks are enriched to varying degrees with carbonized plant detritus. At the base of the section, there is a powerful (Thickness 30-40m) layer of well-sorted sandstones. Thickness on the V. Ustyurt 100 120m, decreases on the Baiterek and Terenkuuduk plateaus to 30-60 m, and in the Takhtakair region 60-166m.

Lithology Pattern:

Siltstone

Relationships and Distribution

Lower contact

The Raushan Fm transgressively overlies the Paleozoic or the Berdak Fm.

Upper contact

It is transgressively overlain by the Kafaklin Fm.

Regional extent

Wells. The stratotype is the section of the Western Shakhpakhty plateau. It is used in the legend of the Priaral (Pre-Aral) subseries sheets of the geological maps of the 1:200000 scale, 1998. It belongs to the Sarydiiyirman Horizon (252) and is a facies analogue of the Degibadam Fm and Tangiduval sFm It corresponds to the productive horizons Akchalak 2 and 3 and is called the Bazaryn rhythm.

GeoJSON

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Fossils

In the Raushan Fm, two complexes of spores and pollen have been identified. In the lower part, spores - Cyathidites minor Couper (30-70), C. junctes (K.-M.) (0-5), Lycopodium sporites subrotundus (K.-M.) Vin. (0-5), Neoraistrickia rotundiforma (K.-M.) (0-7), Osmunda cidites sp. (0-2), Disaccites (0-3), Ginkgocycadophytus (1-13), Classopollis (0-2). This complex is correlated with the Bayossian complex of the C. Caucasus and Mangyshlak. The complex of spores and pollen from the upper part - Cyathidites minor Couper (5-45), C. junctes (K.M.) (2-8), Lycopodiumsporites subrotundus (K.-M.) Vin. (0-24), Neoraistrickia rotundiforma (K.-M.) Tar. (0-8), Osmundacidites jurassicus (K.-M.) Ruz. (0-17), Disaccites sp. (2-30), Ginkgocycadophytus (2-36) - is correlated with the Bathonian complex of Mangyshlak and Tuarkyr, where Bathonian ammonites and marine bivalve mollusks are known. In the Shakhpakhty well (interval 2000-2062m), marine bivalve mollusks - Astarte minima Phill. were identified. The appearance of greenish marine rocks in the described sv. allowed V.N. Polyakov and M.S. Rodovilsky to correlate these deposits with the undifferentiated Bazaryn Fm and Sarydiiyirman Fm of Mangyshlak (383, table 4, p.2).

Age

The age of the formation is accepted as late Bajocian - middle Bathonian.

Age Span:

Beginning stage:

Bajocian

Fraction up in beginning stage:

0.5

Beginning date (Ma):

169.54

Ending stage:

Bathonian

Fraction up in the ending stage:

0.25

Ending date (Ma):

167.45

Depositional setting

Depositional pattern:

Additional Information

V Commercial gas content of the formation has been established on the Akchalak, Kokchalak, and Alambek plateaus

Compiler:

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)”