Rishtan Formation

Rishtan Fm

Period:

Paleogene

Age Interval:

Middle Eocene (Bartonian), F2

Province:
Fergana

Type Locality and Naming

Near the village of Rishtan, Fergana. O.S. Vyalov, 1935 (155, p. 280). Stratotype in the area of the city of Isfara, Fergana Depression. Upper formation in the Turkestan Horizon Gr. Salibaev (397) assigns the lower part to the Subashin Fm, and the upper part to the Nefteabad Fm. Hence these formations are included in Turkestan Horizon Gr in the Fergana depression.

Synonym: Rishtanskaya Suite, Риштанская св.

Lithology and Thickness

Upper part – Silty (aleuritic) clays with shell limestone interlayers. Thickness up to 30 m. Lower part, limestones, sandy limestones, sandstones, shell limestones, marls (IY oil-bearing bed). Thickness up to 15 m. Total thickness over 45 m.

Lithology Pattern:

Shallow-marine marl

Relationships and Distribution

Lower contact

Conformably overlies, in places with erosion, the Turkestan Fm and Gulistan Fm

Upper contact

Conformably overlain by the Isfara Fm, in places with erosion by the Neogene.

Regional extent

Fergana Depression, South-Western Gissar. G.Kh. Correlated with the lower part of the Apataks Fm of the Prishashkent region, and the Ichkibulak and lower part of the Tairsuy Fm of the Tajik Depression (186). Corresponds to the " n " and " o " horizons of K.P. Kalitsky's scheme (213). Previously, the upper part was distinguished as the Tarel horizon (160; 214; 286; 444).

GeoJSON

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Fossils

In the upper part, contains marine bivalve mollusks - Chlamys sokhiensis Korob., Nuculana crispata Koen., Pteria media Desh., Platigena asiatica Rom., Lucina menardi Desh., Pitar Sulcataria Desh., Corbula ficus Sol.; gastropods - Turritella uniangularis Lam.; foraminifers - Haplophragmoides orfaensis Rod., Trochammina masini Sul., Gaudryina superturkestanica N. Byk., Asianella vialovi N. Byk.

In the lower part, Marine bivalve mollusks - Ostrea simplex Desh., Lucina menardi Desh., Pitar nitidula Lam., gastropods - Turritella uniangularis Lam., Calyptraea lamellosa Desh.

R.K. Makarova (282) distinguishes in the suite: 1) layers with Liostrea simplex, 2) layers with Platigena asiatica, 3) layers with Chlamys turgaicus.

Age

Belongs to the middle Eocene (Bartonian stage). In the Stratigraphic Lexicon (444), the age of the suite is late Eocene.

Age Span:

Beginning stage:

Bartonian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

41.03

Ending stage:

Bartonian

Fraction up in the ending stage:

1.0

Ending date (Ma):

37.71

Depositional setting

Depositional pattern:

Additional Information

Compiler:

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