Cenozoic

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

Neoproterozoic

Main source = Baratov, R.B., et al. (1976). Subdivisions of stratified and intrusive rocks of Tajikistan. Publishing House "Donish", Dushanbe, 269 pp. plus tables. Provided by Dr. Jovid Aminov, Nazarbayev University, Astana, Kazakhstan Translated to English by the GeoGPT group, Zhejiang Lab, Hangzhou, China--see About

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Istyk Formation

Istyk Fm

Period:

Triassic

Age Interval:

Norian – Rhaetian (T₃ is), M2

Province:
SE Tajik (SE Pamir)

Type Locality and Naming

Includes in SE Murghab district (Istyk type Dunkeldyk area). It was distinguished by S. I. Klunnikov et al. (1936).

Synonym: Istykskaya suite, Истыкская свита

Reference section:

Lithology and Thickness

It is made up of dark, irregularly bedded, variably-grained quartz-feldspathic and polymictic sandstones, siltstones, silty and clayey slates. The thickness of the suite is 300-1000 m.

Lithology Pattern:

Sandy_claystone

Relationships and Distribution

Lower contact

It lies conformably on the Ladinian-Carnian deposits of the Saratash Fm

Upper contact

It is overlain with erosion and in most cases sharply unconformably by the Lower, Middle Jurassic deposits.

Regional extent

It is spread in the Southeastern Pamir in places with sections of Triassic deposits of intermediate and marginal types (Dronov, Leven, 1961).

GeoJSON

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Fossils

In the lower part of the suite (50-200 m) there are remains of early, middle Norian bivalves: Halobia superbescons Kittl, H. Fallax Mojs., H. plicosa Mojs., H. norica Mojs. Approximately in the middle of the suite, there are middle, late Norian ammonoids of the genus Horistoceras. The upper layers of the suite are not characterized by faunal remains. Most of them are, apparently, Upper Norian, but it is possible that in the upper parts they are partly Rhaetian.

Age

Based on the fossil data, it is considered Norian – Rhaetian.

Age Span:

Beginning stage:

Norian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

227.30

Ending stage:

Rhaetian

Fraction up in the ending stage:

1.0

Ending date (Ma):

201.36

Depositional setting

Depositional pattern:

Additional Information

Compiler:

Extracted from Baratov, R. B. (1976). Subdivisions of stratified and intrusive rocks of Tajikistan. Donish, Dushanbe, 276.