Istemes Formation

Istemes Fm

Period:

Cretaceous

Age Interval:

Middle(?) Aptian, U5

Province:
Ustyurt-Sultanuzdag

Type Locality and Naming

Along Lake Istemes, Sultanuizdag Ridge, South Pre-Aral. S.S. Shul'ts (Jr.), 1967 (509, p.13). Exposed by Stratotype well, probably located along the N-E shore of Lake Istemes.

Synonym: Istemesskaya Suite, Истемесская св.

Lithology and Thickness

On the W and S slopes of Sultanuizdag Ridge, conglomerates with interlayers of sandstones, clays, and siltstone (aleurolites). On the E - kaolinized clays with interlayers of sandstones and clays. Thickness 10-15m.

Lithology Pattern:

Clayey sandstone

Relationships and Distribution

Lower contact

Transgressively overlies the Paleozoic or pre-Aptian weathering crust

Upper contact

Unconformably overlain by the Sultanbobin Fm.

Regional extent

Sultanuizdag Ridge, N-E shore of Lake Istemes.

GeoJSON

null

Fossils

Contains ostracods - Origilyocypris aff. echinata Mand., Cypridea foveolata (Eggor.), Mongolinella aff. palmosa Mand.

Age

Conditionally attributed to the mid-Aptian. (508).

Age Span:

Beginning stage:

Aptian

Fraction up in beginning stage:

0.2

Beginning date (Ma):

119.76

Ending stage:

Aptian

Fraction up in the ending stage:

0.65

Ending date (Ma):

116.07

Depositional setting

Deluvial-proluvial deposits.

Depositional pattern:

Additional Information

Compiler:

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