Obchak Formation

Obchak Fm

Period:

Neogene

Age Interval:

Upper Miocene-Lower Pliocene, F2

Province:
Fergana

Type Locality and Naming

Along the Obchak River, right tributary of the Sumkar River, Fergana Depression. M.G. Gramm, 1958 (467, p.170). B.I. Pinhasov

Synonym: Obchak Suite, Обчакская св.

Lithology and Thickness

Fergana Depression. In S. Fergana - red and pinkish-brown, brownish-gray, alluvial-proluvial siltstone (aleurolites) and sandstones with subordinate gravelites and conglomerates. In E. and S. Fergana - pinkish-red, calcareous sandstones, gravelites, conglomerates, and siltstone (aleurolites) (pale pink suite of oil geologists). Thickness 180-700m.

Lithology Pattern:

Siltstone

Relationships and Distribution

Lower contact

Overlies the Mailisay Fm with erosion

Upper contact

Overlain by the Akchop Fm with erosion

Regional extent

B.I. Pinhasov considers the Obchak Fm to belong to the Middle Tien Shan Gr and correlates it with the lacustrine saline-gypsum deposits of the Tien Shan, containing the hipparion fauna complex.

GeoJSON

null

Fossils

Contains Miocene-Pliocene ostracods - Ilyocypris aff. errabundis Mand., I. bradyi Sars., Candoniella albicans (Br.), C. marcida Mand., C. schubinae Mand., C. pellucida Schn., Herpetocypris elongata Schn., Darwinula stevensoni (Br. et Roberts).

Age

Dated to the Upper Miocene-Lower Pliocene (Messinian-Zanclean)

Age Span:

Beginning stage:

Messinian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

7.25

Ending stage:

Zanclean

Fraction up in the ending stage:

0.9

Ending date (Ma):

3.77

Depositional setting

Depositional pattern:

Additional Information

Compiler:

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