Kosmanchin Formation

Kosmanchin Fm

Period:

Cambrian, Ordovician

Age Interval:

Darriwilian, K5

Province:
Kyzylkum Region

Type Locality and Naming

Along the Kosmanachi quarry, S. Tamdytau. Z.M.Abdouazimova in 1991 (1993), 1998 (9, pp.3-14). Stratotype Along Kosmanachisay. Corresponds to the third sub-suite of the Besapan suite.

Synonym: Kosmanachinskaya Ore-Bearing Tolsha, Косманчинская рудовмещающая т.

Lithology and Thickness

The thickness represents a tectonic body composed of fragments of various facies and age formations, forming tectonic packets, scales, lenses, repeatedly repeating in the section (9).

They include:

1. "Exotic bodies" of silicites and siliceous-carbonate rocks. Thickness from 1-2 to 100 m - analogs of the Tas-Kazgan Fm.

2. Fragments of sections with thicknesses up to 100-150 m. Kurgantau Fm represented by banded intensely metamorphosed carbonaceous-quartz slates, exposed in lenticular bands, which P.A. Muhin et al. (317) interpret as blastomylonites.

3. Fragments of sections Thickness 10-80 m of the Kalsarin Fm, fine-grained limestones, and lenticular layers of dark quartz-siliceous rock characteristic of the Kalsarin Fm in the Nurata Mountains.

4. Essentially slaty packets, thickness 20-30 m, which are analogs of the Badamchali Fm.

5. Fragments of sections of sandy-gravel deposits of the Middle Ordovician; thickness from 2-5 to 30-100 m, represented by variously grained polymictic and oligomictic sandstones and gravelites with graded bedding, flow and slump textures, gravelites and siltstone (aleurolites)

Previous researchers had different views on the structure and age of this thickness.

Lithology Pattern:

Aus Conglomerate

Relationships and Distribution

Lower contact

Schematic stratigraphic column indicates the lower contact as Rokhat Fm

Upper contact

Schematic stratigraphic column indicates the upper contact as Murun Fm

Regional extent

South of Tamdytau, in the sections of the Muruntau ore field.

GeoJSON

null

Fossils

1. "Exotic bodies" (olistoliths?) containing Late Precambrian microphytolites - Ambigolamellatus horridus Z.Zhur., Vesicularites congermans Z.Zhur., Volvatella vadosae Z.Zhur., etc.

2. Fragments of sections – blastomylonites

3. Fragments of sections with cyanobacteria - Nuratella kalsarinica Pjan., N. sp., Stereophycus schochycus Pjan.,

4. Essentially slaty packets, Acontiodus cf. reclinatus Lin (?), Drepanodus arcuatus Pand., Oistodus cf. gracilis Lind., Paracordylodus cf. gracilis Lind. and lower part of the Middle Ordovician - Cordylodus cf. ramosus Had., C. spinatus (Had.), Paracordylodus sp. (369)

5. Fragments of sections of sandy-gravel deposits of the Middle Ordovician, with chitinozoans of the Middle Ordovician - Desmochitina minor typica Eis., Lagenochitina cf. curta Umn., Linochitina pissotensis Paris. and others.

Age

Earlier, it was considered part of the continuously layered Besapan Fm, the age of which was interpreted from Early Silurian (122; 266; 378), Late Ordovician-Early Silurian (Bukharin et al., 1990) to the Precambrian (71; 122; 376). In 1964, P.N. Podkopaev et al. (1966) based on the characteristics of the section, distinguished the formations of this thickness from the Besapan Fm, described it as the Muruntau Fm of the Early Silurian, indicated the heterogeneity of the Besapan Fm section and the presence of formations of different ages in it, which was confirmed by paleontological, structural, and petrological-material data (Abduazimova et al., 1985, 1993, 1996; Aysanov et al., 1986, 316; 317; 369).In 1991, Along the recommendation of the Stratigraphy and Geological Map Commission of the Kyzylkum Geodynamic Polygon of the Geological Survey, the ore-hosting facies was distinguished from the Besapan Fm and described as the Kosmanachin Fm. In the monograph (165) and on the State Geological Map-500 of Uzbekistan (460), it is listed as a suite of Late Cambrian-Middle Ordovician.

Age Span:

Beginning stage:

Darriwilian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

469.42

Ending stage:

Darriwilian

Fraction up in the ending stage:

1.0

Ending date (Ma):

458.18

Depositional setting

Depositional pattern:

Additional Information

Compiler:

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