Minbulak Formation

Minbulak Fm

Period:

Carboniferous

Age Interval:

Bashkirian, CK2

Province:
Chatkal-Kuramin Region

Type Locality and Naming

Named after Mount Minbulak, Karzhantau Ridge. N.P. Vasilkovsky in 1941 (131, p. 62).

Synonym:

Lithology and Thickness

Basalts, trachybasalts, trachyandesibasalts, andesibasalts, trachyandesites, andesites, less frequently - trachytes, quartz trachytes, their tuffs, trachyandesidacites, trachydacites, dacites, trachyriodacites, riolodacites, trachyriolites, riolites, their tuffs and ignimbrites. The characteristic contrast is expressed in the alternation of acidic and intermediate rocks, against which, in the northwestern part of the Ugam-Kumbel region in the Karchantau Ridge, a generally homodromic trend is outlined, while in the Tereklin region, an antidromic trend is observed (64). In the overall mass of volcanites, pyroclastic rocks predominate over lavas. Thin layers of sedimentary volcanomictic sandstones and gravelites have a sharply subordinate role. At the base - basal tuff conglomerates (thickness 75-200m). Thickness varies from 500-1200 to 3000 m (Karchantau Ridge).

Lithology Pattern:

Volcanic_ash

Relationships and Distribution

Lower contact

It lies unconformably on the limestones of the Chukurchak Fm of the Lower Carboniferous and on the Serpukhovian-Lower Bashkirian part of the Uya Fm and is replaced by its upper part, intruded by granitoids of Middle Carboniferous age

Upper contact

It is unconformably overlain by deposits of the Karzhantau Fm, Ravash Fm, or Shurabsay Fm

Regional extent

Karzhantau Range, Chatkal and Kurama ranges, western part of the Sandalash area.

GeoJSON

null

Fossils

In the limestone pebbles of the basal conglomerates, fauna of Serpukhovian age. In the river Uya, in limestone lenses and layers in the lower and middle parts of the M., foraminifers - Planoendothyra spirilliniformis (Br. et Pot.), Eostaffella nauvalia Rum., E. postmosquensis acutiformis Kir., Plectostaffella varvariensis (Br. et Pot.), P. seslavica (Rum.) and others; brachiopods - Linoproductus corrugatus M'Coy, Choristites sp.; conodonts - Declinognathodus noduliferus (El. et Gr.), Neognathodus symmetricus (Lane).

Age

The entire fauna complex unequivocally indicates an early Bashkirian age of the Middle Carboniferous (165). V.P. Korzhaev et al. (1978; 1981) attribute the Minbulak Fm to the Bashkirian stage entirely.

Age Span:

Beginning stage:

Bashkirian

Fraction up in beginning stage:

0.3

Beginning date (Ma):

320.93

Ending stage:

Bashkirian

Fraction up in the ending stage:

1.0

Ending date (Ma):

315.15

Depositional setting

Depositional pattern:

Additional Information

Compiler:

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