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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Raz Formation

Raz Fm

Period:

Ordovician

Age Interval:

Middle-Upper Ordovician (O_2-3), C1c

Province:
Central W Tajik

Type Locality and Naming

Zakhoninsky typesection. This suite was first identified in the section of Mount Daourich as the "Razskaya beds" (Lavrusevich, Menakova, 1966).

Synonym: Razskaya suite

Reference section:

Lithology and Thickness

The Raz Fm is composed of sericitic-chloritic-quartzitic shales and quartzitic sandstones with rare layers of sandy limestones and various volcanic rocks. The true thickness of the suite is unclear, but it is likely more than 1000 m. Middle Ordovician organic remains were discovered by P.D. Vinogradov (1961) in the basin of the Yagnob River near the village of Farkau in a small (200 m) tectonic wedge of green phyllitic slates.

Lithology Pattern:

Sandy limestone

Relationships and Distribution

Lower contact

It is overlain by the Lower Silurian deposits, Isching Fm.

Upper contact

Regional extent

The Zakhoninsky type of sections, apparently, has a wider distribution within the Zarafshan-Gissar region. These deposits are faunistically characterized in the valleys of the rivers Shing, Archamaydan, Iskanderdarya, Yagnob, etc., where they are represented by the Razskaya suite. The relationship of this suite with older rocks in the western part of the Zarafshan-Gissar region has not been established since the lower part is cut off by faults in all studied sections.

GeoJSON

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Fossils

These are trilobites Opsimasaphus (Nobiliasaphus) nobilis (Barr.) and brachiopods Dalmanella kegelensis Alich. Upper Ordovician fossils have been collected (A. Lavrusevich et al., 1972, V. Lavrusevich et al., 1973) in the basins of the rivers Sor, Shing, Zakhona, etc. The most characteristic are Vermiporella aff. acerosa Gn.; Agetolites sp., Esthonia asterisca (Roemer), Propora bacillifera Lindstr., Lyopora regularis Kim, Grewingkia contexta gissarens. According to A. I. Lavrusevich and V.I. Lavrusevich (1973), in the eastern part of the Zarafshan-Gissar region.

Age

the age equivalent of the Raska suite, apparently, is the upper part of the Yagnob Fm. But the fossil assemblage indicates middle-upper Ordovician.

Age Span:

Beginning stage:

Dapingian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

471.26

Ending stage:

Hirnantian

Fraction up in the ending stage:

1.0

Ending date (Ma):

443.07

Depositional setting

Depositional pattern:

Additional Information

It should also be noted that Ordovician deposits in the Zarafshan-Gissar region have become known relatively recently, and although more than 20 localities are now known, much remains unclear. Therefore, in the legend, the division of these deposits into suites is not given.

Compiler:

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