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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Lower Arg Formation

Lower Arg Fm

Period:

Silurian

Age Interval:

Ludlow, C1a, C1b, C1c

Province:
Central W Tajik

Type Locality and Naming

It is in all three Obisafit, Turkparidin, and Chakyklalyan type sections. O.I. Nikiporova (1949) described these deposits as the Arg suite (Argskyio tolshy??), noting the possibility of dividing it into lower layers with Amphipora and upper - with Pholidophyllum asiaticum and Parazyga argensis. In the scheme of the Silurian stratigraphy of Central Asia, accepted by the Tashkent meeting, after the revision of the MSC (Stratigraphy..., 1962), the Arg suite appears with two sub-suites, and the volume of the suite is increased due to the inclusion in it of the overlying limestones, described by O. I. Nikiforova (1949) as marginal layers. In this understanding, the Arg suite is now accepted by most researchers. At the same time, since the Kunjak horizon (marginal layers) is currently attributed to the Lower Devonian, it seems more convenient to divide the suite into three sub-suites, corresponding to the 'amphiporoid', 'pholidophyllid', and 'brachiopod' limestones in the scheme of V. R. Martyshev (1956).

Synonym: lower Arg sub-suite, Arg suite, Argskyio tolshy??

Reference section:

Lithology and Thickness

It is represented by medium and thin-bedded black dolomites with a thickness of 100-400 m.

The dolomites of the Lower Arg Fm gradually change to thick-bedded to massive gray and black limestones to varying degrees dolomitized in the Middle Arg Fm. The thickness is about 350 m. Less often, these limestones are thin-bedded or slaty and contain small layers and nodules of siliceous rocks.

Lithology Pattern:

Dolomitic limestone

Relationships and Distribution

Lower contact

Shing Fm of Chakykalya typesection (based on the table 2 from the extracted book)

Upper contact

Middle Arg Fm

Regional extent

It is distributed in the Zarafshan-Gissar region.

GeoJSON

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Fossils

They are almost devoid of organic remains, but in places contain a multitude of small amphiporoids ('amphiporoid' limestones (Martyshev, 1956). Very rarely in them are also found corals Tryplasma cf. asiaticum (Nikol.) and Fomichevia sp.

A characteristic feature of the sub-suite is the abundance of monotonous rugose corals Tryplasma (Pholidophyllum) asiaticum (Nikol.), thanks to which the limestones received the name 'pholidophyllid' (Martyshev, 1956). In addition, tabulate corals (or algae?) Lithophyllum sokolovi Lel. are frequent; brachiopods Retzia (?) argensis (Nikif.), R. mirus (Nikif.), Lissatrypa caudata Nikif., L. alexandrina Nikif.

Age

Ludlow

Age Span:

Beginning stage:

Gorstian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

426.74

Ending stage:

Gorstian

Fraction up in the ending stage:

0.9

Ending date (Ma):

425.18

Depositional setting

Depositional pattern:

Additional Information

Compiler:

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