Urusay Formation

Urusay Fm

Period:

Silurian

Age Interval:

Upper Silurian (?), U5

Province:
Ustyurt-Sultanuzdag

Type Locality and Naming

Along the Urusay valley, Sultanuizdag Mountains. K.A. Keshishyan in 1965 (1983). Lower formation in Sultanuizdag Gr

Synonym: Urusaiskaya Suite, Урусаиская св.

Lithology and Thickness

The section consists of three sub-suites: lower - greenstone-altered effusives - light and dark green, gray, intensely epidotized, chloritized, finely foliated slates; middle - crystalline, phyllitic slates with layers of quartzites; upper - meta-andesitoids (porphyroids) with layers of crystalline slates and horizons of marblized limestones. Thickness up to 600 m.

Lithology Pattern:

Limestone

Relationships and Distribution

Lower contact

According to A., the lower contact is not exposed

Upper contact

The upper contact is conformable with the Sultanuizdag Fm

Regional extent

Along the western exocontact of the Aktaw granodiorite intrusion, from the south (from Aktaw village) to the north (up to the southern closure of the Tebinbulak ultrabasic massif) for more than 10 km; the southern slope of the central part of the Sultanuizdag ridge to the south of the Darbazatau ridge.

GeoJSON

null

Fossils

In the marblized limestones to the south of the Darbazatau ridge, crinoids - Pentagonocyclicus argensis vulgaris Schew. (in Coll.), Mediocrinus sp. ind., Tetraptocrinus sp.; foraminifers Parastegnammina sp., Eotuberitina sp., Elenella sp.

Age

Along A., the age of the host rocks by organic remains is late Silurian, Pridoli. The age and structure of the section of the suite are not determined unequivocally and have been debated for many years. G.Yu. Alferov (457), A.A. Kulesh et al. (1974), K.A. Keshishyan et al. (1983, 1995) consider the Urusay Fm to be in a continuously layered section of the Silurian-Devonian. M.A. Akhmedjanov et al. (73), Kh.T. Tulyaganov et al. (473), O.I. Kim et al. (1976), V.V. Mikhailov et al. (1988) interpret the structure of Sultanuizdag as an alternation of tectonic scales composed of rocks of different genesis and age, hence the different interpretations of the age of the suite. G.Yu. Alferov (457) considered the upper sub-suite of the Urusay Fm as a dike of augen granites. The rest of the suite was attributed to the Sultanuizdag Fm of the Silurian. M.A. Akhmedjanov et al. (73; 76) based on the high degree of metamorphism of the rocks and radiological age determinations (446-449 and 776 million years) by the K-Ar method on samples from the migmatite-granite complex in the area of the garnet factory, assign the Urusay Fm a conditionally Archean-early Proterozoic age. O.I. Kim (1974) determines the age of the suite as conditionally Proterozoic. V.V. Mikhailov (460) includes the Urusay Fm in the Sultanuizdag series of the conditional Proterozoic, excluding limestones with Silurian-Devonian fauna from its composition, considering them tectonic wedges and scales, exposed among ancient rocks.

Age Span:

Beginning stage:

Gorstian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

426.74

Ending stage:

Ludfordian

Fraction up in the ending stage:

1.0

Ending date (Ma):

422.73

Depositional setting

Depositional pattern:

Additional Information

Compiler:

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