Okunyozh Fm
Type Locality and Naming
In this section, the description of the suite is provided based on the materials of V. S. Luchnikov, which significantly differ from the views of N. G. Vlasov. It was distinguished by N. G. Vlasov (1961).
Synonym: Okunyozhskaya Suite, Иокуньжская свита
Reference section:
Lithology and Thickness
The Okunyozh Fm, in terms of composition and structure, is subdivided into two sub-suites. The lower sub-suite is composed of gray, medium- and large-gravel conglomerates, well-sorted, with well-rounded pebbles, with a clay-carbonate cement in which a significant amount of volcanic material is present. By the composition of the pebbles and cement, the structure of the conglomerates is similar to the Alykagar ones. At the base of the thickness, crushed shells are noted in the cement. Among the coarse clastic rocks, lenses of siltstones and sandstones with fine- and medium-grained particles are encountered, in which single poorly preserved shells of Myophoria sp. indet. and rather abundant fragments of Pleuromeia sp. are identified. The latter is represented by the same species as in the underlying layers. The thickness of the sub-suite is up to 200 m
The upper sub-suite is represented by a complex lenticular interbedding of coarse-grained sandstones and gravelites, almost unsorted, gray, cross-bedded. The thickness of the sub-suite is up to 320 m.
Relationships and Distribution
Lower contact
Upper contact
Regional extent
The suite is distributed in the southwest of the Darvaz district.
GeoJSON
Fossils
In the lower sub-suite, poorly preserved shells of Myophoria sp. indet. and rather abundant fragments of Pleuromeia sp. are identified.
Age
Depositional setting
Additional Information
The author's detailed studies have established the following.
1. The angular unconformity between the Jurassic and the Triassic is 24-27°.
2. Throughout the development zone of the Okunyozhskaya suite, the Jurassic section begins with various horizons of the Bajocian stage.
3. The Alykagar and Okunyozhskaya suites (Аликагарская и иокуньжская свиты) conform and in the contact part of the section are composed of co-facies formations.
4. Both suites contain the same species of Pleuromeia.
5. The entire thickness of the Alykagar suite accumulated only during the first quarter of the Olenekian age (zone of Meekoceras gracilitatis).
It is generally known that the rate of accumulation of coarse clastic material far exceeds the rate of formation of siltstone sediments. It should be noted that the deposits of the Lower Triassic accumulated under conditions of geosynclinal regime, when the sedimentation rate is high.
All the above allows the author to date the deposits of the Okunyozh Fm to the Lower Triassic. *