Alyachapan Fm

Along the Alachapan River, South-West Gissar. G.S. Chikryzov in 1951 (382, p. 81). Stratotype on the watershed of the Kayrak-Alachapan rivers.

Synonym: Alyachapan Suite, Алячапанская св.

According to F.R. Bensh (102), three sub-suites are distinguished. Lower sub-suite (thickness 187m) is assigned to the Fusulinella schwagerinoides zone. At the base of the visible part - bedded and massive limestones, detrital and clastic, transitioning into calcareous gravels and small pebble conglomerates. Above - thin-bedded argillites and siltstone (aleurolites) with rare lenses of clayey limestones and calcareous sandstones.

Lower part (thickness 250m) - conglomerates and sandstones. Conglomerates are massive and thick-bedded, medium- and small pebble. Sandstones range from coarse- to fine-grained with layers of siltstone (aleurolites), less frequently gravels and small pebble conglomerates.

Upper part (thickness 317m) - frequent alternation of thin-bedded sandstones and siltstone (aleurolites) with rare layers of small pebble conglomerates, gravels, and clayey, sandy, and clastic limestones.

Upper sub-suite contains complexes of two zones Montiparus montiparus and Triticites quasiarcticus-T. ferganensis. Massive (thickness about 800m) monotonous thickness of rhythmically interbedded sandstones, siltstone (aleurolites), sometimes argillites. At the base of the sub-suite - massive medium- and mixed pebble conglomerates with layers and lenses of sandstones, siltstone (aleurolites), and limestones (thickness 30-50m).

On the watershed of the Kayrak-Alachapan rivers, this package (thickness 120m) is not distinguished, and the conglomerates are directly replaced by a flyschoid thickness. This part of the section can be tied to the typical complex of the Triticites quasiarcticus-T. ferganensis zone, found in a tectonically isolated package (thickness 123m) of thin interbedded siltstone (aleurolites), argillites and limestones.

Total thickness of formation is about 2000m.

At the base of the visible part – In these basal limestones, foraminifera - Fusulinella bocki Moel., F. ex gr. pseudobocki Lee et Chen, F ex gr. schwagerinoides Depr., F. rara Schlyk., Fusulina cf. cylindrica Fisch. Middle sub-suite includes the complex of the Protriticites pseudomontiparus - Obsoletes obsoletus zone, corresponding to the Jilginsay Horizon (Dzhilginsay Horizon) of the Kasimovian stage of the Upper Carboniferous.

Lower part - re-deposited late Moscovian foraminifera

Upper part - Clastic limestones, which contain foraminifera - Fusulinella cf. adjuncta Schlyk., Protriticites aff. globulus Putrja, P. aff. pseudomontiparus Putrja, P. aff. manukalovae Kir., Obsoletes aff. peculiaris (Grysl), Quasifusulinoides juvenatus Kir., Q. parafusiformis Bensh, Q. aff. Discorbis (Chern.).

Upper sub-suite - limestones with foraminifera - Protriticites sp., Quasifusulinoides juvenatus Kir., Montiparus ex gr. montiparus (Ehr.), M. umbonoplicatus (Raus. et Bel.), M. aff. reticulatus (Ros.), Schwageriniformis ex gr. schwageriniformis (Raus.), characteristic for the Montiparus montiparus zone.