The Chardzhou type of section is topped almost everywhere by 5-15 m of anhydrite.
The Chardzhoun type is so different from the Gaurdak type that its recognition as an independent formation is justified. It may called the Sakar Formation because it is so well developed on the Sakar structure.
Toward the west the sediments of the Sakar Formation pass gradually into the Beurdeshik-Kirpichli type of section. At the base is a transitional zone (member I), which consists of alternating limestone and anhydrite with subordinate siltstone and clay beds. Thickness is 0-230 m. The lower salt (member II) is largely halite with some admixed clastic material. Thickness is 0-150 m. The middle anhydrite (III) has an exceptioannly uniform composition and is 3-10 m thick.
The upper salt member (IV) consists of halite and abundant admixed clastics and anhydrite beds. Thickness ranges from 300-350 m on the east and south and 1-5 m on the north and west. The upper anhydrite member (V) contains admixed clastics; thickness is 3-5 m.
The Beurdeshik-Kirpichi type of section within the Balkui- Ilim downwarp and on the western border of the Amu-Dar'ya regional low has a more complicated composition, structure, and thickness above zones of Callovian-Oxfordian basinal facies. Composition is more uniform above reef buildups. Where the underlying rocks are near-shore facies, thickness of the evaporites is sharply reduced, on to complete pinchout.
The Bayram-Ali type of section consists of the Iolotan, Mary, and Bayram-Ali Formations of Zharkov (1982). It begins with a transitional member of anhydrite 110-140 m thick with beds of gypsum-anhydrite. Then comes a middle anhydrite, thick upper salt, and anhydrite at the top.
The Sandykachi type of section is found in the southern part of the Amu-Dar'ya regional low. It consists largely of anhydrite and beds of limestone and dolomite.
The main criteria for predicting reef complexes in the Kugitang Formation are uniformity of composition and reduced thickness of the overlying evaporites. Abrupt facies change in the evaporites is characteristic of sectors that are in close proximity to barrier reefs and bioherms in the underlying Kugitang Formation. Presence in the evaporites of a large number of thick horizons of potassium salts in the regions of the southwest spurs of the Gissars, Beshkent downwarp, and Chardzhou step indicates absence of any underlying reef complexes.
Copyright 2003 James Clarke. You are encouraged to print
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