The best information on the Permian salt-bearing sediments of the north border of the North Caspian depression has come from drilling on Karachaganak salt dome and on Konchebay dome just to its south. These deposits are largely halite, but they contain variouus amounts of carbonate-sulfate and clastic material.
The upper part of the section of Karachaganak field to a depth of 1500-2000 m consists largely of medium- to coarse- grained salt. Sulfate minerals are concentrated in layers 0.1-1.2 mm thick at spacings of 8-15 cm. A few 10-20-meter beds of anhydrite are present.
The sections of all the wells drilled on Karachaganak dome contain three to four intervals with thickness up to 350 m that are composed largely of sulfate clastic rocks. The clastic material is predominately clay-silt rock of red and gray color, which contains sulfate and carbonate minerals in the lower part of the interval and salt in the upper.
Palynological studies have demonstrated presence in Karachaganak well 1 not only of Kungurian sediments but also Ufimian and Kazanian sediments. The spore-pollen complex of the Kazanian Stage, which is in the 4410-4450 m interval, is characteristic of the Iren Horizon of various parts of the Russian craton. Presence of Ufimian sediments has been established by spore-pollen assemblage in the 3806-4209 m interval. Spores and pollen of the Kazanian Stage are found in gray to dark gray clays within salt in the 2709-2716 m interval.
Similar salt-bearing sediments are present on the Liven dome 60 km to the east of the Karachaganak arch. Well 8 there penetrated salt, clastic-sulfate, carbonate, and potassium-magnesium salts, which have been identified paleotologically as Ufimian, Kazanian, and probably also Kungurian.
Upper Permian salt-bearing sediments are recognized in Gmelin well 3, Zhdanov well 8, and Makat well 3. The salt-bearing sediments of the northern border of the North Caspian depression are thus found to be not only of Kungurian age but also of Ufimian and Kazanian age.
Taken from Pisarenko and others, 1986; digested in Petroleum Geology, Vol. 23, No. 7/8, one cross section of Karachaganak fielld.
Copyright 2003 James Clarke. You are encouraged to
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