Much new information has been gained in recent years on the Middle Paleozoic evaporites of the Tunguska and Vilyuy regional lows of the Siberian craton. These deposits occur in two contemporaneous but separate basins. Drilling in Tunguska basin in 1986-87 in the northwest part of the Siberian craton disclosed salt along practically the entire Devonian section. This was the first time salt had been found in the Yampakhtin, Yuktin, Nakokhox, and Kalargon Formations. Salt-bearing Devonian formations in Tunguska basin are as follows in ascending order. Salt was penetrated in the lower Gedinnian Yampakhtin Formation in the 1469-1496 m interval of Neralakh well 3. There are two main beds 3 and 6 m thick. The salt is gray and has a clearly expressed seasonal layering. In the Zubov Formation of late Gedinnian age the salt occurs in two beds of halite with total thickness of about 10 m. The salt beds of the Manturov Formation of Eifelian- early Givetian age are pale pink to red halite in the lower part of the section and gray to dirty red in the upper. Well expressed seasonal layer is common. The brines of this basin reached the sylvite stage of deposition. The salt of the upper Givetian Yuktin Formation occurs as two thick strata separated by brecciated sulfate and carbonate. Total thickness of this salt ranges from 20 to 80 m. This salt is clear and transparent, and seasonal layering is common. With subsequent introduction of transgressive marine waters the basin was freshened. In the lower Frasnian Nakokhoz Formation the salt occurs as 3 to 4 strata, which range in thickness from 1.5 to 7 m. These are separated by beds of variegated dolomitic marl and gray clay. Precipitation did not go beyond the halite stage. Salt beds are present in the lower and upper parts of the Kalargon Formation, which is late Frasnian - early Famennian in age. The salt is light gray, semi-transparent to transparent. Sylvite was deposited at times. Salt beds are present in the lower part of the Fokin Formation. Three strata are recognized: lower 36-42 m thick, middle about 2 m thick, and upper 13-24 m thick. The salt is pale pink and gray and weakly seasonally layered. Middle Devonian salt has been drilled in three areas of the Vilyuy basin to the northwest of Vilyuysk. Core recovery was poor; however. the geophysical logs indicate thickness of salt-bearing rocks at 10-110 m. Age is probably Eifelian. Upper Devonian salt-bearing rocks are widely distributed in the Kempendyay depression to the south of Vilyuysk. There appears to have been no connection between the Vilyuy and Kempendyay salt basins. Lower Carboniferous salt-bearing sediments have been found on the Siberian craton only in the northeast part of the Kempendyay depression. Judging from the geophysical logs and limited core recovery three to four salt beds ranging from 5 to 20 m are present. Salt has long been known in the far north of the Siberian craton in the Nordvik area. (Taken from Matykhin and Sokolov, 1991; digested in Petroleum Geology, vol. 32, no. 1, 1998; map, correlation chart, and four geophysical well logs.) Copyright 2000 James Clarke. You are encouraged to print out this News Letter and to forward it to others. Earlier News Letters are available at http://geocities.com/internetgeology/