The north-south-trending Ural fold region is a gigantic allochthon, which was thrust westward onto the eastern margin of the East European craton. From east to west the principal tectonic features are: 1) eugeosynclinal zone which contains greenstone terranes, 2) Uraltau igneous-metamorphic complex, 3) miogeosynclinal zone, and 4) Cis-Ural foredeep. These features developed during the Late Paleozoic Hercynian tectonics. The eugeosynclinal zone is a stack of thrust sheets composed of ophiolites and volcanic-sedimentary deposits of Silurian and Devonian age. These rest on younger miogeosynclinal sedimentary rocks. At many places on the west flank of the Urals the eugeosynclinal sheets have been thrust onto Upper Devonian Famennian flysch. The miogeosynclinal formations of the Urals occur as a series of large stacked plates thrust toward the west. For example, on Bashkir anticlinorium plates of Upper Proterozoic Riphean-Vendian sedimentary rocks have been thrust onto platform facies largely of Devonian and Silurian age. Well 281 on the northwest of the Taratash complex passed from Archean gneisses into lower Frasnian-upper Givetian limestones at a depth of 593 m. Then at a depth of 719 m limestones of probable Early Devonian age were penetrated. Farther to the west are the overthrusts of the Cis-Ural foredeep. They have two characteristic features: 1) Their frontal zones are sub-parallel, and associated with them are chains of asymmetrical oil-gas-bearing anticlines; 2) the thrust planes are generally steep at the present surface, in contrast to sub-horizontal dips in the more eastern regions of the Urals. Intersection of faults with different directions of dip has led to formation of wedge-shaped blocks, which are composed of Permian and Upper Carboniferous rocks. Structure is complicated further by deformation of Kungurian salt. Overthrusts that pre-date the Hercynian have had their effect on the formation of traps in the sedimentary cover. Numerous overthrusts that extend for tens and even hundreds of kilometers have now been recognized within the basement of the Volga-Ural oil-gas province. Zhigulev overthrust in Samara and Orenburg Regions extends east-west more than 500 km, and associated with it are anticlines in the overlying sedimentary rocks. In the Minnibayevo area of Tatarstan (Romashkino field) well 20,000 passed through not less than four thrust sheets in Archean rocks. Development of anticlines in the sedimentary cover is attributed to reactivation of these thrusts. Compression on these thrusts may be active today. The Tuymazy high (field) of Bashkortostan is an example of a Paleozoic anticline that formed when an ancient overthrust in the crystalline basement was activated during Hercynian tectonism. This feature is expressed on all marker horizons from the surface of the crystalline basement to the top of the Upper Permian rocks. Tuymazy well 2,000 at the crest of the high determined presence of three tectonic slices thrust one upon the other in the direction of the steep flank of the high. Maximum displacement was at the end of the Middle Proterozoic some 1700 million years ago. Weak movements took place later in the Paleozoic and appear to continue today. (Taken from Kamaletdinov and others, 1988; digested in Petroleum Geology, vol. 27, no. 9/10, 1993, 3 maps and 4 structural cross section). Copyright 2000 James Clarke. You are encouraged to print out this News Letter and to forward it to others. Earlier News Letters can be downloaded at our website - http://geocities.com/internetgeology/ Inquiries concerning the journal Petroleum Geology can be made by telephone at (703) 759-4487 or by FAX at (703) 759-3754.