a fold which occurred in the Late Precam-brian and preceded the Caledonian tectonic age of the Early Paleozoic. The term “Baikal fold” was proposed in 1932 by N. S. Shatskii. The duration of the Baikal fold was initially thought to be from the end of the formation of the Jotnian series of the Baltic Shield (1.2 billion years ago) to the Lower, or even in places, to the Middle Cambrian (500 million years ago). After a detailed study of the geological structure of southern Scandinavia, it was realized that in all probability there existed in this segment of the earth’s history not one but two ages, the Dalslandian (Early Baikal) and the Baikal (or Late Baikal) with a boundary between them at a time of 900 million years ago. The folded systems of the southern edge of the Siberian Platform are typical regions for the development of the geosynclinal formations which were formed as a result of the Baikal fold (Baikalides). The Baikalides form the ancient cores of numerous Paleozoic folded massifs in the Urals, Taimyr, Kazakhstan, Tien Shan, and probably, significant expanses of the basement of the Western Siberian Plain, and elsewhere. The presence of ancient massifs of Baikal fold which to one degree or another have been regenerated by Alpine tectonic movements have been established in the Caucasus, Afghanistan, Iran, and Turkey. Structures of the same age as the Baikalides have developed widely on all continents. In Western Europe (France), the Cadomian (Assynt) fold is analogous to the Baikal fold. In India, there is the Singhbhum-Erinawra (Mus-gravides) fold, which corresponds to the Early Baikalides (Dalslandides); in Australia and North America, the Grenville complex; and in South America, the Minas complex.
In many ancient platforms, the Baikal tectonic age was a time for the formation of the ancient tectonic furrows (au-lakogenes) which were filled by thick masses of sedimentary and sedimento-igneous rocks which form the lower level of the mantles of these platforms. Similar aulakogenes have been established by drilling and by geophysical research in the abyssal areas of the Eastern European and Siberian platforms (the Pachelma, Moscow, Middle Russian, and others). The southern ancient platforms of the earth were strongly broken up by the Baikal fold and experienced processes of magmatism and metamorphism.
In the history of the earth’s development, the Baikal fold is closely related to the tectonic ages of the Phanerozoic (Caledonian, Variscan, and Alpine), and together with them forms a single major tectonic cycle (megacycle or mega-chron), during which (for about 1.2 billion years) there occurred the breakup of the ancient consolidated platforms, the formation and development of the geosynclinal belts and systems, the formation of new platforms, and at the end of the cycle, the creation of oceans and areas with an oceanic-type crust. The structural plan of the earth which was created during the Baikal fold predetermined the placement of the major structural elements of the earth for its entire subsequent history.
A. A. BOGDANOV