Petroliferous basins at continental margins of paleozoic paleoseas: Communication 2. Petroliferous basins at continental margins in the Rheic, Uralian, and Central Asian paleoseas

The continental block of the Earth's crust was separated in the Paleozoic into two unequal parts: (i) huge supercontinent Gondwana located at high latitudes of the Southern Hemisphere and (ii) several small continents (Laurentia, Baltica, Siberia, Kazakhstan, South Chinese block, and North Chinese blocks) located at low latitudes south and north of the equator. Morphology of the Paleozoic seas between these blocks was subjected to changes (expansion and contraction) with time. Their closure was provoked by several orogenic (Taconian, Caledonian, Acadian, and Hercynian) phases. At present, relicts of these ancient orogenic structures extend as belts along the boundaries of many petroliferous basins and record the position of past seas. One of the oldest oil-and-gas deposition belts, which appeared in southern Iapetus in the Precambrian/Phanerozoic, was confined to a passive margin of Gondwana. In the Early Paleozoic, small blocks of the continental crust (Avalonia, Armorica, Perunica, Iberica, and others) were successively detached from the passive margin. This process was accompanied by the opening of a new deep basin (Rheic Sea or Paleotethys). The Uralian and Central Asian paleoseas were formed approximately at the same time. Many petroliferous basins existing now were located in the Paleozoic at the margins of these paleoseas.