Ordovician - Permian palaeogeography of Central Eurasia: Development of Palaeozoic petroleum-bearing basins

In this paper, we discuss three petroleum-bearing basins of Palaeozoic age in Central Eurasia - the Precaspian, Tarim and Chu-Sarysu Basins. We make use of recently published palaeogeographic maps of the Central Eurasian region, six of which are presented here (Late Ordovician, Early-Middle Devonian, Late Devonian, Early Carboniferous, Early Permian and Late Permian). The maps illustrate the development through the Palaeozoic of the Palaeoasian and Palaeotethys Oceans; of the East European, Siberian and Tarim cratons; and of the Kazakhstan and other microcontinental blocks. The Kazakhstan block formed during the Late Ordovician and is a collage of Precambrian and Early Palaeozoic microcontinents and island arcs. It is surrounded by collisional foldbelts (Ob-Zaisan, Ural-Tianshan and Junggar-Balkhash) which formed in the Late Carboniferous - Permian. We believe that the formation of a stable Kazakhstan block is not consistent with the existence of the previously-identified "Kipchak arc" within the Palaeoasian ocean, or (as has previously been proposed) with activity on this arc up to the end of the Palaeozoic. The oil and gas potential of the Precaspian, Tarim and Chu-Sarysu Basins depends to a large extent on their tectonic stability during the Palaeozoic and subsequent time. The Precaspian Basin has been stable since the Cadomian orogeny (Early Cambrian) and is known to have major hydrocarbon potential. The Tarim Basin (NW China) has somewhat lower potential because the margins of the Tarim continental block have been affected by a series of collisional events; that margin with the Palaeotethys Ocean, for example, was active during the Late Palaeozoic. The Chu-Sarysu Basin on the Kazakhstan block is the least stable of the three and contains only minor gas accumulations.