STRATIGRAPHY FROM PALEOBOTANICAL DATA OF JURASSIC AND LOWER CRETACEOUS CONTINENTAL DEPOSITS IN EAST SIBERIA AND THE FAR EAST

Lower and Middle Jurassic coal-bearing deposits occur in the western part of the region under consideration (the Irkutsk basin, the Trans -Baikalia depressions). Far to the east these are found only in the Upper Aldan basin. Upper Jurassic sediments are more widespread, occurring within the southern part of the Lena basin as well as in the Upper Aldan, Amur-Zeya and Bureya basins. The principal coal-forming stage dates back to the earlier Cretaceous; with this are associated most thick and productive strata of the Lena and Bureya basins as well as all coal-bearing strata of the Zyryansk, Suchansk and Suifansk basins. Age determinations of individual coal-bearing suites are chiefly based upon the study of plant remains and establishing leading paleofloristical complexes. At the present the complexes of the Upper Jurassic and Lower Cretaceous sediments are best known. ,The composition of one-age complexes varies with the movement from N to S conditioned by the then existing botanic-geographical zonality. — Auth. English summ.