ENVIRONMENTS OF Yu<sub>2</sub> HORIZON FORMATION OF SOUTH-EASTERN AREAS OF YUGAN PRIOBIE AND ADJACENT TERRITORIES
During formation of Yu2 horizon, the studied territory represented a low-lying constructional and coastal plain from time to time flooded by sea. By types of environments, Yu2 horizon is conditionally divided on 3 parts. During formation of the lower part of Yu2 horizon the territory under study in east, south-east and north-west was occupied by low-lying constructional plain. The western, south-western and north-eastern parts - denudation-constructional plain. By the intermediate time of Yu2 horizon accumulation, the gradual transgression of sea was started resulted in submersion of the most lowered parts of the plain. During formation of the upper part of Yu2 horizon within studied territory, the following two main paleogeographic areas are distinguished: eastern, southern and south-western areas represented a low-lying constructional plain with widespread development of river network and fluvial and watershed types of sections typical for this area. The north-western and northern parts present a low-saline, partially freshening basin. The revealed paleogeographic environments and principal regularities of spatial distribution of Yu2 horizon deposits allowed to outline zones where deposits have most favorable reservoir properties, as well as zone of wedging out of these deposits to which could be confined oil and gas lithological traps.