High-resolution stratigraphy of the Lower and Middle Jurassic petroliferous deposits of northern West Siberia

The Lower-Middle Jurassic petroleum-promising deposits of northern West Sib eria have a complicated structure and are poorly investigated by drilling. Correlation of these deposits, in particular, petroleum-producing and promi sing sand beds, is often disputable. We present results of a detailed corre lation of the deposits by bio-and lithostrigraphy at the level of zonal cyc lites (ZC). Twenty two ZC have been recognized and traced in various struct ure-facies areas. The stratigraphic positions and volumes of sand beds and their notation have been refined. Nineteen regional beds at the bottom of Z C and thirty two local beds occurring at various stratigraphic levels of th e middle and upper predominantly clayey part of ZC have been recognized. A version of sand bed notation is proposed in which numerals are assigned onl y to beds of regional occurrence. Local beds are marked with the number of the main bed and a letter. In this case, the indices of beds more precisely reflect their stratigraphic position. A regional gap has been found at the bottom of the Dzhangoda Horizon. The facies zonation of the Lower Jurassic deposits is refined.