The definition of stratigraphic position of rocks-reser­voirs by a detailed biostratigraphic study of containing sedi­ments is given in the paper. With this purpose the regional stratigraphic scheme of the Triassic deposits of the Southern Mangyshlak and Northern Ustyurt was compiled, in its foundation fractional biostratigrafical dismemberment of the Triassic section was laid. Lithologic-petrographic characteristics and postsedimentation processes of transformation of Triassic rocks-reser­voirs in different structural-facial zones with the purpose of revealing regularities of their distribution were studied. Detailed biostratigraphic study of the Triassic sections allowed to allocate local lithologic-stratigraphic units (suits) and to correlate them on region. Lithologic-stratigraphic stu­dies became the base for drawing up major regional stratigraphic schemes of Southern Mangyshlak and Northern Ustyurt Triassic deposits and regional schemes of their correlation.