ISSN 0024-4902, Lithology and Mineral Resources, 2008, Vol. 43, No. 4, pp. 354–379. © Pleiades Publishing, Inc., 2008. Original Russian Text © Yu.O. Gavrilov, E.V. Shchepetova, M.A. Rogov, E.A. Shcherbinina, 2008, published in Litologiya i Poleznye Iskopaemye, 2008, No. 4, pp. 396–424. Sedimentology, Geochemistry, and Biota of Volgian Carbonaceous Sequences in the Northern Part of the Central Russian Sea (Kostroma Region) Yu. O. Gavrilov, E. V. Shchepetova, M. A. Rogov, and E. A. Shcherbinina Geological Institute, Russian Academy of Sciences, Pyzhevskii per. 7, Moscow, 119017 Russia e-mail:
[email protected],
[email protected] Received January 28, 2008 Abstract—Lithological, geochemical, stratigraphic, and paleoecological features of carbonaceous sediments in the Late Jurassic Volgian Basin of the East European Platform (Kostroma region) are considered. The shale- bearing sequence studied is characterized by greater sedimentological completeness as compared with its stra- totype sections in the Middle Volga region (Gorodishche, Kashpir). Stratigraphic position and stratigraphy of the shale-bearing sequence, as well as the distribution of biota in different sedimentation settings, are specified. It is shown that Volgian sediments show a distinct cyclic structure. The lower and upper elements of cyclites consist of high-carbonaceous shales and clayey–calcareous sediments, respectively, separated by transitional varieties. Bioturbation structures in different rocks are discussed. Microcomponent composition and pyrolytic parameters of organic matter, as well as distribution of chemical elements in the lithologically variable sedi- ments are analyzed. Possible reasons responsible for the appearance of cyclicity and accumulation of organic- rich sediments are discussed. DOI: 10.1134/S002449020804007X The second half of the Late Jurassic Period was 1996).