I. V. Kislukhin, G. L. Rozbaeva

The Ryazanian–Valanginian correlation problem in northeastern West Siberia

Abstract. The paper comprehensively discusses the Lower Cretaceous in the junction zone of different structure-facies areas in northeastern West Siberia: Turukhansk, Tazovsky, and Malaya Kheta structure-facies sub-areas of the Ust-Yenisei region. The authors analyze three-dimensional seismic survey data, well logs, as well as sedimentological and biostratigraphic investigation of core samples. The current Lower Cretaceous regional stratigraphic scheme does not provide a single correlation between coastal and shallow marine types of the Ryazanian and Valanginian productive beds. The research findings pertain to the Tagrinskoye clay unit. An unconformity surface at its bottom in two (out of three) analyzed structure-facies areas gives grounds for extending the results to adjacent territories. Identification of stratigraphic hiatuses after analyzing ichnofacies and lithological composition changes at rock contacts, as well as correlating the results to geological and geophysical data contribute to the stratigraphic hiatus problem solution. It is proposed to consider the regional unconformity surface reflecting the boundary of two formation complexes as a validation criterion when correlating well logs. This statement should be included in the current stratigraphic schemes. Using the regional stratigraphic hiatus surface as a correlation criterion will increase reliability of stratigraphic schemes in various structure-facies zones.

Keywords: Lower Cretaceous deposits, stratigraphy, unconformity surface, marker horizon, structure-facies area