High-resolution sequence stratigraphic analysis and sea-level interpretation of the middle and upper Jurassic strata of the Nyurolskaya depression and vicinity (southeastern West Siberia, Russia)

Abstract

In this article, we present the first application of high-resolution sequence stratigraphic analysis to the Jurassic Vasyugan deposits of West Siberia. On the basis of wireline logs, lithologies, and sedimentary facies we identified a series of third-order depositional sequences that formed on a low-gradient siliciclastic ramp in shallow marine to paralic environments. Our sequence stratigraphic framework helped to properly distinguish specific stratigraphic units (productive sand beds), while enhancing stratigraphic correlation. Sequence stratigraphic procedures particularly aided in recognition of fluvial channels and prograding shorelines in marginal parts of positive structures that usually represent the most favorable reservoir zones. The depositional architecture of sequences throughout the entire area of study was primarily controlled by synchronous oscillations of relative sea level. Comparison of interpreted sea-level changes with our Quantified Eustatic Curve (QEC) derived from Russian Platform stratigraphy revealed close correspondence of timing of sea-level events for the late Bathonian-late Oxfordian interval. This indicates that sea level events occurred simultaneously in West Siberia and the Russian Platform, and suggests that eustasy was the main factor controlling sedimentation in southeastern West Siberia during that time interval. In addition, it supports the validity of the late Bathonian-late Oxfordian interval of the QEC demonstrating its utility for further application to West Siberia and other sedimentary basins.