Geochemical heterogeneity and dismemberment of Upper Cenomanian sediments of Van-Yogan field (Western Siberia)

In this paper, the technique of analysis to establish lithogeochemical vertical heterogeneity of the sedimentary section is shown and a plan based on the correlation of strata petrogeochemical indicators is proposed. Studies have shown that within the framework of Van -Yogan vertical geochemical heterogeneity of the top of the Pokursky suite is expressed ion in polycyclic changes in the level of concentrations of manganese, silicon, iron, calcium, aluminum and rare earth elements which reflect the variability of the physico-chemical parameters, mechanisms of sedimentation and, to a lesser extent, sediment sources. The boundaries between the geochemical cycles of high-order have anomalously high values (> 370) of the Mn/U ratio and greater rock carbonation, which is associated with abrupt changes in the salinity of the basin due to lower hydrodynamic activity. The geochemical structure of macro-cyclites emphasizes the presence in the base of high-silicon sediments with the clay content of montmorillonite-kaolinite (NKM < 0.2) which are replaced upsection by more glandular illite-montmorillonite (NKM > 0.22) rocks and reflect enhancement of marine sedimentation regime. Accompanying increase in the concentrations of rare earth elements emphasizes strengthening of the role of chemogenic sedimentation due to coagulation of colloidal forms of lanthanides. The main geochemical difference of the sediments of the formation Saccammina micra, Ammomarginulina sibirica from Trochammina wetteri tumida, Verneuilinoides kansasensis is the relative enrichment of the latter with alumina. Given the changes of Al203 and Fe203, in the geochemical cycles of the formation Trocham-mina wetteri tumida, Verneuilinoides kansasensis, we can assume involvement of redeposited, intensively substituted fragments of feldspars in sedimentation. Strict conformity of the identified boundaries of geochemical cycles of the first order with the volume of the previously set section components (G.N. Aleksandrova, V.B. Beloserov, V.M. Podobina) indicates the accuracy of the proposed scheme of section geochemical division. The observed regularities of vertical variations in the composition of sedimentary rocks associated with the genetic parameters of sedimentation empower geochemical methods in the local correlation of lithological sequences. It should be emphasized that the use of indicator ratios are purely individual and must be adjusted in each case.

Keywords

Authors

References