The role of skeletal and nonskeletal biogenic material in the accumulation of organic matter of the Bazhenov Formation

Organic matter of the Upper Jurassic-Lower Cretaceous highly carbonaceous black-shale Bazhenov Formation in the central part of the West Siberian sea basin is composed of predominantly sapropelic planktonogenic material, which was earlier assumed to have derived from siliceous-skeletal microorganisms (first of all, radiolarians) and nonskeletal ones (bacteria and algae). Comparative analysis for organic carbon in the formation rocks and in radiolarites and radiolarian oozes from some other areas showed that the siliceous-skeletal organisms make up <1% of the organic matter of the Bazhenov Formation. This is confirmed by correlation analysis of two main types of Bazhenov rocks — siliceous-argillaceous (bazhenovites) and argillaceous (mudstones), — which showed the absence of correlation between the contents of organic carbon and quartz (which is mainly authigenic) for both rocks.