Origin of contrasting features and preservation pathways in kerogens from the Kashpir oil shales (Upper Jurassic, Russian Platform)

A kerogen, termed aBS base, from the Gorodische section (Russian Platform) was studied using a combination of microscopic, spectroscopic and pyrolytic methods in order to determine its chemical structure, source organisms and formation pathway(s). This kerogen was mainly formed via degradation-recondensation of phytoplanktonic material. Selective preservation and natural sulphurisation pathways only played a minor role, whereas a substantial contribution of ether linked lipids was noticed, revealing large oxygen cross-linking. Such observations allowed us to put forward, for the first time to the best of our knowledge, a substantial role for the oxidative reticulation pathway in the formation of a kerogen. Comparision with a previously studied sample from the same outcrop revealed contrasting features which reflect differences in preservation pathways triggered by different depositional conditions.