Rare-earth elements as geochemical criteria of endogenous sources of microelements contained in oil

This article presents data on the REE contained in 50 oil samples taken from six oil and gas regions that are based on oil fraction composition analysis using ICP MS. It is shown that regardless of the geological and tectonic structure of regions, oil composition, depth of deposit occurrence, and lithology of enclosing rocks, chondritenormalized curves of REE distribution in oil are different and have a europium maximum. The europium anomaly and the regularly increasing (Eu/Sm) (N) and Eu/Eu* ratios under transition from asphaltene components to tars and then to oils are geochemically substantiated. Unlike oil, Devonian domanicites and Jurassic bazhenites, as well as their bituminous substance are characterized by a prominent negative europium anomaly (in the (Eu/Sm) (N) ratio), which is typical of sedimentary rocks, modern seawater, and the upper crust of the earth as a whole. Based on the data obtained, the conclusion on the participation of deep fluid systems in the formation of the geochemical appearance of naphtydes is made.