Unordinary Interpretation of Paleozoic Rocks Pyrolysis Rock-Eval Data

By

Irina Slivko¹

(1) Geology faculty of Moscow State University, Moscow, Russia

 Studied is the Paleozoic samples area from Predkolymskaya structure loop in the Northeast of Russia. The Silurian / Devonian carbonate-clay rocks are accumulated in reef and lagoon conditions of carbonate platform. The clear rhythms stand out in this section, with the content of clay increasing to subface of stratum. In the region are petroleum shows - from gases to solid bitumen. The quantity of organic carbon (TOC) is changing very sharply from 0.1 to 5 %. When the carbonate content decreases, the TOC increases. There is an increase of TOC to subface of stratum. Based on hydrogen index (HI) vs oxygen index(OI), part of the samples belongs to the zone of II type kerogen, several - to the I type, and part - to the III type (terrestrial OM). But, in Lower Paleozoic rock we can’t found terrestrial OM; we must search new explanation of the same pyrolysis data. Most of samples are in the zone of dislocated OM, which is characterized by more high S1 (free hydrocarbons), sufficiently low T max (less than 380^oC) and wide range of HI (although the samples are from the sufficiently homogeneous section). It is interesting that this dislocated OM associated with carbonates in general and the OM of argillites is characterized by classical pyrolysis parameters. There are several samples with high maturity. It means that they were found at the places of contact with intrusions or thrusts zones. All samples can be classified as being from ex-source rocks with exhausted generation potential.