Catagenesis (geology)

The Katagenese is the main phase of oil formation of finely divided organic material in sediments. This phase is between diagenesis and metagenesis. The term deriving from the Greek ( κατα = completely and γένεσις = emergence ) was introduced by the Russian petroleum geologist Nikolai Vassoevich 1969.

Processes involved in the Katagenese

During deposition of sediments and organic particles such as algae, bacteria, and the radicals of higher plants are embedded. If the oxygen content in the pore waters is not sufficient to oxidize these radicals, they are preserved and are referred to as kerogen. In the diagenesis rock is sunk by superimposing new sediment or tectonic processes and is subject to increasing temperature and increasing lithostatic pressure. Only at temperatures between 50 and 150 ° C and 300 to 1500 bar pressure, corresponding to an absorption of about 1500 to 4000 m, escape at the Katagenese liquid hydrocarbons and methane from kerogen. This process is referred to as pyrolysis. With increasing temperature, the chain-like hydrocarbons are more split, so in the end only short-chain hydrocarbons, the basic components of natural gas are released. Pyrolysis is facilitated by the catalytic effect of clay minerals such as montmorillonite. The process is much more dependent on the temperature as the pressure. The change of the organic material at higher temperatures will be referred to as metagenesis.

Demarcation

The exact boundary between diagenesis, Katagenese and metagenesis is performed microscopically using the reflectivity of certain organic particles ( vitrinite ). This one uses the property of organic particles, with increasing temperature to reflect more light. The Katagenese is defined as the area of ​​the vitrinite between 0.5 and 2 %.