Kerogens

Kerogen (Greek κηρός "wax" and -gen, γένεση "birth") is a mixture of organic chemical compounds that make up a portion of the organic matter in sedimentary rocks. It is insoluble in normal organic solvents because of the high molecular weight (upwards of 1,000 daltons or 1000 Da; 1Da= 1 atomic mass unit) of its component compounds. The soluble portion is known as bitumen. When heated to the right temperatures in the Earth's crust, (oil window c. 50–150 °C, gas window c. 150–200 °C, both depending on how quickly the source rock is heated) some types of kerogen release crude oil or natural gas, collectively known as hydrocarbons (fossil fuels). When such kerogens are present in high concentration in rocks such as shale, they form possible source rocks. Shales rich in kerogens that have not been heated to a warmer temperature to release their hydrocarbons may form oil shale deposits.

The name "kerogen" was introduced by the Scottish organic chemist Alexander Crum Brown in 1906.

With the demise of living matter, such as diatoms, planktons, spores and pollens, the organic matter begins to undergo decomposition or degradation. In this break-down process, large biopolymers from proteins and carbohydrates begin to dismantle either partially or completely. (According to Maurice Tucker (1988), this break-down process is basically the reverse of photosynthesis). These dismantled components are units that can then polycondense to form polymers. This polymerization usually happens alongside the formation of a mineral component (geopolymer) resulting in a sedimentary rock like kerogen shale.

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