1. n. [Geology, Shale Gas]
The physical and chemical alteration of sediments and pore fluids at temperatures and pressures higher than those of diagenesis. Catagenesis involves heating in the range of 50 to 150 degC [122 to 302 degF]. At these temperatures, chemical bonds break down in kerogen and clays within shale, generating liquid hydrocarbons. At the high end of this temperature range, secondary cracking of oil molecules can generate gas molecules.