Comparing the state of reaction advancement of I/S (illite content of illite/smectite mixed layer minerals) and organic matter (vitrinite reflectance) in instances of high temperature gradients allows one to observe the evolution of geologic materials under extreme conditions. In a geothermally heated sedimentary series (Salton Sea area, California), both clays and organics have reacted to completion in the temperature gradient range of 200°-400oC/km during heating episodes of 104 years. We observed an instance of rapid heating, through magmatic intrusion into the Meso-Paleozoic eastern Paris Basin sedimentary series in late Permian time, which induced changes in the organic material, but where clays are apparently unaffected.
