The Rock–Eval 6 technique provides several measurements from the successive pyrolysis and oxidation of a sample (Espitalié et al., 1977, 1985). First, the splitting of the pyrolysis effluent (under N2) into two halves at the outlet of the pyrolysis oven, allows the simultaneous detection and quantitation of hydrocarbonaceous effluents with flame ionization detection (FID) and CO and CO2 with infra-red (IR) detection, respectively. The S1 and S2 signals successively determined with FID, correspond first to the amount of free hydrocarbons (S1, gas + oil) volatilized for 3 min at 300 °C, the second peak (S2) representing the hydrocarbons generated from kerogen cracking between 300 and 650 °C, with a heating rate of 25 °C/min (bulk rock method and basic mode). The amounts of CO2 and CO represent the S3 and S3CO peaks, respectively. All basic parameters are expressed either in mg of hydrocarbons or CO2/CO per gram of rock. Tmax is the temperature at which the maximum hydrocarbon yield resulting from kerogen cracking occurs. The residual organic and inorganic carbon content (in wt%) of the pyrolyzed sample is obtained by combustion in air from 300 to 850 °C, with a heating rate of 20 °C/min. The CO2 and CO resulting from this combustion are also detected with an IR cell and correspond to peaks S4 and S5 for CO2 and peak S4CO for CO.

From these basic parameters, the total organic carbon content (TOC, wt%) is calculated as the sum of pyrolyzed OC and residual OC. The hydrogen index (HI, mg HC/g TOC) corresponds to the quantity of pyrolyzable organic compounds (S2 peak) relative to TOC. The oxygen index (OI, mg CO2/g TOC) corresponds to the quantity of CO2 (S3 peak) relative to TOC. The Rock–Eval 6 device, which measures CO2 and CO separately, allows three OIs to be defined: one for CO2, one for CO and an additional one for CO2 + CO, called OIRE6. The latter is expressed in mg O2/g TOC. Finally, the mineral carbon (MinC) is also calculated as the S3’ + S3’CO + S5 peaks.