A rock sample includes multiple rock samples that are each obtained from the borehole. The rock samples have been exposed to contamination during a drilling operation to drill the borehole. The rock sample is split into a first sample portion and a second sample portion. The first sample portion is decontaminated with a solvent. The second sample portion is decontaminated by thermovaporization for an initial duration of time at an initial thermovaporization temperature below that of a cracking temperature of an organic matter carried within the rock sample. A difference between a first pyrolysis Tmax value of the first sample portion decontaminated by the solvent and a second pyrolysis Tmax value of the second sample portion decontaminated by the thermovaporization is determined to satisfy a decontamination level threshold. The remainder of rock samples are decontaminated by the thermovaporization in response to determining that the difference satisfies the decontamination level threshold.