Sorg was obtained by subtracting pyritic S (calculated from Fe content assuming that Fe exclusively occurs as pyrite) from total S (measured by elemental analysis). Accordingly, these values, and hence the Sorg/C ratios, are not obtained with high precision and rounded numbers are reported. However, (i) these Sorg/C values point to a low level of sulfurisation for the proto-kerogen of the shallowest sample (in agreement with S measurements from Were et al., 2003, doi:10.1016/S0009-2541(02)00393-5) and to an increasing trend with depth and (ii) these two features are supported by light microscopy and pyrolysis observations.