Thirty-seven Kupferschiefer samples from southwestern Poland were analyzed by microscopy, Rock-Eval approach and instrumental neutron activation analysis to understand the geochemical and morphological characteristics of kerogen present in the samples. The analytical results indicate that there are two different types of kerogens. One type was only subjected to thermal alteration processes, and the other was further oxidized after deposition of the sediment. In the oxidized samples migrabitumen was transformed into pyrobitumen. Rock|Eval analyses show a significant decrease in HI values in the oxidized samples and an increase in OI values in relation to the samples that were not influenced by oxidation. Variations in S2 versus C-{org} contents indicate a change in kerogen from Type II to Type III with progressing oxidation. The presence of pyrobitumen and the depletion of hydrogen in the altered kerogen allow one to conclude that the kerogen was used as hydrogen donor for thermochemical sulfate reduction (TSR). Thirty-seven Kupferschiefer samples from southwestern Poland were analyzed by microscopy, Rock-Eval approach and instrumental neutron activation analysis to understand the geochemical and morphological characteristics of kerogen present in the samples. The analytical results indicate that there are two different types of kerogens. One type was only subjected to thermal alteration processes, and the other was oxidized after deposition of the sediment. In the oxidized samples migrabitumen was transformed into pyrobitumen. Rock | Eval analyzes show a significant decrease in HI values ​​in the oxidized samples and an increase in OI values ​​in relation to the samples that were not influenced by oxidation. Variations in S2 versus C - {org } contents change a kerogen from Type II to Type III with progressing oxidation. The presence of pyrobitumen and the depletion of hydrogen in the altered kerogen allow one to conclude that the kerogen was used as hydrogen donor for therm ochemical sulfate reduction (TSR).