Could we classify oil shale as a biochemical sedimentary rock ? Oil shale is a muddy rock contains Kerogen. So I think in oil shale to be a mixture of Kerogen and mud sediments, and that's not the case, for instance, with the biochemical limestone where the solid remains of the living organisms formed the rock. So in limestone the organic material formed the rock, but in oil shale the organic material didn't, it is just, in my thoughts, preserved in the rock, or I am wrong ? enlighten me, please !