The sedimentary rock carbon pool is larger still than the ocean, land, or atmospheric pools.

carbon in the solid earth exists in the form of limestones,caco3, and to a lesser extent organic carbon.most of the organic carbon in the sedimentary rocks is in a form called kerogen.

kerogen is useless as a fossil fuel because it is diluted, usually less than 1% by weight of sedimentary, and because it is in a solid for, making it difficult to extract.