Insoluble Organic Matter (Kerogen) in Sedimentary Rocks of Marine Origin1
Kerogen was isolated, by techniques developed in this study, from 21 rock samples representing a wide variety of ages, lithologies, and environments of deposition. The new techniques make it possible to separate relatively mineral-free kerogen from rocks containing less than one per cent of organic matter. With the recovery of relatively pure kerogen, it becomes possible to make reliable measurements of physical and chemical properties which otherwise would be difficult or impossible to obtain.
Rocks deposited under marine conditions appear to contain either of two types of kerogen. One type is remarkably similar to coal in many of its properties, whereas the other is more like the kerogen of oil shales.
Although age and lithology show little correlation with kerogen properties, there is evidence that the elemental composition of kerogen is controlled to some extent by the environments under which the rocks were deposited. Metamorphic forces also have affected the properties of kerogen, just as they have in coal. Two metamorphosed rocks yielded anthracite-like kerogen, and in one of these the presence of graphite was indicated by X-ray diffraction.
Evidence is also presented that nitrogen occurs in both the organic and inorganic phases of sedimentary rocks. Metamorphic forces do not appear to have changed the nitrogen content of kerogen relative to carbon, except during the late stages of metamorphism.
Although most oil probably originated from hydrocarbons in living organisms, some of the observations made in this study offer support for the theory that some oil may have been derived from kerogen.