ABSTRACT

A suite of phosphorites ranging from Tertiary to Precambrian in age has been examined for organic content. The average organic carbon value of the phosphorites is intermediate between that of shales and carbonate rocks. They differ from shales by having a larger proportion of organic matter which is soluble in organic solvents, a higher asphalt content, and a more complex saturated hydrocarbon fraction. The n-paraffin distributions indicate that organic matter in phosphorites is derived primarily from microorganisms. The insoluble organic matter (kerogen) isolated from phosphorites is rich in nitrogen, sulfur, and oxygen compared with that from other sedimentary rocks, and reflects the highly euxinic nature of the phosphorite-forming environment. The composition of the associated kerogens supports the contention that oils with high nitrogen contents are derived from phosphatic source beds. The high proportion of soluble organic matter in unaltered phosphorites suggests that oils derived from phosphatic source beds ore capable of migration at an early stage of diagenesis.

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