Phosphatic facies are useful in oil exploration as tools for stratigraphic analysis, and as identifiable sources of hydrocarbons. Such discrete, near-continuous phosphate-bearing strata of mid-Eocene age have extended over 20,000 sq mi in southern and central California. Foraminiferal studies establish that correlative phosphate deposition began in Relizian time, was particularly widespread in the early Luisian, and continued locally in Mohnian time. Other extensive facies appear in late Eocene and in early late Pliocene beds.

The use of phosphatic facies in stratigraphic studies may be cited in four examples: (1) they may represent condensations of large thicknesses of strata, (2) differentiate between apparently similar formations, (3) establish equivalency of units on either side of major faults, and (4) have shown that formations of the same apparent lithology and foraminiferal age, juxtaposed across major faults, are not continuous.

Because phosphorus-rich waters nourish phytoplankton, underlying strata are commonly rich both in phosphate and organic remains. Five examples of phosphatic facies as source beds for the generation of oil of giant fields may be given: in California, in Colombia and Venezuela, in eastern Kansas, in Alaska, and in Wyoming. Other examples are known around the world. In California, the regional distribution of phosphate correlates with the regional distribution of petroleum.

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