Eight characteristics of sediments are considered as possible means of recognizing source beds: 1, quantity of organic matter in the sediments; 2, reducing power, which is a measure of ability of the sediments to reduce chromic acid; 3, color of sediments4; , volatility of sediments; 5, degree of volatility, which is a measure of the volatility with respect to the organic content; 6, ratio of carbon to nitrogen in the sediments; 7, oxidation factor, which is an index of the state of oxidation of the sediments, and is the ratio of the carbon content to the reducing power; and, 8, the nitrogen-reduction ratio, which is the ratio of the nitrogen content to the reducing power. Several thousand determinations of these characteristics have been made and averaged from more than 800 lithologic units from many areas in the California, Rocky Mountain, Mid-continent, East Texas, and Gulf Coast oil regions. The thickness of these units ranges from 50 ft. to 500 ft. Each of them has been classified according to its probable richness in source material of petroleum. Nearness to producing zones has been the basis of classification, as it seems more reasonable to assume that oil in general accumulates near where it is generated than to assume that it ordinarily accumulates far from where it is made. Three classes were made: 1, lithologic units within 250 ft. stratigraphically above or below an oil zone and less than 2 miles from an oil field; 2, (a) units within 500 ft. above or below an oil zone and within 15 miles of an oil field (excluding, of course, those that belong to the first class) and (b) units within 250 ft. stratigraphically of a horizon and more than 15 miles distant from an oil field, provided the unit is located within a region in which the horizon is generally productive of oil or yields significant quantity of oily substances when extracted with ether; and, 3, all other beds, viz., those more than 500 ft. above or below an oil horizon or more than 15 miles distant from an oil field and beds at greater distance if they are within 250 ft. of horizons that generally contain oil in the area. These three classes are designated in this report as "productive," "questionably productive," and "barren." "Productive" units naturally may contain some beds that are poor in source material, and "barren" units may contain beds that are rich in source material ; but, on the whole, the productive " units-because of their nearness to oil zones are more likely to be richer in mother substances of petroleum than are the "barren" units. Each of the eight characteristics was averaged for each of the three classes of productivity, for each of the five oil areas: California, Rocky Mountains, Mid Continent, East Texas, and Gulf Coast. The average organic content, of the "productive" and "barren" units was found to be approximately the same in each region studied, from which it is inferred that the quantity of organic matter in a sediment probably is not a reliable guide of the ability of the sediments to generate oil.

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