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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 44 (1960)

Issue: 4. (April)

First Page: 423

Last Page: 432

Title: Can Petroleum be of Pedogenic Origin?

Author(s): Robert B. Cate, Jr. (2)


Many soils provide conditions similar to the marine reducing environment considered essential for petroleum genesis. Carbon isotope ratios indicate that petroleum may be derived from non-marine organic matter. This paper presents the hypothesis that podzolization (the joint downward movement of organic matter, metals, and clay through the weathering profile) may involve the catalytic transformation of some of the organic matter to bituminous substances. Somewhat similar materials do occur in soils, and soil organic matter does move downward through the profile. There is much evidence and opinion for the concept that many metal deposits, especially laterites, are formed in part by podzolization, possibly with the concomitant formation of bitumens. Organic podzolizing agent appear to be derived mainly from leaf exudates and decomposing leaves, as well as from root and bacterial exudates and decomposition. The active agents from leaves are apparently primarily acidic polysaccharides and polyphenols, and may include amino acids, simple sugars, and enzymes with a porphyrin structure. Soils commonly contain large amounts of acid-type catalysts, especially iron and aluminum ions. In the presence of such catalysts, carbohydrates can undergo reactions which might lead to the formation of hydrocarbons. The various bituminous materials found in nature seem to form a continuum which includes petroleum, oil shale, and bituminous coal. This continuum is a logical corollary of the pedogenic hypothesis. The common association of oil with other bituminous substances, cou led with evidence of downward migration, provides some geological basis for considering this problem from the pedogenic point of view. If the preceding ideas are reasonable, further "geopedological" research might be justified, similar to that done by Proshliakov on vanadium movement in the oxidized zone of an oil-bearing limestone. The oil fields of northeastern Brazil might be a logical site for study, in view of the widespread occurrence there of massive laterite, underlain by a variety of "bitumens," some of which seem to have migrated downward.

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