16 GOLDBERG [CHAP. 1 



The occurrence of tetravalent uranium in certain environments of the 

 oceans is probably more widespread than has been heretofore realized. For 

 example, the author has found within the skeletal structure of corals, from 

 modern to thousands of years in age, not immodest amounts of this species. 

 The implication that highly reduced conditions may prevail within calcium 

 carbonate lattices, resulting most probably from the decomposition of organic 

 matter, invites further investigation. 



The authigenic clay mineral glauconite often occurs in deposits with the 

 marine phosphorites and the conditions that lead to its formation may be in- 

 ferred in part from such an association. Bank tops, ridge crests, hills that rise 

 above shelves and some slope areas are hosts to this mineral at depths from 50 

 to more than 2000 m (Emery, 1960). Glauconite is a monoclinic mica, often 

 disordered and interlayered, whose composition is characterized by 7-8% K2O 

 and an iron content of 20-25% with the Fe 3+ /Fe 2+ ratio varying between 

 3 and 9. 



Burst (1958) suggests four pathways for its formation : (1) the transformation 

 of fecal pellets or coprolites ; (2) the conversion of materials filling foraminiferal 

 tests ; (3) the conversion of biotite booklets which yields rounded pellets 

 retaining some of the book-like laminations of the parent material ; and (4) 

 the agglomeration of shale pellets or bottom clays with a subsequent trans- 

 formation to glauconite. 



If a reducing environment within the sedimentary phases is postulated for 

 glauconite, as in the case of the phosphorites, a number of rather anomolous 

 observations on this clay mineral can be brought into accord. For example, 

 Emery (op. cit.) points out that the areas in which glauconite is most abundant 

 are those in which the sea- water is oxygenated. In such environments the 

 accumulation of large amounts of organic matter on the sea-floor can serve as 

 a buffer against the intrusion of oxygen into the deposit site and can thus 

 allow reducing atmospheres to be built up. 



The existence of ferrous iron in the structure, where normally present in 

 aerated waters are the oxides of ferric iron, directs one to a reducing environ- 

 ment for glauconitization — the interior of a foraminiferal shell, a fecal pellet, 

 a clay agglomerate containing organic phases. Variations in the Fe 3+ /Fe 2+ 

 ratio probably stem not only from the existing redox potential of a given 

 environment, but also from the amounts and types of organic matter that can 

 form complexes with the various species of iron and hence can determine the 

 relative availability of both the oxidized and reduced forms. Further, the 

 character of the argillaceous progenitors of glauconite will strongly influence 

 the chemical composition of the resultant mineral, as described by Burst in his 

 rather extensive studies. 



Finally, it is inviting to seek out further evidence to confirm or deny this 

 concept of a reducing environment in the sediment for glauconitization. 

 Investigations on the presence or absence of tetravalent uranium in the mineral 

 would be most revealing in this regard. 



Of equal interest to the reactions in anaerobic environments are those 



