Regional sedimentologic and stratigraphic studies of Miocene phosphorites on the continental margin of the southeastern United States demonstrate a strong structural control over the formation and deposition of major concentrations of phosphorite in the Hawthorn and Pungo River Formations. The first-order structures controlled the regional limits of the phosphogenic system and provided the necessary depositional environments. Major phosphate sedimentation was concentrated along the nose and flanks of the Ocala arch and Carolina platform and decreased to a minimum into the intervening Southeast Georgia and Hatteras Embayments. Recent discoveries of Miocene phosphorite on the North Carolina continental shelf, in combination with the extensive lag deposits of phosphate on th Blake Plateau, represent a major phosphogenic system which occupies a position relative to the Carolina platform that is analogous to that of the major central and south Florida phosphogenic province relative to the Ocala arch.

Superimposed upon the regional structural framework is a series of second- and third-order structural highs and adjacent basins. Each structural high producing a platform or shoaling environment with the necessary associated accumulation basins, may contain one or more phosphate deposits. The specific location, size, and geometry of the resulting deposit is dictated by the folding or faulting, subaerial or submarine erosion, primary depositional processes, groundwater solution and collapse, etc. The location of the second- and third-order structures and the first-order structural highs dictates the subsequent depositional-erosional history. The latter determines the ultimate preservation and degree of secondary alteration of each phosphate deposit.

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