Oxidative sedimentation

Reductive diagenesis

The source of phosphate is above-ground water; the high content of Mg²⁺ in it prevents the deposition of Ca-phosphate; therefore, the phosphate formed in diagenesis dissolves. Microconcretionary early glauconitis “matures”—it is enriched with potassium, absorbing it from the bottom water. Fe hydroxides are formed, capturing dissolved phosphate from above-bottom water according to the scheme of the “iron-phosphate conveyor” by P. Frelich et al., 1988 [67] or T. Algeo and E. Ingalla, 2007 ( [68] , p. 131).

The source of phosphate is pore waters, where it enters when phosphate-containing Fe hydroxides are dissolved. An early, relatively potassium-poor microconcretionary glauconite is formed, with a high proportion of smectite packets and with Fe²⁺ in the octahedral layers of the structure. This early glauconite absorbs Mg²⁺ from the pore waters, so the formation of Ca-phosphate becomes possible.