Mobilization of major inorganic ions during experimental diagenesis of characterized peats

Laboratory experiments were undertaken to study changes in concentrations o f major inorganic ions during simulated burial of peats to about 1.5 km. Cl adium, Rhizophora, and Cyrilla peats were first analyzed to determine catio n distributions among fractions of the initial materials and minerals in re sidues from wet oxidation. Subsamples of the peats (80 g) were then subject ed to increasing temperatures and pressures in steps of 5 degrees C: and 30 0 psi at 2-day intervals and produced solutions collected. After six steps, starting from 30 degrees C and 300 psi, a final temperature of 60 degrees C and a final pressure of 2100 psi were achieved. The system was then allow ed to stand for an additional 2 weeks at 60 degrees C and 2100 psi. Treatme nts resulted in highly altered organic solids resembling lignite and expell ed solutions of systematically varying compositions. Solutions from each st ep were analyzed for Na+, Ca2+, Mg2+. total dissolved Si (Si-T), Cl-, SO42- , and organic acids and anions (OAAs). Some data on total dissolved Al (Al- T) were also collected. Mobilization of major ions from peats during these experiments is controlled by at least three processes: (1) loss of dissolve d ions in original porewater expelled during compaction, (?) loss of adsorb ed cations as adsorption sites are lost during modification of organic soli ds, and (3) increased dissolution of inorganic phases at later steps due to increased temperatures (Si-T) and increased complexing by OAAs (Al-T), In general, results provide insight into early post-burial inorganic changes o ccurring during maturation of terrestrial organic matter. (C) 2000 Elsevier Science B.V. All rights reserved.