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Mobile Inorganic Constituents in Peat and Their Loss During Diagenesis

Alan Bailey, Elisabeth Kosters, John Blackson

To understand diagenesis in organic-rich sediments, mobile components in peat must be evaluated. Therefore, we determined the concentrations of water-soluble ions for peats in the Mississippi delta. These peats contain high concentrations of mobile Na+, K+, Ca+2, Mg+2, Cl-, SO-24 and, in places, Fe+2. The most abundant of these are Na+, SO-24, and Cl-. Na+ ranges from > 10,000 ppm on a dry-weight basis in marine-influenced samples to 400 ppm in freshwater samples. Ca+2 and Mg+2 are slightly less abundant, and K+ and Fe+2 are much less abundant than Na+. Total concentrations f water-soluble ions may be 25-50% of the ash content of the peat on a dry-weight basis and increases as the organic content increases.

Because large amounts of water are lost during diagenesis, many water-soluble ions may be lost with the water. In compaction experiments, solutions were filter pressed from samples. Compression of a freshwater peat up to 1,000 psi at 50°C produced solutions containing appreciable Na+, K+, Ca+2, Mg+2, Cl-, and SO-24, but not Fe+2. Further compression to 3,000 psi released progressively less concentrated solutions. Some organic compounds were produced, and the solid residue was much darker than the original material. These experiments indicate that the net change in ash content resulting from loss of mobile constituents will be determined by relative losses of inorganic versus organic material. urther, released solutions may significantly influence adjacent sediments during early diagenesis.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.