Notable compositional changes of organic matter are observed below the silica transition zone in thermally immature sediments. The increase of bitumen ratio, and hopane and sterane isomerization parameters indicate an acceleration of the kinetics of the chemical reactions which transform the organic matter. This phenomenon is probably due to the numerous mineral and textural changes induced by the transformation of amorphous biogenic silica into crystalline authigenic silica.

Hopane and sterane parameters are calculated from peak heights in the m/z =426 and 217 reconstructed ion chromatograms.

Supplement to: Lichtfouse, Eric; Rullkötter, Jürgen (1994): Accelerated transformation of organic matter below the silica transition zone in immature sediments from the Japan Sea. Organic Geochemistry, 21(5), 517-523