LABORATORY OXIDATION OF FOSSIL ORGANIC-MATTER STUDIED BY IN-SITU INFRARED-SPECTROSCOPY, ROCK-EVAL PYROLYSIS AND PYROLYSIS-GAS CHROMATOGRAPHY MASS-SPECTROMETRY

Fossil organic matter in Miocene and Silurian sediments was subjected to experimental oxidation, which was investigated by Rock-Eval pyrolys is, the ''off-line'' pyrolysis-gas chromatography-mass spectrometry co mbination, and continuous FTIR monitoring. The pyrolysate yield decrea sed during the oxidation particularly in the low-matured, predominantl y aliphatic organic matter from the Miocene sediments (type I kerogen, algae-type kerogen). This suggests that aliphatic chains are preferen tially oxidized, which is in agreement with the marked decrease in the intensify of the nu(CH2) and nu(CH3) IR bands. The n-alkane distribut ion in the chromatographic profile was unaffected by the oxidation; he nce, the oxidation of the alkane chains was not selective. At the same time, the bands within the 1 900-1 550 cm(-1) range grew in intensity for both the aliphatic and mixed-type (type II kerogen) organic matte r. The oxidation of the aromatic (humic) type of organic fossil matter in the Miocene sediments (type III kerogen, coal-type kerogen) was on ly accompanied by very small changes in the FTIR spectra. The results of the ''of-line'' pyrolysis are consistent with those of the Rock-Eva l pyrolysis. For all samples, the oxidation was accompanied by a gradu al decrease in the hydrogen index (HI) as well as in the pyrolysis tem perature maximum (T-max). The changes in the S-2/S-1 ratio (''bound''- to-''free'' hydrocarbons) indicate that the ''free'' hydrocarbons in t he rocks are preferentially oxidized during the first 8-16 h of the ex perimental run. Subsequently, hydrocarbon chains involved in the kerog en macromolecule are attacked.