COMPARATIVE-STUDY BY INFRARED-SPECTROSCOPY OF THE ORGANIC-MATTER OF PHOSPHATE-RICH (OULAD ABDOUN BASIN) AND BLACK SHALE (TIMAHDIT BASIN) SERIES (MOROCCO)

Fourier transform infrared spectroscopy has been used to get quantitative information on the oxidation state of the organic matter of stable residues extracted from strata of the phosphate-rich basin of Oulad Abdoun and from oil shales of the Timahdit basin, Morocco. Throughout the respective filling of both basins the redox conditions have been more oxidizing in the top part of the sediments in Oulad Abdoun basin than in the Timahdit basin. This is interpreted as the result of the structural evolution of the basins, Oulad Abdoun basin having evolved in stable platform conditions while the Timahdit basin evolved in subsiding ones. The phosphate-rich beds contain the more oxidized organic stable residues. Sedimentological evidence shows that the oxidation was associated with reworking processes. These processes are responsible for the progressive concentration of the phosphatic grains and prove to be necessary for the P2O5 content to become higher than 10%, this value being the highest encountered in the sediment within which the phosphatic grains form.