Appraisal of pyrolytic techniques on different forms of organic matter from a Cretaceous basement in Central Spain

Abstract

Pyrolytic techniques were used to characterize three different forms of fossil organic matter in Cerro de la Mesa (an important Cretaceous paleobotanic basement in Central Spain): two kerogens isolated from carbonaceous marls, and from lignitiferous layers, and well-preserved remains of the fossil Gymnosperm Frenelopsis oligostomata. By conventional flash pyrolysis the Frenelopsis remains released mainly alkyl-substituted phenols and polyaromatic compounds, whereas the organic matter from the lignitiferous layer is dominated by phenols and that from the carbonaceous marls by polycyclic and aliphatic compounds. Pyrolysis-thermochemolysis alkylation in the presence of tetramethylammonium hydroxide (TMAH) allowed the detection of additional diagnostic compounds, such as series of methylated fatty acids, benzenecarboxylic and phenolic acids, which revealed further differences between the three materials studied. The chemical characterization of the organic matter in addition to the micropalaeontological study suggests that the Frenelopsis remains consist mainly of heavily altered lignin and cuticular lipid biomacromolecules, whereas the materials from the lignitiferous layers and the carbonaceous marls correspond to intermediate coalification stages of woody plants, the latter showing the greatest degree of selective preservation of aliphatic structures. The comparison of the above results with those obtained by thermochemolysis suggests that the latter technique produces independent and complementary reactions to conventional pyrolysis, providing additional information to an extent which depends mainly on the polyalkyl and oxidized character of the sample.