Characterization of high-molecular-weight organic matter in the marls of Salt IV Formation of the Mulhouse basin

Abstract

High-molecular-weight organic matter of six marl samples of the Mulhouse Basin has been characterized. The kerogen, asphaltene and polar fractions were analysed by flash pyrolysis-GC-(MS). In addition, sulphur-rich geomacromolecules present in the polar fractions were also desulphurized with Raney Ni and the released hydrocarbons were characterized by GC-MS. The kerogen and asphaltene pyrolysates are dominated by linear and isoprenoid alkanes and alkenes most likely derived from aliphatic biopolymers of algae (algaenans), and contain moderate to low amounts of alkylated thiophenes. Marls deposited under hypersaline conditions contain more organically-bound sulphur and less isoprenoid algaenans in their kerogen asphaltene fractions than marls deposited under less saline conditions. High contributions of terrestrial organic matter are not revealed by abundant (alkyl)phenols in the pyrolysates. Desulphurization of sulphur-rich geomacromolecules present in the polar fractions yields hydrocarbons with distributions different from those of the free saturated hydrocarbons, but the amounts released are low relative to the hydrocarbons present as such.