Alteration of organic material during maturation: A pyrolytic and infrared spectroscopic study of isolated bisaccate pollen and total organic matter (Lower Jurassic, Hils Syncline, Germany)

Six samples of Lower Jurassic mudstones (uppermost Pliensbachian, uppermost Lias δ) from boreholes drilled at the southwestern rim of the Hils Syncline (Lower Saxony Basin, NW-Germany), covering a thermal maturity series ranging from immature to overmature, were analyzed to gain insight into the chemical structure and alteration of bisaccate pollen during maturation as well as the differences in results from various analytical methods. Laser-pyrolysis-gas chromatography-mass spectrometry (La-Py-GC-MS) and micro-Fourier transform infrared (μ-FTIR) spectroscopy applied to handpicked bisaccate pollen, and Curie Point-Py (CP-Py-GC-MS) and FTIR spectroscopy applied to sieve-fractionated kerogen concentrate from the same samples indicated considerable differences in composition. Ratios of the main compound groups, e.g. O containing components, aliphatic hydrocarbons and aromatic hydrocarbons, plotted vs. maturity showed systematic changes in composition with maturation. The study also focussed on the comparability of micro- and macroscale spectroscopic and Py methods. The results from FTIR analysis and μ-FTIR analysis, as well as those from La-Py-GC-MS, showed similar trends, e.g. defunctionalization and increasing aromatization, which mostly agree with common knowledge about the changes in the structure of organic matter, whereas the results from CP-Py-GC-MS showed wide differences, especially at higher stages of maturity, i.e. a strong increase in aliphatic vs. aromatic hydrocarbons. Together, the results indicate that both IR spectroscopy and Py-GC-MS are suitable for studying the alteration of palynomorphs during maturation and their complementary use is recommended for comprehensive characterization of alteration.