Geochemical interpretation and comparison of biomarker composition of bitumens obtained from coals and surrounding rocks

The bitumens obtained as the extraction products from a series of coals and surrounding rocks samples were fractionated onto aliphatic, aromatic and polar fractions. Aliphatic and aromatic fractions were then submitted to analysis using modern gas chromatography - mass spectrometry method. The distribution of n-alkanes was compared and parameters values characterising conditions of sedimentation and type of primary organic matter were calculated. In aliphatic fractions, a series of biomarkers was also identified as steranes, diasteranes, tricyclic diterpanes, hopanes and moretanes. The relatively high content of diasteranes was observed in the bitumens from shales bordering on coals. It confirms the literature data indicating possibility of catalytic influence of claystones on arrangement of steranes to diasteranes. The values of parameters calculated from the data characterising distribution of hopanes have indicated a possibility of generation of oils by some of analysed coals: flame as well as orthocoking coals.The aromatic compounds were also identified, mainly phenanthrenes being an important stage of aromatisation process of fossil organic matter.The comparison of characteristics of bitumens obtained from coals and surrounding rocks suggests a possibility of migration of various groups of organic compounds from coal layers to rocks bordering on them. The migration of organic mobile matter seems to be as well a result of a great difference of concentration between coal and surrounding rocks layers as of action of circulating waters or hydrothermal solutions. The temperature gradient and local intrusive bodies are of great significance for processes of oil migration. The examinations and conclusions presented in this work should be, however, taken as the introductory ones and have to be confirmed by analysis of a greater number of samples of various geological characteristics.