The influence of mineral matter on the separation of amorphous marine kerogens using density gradient centrifugation

Three relatively immature amorphous marine kerogens were subjected to density gradient centrifugation (DGC). The density fractions obtained were analyzed by Curie-point pyrolysis in combination with gas chromatography (Py-GC) and with gas chromatography-mass spectrometry (Py-GC-MS). Despite the variations in density, no significant variations were observed in chemical compositions of the flash pyrolysates of the density fractions of each kerogen. The variations in density were due to varying amounts of inorganic matter, in particular pyrite, which remained after chemical demineralization procedures and was insufficiently removed during the sample processing. This was substantiated by the ash content of individual density fractions, which is linearly correlated to the densities of the kerogen density fractions. Further micronization and cryogenic treatment followed by a sink-float procedure of the Posidonia kerogen prior to DGC resulted in only a partial removal of the inorganic phase, as indicated by a shift of the average density towards lower densities. These results demonstrate the substantial effect of mineral matter, in particular pyrite, on the separation of amorphous marine kerogens into chemically distinct entities due to an intimate association of the organic and inorganic phase