The molecular composition of kerogen in Pliocene Mediterranean sapropels and associated homogeneous calcareous ooze

Abstract

The organic matter of three time-equivalent Pliocene sapropels was characterized as being predominantly Type II kerogen using RockEval pyrolysis. It is dominated by amorphous organic matter, originating mainly from marine organisms, as indicated by the relatively high abundances of algaenan- and chlorophyll-derived pyrolysis products in the Curie-point pyrolysates of the kerogen of the sapropels. However, a small amount of terrigenous organic matter was also observed in the form of pollen and spores that most probably yielded the oxygenated aromatic pyrolysis products known to derive from sporopollenin. Lignin pyrolysis products, such as methoxyphenol and catechol (1,2-benzenediol), commonly used as unequivocal evidence for a contribution of terrestrial higher plants in the form of woody material to the kerogen, were absent from the kerogen pyrolysates. No major spatial and temporal differences in the kerogen composition of the three time-equivalent sapropels were observed. Palynological studies revealed that organic matter in the homogeneous intervals, below and above the sapropels, consisted of pollen, spores and amorphous organic matter. This was confirmed by Curie-point pyrolysis – GC/MS results showing a relatively high abundance of algaenan-derived compounds and the presence of oxygenated aromatic pyrolysis products. The differences observed between the kerogen pyrolysates of the sapropels and their homogeneous intervals are suggested to be governed primarily by enhanced preservation conditions, resulting in increased preservation of marine organic matter in the sapropels.