From biomolecules to geomolecules

Early diagenesis

Upon death of the primary producers and heterotrophic organisms begin a transformation (diagenesis) that will lead to the destruction of their most labile compounds, and for the recalcitrant ones, the progressive disappearance of chemical functions such as hydroxyl  groups, ketones, and unsaturations. The classic example of such a process is the loss the alcohol group and unsaturation of the steroid cholesterol (a biomolecule), resulting in the hydrocarbon skeleton cholestane (a geomolecule).

Similarly, the ciliate derived tetrahymanol loses its functions to form the hydrocarbon skeleton gammacerane, fig. 2).  

Diagenesis may also induce the full saturation of the Chlorobiaceae pigment isorenieratene to isorenieratane. It can also induce cyclization of isorenieratene, which also can lose C7 or C8 moeities to form C32 and C33 diaryl isoprenoids. 

Further Reading

• Sinninghe Damsté J.S., Kenig F., Koopmans M.P., Koster J., Schouten S., Hayes J.M. and J.W. de Leeuw (1995) Evidence for gammacerane as an indicator of water column stratification. Geochimica Cosmochimica Acta 59, 9, 1895-1900. 
• Koopmans M. P., Koster J., van Kaam-Peters H.M.E., Kenig F., Schouten S., Hartgers W.A., de Leeuw J.W. and J.S. Sinninghe Damsté (1996) Diagenetic and catagenetic products of isorenieratene: Molecular indicators for photic zone anoxia. Geochimica Cosmochimica Acta. 60, 22, 4467-4496. 
• Kenig F., Sinninghe Damsté J. S., Frewin N.., Hayes J.M. and J.W. de Leeuw (1995) Molecular indicator for palaeoenvironmental change in a Messinian evaporitic sequence (Vena del Gesso, Italy): II. Stratigraphic variations in abundancies and 13C contents of free and sulphur bound carbon skeletons in a single marl bed. Organic Geochemistry 23, 6, 485-526.