A thermal and chemical degradation approach to decipher pristane and phytane precursors in sedimentary organic matter

A thermal and chemical degradation approach was followed to determine the p recursors of pristane (Pr) and phytane (Ph) in samples from the Gessoso-sol fifera, Ghareb and Green River Formations. Hydrous pyrolysis of these sampl es yields large amounts of Pr and Ph carbon skeletons, indicating that thei r precursors are predominantly sequestered in high-molecular-weight fractio ns. However, chemical degradation of the polar fraction and the kerogen of the unheated samples generally does not release large amounts of Pr and Ph. Additional information on the precursors of Pr and Ph is obtained from fla sh pyrolysis analyses of kerogens and residues after hydrous pyrolysis and after chemical degradation. Multiple precursors for Pr and Ph are recognise d in these three samples, The main increase of the Pr/Ph ratio with increas ing maturation temperature, which is associated with strongly increasing am ounts of Pr and Ph, is probably due to the higher amount of precursors of P r compared to Ph, and not to the different timing of generation of Pr and P h. (C) 1999 Elsevier Science Ltd. All rights reserved.