COMPARATIVE-STUDIES OF THE KINETIC-PARAMETERS OF VARIOUS ALGAENANS AND KEROGENS VIA OPEN-SYSTEM PYROLYSES

Kinetic parameters were determined for the first time, via open-system pyrolyses, on algaenans (highly resistant biomacromolecules that are selectively preserved during kerogen formation) isolated from extant m icroalgae. Parallel studies were also carried out on 10 kerogens exhib iting, with one exception, a low level of maturity. These kerogens inc luded samples chiefly derived from the selective preservation of the a bove algaenans and samples mainly, or almost exclusively, derived from the ''natural vulcanization'' pathway. Important differences in activ ation energy (E-a) distributions were observed between the four algaen ans investigated and correlated with their chemical structures. The ke rogens predominantly derived from algaenan-selective preservation (Pul a alginite, NE 70 and BJ 248 Torbanites, Rundle Oil Shale) also exhibi ted pronounced differences in E-a distributions. These distributions p rovided: (i) information on the diversity of the source materials; and (ii) reflected the occurrence of important differences in chemical st ructures and thermal behaviour between three of the tested kerogens, e ven though they are all classified as low maturity type I, The Kimmeri dge Clay samples and the Lorca Oil Shale showed broad E-a distribution s shifted to low energies when compared with the above algaenans and k erogens. Such shifts reflect an important (or even almost exclusive fo r some of these kerogens) contribution of materials originating from s ulphur incorporation into various lipids during early diagenesis. Fina lly, the kinetic data derived for the nine low maturity fossil samples were extrapolated to a very low, geological heating rate of 3 degrees C Ma(-1) and the generation rate curves and cumulative yield curves t hus obtained were compared. (C) 1997 Elsevier Science Ltd.