i — r 



3400 3000 



1600 



STATION 6 



31-03-78 



FIGURE 14. Infra-red spectrometry of the resins. 



by Tissot et al ; they were calculated for the earliest samples only 



2(C29 + C31) 



R 29-31 = 



C28 + 2C30 + C32 



The relationship shows that in this case, the n-C29 and n-C31 

 predominate. Where the value is over 1, the odd-numbered carbons pre- 

 dominate. In Table 2, a compilation of these values for all the 

 stations, it is seen that R is much higher than 1 at Stations 6 and 8. 



Even in March 1978, this presence of natural compounds modified 

 the distribution of hydrocarbons by family : 



- saturated hydrocarbon contents were low ,- 



- polar-compound contents (resins and asphaltenes) high. 



While the ratio of SAT/ARO decreased slightly, as at Stations 5 

 and 6 (Fig. 17), degradation of n-alkanes and isoprenoids (pristane 

 and phytane) was observed throughout the period, showing clearly which 

 polycyclic alkanes are most resistant to degradation. 



The chroma tograms of the aromatic hydrocarbons have very marked 

 profiles under photometric detection (FPD) , and a persistence in the 

 unresolved complex mixture (FID) (Fig. 16). Comparison of the results 

 of the GPC with those of the high resolution MS undertaken on the re- 

 ference samples of March 23, 1981 at Portsall, and the sampling taken 



126 



