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1,700 cm -1 ; (Figure 6). The elemental analyses of
the resins confirm this tendency toward oxidation over time (oxygen
levels in March 1978 were 5.4 % ; in June 1980, 7 %).
3400 3000 1700 1100 700 cm
1600
31 03-78
22-11-78
20 06-79
17-01-80
24-06-80
Station 5 - FIGURE 6. Infra-red spectrometry of the resins.
The distribution of saturated hydrocarbons determined by gas
phase chromatography (Fig. 7) demonstrates the evolution which led to
the degradation of the n-alkanes (5.99 % to 3.33 %) to n-C30 (Table 1).
It should be noted that by March 31, 1978, this degradation appears to
have begun. Thus there was an increase in the ratios of pristane/n-Cl7
and phytane/n-Cl8 (Table 1). The isoprenoids degraded less easily than
the n-alkanes (TISSOT and al . ) , but by June 1980 these compounds could
no longer be detected. As degradation advanced, the contribution of the
biogenic hydrocarbons increased, and n-alkanes of odd carbon numbers
between n-C25 and n-C35 -- characteristic of the cuticle waxes of higher
plants (Eglington and Hamilton - 1963) — appeared, confirming the terrestrial
contribution to the contents of organic matter in the sediments.
Moreover, the disappearance of the n-paraffins points up
a relative
enrichment in the unresolved complex mixture of the isoalkane and cycloalkane
compounds, and generally in the compounds around n-C30 . It was
possible to demonstrate these last compounds by GPC/MS by measuring
the masses : m/e 217 being characteristic of the tetracyclic
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