Steranes isomerization ratio

Sterane isomerization ratios indicate that the Assekaifaf, Dome, Hassi Messaoud, and Zemlet oil samples experienced thermal maturities near or past the peak of the oil window, while the Zarzaitine and Oued Zenani samples are less mature (Fig. 5). This interpretation is supported by terpane data, such as the Ts/(Ts + Tm) and tricyclics/(tricyclics + hopanes) ratios (Table 2), which are lower for the Zarzaitine and Oued Zenani samples than the other oil samples. Both of these terpane ratios depend partly on organic facies, but the data in the table suggest that maturity rather than source input is the main control on high tricyclic terpanes and Ts in these oil samples. 

Fig. 5. Sterane isomerization ratios (Table 2) indicate that Oued Zenani and Zarzaitine oil samples are below the peak oil window, while the other oil samples have higher thermal maturity (diagonal arrow). Ratios are insensitive to further maturation in stippled areas (Peters and Moldowan, 1993).

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