Pristane/phytane index

Pristane/Phytane Index. The data obtained for the stratigra-phic column CERI-1 (33) say that the ratio pristane/phytane varies froml.l (at the topof thelst layer) to 2.0 (2m below the previous point). It keeps approximately constant at 1.5 for therest of the col umn. Carvalhaes (23) found the value 1.94 for a sample of the same formation. In all samples so far analysed from the Irati F. the ratio is greater than one. 

G.C.-M.S, analysis. The n-alkane distribution is distinctive, with a marked preference of odd over even carbon number (carbon preference index, 1.9, as in low-rank coals) in the range above C25 but with a smooth, nearly Gaussian, distribution for the lower range (peaked at Cie or C17) also, the pristane/phytane ratio is high (U.5), as in sediments of marine origin. 

Figure 5. Three-dimensional diagram showing the distribution of selected aromatic hydrocarbons in samples from the North Atlantic OCS areas. I, Biphenyl 2, C2-naphthalenes 3, Cs-naphthalenes 4, Crphe-nanthrenenes 5, fluoranthene 6, pyrene 7, C20H12 CPI, Carbon Preference Index (n-C20 to n-CS1) Pr., pristane Ph., phytane.

Table 2. Variation in pristane to phytane (PrfPhJ. prisiane to n-Cn and n-C[j and the carbon preference index (CPI) in Smorbukk. Maturity and phase fractionation are the main factors responsible for the variation...

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