DPEP/etio ratio

Mass spectrometric parameters of a typical immature metallopor-phyrin fraction are given in Table II. These parameters were used to interpret mass spectra of porphyrin samples recovered within known distances from a 13.5 m diabase sill (Table IV). The complexity imposed by temperature-controlled reactions (transalkylation and conversion of DPEP to etio series) can cloud trends within an individual parameter, but used together, the parameters permit definition of these reactions. As the sill is approached, tihe DPEP/etio ratio approaches zero for both... 

The combination of two techniques that measure independent components of the same geological environment permits more dependable interpretations than when used separately. The changes in mass spec-trometric parameters, particularly an increase in band width and A.I. and a decrease in DPEP/etio ratio, as well as changes in the EPR signal can be used collectively to discern onset through completion of thermally dependent reactions. While the mass spectral method gives a detailed resolution of many of the specific reactions involved, EPR provides a better overall view of maturation and covers some areas inaccessible to the former. 

As discussed above, there are a number of parameters from the study of the biogenesis of porphyrin that can yield important insights in exploration and prospecting. With some of these parameters, e. g. j, the ratio of DPEP to Etio, the bandwidth already is useful in approximating age in organic geochemistry.Other parameters such as V/Ni ratio have been used for correlation, although... 

We shall not deal with the detailed statistical analysis of petroporphyrin mass spectra, the interested reader being referred to more authoritative texts. It is enough to say that the ratio of DPEP-type to etio-type porphyrins in a sediment is a good indicator of the amount of thermal stress that the sediment has been subjected to the higher the ratio of etiopor-phyrins, the greater the degree of thermal stress. 

It was earlier observed that V/Ni or V/ (V+Ni) ratio was constant in crude oils of common rock source and was dependent on geological age of the rocks (Ball et al., 1960) and this ratio was used for tracing source effects (Shahristani and Al-Alyia,1972), (Gayer et al., 2002). The studies on the thermal evolution of the major VO complex of DPEP to etio indicated a maturity dependence (Didyk et al., 1975), (Barwise et al., 1987), thus suggesting these compounds as biomarkers (Peters et al., 2004), (Duyck et al., 2007). 

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