**4. Examples of parameters used in fingerprinting**

#### **4.1 Normal -alkanes characteristics**

The distribution of n-alkanes in crude oils can be used to indicate the organic matter source (Duan and Ma, 2001). For example, the increase in the n-C15 to n-C20 suggests marine organic matters with contribution to the biomass from algae and plankton (Peters and Moldowan, 1993). Oil samples characterized by uniformity in n-alkanes distribution patterns suggest that they are related and have undergone similar histories with no signs of biodegradation (Ficken et al. 2000 and Duan and Ma, 2001).

#### **4.2 Carbon preference index (CPI)**

Carbon preference index, obtained from the distribution of n-alkanes, is the ratio obtained by dividing the sum of the odd carbon-numbered alkanes to the sum of the even carbonnumbered alkanes. CPI is affected by both source and maturity of crude oils (Tissot and Welte, 1984). CPI of petroleum oils ranging about 1.00 generally shows no even or odd carbon preference indicates mature samples. Also, it can be used in source identification; petroleum origin contaminants characteristically have CPI values close to one (Maioli et al., 2011).

#### **4.3 Degree of waxiness**

The degree of waxiness can be expressed by the ΣC21-C31/ΣC15-C20 ratios. The oils characterized by high abundance of n-C15to n-C20 n-alkanes in the saturate fractions

Biomarkers 173

Together with steranes, triterpanes belong to the most important petroleum hydrocarbons that retain the characteristic structure of the original biological compounds. Tricyclic, tetracyclics hopanes and other compounds contribute to the terpane fingerprint mass chromatogram (m/z=191) are commonly used to relate oils and source rocks (Hunt, 1996). Mass fragmentogram at m/z=191 can be used to detect triterpanes in the saturate

Aquino et al. (1983) indicated that tricyclic terpanes are normally associated with marine source. In addition it has been used as a qualitative indicator of maturity (Van Grass, 1990). In high mature oils, the tricyclic terpanes is dominated more than in low mature oils (Hunt,

The homohopanes (C31 to C34) are believed to be derived from bacteriopolyhopanol of prokaryotic cell membrane. C35 homohopane may be related to extensive bacterial activity in the depositional environment (Ourisson et al., 1984). Homohopane index can be used as an indicator of the associated organic matter type, as it can also be used to evaluate the oxic/anoxic conditions of source during and immediately after deposition of the source sediments (Peters and Moldowan, 1991). Low C35 homohopanes is an indicator of highly reducing marine conditions during deposition whereas high C35 homohopane concentrations are generally observed in oxidizing water conditions during deposition,

Gammacerane, originally thought to be as hypersalinity indicator (Sinninghe-Damste et al., 1995), is associated with both marine and lacustrine environments of increasing salinity

consistent with the oxic conditions (Peters and Moldowan, 1991).

(Waples and Machihara, 1991; and Peters and Moldowan, 1993).

**5.4 Triterpanes (m/z 191) distribution** 

hydrocarbon fraction.

**5.4.2 Homohopanes** 

**5.4.3 Gammacerane** 

Fig. 5. Gammacerane chemical structure.

1996).

**5.4.1 Tricyclic terpanes** 

reflecting low waxy (Moldowan et al., 1994). Generally, the degree of waxness < 1 reveals low waxy nature and suggests marine organic sources (Peters and Moldowan, 1993) mainly of higher plants deposited under reducing condition.

### **5. Examples of parameters used in biomarker fingerprinting**

#### **5.1 Pristane/phytane ratio**

Both pristine (2,6,10,14- tetramethyl pentadecane) and phytane (2,6,10,14- tetramethyl hexadecane) are derived from the phytol side chain of chlorophyll, either under reducing conditions (phytane) or oxidizing conditions (pristane). Also both pristine and phytane became dominant saturated hydrocarbon components of highly weathered crude oils until they are degraded (Moustafa et al., 2004).

The pristane/phytane (Pr/Ph) ratio is one of the most commonly used correlation parameters which have been used as an indicator of depositional environment (Peters et al., 2005). It is believed to be sensitive to diagenetic conditions; Pr/Ph ratios substantially below unity could be taken as an indicator of petroleum origin and/or highly reducing depositional environments. Very high Pr/Ph ratios (more than 3) are associated with terrestrial sediments. Pr/Ph ratios ranging between 1 and 3 reflect oxidizing depositional environments (Hunt, 1996)**.**

According to Lijmbach (1975) low Pr/Ph values (<2) indicate aquatic depositional environments including marine, fresh and brackish water (reducing conditions), intermediate values (2–4) indicate fluviomarine and coastal swamp environments, whereas high values (up to 10) are related to peat swamp depositional environments (oxidizing conditions).

#### **5.2 Isopreniods/n-alkanes**

Waples (1985) stated that by increasing maturity, n-alkanes are generated faster than iosprenoids in contrast to biodegradation. Accordingly, isopreniods/n-alkanes (Pr/*n*-C17 and Ph/*n*-C18) ratios provide valuable information on biodegradation, maturation and diagenetic conditions. The early effect of microbial degradation can be monitored by the ratios of biodegradable to the less degradable compounds. Isoprenoid hydrocarbons are generally more resistant to biodegradation than normal alkanes. Thus, the ratio of the pristane to its neighboring n-alkane C17 is provided as a rough indication to the relative state of biodegradation. This ratio decreases as weathering proceeds.

#### **5.3 Steranes (m/z 217) distribution**

The distribution of steranes is best studied on GC/MS by monitoring the ion m/z=217 which is a characteristic fragment in the sterane series. It is agreed that the relative amounts of C27-C29 steranes can be used to give indication of source differences (Lijmbach, 1975). For example, predominance of C28, C29 and C30 steranes indicate an origin of the oils derived mainly from mixed terrestrial and marine organic sources, while oils show slightly low abundance of C28 and C29 and relatively higher concentrations of C27 steranes indicate more input of marine organic source.

reflecting low waxy (Moldowan et al., 1994). Generally, the degree of waxness < 1 reveals low waxy nature and suggests marine organic sources (Peters and Moldowan, 1993) mainly

Both pristine (2,6,10,14- tetramethyl pentadecane) and phytane (2,6,10,14- tetramethyl hexadecane) are derived from the phytol side chain of chlorophyll, either under reducing conditions (phytane) or oxidizing conditions (pristane). Also both pristine and phytane became dominant saturated hydrocarbon components of highly weathered crude oils until

The pristane/phytane (Pr/Ph) ratio is one of the most commonly used correlation parameters which have been used as an indicator of depositional environment (Peters et al., 2005). It is believed to be sensitive to diagenetic conditions; Pr/Ph ratios substantially below unity could be taken as an indicator of petroleum origin and/or highly reducing depositional environments. Very high Pr/Ph ratios (more than 3) are associated with terrestrial sediments. Pr/Ph ratios ranging between 1 and 3 reflect oxidizing depositional

According to Lijmbach (1975) low Pr/Ph values (<2) indicate aquatic depositional environments including marine, fresh and brackish water (reducing conditions), intermediate values (2–4) indicate fluviomarine and coastal swamp environments, whereas high values (up to 10) are related to peat swamp depositional environments (oxidizing

Waples (1985) stated that by increasing maturity, n-alkanes are generated faster than iosprenoids in contrast to biodegradation. Accordingly, isopreniods/n-alkanes (Pr/*n*-C17 and Ph/*n*-C18) ratios provide valuable information on biodegradation, maturation and diagenetic conditions. The early effect of microbial degradation can be monitored by the ratios of biodegradable to the less degradable compounds. Isoprenoid hydrocarbons are generally more resistant to biodegradation than normal alkanes. Thus, the ratio of the pristane to its neighboring n-alkane C17 is provided as a rough indication to the relative

The distribution of steranes is best studied on GC/MS by monitoring the ion m/z=217 which is a characteristic fragment in the sterane series. It is agreed that the relative amounts of C27-C29 steranes can be used to give indication of source differences (Lijmbach, 1975). For example, predominance of C28, C29 and C30 steranes indicate an origin of the oils derived mainly from mixed terrestrial and marine organic sources, while oils show slightly low abundance of C28 and C29 and relatively higher concentrations of C27 steranes indicate

state of biodegradation. This ratio decreases as weathering proceeds.

of higher plants deposited under reducing condition.

**5.1 Pristane/phytane ratio** 

environments (Hunt, 1996)**.**

**5.2 Isopreniods/n-alkanes** 

**5.3 Steranes (m/z 217) distribution** 

more input of marine organic source.

conditions).

they are degraded (Moustafa et al., 2004).

**5. Examples of parameters used in biomarker fingerprinting** 

#### **5.4 Triterpanes (m/z 191) distribution**

Together with steranes, triterpanes belong to the most important petroleum hydrocarbons that retain the characteristic structure of the original biological compounds. Tricyclic, tetracyclics hopanes and other compounds contribute to the terpane fingerprint mass chromatogram (m/z=191) are commonly used to relate oils and source rocks (Hunt, 1996). Mass fragmentogram at m/z=191 can be used to detect triterpanes in the saturate hydrocarbon fraction.

#### **5.4.1 Tricyclic terpanes**

Aquino et al. (1983) indicated that tricyclic terpanes are normally associated with marine source. In addition it has been used as a qualitative indicator of maturity (Van Grass, 1990). In high mature oils, the tricyclic terpanes is dominated more than in low mature oils (Hunt, 1996).
