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Explanations: SN = Sample number; TOC = Total organic carbon content (wt%); $1 = Thermolabile hydrocarbon (mg HC/g rock); S2 = Thermally cracked hydrocarbon (mg HC/g rock); GP = Genetic potential (mg HC/g rock); HI = Hydrogen index (mg HC/g TOC); OI = Oxygen index (mg CO,/g TOC); PI = Production index; Tyax = Temperature (°C) at which maximum amount of pyrolyzate is released from the kerogen; Romv = Mean random vitrinite reflectance (%). Table 6. Rock Eval pyrolysis and mean random vitrinite reflectance data of the shale samples reported from Varma et al. (2018)

Table 6 Explanations: SN = Sample number; TOC = Total organic carbon content (wt%); $1 = Thermolabile hydrocarbon (mg HC/g rock); S2 = Thermally cracked hydrocarbon (mg HC/g rock); GP = Genetic potential (mg HC/g rock); HI = Hydrogen index (mg HC/g TOC); OI = Oxygen index (mg CO,/g TOC); PI = Production index; Tyax = Temperature (°C) at which maximum amount of pyrolyzate is released from the kerogen; Romv = Mean random vitrinite reflectance (%). Table 6. Rock Eval pyrolysis and mean random vitrinite reflectance data of the shale samples reported from Varma et al. (2018)

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Fig. 2 (a) n-alkane peaks in the representative shale samples
Fig. 2 (a) n-alkane peaks in the representative shale samples
Fig. 2 (b) Pentacyclic triterpenoid distribution in the representative shale samples
Fig. 2 (b) Pentacyclic triterpenoid distribution in the representative shale samples
239 Table 1. Distributions of n-alkanes, acyclic isoprenoids and related ratios in the shale samples
239 Table 1. Distributions of n-alkanes, acyclic isoprenoids and related ratios in the shale samples
The concentrations of n-alkane exhibit wide disposition in the studied shale samples. In the present study, the n-alkane distribution is divided into three parts - short chain length n-alkanes (SCLAs: Cj4-C29), intermediate chain length n-alkanes (ICLAs, C2;-C26) and long chain length n-alkanes (LCLAs: Cp7-C31) (Table 1, Fig. 3). The SCLAs that constitute an average of 21.19% in total concentration (Table 1) of n-alkanes are obtained mainly from the algal biomass or microbial sources. Algal lipids may be distinguished by having maximum at n-C;5 and n-Ci7 (Resmi et al., 2016; Meyers and Ishiwatari, 1995). However, the n-C,7 and n-Ci5 show very low concentrations. Hence, the algae may have contributed a little to produce SCLAs, here. On the other hand, bacterial lipids may also contribute SCLAs evident by peaks at n-Cig and n-C2 (Resmi et al., 2016; Elias et al., 1997). The studied samples exhibit reasonable concentration of n-Cx9 among the SCLAs and therefore, may imply significant contribution of organic matter from the photosynthetic bacteria.
The concentrations of n-alkane exhibit wide disposition in the studied shale samples. In the present study, the n-alkane distribution is divided into three parts - short chain length n-alkanes (SCLAs: Cj4-C29), intermediate chain length n-alkanes (ICLAs, C2;-C26) and long chain length n-alkanes (LCLAs: Cp7-C31) (Table 1, Fig. 3). The SCLAs that constitute an average of 21.19% in total concentration (Table 1) of n-alkanes are obtained mainly from the algal biomass or microbial sources. Algal lipids may be distinguished by having maximum at n-C;5 and n-Ci7 (Resmi et al., 2016; Meyers and Ishiwatari, 1995). However, the n-C,7 and n-Ci5 show very low concentrations. Hence, the algae may have contributed a little to produce SCLAs, here. On the other hand, bacterial lipids may also contribute SCLAs evident by peaks at n-Cig and n-C2 (Resmi et al., 2016; Elias et al., 1997). The studied samples exhibit reasonable concentration of n-Cx9 among the SCLAs and therefore, may imply significant contribution of organic matter from the photosynthetic bacteria.
1), which may suggest dominant contribution of organic matter from submergent plant species. The P,g parameter, furthermore, exhibits strong negative linear correlation (r = -0.97) (Fig. 4a) with average chain length (ACL) values (another proxy to determine the sources of LCLAs), which may suggest that the submergent plants dominantly contributed to the organic matter rather than the terrestrial plants to the peat mire in the Auranga basin. Additionally, this parameter shows positive correlation (r = 0.74) (Fig. 4b) with concentration of ICLAs, which may further point towards the derivation of ICLAs from the aquatic submergent plants. Hence, the n-alkane distribution and the related parameters may suggest that the derivation of organic matter dominantly from submerged aquatic vegetation and additionally, reasonable amount from algae and microorganisms as well as very low amount from vascular land plants.
1), which may suggest dominant contribution of organic matter from submergent plant species. The P,g parameter, furthermore, exhibits strong negative linear correlation (r = -0.97) (Fig. 4a) with average chain length (ACL) values (another proxy to determine the sources of LCLAs), which may suggest that the submergent plants dominantly contributed to the organic matter rather than the terrestrial plants to the peat mire in the Auranga basin. Additionally, this parameter shows positive correlation (r = 0.74) (Fig. 4b) with concentration of ICLAs, which may further point towards the derivation of ICLAs from the aquatic submergent plants. Hence, the n-alkane distribution and the related parameters may suggest that the derivation of organic matter dominantly from submerged aquatic vegetation and additionally, reasonable amount from algae and microorganisms as well as very low amount from vascular land plants.
Table 2. Identified pentacyclic triterpenoids in the shale samples 4.2 Biodegradation of organic matter
Table 2. Identified pentacyclic triterpenoids in the shale samples 4.2 Biodegradation of organic matter
5. (a) Depositional environment based on pr/n-C;7 ratio, (b) Cross-plot between Pr/n-C,7 and Ph/n-C;g depicting the source as well as palaeodepositional ironments of the organic matter in the studied shales lanations: Pr = Pristane; Ph = Phytane; n-C,7 = normal straight chain acyclic alkane with 17 carbon atoms; n-C,g = normal straight chain acyclic alkane with 18 yon atoms; Y axis represents the number of the samples
5. (a) Depositional environment based on pr/n-C;7 ratio, (b) Cross-plot between Pr/n-C,7 and Ph/n-C;g depicting the source as well as palaeodepositional ironments of the organic matter in the studied shales lanations: Pr = Pristane; Ph = Phytane; n-C,7 = normal straight chain acyclic alkane with 17 carbon atoms; n-C,g = normal straight chain acyclic alkane with 18 yon atoms; Y axis represents the number of the samples
Explanations: Concentration of the elements are reported in elemental percentage (wt%); SN= Sample No.; PIA= Plagioclase Index of Alternation; Si = Silicon; Al = Aluminium; Fe = Ferum (Iron); K = Kalium (potassium); Ca = Calcium; Mg = Magnesium; Na = Natrium (sodium); Ti = Titanium; P = Phosphorous; PIA = Plagioclase index of alteration; P/Ti = Ratio of phosphorous to titanium; CIA = Chemical index of alteration; * = Data mentioned from Varma et al. (2018).
Explanations: Concentration of the elements are reported in elemental percentage (wt%); SN= Sample No.; PIA= Plagioclase Index of Alternation; Si = Silicon; Al = Aluminium; Fe = Ferum (Iron); K = Kalium (potassium); Ca = Calcium; Mg = Magnesium; Na = Natrium (sodium); Ti = Titanium; P = Phosphorous; PIA = Plagioclase index of alteration; P/Ti = Ratio of phosphorous to titanium; CIA = Chemical index of alteration; * = Data mentioned from Varma et al. (2018).
Table 4. Trace element ratios and palaeoclimatic factor (PF) in the selected shale samples
Table 4. Trace element ratios and palaeoclimatic factor (PF) in the selected shale samples
Fig. 8. Palaeoclimatic factor (PF) introduced in this study to document the palaeohumidity level of the atmospher (modified after Zhao et al., 2007)
Fig. 8. Palaeoclimatic factor (PF) introduced in this study to document the palaeohumidity level of the atmospher (modified after Zhao et al., 2007)
Fig. 9. Ba- moretane/AP- hopane ratio within the selected shale samples
Fig. 9. Ba- moretane/AP- hopane ratio within the selected shale samples
relatively immature nature to early mature state of the organic matter. Homohopanes carry a 22R configuration that changes to both 22R and 22S with maturity (Peters et al., 2005). Subsequently, in mature source rocks the S optical isomer will be more abundant than R. Thus, the 22S/(22S + 22R) homohopane ratio is used widely in the maturity analysis of sediments. The 22S/(22S+22R) homohopane ratio may imply that the samples S#20 and S#34 (0.74 and 0.78, respectively) have surpassed the peak oil generative stage (Table 1, Fig. 10). However, the average value of 0.34 of this parameter may reveal that the rest of the samples contain immature organic matter. The cross-plot of 22S/(22S+22R) Homohopane and Moretane/Hopane parameters, (Fig. 11) additionally, reveals that the organic matter in most of the samples is immature. The ratio of 30-norhopane/C39-hopane can be used as another supplementary proxy for determining maturity of the organic matter. Norhopane shows more stability compared to the hopane and the ratio of 30-norhopane/C39-hopane rises with maturity of the sediments (Peters et al., 2005). Here, the ratio varies from 0.47 to 1.51 (Table 1) indicating relatively immature nature to early mature state of the organic matter. Fig. 10. 22S/(22S+22R) homohopane ratio indicating maturity level of the organic matter in some selected shale samples
relatively immature nature to early mature state of the organic matter. Homohopanes carry a 22R configuration that changes to both 22R and 22S with maturity (Peters et al., 2005). Subsequently, in mature source rocks the S optical isomer will be more abundant than R. Thus, the 22S/(22S + 22R) homohopane ratio is used widely in the maturity analysis of sediments. The 22S/(22S+22R) homohopane ratio may imply that the samples S#20 and S#34 (0.74 and 0.78, respectively) have surpassed the peak oil generative stage (Table 1, Fig. 10). However, the average value of 0.34 of this parameter may reveal that the rest of the samples contain immature organic matter. The cross-plot of 22S/(22S+22R) Homohopane and Moretane/Hopane parameters, (Fig. 11) additionally, reveals that the organic matter in most of the samples is immature. The ratio of 30-norhopane/C39-hopane can be used as another supplementary proxy for determining maturity of the organic matter. Norhopane shows more stability compared to the hopane and the ratio of 30-norhopane/C39-hopane rises with maturity of the sediments (Peters et al., 2005). Here, the ratio varies from 0.47 to 1.51 (Table 1) indicating relatively immature nature to early mature state of the organic matter. Fig. 10. 22S/(22S+22R) homohopane ratio indicating maturity level of the organic matter in some selected shale samples
Fig. 11. Cross-plot between 22S/(22S+22R) homohopane ratio and Ba- moretane/a@B- hopane reflecting maturity stage of the organic matter in some selected shale samples
Fig. 11. Cross-plot between 22S/(22S+22R) homohopane ratio and Ba- moretane/a@B- hopane reflecting maturity stage of the organic matter in some selected shale samples
Fig. 14. Palaeotectonic setting of the clastic sediments in the Auranga shales interpreted from the major elemental oxides using discriminant function diagram
Fig. 14. Palaeotectonic setting of the clastic sediments in the Auranga shales interpreted from the major elemental oxides using discriminant function diagram
Fig. 15: (a) Th vs Sc diagram, Th/Sc =1 ratio is that of upper continental crust (Taylor and McLennan, 1985) (b) La vs Th plot, La/Th =2.8 ratio is that of upper continental crust (Taylor and McLennan, 1985) (c) Zr/Sc vs Th/Sc plot (after McLennan et al., 1993) showing the source affinity of the minerals and addition of zircon due to sediment recvcling.
Fig. 15: (a) Th vs Sc diagram, Th/Sc =1 ratio is that of upper continental crust (Taylor and McLennan, 1985) (b) La vs Th plot, La/Th =2.8 ratio is that of upper continental crust (Taylor and McLennan, 1985) (c) Zr/Sc vs Th/Sc plot (after McLennan et al., 1993) showing the source affinity of the minerals and addition of zircon due to sediment recvcling.
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GeologyGeochemistryEnvironmental ChemistryPalaeoclimatic ReconstructionPetroleum Science and EngineeringSource Rock
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