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Fig. 11: Bivariate plot of Ni/Co versus V/ (V+Ni) (Rimmer, 2004) shows oxic to euxinic conditions during deposition of DF-2 well sediment. Table 5: Some trace elemental ratios to define the paleo oxygenation condition of ancient sediments after Jones anc Manning, (1994); Nath et al., (1997); Akinyemi et al/., (2013);Adebayo et al., (2015a).

Figure 11 Bivariate plot of Ni/Co versus V/ (V+Ni) (Rimmer, 2004) shows oxic to euxinic conditions during deposition of DF-2 well sediment. Table 5: Some trace elemental ratios to define the paleo oxygenation condition of ancient sediments after Jones anc Manning, (1994); Nath et al., (1997); Akinyemi et al/., (2013);Adebayo et al., (2015a).

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Fig. 1a: Map of Africa showing the Location of Nigeria and the Niger Delta region. 1b. Map of the Niger Delta basin showing the different depositional belts (depobelts) and location of DF-2 well. (After Doust and Omatsola, 1990). (2013); Chen eft al., (2016); Mitra et al., (2018); Amiewalan and Lucas, (2020) among others, had worked on the Niger Delta sediments and other Basins to interpret their provenance, tectonic history, paleo- depositional conditions and classification of associated sandstone facies. This study intends to use the major and trace element geochemistry to define the provenance, tectonic history, paleo-depositional conditions of sediments in the DF-2 well, offshore western Niger Delta .This will further enhance the already existing information in this region and would be of immense value to researchers and explorationists.
Fig. 1a: Map of Africa showing the Location of Nigeria and the Niger Delta region. 1b. Map of the Niger Delta basin showing the different depositional belts (depobelts) and location of DF-2 well. (After Doust and Omatsola, 1990). (2013); Chen eft al., (2016); Mitra et al., (2018); Amiewalan and Lucas, (2020) among others, had worked on the Niger Delta sediments and other Basins to interpret their provenance, tectonic history, paleo- depositional conditions and classification of associated sandstone facies. This study intends to use the major and trace element geochemistry to define the provenance, tectonic history, paleo-depositional conditions of sediments in the DF-2 well, offshore western Niger Delta .This will further enhance the already existing information in this region and would be of immense value to researchers and explorationists.
few shalyintercalations (Esan, 2002). The shale content increases towards the basal part of the Formation. It is a continental deposit from latest Eocene to Recent, deposited in alluvial or coastal plain environments following a southward shift of deltaic environments (Esan, 2002). The Formation is up to 2,000 m thick. (Avbovbo, 1978). Fig 2: Regional stratigraphy of the Niger Delta showing different Formations (after Ozumba, 2013). delta-topset, and fluvio-deltaic environments. It is the major petroleum-bearing unit of the Niger Delta (Reijers, (1996), which began in the Eocene and continues into the Recent. The thickness ranges from 9,600 ft. - 14,000 ft. (3,000 m - 4,200 m) (Avbovbo, 1978). The Benin Formation, which is the youngest stratigraphic unit in the Niger Delta, mainly comprised non-marine sands with a
few shalyintercalations (Esan, 2002). The shale content increases towards the basal part of the Formation. It is a continental deposit from latest Eocene to Recent, deposited in alluvial or coastal plain environments following a southward shift of deltaic environments (Esan, 2002). The Formation is up to 2,000 m thick. (Avbovbo, 1978). Fig 2: Regional stratigraphy of the Niger Delta showing different Formations (after Ozumba, 2013). delta-topset, and fluvio-deltaic environments. It is the major petroleum-bearing unit of the Niger Delta (Reijers, (1996), which began in the Eocene and continues into the Recent. The thickness ranges from 9,600 ft. - 14,000 ft. (3,000 m - 4,200 m) (Avbovbo, 1978). The Benin Formation, which is the youngest stratigraphic unit in the Niger Delta, mainly comprised non-marine sands with a
As shown in Table 1, there is enormous difference between SiO. content and other oxides in all the analyzed samples. For instance, the SiOz contents ranges from 79.20 wt. % to 93.10 wt. % (av. 84.2 wt. %.) in the well. According to Lindsey, (1999), silica enhancement shows the degree of sandstone maturity, and the reflection of the extent and strength of weathering and damages of other minerals in the course of transportation. Al,O3 content varies from 2.10 wt. % to 12.90 wt. %.Cingolani et al., (2003), opined that the compositional variations of rocks arising from weathering result in the reduction of alkalis and alkaline earth elements and special enhancement of Al,O3. Fe,O3 content ranges from 1.47 wt. % to 6.64 wt. %. The low content may be due to weathering. The MnO content ranges from 0.03 wt. % to 0.06 wt. %; MgO from 0. 20 wt. % to 0.98 wt. %.; CaO from 0. 88 wt. % to AAC. ...4NA/ ...2Lobe RID Om . we tw OF NOAA LLL OUONYOULL RON MN Table 1: Major oxides geochemical composition of DF-2 Well. Post Archean Australian Average Shale (PAAS). Tayl« and Mclenna, (1985) and Upper Continental Crust (UCC) Mclenna, (2001). wt. %. The low values might perhaps be the result of post depositional processes or from sediment source. Ranges of value of other oxides are; K 0; 0.51 wt. % to 1.51 wt. %, TiO2; 0.12 wt. % to 1.37 wt. % and P2Os. 0.02 wt. % to 0.13 wt. %.
As shown in Table 1, there is enormous difference between SiO. content and other oxides in all the analyzed samples. For instance, the SiOz contents ranges from 79.20 wt. % to 93.10 wt. % (av. 84.2 wt. %.) in the well. According to Lindsey, (1999), silica enhancement shows the degree of sandstone maturity, and the reflection of the extent and strength of weathering and damages of other minerals in the course of transportation. Al,O3 content varies from 2.10 wt. % to 12.90 wt. %.Cingolani et al., (2003), opined that the compositional variations of rocks arising from weathering result in the reduction of alkalis and alkaline earth elements and special enhancement of Al,O3. Fe,O3 content ranges from 1.47 wt. % to 6.64 wt. %. The low content may be due to weathering. The MnO content ranges from 0.03 wt. % to 0.06 wt. %; MgO from 0. 20 wt. % to 0.98 wt. %.; CaO from 0. 88 wt. % to AAC. ...4NA/ ...2Lobe RID Om . we tw OF NOAA LLL OUONYOULL RON MN Table 1: Major oxides geochemical composition of DF-2 Well. Post Archean Australian Average Shale (PAAS). Tayl« and Mclenna, (1985) and Upper Continental Crust (UCC) Mclenna, (2001). wt. %. The low values might perhaps be the result of post depositional processes or from sediment source. Ranges of value of other oxides are; K 0; 0.51 wt. % to 1.51 wt. %, TiO2; 0.12 wt. % to 1.37 wt. % and P2Os. 0.02 wt. % to 0.13 wt. %.
Table 2: Trace Elements Composition of DF-2 Well. V and Zn are depleted when compared to PAAS and enriched in relation to UCC. The depletion of Ni and V elements shows an insignificant role of basic rocks as he provenance. The average concentration of Th Thorium) (7.79) is depleted when compared with PAAS 14.6) and UCC (10.7)as a result of dilution of the elemental concentration by quartz. Sr (Strontium) with a mean value of 149.42 is depleted when related with PAAS (200) and UCC (350). Studies of sedimentary processes have showed that Sr is rapidly lost during chemical weathering and its depletion is in proportion to he degree of weathering (Wronkiewicz and Condie, 1987). The comparative abundance of trace elements in sediment is measured by _ sedimentation _ rate, terrigenous influx, biogenic influx, hydrothermal input, diagenesis and eventually, weathering (Leventhal, 1998). Some of these elements are depleted while others are enriched in relation to UCC and PAAS respectively(Table 2).
Table 2: Trace Elements Composition of DF-2 Well. V and Zn are depleted when compared to PAAS and enriched in relation to UCC. The depletion of Ni and V elements shows an insignificant role of basic rocks as he provenance. The average concentration of Th Thorium) (7.79) is depleted when compared with PAAS 14.6) and UCC (10.7)as a result of dilution of the elemental concentration by quartz. Sr (Strontium) with a mean value of 149.42 is depleted when related with PAAS (200) and UCC (350). Studies of sedimentary processes have showed that Sr is rapidly lost during chemical weathering and its depletion is in proportion to he degree of weathering (Wronkiewicz and Condie, 1987). The comparative abundance of trace elements in sediment is measured by _ sedimentation _ rate, terrigenous influx, biogenic influx, hydrothermal input, diagenesis and eventually, weathering (Leventhal, 1998). Some of these elements are depleted while others are enriched in relation to UCC and PAAS respectively(Table 2).
Sandstone Petrology Table 3: Ratios of some important major oxides and trace elements S based on results from Tables 1 and 2.
Sandstone Petrology Table 3: Ratios of some important major oxides and trace elements S based on results from Tables 1 and 2.
Using Herron (1988) diagram as shown in Fig. 4, majority of the DF-2 samples (70%) plotted mainly in the Fe-sand zone, indicating that they are ferruginous. The rest of the samples (30%) are scattered within the quartz arenite, sublitharenite and litharenite zones. Arising from Pettiionn (1972) plot of log (SiO./AI,03) vs. log Fig. 4: Chemical classification of the DF-2 well sediments based on log (SiO2/Al2O3) vs. log (Fe203/K2O) diagram of Herron, (1988). (Na,O/K20) (Fig. 5), the studied samples plotmainly in quartz arenite with a few in sublitharenite zones. This may perhaps be the consequent of recycling/prolonged abrasion as well sedimentary influx from more than one source.
Using Herron (1988) diagram as shown in Fig. 4, majority of the DF-2 samples (70%) plotted mainly in the Fe-sand zone, indicating that they are ferruginous. The rest of the samples (30%) are scattered within the quartz arenite, sublitharenite and litharenite zones. Arising from Pettiionn (1972) plot of log (SiO./AI,03) vs. log Fig. 4: Chemical classification of the DF-2 well sediments based on log (SiO2/Al2O3) vs. log (Fe203/K2O) diagram of Herron, (1988). (Na,O/K20) (Fig. 5), the studied samples plotmainly in quartz arenite with a few in sublitharenite zones. This may perhaps be the consequent of recycling/prolonged abrasion as well sedimentary influx from more than one source.
Fig. 5: Chemical classification of the samples based on log (SiO2/Al2O3) vs. log (Na2O/K20) diagram of Petti John scheme, (1972).
Fig. 5: Chemical classification of the samples based on log (SiO2/Al2O3) vs. log (Na2O/K20) diagram of Petti John scheme, (1972).
Fig. 6: Tectonic discrimination plot of Roser and Korsch, (1986). Using K2O/Na,O ratio against SiO. for DF-2 sediments. Fig. 7: Log (K20/Na2O) against Log (SiO2/Al,O03) tectonic discrimination diagram of Maynard et al/., (1982). Passive Margin = PM, active continental margin = ACM, arc setting, basaltic and andesitic detritus = A1 and evolved arc setting = A2.
Fig. 6: Tectonic discrimination plot of Roser and Korsch, (1986). Using K2O/Na,O ratio against SiO. for DF-2 sediments. Fig. 7: Log (K20/Na2O) against Log (SiO2/Al,O03) tectonic discrimination diagram of Maynard et al/., (1982). Passive Margin = PM, active continental margin = ACM, arc setting, basaltic and andesitic detritus = A1 and evolved arc setting = A2.
Table 4: Range of elemental ratios of DF-2 well sediments compared to the ratios derived from felsic (Cullers 2000) and mafic rocks (Cullers, 2000), UCC (Taylor and McLennan, 1985) and PAAS (Taylor and McLennan 1985). respectively. In this study, the average concentrations of Cr (70.92) and Ni (24.42) are low, confirming felsic rock as the source areas. This is further supported by Fig. 8, which shows cross plot of La/Sc versus Th/Co (Cullers, 2002) and Fig. 9, which indicates the cross plot of Zr versus TiO2 (Hayashi et a/., 1997), all pointing to felsic source rocks for the sediments.
Table 4: Range of elemental ratios of DF-2 well sediments compared to the ratios derived from felsic (Cullers 2000) and mafic rocks (Cullers, 2000), UCC (Taylor and McLennan, 1985) and PAAS (Taylor and McLennan 1985). respectively. In this study, the average concentrations of Cr (70.92) and Ni (24.42) are low, confirming felsic rock as the source areas. This is further supported by Fig. 8, which shows cross plot of La/Sc versus Th/Co (Cullers, 2002) and Fig. 9, which indicates the cross plot of Zr versus TiO2 (Hayashi et a/., 1997), all pointing to felsic source rocks for the sediments.
Fig. 8: La/Sc versus Th/Co; after Culler, (2002), indicates the derivation of DF-2 sediments from felsic source rocks. Ganai and Rashid, (2015), had posited that sensitive diagenetical trace elements such as Zr, Hf, Nb, Y, Sc, V, Cr, Cu, Co, Ni and Zn can infer provenance and environment of deposition owing to their fairly low movement during weathering, transport, diagenesis, and metamorphism. Garver et al., (1996), recommended that when Cr >150 ppm and Ni >100 ppm in abundance, they are indications of mafic or ultramafic source
Fig. 8: La/Sc versus Th/Co; after Culler, (2002), indicates the derivation of DF-2 sediments from felsic source rocks. Ganai and Rashid, (2015), had posited that sensitive diagenetical trace elements such as Zr, Hf, Nb, Y, Sc, V, Cr, Cu, Co, Ni and Zn can infer provenance and environment of deposition owing to their fairly low movement during weathering, transport, diagenesis, and metamorphism. Garver et al., (1996), recommended that when Cr >150 ppm and Ni >100 ppm in abundance, they are indications of mafic or ultramafic source
Fig. 9: Cross plots of Zr versus TiO. for studied samples (after Hayashi et a/.,1997).
Fig. 9: Cross plots of Zr versus TiO. for studied samples (after Hayashi et a/.,1997).
Fig.10: Bivariate plot of Ni/Co versus V/Cr (Suttner and Dutta, 1986) specifies oxic condition during deposition of DF-2 well sediment.
Fig.10: Bivariate plot of Ni/Co versus V/Cr (Suttner and Dutta, 1986) specifies oxic condition during deposition of DF-2 well sediment.
Fig. 12: The Cross plot of vanadium versus nickel of DF-2 samples from studied area shows that the sediments had mixed marine and terrigenous source input and were deposited under oxic to dyoxic condition (Modified after Kafousia, et al., 2010). versus V/ (V+Ni) (Rimmer, 2004; Fig. 11), which strongly amplify oxic conditions of deposition for the sediments. Wang, (1996), posited that when V/V+ Ni ratio is >0.84, it submits euxinic conditions, from 0.54 - 0.82 characterize sanoxic condition, 0.46 - 0.60 implies dyoxic conditions and <0.46 infers oxic condition. The V/Vi + Ni ratios for the samples ranges from 0.42 to 0.91 average = 0.82), (Table 3) which indicate anoxic environment of deposition. As a result, the above constraints submit that the depositional conditions for he studied samples were oxic to euxinic. The Cross plot of vanadium versus nickel after Kafousia, et a/., (2010), illustrates that the sediments had mixed marine and errigenous source input and were deposited under oxic (e) dyoxic condition. Fig. 12. indicates low values trom 0.20 - 0.49 (av. 0.26; Tables 3), which confirmed deposition in oxic environment. According to Jones and Manning, (1994). The ratio of Ni/Co in DF-2 well varies from 1.56- 4.81 with an average value of 2.79, and implies oxic environments of deposition (Table 3). Moreover, the Cu/Zn ratios could also be used as a redox proxy; low ratios reveals oxic conditions while high ratios deduce reducing depositional conditions (Deng and Qian, 1993). In the studied sediments, the ratio of Cu/Zn varies from 0.14 to 14.10 with an average of 1.53, and inferring deposition under oxic environments (Table 3).The bivariate plot of Ni/Co versus V/Cr (Suttner and Dutta, 1986; Fig. 10) designates oxic condition during deposition of DF-2 well sediments. This is further supported by the plot of Ni/Co
Fig. 12: The Cross plot of vanadium versus nickel of DF-2 samples from studied area shows that the sediments had mixed marine and terrigenous source input and were deposited under oxic to dyoxic condition (Modified after Kafousia, et al., 2010). versus V/ (V+Ni) (Rimmer, 2004; Fig. 11), which strongly amplify oxic conditions of deposition for the sediments. Wang, (1996), posited that when V/V+ Ni ratio is >0.84, it submits euxinic conditions, from 0.54 - 0.82 characterize sanoxic condition, 0.46 - 0.60 implies dyoxic conditions and <0.46 infers oxic condition. The V/Vi + Ni ratios for the samples ranges from 0.42 to 0.91 average = 0.82), (Table 3) which indicate anoxic environment of deposition. As a result, the above constraints submit that the depositional conditions for he studied samples were oxic to euxinic. The Cross plot of vanadium versus nickel after Kafousia, et a/., (2010), illustrates that the sediments had mixed marine and errigenous source input and were deposited under oxic (e) dyoxic condition. Fig. 12. indicates low values trom 0.20 - 0.49 (av. 0.26; Tables 3), which confirmed deposition in oxic environment. According to Jones and Manning, (1994). The ratio of Ni/Co in DF-2 well varies from 1.56- 4.81 with an average value of 2.79, and implies oxic environments of deposition (Table 3). Moreover, the Cu/Zn ratios could also be used as a redox proxy; low ratios reveals oxic conditions while high ratios deduce reducing depositional conditions (Deng and Qian, 1993). In the studied sediments, the ratio of Cu/Zn varies from 0.14 to 14.10 with an average of 1.53, and inferring deposition under oxic environments (Table 3).The bivariate plot of Ni/Co versus V/Cr (Suttner and Dutta, 1986; Fig. 10) designates oxic condition during deposition of DF-2 well sediments. This is further supported by the plot of Ni/Co
Fig. 13: Bivariate plot of SiO. versus (Al,O3 + Na2O + KO) to discriminate palaeo-climatic condition during the deposition of the studied samples (Modified after Galarraga, et al., 2008).
Fig. 13: Bivariate plot of SiO. versus (Al,O3 + Na2O + KO) to discriminate palaeo-climatic condition during the deposition of the studied samples (Modified after Galarraga, et al., 2008).
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