Published

2014-01-01

Using aromatic biological markers as a tool for assessing thermal maturity of source rocks in the Campano-Maastrichtian Mamu Formation, southeastern Nigeria

DOI:

https://doi.org/10.15446/esrj.v18n1.34799

Keywords:

Aromatic biomarkers, Maturity, Mamu Formation, Anambra Basin. (en)
Biomarcadores aromáticos, Madurez geológica, Formación Mamu, cuenca de Anambra. (es)

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Authors

  • Jude E. Ogala Delta State University
  • Mike I. Akaegbobi University of Ibadan
The concentration and distribution of aromatic biomarkers in coals and shales from five boreholes penetrating the Maastrichtian Mamu Formation of the Anambra Basin, southeastern Nigeria, were investigated by gas chromatography-mass spectrometry to assess the thermal maturity and organic matter input. The study focused on the variations of the relative abundances of naphthalenes, phenanthrenes, and monaromatic and triaromatic steroids identified on the mass fragmentograms. Trimethylnaphthalene (TMN) is the most abundant member of the naphthalene family while methylphenanthrene (MP) is the most abundant phenanthrene family member. The total of phenanthrenes and their isomers was greater than that of naphthalenes. The distribution of these aromatic hydrocarbons and their akyl derivatives was strongly controlled by a selective expulsion mechanism and thermal maturation of organic matter. The low dibenzothiophene/phenanthrene (DBT/PHEN) ratios (0.01-0.06), as well as the enhanced concentrations of 1,2,5-TMN relative to 1,2,7- TMN, indicates organic matter derived mainly from higher plants, and the extract ternary plot of C27, C28and C29 monoaromatic steroids suggests a Type III and mixed Type II/III kerogen. The calculated mean vitrinite reflectance (%Rm), determined from the distributions of the isomers of methyldibenzothiophene ratio (MDR) in the rock extracts, ranged from 0.51 to 1.43. These maturity values indicate that the coal and shale extracts are marginally mature for hydrocarbon generation.
La concentración y distribución de biomarcadores aromáticos en carbones y esquistos de cinco perforaciones en la formación Maastrichtian Mamu de la cuenca de Anambra, en el sureste de Nigeria, fueron analizados a través de un estudio de espectometría cromatográfico y de masa del gas para medir la madurez termal y la entrada de material orgánico. El estudio está enfocado en las variaciones de la abundancia relativa de naftalinas y fenantrenos, y en los esteroides monoaromáticos y triaromáticos identificados en los fragmentogramas de masas. La trimetinaftalina (TMN) es la más abundante de la familia de las naftalinas mientras el metilfenantreno (MP) es el más abundante de los fenantrenos. El tota de los fenantrenos y sus isómeros fue mayor que el de las naftalinas. La distribución de estos hidrocarbones aromáticos y sus alquilos derivados fue controlada ampliamente por un mecanismo de expulsión selectiva y de la maduración térmica de material orgánico. La baja proporción dibenziotofeno/fenantreno (DBT/PHEN) (0.01-0.06), al igual que las concentraciones mejoradas de 1,2,5-TMN relativas de 1,2,7-TMN indican que la materia orgánica se deriva principalmente de plantas mayores, y del diagrama terniario de los esteroides monoaromáticos C27, C28 y C29 sugiere un tipo III mezclado con tipos II/III de querógenos. El valor calculado de la reflectancia de vitrinita (%Rm) determinado de la proporción de isómeros de metildibenziotofeno (MDR) en los extractos rocosos oscila de 0.51 a 1.43. Estos valores de madurez indican que los extractos de carbones y esquistos son marginalmente maduros para la generación de hidrocarbono.

PETROLEUM GEOLOGY

Using aromatic biological markers as a tool for assessing thermal maturity of source rocks in the Campano-Maastrichtian Mamu Formation, southeastern Nigeria

1. Jude E Ogala, Delta State University, Nigeria. Email: etunimogala@yahoo.com

2. Mike I Akaegbobi, University of Ibadan, Nigeria. Email: izumike20022002@yahoo.com

Record
Manuscript received: 06/11/2012 Accepted for publication: 29/04/2014


ABSTRACT

The concentration and distribution of aromatic biomarkers in coals and shales from five boreholes penetrating the Maastrichtian Mamu Formation of the Anambra Basin, southeastern Nigeria, were investigated by gas chromatography-mass spectrometry to assess the thermal maturity and organic matter input. The study focused on the variations of the relative abundances of naphthalenes, phenanthrenes, and monaromatic and triaromatic steroids identified on the mass fragmentograms. Trimethylnaphthalene (TMN) is the most abundant member of the naphthalene family while methylphenanthrene (MP) is the most abundant phenanthrene family member. The total of phenanthrenes and their isomers was greater than that of naphthalenes. The distribution of these aromatic hydrocarbons and their akyl derivatives was strongly controlled by a selective expulsion mechanism and thermal maturation of organic matter. The low dibenzothiophene/phenanthrene (DBT/PHEN) ratios (0.01-0.06), as well as the enhanced concentrations of 1,2,5-TMN relative to 1,2,7- TMN, indicates organic matter derived mainly from higher plants, and the extract ternary plot of C27, C28 and C29 monoaromatic steroids suggests a Type III and mixed Type II/III kerogen. The calculated mean vitrinite reflectance (%Rm), determined from the distributions of the isomers of methyldibenzothiophene ratio (MDR) in the rock extracts, ranged from 0.51 to 1.43. These maturity values indicate that the coal and shale extracts are marginally mature for hydrocarbon generation.

Key words: Aromatic biomarkers, Maturity, Mamu Formation, Anambra Basin

RESUMEN

La concentración y distribución de biomarcadores aromáticos en carbones y esquistos de cinco perforaciones en la formación Maastrichtian Mamu de la cuenca de Anambra, en el sureste de Nigeria, fueron analizados a través de un estudio de espectometría cromatográfico y de masa del gas para medir la madurez termal y la entrada de material orgánico. El estudio está enfocado en las variaciones de la abundancia relativa de naftalinas y fenantrenos, y en los esteroides monoaromáticos y triaromáticos identificados en los fragmentogramas de masas. La trimetinaftalina (TMN) es la más abundante de la familia de las naftalinas mientras el metilfenantreno (MP) es el más abundante de los fenantrenos. El tota de los fenantrenos y sus isómeros fue mayor que el de las naftalinas. La distribución de estos hidrocarbones aromáticos y sus alquilos derivados fue controlada ampliamente por un mecanismo de expulsión selectiva y de la maduración térmica de material orgánico. La baja proporción dibenziotofeno/fenantreno (DBT/PHEN) (0.01-0.06), al igual que las concentraciones mejoradas de 1,2,5-TMN relativas de 1,2,7-TMN indican que la materia orgánica se deriva principalmente de plantas mayores, y del diagrama terniario de los esteroides monoaromáticos C27, C28 y C29 sugiere un tipo III mezclado con tipos II/III de querógenos. El valor calculado de la reflectancia de vitrinita (%Rm) determinado de la proporción de isómeros de metildibenziotofeno (MDR) en los extractos rocosos oscila de 0.51 a 1.43. Estos valores de madurez indican que los extractos de carbones y esquistos son marginalmente maduros para la generación de hidrocarbono.

Palabras clave: Biomarcadores aromáticos; Madurez geológica; Formación Mamu, cuenca de Anambra.


INTRODUCTION

Aromatic biomarkers and their structural isomers have been found useful for the maturity assessment of oils, source rocks and coals (Radke et al., 1982a; Radke and Welte, 1983; Alexander et al., 1985; Radke et al., 1986; Garrigues et al., 1988; Strachan et al., 1988; Akaegbobi et al., 2000; Akinlua et al., 2007; Sonibare et al., 2008). Complex mixtures of aromatic hydrocarbons have been identified in crude oils (Cumbers et al., 1986), organic extracts of coals (Radke et al., 1982a, b; Puttman and Villar, 1987) and ancient sediments (Alexander et al., 1985; Garrigues et al., 1988, 1990). These complex mixtures of polyaromatic hydrocarbons (PAHs) are usually not generated through biosynthetic processes by living organisms in the sediments. However, some living organisms may synthesize benzoyl-derivatives in large quantities (Akaegbobi et al., 2000).

Aromatic compounds found in crude oils and ancient sediments are believed to have been derived from modification through degradation of biologically produced compounds such as steroids and terpenoids (Hall et al., 1984; Strachan et al., 1988). They also observed that steroids give rise to substituted phenanthrenes, and terpenoids produce alkylnaphthalenes. Other potential sources of alkylnaphthalene include the thermal degradation of spores, coals, and sporopollenin (Allan and Larter, 1981), and of kerogens and cyclic sesquiterpenoids present in resinous components (Anderson et al., 1992). For the alkylated phenanthrenes, the terpenoids derived from higher plant constituents such as resins and waxes seem to be one major source. Radke et al. (1982a) suggested that direct methylation of phenanthrene during catagenesis could be a substantial source of alkyl phenanthrene. Furthermore, the conversion of higher-plant triterpenoids in sediments into aromatic hydrocarbons is through the release of oxygen functional groups and subsequent aromatization of the rings (Johns, 1986; Radke, 1987; Rullkotter et al., 1994; Akaegbobi et al., 2000). The ultimate products of such processes are therefore tetracyclic and pentacyclic aromatic hydrocarbons. Through cleavages of bonds within the rings coupled with photochemical and acid catalyzed processes during diagenesis/catagenesis, these tetracyclic and pentacyclic aromatic hydrocarbons could be broken into methyl-substituted naphthalenes and phenanthrenes, respectively. Therefore, relative variations in the concentrations of akylnaphthalenes and alkylphenanthrenes in the sediments could supply information on the maturity of organic matter, organic facies input and depositional environment (Seifert and Moldowan, 1978, 1986; Radke et al., 1982a, b; Radke, 1988).

The aim of this paper is to examine the ratios of aromatic compounds in coal and shale extracts from the Maastrichtian Mamu Formation in the Anambra Basin, southeastern Nigeria, and to assess the organic matter input and thermal maturity for the source rocks.

GEOLOGICAL SETTING

The Anambra Basin, constituting the southwestern portion of the Benue Trough (Fig. 1), is a roughly triangular-shaped sedimentary depression covering an area of approximately 40,000 km2 (Akaegbobi et al., 2000). The present study area lies within latitudes 6#º20/ to 7#º55/ N and longitudes 7#º10/ to 8#º00/ E (Fig. 2). The Anambra Basin was initiated in the Early Cretaceous with the formation of the Benue-Abakaliki Trough as a failed arm of a rift triple junction associated with the separation of the African and South American continents and the subsequent opening of the South Atlantic Ocean (Murat, 1972).The NE-SW trending Benue-Abakaliki Trough is believed to be the result of a pre-Albian rifting of the African Shield prior to the opening of the South Atlantic Ocean (Uzuakpunwa, 1974). The movements were reactivated by further plate activity in the Lower Tertiary soon after the intermittent Upper Cretaceous rifting (Petters, 1978). The Anambra Basin contains over 6 km thick Cretaceous/Tertiary sediments and provides a structural link between the Cretaceous Benue Trough and the Tertiary Niger Delta (Whiteman, 1982; Onuoha, 1986; Mohammed, 2005).

The stratigraphic succession ranges from Late Santonian to Eocene (Fig. 3), with sediments of fluvial, deltaic, pro-delta, and shelf facies origins. Accumulation of sediments in the Anambra Basin commenced with the Campano-Maastrichtian marine and paralic shales of the Enugu and Nkporo Formations, along with the deltaic Owelli Sandstone equivalent. These basal units are overlain successively by the coal measures of the Mamu Formation (Lower Coal Measures), the Ajali Sandstone (Middle Coal Measures) and the Nsukka Formations (Upper Coal Measures).The Nsukka Formation, which overlies the Ajali Sandstone, begins with coarse- to medium-grained sandstones and passes upward into well-bedded blue clays, fine-grained sandstones, and carbonaceous shales with thin bands of limestone. The marine shales of the Imo Formation were deposited in the Paleocene, and overlain by the Ameki Formation (lateral equivalents of the tidal Nanka Sandstones) of Eocene age which constitutes the Tertiary succession (Petters and Ekweozor, 1982)(Fig. 3).

MATERIALS AND METHODS

Seven core samples consisting of coal (4) and shale (3) having total organic carbon (TOC) values ranging from 3.35 to 55.07 wt.% were carefully selected at various depth intervals (75-221 m) from five boreholes penetrating the Mamu Formation in the Anambra Basin in three Coal fields at Enugu, Ezimo and Ogboyoga (Fig. 2). Pulverized samples were exhaustively extracted by Soxhlet extraction using dichloromethane as solvent. All samples were prepared according to standard organic geochemical sample preparation techniques (Radke et al., 1980, 1984). Aliquots of the extracts were separated into saturated and aromatic hydrocarbons and heterocyclic compounds by liquid chromatography using a dual column system and a back-flushing technique as a preparatory step for biomarker analysis. The asphaltene fraction of the sample was recovered by precipitation in pentane overnight at room temperature. The pentane soluble portion of the sample (i.e., the maltenes) was further separated by liquid chromatography into saturated, aromatic and resin fractions using a large column containing silica gel with fractions quantified by gravimetric analysis. Aromatic hydrocarbons were eluted using 40 mL of 90:10 (v/v) pentane/dichloromethane mixtures. The aromatic fractions were diluted with 10 µl of carbon disulfide (CS2) per mg of fraction and analyzed by Gas Chromatography-Mass Spectrometry using a Hewlett Packard 6890 GC/5973 MSD system (Agilent Technologies, California, U.S.A.) equipped with a high-resolution column (60 m, DB-1 phase, 0.2 mm i.d., 0.2 µm film). A constant flow of hydrogen carrier gas was used during the entire gas chromatographic run. The GC was temperature programmed from 80 °C (2 minutes hold) to 3200C at 3.5 0C/minute with a final hold time of 20 minutes. There was a 7.5-minute solvent delay on acquisition, and selected ion monitoring (SIM) was the standard method for analysis.

RESULTS

Biomarker Chemistry

The mass chromatograms of naphthalenes, phenanthrenes and akyl derivatives of representative coal and shale extracts from the Maastrichtian Mamu Formation in the Anambra Basin are shown in Figures 4a-b and 5a-b, respectively. The identification of the peaks labeled in Figures 4a-b and 5a-b are reported in Tables 1 and 2. Two methylnaphthalenes (MN), two ethylnaphthalenes (EN), nine dimethylnaphthalenes (DMN), ten trimethylnaphthalenes (TMN), eleven tetramethylnaphthalenes (TeMN) and two ethyl-methyl-naphthalenes (EMN) isomers were identified in the aromatic fractions of the coal and shale extracts (Figs. 4a-b). Among the tricyclic aromatic hydrocarbons, four methylphenanthrenes (MP), and fourteen dimethylphenanthrene isomers were identified (Figs. 5a-b). Dimethylnaphthalene was the most abundant among the naphthalene family (Fig. 6). All samples have similar distributions of phenanthrenes (m/z 178).

Dimethylphenanthrene was the least abundant of the phenanthrene homologues (Fig. 7). The distribution of total naphthalenes and phenanthrenes in the coal and shale extracts from the Mamu Formation indicates that the total sum of the phenanthrenes and their isomers was greater than that of the naphthalenes in all the samples analyzed (Fig.8). The distribution of these aromatic hydrocarbons and their akyl derivatives was strongly controlled by a selective expulsion mechanism and thermal maturation of organic matter (Akaegbobi et al., 2000). In the present study, the relative abundance of the phenanthrenes and their akyl derivatives was greater than that of the naphthalenes. Radke et al. (1982a) suggested that a substantial source of alkyl phenanthrene could be the direct methylation of phenanthrene during catagenesis. The results obtained in this study corroborate with those reported by Akinlua et al. (2007).These isomers were applied in the calculation of temperature-sensitive maturity parameters such as methylphenanthrene indices (MPI-1 and MPI-2), methyldibenzothiophene ratio (MDR), dimethylnaphthalene ratios (DNR-1 and DNR-2) and trimethylnaphthalene ratio (TNR-1).

DISCUSSION

Thermal maturity

The concentration of aromatic compounds, such as naphthalenes, phenanthrenes, dibenzothiophenes and their structural isomers are at present attracting increasing attention as maturity indicators for coals and shale source rocks. These indicators rely either on an increase in maturity with the degree of alkylation of a given parent compound, or a shift in the isomer distribution of alkyl-aromatic homologues increasing towards isomers with greater thermal stability (Radke, 1988). The aromatic isomer ratios and indexes (DNR-1, DNR-2, TNR-1, TDE-1, TDE-2, MPI-1, MPI-2, and MDR) used in this study are reported in Table 5.

Table 5.

The total concentration of naphthalene and its isomers is greater than that of the phenanthrenes. The higher abundances of naphthalenes relative to phenanthrenes can be attributed to selective expulsion mechanisms and direct methylation during diagenesis/catagenesis (Akaegbobi et al., 2000; Radke et al., 1982a). The increase in the concentrations of naphthalenes along with an increase in the number of alkyl substitutes indicates that the oils are mature. This increase in the number of methyl substituents of naphthalene in mature oils occurs because of the thermal rearrangement of methylnaphthalene with increasing thermal stress (Akaegbobi et al., 2000). Furthermore, the coal and shale extracts contain enhanced concentrations of 1, 2, 5-trimethylnaphthalene relative to 1, 2, 7-trimethylnaphthalene (Table 4). This is typical of mature oils (Strachan et al., 1988; Akinlua et al., 2007). However, in the present study, the relative abundance of the total of phenanthrene and its isomers was greater than that of naphthalenes (Table 3, Fig.9). The abundance of phenanthrenes relative to naphthalenes suggests that the rock extracts are mature (Akinlua et al., 2007).

A number of aromatic maturity parameters based on the distribution of naphthalene, phenanthrene and alkyl isomers were calculated for the study samples after Radke et al. (1982a), Radke et al. (1986) and Alexander et al. (1985, 1986). Radke (1988) observed that aromatic hydrocarbons do change in a regular fashion with increasing maturity and thus developed maturity parameters based on the distributions of alkylnaphthalene and alkylphenanthrene.The maturity parameters computed from the aromatic biomarker distributions in the coal and shale extracts are listed in Table 5. The maturity parameters computed from naphthalene and its isomers, the dimethylnaphthalene ratios (DNR-1 and DNR-2) and trimethylnaphthalene ratio (TNR-1) ranged from 2.04 to 6.03, 1.21 to 3.37 and 0.73 to 1.22, respectively (Table 5).

The methylphenanthrene index (MPI-1) is one of the most widely used maturity parameters based on aromatic hydrocarbons (Radke et al., 1982a, 1982b; Radke, 1988). The parameter relies on a shift with maturity in the methylphenanthrene distribution towards a preponderance of β-type isomers. The methylphenanthrene indices (MPI-1 and MPI-2) were computed based on the relative concentrations of the 1-MP, 2-MP, 3-MP, 9-MP and phenanthrene (P). This was based on the assumption that the 2-MP and 3-MP are derived from the rearrangement of the 1-MP and 9-MP, and from phenanthrene (P) through methylation reactions. The relative abundances of the alkyl homologs of the aromatic hydrocarbons (phenanthrenes) were used to calculate the vitrinite reflectance (% Rc) after the method of Radke et al., (1982a, b) and Radke (1988). The MPI-1 is often used for estimating the equivalent vitrinite reflectance values (% Rc) for crude oils and source rocks. The MPI-1 and % Rc values calculated for the coal and shale extracts range from 0.10 to 0.23 and 0.43 to 0.51, respectively (Table 5). MPI-1 calculated reflectance (%Rc) was carried out because of insufficient and good reflecting vitrinite in the samples.

Maturity parameters based on the isomers of the methyldibenzothiophene (MDBT) were calculated (Radke et al., 1986). This ratio (MDR) generally increases with increasing maturity and correlates well with vitrinite reflectance and the Rock-Eval Tmax of source rock (Radke, 1988). The ratio is also useful in calculating mean vitrinite reflectance (% Rm). The methyldibenzothiophene ratio (MDR) and mean vitrinite reflectance (%Rm) for the coal and shale extracts ranged from 0.40 to 6.56 and 0.51 to 1.43, respectively (Table 5). The high MDR exhibited by some of the samples may be a result of the effect of heating rates or thermal stress (Akaegbobi et al., 2000). The % Rm values show that the coal and shale extracts range from immature to mature (Table 5).

Monoaromatic and triaromatic steroids were detected in all samples in the m/z 253 and m/z 231 fragmentograms (Figs. 10a-b). Both 20R and 20S homologues of C26-C28, C20 and C21 triaromatic compounds are present (Figs. 10a-b).

Peters and Moldowan (1993) and El-Gayar (2005) suggested that the extent of cracking in the side chains of triaromatic steroids can be used to provide information about petroleum maturity. The triaromatic steroid maturity parameters C20/C20+C28 (20R) and (C20+C21)/ (C20+C21+C26 to C28 20R and 20S) were used to evaluate the thermal maturity of the coal and shale extracts in this study (Peters and Moldowan, 1993; Peters et al., 2005). The maturity parameters computed from the peak areas of the m/z 231 ranged from 0.08 to 0.72 and 0.09 to 0.52, respectively (Table 5). These values indicate an immature to marginally mature status of the source rock.

The monoaromatic steroid ratios (MAS Dia/Reg C27 and MAS C21+C22/all MAS) were measured from the m/z 253 fragmentograms (Table 5) and used to evaluate the source-rock depositional environment and thermal maturity (Peters and Moldowan, 1993). Both of these ratios increase with higher thermal maturity (Mackenzi et al., 1981; Moldowan and Fago, 1986). The MAS Dia/Reg C27 sterane ratio ranges from 0.69 to 2.19 (Table 5). The coal and shale extracts in the Mamu Formation contain significant amounts of diasteranes, which appear to form through the interaction of steranes with clay mineral surfaces in source rocks (Rubinstein et al., 1975; Sieskind et al., 1979). Thus, the presence of significant amounts of diasteranes relative to regular steranes in oils has been used as evidence of petroleum generation from argillaceous source rocks, whereas low concentrations are considered an indication of a source rock lacking in clay minerals (Hughes, 1984; Mello et al., 1988a, 1988b; Hill et al., 2007). The calculated monoaromatic maturity ratio (MAS C21+C22/all MAS) ranges from 0.04 to 0.05 (Table 5).

Thermal maturity was also evaluated on the basis of monoaromatic and triaromatic steroids because they are more resistant to the effects of biodegradation than alkane-type biological markers (Volkman et al., 1983). According to Tissot and Welte (1984), aromatization of C-ring steroid hydrocarbons occurs in mature oils. With an increase in thermal maturation, there is a conversion of C-ring monoaromatic steroid hydrocarbons to ABC-ring triaromatic steroid hydrocarbons (Akinlua and Ajayi, 2009). The TAS/ (TAS+MAS) and TAS 28/ (TAS 28+MAS 29) ratios ranged from 0.22 to 0.59 and 0.39 to 0.88, respectively (Table 5), indicating an immature to marginally mature status of the rock extracts.

Source of organic matter

The trimethylnaphthalene is dominated by 1, 2, 5- TMN in all the samples analyzed (Figs. 4a-b and Table 4). The high abundance of the naphthalenes, especially the dimethyl- and trimethyl-isomers, indicates organic matter derived mainly from higher plants (Strachan et al., 1988). High concentrations of 1, 2, 5- and 1, 2, 7- trimethylnaphthalene (TMN) in oils have been attributed to aromatization and cleavage of the ring-C of β-amyrin in angiosperms (Strachan et al., 1988). 1, 2, 5- and 1, 2, 7- trimethylnaphthalenes can form as diagenetic products of oleanane-type triterpenoids (Chaffee and Johns, 1983; Chaffee et al., 1984; Sonibare et al., 2008). The presence of 1, 2, 5-TMN in the studied samples could be linked to aromatization of oleanane, as indicated by the absence of appreciable amounts of oleanane in the m/z 191 fragmentograms. This compound can also be formed from gymnosperm resins (van Aarssen et al., 1999) or from hopanoid precursors (Villar et al., 1988). Among the tetramethylnaphthalene family, 1, 2, 5, 6- tetramethylnaphthalene is the most abundant (Figs. 4a-b).

Strachan et al. (1986) used two related ratios (TDE-1 and TDE-2) of trimethylnaphthalenes to differentiate coal swamps from marine, lacustrine, and deltaic environments. 1, 2, 7- trimethylnaphthalene (TMN) has been used as a marker of angiosperm input. 1, 2, 5-trimethylnaphthalene and 1, 2, 7- trimethylnaphthalene can form as diagenetic products of oleanane-type triterpenoids (Chaffee and Johns, 1983; Chaffee et al., 1984). Strachan et al. (1988) compared the relative abundance of trimethylnaphthalene isomers in Southeast Asian samples ranging in age from Permian to Tertiary. They found that the relative concentrations of the 1, 2, 7-trimethylnaphthalenes were appreciably higher in most oils derived from post-Cretaceous source rocks dominated by the input of higher-plants, and in extracts from Cretaceous and younger samples, than in samples of older age or with little or no terrigenous plant input. Oils of this type yielded ratios of 1, 2, 7-/1, 3, 7-trimethylnaphthalenes from 0.46 to 1.36, while oils from older source rocks containing higher-plant material yielded ratios from 0.34 to 0.16, and oils from marine source rocks yielded ratios from 0.15 to 0.32. In this study, the rock extracts yielded ratios of 1, 2, 7-/1, 3, 7-trimethylnaphthalenes ranging from 0.40 to 1.07 (Table 5). The computed TDE-1 and TDE-2 ratios for the study samples range from 4.41 - 15.21 and 0.20 - 0.53, respectively (Table 5). The presence of 1, 2, 5- and 1, 2, 7-TMN in the rock extracts (Figs. 4a-b; Table 4) indicate both angiosperm and gymnosperm material contribution to the organic matter that formed the coals and shales (Killops and Killops, 2005; Adedosu et al., 2012). Furthermore, the occurrence of appreciable amounts of 1, 6- and 2, 6-DMNs in all the samples indicate terrestrial organic matter input (Achari et al., 1973). Additionally, the occurrence of 1, 7-DMP in the analyzed samples (Figs. 5a-b) is attributed to terrestrial organic matter (Simoneit et al., 1986), while plots of C27,C28 and C29 monoaromatic steranes (Fig. 11) indicate that the kerogens were derived from mixed terrestrial and marine organic matter.

The distribution of the aromatic sulfur compounds including dibenzothiophenes (DBTs) and their methyl homologues in the coal and shale extracts are reported in Figures 12a-b. The dibenzothiophene/phenanthrene (DBT/PHEN) ratio together with the Pr/Ph ratio can be used to infer source rock depositional environments and lithologies (Hughes et al., 1995). High DBT/PHEN ratios are found in oils from marine carbonates, and low ratios are found in oils from marine shales and most lacustrine rocks (Petersen et al., 2007). The coal and shale extracts (Table 5) have low DBT/PHEN ratios (0.01 – 0.06), indicating a strong input of terrigenous Type III organic matter. However, DBT/PHEN (Table 5) and Pr/Ph ratios only reflect the Eh and pH irrespective of depositional environment, and a cross-plot of the two ratios by itself cannot be used to distinguish lacustrine from marine oils (Petersen et al., 2007). The presence of organic sulfur compounds and sulfur-containing aromatics in rock extracts and crude oils indicates an anoxic depositional environment (Sinninghe Damste et al., 1988, 1989a, 1989b; Hughes et al., 1995). 1-methyldibenzothiophene (1-MDBT), 2+3-methyldibenzothiophene (2+3-MDBT) and 4-methyldibenzothiophene (4-MDBT) were detected in all the samples analyzed (Figs. 12a-b; Table 6). The high relative abundance of dibenzothiophenes (DBTs) in all of the samples is indicative of probable oxic/anoxic conditions prevailing during deposition (Table 6). The distribution of DBTs has been proposed as an indicator of crude oils derived from carbonate versus siliciclastic sources (Hughes, 1984; Hegazi and El-Gayar, 2009). The presence of a definite V pattern (4-methyl > 2+3-methyl < 1-methyl) in the methyldibenzothiophenes is generally associated with oils from predominantly carbonate source rocks, while a stair-step pattern (4-methyl > 2+3-methyl > 1-methyl) is associated with predominantly siliciclastic source rocks, or oils of advanced maturity (late- to post-oil window) from carbonate sources (Hegazi and El-Gayar, 2009). Furthermore, oils from carbonate sources are characterized by an abundance of benzothiophenes (BTs) and a fairly equal distribution of substituted DBTs, while siliciclastic oils exhibit low concentrations of BTs and decreasing amounts of dimethyldibenzothiophenes and trimethyldibenzothiophenes relative to methyldibenzothiophenes (Hughes, 1984; Hegazi and El-Gayar, 2009). The results obtained in this study indicate that the 4-methyldibenzothiophenes (24.0%) are more abundant than the 2+3-methyldibenzothiophenes (20.4%) and 1-methyldibenzothiophenes (4.4%) (Table 6), indicating a siliciclastic source rock input for the organic matter (Hegazi and El-Gayar, 2009).

(a)

The mass chromatograms (m/z 184 and m/z 198) of the extracts representing the DBTs in this study show a high concentration of DBTs (51.2%) and decreasing amounts of dimethyldibenzothiophenes (24.0%) and trimethyldibenzothiophene (20.4%) relative to methyldibenzothiophenes (4.4%) (Figs. 12a-b and Table 6). These results are consistent with previous analyses that indicate that the coal and shale extracts in this study were generated by a siliciclastic source rock (Hegazi and El-Gayar, 2009).

Benzohopanes are formed by the cyclization of extended hopanoid side chains followed by aromatization (Hussler et al., 1984a, 1984b). Benzohopanes range in carbon number from C32 to C35. He and Lu (1990) observed that oils and bitumens from evaporitic and carbonate source rocks have the highest concentrations of benzohopanes, which occur in trace amounts in most source rocks and crude oils. Benzohopanes were identified in all the rock extracts, but concentrations are low (Figs. 13a-b). All samples have similar distributions of benzohopanes (m/z 191). The distribution of benzohopanes (Figs. 13a-b) shows that C32 benzohopane is the most abundant member of the bezohopane family. The relative concentrations of the various members of the aromatic hopane series seem to follow that of the regular hopanes in the saturated hydrocarbon fraction, and like the saturated hopanes, they most likely have a bacterial origin (Petersen et al., 2007).

CONCLUSION

The results of this study indicated that the aromatic hydrocarbons contained in the coal and shale samples from the Campano-Maastrichtian Mamu Formation of the Anambra Basin are marginally mature. The kerogens were formed from organic matter of mixed origin (terrestrial and marine). The distributions/concentrations of naphthalenes and phenanthrenes show that trimethylnaphthalene is the most abundant member of the naphthalene family and methylphenanthrene is the most abundant phenanthrene family member. All samples have similar distributions of phenanthrenes. The relative abundance of the total of phenanthrene and its isomers was greater than that of the naphthalenes. Thus, the distributions of aromatic hydrocarbons in the rock extracts are influenced by methylation reactions at elevated maturity. The slightly higher concentrations of C29 monoaromatic steranes (49%), compared with C28 (22%) and C27 (29%) monoaromatic steranes, suggests a mixed input of terrestrial and marine organic matter.

ACKNOWLEDGEMENT

We are grateful to Daniel M. Jarvie and the staff of Humble Geochemical Laboratory, Texas, USA, for the assistance rendered during the geochemical analyses. We gratefully acknowledge the Nigerian Geological Survey Agency (NGSA) for providing the core samples used in this study, and the anonymous reviewers for their helpful comments.


REFERENCES

Achari, R.G., Shaw, G., and Holleyhead, R., 1973. Identification of ionene and other carotenoid degradation products from the pyrolysis of sporopollenins derived from some pollen exines, a spore coal and the green river shale. Chemical Geology, volume 12, pp. 229-234.

Adedosu, T.A., Sonibare, O.O., Tuo, J., and Ekundayo, O., 2012. Biomarkers, carbon isotopic composition and source rock potentials of Awgu coals, middle Benue trough, Nigeria. Journal of African Earth Sciences, volumes 66-67, pp. 13-21.

Akaegbobi, I.M., Nwachukwu, J.I., and Schmitt, M., 2000. Aromatic hydrocarbon distribution and calculation of oil and gas volumes in post-Santonian shale and coal, Anambra Basin, Nigeria. In: Mello, M.R., and Katz, B.J., (eds.), Petroleum systems of south Atlantic margins. AmericanAssociation of Petroleum Geologists Memoir, volume 73, p.233-245.

Akande, S.O., Ogunmoyero, I.B., Petersen, H.I., and Nytoft, H.P., 2007. Source rock evaluation of coals from the lower Maastrichtian Mamu Foundation, SE Nigeria. Journal of Petroleum Geology, volume 30, number 4, pp. 303-324.

Akinlua, A., Torto., N., and Ajayi., T.R., 2007. Oils in the Northwestern Niger Delta: Aromatic hydrocarbons content and infrared spectroscopic characterization. Journal of Petroleum Geology, volume 30, number 1, pp. 91-100.

Akinlua, A., and Ajayi, T.R., 2009. Chemical characterization of Central Niger Delta oils. Journal of Petroleum Geology, volume 32, number 4, pp. 373-382.

Alexander, R., Kagi, R.I., Roland, S.J., Sheppard, P.N., and Chirila, T.V., 1985. The effects of thermal maturity on distributions of dimethylnaphthalenes and trimethylnaphthalenes in some ancient sediments and petroleum. Geochimica Cosmochimica Acta, 49, pp. 385-395.

Alexander, R., Cumbers, A.M., and Kagi, R.I., 1986. Alkylbiphenyls in ancient sediments and petroleums. Organic Geochemistry, 10, pp. 841-845.

Allan, J., and Larter, S.R., 1981. Aromatic structures in coal maceral extracts and kerogens. In: Bjoroy, M. et al., (editors), Advances in Organic Geochemistry, John Wiley and Sons Ltd., New York, pp. 534-545.

Anderson, K.B., Winans, R.E., and Botto, R.E., 1992. The nature and fate of natural resins in the geosphere- II: Identification, classification and nomenclature of resinites. Organic Geochemistry, volume 18, pp. 829-841.

Chaffee, A.L., and Johns, R.B., 1983. Polycyclic aromatic hydrocarbons in Australian coals: I. Angularly fused pentacyclic tri- and tetraaromatic components of Victorian brown coal. Geochimica et Cosmochimica Acta, 47, pp. 2141-2155.

Chaffee, A.L., Strachan, M.G., and Johns, R.B., 1984. Polycyclic aromatic hydrocarbons in Australian coal: II. Novel tetracyclic components from from Victorian brown coal. Geochimica et Cosmochimica Acta, 48, pp. 2037-2043.

Cumbers, K.M., Alexander, R., and Kagi, R.I., 1986. Methylbiphenyl, ethylbiphenyl and dimethylbiphenyl isomer distributions in some sediments and crude oils. Geochimica Cosmochimica Acta, volume 51, pp. 3105-3112.

El-Gayar, M.Sh., 2005. Aromatic steroids in mideastern crude oils: Identification and geochemical application. Petroleum Science Technology, volume 23, pp. 971-990.

Garrigues, P., De Sury, R., Angelin, M.L., Bellocq, J., Oudin, J.L., and Ewald, M., 1988. Relation of methylated aromatic hydrocarbon distribution pattern to the maturity of organic matter in ancient sediments from the Mahakam Delta. Geochimica Cosmochimica Acta, volume 52, pp. 375-384.

Garrigues, P., Oudin, J.L., Parlanti, E., Monin, J.C., Robcis, S., and Bellocq, J., 1990. Akylated phenanthrene distribution in artificially matured kerogens from Kimmeridge clay and Brent Formation (North Sea). Organic Geochemistry, volume 16, pp. 167-173.

Hall, P.B., Schou, L., and Bjoroy, M., 1984. Aromatic hydrocarbon variations in North Sea Wells. In: Thomas, B.M. et al., (editors) Petroleum Geochemistry in Exploration of Norwegian Shelf, Norwegian Petroleum Society, Graham and Trotman Ltd., London, pp. 293-301.

Hegazi, A.H., and El-Gayar, M.Sh., 2009. Geochemical characterization of a biodegraded crudeoil, Assran Field, Central Gulf of Suez. Journal of Petroleum Geology, volume 32, number 4, pp. 343-355.

Hill, R.J., Jarvie, D.M., Zumberge, J., Henry, M., and Pollastro, R.M., 2007. Oil and gas geochemistry and petroleum systems of the Fort Worth Basin. American Association of Petroleum Geologist Bulletin, volume 91, number 4, pp. 445-473.

Hughes, W.B., Holba, A.G., and Dzou, L.I.P., 1995. The ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks. Geochimica Cosmochimica Acta, volume 59, pp. 3581-3598.

Johns, R.B., 1986. Biological Markers in the Sedimentary Records. Elsevier, New York, 460p.

Killops, S.D., and Killops, V.J., 2005. Introduction to organic geochemistry. 2nd Edition, Blackwell Science Publishing Limited.

Mackenzie, A.S., Hoffmann, C.F., and Maxwell, J.R., 1981. Molecular parameters of maturation in the Toarcian shales, Paris Basin, France-III: Changes in aromatic steroid hydrocarbons. Geochimica Cosmochimica Acta, volume 45, pp. 1345-1355.

Mello, M.R., Gaglianone, P.C., Brassel, S.C., and Maxwell, J.R., 1988a. Geochemical and biological marker assessment of depositional environments using Brazilian offshore oils. Marine and Petroleum Geology, volume 5, pp. 205-223.

Mello, M.R., Telnaes, N., Gaglianone, P.C., Chicarelli, M.I., Brassel, S.C., and Maxwell, J.R., 1988b. Organic geochemical characterization of depositional environments in Brazilian marginal basins. Organic Geochemistry, volume 13, pp. 31-46.

Mohammed, Y., 2005. Predictive Petroleum System Model of Prospective Anambra Basin, Nigeria.Nigerian Association of Petroleum Explorationists/American Association of Petroleum Geologists Abstracts (NAPE/AAPG) Publication, pp.70.

Moldowan, J.M., and Fago, F.J., 1986. Structure and significance of a novel rearranged monoaromatic steroid hydrocarbon in petroleum. Geochimica Cosmochimica Acta, volume 50, pp. 343-351.

Murat, R.C., 1972. Stratigraphy and palaeogeography of the Cretaceous and Lower Tertiary in southern Nigeria. In: T.F.J. Dessauvagie and A.J. Whiteman (Editors), African Geology. University of Ibadan, Nigeria, pp. 251-266.

Onuoha, M.K., 1986. Basin subsidence, sediment decomposition and burial history modeling techniques: Applicability to the Anambra Basin. Nigerian Association ofPetroleum Explorationists Bulletin, volume 2, number 1, pp. 6-17.

Peters, K.E., and Moldowan, J.M., 1993. The biomarker guide: interpreting molecular fossils in petroleum and ancient sediments. Englewood cliffs, New Jersey, Prentice Hall, 363p.

Peters, K.E., Walters, C.C., and Moldowan, J.M., 2005. The biomarker guide, 2nd edition. Cambridge University Press, New York, 1155p.

Petersen, H.I., Nytoft, H.P., Ratanasthien, B., and Foopattthanakamol, A., 2007. Oils from Cenozoic Rift-Basins in Central and Northern Thailand: Source and thermal maturity. Journal Petroleum Geology, volume 30, number 1, pp. 59-78.

Petters, S.W., 1978. Stratigraphic evolution of the Benue Trough and its implications for Upper Cretaceous paleogeography of west Africa. Journal of Geology, volume 86, pp. 311- 322.

Petters, S.W., and Ekweozor, C.M., 1982. Petroleum Geology of Benue Trough and southeastern Chad Basin, Nigeria. American Association of Petroleum Geologists Bulletin, volume 66, pp. 1141-1149.

Puttman, W., and Villar, H., 1987. Occurrence and geochemical significance of 1, 2, 5, 6- tetramethylnaphthalene.Geochimica Cosmochimica Acta, volume 51, pp. 3023-3029.

Radke, M., 1987. Organic geochemistry of aromatic hydrocarbons. In: J. Brooks and D. Welte, (editors) Advances in Petroleum Geochemistry, Academic Press, New York, pp. 141-207.

Radke, M., 1988. Application of aromatic compounds as maturity indicators in source rocks and crude oils. Marine and Petroleum Geology, volume 5, pp. 224-236.

Radke, M., and Welte, D.H., 1983. The Methylphenanthrene Index (MPI): A maturity parameterbased on aromatic hydrocarbons. In: M. Bjoroy, C. Albrecht, C. Cornford, et al., (editors), Advances in Organic Geochemistry, John Wiley and Sons, New York, pp. 504 - 512.

Radke, M., Willsch, H., and Welte, D.H., 1980. Preparative hydrocarbon group type determination by automated medium pressure liquid chromatography. Analytical Chemistry, volume 52, pp. 406-411.

Radke, M., and Welte, D.H., and Willsch, H., 1982a. Geochemical study on a well in the Western Canada Basin: relation of the aromatic distribution pattern to maturity of organic matter. Geochimica Cosmochimica Acta, volume 46, pp.1-10.

Radke, M., Willsch, H., Leythaeuser, D., and Teichmuller, M., 1982b. Aromatic components of coals: relation of distribution pattern to rank. Geochimica Cosmochimica Acta, volume 46, pp.1831-1848.

Radke, M., Willsch, H., and Welte, D.H., 1984. Class separation of aromatic compounds in rock extracts and fossil fuels by liquid chromatography. Analytical Chemistry, volume 56, pp. 2538-2546.

Radke, M., and Welte, D.H., and Willsch, H., 1986. Maturity parameters based on aromatic hydrocarbons: Influence of the organic matter type. Organic Geochemistry, volume 10, pp. 51-63.

Reyment, R.A., 1965. Aspects of geology of Nigeria. University of Ibadan press. 145p.

Rubenstein, I., Sieskind, O., and Albrecht, P., 1975. Rearranged steranes in a shale: Occurrence and simulated formation. Journal of Chemical Society, Perkin Transactions I, pp. 1833- 1836.

Rullkotter, J., Peakman, T.M., and ten Haven, H.l., 1994. Early diagenesis of terrigenous triterpenoids and its implications for petroleum geochemistry. Organic Geochemistry, volume 21, pp. 215-233.

Seifert, W.K., and Moldowan, J.M., 1978. Applications of steranes, terpanes, and monoaromatics to the maturation, migration, and source of crude oils. Geochimica et Cosmochimica Acta, volume 43, pp. 77-95.

Sieskind, O., Joly, G., and Albrecht, P., 1979. Simulation of the geochemical transformation of sterols: superacid effects of clay minerals. Geochimica Cosmochimica Acta, volume 43, pp. 1695-1659.

Simoneit, B.R.T., 1986. Cyclic terpenoids of the geosphere. In: R.B. Johns (Editors), Biological markers in the sedimentary records, Elsevier Science Publishers, Amsterdam, pp. 43-99.

Sinninghe Damste, J.S., Rijpstra, I.C., de Leeuw, J.W., and Schenck, P.A., 1988. Origin of organic sulfur compounds and sulfur-containing high molecular weight substances in sediments and immature crude oils. Organic Geochemistry, volume 13, pp. 593-606.

Sinninghe Damste, J.S., van Koert, E.R., Kock-van Dalen, A.C., de Leeuw, J.W., and Schenck, P.A, 1989a. Characterisation of highly branched isoprenoid thiophenes occurring in sediments and immature crude oils. Organic Geochemistry, volume 14, pp. 555-567.

Sinninghe Damste, J.S., Rijpstra, I.C., de Leeuw, J.W., and Schenck, P.A., 1989b. The occurrence and identification of series of organic sulfur compounds in oils and sediment extracts II: Their presence in samples from hypersaline and non-hypersalinepaleoenvironments and possible application as source, paleoenvironmental and maturity indicators. Geochimica Cosmochimica Acta, volume 53, pp. 1323-1341.

Sonibare, O.O., Adedosu, T., Ekundayo, A.O., and Jarvie, D.M., 2008. Hydrocarbon potential and organic geochemistry of coals from Benue Trough, Nigeria. Journal of Applied Sciences Research, volume 4, number11, pp. 1511-1520.

Strachan, M.G., Alexander, R., and Kagi, R.I., 1986. Trimethylnaphthalenes as depositional environmental indicators. Presented at the 192nd Annual American Chemical Society Meeting, Anaheim, California.

Strachan, M.G., Alexander, R., and Kagi, R.I., 1988. Trimethylnaphthalenes in crude oils and sediments: Effects of source and maturity. Geochimica Cosmochimica Acta, volume 52, pp. 1255-1264.

Tissot, B.P., and Welte, D.H., 1984. Petroleum Formation and occurrence. 2nd edition, Springer Verlag, Berlin, 699p.

Uzuakpunwa, A.B., 1974. The Abakaliki pyroclastics - eastern Nigeria: new age and tectonic implications. Geological Magazine, volume 111, pp. 65-70.

Van Aarssen, B.G.K., Fisher, S.J., Bastow, T.P., and Alexander, R., 1999. Distribution of methylated naphthalenes in crude oils: Indicators of maturity, biodegradation and mixing Organic Geochemistry, volume 30, pp. 1011-1021.

Villar, J.H., Puttmann, W., and Wolf, M., 1988. Organic geochemistry and petrography of Tertiary coals and carbonaceous shales from Argentina. Organic Geochemistry, volume 13, pp. 1011-1021.

Volkman, J.K., Alexander, R., Kagi, R.I., and woodhouse, G.W., 1983. Demethylated hopanes in crude oils and their applications in petroleum geochemistry. Geochimica et Cosmochimica Acta, volume 47, pp. 785-794.

Whiteman, A., 1982. Nigeria: Its petroleum geology, resources and potentials, volumes I and II. Grahamand Trotman, 394p.

References

Achari, R.G., Shaw, G., and Holleyhead, R., 1973. Identification of ionene and other carotenoid degradation products from the pyrolysis of sporopollenins derived from some pollen exines, a spore coal and the green river shale. Chemical Geology, volume 12, pp. 229-234.

Adedosu, T.A., Sonibare, O.O., Tuo, J., and Ekundayo, O., 2012. Biomarkers, carbon isotopic composition and source rock potentials of Awgu coals, middle Benue trough, Nigeria. Journal of African Earth Sciences, volumes 66-67, pp. 13-21.

Akaegbobi, I.M., Nwachukwu, J.I., and Schmitt, M., 2000. Aromatic hydrocarbon distribution and calculation of oil and gas volumes in post-Santonian shale and coal, Anambra Basin, Nigeria. In: Mello, M.R., and Katz, B.J., (eds.), Petroleum systems of south Atlantic margins. AmericanAssociation of Petroleum Geologists Memoir, volume 73, p.233-245.

Akande, S.O., Ogunmoyero, I.B., Petersen, H.I., and Nytoft, H.P., 2007. Source rock evaluation of coals from the lower Maastrichtian Mamu Foundation, SE Nigeria. Journal of Petroleum Geology, volume 30, number 4, pp. 303-324.

Akinlua, A., Torto., N., and Ajayi., T.R., 2007. Oils in the Northwestern Niger Delta: Aromatic hydrocarbons content and infrared spectroscopic characterization. Journal of Petroleum Geology, volume 30, number 1, pp. 91-100.

Akinlua, A., and Ajayi, T.R., 2009. Chemical characterization of Central Niger Delta oils. Journal of Petroleum Geology, volume 32, number 4, pp. 373-382.

Alexander, R., Kagi, R.I., Roland, S.J., Sheppard, P.N., and Chirila, T.V., 1985. The effects of thermal maturity on distributions of dimethylnaphthalenes and trimethylnaphthalenes in some ancient sediments and petroleum. Geochimica Cosmochimica Acta, 49, pp. 385-395.

Alexander, R., Cumbers, A.M., and Kagi, R.I., 1986. Alkylbiphenyls in ancient sediments and petroleums. Organic Geochemistry, 10, pp. 841-845.

Allan, J., and Larter, S.R., 1981. Aromatic structures in coal maceral extracts and kerogens. In: Bjoroy, M. et al., (editors), Advances in Organic Geochemistry, John Wiley and Sons Ltd., New York, pp. 534-545.

Anderson, K.B., Winans, R.E., and Botto, R.E., 1992. The nature and fate of natural resins in the geosphere- II: Identification, classification and nomenclature of resinites. Organic Geochemistry, volume 18, pp. 829-841.

Chaffee, A.L., and Johns, R.B., 1983. Polycyclic aromatic hydrocarbons in Australian coals: I. Angularly fused pentacyclic tri- and tetraaromatic components of Victorian brown coal. Geochimica et Cosmochimica Acta, 47, pp. 2141-2155.

Chaffee, A.L., Strachan, M.G., and Johns, R.B., 1984. Polycyclic aromatic hydrocarbons in Australian coal: II. Novel tetracyclic components from from Victorian brown coal. Geochimica et Cosmochimica Acta, 48, pp. 2037-2043.

Cumbers, K.M., Alexander, R., and Kagi, R.I., 1986. Methylbiphenyl, ethylbiphenyl and dimethylbiphenyl isomer distributions in some sediments and crude oils. Geochimica Cosmochimica Acta, volume 51, pp. 3105-3112.

El-Gayar, M.Sh., 2005. Aromatic steroids in mideastern crude oils: Identification and geochemical application. Petroleum Science Technology, volume 23, pp. 971-990.

Garrigues, P., De Sury, R., Angelin, M.L., Bellocq, J., Oudin, J.L., and Ewald, M., 1988. Relation of methylated aromatic hydrocarbon distribution pattern to the maturity of organic matter in ancient sediments from the Mahakam Delta. Geochimica Cosmochimica Acta, volume 52, pp. 375-384.

Garrigues, P., Oudin, J.L., Parlanti, E., Monin, J.C., Robcis, S., and Bellocq, J., 1990. Akylated phenanthrene distribution in artificially matured kerogens from Kimmeridge clay and Brent Formation (North Sea). Organic Geochemistry, volume 16, pp. 167-173.

Hall, P.B., Schou, L., and Bjoroy, M., 1984. Aromatic hydrocarbon variations in North Sea Wells. In: Thomas, B.M. et al., (editors) Petroleum Geochemistry in Exploration of Norwegian Shelf, Norwegian Petroleum Society, Graham and Trotman Ltd., London, pp. 293-301.

Hegazi, A.H., and El-Gayar, M.Sh., 2009. Geochemical characterization of a biodegraded crudeoil, Assran Field, Central Gulf of Suez. Journal of Petroleum Geology, volume 32, number 4, pp. 343-355.

Hill, R.J., Jarvie, D.M., Zumberge, J., Henry, M., and Pollastro, R.M., 2007. Oil and gas geochemistry and petroleum systems of the Fort Worth Basin. American Association of Petroleum Geologist Bulletin, volume 91, number 4, pp. 445-473.

Hughes, W.B., Holba, A.G., and Dzou, L.I.P., 1995. The ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks. Geochimica Cosmochimica Acta, volume 59, pp. 3581-3598.

Johns, R.B., 1986. Biological Markers in the Sedimentary Records. Elsevier, New York, 460p.

Killops, S.D., and Killops, V.J., 2005. Introduction to organic geochemistry. 2nd Edition, Blackwell Science Publishing Limited.

Mackenzie, A.S., Hoffmann, C.F., and Maxwell, J.R., 1981. Molecular parameters of maturation in the Toarcian shales, Paris Basin, France-III: Changes in aromatic steroid hydrocarbons. Geochimica Cosmochimica Acta, volume 45, pp. 1345-1355.

Mello, M.R., Gaglianone, P.C., Brassel, S.C., and Maxwell, J.R., 1988a. Geochemical and biological marker assessment of depositional environments using Brazilian offshore oils. Marine and Petroleum Geology, volume 5, pp. 205-223.

Mello, M.R., Telnaes, N., Gaglianone, P.C., Chicarelli, M.I., Brassel, S.C., and Maxwell, J.R., 1988b. Organic geochemical characterization of depositional environments in Brazilian marginal basins. Organic Geochemistry, volume 13, pp. 31-46.

Mohammed, Y., 2005. Predictive Petroleum System Model of Prospective Anambra Basin, Nigeria.Nigerian Association of Petroleum Explorationists/American Association of Petroleum Geologists Abstracts (NAPE/AAPG) Publication, pp.70.

Moldowan, J.M., and Fago, F.J., 1986. Structure and significance of a novel rearranged monoaromatic steroid hydrocarbon in petroleum. Geochimica Cosmochimica Acta, volume 50, pp. 343-351.

Murat, R.C., 1972. Stratigraphy and palaeogeography of the Cretaceous and Lower Tertiary in southern Nigeria. In: T.F.J. Dessauvagie and A.J. Whiteman (Editors), African Geology. University of Ibadan, Nigeria, pp. 251-266.

Onuoha, M.K., 1986. Basin subsidence, sediment decomposition and burial history modeling techniques: Applicability to the Anambra Basin. Nigerian Association ofPetroleum Explorationists Bulletin, volume 2, number 1, pp. 6-17.

Peters, K.E., and Moldowan, J.M., 1993. The biomarker guide: interpreting molecular fossils in petroleum and ancient sediments. Englewood cliffs, New Jersey, Prentice Hall, 363p.

Peters, K.E., Walters, C.C., and Moldowan, J.M., 2005. The biomarker guide, 2nd edition. Cambridge University Press, New York, 1155p.

Petersen, H.I., Nytoft, H.P., Ratanasthien, B., and Foopattthanakamol, A., 2007. Oils from Cenozoic Rift-Basins in Central and Northern Thailand: Source and thermal maturity. Journal Petroleum Geology, volume 30, number 1, pp. 59-78.

Petters, S.W., 1978. Stratigraphic evolution of the Benue Trough and its implications for Upper Cretaceous paleogeography of west Africa. Journal of Geology, volume 86, pp. 311- 322.

Petters, S.W., and Ekweozor, C.M., 1982. Petroleum Geology of Benue Trough and southeastern Chad Basin, Nigeria. American Association of Petroleum Geologists Bulletin, volume 66, pp. 1141-1149.

Puttman, W., and Villar, H., 1987. Occurrence and geochemical significance of 1, 2, 5, 6- tetramethylnaphthalene.Geochimica Cosmochimica Acta, volume 51, pp. 3023-3029.

Radke, M., 1987. Organic geochemistry of aromatic hydrocarbons. In: J. Brooks and D. Welte, (editors) Advances in Petroleum Geochemistry, Academic Press, New York, pp. 141-207.

Radke, M., 1988. Application of aromatic compounds as maturity indicators in source rocks and crude oils. Marine and Petroleum Geology, volume 5, pp. 224-236.

Radke, M., and Welte, D.H., 1983. The Methylphenanthrene Index (MPI): A maturity parameterbased on aromatic hydrocarbons. In: M. Bjoroy, C. Albrecht, C. Cornford, et al., (editors), Advances in Organic Geochemistry, John Wiley and Sons, New York, pp. 504 - 512.

Radke, M., Willsch, H., and Welte, D.H., 1980. Preparative hydrocarbon group type determination by automated medium pressure liquid chromatography. Analytical Chemistry, volume 52, pp. 406-411.

Radke, M., and Welte, D.H., and Willsch, H., 1982a. Geochemical study on a well in the Western Canada Basin: relation of the aromatic distribution pattern to maturity of organic matter. Geochimica Cosmochimica Acta, volume 46, pp.1-10.

Radke, M., Willsch, H., Leythaeuser, D., and Teichmuller, M., 1982b. Aromatic components of coals: relation of distribution pattern to rank. Geochimica Cosmochimica Acta, volume 46, pp.1831-1848.

Radke, M., Willsch, H., and Welte, D.H., 1984. Class separation of aromatic compounds in rock extracts and fossil fuels by liquid chromatography. Analytical Chemistry, volume 56, pp. 2538-2546.

Radke, M., and Welte, D.H., and Willsch, H., 1986. Maturity parameters based on aromatic hydrocarbons: Influence of the organic matter type. Organic Geochemistry, volume 10, pp. 51-63.

Reyment, R.A., 1965. Aspects of geology of Nigeria. University of Ibadan press. 145p.

Rubenstein, I., Sieskind, O., and Albrecht, P., 1975. Rearranged steranes in a shale: Occurrence and simulated formation. Journal of Chemical Society, Perkin Transactions I, pp. 1833- 1836.

Rullkotter, J., Peakman, T.M., and ten Haven, H.l., 1994. Early diagenesis of terrigenous triterpenoids and its implications for petroleum geochemistry. Organic Geochemistry, volume 21, pp. 215-233.

Seifert, W.K., and Moldowan, J.M., 1978. Applications of steranes, terpanes, and monoaromatics to the maturation, migration, and source of crude oils. Geochimica et Cosmochimica Acta, volume 43, pp. 77-95.

Sieskind, O., Joly, G., and Albrecht, P., 1979. Simulation of the geochemical transformation of sterols: superacid effects of clay minerals. Geochimica Cosmochimica Acta, volume 43, pp. 1695-1659.

Simoneit, B.R.T., 1986. Cyclic terpenoids of the geosphere. In: R.B. Johns (Editors), Biological markers in the sedimentary records, Elsevier Science Publishers, Amsterdam, pp. 43-99.

Sinninghe Damste, J.S., Rijpstra, I.C., de Leeuw, J.W., and Schenck, P.A., 1988. Origin of organic sulfur compounds and sulfur-containing high molecular weight substances in sediments and immature crude oils. Organic Geochemistry, volume 13, pp. 593-606.

Sinninghe Damste, J.S., van Koert, E.R., Kock-van Dalen, A.C., de Leeuw, J.W., and Schenck, P.A, 1989a. Characterisation of highly branched isoprenoid thiophenes occurring in sediments and immature crude oils. Organic Geochemistry, volume 14, pp. 555-567.

Sinninghe Damste, J.S., Rijpstra, I.C., de Leeuw, J.W., and Schenck, P.A., 1989b. The occurrence and identification of series of organic sulfur compounds in oils and sediment extracts II: Their presence in samples from hypersaline and non-hypersalinepaleoenvironments and possible application as source, paleoenvironmental and maturity indicators. Geochimica Cosmochimica Acta, volume 53, pp. 1323-1341.

Sonibare, O.O., Adedosu, T., Ekundayo, A.O., and Jarvie, D.M., 2008. Hydrocarbon potential and organic geochemistry of coals from Benue Trough, Nigeria. Journal of Applied Sciences Research, volume 4, number11, pp. 1511-1520.

Strachan, M.G., Alexander, R., and Kagi, R.I., 1986. Trimethylnaphthalenes as depositional environmental indicators. Presented at the 192nd Annual American Chemical Society Meeting, Anaheim, California.

Strachan, M.G., Alexander, R., and Kagi, R.I., 1988. Trimethylnaphthalenes in crude oils and sediments: Effects of source and maturity. Geochimica Cosmochimica Acta, volume 52, pp. 1255-1264.

Tissot, B.P., and Welte, D.H., 1984. Petroleum Formation and occurrence. 2nd edition, Springer Verlag, Berlin, 699p.

Uzuakpunwa, A.B., 1974. The Abakaliki pyroclastics - eastern Nigeria: new age and tectonic implications. Geological Magazine, volume 111, pp. 65-70.

Van Aarssen, B.G.K., Fisher, S.J., Bastow, T.P., and Alexander, R., 1999. Distribution of methylated naphthalenes in crude oils: Indicators of maturity, biodegradation and mixing Organic Geochemistry, volume 30, pp. 1011-1021.

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How to Cite

APA

Ogala, J. E. and Akaegbobi, M. I. (2014). Using aromatic biological markers as a tool for assessing thermal maturity of source rocks in the Campano-Maastrichtian Mamu Formation, southeastern Nigeria. Earth Sciences Research Journal, 18(1), 51–62. https://doi.org/10.15446/esrj.v18n1.34799

ACM

[1]
Ogala, J.E. and Akaegbobi, M.I. 2014. Using aromatic biological markers as a tool for assessing thermal maturity of source rocks in the Campano-Maastrichtian Mamu Formation, southeastern Nigeria. Earth Sciences Research Journal. 18, 1 (Jan. 2014), 51–62. DOI:https://doi.org/10.15446/esrj.v18n1.34799.

ACS

(1)
Ogala, J. E.; Akaegbobi, M. I. Using aromatic biological markers as a tool for assessing thermal maturity of source rocks in the Campano-Maastrichtian Mamu Formation, southeastern Nigeria. Earth sci. res. j. 2014, 18, 51-62.

ABNT

OGALA, J. E.; AKAEGBOBI, M. I. Using aromatic biological markers as a tool for assessing thermal maturity of source rocks in the Campano-Maastrichtian Mamu Formation, southeastern Nigeria. Earth Sciences Research Journal, [S. l.], v. 18, n. 1, p. 51–62, 2014. DOI: 10.15446/esrj.v18n1.34799. Disponível em: https://revistas.unal.edu.co/index.php/esrj/article/view/34799. Acesso em: 28 mar. 2024.

Chicago

Ogala, Jude E., and Mike I. Akaegbobi. 2014. “Using aromatic biological markers as a tool for assessing thermal maturity of source rocks in the Campano-Maastrichtian Mamu Formation, southeastern Nigeria”. Earth Sciences Research Journal 18 (1):51-62. https://doi.org/10.15446/esrj.v18n1.34799.

Harvard

Ogala, J. E. and Akaegbobi, M. I. (2014) “Using aromatic biological markers as a tool for assessing thermal maturity of source rocks in the Campano-Maastrichtian Mamu Formation, southeastern Nigeria”, Earth Sciences Research Journal, 18(1), pp. 51–62. doi: 10.15446/esrj.v18n1.34799.

IEEE

[1]
J. E. Ogala and M. I. Akaegbobi, “Using aromatic biological markers as a tool for assessing thermal maturity of source rocks in the Campano-Maastrichtian Mamu Formation, southeastern Nigeria”, Earth sci. res. j., vol. 18, no. 1, pp. 51–62, Jan. 2014.

MLA

Ogala, J. E., and M. I. Akaegbobi. “Using aromatic biological markers as a tool for assessing thermal maturity of source rocks in the Campano-Maastrichtian Mamu Formation, southeastern Nigeria”. Earth Sciences Research Journal, vol. 18, no. 1, Jan. 2014, pp. 51-62, doi:10.15446/esrj.v18n1.34799.

Turabian

Ogala, Jude E., and Mike I. Akaegbobi. “Using aromatic biological markers as a tool for assessing thermal maturity of source rocks in the Campano-Maastrichtian Mamu Formation, southeastern Nigeria”. Earth Sciences Research Journal 18, no. 1 (January 1, 2014): 51–62. Accessed March 28, 2024. https://revistas.unal.edu.co/index.php/esrj/article/view/34799.

Vancouver

1.
Ogala JE, Akaegbobi MI. Using aromatic biological markers as a tool for assessing thermal maturity of source rocks in the Campano-Maastrichtian Mamu Formation, southeastern Nigeria. Earth sci. res. j. [Internet]. 2014 Jan. 1 [cited 2024 Mar. 28];18(1):51-62. Available from: https://revistas.unal.edu.co/index.php/esrj/article/view/34799

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CrossRef citations9

1. Yanli Yang, Qiaojing Zhao. (2018). Analysis of aromatic hydrocarbon in medium- to high-sulfur coals from Fenxi, Shanxi Province. World Journal of Engineering, 15(6), p.786. https://doi.org/10.1108/WJE-07-2017-0179.

2. Jude Etunimonuwa Ogala. (2022). Depositional conditions of the Upper Cretaceous shales from the Anambra Basin, SE Nigeria: Constraints from mineralogy and geochemistry. Journal of African Earth Sciences, 196, p.104670. https://doi.org/10.1016/j.jafrearsci.2022.104670.

3. Selin Karadirek. (2023). Paleoenvironmental Settings of the Soma Coal Basin (Turkey): Insights from Maceral Data, Biomarker, and Carbon Isotopic Composition. ACS Omega, 8(50), p.47974. https://doi.org/10.1021/acsomega.3c06635.

4. Ruwei Wang, Ruoyu Sun, Guijian Liu, Balal Yousaf, Dun Wu, Jian Chen, Hong Zhang. (2017). A review of the biogeochemical controls on the occurrence and distribution of polycyclic aromatic compounds (PACs) in coals. Earth-Science Reviews, 171, p.400. https://doi.org/10.1016/j.earscirev.2017.06.011.

5. A. R. Akhmedova, O. V. Serebrennikova, O. V. Shiganova. (2023). Saturated and Aromatic Hydrocarbons Biomarkers in Crude Oil and Bitumens from Kugas 364-0 Parametric Well (Sakha (Yakutia) Republic, Russia). Petroleum Chemistry, 63(1), p.82. https://doi.org/10.1134/S0965544123020056.

6. Gbenga O. Ogungbesan, Taofik A. Adedosu. (2020). Geochemical record for the depositional condition and petroleum potential of the Late Cretaceous Mamu Formation in the western flank of Anambra Basin, Nigeria. Green Energy & Environment, 5(1), p.83. https://doi.org/10.1016/j.gee.2019.01.008.

7. Rajaa Bouamoud, Raphael Mulongo-Masamba, Adnane El Hamidi, Mohammed Halim, Said Arsalane. (2022). Structural assessments of kerogen-rich oil shale from the Central Kongo formation by solid-state 13C nuclear magnetic resonance and thermal processes. Journal of Thermal Analysis and Calorimetry, 147(4), p.3483. https://doi.org/10.1007/s10973-021-10699-1.

8. Lua Morena Leoncio de Oliveira, Diego Nery do Amaral, Kalil Lopes de Amorim Ferreira, Carolina Santiago Souza, Gisele Mara Hadlich, Maria Elisabete Machado. (2023). Polycyclic aromatic sulfur heterocycles used as molecular markers in crude oils and source rocks. Organic Geochemistry, 178, p.104571. https://doi.org/10.1016/j.orggeochem.2023.104571.

9. Jude Etunimonuwa Ogala, Stavros Kalaitzidis, Kimon Christanis, Omoleomo Olutoyin Omo-Irabor, Adewale Akinmosin, Caleb Ugbede Yusuf, Nikos Pasadakis, Miltiadis Constantinopoulos, Helen Papaefthymiou. (2019). Geochemical and organic petrological study of bituminous sediments from Dahomey Basin, SW Nigeria. Marine and Petroleum Geology, 99, p.577. https://doi.org/10.1016/j.marpetgeo.2018.10.033.

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