River deltas, low-lying landforms that host critical economic infrastructures and diverse ecosyst... more River deltas, low-lying landforms that host critical economic infrastructures and diverse ecosystems as well as high concentrations of human population, are highly vulnerable to the effects of global climate change. In order to understand the wave climate, their potential changes and implication on coastline evolution for environment monitoring and sustainable management of the Niger Delta in the Gulf of Guinea, an investigation was carried out based on offshore wave statistics of an 110-year time series (1900–2010) dataset obtained from the ECMWF ERA-20C atmospheric reanalysis. Results of multivariate regression analyses indicate that interannu-al mean values of Hs and Tm trends tended to increase over time, especially in the western part of the delta coast, so that they are presently (1980 and 2010) up to 264 mm (300%) and 0.32 s (22%), respectively, higher than 80 years (1900–1930) ago. The maximum directions of the wave have become more westerly (southward) than southerly (westward) by up to 2° (33%) and the mean longshore sediment transport rate has increased by more than 8% over the last 80 years. The linear regression analysis for shoreline changes from 1987 to 2013 shows an erosional trend at the western part of the delta and accretional trends towards eastern part. The relationship between wave climate of the study area and atmospheric circulation using Pearson's correlation shows that the Atlantic Multidecadal Oscillation (AMO), North Atlantic Oscillation (NAO), East Atlantic pattern (EA) and El-Nino/Southern Oscillation (ENSO) Index explain significant proportion of the seasonal and annual wave variabilities compared to other indices. But it is most likely that the combination of these climatic indices acting together or separately constitutes a powerful and effective mechanism responsible for much of the variability of the offshore Niger Delta wave climate. The study concludes that changing wave climate off the Niger Delta has strong implications on the delta coastline changes. However, other processes (such as fluvial discharge variability due climatic variability and anthropogenic effect) may be acting concomitantly with changes in wave regime and associated littoral transport to influence shoreline evolution along the Niger Delta coast.
The Toro symmetrical complex is localized within the Precambrian Basement Complex of the north ce... more The Toro symmetrical complex is localized within the Precambrian Basement Complex of the north central Nigeria. The complex is composed of three granites types surrounding an orthoenstantite dioritic core. Amphiboles samples from the diorite have higher Mg/ (Mg+Fe) values and are richer in Si, Ti and poorer in Al and Na+K than those in the granites. The calculated P-T results show that diorite crystallized at pressures between 4.7 kbar and 5.4 kbar and temperatures of 796°C to 821°C. The hornblende-biotite granite crystallized at pressures between 5.8 kbar to 8.5 kbar and temperatures between 633°C to 771°C. The average pressure (5.1 kbar ) for dioritic amphibole corresponds approximately to 19 km in depth of emplacement for the diorite and 24km in depth of emplacement for both hornblende-biotite (average pressure = 6.5 kbar) and porphyritic hornblende-biotite granites (average pressure = 6.4 kbar). Nature of dioritic amphibole evolution, coupled with its P-T suggests that the Toro ...
Deltaic coasts are dynamic geomorphic systems where continuous changes occur on diverse spatial a... more Deltaic coasts are dynamic geomorphic systems where continuous changes occur on diverse spatial and temporal scales, and these changes constitute an important aspect of their evolution. Based on three-year satellite-derived shoreline data coupled with re-analyzed wave data and hydro-meteorological data, a comprehensive analysis of the dominant processes governing the seasonal shoreline changes along the oil-rich arcuate section of the Niger Delta, in the Nigerian Shelf of the North Atlantic Ocean has been undertaken. Shoreline analysis results show that the delta coast is characterized by predominant summer erosion and maximum winter accretion. Between 2010 and 2012, erosion dominated over accretion and a total of 9.1 km2 deltaic land was lost to coastline erosion at an annual average erosion rate of 4.55 ± 1.21 km2/yr. A greater understanding of the dominant factors responsible for the change is presented. Shoreline change interactions with cross-shore sediment exchange processes are prominent at seasonal timescale (Summer R2 = -0.85 and Winter R2 = 0.7), and interannual timescale (R2 = -0.93) with longshore sediment transport processes. Correlation analysis reveals a gradual degeneration of relationship between the suspended sediment flux and coastal hydrodynamics beginning from 2010 to 2012 (cross-shore transport, R = 0.68, 0.36 and 0.2 for 2010, 2011 and 2012, respectively; longshore transport R = 0.63, 0.44 and 0.2 for 2010, 2011 and 2012, respectively). The study concludes that the effect of fluvial sediment reduction to the delta coast due to capital dredging of the Lower Niger River channels between 2009 and 2012, and periodic fluctuations in the nearshore hydrodynamics processes caused the observed annual shoreline erosion that eventually forced the deltaic coastline toward a state of landward migration during the study period.
There is growing evidence that the world river deltas are influenced by climate change and anthro... more There is growing evidence that the world river deltas are influenced by climate change and anthropogenic activities. In this study, shoreline changes along the Niger Delta coast of the Gulf of Guinea, North Atlantic Ocean in the last ten decades were investigated. The relationships between these changes and hydrometeorologic variables of rainfall and river discharge were considered. Topographic maps and satellite imagery, in addition to rainfall and hydrological data from the lower Niger River basin, were used for the study.
The results show two distinct shoreline dynamics patterns/phases: first, mobility with high net retreat between 1923 and 1987 interval and; second, mobility with low net progradation from 1987 to 2013. During the first phase, shoreline retreat is mainly concentrated on the western and arcuate sections of the delta. In the second phase, all sections of the Niger Delta coast prograded seaward.
Strong correlations between: shoreline change and the river discharge (R2 = 0.95), shoreline change and rainfall variability (R2 = 0.8), and rainfall variability and river discharge (R2 = 0.63) further confirm that shoreline changes of the delta during the last 100 years have been influenced by the variations in river discharge and rainfall, which are ultimately driven by climate change. It is therefore concluded that shoreline changes during the last 100 years along the Niger Delta coast have been influenced by rainfall variability and the resultant river discharge variations, which are ultimately driven by the regional climate change.
The compositional systematics of biotites from diorites of Toro and Dass, north Central Nigeria h... more The compositional systematics of biotites from diorites of Toro and Dass, north Central Nigeria have been examined for the purpose of describing the nature of the granitic magma. Based on chemistry of biotites, Toro and Dass diorites are formed from the transition between peraluminous and calc-alkaline magmas. This type of magma is typically produced in subduction environments. It means that the diorites could have formed in an orogenic suit from calc-alkaline magma derived from melting in a subduction zone slab. There is little evidence of either magma mixing or large-scale crustal contamination.
The petrographic studies of the representative samples of diorite from Toro show biotite replacing pyroxenes, which necessarily produce a biotite-pyroxene-plagioclase paragenesis from pre-existing assemblage. The Dass diorite samples show biotite overgrowing amphiboles and also replacement of biotite by chlorite.
International Journal of Basic and Applied Chemical Sciences , Sep 30, 2012
Amphibole compositions of the charnockites from Bauchi and Saminaka, North-central Nigeria have b... more Amphibole compositions of the charnockites from Bauchi and Saminaka, North-central Nigeria have been
studied by electron probe micro analysis. Generally, the amphiboles are all calcic, silica and magnesia poor, ferroan rich weakly titaniferous and have most of their aluminum in tetrahedral site. Si contents average 6.35 apfu (Bauchi) and 6.42 apfu (Saminaka). Ca is always above 1.7 apfu for both areas. NaA is always > Na M4. K2O contents are high. All samples exhibit low AlVI and high AlIV contents equate to more than 90% of Al to the tetrahedrical site. TiO2 contents average 1.60% (Bauchi) and 1.65% (Saminaka). FeOT contents are high. Most of the amphiboles are characterized by low Fe3+ and high Fe2+ contents. Xmg ratio varies between 0.18 and 0.64 (Bauchi) and 0.26 to 0.37 (Saminaka). They may be divided into two sub-groups: On the one hand the magnesio-hastingsite - hastingsite and pargasite group and on the other hand the tschermakite group. The amphiboles from Bauchi and Saminaka charnockites plot in the igneous field of the diagram. From thermobarometric investigations, Amphiboles in the
charnockites solidified between 4.4 to 7.2 kbar (Bauchi) and 5.3 to 5.6 kbar as estimated by its Al contents, while temperature of crystallization range from 826º to 599º C (Bauchi) and 826º to 650º C (Saminaka). Nevertheless, Bauchi charnockite’s amphibole-core temperatures decrease continuously from
826º C for hastingsite to magnesio-hornblende 599º C. These conditions correspond to a shallow crustal chamber (15-20 km depth).
International Journal of Geology, Earth and Environmental Sciences, Sep 30, 2012
Biotites from the charnockites of Bauchi and Saminaka in the Basement Complex of north central Ni... more Biotites from the charnockites of Bauchi and Saminaka in the Basement Complex of north central Nigeria have been examined. The microprobe data of the analyzed biotites are presented. The behavior of major elements in the examined biotites is discussed according to different discrimination models. Based on the geochemical and petrographical characteristics of the biotites analyzed, the biotite of Bauchi charnockite is transitional in nature and may have been associated with magmas having physicochemical properties between calc-alkaline and peraluminous series while those of Saminaka charnockite is peraluminous in nature. This may have resulted from either magma differentiation by mixing or large-scale crustal contamination.
River deltas, low-lying landforms that host critical economic infrastructures and diverse ecosyst... more River deltas, low-lying landforms that host critical economic infrastructures and diverse ecosystems as well as high concentrations of human population, are highly vulnerable to the effects of global climate change. In order to understand the wave climate, their potential changes and implication on coastline evolution for environment monitoring and sustainable management of the Niger Delta in the Gulf of Guinea, an investigation was carried out based on offshore wave statistics of an 110-year time series (1900–2010) dataset obtained from the ECMWF ERA-20C atmospheric reanalysis. Results of multivariate regression analyses indicate that interannu-al mean values of Hs and Tm trends tended to increase over time, especially in the western part of the delta coast, so that they are presently (1980 and 2010) up to 264 mm (300%) and 0.32 s (22%), respectively, higher than 80 years (1900–1930) ago. The maximum directions of the wave have become more westerly (southward) than southerly (westward) by up to 2° (33%) and the mean longshore sediment transport rate has increased by more than 8% over the last 80 years. The linear regression analysis for shoreline changes from 1987 to 2013 shows an erosional trend at the western part of the delta and accretional trends towards eastern part. The relationship between wave climate of the study area and atmospheric circulation using Pearson's correlation shows that the Atlantic Multidecadal Oscillation (AMO), North Atlantic Oscillation (NAO), East Atlantic pattern (EA) and El-Nino/Southern Oscillation (ENSO) Index explain significant proportion of the seasonal and annual wave variabilities compared to other indices. But it is most likely that the combination of these climatic indices acting together or separately constitutes a powerful and effective mechanism responsible for much of the variability of the offshore Niger Delta wave climate. The study concludes that changing wave climate off the Niger Delta has strong implications on the delta coastline changes. However, other processes (such as fluvial discharge variability due climatic variability and anthropogenic effect) may be acting concomitantly with changes in wave regime and associated littoral transport to influence shoreline evolution along the Niger Delta coast.
The Toro symmetrical complex is localized within the Precambrian Basement Complex of the north ce... more The Toro symmetrical complex is localized within the Precambrian Basement Complex of the north central Nigeria. The complex is composed of three granites types surrounding an orthoenstantite dioritic core. Amphiboles samples from the diorite have higher Mg/ (Mg+Fe) values and are richer in Si, Ti and poorer in Al and Na+K than those in the granites. The calculated P-T results show that diorite crystallized at pressures between 4.7 kbar and 5.4 kbar and temperatures of 796°C to 821°C. The hornblende-biotite granite crystallized at pressures between 5.8 kbar to 8.5 kbar and temperatures between 633°C to 771°C. The average pressure (5.1 kbar ) for dioritic amphibole corresponds approximately to 19 km in depth of emplacement for the diorite and 24km in depth of emplacement for both hornblende-biotite (average pressure = 6.5 kbar) and porphyritic hornblende-biotite granites (average pressure = 6.4 kbar). Nature of dioritic amphibole evolution, coupled with its P-T suggests that the Toro ...
Deltaic coasts are dynamic geomorphic systems where continuous changes occur on diverse spatial a... more Deltaic coasts are dynamic geomorphic systems where continuous changes occur on diverse spatial and temporal scales, and these changes constitute an important aspect of their evolution. Based on three-year satellite-derived shoreline data coupled with re-analyzed wave data and hydro-meteorological data, a comprehensive analysis of the dominant processes governing the seasonal shoreline changes along the oil-rich arcuate section of the Niger Delta, in the Nigerian Shelf of the North Atlantic Ocean has been undertaken. Shoreline analysis results show that the delta coast is characterized by predominant summer erosion and maximum winter accretion. Between 2010 and 2012, erosion dominated over accretion and a total of 9.1 km2 deltaic land was lost to coastline erosion at an annual average erosion rate of 4.55 ± 1.21 km2/yr. A greater understanding of the dominant factors responsible for the change is presented. Shoreline change interactions with cross-shore sediment exchange processes are prominent at seasonal timescale (Summer R2 = -0.85 and Winter R2 = 0.7), and interannual timescale (R2 = -0.93) with longshore sediment transport processes. Correlation analysis reveals a gradual degeneration of relationship between the suspended sediment flux and coastal hydrodynamics beginning from 2010 to 2012 (cross-shore transport, R = 0.68, 0.36 and 0.2 for 2010, 2011 and 2012, respectively; longshore transport R = 0.63, 0.44 and 0.2 for 2010, 2011 and 2012, respectively). The study concludes that the effect of fluvial sediment reduction to the delta coast due to capital dredging of the Lower Niger River channels between 2009 and 2012, and periodic fluctuations in the nearshore hydrodynamics processes caused the observed annual shoreline erosion that eventually forced the deltaic coastline toward a state of landward migration during the study period.
There is growing evidence that the world river deltas are influenced by climate change and anthro... more There is growing evidence that the world river deltas are influenced by climate change and anthropogenic activities. In this study, shoreline changes along the Niger Delta coast of the Gulf of Guinea, North Atlantic Ocean in the last ten decades were investigated. The relationships between these changes and hydrometeorologic variables of rainfall and river discharge were considered. Topographic maps and satellite imagery, in addition to rainfall and hydrological data from the lower Niger River basin, were used for the study.
The results show two distinct shoreline dynamics patterns/phases: first, mobility with high net retreat between 1923 and 1987 interval and; second, mobility with low net progradation from 1987 to 2013. During the first phase, shoreline retreat is mainly concentrated on the western and arcuate sections of the delta. In the second phase, all sections of the Niger Delta coast prograded seaward.
Strong correlations between: shoreline change and the river discharge (R2 = 0.95), shoreline change and rainfall variability (R2 = 0.8), and rainfall variability and river discharge (R2 = 0.63) further confirm that shoreline changes of the delta during the last 100 years have been influenced by the variations in river discharge and rainfall, which are ultimately driven by climate change. It is therefore concluded that shoreline changes during the last 100 years along the Niger Delta coast have been influenced by rainfall variability and the resultant river discharge variations, which are ultimately driven by the regional climate change.
The compositional systematics of biotites from diorites of Toro and Dass, north Central Nigeria h... more The compositional systematics of biotites from diorites of Toro and Dass, north Central Nigeria have been examined for the purpose of describing the nature of the granitic magma. Based on chemistry of biotites, Toro and Dass diorites are formed from the transition between peraluminous and calc-alkaline magmas. This type of magma is typically produced in subduction environments. It means that the diorites could have formed in an orogenic suit from calc-alkaline magma derived from melting in a subduction zone slab. There is little evidence of either magma mixing or large-scale crustal contamination.
The petrographic studies of the representative samples of diorite from Toro show biotite replacing pyroxenes, which necessarily produce a biotite-pyroxene-plagioclase paragenesis from pre-existing assemblage. The Dass diorite samples show biotite overgrowing amphiboles and also replacement of biotite by chlorite.
International Journal of Basic and Applied Chemical Sciences , Sep 30, 2012
Amphibole compositions of the charnockites from Bauchi and Saminaka, North-central Nigeria have b... more Amphibole compositions of the charnockites from Bauchi and Saminaka, North-central Nigeria have been
studied by electron probe micro analysis. Generally, the amphiboles are all calcic, silica and magnesia poor, ferroan rich weakly titaniferous and have most of their aluminum in tetrahedral site. Si contents average 6.35 apfu (Bauchi) and 6.42 apfu (Saminaka). Ca is always above 1.7 apfu for both areas. NaA is always > Na M4. K2O contents are high. All samples exhibit low AlVI and high AlIV contents equate to more than 90% of Al to the tetrahedrical site. TiO2 contents average 1.60% (Bauchi) and 1.65% (Saminaka). FeOT contents are high. Most of the amphiboles are characterized by low Fe3+ and high Fe2+ contents. Xmg ratio varies between 0.18 and 0.64 (Bauchi) and 0.26 to 0.37 (Saminaka). They may be divided into two sub-groups: On the one hand the magnesio-hastingsite - hastingsite and pargasite group and on the other hand the tschermakite group. The amphiboles from Bauchi and Saminaka charnockites plot in the igneous field of the diagram. From thermobarometric investigations, Amphiboles in the
charnockites solidified between 4.4 to 7.2 kbar (Bauchi) and 5.3 to 5.6 kbar as estimated by its Al contents, while temperature of crystallization range from 826º to 599º C (Bauchi) and 826º to 650º C (Saminaka). Nevertheless, Bauchi charnockite’s amphibole-core temperatures decrease continuously from
826º C for hastingsite to magnesio-hornblende 599º C. These conditions correspond to a shallow crustal chamber (15-20 km depth).
International Journal of Geology, Earth and Environmental Sciences, Sep 30, 2012
Biotites from the charnockites of Bauchi and Saminaka in the Basement Complex of north central Ni... more Biotites from the charnockites of Bauchi and Saminaka in the Basement Complex of north central Nigeria have been examined. The microprobe data of the analyzed biotites are presented. The behavior of major elements in the examined biotites is discussed according to different discrimination models. Based on the geochemical and petrographical characteristics of the biotites analyzed, the biotite of Bauchi charnockite is transitional in nature and may have been associated with magmas having physicochemical properties between calc-alkaline and peraluminous series while those of Saminaka charnockite is peraluminous in nature. This may have resulted from either magma differentiation by mixing or large-scale crustal contamination.
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The results show two distinct shoreline dynamics patterns/phases: first, mobility with high net retreat between 1923 and 1987 interval and; second, mobility with low net progradation from 1987 to 2013. During the first phase, shoreline retreat is mainly concentrated on the western and arcuate sections of the delta. In the second phase, all sections of the Niger Delta coast prograded seaward.
Strong correlations between: shoreline change and the river discharge (R2 = 0.95), shoreline change and rainfall variability (R2 = 0.8), and rainfall variability and river discharge (R2 = 0.63) further confirm that shoreline changes of the delta during the last 100 years have been influenced by the variations in river discharge and rainfall, which are ultimately driven by climate change. It is therefore concluded that shoreline changes during the last 100 years along the Niger Delta coast have been influenced by rainfall variability and the resultant river discharge variations, which are ultimately driven by the regional climate change.
The petrographic studies of the representative samples of diorite from Toro show biotite replacing pyroxenes, which necessarily produce a biotite-pyroxene-plagioclase paragenesis from pre-existing assemblage. The Dass diorite samples show biotite overgrowing amphiboles and also replacement of biotite by chlorite.
studied by electron probe micro analysis. Generally, the amphiboles are all calcic, silica and magnesia poor, ferroan rich weakly titaniferous and have most of their aluminum in tetrahedral site. Si contents average 6.35 apfu (Bauchi) and 6.42 apfu (Saminaka). Ca is always above 1.7 apfu for both areas. NaA is always > Na M4. K2O contents are high. All samples exhibit low AlVI and high AlIV contents equate to more than 90% of Al to the tetrahedrical site. TiO2 contents average 1.60% (Bauchi) and 1.65% (Saminaka). FeOT contents are high. Most of the amphiboles are characterized by low Fe3+ and high Fe2+ contents. Xmg ratio varies between 0.18 and 0.64 (Bauchi) and 0.26 to 0.37 (Saminaka). They may be divided into two sub-groups: On the one hand the magnesio-hastingsite - hastingsite and pargasite group and on the other hand the tschermakite group. The amphiboles from Bauchi and Saminaka charnockites plot in the igneous field of the diagram. From thermobarometric investigations, Amphiboles in the
charnockites solidified between 4.4 to 7.2 kbar (Bauchi) and 5.3 to 5.6 kbar as estimated by its Al contents, while temperature of crystallization range from 826º to 599º C (Bauchi) and 826º to 650º C (Saminaka). Nevertheless, Bauchi charnockite’s amphibole-core temperatures decrease continuously from
826º C for hastingsite to magnesio-hornblende 599º C. These conditions correspond to a shallow crustal chamber (15-20 km depth).
The results show two distinct shoreline dynamics patterns/phases: first, mobility with high net retreat between 1923 and 1987 interval and; second, mobility with low net progradation from 1987 to 2013. During the first phase, shoreline retreat is mainly concentrated on the western and arcuate sections of the delta. In the second phase, all sections of the Niger Delta coast prograded seaward.
Strong correlations between: shoreline change and the river discharge (R2 = 0.95), shoreline change and rainfall variability (R2 = 0.8), and rainfall variability and river discharge (R2 = 0.63) further confirm that shoreline changes of the delta during the last 100 years have been influenced by the variations in river discharge and rainfall, which are ultimately driven by climate change. It is therefore concluded that shoreline changes during the last 100 years along the Niger Delta coast have been influenced by rainfall variability and the resultant river discharge variations, which are ultimately driven by the regional climate change.
The petrographic studies of the representative samples of diorite from Toro show biotite replacing pyroxenes, which necessarily produce a biotite-pyroxene-plagioclase paragenesis from pre-existing assemblage. The Dass diorite samples show biotite overgrowing amphiboles and also replacement of biotite by chlorite.
studied by electron probe micro analysis. Generally, the amphiboles are all calcic, silica and magnesia poor, ferroan rich weakly titaniferous and have most of their aluminum in tetrahedral site. Si contents average 6.35 apfu (Bauchi) and 6.42 apfu (Saminaka). Ca is always above 1.7 apfu for both areas. NaA is always > Na M4. K2O contents are high. All samples exhibit low AlVI and high AlIV contents equate to more than 90% of Al to the tetrahedrical site. TiO2 contents average 1.60% (Bauchi) and 1.65% (Saminaka). FeOT contents are high. Most of the amphiboles are characterized by low Fe3+ and high Fe2+ contents. Xmg ratio varies between 0.18 and 0.64 (Bauchi) and 0.26 to 0.37 (Saminaka). They may be divided into two sub-groups: On the one hand the magnesio-hastingsite - hastingsite and pargasite group and on the other hand the tschermakite group. The amphiboles from Bauchi and Saminaka charnockites plot in the igneous field of the diagram. From thermobarometric investigations, Amphiboles in the
charnockites solidified between 4.4 to 7.2 kbar (Bauchi) and 5.3 to 5.6 kbar as estimated by its Al contents, while temperature of crystallization range from 826º to 599º C (Bauchi) and 826º to 650º C (Saminaka). Nevertheless, Bauchi charnockite’s amphibole-core temperatures decrease continuously from
826º C for hastingsite to magnesio-hornblende 599º C. These conditions correspond to a shallow crustal chamber (15-20 km depth).