Zugl.: Stuttgart, Univ., Diss., 2008.

Der Klimawandel und insbesondere die globale Erwärmung gehören aktuell zu den größten Herausforderungen an Politik und Wissenschaft. Steigende CO2-Emissionen sind hierbei maßgeblich für die Klimaerwärmung verantwortlich. Ein regulierender Faktor beim CO2-Austausch mit der Atmosphäre ist die Vegetation, welche als CO2-Senke aber auch als CO2-Quelle fungieren kann. Diese Funktionen können durch Analysen der Landbedeckungsänderung in Kombination mit Modellierungen der Kohlenstoffbilanz quantifiziert werden, was insbesondere von aktuellen und zukünftigen politischen Instrumenten wie CDM (Clean Development Mechanism) oder REDD (Reducing Emissions from Deforestation and Degradation) gefordert wird. Vor allem in Regionen mit starker Landbedeckungsänderung und hoher Bevölkerungsdichte sowie bei geringem Wissen über die Produktivität und CO2-Speicherpotentiale der Vegetation, bedarf es einer Erforschung und Quantifizierung der terrestrischen Kohlenstoffspeicher. Eine Region, für die dies in besonderem Maße zutrifft, ist Westafrika. Jüngste Studien haben gezeigt, dass sich einerseits die Folgen des Klimawandels und Umweltveränderungen sehr stark in Westafrika auswirken werden und andererseits Bevölkerungswachstum eine starke Änderung der Landbedeckung für die Nutzung als agrarische Fläche bewirkt hat. Folglich sind in dieser Region die terrestrischen Kohlenstoffspeicher durch Ausdehnung der Landwirtschaft und Waldrodung besonders gefährdet. Große Flächen agieren anstelle ihrer ursprünglichen Funktion als CO2-Senke bereits als CO2-Quelle. [...] / Global warming associated with climate change is one of the greatest challenges of today's world. One regulating factor of CO2 exchange with the atmosphere is the vegetation cover. Measurements of land cover changes in combination with modeling of the carbon balance can therefore contribute to determining temporal variations of CO2 sources and sinks, which is an essential necessity of existing and prospective political instruments like CDM (Clean Development Mechanism) or REDD (Reducing Emissions from Deforestation and Degradation). The need for quantifiable terrestrial carbon stocks is especially high for regions, where rates of land cover transformation and population density are high and knowledge on vegetation productivity is low. One region which is characterized by these criteria is West Africa. Therefore, carbon stocks in this region are seriously endangered by land cover change like the expansion of agriculture and forest logging. Large areas already act as carbon sources on a yearly basis instead of their previous function as carbon sink. Since only a few studies have analyzed the terrestrial carbon stocks in Africa and especially regional analysis in West Africa are missing, the following study focuses on regional scale modeling of the actual terrestrial carbon stocks. Additionally, the potential carbon stocks of unmanaged land cover and the potential for CO2 payments have been analyzed in this work. To quantify and assess carbon fluxes as well as the loss of carbon, net primary productivity of vegetation has been modeled, based on the plants characteristics to fix carbon from the atmosphere during photosynthesis. Modeling vegetation dynamics and net primary productivity has been realized by using MODIS 250m time series for semi-humid and semi-arid savanna ecosystems in West Africa. This study aimed to quantify CO2 exchanges of the Savanna regions in the Volta basin by applying and adapting the Regional Biomass Model (RBM). The RBM was developed by Jochen Richters (2005) at a resolution of 1000m for the Namibian Kaokoveld. In this study the model was optimized to the scale of 232m to consider the heterogeneous landscape in West Africa (RBM+). New input parameters with higher accuracies and resolution were generated instead of using the global standard products. The most important parameters for the modeling are FPAR and the fractional cover of herbaceous and woody vegetation. To enhance the MODIS FPAR product, linear interpolation and downscaling algorithms were applied. The main objective of the downscaling is a better representation of the finely scattered vegetation by the 232m resolution FPAR. The second optimized parameter, the fractional cover of herbaceous and woody vegetation was represented by the Vegetation Continuous Fields product (VCF) from MODIS in the originally version of the RBM. This global product reflects the vegetation structure of West Africa poorly, since few high resolution training data is available for this region, and the dynamic savanna vegetation can hardly be classified by not regionally adapted methods. Additionally, the data is only available with 500m resolution. Therefore, in this study a new product with 232m resolution was developed which represents the spatial heterogeneity well and, due to the regional adaptation, shows higher accuracies. The percentage cover of woody and herbaceous vegetation and bare soil on 232m MODIS data was calculated in a multi scale approach. Based on very high resolution data, represented by Quickbird and Ikonos with 0.6-4m resolution, and high resolution data from Landsat with 30m resolution, the percentage coverage was estimated for representative focus regions. These classifications were used as a training data set to determine the percentage coverage on the 232m scale with MODIS time series for the whole study region. Based on these optimized and adapted input parameters, the net primary productivity was modeled. Data from a meteorological station and an Eddy-Covariance-Flux allowed a detailed validation of the input parameters and of the model results. The model led to good results as it only overestimated the net primary productivity for the two analyzed years 2005 and 2006 by 8.8 and 2.0 %, respectively. The second aim of the study was an analysis of the potential for long term terrestrial carbon sinks. Classifications of the actual and of the potential land cover were calculated for this analysis. Considering the overall long time CO2 fixation behavior of trees, which depends on their age, longterm carbon stocks for 100 years were simulated. As carbon fixing could be paid by emission trading, which is in future depending on the political Post-Kyoto programs, potential alternative income was calculated with different price scenarios for the three countries. A comparison with the gross domestic products of these countries and with developing aid, showed the significance of CO2 trading in this region.

Univ., Diss.--Bonn, 2004.

Univ., Diss.--Bonn, 2004.

Zugl.: Bonn, University, Diss., 2004.

Within the framework of this research, the complex geological history of the Pan African-Volta basin has been systematically reconstructed. Based on a broad review of literature and new data, 5 stages of geological-tectonic development have been identified. For the first time a systematic review of the mineral potential of the Pan-African Volta Basin was executed. Known and potentially existing mineralization have been related to the geotectonic history and metallogenetic conclusions have been drawn. Based on the findings of this research, the folded thrust belt located at the eastern rim of the Volta basin has been identified as the most prospective area for the ultramafic rocks with chromite, nickel mineralization and PGEs, hydrothermal gold and banded iron formation (BIF) but this will require further work.

Within the framework of this research, the complex geological history of the Pan African-Volta basin has been systematically reconstructed. Based on a broad review of literature and new data, 5 stages of geological-tectonic development have been identified. For the first time a systematic review of the mineral potential of the Pan-African Volta Basin was executed. Known and potentially existing mineralization have been related to the geotectonic history and metallogenetic conclusions have been drawn. Based on the findings of this research, the folded thrust belt located at the eastern rim of the Volta basin has been identified as the most prospective area for the ultramafic rocks with chromite, nickel mineralization and PGEs, hydrothermal gold and banded iron formation (BIF) but this will require further work.:Table of contents Table of contents iii List of tables v List of figures 1 Introduction 5 Summary of work done 6 Acknowledgements 6 1 In the Geology and regional geotectonic development of the West African Shield 7 1.1 Introduction 7 1.2 The basement of the Proterozoic sedimentary platform cover 9 1.3 Connection of West African Shield to Brazil 10 1.4 The Neoproterozoic sedimentary sequence and the extent of the Volta Basin 13 1.4.1 Introduction 13 1.4.2 The Neoproterozoic Sedimentary Sequence 15 1.5 The Pan-African Mobile Belt 23 1.5.1 The Buem Fold and thrust belt 23 1.5.2 New defined units 30 1.6 Interpretation of the deep structure of the Volta Basin 35 1.7 Metallic Minerals 37 1.7.1 Introduction 37 1.7.2 Iron (Fe) 39 1.7.3 Aluminium (Al) 46 1.7.4 Manganese (Mn) 50 1.7.5 Lead (Pb) 52 1.7.6 Copper (Cu) 55 1.7.7 Mineralisation related to ultramafic rocks 57 1.7.8 Gold (Au) 69 1.7.9 Tantalum (Ta) 72 1.7.10 Zirconium (Zr) 73 1.7.11 Heavy minerals in sands of Paleochannels 76 1.8 Non-metallic minerals 83 1.8.1 Introduction 83 1.8.2 Limestone (CaCO3) 84 1.8.3 Magnesite (MgCO3) 91 1.8.4 Barite (BaSO4) 93 1.8.5 Diamonds 97 1.8.6 Bitumen 100 1.9 Mineral Prediction with advangeo® Prediction Software 102 2 Minerogeny 109 2.1 Mineralisation controls and indicators 109 2.1.1 Geochemical Properties of selected stratigraphic units 109 2.1.2 Intrusive rocks 114 2.1.3 Volcanic rocks 118 2.1.4 Fault structural controls 119 2.1.5 Reactive Rocks 121 2.1.6 Other sedimentary controls: placers and paleoplacers 122 2.1.7 Laterites 122 2.1.8 Control of diamond occurrences 132 2.2 Key stages of metallogenic development 132 3 Discussion and recommendations 136 3.1 Recommendations 138 4 List of References 139 5 Appendices 144 5.1.1 Sample G113RK1 144 5.1.2 Sample G109RK1 145 5.1.3 Sample G116RK1 147 5.1.4 Sample G121RK1 149 5.1.5 Sample G121RK2 151 5.1.6 Sample G121RK3 152 5.1.7 Sample G131RK1 154 5.1.8 Sample G144RK2 155 5.1.9 Sample G145RK1 156 5.1.10 Sample G147RK1 157 5.2 Thin Sections 159 5.3 Deep drilling Data 174 5.4 Geophysical Datasets 176 5.5 Geochemical properties of volcanic rocks 181 5.6 Regional Geochemical Datasets (MSSP) 186 5.6.1 Methodology of data processing 188 5.7 Geochemical analysis – Electronic Dump 190 5.8 Geochemical properties of selected geo-tectonic units 190 5.8.1 Epicratonic basin 190 5.8.2 Foreland Basin 195 5.8.3 Thrusted continental margin 202