Sedimentary rocks are naturally occurring rocks with significant physical and chemical properties. They are of three types, namely clastic, chemical and organic. While clastic sedimentary rocks form as a result of consolidation of minerals or rock fragments, chemical sedimentary rocks form through the precipitation of minerals from solutions . On the other hand, organic sedimentary rocks form as a result of compression of plant and animal remains. Sedimentary rocks form near the surface of the earth and depend on the environment of their deposition and transporting agents. Some of the common examples of sedimentary rocks are limestone, conglomerate, sandstone, coal, shale and many others . Groundwater is dynamic and flows in between the rocks. The ease of groundwater flow depends on the permeability of rocks. In the case of sedimentary rocks, tectonics of rock structure, level of lithification and displacement of the rocks are responsible for groundwater formation .
In sub-Saharan Africa, groundwater supplies are accessible through springs and hand-dug wells. Groundwater is available in abundance in the eastern, western and southeastern parts of the region as they are relatively dry with an annual precipitation of less than 1000 millimeter per year . The void spaces of sedimentary rocks in sub-Saharan Africa contain higher amounts of groundwater and depend on the porosity of these rocks. Coarse-grained sedimentary rocks have higher amounts of groundwater, while fine-grained sedimentary rocks have lower quantities of groundwater. Cemented sedimentary rocks also have lower quantities of groundwater as cements fill up the gap in between the pores. Greater deposits of sedimentary rocks in sub-Saharan Africa have led to an increase in the prominence of groundwater in the region as a predominant water source for three significant reasons. The storage capacity of groundwater is not only higher, but also ensures better quality . Furthermore, the infrastructure used to retrieve groundwater is more affordable by poorer communities of the region. Even during the times of drought, groundwater is available in abundance and meets the needs of the people living in sub-Saharan Africa.
In sub-Saharan Africa, groundwater management has not yet been featured strongly in national and local agendas. An assessment of the physical environment of the region, especially the water resources with respect to socioeconomic situation of the region indicate that in spite of low-yielding resources, groundwater is crucial to the accomplishment of water development . It is a primary source for domestic and sanitation purposes, including productive necessities, such as stock watering, community gardens, brick-making and securing fundamental livelihood. Extensive contamination of groundwater resources and negligence of groundwater preservation tend to pose serious concerns to the people living in sub-Saharan Africa. Since the region is subject to spatial and temporal variability of rainfall, the widely distributed sedimentary deposits tend to generate relatively lower levels and uncertain rates of groundwater renewal . Amidst such circumstances, the sedimentary aquifers of sub-Saharan Africa offer positive prospects of groundwater yields.
According to the 2013 statistics, sub-Saharan Africa has crude oil reserves of over 62.6 billion barrels. Over 7 percent of the total oil production across the world arrives from sub-Saharan Africa. The shale and sandstone deposits in the sedimentary rocks of sub-Saharan Africa have increased over eight times in the past decade in spite of several unexplored basins in the region. Over years, the tropical swamps of sub-Saharan Africa converted into sedimentary rocks that contain oil. As sediments pile up, they undergo various changes due to heat, pressure and other reactions, thereby turning into shale rocks and sandstones . Sandstones with silt-sized sediments are available in abundance in sub-Saharan Africa. As such, several regions of sub-Saharan Africa, such as the Congo basin, Nigeria, Gabon, southern and western Africa are rich in shale oil . Since the sediments of sandstone in these regions are less coarse, it becomes easier to extract oil and other minerals. Sub-Saharan Africa is also rich in sedimentary rocks capable of generating crude oil from organic matter of plant and animal debris.
One of the major problems encountered with regards to groundwater availability in sub-Saharan Africa is seasonal, temporal and spatial unevenness, including higher rates of evaporation and increasing demands of socioeconomic characteristics. With an increased use of groundwater resources as a substitute to surface water triggers concerns of lower groundwater availability in the near future. Furthermore, lack of comprehensive groundwater policies in sub-Saharan Africa creates challenges in terms of groundwater management . The persistent droughts of eastern Africa often result in poor quality groundwater as a result of variations in chemical composition. On the other hand, significant concerns arise while extracting oil in sub-Saharan Africa due to technical complexities and higher expenses involved in the extraction process. Since oil available from shale is in solid form, it becomes difficult to pump it directly from underground and the process requires mining and heating oil shale to higher temperatures . Another major challenge is lack of technical viability to pump oil at commercial levels, which demands progress in surface retorting technology. Oil production in sub-Saharan Africa requires several barrels of water. Lack of adequate surface water in the region compels making use of ground water for oil extraction, which causes a serious social and economic impact on the region.
Works Cited
EIA. "Oil and Natural Gas in Sub-Saharan Africa." US Energy Information Administration (2013): 1-25.
Monroe, James S. and Reed Wicander. The Changing Earth: Exploring Geology and Evolution. Boston, MA: Cengage Learning, 2011.
Pavelic, Paul, et al. "Groundwater Availability and Use in sub-Saharan Africa: A Review of 15 Countries." Research Program on Water, Land and Ecosystems (2012): 1-274.
