1 Introduction
Somaliland (Northwestern Somalia) is situated on the northern side of the Horn of Africa with the Gulf of Aden to the north, Ethiopia to the south and west and Djibouti to the northwest (Figure 1). The country is underlain mainly by Mesozoic and Tertiary continental-margin and marine sedimentary rocks deposited unconformably on Precambrian metamorphic and igneous rocks (Ali, 2006).
Figure 1 Map of Somaliland and surrounding regions showing plate boundaries and rift zone-transform faults of the Gulf of Aden and the Red Sea (see online version for colors)
Three major plate boundaries meet in the Horn of Africa. They are the oceanic spreading ridges of the Red Sea and the Gulf of Aden and the continental East African Rift system (Figure 1). As a result, the structure of the country is dominated by the Gulf of Aden, Red Sea and East African trends (Figure 2). The opening of the Gulf of Aden has subjected the country to extensional tectonics, giving rise to a major system of E-W to ENE-WSW striking normal faults. These faults divide the country into two morphological regions, the down-faulted Guban area and the relatively uplifted
Somaliland plateau which exposed high-grade Proterozoic migmatites, granitoides, and pegmatites. Faults of the Red Sea have a trend of NW-SE to WNW-ESE direction whereas the East African faults trend almost due N-S. The East African faults are less frequent and they mainly affect the western part of the country. Field observations indicate that NW-SE faults are the most dominant trends (Figure 2) and old basement structural trends exerted a controlling influence on younger fault trends.
The movement of older faults appears to have taken place during the Mesozoic time and may be related to the early breaking up of Gondwanaland (SOEC, 1954; Bosellini, 1992). The Daban Basin (southeast of Berbera) is an example of an onshore basin that was formed as a result of the reactivation of the older NW-SE trending fault and subsequently filled with Oligocene-Miocene continental to marginal-marine sediments (Bott et al., 1992).
Figure 2 Simplified geological map of Somaliland showing locations of coal deposits (see online version for colors)
The exploration and exploitation of lignite and bituminous coal is important for developing countries such as Somaliland and can provide a vital, alternative fuel source for the country. In Somaliland, the traditional fuel supply is wood which has become severely depleted, while imports of petroleum products have become too expensive. However, extensive lignitic to sub-bituminous coal deposits of various ages from Jurassic to Oligocene-Miocene have been reported (e.g., Farquharson, 1924; MacFadyen, 1933; Grundstofftechnik, 1983). These deposits are known to exist in several localities in the country including Daban Basin southeast of Berbera, Hed-Hed valley south of Onkhor and various locations north of Erigavo. Although a number of geologic investigations were intermittently carried out since 1915, the quality of these deposits and the reserves has not been accurately determined.
In this paper, field mapping and available geological and drilling data have been used to review and document the occurrence of coal and carbonaceous shale in Somaliland. These observations provide the basis for future coal exploration, mining geology, feasibility studies and geological investigation in Somaliland.
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