The East African Rift System – A View from Space

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Remote sensing data has given a unique perspective on the East African Rift System, allowing both large regional structures and more subtle features to be identified and placed in context

 

 

East Africa, overlooked in terms of its hydrocarbon potential for many years, is increasingly viewed as an exploration hot spot, with recent discoveries in the Albertine Rift and offshore Tanzania leading to a resurgence in interest. Dominated by the East Africa Rift System (EARS), the region has a complex geological history and provides the potential to bring together modern techniques to aid geological understanding and to help efficiently target hydrocarbon exploration.

 

One technique particularly suited to frontier exploration is the use of medium resolution Earth Observation data in the form of satellite imagery and Digital Elevation Models (DEMs). These geo-information datasets can contribute in two main ways. Firstly, optical satellite imagery and DEMs can provide information on surface structure, geomorphology and stratigraphy, enabling a consistent regional interpretation of the surface geology to be undertaken. Secondly, radar imagery can assist in the identification of natural oil seeps that have been reported both offshore and on many of the rift lakes such as Albert, Tanganyika, and Nyasa (Malawi).

 

Astrium has recently completed an ambitious project to interpret the complete EARS, an area of approximately four and a half million square kilometres, at a scale of between 1:100,000 to 1:500,000. The project incorporates a broad range of territories including, from north to south; Eritrea, Djibouti, Somaliland, Eastern Ethiopia, south-east Sudan, Uganda, Kenya, Rwanda, Burundi, eastern border area of Democratic Republic of Congo, Tanzania, Malawi, Mozambique, and the border zones of Zambia, Swaziland and South Africa.

 

 

 

Hydrocarbon Opportunities

Tertiary fluvio-lacustrine deposits within the rift grabens and older Karoo Supergroup deposits are the main onshore Petroleum Systems. In Somaliland, similarities are also thought to be found with the Petroleum Systems of Southern Yemen.

 

In the northern section of the study area, contrasting characteristics of the Eastern and Western Branches of the rift have been observed. The Western Branch, initiating in the Albertine Graben in northern Kenya, displays a high level of seismic activity, has less active volcanism and generally a greater thickness of sediment in comparison to the Eastern Branch, excluding the rifts of the Turkana Depression. These factors are likely to have a corresponding influence on prospectivity, supported by recent discoveries in the Albertine Graben. However, previous studies of the Turkana Depression region have also emphasized hydrocarbon opportunities in the Northern and Central Kenya Rifts of the Eastern Branch. These are thought to be the oldest and longest-lived sedimentary basins of the Tertiary-Quaternary EARS because they represent an overlap area with the Cretaceous rifts.

 

The oil seeps identified by this study - in the rift lakes of Lake Tanganyika, Edward and Nyasa (Malawi) - may indicate the presence of a similar petroleum play involving the Tertiary sections, as discovered recently at Lake Albert. Additionally, for the lakes in the south, there is the potential for the seeps to be derived from older Karoo sediments common in the southern part of the EARS. Recent exploration on the Karoo basins such as the Ruhuhu and Upper Zambezi Grabens has revealed large reserves of Gondwana coals within the lower part of the Karoo Supergroup. These may yield commercial amounts of coal-bed methane as well as reasonable quality coals for future exploitation. Other prospective regions include the ****** Basin in Eastern Ethiopia. This is an area of proven hydrocarbon reserves with large gas discoveries and frequent oil shows from the Mesozoic.

 

Similarities exist between the Petroleum Systems in Somaliland and the proven hydrocarbon regions of Yemen, with the Balhaf Graben in Yemen thought to be a continuation of the Berbera Basin in Somaliland. Jurassic shales are the main source rocks in this region and the satellite imagery has identified numerous roll-over anticlines, closely associated with listric fault growth, that are likely to be most significant structural traps.

 

Incorporating a structural and stratigraphic interpretation this 1:100,000-1:500,000 study has identified evidence of the main rifting events that have defined its current morphology. There is considerable potential to add further detail to the study using higher resolution satellite imagery over specific sub areas.

 

http://www.geoexpro.com/article/The_East_African_Rift_System_A_View_from_Space/538b9edd.aspx