Preliminary lithostratigraphy and structural investigation for
groundwater potential assessment of the Mekele outlier, Northern
Ethiopia
By: Bedru Hussien, Kurkura Kabeto, Desta Horecha
Mekele outlier is located in northern Ethiopia forming the upper catchments of
Tekeze river basin and Danakil basin to the west and east respectively. It is bounded by
longitudes 38° 58’ - 40° 23’ and latitudes 12° 55’ – 13° 58’, and covers an area of 15822
sqkm.
Primary aim of the geologic and structure investigation is to provide lithological,
structural, and tectonics understanding of the Mekele outlier as a basis for hydrogeological
and related studies on the groundwater potential of the project area. The preliminary
geologic investigation include review of previous works relevant to the present study,
remote sensing studies on both medium and high spatial resolution satellite images
(Landsat ETM+, Aster and Spot multispectral data) and field investigations.
Tasks of the investigation encompasses preparation of regional litho-structure and
geomorphologic map (1:250,000 scale), detailed geologic map of selected groundwater
potential areas at a scale of 1:50,000 and writing of a comprehensive report explaining the
maps and other features.
The geology of the Mekele outlier has been previously studied for various purposes and
detailed works focused on groundwater resource investigation. The information content of
previous geologic works is variable and there is no good agreement on the geologic
divisions adopted by different workers. There appears certain unfits along map boundaries
prepared by different investigators. Besides The lithologic and structural detail is variable
and they lack lithostructural attributes pertinent to the present study.
Physiography of the Mekele outlier is characterized by contrasting landscape that is
remarkable when traveling across the area. It consists of a warped upland plateau
straddling the watershed divide of Tekeze and Danakil basins to the west and east
respectively.
The outlier is made up of a variety of clastic (Enticho and Adigrat formation) and
calcareous sedimentary rocks (Antalo formation) capped by thin layers of clastic
1
sedimentary rocks (Ambaradom formation). The upper members of Antalo formation are
intruded locally by basaltic rocks. The sedimentary outlier is inturn coverd by extensive
basalt flows (Trap series) in the south. The Paleozoic-Mesozoic sedimentary sequence
(outlier) is bounded in the north, west and east by Precambrian metamorphic rocks.
The classification of Antalo group into members and formations is not consistent,
though it appears to be based on lithologic alternation, fossil type and nature of exposure.
It is mainly an alternation of thickly bedded limestone members forming cliffs and thinly
bedded marl-limemudstone-limestone association.
Main structural features noted in the sedimentary rocks include bedding with
variable thickness, high degree of fracturing and tilting of the sedimentary bedding in
different directions: south, north, west and east. The major regional structural element
related to tectonics in the area are normal faults with varying trends, lineaments and
fractures. Two systems of faulting are noted in many places. The earliest faulting generally
trends WNW-ESE and is the oldest. This system is affected by relatively small N-S
faulting dipping to the east or west at higher angles.
2