Advancement in Understanding the Structural and Stratigraphic Evolution of the Blue Nile Basin, Northwestern Ethiopian Plateau by Integrating Optical-Radar Remote Sensing Analysis with Field Studies

Nahid D. Gani¹, Mohamed G. Abdelsalam², Solomon Gera³, and M. Royhan Gani^1
1Energy & Geoscience Institute (EGI), University of Utah, Salt Lake City, UT
²Department of Geological Sciences and Engineering, University of Missouri-Rolla, Rolla, MO
³Regional Geological Mapping Department, Geological Survey of Ethiopia, Addis Ababa, Ethiopia

One of the recent advancement in structural geology is to incorporate remote-sensing-analysis with field-studies to delineate geological evolution of a region. We integrate optical-radar data with field-studies to understand structural and stratigraphic evolution of the Blue Nile Basin. The basin, within the Northwestern Ethiopian Plateau comprises ~1200m-thick Mesozoic sedimentary strata underlain by Neoproterozoic basement and overlain by Tertiary-Quaternary volcanics. Our study shows, the basin has evolved in three phases: Pre-sedimentation, involving pre-rift peneplanation of Neoproterozoic basement; Sedimentation phase including deposition of Mesozoic sandstone, glauconitic-mudstone and limestone units through repetitive transgression and regression; Post-sedimentation phase, including early volcanic event erupting ~2000m-thick Tertiary volcanics mostly related to Afar Mantle Plume and late volcanic events emplacing ~300m-thick Quaternary volcanics associated with continued opening of Afar Depression and Main Ethiopian Rift (MER). The sedimentary and volcanic units were formed under extensional deformation manifested by NW- and NE-trending normal faults and fractures. We interpret the origin of these extensional structures as early as Triassic-Cretaceous NE-SW-directed-extension related to Mesozoic Gondwana rifting. This event formed the Blue Nile Basin as NW-trending-rift, where much of the Mesozoic sediments were deposited. This was followed by Tertiary NW-SE-directed extension related to MER. This extension developed NE-trending faults concentrated in Tertiary volcanics and upper part of the Mesozoic section. The region was subsequently affected by Quaternary E-W and NNE-SSW-directed-extensions related to oblique opening of MER and development of E-trending transverse faults, and NE-SW and E-W-directed extensions in southern and western Afar respectively.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas