Original paper

Sandstone columns of the 3rd Nile Cataract (Nubia, Northern Sudan)

Cílek, Václav; Adamovič, Jiří; Suková, Lenka

Abstract

A large outcrop of columnar-jointed Upper Cretaceous “Nubian” sandstone of Cenomanian-Turonian age was found beneath the Medieval and post-Medieval fortified settlement of Jebel Wahaaba overlooking the northern rapids of the 3rd Nile Cataract. The site itself may represent the largest and the best developed example of its kind on a global scale. The genesis of sandstone columns has been often understood as more-or-less analogous to the origin of columnar cooling cracks in volcanic rocks. The absence of tensional indicators on joint faces of the columns at Jebel Wahaaba argues against their origin by host-rock cooling. Instead, the dominance of heat convection – rather than heat conduction – and extensive quartz grain microfracturing point to dynamic fragmentation by expanding liquid and gas phases related to magma emplacement and a subsequent relaxation. Fluid convection in the columnar-jointed sandstone at Jebel Wahaaba is documented by the presence of corrosive secondary pores along joints which functioned as subsidiary heat sources. The joint pattern on a plane perpendicular to column axes can be best described by Voronoi fragmentation.

Keywords

nubian sandstonecolumnar jointingsudanvoronoi fragmentation3rd nile cataract