Though southern Egypt is currently hyperarid, relict freshwater carbonate deposits called tufas near Kurkur (region centered at 23 540 N, 32 190 E) indicate that ambient rainwater-fed alkaline springs
formerly sourced drainages in the Sinn El-Kaddab or Eocene scarp, and precipitated carbonate tufa deposits
at waterfall cascades, pools, and streams. Petrographic analysis enables the reconstruction of a
variety of vegetated microenvironments during Quaternary time. The Kurkur tufas are very porous rocks
with an abundance of fossil plant casts and molds making up the petrofabrics at the macroscale. The
tufas also preserve laminations of successive generations of calcified remains of microbes visible at the
microscopic scale. Original carbonate framework architectures are massive carbonate structures to the
decameter scale, with characteristic highly porous and permeable rock fabrics, including vegetation-rich
phytoherms and stromatolite forms. The tufas are relatively pristine, preserving their original rock
textures with minimal post-depositional alteration. Structural controls affecting the development of tufa
deposits near Kurkur include fissure, cracks and fault planes that would have enhanced groundwater
recharge and emergence of carbonate-saturated springs from perched aquifers above the Nubian Aquifer
System during periods of greater effective rainfall in the past when the water table was significantly
higher. The Kurkur tufas are relict archives from phases when groundwater discharge supported
comparatively more vegetation than the modern day, and spring flows sustained baseflow in the Wadi
Kurkur tributary of the Upper Nile. Episodes of tufa deposition along now-defunct tributaries therefore reflect phases of a more integrated Nile drainage system. |
