The rich geology of Egypt permits new insights into the diversity of
sedimentary rocks, including terrestrial carbonates and coarse-grained
siliciclastics.
Spectacular manifestation of terrestrial carbonates has been found
in the Dungul Oasis in southern Egypt (Nicoll and Sallam 2017;
Sallam et al. 2018a). Laminated, grey-to-dark grey tufa deposits are
established at Gebel El-Digm. These are characterized by concentric,
spherical-shaped, laminar accretions, and stromatolitic and pillow,
ball-like structures (Fig. 1a). The inner core in cross section is
porous and contains rich phytoherms, whereas the cortex is wavy,
convolute-laminated (1–2 mm-thick each), and showing concentriclamellae
with exfoliated structure. The tufa was formed as a result of
palaeospring activity on the land, between the epeiric palaeogulf of
the Mediterranean and the topographic highs rounded this palaeogulf
(Golonka 2004; Guiraud et al. 2005).
The occurrence of semi-detached megaclasts in the Faiyum Oasis
in central Egypt (Sallam et al. 2018b) contributes to filling gaps in the
knowledge of coarse-grained siliciclastics. The locality demonstrates
an effective process of megaclast formation. This process is differential
erosion by sandstorms, which leads to sculpturing of peculiar
landforms in Wadi Hitan (Fig. 1b). The erosion takes place intensively
at the very base of these landforms, and huge blocks become
semi-detached from the parent rock. Full detachment because of further
erosion and/or gravity leads to the formation of true megaclasts.