LAUSR

D. A. Ruban (*) Cherepovets State University, Sovetskiy Avenue 10, Cherepovets, Vologda Region 162600, Russia e-mail: [email protected] 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.