Non-Glacial Origin of the Neoproterozoic Atud Diamictite, Arabian-Nubian Shield: Implications for Pan-African Tectonics and the Snowball Earth Hypothesis

The Neoproterozoic Atud diamictite of the Central Eastern Desert, Egypt, has long been regarded as a tillite and cited as evidence of glaciation in the Arabian–Nubian Shield. This interpretation, however, rests on data from Wadi Kareim, a correlative section, rather than from the Atud stratotype itself. Here we present new field observations from East of Gabal Atud that challenge the glacial model. The Atud succession is a thick alternation of conglomerates and greywackes, forming distinct fining-upward cycles. Conglomerates are massive, poorly sorted, and exhibit large-scale grading, while greywackes show fining-upward trends, together defining a high-energy depositional system. Sorting is generally poor, and primary sedimentary structures are sparse due to subsequent deformation, yet the overall facies architecture is clear. The diamictite is a coarse, matrix-supported deposit with clasts up to 60 cm in diameter. Petrographic analysis reveals a texturally immature sediment load derived from a diverse suite of igneous, metamorphic, and reworked sedimentary rocks. The deposits lack reliable glacial indicators such as striated pavements, faceted clasts, or lodgement tills, and lack deep-marine features such as turbidites or slumps. Instead, the facies associations are consistent with a Gilbert-type fan-delta/mass flow deposited in a syn-orogenic foreland basin during Pan-African collision. Clast lithologies and published detrital zircon ages indicate mixed sources from juvenile Neoproterozoic arcs and older cratonic crust, signifying continental-scale sediment dispersal during Gondwana assembly. This reinterpretation removes the Atud diamictite as definitive evidence for Cryogenian glaciation in northeast Africa. It highlights the risk of incorporating diamictites into global Snowball Earth compilations without robust type-locality analysis. The Atud succession instead records tectonically driven molasse sedimentation in a foreland basin adjacent to the Pan-African orogen.