Fluvial architecture of the Upper Cretaceous Nubia Sandstones: An ancient example of sandy braided rivers in central Eastern Desert, Egypt

The present paper focuses on the fluvial architecture and depositional facies model of the Late Cretaceous large
sandy braided-river system of the Nubia Formation in the central Eastern Desert of Egypt. Six lithofacies types
and two paleosol pedotypes (entisol and vertisol) are arranged in channel and overbank architectural elements
that display first- to fifth-order bounding surfaces. Two distinctive fluvial architectural styles are recognized. The
Fluvial architecture of the lower member identifies a lowsinuous and energetic sandy braided river, inwhich the
channels cover the entire of fluvial landformswith limited overbank areas. The suggested depositional model resembles
the classic Platte-type braided river with its broad, low sinuosity streams, rich sand bedload and minor
overbank sediments. Recurrent autogenic fining-upward cycles, rarely preserved overbank deposits, dominant
entisol pedotype, prevailing trough cross-bedded sandstones, sporadic to absent planar cross-bedded sandstone,
and dominant downstream accretion also imply perennial, sandy braided rivers. By contrast, the fluvial architecture
of the upper member is characterized by fining-upward cycles, downstream and lateral accretion elements,
and commonly preserved overbank deposits (overprinted by the mature vertisol pedotype). This architecture
style is ascribed to a perennial sandy braided river characterized by sinuous energetic streams and laterally developed
overbank areas, similar to the modern South Saskatchewan River in Canada. The fluvial depositional system
and sequences in the Nubia Formation are strongly controlled by Late Cretaceous base-level fluctuations and
tectonic pulses of the Laramide Orogeny.