Reflection Seismic Insights Into the Pleistocene An-Nafud Sand Sea and the Underlying Paleozoic to Ediacaran Geology North of the Arabian Shield

The An-Nafud sand sea formed during the Pleistocene and occupies approximately 60,200 km ² of northern Saudi Arabia. The erg has regional significance within the North African – Arabian Pleistocene desert trend, recording aeolian system development and early hominin migrations, while the underlying geology represents the poorly-documented Ediacaran and Paleozoic history of the northern sector of the Arabian plate. Reflection seismic data and deep wells have been used to establish the first description of the 3D geometry of this erg and the tectonostratigraphy of the underlying bedrock geology. The total volume of the erg is calculated at 9,399 km ³ , equivalent to 17.4 trillion tons of sand. The erg infills a cuesta topography eroded into gently-dipping Paleozoic strata. A widespread lake deposit is interpreted within the erg from reflection seismic, and relationships between major units within the erg include Late Pleistocene lake beds with hominin footprints overlain by 100 m - scale megadunes. A subcrop map to the erg establishes continuity of the pre-Pleistocene formation boundaries that trend away from the erg margins. A system of extensional faults with up to 1 km throw mapped within the Paleozoic strata is part of a more extensive trend associated with Red Sea rifting. One fault appears to offset the base of the erg by 125 m and related seismicity may have impacted Pleistocene hominins. The top of Precambrian basement occurs at depths of up to 6 km, infilling Ediacaran paleotopography that causes the oldest Paleozoic strata to onlap and differentially compact over features interpreted as eroded, castellated Precambrian granitic plutons.