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Abstract:
Sahara sands have been proposed to result from the extensive and repetitive recycling of much older sedimentary rocks -- a necessary mechanism to explain their petrographic maturity and the similarity of their detrital zircon populations at continental scale. Where and how this recycling occurs today remain poorly understood. This study investigates the source of modern sands from the southeastern Sahara by leveraging on a large (n > 7800) new dataset of detrital zircon ages from source rocks, modern and ancient dune fields in Chad and Cameroon. We show that zircon age populations show noticeable regional differences when analyzing a large n amount of ages, questioning the similarity of detrital zircon populations in Saharan sands. Dune fields from the driest parts of our sampling area have distinct age distributions that imply discrete sources with differences in bedrock zircon age populations at regional (several 100 km) scale. In the wetter, Sahelian part of our sampling area, the zircon age distribution of dune fields is best-explained by a significant contribution of recent alluvium from local wadis and rivers to the aeolian sedimentary budget. The origin of aeolian sands in the southeastern Sahara is thus local and polygenetic. Recycling of older sedimentary rocks via physical abrasion is only prominent in the driest parts of our sampling area and does not result in the homogenization of Saharan sands.
