Pleistocene pedogenic carbonates from alluvial paleosols in eastern Sudan reveal a semi-arid and seasonal climate, similar to today

Abstract

Pedogenic carbonates can provide important information regarding paleoclimatic conditions. Compared with East Africa, Pleistocene pedogenic carbonates in Sudan, particularly calcretes, have received very little attention, particularly with regard to local paleoclimatic reconstructions. Pleistocene alluvial sediments aged from ∼230 to <17 ka were deposited along the middle Atbara River in eastern Sudan. Intercalated in these alluvial deposits are paleosols in which different types of pedogenic carbonates occur. Petrographic, mineralogical and isotopic analyses were performed to reconstruct the regional paleoenvironmental conditions. The investigated pedogenic carbonates are appropriate for paleoclimatic reconstruction because they are free of inherited carbonate and diagenetic modification. The paleosols identified in a previous study as Aridisols/Calcisols contain calcrete horizons that consist of an orthic nodular horizon, sometimes overlain by a laminar horizon. Paleosols identified as Vertisols contain slickensides, and disorthic and septaric nodules. The paleosols show stable carbon and oxygen isotope values ranging between −9.12 and −5.12 ‰, and between −7.25 and −4.09 ‰, respectively. Supporting the previous study, the inferred climatic conditions were arid to semi‐arid, with a mixture of C₃ and C₄ vegetation cover, and paleoprecipitation greater than 350 mm/yr, similar to that of the present-day, with likely higher rainfall during the formation of Vertisols than Aridisols/Calcisols. The thickness and morphology of Pleistocene calcretes in eastern Sudan are similar to those in East Africa, suggesting similar climatic conditions during their formation. Well-and weakly-developed calcretes in Aridisols formed in distal and proximal floodplains, respectively, whereas well-developed vertic horizon in Vertisols formed in distal floodplains.