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LATE QUATERNARY SEDIMENTARY AND PALEOCLIMATIC EVOLUTIONOF KORDOFAN, SUDAN

Abstract : This study is conducted in the Kordofan region, central-southern Sudan. The study area is bounded by longitudes 28° 00' and 31° 00' E, and latitudes 11° 30' and 15°00' N and covers an area of about 125835 km2. The Kordofan region is located at the southern end of the present-day Sahara. Late Pleistocene-Holocene deposits in Kordofan, recorded sedimentary discontinuities that probably reflect climatic fluctuations during the latest Quaternary. 14C dating and some archeological findings have been used to date the latest Pleistocene-Holocene succession. In the investigated sections, four stratigraphic units have been recognized, which exhibit eight sedimentological facies.The first unit is older that ≈ 10 ky BP and is formed of mottled sandstone or siltstone facies of aeolian origin. The second unit (≈ 10 to 6 ky BP) comprises palustrine and lacustrine facies in the central and northern parts, and fluviatile facies in the South. The third unit ranges from ≈ 6 to 3 ky BP and is restricted to the southern part; it is made of aoelian deposits intercalated with fluviatile or flood plain facies. The fourth unit is younger than 1000 y BP, and is dominated by aeolian red sandstone in the North, and by flood plain facies to the South. Between ≈ 6 and 1 ky BP in the North and between ≈ 3 and 1 ky BP in the South, no deposits are recorded. This hiatus is marked by deflation surfaces in the North, and is interpreted as a period of strong aeolian activity, which prevented deposition, or even eroded part of the sediments deposited between 6 and 3 ky BP.Several proxies (sedimentology, gastropod sub-fossil shells, pollens, stable isotopes, major element chemistry, clay mineralogy and paleohydrology) have been used to reconstruct the climatic evolution of the region for the past 13 ky, which can be correlated to the well-known evolution of Eastern Sahara during this time-span. Our results indicate that the region has been subjected to arid climate prior to 10 ky BP as evidenced by thick aeolian deposits. Between 10 and 6 ky BP, the region experienced a wet climate as evidenced by the development of pedogenetic calcareous nodules, local deposition of palustrine and lacustrine limestone, abundance of aquatic and semi-aquatic gastropods, high lake levels, and depleted δ18O values from gastropod shells and calcareous nodules. After ≈ 6 ky BP, climate evolved to dry conditions in the northern part of the region as indicated by an strong aeolian activity recorded by erosion features, sedimentary hiatus and deflation surfaces, while its southern part remained more humid, as shown by channel and flood plain deposits, and tropical and aquatic pollen taxa. From 1000 yr BP to Present, and probably after 3 ka BP, the region became arid as evidenced by aeolian deposits, the predominance of arid indicator pollens and the enrichment in 18O of land snail shells.
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Ahmed Dawelbeit Mohammedahmed Eltahir. LATE QUATERNARY SEDIMENTARY AND PALEOCLIMATIC EVOLUTIONOF KORDOFAN, SUDAN. Earth Sciences. Université Grenoble Alpes, 2018. English. ⟨NNT : 2018GREAU022⟩. ⟨tel-01926749⟩

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