Palaeoenvironmental Transitions Between 22 ka and 8 ka in Monsoonally Influenced Namibia
The paper presents a preliminary reconstruction of the development of different palaeoenvironments between the Last Glacial Maximum (LGM; c. 22 - 18 ka) and the Holocene Altithermal (HA; c. 8 ka - 4 ka) in Namibia. The synopsis is based on 36 optical datations of dune sands and fine-grained, silty deposits (OSL and TL). Most of the data were published by different research groups during the last decade. The synoptic view of all available optical age determinations is necessary because palaeoclimatic interpretations for southwestern Africa are not possible using results based only on local studies and on partly unreliable datations (e. g. 14C ages of calcretes).
The compilation of all available datations and a synoptical interpretation such as the one presented here, show that gradual transitions and not abrupt changes from arid to more humid conditions occurred. These transitions did not affect all regions of Namibia at the same time and intensity. Differentiations in time and space are necessary for arriving a consistent model of the palaeoenvironmental transitions between LGM and HA.
The data compiled confirm previous results that during the LGM aridity affected all parts of Namibia, possibly with the exception the Kaprivi strip (northeastern Namibia) because dune fixation provides evidence that in the northern Kalahari basin desert changed to semiarid savanna conditions between c. 22 ka and 21 ka. At present this region receives 500 to more than 700 mm of mean annual rainfall. During the Mid-Holocene it was most probably slightly more. During the Late Pleistocene and Early Holocene the monsoonal influence increased, moister conditions shifted further south and west and at 14 ka reached the Windhoek highlands where savanna environments were established. In the dry transitional zone from the northern Namib Desert to the monsoonal Namibian highlands weak climatic oscillations are documented in sediments and soils. These oscillations, between c. 21 ka and c. 9 ka, agree with vegetation patterns which are suggested on the basis of marine core palynological studies off the Kunene River mouth for the Late Pleistocene and Early Holocene. In Namibia the most humid period since the LGM started approximately at 9-8 ka when the southwestern Kalahari, the arid core area of the intracontinental basin, changed to a savanna environment. At the same time monsoonal, more humid climates advanced against the eastern margin of the Skeleton Coast Desert (northern Namib Desert). After approximately 4 ka somewhat drier environmental conditions prevailed over the humid phase, and only minor hygric oscillations occurred until the present.
KeywordsLate Pleistocene Dune System Silty Deposit Kalahari Desert Linear Dune
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