New results on palaeoenvironmental conditions in equatorial Africa derived from alluvial sediments of Cameroonian rivers |
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| Authors: | Mark Sangen |
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| Institution: | Institute of Physical Geography, Johann Wolfgang Goethe-University Frankfurt, Campus Riedberg, Altenhofer Allee 1, 60438 Frankfurt am Main, Germany |
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| Abstract: | The ReSaKo project undertook extended fieldwork across southern Cameroon to explore the palaeoenvironmental information recorded in the alluvial sediments of equatorial African rivers. 160 hand-corings reaching maximum depths of 550 cm were carried out on alluvial ridges and floodplains of major Cameroonian fluvial systems. These multilayered, sandy to clayey alluvia contain sedimentary form-units and palaeosurfaces, which provide excellent additional proxy data archives for the reconstruction of palaeoenvironmental conditions in western equatorial Africa. Coring transects and sedimentary profiles document grain-size shifts and distinguishable sedimentary units in the stratigraphic record, which evidence (fluvial-)morphological adjustments of the fluvial systems in response to external forcing and (river-) intrinsic variability. 76 14C-(AMS)-dated samples from organic sediment and macro-rests (fossil organic remains like wood, leafs, etc.) embedded in these sedimentary units indicate Late Pleistocene to recent ages (uncalibrated 14C-ages: 48–0.2 ka BP). The tentative interpretation of the alluvial record yields excellent additional information on the complex feedbacks between climate, ocean, fluvial as well as ecological systems and human activity in a little-studied region with high sensitive tropical ecosystems. δ13C-values (?35.5 to ?18.0‰) of the dated samples indicate the persistence of C3-dominated gallery forests across the rivers (‘fluvial rain forest refuges’) despite several climatic fluctuations (aridifications, e.g. Last Glacial Maximum around 20 ka BP, Younger Dryas 13–11 ka BP). This research complements earlier results from additional terrestrial and marine proxy data archives on the Late Quaternary history of monsoonal western equatorial Africa. |
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