Geomorphology and sedimentary structures of Upper Pleistocene to Holocene alluvium within the Nyabarongo Valley (Rwanda). Palaeo-climate and palaeo-environmental implications

Authors

  • Patrick Wassmer Université Panthéon-Sorbonne (Paris 1), PRES HESAM, Laboratoire de Géographie Physique, UMR 8591 CNRS, 1, Meudon, France Author
  • Dominique Schwartz Université de Strasbourg, LIVE, UMR 7362 CNRS, 3, Strasbourg, France Author
  • Christopher Gomez Department of Geography, College of Science, Natural Hazards Research Centre, Waterways: Freshwater Management, University of Canterbury, New Zealand Author
  • Stephen Ward Department of Geography, College of Science, University of Canterbury, New Zealand Author
  • Pierre Barrère Institut de Géographie Louis Papy, Université Michel de Montaigne, Bordeaux 3, France Author

DOI:

https://doi.org/10.4461/GFDQ.2013.36.17

Keywords:

Rwanda, Nyabarongo and Mukungwa rivers, Alluvium terrace, Sedimentary structures, Upper Pleistocene to Holocene palaeoenvironment

Abstract

At the confluence of the Nyabarongo River with the Mukungwa River, to the North of present Rwanda, there are thick alluvial sedimentary sequences, which can reach 30 m in thickness, where they are capped by tufa deposits. From these deposits, two different sedimentary sequences have been identified, with (i) a first sedimentation stage characteristic of an obstructed valley controlled by contrasted seasonal flows during a dryer and cooler climate than at present, and (ii) on top of this unit a more recent sequence of alluvial terraces that were emplaced during a wetter and warmer context allowing the development and stabilisation of the rain forest. Palynological data and their comparison with a database at the East African regional scale have proven that the first rapid sedimentation stage started around 40,000 BP and might have ended abruptly around 14,000 BP. This process has been then followed by a natural embanking stage of the alluvial corridor. These different terraces have been dated thanks to a series of proxies: the discovery of a Stenoece animal remains in the upper part of a terrace confirmed the palaeo-origin of the sequence; a bone harpoon with typical manufacturing characteristics that indicated a human settlement around 9,000 BP on another terrace; and the tufa deposits provided a maximum age for the terraces below 7,000 years. This multi-proxy approach, therefore, provides an interesting series of benchmarks for the development of the palaeoenvironment in Northern Rwanda and is of high importance for the reconstruction of the river bio-geomorphological adaptation to climatic changes.

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Published

2013-06-30

Issue

Section

Research and review papers

How to Cite

Wassmer, P., Schwartz, D., Gomez, C., Ward, S., & Barrère, P. (2013). Geomorphology and sedimentary structures of Upper Pleistocene to Holocene alluvium within the Nyabarongo Valley (Rwanda). Palaeo-climate and palaeo-environmental implications. Geografia Fisica E Dinamica Quaternaria, 36(1), 199-210. https://doi.org/10.4461/GFDQ.2013.36.17

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