The Mai Maikden sedimentary sequence: a reference point for the environmental evolution of the highlands of northern Ethiopia

This paper presents a geomorphologic-stratigraphic analysis of a travertine dammed lacustrine-swampy sedimentary sequence, composed of clay, peaty layers and phytoclastic travertine sands, deeply incised by the Mai Maikden river, on the Highlands of Tigray (Northern Ethiopia), Radiocarbon datings of peaty deposits allow us to establish that the travertine dams have developed at least between 7310 +/- 90 yr B.P. and 5160 +/- 80 yr B.P. In the upper part of the sequence, palaeochannels filled with travertine and limestone coarse gravels and blocks, indicate the activation of concentrated erosion on the surrounding slopes, Later, both the travertine dam and the lacustrine-swampy deposits were buried by alluvial and colluvial sediments, still mixed with large amounts of organic matter, testifying to generalized slope erosion processes. The end of travertine deposition may be connected with a progressive reduction of vegetation cover and the subsequent decrease of CO2 in groundwater. The occurrence of the latter phenomena may be related to the onset of drier climatic conditions even though the finding of a large prehistoric settlement in the area, also indicates some influence of human impact. (C) 1998 Elsevier Science B.V. All rights reserved.