The Late Neogene to Quaternary Drainage Evolution of the Uplifted Neogene Sedimentary Basins of Almería, Betic Chain

Abstract

The evolution of an incising drainage network controls regional geomorphic development, but is in turn controlled by four sets of dynamic factors. These are as follows: tectonics, including both regional epeirogenic uplift and more local tectonic deformation; climatic change, affecting variations in flood power and sediment supply; base level; and local factors such as river capture, related to the development of the drainage network itself. The geomorphology of four uplifted Neogene sedimentary basins in the eastern Betic Cordillera of Almeria, Spain, demonstrates how these factors interact and operate over a range of temporal and spatial scales. The basins were marine basins until the early Pliocene, when differential epeirogenic uplift caused emergence and the initiation of the drainage networks; first in the Tabernas, then in the Sorbas, and finally in the Vera and Almeria basins. The last two became terrestrial in the early Pleistocene. The modern landscape reflects the influence of differential regional uplift rates on the long-term dissectional history, operating regionally over the whole period of landform development. The extremes are represented on the one hand by the deeply dissected Tabernas basin and on the other hand by the centre of the Almeria basin, which is dominated by coalescent aggrading alluvial fans. The Quaternary climatic signal is another regional signal, expressed by the sediment-led terrace sequence, with aggradation occurring primarily during Pleistocene global glacials and incision during the interglacials. These regional signals are modified locally by the other factors. Local neotectonic deformation is particularly important in the Tabernas and Almeria basins. Base-level change induced by tectonic activity and by river capture is important locally throughout the area, but the effects of base-level change induced by Quaternary sea-level change are restricted to the coastal zone. River capture has had profound effects, modifying the drainage areas. The Vera basin has gained drainage area substantially, whereas that of the Almeria basin has decreased. The most important effects have been on base level and incision rates, especially in the Sorbas basin. The overriding long-term control on drainage development and therefore on landform dynamics has been the pattern of regional epeirogenic uplift, onto which the Quaternary climatically controlled aggradation/dissection sequence has been imposed. These are regional signals that have been modified locally by the more spatially and temporally restricted signals generated by base-level change and river capture.