The School of Geography, Earth and Environmental Sciences organises a regular series of research seminars throughout the academic year to which everyone is welcome to attend. Speakers - both external and internal to the University - will talk on topics related to all aspects of Earth Sciences.
Today's speaker is Dr Martin Stokes from the School of Geography, Earth and Environmental Sciences at Plymouth University.
North West Africa comprises a mountainous desert landscape on the margins of the Sahara Desert and the southernmost limits of Alpine deformation. This seminar explores the use of river terraces to provide insights into the controls and timing of Quaternary mountain landscape development.
Terraces have been mapped and OSL dated from a 60km long study reach of the Dades River in the High Atlas Mountains. Terraces occur at regular 10m altitudinal intervals up to 140m above the valley floor. The study area encompasses key tectonic components of the High Atlas orogen, with river routing downstream through fold-thrust belt, wedge top basin, thrust front settings into a downstream foreland basin.
Variations in orogen rock strength, stratigraphy and structural configurations have influenced river behaviour, suppressing or enhancing fluvial incision-aggradation patterns and controlling drainage routing. Climatically, individual terrace levels form over 100ka climate cycles. Valleys floors aggrade during glacial-interglacial transitions, incision commences during interglacials and continues into glacials. Bedrock straths are cut during valley widening episodes in transitional phases between incision-aggradation periods. The 100ka climate cycle relationship suggests prolonged Late-Middle Pleistocene fluvial landscape development. The consistent terrace spacing and orogen distribution suggests sustained base-level lowering linked to uplift-exhumation of the High Atlas. The low incision rates (<0.2 mm a-1) and general absence of terrace deformation suggests base-level lowering is isostatic and that the current relief configuration is Early Pleistocene or older.