Chronology for mountainous river terraces: OSL/IRSL and rock dating techniques applied to carbonate-rich terraces in the Atlas Mountains
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Improvements in numerical dating methods continues to open new possibilities for understanding sedimentary archives and thus unravelling Earth surface processes (e.g. Rixhon et al, 2017). In general, the Optically Stimulated Luminescence (OSL) dating is successful for deposits spanning last 100 ka, while Infra-Red Luminescence (IRSL) dating of feldspar can be applied on longer timescales (Buylaert et al, 2012). The Atlas Mountains in Morocco contain an abundance of carbonate-rich river terraces recording glacial-interglacial river evolution (Stokes et al., 2017) and are an ideal place to apply OSL techniques on mountainous river sediments deposited at distinct time scales. River strath terraces are formed by transition between valley widening and downcutting of terraces in response to local divergence of sediment-transport capacity (Hancock; and Anderson, 2002). The formation of terraces in response to a change in climate can be distinguished from a response to a change in local uplift rates (Hancock; and Anderson, 2002). While separating climatic from tectonic signals in the geomorphic record remains a challenges, it is possible using the records of erosional surfaces and sediments of river terraces. Where river strath terraces and their sediments are preserved in mountainous settings they form the ideal opportunity to test the timescales and responses of surface process to climate and tectonic histories. This requires high resolution dating of river terraces and their coarse-grained sediments. IRSL dating has the potential to provide insight into glacial-interglacial erosional and depositional processes over the last few cycles. An experimental method of bedrock exposure (Sohbati et al, 2012) has the potential to unlock insight into erosional processes on the timescale of river terrace formation. Analysis of sediments, bedrock and pebbles was undertaken in the summer of 2018 after a terrace mapping and sampling campaign in the Atlas. OSL and IRSL analysis of the material resulted in age estimates and has established the sensitivities of various rock material to Luminescence signals. Further work will include extensive sampling and dating of terrace conglomerates, as well as targeted sampling for rock exposure dating.
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