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UK Luminescence and ESR Dating Meeting Sheffield, 11th-12th September 2018
50
Chronology for mountainous river terraces: OSL/IRSL and rock
dating techniques applied to carbonate-rich terraces in the Atlas
Mountains
J.R. Zondervan1,*, M. Stokes1, M. Jain2, J.P. Buylaert2,3, M.W. Telfer1, A.S. Murray3
1School of Geography, Earth and Environmental Sciences, Plymouth University, Plymouth
PL4 8AA, United Kingdom
2Center for Nuclear Technologies, Technical University of Denmark, DTU Risø Campus, DK-4000 Roskilde, Denmark
3Nordic Laboratory for Luminescence Dating, Department of Geoscience, University of Aarhus, Risø Campus,
Frederiksborgvej 399, 4000 Roskilde, Denmark
*Corresponding author; Email: jesse.zondervan@plymouth.ac.uk
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.
References
Buylaert, J. P., Jain, M., Murray, A. S., Thomsen, K. J., Thiel, C., and Sohbati, R., 2012, A robust feldspar luminescence
dating method for Middle and Late Pleistocene sediments: Boreas, v. 41, no. 3, p. 435-451.
Hancock;, G. S., and Anderson, R. S., 2002, Numerical modeling of fluvial strath-terrace formation in response to
oscillating climate: GSA Bulletin, v. 114, no. 9, p. 1131-1142.
Rixhon, G., Briant, R. M., Cordier, S., Duval, M., Jones, A., and Scholz, D., 2017, Revealing the pace of river landscape
evolution during the Quaternary: recent developments in numerical dating methods: Quaternary Science Reviews, v. 166,
p. 91-113.
Sohbati, R., Murray, A. S., Chapot, M. S., Jain, M., and Pederson, J., 2012, Optically stimulated luminescence (OSL) as
a chronometer for surface exposure dating: Journal of Geophysical Research: Solid Earth, v. 117, no. B9.
Stokes, M., Mather, A. E., Belfoul, M., Faik, F., Bouzid, S., Geach, M. R., Cunha, P. P., Boulton, S. J., and Thiel, C.,
2017, Controls on dryland mountain landscape development along the NW Saharan desert margin: Insights from
Quaternary river terrace sequences (Dadès River, south-central High Atlas, Morocco): Quaternary Science Reviews, v.
166, p. 363-379.