Contrasted terrace systems of the lower Moulouya River as indicator of crustal deformation in NE Morocco

Abstract

The Moulouya river has the largest catchment in Morocco and drains an area characterised by active crustal deformation during the Late Cenozoic due to the N-S convergence between the African and Eurasian plates. As yet, its Pleistocene terrace sequence remains poorly documented. Our study focuses on the lowermost reach of the river in north-eastern Morocco, which drains the Zebra-Triffa sedimentary basin directly upstream of the estuary. New field observations, measurements and sedimentological data reveal contrasted fluvial environments on each side of a newly identified, W-E striking thrust zone disrupting the sedimentary basin. On the one hand, long-lasting fluvial aggradation, materialized by = 37 m-thick stacked terraces, has occurred in the footwall of the thrust. On the other hand, the hanging wall is characterised by a well-preserved terrace staircase, with three Pleistocene terrace levels. Whilst the identification of this thrust zone question some previous interpretations about the local (hydro-)geology, it is consistent with the statement that most of the Plio-Quaternary deformation in the eastern Rif mountains has concentrated in this region of Morocco. Our new data and interpretations also agree with morphometric indicators stating that the whole Moulouya catchment, showing several knickzones in its long profile, is at disequilibrium state. We also suggest that the knickzone in the Beni Snassen gorge, located directly upstream of the Zebra-Triffa sedimentary basin, could (partly) result from a transient fluvial reaction to Late Cenozoic thrusting activity and correlated uplift in the hanging wall.

Resources

• Rixhon_etal_2017_terrace moulouya.pdf

Bibliography

Rixhon, G., Bartz, M., el Ouahabi, M., Szemkus, N., Brückner, H. (2017): Contrasted terrace systems of the lower Moulouya River as indicator of crustal deformation in NE Morocco. – In: Journal of African Earth Sciences Vol. 126, February 2017, Pages 45–57, DOI: 10.1016/j.jafrearsci.2016.11.005