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Title: Single-grain TT-OSL dating results confirm an Early Pleistocene age for the lower Moulouya River deposits (NE Morocco)
Authors: Bartz, Melanie
Arnold, Lee J.
Demuro, Martina
Duval, Mathieu
King, Georgina
Rixhon, Gilles
Álvarez-Posada, Claudia
Parés, Josep María
Brückner, Helmut
Keywords: Single-grain;TT-OSL;Quartz;Fluvial terraces;Morocco
Issue Date: Feb-2019
Publisher: Elsevier
Citation: Quaternary Geochronology, 2019, 49, 138-145
Abstract: The lower Moulouya River (NE Morocco) drains a tectonically active area related to the NW-SE convergence of the African and Eurasian plates. Fluvial deposits preserved in the lower Moulouya have been dated to ∼1.5–1.1 Ma as part of a recent multi-technique geochronology study. The present work aims to verify and refine the existing Early Pleistocene (∼1.8–0.8 Ma) ages for the Moulouya deposits using single-grain thermally transferred-OSL (TT-OSL) dating. The single-grain TT-OSL De distributions are characterised by high overdispersion (77–91%), significant negative skewness, and several discrete populations can be identified when applying the finite mixture model (FMM). The lowest FMM dose components of the TT-OSL datasets comprise relatively dim grains that have very slow decays. The Fast Ratio (FR) was therefore used to explore whether the presence of slower-decaying TT-OSL components might have exerted a significant effect on our De values. Our samples show a 40–50% increase in weighted mean De and a 50–100% decrease in overdispersion when applying a FR acceptance threshold of 2, resulting in the elimination of the lowest FMM component. Application of a higher FR value does not result in any additional change in TT-OSL De value. Dose recovery tests confirm the suitability of the single-grain TT-OSL protocol and use of an additional FR acceptance threshold of ≥2 for final age determination. Previous geomorphic interpretations suggested a capture event occurred at the Beni Snassen gorge between 1.04 and 1.36 Ma at the latest. This interpretation is supported by the newly obtained TT-OSL ages, which reveal that fluvial deposition occurred between ∼1.09 and ∼1.15 Ma.
ISSN: 1871-1014
DOI: 10.1016/j.quageo.2018.04.007
Type: Article
Appears in Collections:Geocronología y Geología

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