We provide new numerical age constraints to the Plio-Pleistocene section of Dhar Iroumyane (Morocco) and the associated fossil locality of Guefaït-4, which has yielded an exceptionally rich and diverse faunal assemblage, through a combination of Electron Spin Resonance (ESR) and Terrestrial Cosmogenic Nuclides (TCN) dating of quartz. While challenging in many aspects, the application of these dating methods to the same deposits located about 5 m below the fossiliferous horizon returns consistent numerical dating results within respective uncertainties. More specifically, the age overlap enables to propose a combined ESR-TCN age of 2.87 ± 0.11 Ma (1σ), which may be regarded a maximum age constraint for Guefaït-4 from a chronostratigraphic point of view. These results allow us to narrow down the options of chronological interpretation proposed in a previous study by Parés et al. (2023), by supporting a correlation of the magnetic reversal initially identified a few meters above the site to the Gauss-Matuyama transition (2.61 Ma). A final age estimate of ∼2.7 Ma may be inferred for the fossil horizon through a series of sensitivity tests based on sedimentation rates. With this approach, the normal polarity interval identified in the upper part of the sequence is most likely correlated to the Olduvai Subchron (1.93–1.78 Ma), and the two short reversals in the lowermost deposits with dominantly normal polarity may be reasonably associated to the intra-Gauss Mammoth (3.33–3.21 Ma) and Kaena (3.12–3.03 Ma) Subchrons. Consequently, the present work help position Guefaït-4 as a key Late Pliocene fossil locality in N Africa for the establishment of a robust regional Plio-Pleistocene biochronology, although further work is required in the future to increase the chronological resolution along the sedimentary sequence. While we do acknowledge the intrinsic uncertainty associated with the ESR and TCN dating results (including the limited number of samples processed in the present study), these encouraging results nevertheless illustrate the interest of using a multi-technique approach to constrain Plio-Pleistocene deposits, and the importance of combining numerical dating with magnetostratigraphy and biostratigraphy/biochronology in non-volcanic sedimentary context. Such approach also contributes to a better understanding of the potential and limitations of each dating method, and helps providing critical insights into the avenues worth exploring in the future from a methodological and sampling point of view in order to ensure future successful ESR and TCN dating applications beyond 2 Ma.

Funding for this research was provided by: Palarq Foundation, Spanish Ministry of Culture and Sport, Spain (Ref: 42-T002018N0000042853 & 170-T002019N0000038589), Faculty of Sciences (Mohamed First University of Oujda, Morocco), Direction of Cultural Heritage (Ministry of Youth, Culture and Communication, Morocco) and INSAP (Institut National des Sciences de l’Archéologie et du Patrimoine, Morocco). The Ramón y Cajal fellowships granted to M.D. (RYC2018-025221-I), A.R.-H. (RYC2022-037802-I), and P.P. (RYC2023-044218-I) are funded by MCIN/AEI/10.13039/501100011033 and by ‘‘ESF Investing in your future”. This work is also part of Grants PID2021-123092NB-C21 and PID2021-123092NB-C22 funded by MCIN/AEI/ 10.13039/501100011033/’ERDF A way of making Europe’. Parts of this research were carried out at the Ion Beam Centre (IBC) at the Helmholtz-Zentrum Dresden-Rossendorf e. V., a member of the Helmholtz Association. AMS measurements at DREAMS have been supported by the RADIATE project under the Grant Agreement 824096 from the EU Research and Innovation programme HORIZON 2020 (Radiate Transnational Access Proposal# 23003288-ST). We would like to thank the DREAMS operator team for their assistance with AMS-measurements. Research Groups Support of the Catalonia Government (2021 SGR 01238 - 2023PFR-URV-01238 (URV) Palhum (AGAUR) and 2021 SGR 01237 GAPS (AGAUR)- 2023PFR-URV-01237 (URV)). The IPHES-CERCA has received financial support through the “María de Maeztu” program for Units of Excellence (CEX2024-01485-M/funded by MICIU/AEI/10.13039/501100011033). R.S-R, M.G.Ch., and J.A. research is funded by CERCA Programme/Generalitat de Catalunya. J.v.d.M. received funding from PID2022-137070NB-I00 and PID2021-122355NB-C33 financed by MCIN/AEI/10.13039/501100011033/FEDER, UE. M.F. is beneficiary of a Joan Oró predoctoral fellowship (2023 FI-1 00578) funded by AGAUR and the European Social Fund (ESF). We thank Dr Santiago Padilla, Ms Leticia Miguens and Mr Jorge Revilla, CENIEH for target preparation for cosmogenic nuclide dating, as well as Ms María Jesús Alonso Escarza, CENIEH, for invaluable support with the ESR dating analytical procedure. Special thanks to Prof. Gilles Rixhon, University of Strasbourg, France, for kindly providing Fig. 1A, and to Prof. Anton Wallner from HZDR for logistical arrangement for AMS measurements. Finally, we would like to thank all the people who took part in the excavation of the site from 2017 to 2019 and the restoration of the fossils to date.

With funding from the Spanish government through the "Unit of Excellence Maria de Maeztu" accreditation (CEX2024-01485-M).

M. Duval et al.

Peer reviewed