New surface exposure age data using cosmogenic radionuclides 10Be and 14C to constrain the age of the last deglaciation in the Retezat Mts, Southern Carpathians, Romania

The presence of cosmogenic radionuclide concentrations inherited from previous exposure(s) of glacially transported boulders and moulded bedrock surfaces may hinder the determination of the surface exposure age (SED) of the last phase of (de)glaciation.

A previous study revealed that glacial landforms of the cirque area in the southern side of the Retezat Mountains (Southern Carpathians, Romania) hold significant amount inherited ¹⁰Be (t_1/2=1.4 My), which was used for a tentative estimation of the amount of glacial erosion, assuming that the lowest ¹⁰Be concentration was representative of the true age of deglaciation (Ruszkiczay-Rüdiger et al., 2021, Geomorphology 384, 107719).

In this study, a western valley, the Zlătuia-Dobrunu valley of the Retezat Mts was sampled for ¹⁰Be SED. The novel data are in agreement with the previous datasets suggesting that the most extended glaciers belonged to the Last Glacial Maximum. However, the old apparent exposure durations based on ¹⁰Be analysis of samples from the cirque area provided firm evidence for the presence of excessive abundances of cosmogenic ¹⁰Be in this valley as well.

The use of the short-lived in situ produced ¹⁴C (t_1/2= 5.7 ky) provides an independent age constraint for the timing of the last deglaciation, because all ¹⁴C inventories that might be inherited from a previous exposure would have already been decayed. As a consequence, the ¹⁴C concentrations are not biased by inheritance, thus i) enable the age determination of the landforms belonging to the last phases of deglaciation and ii) the ¹⁴C exposure ages compared to the ¹⁰Be data will allow an assessment of the inherited amount of ¹⁰Be and thus a more precise determination of the amount of glacial erosion.

In this study the new ¹⁰Be and ¹⁴C SED ages will be presented together with the mapped glacial landforms, reconstructed paleoglaciers and their Equilibrium Line Altitudes.

Funding: NKFIH FK124807, INSU/CNRS, ANR - “EQUIPEX Investissement d’Avenir”, IRD and CEA, the PNRR-III-C9-2022 - I8, no. 760055/23.05.2023, CF 253/29.11.2022. and Horizon 2020 grant 871149 ”EUROPLANET”.