The Continental Intercalaire groundwaters of the Tidikelt (In-Salah region, Algeria). Hydrochemical and isotopic features

ABSTRACT

The Continental Intercalaire (CI) groundwaters of the Tidikelt (In-Salah region) are characterized by a high salinity and ion concentrations higher than the maximum standards for drinkability. The total dissolved solids range from 850 to 3390 mg L^–1 for conductivities ranging from 1470 to 6780 μS cm^–1. Their chemical facies is dominated by Cl^–, SO₄^2– and Na⁺, respectively. Alkali ions, Cl^– and SO₄^2– are acquired through the dissolution of Halite (NaCl) and Gypsum (CaSO₄, 2H₂O). CI waters have depleted δ values for ¹⁸O and ²H, corresponding to a cold end-member. This is an indication of a very homogeneous aquifer which is similar to what was observed for the CI in the eastern sub-basin (Great Oriental Erg) and for palaeowaters elsewhere in the Middle-East and Libya. Tritium analyses show that these waters are all very weakly tritiated, which is a testimony of the non-renewed character for these waters. Both δ¹³C and ¹⁴C measured on more than a dozen of samples also show that CI groundwaters are old, with ages comprised between 19,000 and 35,000 years with an average δ¹³C of –10 ‰. This means that these waters are derived from old precipitation whose features were totally different from the very scarce prevailing ones.

KEYWORDS:

• Algeria
• carbon-13
• carbon-14
• central Sahara
• groundwater
• hydrogen-2
• hydrogen-3
• isotope hydrology
• oxygen-18
• Tidikelt

Acknowledgements

The authors are indebted to the local water authorities (Tamanrasset Water Resources Directorate) for providing all the technical assistance during the field sampling campaigns. The authors also wish to express their gratitude to all their colleagues who were either closely or remotely involved. A special mention goes to the staff, both the present and retired ones, of the Dating and Isotope Tracing Department for their constant help and support during laboratory work. Sincere thanks go to the colleagues of the Tamanrasset Nuclear Research Centre for their great logistical support during the field trips. Sincere thanks are also due to Dr Samir Toumi for his appreciated contribution in GIS mapping. The two anonymous reviewers are gratefully thanked for their valuable comments which undoubtedly and substantially helped in improving the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was supported by the Government of Algeria; Algiers Nuclear Research Centre.