[en] Full text: The groundwaters occurring in the Northeastern Sahara (Algeria-Tunisia and Libya) constitute huge water reservoirs whose major component is very old (Paleowaters). Water managers are there facing problems related to resource management in terms of estimating budget parameters (recharge, evaporation, leakage, mixing), degradation of the water quality, but also the renewable rate (residence time). The Continental Intercalaire from Sahara is one of the largest confined aquifers in the world. The aquifer material is made of complex layers of sandstone alternating with clayish levels. The depth of the aquifer ranges between 400 and 1800 metres giving rise to temperature up to 70 deg. C and total dissolved salts of 1.5 to 5 g.l-1, in mainly Ci-Na-SO4. Sampled groundwaters show a quite wide range of ³⁶Cl contents, ranging from 8 to 99 10^-15 at.at^-1, expressed as ³⁶Cl/Cl atomic ratio. The space distribution of ³⁶Cl contents fits fairly well with what is known about the piezometric contours of the aquifer: a decrease is observed from recharge to discharge zones. If this decrease is radioactive decay, it can be interpreted in terms of groundwaters transit time. Maximum time intervals of about 3 half-lives (900 Ka) may be computed using ³⁶Cl specific activities (at.l^-1). In order to evaluate the epigene production, Measurements were performed on chloride extracted by leaching from a soil profile. The results are the same order of magnitude (10^-15 at.at^-1) as for groundwater chloride sampled near recharge areas and could reflect the true value of initial ³⁶Cl input. However, the values measured on the groundwaters sampled near recharge areas (100 Km) are equivalent (order of magnitude: 10⁸ at.l^-1) when compared to the calculated values for precipitations in the region. The equivalence between the measured activity in this zone and the expected initial activity could thus be explained by two phenomena: dissolution of Cl^- within the aquifer, and/or radioactive decay of ³⁶Cl .The residence time determined on the main flow line where the radiodecay is observed are expressed in terms of minimum ages (16 to 500 Ka) and maximum ages (25-1200 Ka). New noble gas data are presented to improve the palaeoclimatic and residence time interpretation for the Continental Intercalaire aquifer system. The groundwater recharge temperatures (RT) were estimated from the averaged amounts of noble gases (Ne, Kr, Xe) corrected for the excess air effect. The RT's for most groundwaters are generally lower than the present day recharge temperatures. Along the main flow direction (south-east from the Atlas mountains), the CI palaeowaters (ages 20 to 40ka BP) have an average RT of 16.9 deg. C which is some 5 deg. C cooler than at the present day. Recharge temperatures calculated in four samples from the CT aquifer (30-150m depth) average 19.7, close to the present day mean annual temperature of 21 deg. C. (author)