Chlorine-36 dating of deep groundwater from northern Sahara

Guendouz, A.; Michelot, Jean‐Luc

doi:10.1016/j.jhydrol.2006.01.002

Cited by 43 publications

(11 citation statements)

References 13 publications

(15 reference statements)

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“…10d. This confirms that Na and Cl concentrations are primarily controlled by dissolution of the saliferous Triassic formations rich in halite (Iundt, 1971;Kamel et al, 2005;Guendouz and Michelot, 2006;Inoubli et al, 2006;Trabelsi et al, 2009), which buffers the Na/Cl ratio of most samples at~1. This process is active over the three Tunisian domains.…”

Section: Geochemical Processes : Sources Of Salts and Link With Geologysupporting

confidence: 59%

Regional variations in the chemical and helium–carbon isotope composition of geothermal fluids across Tunisia

et al. 2011

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Tunisia has numerous thermo-mineral springs. Previous studies have shown that their chemical composition and occurrence are strongly influenced by the regional geology. However little work has been done so far to study the isotopic composition of volatiles associated with these geothermal manifestations. Here, we report on the results of an extensive survey of both natural hot springs and production wells across Tunisia, aimed at investigating the spatial distribution of thermal fluids' geochemical characteristics and He-C isotopic composition. The chemistry of the analyzed samples highlights the heterogeneity of the water mineralization processes in Tunisia, as a consequence of the complex geological and tectonic setting of the country. In terms of chemical composition, we are able to conclude, however, that dissolution of halite and gypsum plays a key control on groundwater chemistry. Helium and carbon isotope systematics confirm the prevalently crustal origin of the volatiles interacting with the aquifer systems, consistent with the absence of any recent magmatism. Most samples are characterized by crustal-type helium ( He ratio reaches 2.4 Ra (corresponding to 30% of mantle-derived helium) at the Ain Garci site, a CO 2 rich mineral spring located some 30 km south of the city of Zaghouan. This mantle signature is consistent with the fact that the Pelagian Block, to which Eastern Tunisia belongs, has been deeply affected by extensional and transtensional tectonics since the opening of the Tethys, a process which is still ongoing in the Sicily channel (Pantelleria Rift). As a whole however, our results show that the Italian mantle gas anomaly only marginally extends to Northwestern Africa.

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Section: Geochemical Processes : Sources Of Salts and Link With Geologysupporting

confidence: 59%

Regional variations in the chemical and helium–carbon isotope composition of geothermal fluids across Tunisia

et al. 2011

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“…Slow flow through the formation suggests hydraulic ages of up to ~1 M.yr., and this appears to be confirmed by ages based on 36 Cl (Guendouz and Michelot, 2006). Figure 8b shows a plot of δ 18 O versus residence time.…”

Section: Figuresupporting

confidence: 58%

“…18 O and noble gas (NG) recharge temperature versus 14 C age for waters from the Uitenhage aquifer, South Africa (based on data of Heaton et al, 1986). Lehmann et al, 2003), (b) the Continental Intercalaire of Tunisia and northern Algeria (data from Guendouz and Michelot, 2006), and (c) the Nubian sandstone of western Egypt (data from Sturchio et al, 2004;Patterson et al, 2005). …”

Section: Plots Ofmentioning

confidence: 99%

The isotope hydrology of quaternary climate change☆

Darling

2011

Journal of Human Evolution

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Understanding the links between climate change and human migration and culture is an important theme in Quaternary archaeology. While oxygen and hydrogen stable isotopes in high-latitude ice cores provide the ultimate detailed record of palaeoclimate extending back to the Middle Pleistocene, groundwater can act as a climate archive for areas at lower latitudes, permitting a degree of calibration for proxy records such as lake sediments, bones and organic matter. Not only can oxygen and hydrogen stable isotopes be measured on waters, but the temperature of recharge can be calculated from the amount of the noble gases neon, argon, krypton and xenon in solution, while residence time can be estimated from the decay of the radioisotopes carbon-14, chlorine-36 and krypton-81 over timescales comparable to the ice core record. The Pleistocene-Holocene transition is well characterised in aquifers worldwide, and it is apparent that isotope-temperature relationships of the present day are not necessarily transferable to past climatic regimes, with important implications for the interpretation of proxy isotope data. Groundwaters dating back to one million years, i.e. to beyond the Middle Pleistocene, are only found in major aquifer basins and information is relatively sparse and of low resolution. Speleothem fluid inclusions offer a way of considerably increasing this resolution, but both speleothem formation and large-scale groundwater recharge require humid conditions which may be relatively infrequent for areas currently experiencing arid climates. Both types of record therefore require caution in their interpretation when considering a particular archaeological context.

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“…The main outputs are the natural discharge towards the Tunisian and Libyan coasts (Gulf of Gabès and Syrte) and the important withdrawals resulting from irrigated agriculture and domestic uses of the oasis systems. Groundwater is often considered a nonrenewable or fossil resource [ Guendouz and Michelot , ; Church et al , ]. Indeed, we often speak of a negligible modern recharge assuming that most of the recharge occurred during past humid periods.…”

Section: Geological and Hydrogeological Contextmentioning

confidence: 99%

Quantifying the modern recharge of the “fossil” Sahara aquifers

Gonçalvès

Petersen

Deschamps

et al. 2013

Geophysical Research Letters

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[1] The North-Western Sahara Aquifer System (NWSAS), one of the world's largest groundwater systems, shows an overall piezometric decline associated with increasing withdrawals. Estimating the recharge rate in such a semiarid system is challenging but crucial for sustainable water development. In this paper, the recharge of the NWSAS is estimated using a regional water budget based on GRACE terrestrial water storage monthly records, soil moisture from the GLDAS (a land data system that assimilates hydrological information), and groundwater pumping rates. A cumulated natural recharge rate of 1.40˙0.90 km 3 yr -1 is estimated for the two main aquifers. Our results suggest a renewal rate of about 40% which partly contradicts the premise that recharge in this area should be very low or even null. Aquifer depletion inferred from our analysis is consistent with observed piezometric head decline in the two main aquifers in the region. Annual recharge variations were also estimated and vary between 0 and 4.40 km 3 yr -1 for the period [2003][2004][2005][2006][2007][2008][2009][2010]. These values correspond to a recharge between 0 and 6.75 mm yr -1 on the 650,000 km 2 of outcropping areas of the aquifers, which is consistent with the expected weak and sporadic recharge in this semiarid environment. These variations are also in line with annual rainfall variation with a lag time of about 1 year.

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Chlorine-36 dating of deep groundwater from northern Sahara

Cited by 43 publications

References 13 publications

Regional variations in the chemical and helium–carbon isotope composition of geothermal fluids across Tunisia

Regional variations in the chemical and helium–carbon isotope composition of geothermal fluids across Tunisia

The isotope hydrology of quaternary climate change☆

Quantifying the modern recharge of the “fossil” Sahara aquifers

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