Effects of sulphate reduction and geogenic CO sub(2) incorporation on the determination of super(14)C groundwater ages-a case study of the Palaeogene groundwater system in north-eastern Syria

• Published in: Hydrogeology journal 2002-08, Vol.10 (4), p.495-508
• Main Author: Kattan, Z
• Format: Article
• Language: English
• Subjects: Age; Carbon dioxide; Carbonates; Dissolution; Groundwater; Mathematical models; Reduction; Sulfates
• ISSN: 1431-2174; 1435-0157
• DOI: 10.1007/s10040-002-0199-3

Groundwater from the Palaeogene aquifer system in north-eastern Syria has been studied using chemical and isotopic methods to determine the effects of carbonate dissolution, sulphate reduction and geogenic CO sub(2) incorporation in the dilution of super(14)C activity, and later to correct the conventional super(14)C water ages. The reason for this non-classical approach of correction is because the groundwater in this karstified and Nummulitic carbonate aquifer occurs under confined and partly confined conditions, and is located in an area very close to deep faults and fractures. Furthermore, the interconnection with the Upper Cretaceous formations, which commonly contain gypsum and hydrocarbons, can facilitate the processes of sulphate reduction and geogenic CO sub(2) incorporation, which should not be excluded. The dilution factor related to carbonate dissolution was estimated to be about 0.60-0.75. The dilution factor associated with sulphate reduction, which only depends on H sub(2)S content, was rather low (about 0.95). However, as a result of the local tectonic setting in this area, the influence of geogenic CO sub(2) incorporation was clearly high. The dilution factor associated with this effect ranges between 0.24-0.64. Consequently, the corrected super(14)C ages are considerably reduced compared with those determined by classical models. Accordingly, the groundwater in the study area can be divided into three main groups: (1) fresh, shallow and cold water of less than 1 ka age; (2) brackish, deep and thermal water of rather old age (10.9-12.3 ka B.P.); and (3) an admixed groundwater of intermediate quality and age (1.9-6.7 ka B.P.).Original Abstract: L'eau du systeme aquifere du Paleogene du nord-est de la Syrie a ete etudiee au moyen des methodes chimiques et isotopiques afin de determiner les effets de la dissolution des carbonates, de la reduction des sulfates et de l'introduction de CO sub(2) d'origine geologique responsable de la dilution du super(14)C, pour corriger ensuite les ages super(14)C conventionnels des eaux. La raison de cette approche de correction, qui n'est pas classique, est due au fait que l'aquifere carbonate karstifie du Nummulitique est captif ou partiellement captif, et qu'il est situe dans une region tres proche de failles et de fractures profondes. En outre, la connexion avec les formations du Cretace superieur, qui contient habituellement du gypse et des hydrocarbures, peut faciliter les processus de reduction des sulf