E3S Web Conf.
Volume 98, 201916th International Symposium on Water-Rock Interaction (WRI-16) and 13th International Symposium on Applied Isotope Geochemistry (1st IAGC International Conference)
|Number of page(s)||5|
|Section||Geological Evolution of Water-Rock System: Mechanisms, Processes, Factors, Stages. The Session Dedicated to Stepan Shvartsev’s Memory|
|Published online||07 June 2019|
Water-rock interaction of the Jilh and Tawil aquifers in the Wadi Sirhan Basin, NW Saudi Arabia
Groundwater Division, Saudi Aramco, 31311 Dhahran, Saudi Arabia
2 EXPEC Advanced Research Centre, Saudi Aramco, 31311 Dhahran, Saudi Arabia
3 Earth Sciences Department, Durham University, DH1 3LE Durham, United Kingdom
* Corresponding author: firstname.lastname@example.org
A total of 79 groundwater samples from the Upper Silurian-Lower Devonian Tawil and Triassic Jilh aquifers in NW Saudi Arabia were analysed for hydrochemical and strontium isotopic composition. A sequential extraction and 87Sr/86Sr analysis were conducted on 32 cutting samples from the groundwater host rocks and the underlying shale bed. The chemical composition of the groundwater was distinct from that of the host rock lithologies in terms of elemental abundance (i.e., Na+ was dominant in the groundwater and K and Ca were the main constituents of the aquifer units). Principal component analysis (PCA) of water samples showed a positive loading of Na+ and negative loadings of Ca2+ and SO42-. The replacement of gypsiferous waters by Na+-rich waters is suggested by this ion exchange. The shale rock samples showed Na to be the dominant chemical constituent. 87Sr/86Sr ratios of the groundwater (0.707673-0.711577) and host rock samples (0.707930-0.712477) suggest that groundwater inherits the Sr signature of the rock from the exchangeable, carbonate, and the oxides phase, reflecting reducing conditions in Tawil aquifer. The elevated groundwater 87Sr/86Sr ratios were found in deeper sections of the aquifers, which coincided with the radiogenic 87Sr/86Sr of the deeper aquifer lithologies and the underlying shale bed.
© The Authors, published by EDP Sciences, 2019
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