Controls on stable isotope profiles in the Chalk aquifer of north-east Norfolk, UK, with special reference to dissolved sulphate

N. A. Feast, K. M. Hiscock, P. F. Dennis, S. H. Bottrell

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Groundwater samples were collected at a site in N Norfolk, UK, comprising a borehole penetrating Upper Chalk and piezometers open within the overlying glacial deposits and intervening, weathered Putty Chalk. The samples were analyzed for δ18O (water), δ34S and δ18O (SO4) and δ13C (HCO3) as well as major ions. Variations in solute concentration and isotopic composition with depth were found to be caused by limited groundwater circulation at the site and incomplete flushing of old groundwater. The isotopic data prove the existence of a mineralized palaeowater at depth, which has undergone SO4 reduction and is being slowly modified by mixing with recent groundwater circulating at a shallow depth in a more transmissive Chalk horizon. One measured δ18O (H2O) value of - 8.25‰(VSMOW) represents the lightest value reported for the Norfolk Chalk aquifer and is evidence for a component of Late Pleistocene recharge trapped at depth. The wide range of observed isotope ratios at the site, e.g. δ34S and δ18O SO4 between 7.8 to 27.8‰(CDT) and 5.2 to 20.0‰(VSMOW) respectively, demonstrates the importance of vertical stratification of solutes and the implications this has for interpreting spatial hydrochemical surveys of groundwater.

Original languageEnglish
Pages (from-to)803-812
Number of pages10
JournalApplied Geochemistry
Issue number6
Publication statusPublished - Nov 1997

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