Pleistocene age paleo-groundwater inferred from water-stable isotope values in the central part of the Baltic Artesian Basin

Abstract

A new data set of δ(2)H and δ(18)O in the groundwater from the central part of the Baltic Artesian Basin is presented. The hydrogeological section is subdivided into stagnation, slow exchange and active exchange zones. Na-Ca-Cl brine found at the deepest part - the stagnation zone - is characterized by δ(18)O values above -5 ‰ and δ(2)H values approaching -40 ‰ with respect to Vienna Standard Mean Ocean Water. The slow exchange zone where waters of mostly intermediate salinity reside is characterized by δ(18)O values around -11.7 ‰ and δ(2)H values around -85.3 ‰. Mean δ(18)O and δ(2)H values of the fresh groundwater in the active water exchange zone are -11.1 and -79.9 ‰, respectively. Characteristically, the groundwater in the active and slow exchange zone is isotopically more depleted compared with the precipitation values observed, and the depletion increases with depth down to the level where strongly enriched brines are encountered.

Calibrated geochemical ages of the Baltic Artesian Basin groundwater

“…Groundwater isotope geochemistry in Estonia is distinct from other localities within the BAB. Stable isotope content is depleted (δ 18 O is found down to -23‰), mainly due to cold climate-induced processes which occurred during the Pleistocene (Mokrik and Vaikmäe, 1988;Yezhova et al, 1996;Mokrik, 1997;;Vaikmäe et al, 2001;Raidla et al, 2012Raidla et al, , 2019bBabre et al, 2016;Sterckx et al, 2017Sterckx et al, , 2018Pärn et al, 2019;Mokrik and Samalavičius, 2022;Samalavičius and Mokrik, 2021;Samalavičius, 2022). The groundwater in aquifers in Lithuania and Latvia is above δ 18 O −14‰ (Delina et al, 2012).…”

“…Accordingly, the groundwater facies of deep and intermediate aquifers usually are Ca-Na-Cl or Na-Cl (Mokrik, 1997(Mokrik, , 2003. Sulphate-type groundwater is found in Lithuania's karst region (Juodkazis and Mikalauskas, 1994;;Paukstys and Narbutas, 1996;Paukstys et al, 1999;Juodkazis, 2003;Mokrik, 2003) and in Latvia (Levins et al, 1998;Delina et al, 2012;Babre et al, 2016) being mostly associated with sulphate mineral deposits. Despite the common background values of groundwater composition, multiple anom-alies are observed as well (Samalavičius, 2022).…”

Environmental isotopes and noble gas ages of the deep groundwater with coupled flow modelling in the Baltic artesian basin

“…Due to the fact that most of the Cm-V and O-Cm groundwater date back to the Pleistocene it is safe to assume that global glaciation and climate change processes could have affected its isotope hydrochemistry. Multiple formation scenarios are suggested to explain the origin of the Cm-V and O-Cm groundwater isotope geochemistry: glacial time precipitation recharge and meltwater injection, seawater intrusion, modern groundwater recharge and cryogenic alteration [6,8,19,20,[33][34][35][36][37].…”

Late Pleistocene and Holocene groundwater flow history in the Baltic Artesian Basin: a synthesis of numerical models and hydrogeochemical data

“…The salinity is mostly above 100 g L -1 and can exceed 180 g L -1 with the dominant Na-Cl and Na-Ca-Cl water types in the southern and deeper parts of the BAB (Kalvāns 2012). Brines with a salinity of 110 g L -1 have been reported from the Cambrian aquifer system (CAS) in Riga, Latvia (Babre et al 2016) and 158 g L -1 in Klaipeda, Lithuania (Gerber et al 2017). Oil and natural gas are found in the deeper southern parts of the O-Cm aquifer system (Kalvāns 2012).…”