Application of carbon isotopes to the study of the Ordovician and Silurian of the BalticMartma, Tõnu2006 https://digi.lib.ttu.ee/i/?107 https://www.ester.ee/record=b2209327*est Origin and geochemical evolution of palaeogroundwater in the northern part of the Baltic artesian basin = Paleopõhjavete päritolu ja geokeemiline areng Balti arteesiabasseini põhjaosasPärn, Joonas2018 https://digi.lib.ttu.ee/i/?10917