Wenlock and uppermost Llandovery bentonites as stratigraphic markers in Estonia, Latvia and Sweden

Fifty-nine Wenlock and uppermost Llandovery bentonite samples from the Estonian and Latvian Aizpute drill-core sections were studied by analysing magmatic sanidine composition by XRD. On the basis of sanidine composition and geochemical data the Estonian bentonites can be grouped into six types, which probably reflect different volcanic sources. These bentonites originate from 33 different eruptions, 16 of which can be recognised on the basis of their sanidine composition. Four bentonites from the Llandovery/Wenlock boundary interval in Estonia are correlated with the Aizpute core in Latvia and with outcrops on Gotland in Sweden.