Wenlock bentonites in Lithuania and correlation with bentonites from sections in Estonia, Sweden and Norway

摘要

Seven Wenlock bentonite beds from four drill cores in Lithuania with sufficient thickness for sampling were analysed by XRD and XRF. The sanidine composition of bentonites combined with graptolite biozonation of the host rock were used for correlations. Two of the studied bentonite samples at the antennularius/flexilis biozone boundary can be confidently correlated between two Lithuanian sections. Four of the studied bentonites can be correlated with lower or higher probability with earlier studied bentonites in Estonia and Sweden. Identification of the Grotlingbo Bentonite in the Vidukle-61 drill core, and descriptions of other east Baltic sections enables composition of it thickness map of the Grotlingbo Bentonite. The thickness pattern with two axes, and the layered composition of the Grotlingbo Bentonite, indicate a change of the wind direction during a long lasting eruption. Hypothetical location of the volcanic source in the Silurian was within the zone of the Baltica-Laurentia collision.