Lower Ordovician Leetse Formation in the North Estonian Klint area

Abstract

Sequences of the Leetse Formation were studied in order to find out the conodont biozonation, grain-size distribution, and glauconite mineral properties and their variations along the North Estonian Klint. On the basis of the conodont zonation of the Saka section, combined with earlier data, it was found that the Leetse Formation belongs to the Paroistodus proteus, Prioniodus elegans, and Oepikodus evae zones of various thickness and completeness along the North Estonian Klint. The Pr. elegans Zone of the Saka section was found to be remarkably complete and correlate well with equivalent intervals of sections in the St. Petersburg Region. Poorly lithified glauconitic sandstones of the Leetse Formation vary lithologically vertically as well as laterally. The Leetse Formation in the west has been repeatedly redeposited and is depleted in suspended fraction, while in the east it is more homogeneous and represents continuous shallow-water conditions. Glauconite is represented by a potassium- rich variety (about 9% K2O) and most likely forms at least two discrete modifications. Laterally, glauconite of the Leetse Formation in the western part of the klint contains less K than that of the eastern part, indicating faster sedimentation. The d(001) value of glauconite diminishes upwards in the sequence, indicating acceleration of the sedimentation rate.