Clypeusfloran i postglaciala fornsjölagerföljder i östra Mellansverige

Abstract

The following diagrams show the variations of the diatom flora in the deposits of the lake Myskjasjon in Uppland. In the lower strata a salt-water diatom flora is found that belongs to the ocean stage of the lake; in the middle part a brackish-water flora dominates as halinity has decreased because of the regression of the sea, and at the isolation contact at the transition to the upper strata a typical lagoon flora is developed. The frequency of the latter as well as the brackish-water flora then rapidly decreases and both are replaced by a lacustrine flora which dominates all the way up to the surface. Some few species of the lagoon flora are still found at a very low percentage throughout the whole sequence of strata, but nowhere in such a frequency that a transgression of the sea can come into consideration as underlying cause. Diagrams from Littorina period transgression sequences in Södermanland are shown as a comparison. A distinct correlation is found there between movements of the shore-line and the fossil diatom flora.