Dynamics of phytoplankton in relation to the upper Homerian (Lower Silurian) lundgreni event – An example from the Eastern Baltic Basin (Western Lithuania)

• In the middle and the upper Homerian five phytoplankton assemblages were distinguished.
• The lundgreni event had minor effect on the composition of the phytoplankton.
• The 4th order sea level cycles had major influence on the phytoplankton diversity.

The Silurian period was a time of significant environmental change punctuated by a series of bioevents. The mid-Homerian lundgreni event was one of the most severe extinction episodes of the mid-Paleozoic, which mostly affected pelagic organisms, while simultaneously sparing benthos. Despite the great importance of phytoplankton in determining the causal mechanisms of ecosystem collapse, there are very few studies on the effects of the lundgreni event on this ecological super-guild.Here we present a detailed quantitative paleoecological analysis of the green algae and acritarchs of the upper Wenlock of the Viduklė-61 section (Western Lithuania). Independent high-resolution graptolite biostratigraphic and δ13C chemostratigraphic control ensures accurate calibration of the micro-phytoplankton diversity and community compositional trends. The constrained clustering and assemblage zoning revealed five distinct assemblages separated by sharp changes in genus diversity and sample taxonomic composition. The statistically estimated local genus richness curves revealed similarity with previously determined 4th order sedimentary cycles. Interestingly, though, it appears that the lundgreni (mid-Homerian) biotic event had a significantly smaller effect on the studied ecological super-guild than the subsequent mid-upper Homerian regression.

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