Trace fossils from Late Pleistocene varved lacustrine sediments in eastern Lithuania

Trace fossils Cochlichnus anguineus, Glaciichnium liebegastensis, Gordia carickensis (new combination, youngest occurrence), Gordia isp., Warvichnium ulbrichi, cf. Warvichnium isp. have been found in varved sediments of a small proglacial lake (17–16 kyr BP) in East Lithuania. They occur mostly in summer and transitional laminae along bunches of discrete microlaminae. Vertical reworking is absent. Horizontal distribution of trace fossils along microlaminae studied in one varved package points to a patchy distribution of trace fossils, resulting from a patchy distribution of food. Locally C. anguineus dominates and commonly this is the only trace fossil. Its co-occurrence with G. liebegastensis is distinctly rarer than with other ichnotaxa, probably due to a competition between their tracemakers. The trace fossil assemblage can be ascribed to the Mermia ichnofacies, in which the Glaciichnium ichnocoenosis (arthropod trackways dominate) and Cochlichnus ichnocoenosis (grazing traces dominate) can be distinguished as the end members. Replacement of the Glaciichnium ichnocoenosis by the Cochlichnus ichnocoenosis can be interpreted as shallowing of hypolimnion and degrading ecological conditions.