Glacial Environments - Trace Fossils as Indicators of Sedimentary Environments - page 299

FIGURE 2 Some trace fossils from Pleistocene varved lacustrine sections south of Kaunas, Lith-
uania. (A) Three different Cochlichnus anguineus ( Co ) and Gordia ( ¼ Mermia) carickensis ( Gc );

Ppr-2-31 (lower parting surface), Paˇamin˙ section. (B) Glaciichnium liebegastensis ( Gl ) and
Helminthoidichnites isp. ( He ); Ppr-13-14, Paˇamin˙ section. (C) Gordia carickensis , Balbieriˇkis
section. (D) Gordia isp., Balbieriˇkis section. (E) Warvichnium ulbrichi ( Wa ) and Glaciichnium
liebegastensis ( Gl ); Ppr-2-41, Paˇamin˙ section. Scale bars ¼ 10 mm, except in (C) ( ¼ 5 mm).

Gondwana varve-like rhythmites (Supplementary Table 1 in http://booksite.
elsevier.com/9780444538130 ; Fig. 3 B, C, G, H, and K-M).
This ichnofauna occurs exclusively on parting surfaces of most rhythmite
laminae, including microlaminae of proximal varves. The bioturbated varves,
that compose the European Pleistocene glacigenic deposits, reflect events during
the summer and on the transitions to clay laminae interpreted as winter laminae.
The colonization surfaces are only 0.1-0.3 mm thick and the trace fossils are less
common in silt microlaminae within clay (winter) laminae, suggesting that the
tracemakerswere activemostly during summers and transitional periods. Cryptic
bioturbation, marked by reorientation of clay-mineral flakes, is noted in some
varved sediment ( O'Brien and Pietraszek-Matter, 1998 ). Preservation potential
was highest when the tracemaker moved on or through the thin silt couplet. How-
ever, trace fossils are not always present in such situations. Intervals with
increased abundance and diversity of trace fossils may reflect warming during
interstadials and retreating ice cover ( Netto et al., 2009; Uchman et al., 2008 ).
Trace fossils produced by vertebrates and invertebrates also occur in the
Pleistocene varved sediments of the Connecticut and Merrimack valleys
(USA; Benner et al., 2008, 2009; Knecht et al., 2009 ), revealing a general pat-
tern of benthic ecosystem development in deep, narrow glacial lake basins
( Table 1 ). The assemblage is dominated by fish trace fossils represented by
Broomichnium flirii , Piscichnus isp., Undichna bina , U. britannica , U. simpli-
citas , U. unisulca , and other piscine trace fossils. Cochlichnus isp. is the only