Glacial Environments - Trace Fossils as Indicators of Sedimentary Environments - page 296

2010 and references therein). Most trace-fossil assemblages occur within post-
glacial facies and have been recorded in Brazilian, South African, and Argen-
tinian Basins (see references in Supplementary Tables 1 and 2 in http://booksite.
elsevier.com/9780444538130 ), which represent deposition in coastal lakes and
fjords that opened toward a shallow sea. The Quaternary Ice Age sedimentary
record is well exposed in the Northern Hemisphere, with sedimentary facies sim-
ilar to those recorded from rocks of the Late Paleozoic Gondwana Ice Age. The
preservation of Quaternary rhythmites is extensive and they provide geological
evidence that support the interpretation of a seasonal (winter-summer) control of
depositional cycles. Trace fossils fromQuaternary glacigenic deposits have been
recorded chiefly in varved glaciolacustrine sediments from the northern hemi-
sphere, in Austria, Canada, England, Finland, Germany, Lithuania, Poland,
Sweden, and the USA (see Uchman et al., 2008, 2009 and references therein;
Benner et al., 2008, 2009; Fliri et al., 1970; Knecht et al., 2009 ).
Despite occurring in disparate time periods, glacial trace-fossil assemblages
share some characteristics. The same overall trace-fossil composition has been
recorded in glaciolacustrine (or closely related settings strongly influenced by
freshwater due to meltwater discharge) deposits of both ages (see Supplementary
Table 1 in http://booksite.elsevier.com/9780444538130) . Typically these deposits
are dominated by horizontal biogenic structures including arthropod trackways,
trails, furrows, and resting traces; fish swimming trails; and regularly sinuous to
randomly meandering tiny shallow burrows produced byworm-like animals. Gla-
ciolacustrine trace-fossil assemblages occur almost exclusivelywithin and onbed-
ding planes, show a relatively low ichnodiversity, high abundance, and patchy
distribution ( Uchman et al., 2008, 2009 ). Aquatic and terrestrial suites may occur
on the same bedding plane in palimpsest-type preservation, the latter generally
superimposing the former, suggesting a diminished water table and community
succession ( Netto et al., 2009 ). Despite the significant mammal body fossils from
the Cenozoic to earlyHolocene, their tracks and trackways have not been recorded
from glaciogenic deposits until the present day ( Martin, 2009 ).
3.2 Glaciolacustrine Trace-Fossil Assemblages
The pattern of biogenic structures observed on the bedding planes of ancient ice-
proximal glaciolacustrine deposits, the common presence of fish swimming
trails, and the patchy distribution of trace fossils, are consistent with the oppor-
tunistic colonization pattern observed in modern glaciolacustrine settings. Inter-
estingly, modern pioneer invertebrate communities had the same small-scale
spatial heterogeneity and strong correlation with environmental conditions as
the older, established sites; a fact that may explain the observed similarity of
freshwater invertebrate trace-fossil assemblages across different ages and basins
(see Supplementary Table 1 in http://booksite.elsevier.com/9780444538130 )
and references therein.
The freshwater trace-fossil assemblages recorded in both Late Paleozoic
Gondwana and Quaternary varve-like rhythmites are characterized by the