Glacial Environments - Trace Fossils as Indicators of Sedimentary Environments - page 290

during glaciations has strongly impacted the original landscape, promoting
surficial weathering and deep erosion. During interglacial periods, immense
meltwater discharges influenced sedimentation ( Buatois et al., 2006, 2010 )
in addition to exerting erosional forces. Drastic oscillations in climate
( Balistieri, 2003; Buatois et al., 2006, 2010; Netto et al., 2009 ) and the resulting
change in the land surface of glaciated regions has impacted the distribution,
abundance and, subsequently, evolution of biota through time.
Large-scale glaciations occur about every 200 million years and five
inferred global-scale glaciations are known to have impacted the biotic realm
(e.g., Clark et al., 2009; Ehlers and Gibbard, 2004; Eyles, 1993; Hoffman
et al., 1998; Isbell et al., 2003a,b; Le Heron, 2010; Rieu et al., 2007 ). Trace fos-
sils from glacial environments are well documented in the Gondwana, and the
Quaternary ice ages, and case studies of those glacial periods are presented
herein. Thus, the objectives of this chapter are to discuss the main characteris-
tics of trace-fossil assemblages from glacial environments, to evaluate the main
abiotic stress factors that constrained tracemakers' impact on trace-fossil abun-
dance and diversity, and to characterize the overall trace-fossil distribution in
glacial settings. Inherently, the discussion must be limited to those glacial envi-
ronments which best preserve trace fossils, and while that includes primarily
aquatic depositional environments, some emergent and fully terrestrial environ-
ments are considered as well.
2. ECOLOGICAL AND ENVIRONMENTAL CONSTRAINTS IN
GLACIAL SETTINGS
The exposure of new environments after the culmination of a glacial period
stimulates dispersion of biota from glacial refugia and the establishment of
new communities. Ecologic studies on biotic communities from Antarctica
suggested that temporary freshwater ecosystems surrounded by ice might have
provided oases for a few aquatic species adapted to extreme conditions ( Brinck,
1966 ). In other cases, ice-free high-elevation areas may have provided refuge
for certain terrestrial organisms. These resilient species may opportunistically
recolonize areas when new habitats become available during glacial retreat. An
understanding of this process is critical to the interpretation of the ichnological
record of formerly glaciated regions, as environmental constraints placed strict
controls on successional patterns in these environments.
2.1 Environmental Stress in Glacial Settings
Physical environmental stress is predominant in glacial environments, and sea-
sonal or episodic variations in physical processes can be extreme and abrupt.
The impact of rapid environmental changes upon terrestrial and subaquatic
freshwater fauna from glacial foreland environments is amplified relative to