Lacustrine Environments - Trace Fossils as Indicators of Sedimentary Environments - page 376

and lake-margin areas, and may be produced either subaqueously or subaerially,
depending on the tracemaker, their behavior, and the environmental setting. Insect
nests and mammal burrows may also be present in lacustrine or lake-margin
deposits if lake levels drop sufficiently following sedimentation (e.g., Genise
et al., 2010; Melchor et al., 2002; Scott et al., 2009; Smith and Mason, 1998 ).
Neoichnological studies of lacustrine and lake-marginal environments have
documented many types of biogenic structures produced by a variety of conti-
nental organisms (e.g., Chamberlain, 1975; Clark and Ratcliffe, 1989; Garcia
and Niell, 1991; Genise et al., 2009; Gingras et al., 2007; Hasiotis and Mitchell,
1993; Knecht et al., 2009; Metz, 1987, 1990; Ratcliffe and Fagerstrom, 1980;
Uchman, 2005 ), although much work remains to characterize the plethora of
trace types produced by plants, invertebrates, and vertebrates. Studies that con-
sider the distribution of different infaunal and epifaunal biological communities
and the resultant traces produced and potentially preserved in terms of environ-
mental controls are comparatively rare (e.g., Cohen, 1982; Cohen et al., 1991,
1993; Fisher, 1982; Hamer and Sheldon, 2010; McCall and Tevesz, 1982; Scott
et al., 2007, 2009 ). Biological studies of epifaunal and infaunal animals in lacus-
trine and lake-margin settings (e.g., oligochaetes, insect larvae, bivalves) are
numerous (e.g., Fisher and Beeton, 1975; Knisley, 1984; McCall et al., 1986 ),
although in many cases the different research focuses of ichnologists and
biologists make the translation of the results necessary.
Although it is sometimes assumed that little has been published on the trace-
fossil record of lakes, recent compilations reveal a large volume of literature on
lacustrine and lake-margin ichnofaunas ( Buatois and M´ngano, 2007; Minter
et al., 2007 ). This reflects not only ecological aspects, but also that traces
emplaced in lacustrine sediments have the highest preservation potential of
all continental trace fossils ( Buatois and M´ngano, 2011 ). The highest preser-
vation potential of biogenic structures within lakes is in low-energy areas, such
as those that are only weakly affected by wave action. In deep lake environ-
ments, alternation of very fine-grained sands and muds deposited from under-
flow or turbidity currents, or the seasonal to short-term variations in
sedimentation rates or sediment composition (e.g., varves), promotes the pre-
servation of delicate and tiny surface trails, as well as very shallow-tier burrows
and insect trackways ( Benner et al., 2009; Buatois and M ´ ngano, 1998, 2007;
Netto et al., 2012; Uchman et al., 2009 ). In low-energy shoreline deposits,
trace-fossil preservation commonly results from the rapid influx of sand via
non-erosive sheet floods (e.g., Minter et al., 2007; Zhang et al., 1998 ). A unique
preservational pathway, particularly common in underfilled lakes, involves the
rapid cementation of substrates in carbonate and/or saline, alkaline lakes (e.g.,
by calcite, dolomite, zeolites; Scott et al., 2008; Scrivner and Bottjer, 1986 ). In
subaerially exposed substrates, however, superficial traces are particularly
susceptible to destructive processes (e.g., deflation, salt efflorescence) where
they are not protected by clay drapes, surface crusts, or microbial mats (e.g.,
Cohen et al., 1991; Scott et al., 2010 ).