Lacustrine Environments - Trace Fossils as Indicators of Sedimentary Environments - page 369

exposureand the depth to thewater table,whichcanapproximate the extent of lake-
level changes (e.g., de Gibert and S´ez, 2009; Genise et al., 2004 ). By recognizing
biogenic structures that are produced subaqueously and cross-cut by those pro-
duced subaerially, for example, a change in substrate conditions can be identified
(e.g., Buatois et al., 1997; Kim et al., 2002; Metz, 1996 ).
Recurrent assemblages of plant and animal trace fossils through geological
time (i.e., ichnofacies) provide a guide to recognizing the sets of environmental
controls towhich the organisms responded, and hence to the general depositional
setting. A consideration of the “taphonomic pathways” of these assemblages
leads to a better understanding of changing conditions ( Buatois and M ´ ngano,
2004, 2011 ). Through the more detailed recognition of recurrent associations
of biogenic structures (i.e., at the scale of suites, ichnofabrics, or ichnocoenoses),
together with an analysis of their vertical distribution within a sedimentary
succession, ichnology can be applied to the reconstruction of the depositional
system (e.g., Melchor, 2004; Melchor et al., 2006; Porter and Gallois, 2008;
Voigt and Hoppe, 2010 ). Tiering within a single infaunal community may be
uncommon in lake basins, except in well-oxygenated freshwater lakes (e.g.,
McCall and Tevesz, 1982 ) and in well-developed paleosols with insects that
burrow and nest at different depths (e.g., Genise et al., 2004; Hasiotis, 2007 ).
Palimpsest and/or exhumed substratesmay be particularly common in frequently
exposed lake-marginal deposits where net sedimentation rates are low and ich-
nofacies or suites are commonly overprinted (e.g., Buatois and M´ngano, 2004,
2009; Scott et al., 2009; Uchman and ´ lvaro, 2000 ). These types of substrates
represent surfaces that are important for the sequence stratigraphy of lake basins
and for deciphering the dynamic history of the lake.
The sedimentary environments in lake basins are dictated by complex sets of
controls, many of which also directly impact the biodiversity (numbers of spe-
cies, abundance) of microorganisms, plants, and animals within the basin
( Fig. 1 ; e.g., Carroll and Bohacs, 2001; Cohen, 2003; Gierlowski-Kordesch
and Park, 2004; Renaut and Gierlowski-Kordesch, 2010; Talbot and Allen,
1996 ). Deposition in lake basins is closely related to both the climate and the
tectonic setting, through factors such as the precipitation/evaporation ratio,
the size and shape of the basin, and variable subsidence rates ( Bohacs et al.,
2000 ). The stratigraphic packaging of the basin fill is a direct response to the
relationship between the amount of sediment plus water input to the basin
and the potential accommodation, or the spatial volume at elevations lower than
basin-bounding structural or geomorphological features ( Carroll and Bohacs,
1999 ). The distribution of terrestrial versus aquatic settings within a lake basin
is dependent on this relationship, resulting in lake basins that can be either rel-
atively full with water or relatively empty, and which can vary through time.
The tectonic setting can also influence whether the inflow to the lake is
provided by rivers and/or springs, with specific structural features in the basin
controlling the distribution of the fluvio-lacustrine systems and spring-fed wet-
lands, for example, as well as the spill points over which lake waters can flow
out of the basin (e.g., Pietras and Carroll, 2006 ). The gradient of the basin floor