Lacustrine Environments - Trace Fossils as Indicators of Sedimentary Environments - page 374

across a lake basin. Depending on the mixing regime of the lake and on whether
it is hydrologically open or closed, among other controls, the environmental
characteristics affecting sedimentation and biogenic activity within each zone
may differ significantly. The particular environmental conditions between zones
in wave/wind-influenced lacustrine depositional systems, alluvial to fluvio-
lacustrine depositional systems, or low-energy lacustrine depositional systems
are extremely variable. Nevertheless, several parameters affect lakes of all types
as well as the distribution and behavior of organisms and the production and
preservation of trace fossils ( Table 1 ).
The lake-type model of Carroll and Bohacs (1999) and Bohacs et al. (2000)
recognizes three types of lake basins according to the input of sediment andwater
to the basin and the accommodation potential of the basin: overfilled, balanced-
fill, and underfilled. In overfilled lake-type basins, the input of water and sedi-
ment exceeds the potential accommodation, and lakes overflow into an adjacent
basin. Balanced-fill lake-type basins are characterized by rates of sediment and
water supply approximately in balance with potential accommodation, so that
balanced-fill lake types periodically shift between being hydrologically open
or closed. In underfilled lake-type basins, the potential accommodation exceeds
the amount of sediment and water input. This relationship influences the domi-
nant sedimentary facies, the stratal packaging of parasequences, the dominant
types of organic matter, and the distribution and flow characteristics of source
rocks, reservoirs, and seals ( Bohacs et al., 2000; Carroll and Bohacs, 2001 ). This
relationship also determines the distribution of habitats and the main limiting
environmental controls on trace-producing organisms.
Buatois andM´ngano (2004, 2007, 2009) integrate the lake-type basinmodel
with the ichnofacies model of lacustrine and lake-margin environments. This
approach is followed here in order to showhow the dynamic interactions between
lake-basin sedimentary environments and trace-producing plants and animals
can be applied to reconstructing depositional systems and the sequence-
stratigraphic interpretation of the basin fill. The extreme complexity and variabil-
ity of lacustrine systems should always be considered when applying ichnology
to the reconstruction of lake-basin successions. However, the lake-type model
permits the detection of several general ichnological trends and the placement
of documented case studies within an already existing, useful stratigraphic
model. Although terrestrial and fluvial systemsmay bewidespread in lake basins,
especially in underfilled lake basins, this chapter focuses on the aquatic zones of
lakes, as well as the zone of typical lake-level rise and fall ( Table 1 ).
2. ICHNOLOGY
2.1 Biogenic Activity and Structures in Lake Basins
The diversity and distribution of organisms within and surrounding a lake are
controlled by numerous abiotic and biotic factors ( Table 1 ; e.g., Cohen, 2003;
Hammer, 1986; Miller and White, 2007; Wetzel, 2001 ). Lakes contain a large