Environmental Engineering Reference
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lakes based on their prevalent facies associations. The model is useful to summa-
rize the factors that influence the composition and distribution of traces produced
by plants and animals. However, few researchers in continental ichnology have
considered the basin-scale distribution of deposits that preserve particular trace-
fossil assemblages, and much work remains to determine how ichnology can be
applied to the interpretation of lake-basin depositional systems at this scale. Nev-
ertheless, numerous documented case studies can be considered within the frame-
work of the lake-type model and improve the present understanding of how
organism/sediment interactions in lacustrine basins can be applied to paleoenvi-
ronmental reconstructions and stratigraphy ( Buatois and M ยด ngano, 2009 ).
When applying the lake-type basin model, it is important to distinguish
between the accommodation potential in the lake basin and the accommodation
within the water body itself, related to the depth of the lake ( Bohacs et al., 2003 ).
It is the accommodation potential of the basin relative to the amount of sediment
and water that enters the basin that determines whether a lake is open or closed,
whereas the accommodation within the lake itself influences sedimentation. In
each of the lake-type basins, the lakes may be deep or shallow, depending on the
elevation difference between the basin floor and the sill height, and the depth of
the water body relative to this difference. This strongly influences the mixing
regime and oxygenation of lacustrine waters and sediments.
In overfilled lake-type basins, terrestrial environments and trace-fossil
assemblages produced in drier, terrestrial environments are of limited extent
because the basin is relatively filled with water and water tables are high in mar-
ginal environments ( Bohacs et al., 2007b ). The presence of terrestrial and lake-
marginal environments in balanced-fill lake-type basins is variable, depending
on whether the lake-basin is at or overflowing the basin sill and relatively full or
well below the basin sill with widespread subaerially exposed areas. In under-
filled lake-type basins, terrestrial and lake-marginal environments are relatively
widespread and may form thick packages of sediments toward the basin mar-
gins. However, large-scale fluctuations of the lake level also occur in under-
filled basins, and lacustrine sediments may form thick vertical successions
near the basin margins if they were deposited during high lake levels that
remained below the sill height. Lacustrine transgressions may also be due to
tectonic activity affecting localized areas with higher subsidence rates and
may be best observed in underfilled basins. These factors together determine
the distribution and stacking patterns of sedimentary deposits, as well as the
composition and distribution of biogenic structures in lake basins.
3.1 Overfilled Lake-Type Basins
Overfilled lake-type basins ( Fig. 5 ) are characterized by fluvio-lacustrine
deposits in freshwater lakes with open hydrology, which develop when the rate
of sediment and water input exceeds the potential accommodation in the basin
( Bohacs et al., 2000, 2003; Carroll and Bohacs, 1999 ). Parasequences are
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