Estuaries - Trace Fossils as Indicators of Sedimentary Environments - page 457

FIGURE 4 Pleistocene examples fromWillapa Bay, Washington, USA (see Gingras et al., 2000 ).
(A) Typical vertical succession observed in a tidally influenced bay and in estuary settings (e.g.,
Anima et al., 1989; Clifton, 1983; Gingras et al., 1999; Pearson and Gingras, 2006 ). (B) An erosional
channel base (white arrows) demarcated by a suite attributable to the Glossifungites Ichnofacies,
comprising firmground Thalassinoides and a tubular tidalite infill (tt). (C and D) Moderately to
intensely bioturbated intertidal strata: in these examples, the outer tidal flat is characterized by
Siphonichnus ( Si ) and the inner tidal flat by Thalassinoides ( Th ). (E) Subtidal laterally accreted
units. These beds are characteristically rarely burrowed; however, moderate bioturbation may be
present with either the sand- or the mud-dominated members of the IHS. In this example, Psilonich-
nus ( Ps ) and Skolithos ( Sk ) are indicated.
stages of the falling tide (summarized in Gingras and MacEachern, 2012 ).
This and other factors lead to a preponderance of surface and subsurface
deposit-feeding and infaunal lifestyles (discussed above) and also result in a
characteristic distribution of trace fossils ( Fig. 4 A). Coupled to this, due to
the presence of stronger currents in the deeper parts of channels, tidally influ-
enced bars (i.e., point bars and longitudinal bars) characteristically display an