Geology Reference
In-Depth Information
Fig. 4.8 Distinctive trace fossils of tidal settings. ( a ) Stellate,
iteratively branched interface-feeding trace (presumably made
by an annelid). Eocene Baronia Formation, Spain. ( b ) Modern
feeding traces analogous to that shown in ( a ) made by Nereid
polychaetes. Field of view 14 cm across. Modern tidal flat,
Kouchibouguac, New Brunswick, Canada. ( c ) Highly biotur-
bated zone dominated by Planolites (Pl) and Teichichnus (Te).
Miocene Pebas Formation, Peru. ( d ) Siphonichnus (Si) at
transition to intertidal flat. Field of view is approximately
110 cm across. Pleistocene, Willapa Bay, Washington, USA.
( e ) Undiagnosed meandering, dominantly horizontal mud-filled
burrows showing high level of resource optimization. Tidal dune
toeset, Eocene, Baronia Formation, Spain
7. Demonstrably mappable ichnological data (particu-
larly size and diversity trends) that can be related to
the landward decrease of salinity in the tidal-fluvial
transition zone.
8. The common presence of a brackish-water fauna
(as expressed by the dominance of simple, facies-
crossing ichnogenera).
for ichnological datasets. Limitations of identifying
tidal influence from ichnological datasets are, in part,
intrinsic: due to the seasonal nature of larval recruit-
ment and the longer time scales represented by bio-
genic sedimentary structures, trace fossils generally do
not represent organism responses to rhythmic changes
in energy associated with diurnal or semidiurnal tidal
cycles. On the other hand, careful documentation of
specific trace-fossil characteristics (lining and infill),
documentation of the episodic character of mud/food
deposition and their distributions in the sediment,
interpreted in the context of the detailed analysis of the
composition of the trace-fossil assemblage, can be
linked strongly to tidal transport of sediment and
food. Characterization of vertical successions and the
identification of intertidal-flat deposits, which are
4.5
Summary
The potential of trace fossils in helping to identify tidal
influence on sedimentation and faunal colonization is
at its inception. Although relatively sophisticated anal-
yses of tidally generated sedimentary structures have
been established and refined, the same cannot be said
 
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