Environmental Engineering Reference
In-Depth Information
Seilacher
Martinsson
Full relief
Exichnia
Convex
Concave
Semirelief
(Epirelief)
Epichnia
Full relief
Endichnia
Semirelief
(Epirelief)
Hypichnia
Full relief
Exichnia
FIGURE 1
Toponomy of trace fossils, after
Seilacher (1953)
and
Martinsson (1970)
, with inspi-
ration from
Bromley (1996)
.
The above classification is simple, easy to use, and informative, but more
advanced observers can glean much more from the trace fossils. For example,
a convex hypichnion may be produced by casting a surface trace, by collapsing
an open burrow, by passive fill of a previously open burrow, by active fill of a
burrow by its maker, or by scouring out a previously buried burrow (
Fig. 2
).
Distinction of
passive fill
and
active fill
(sometimes called
infill
) is partic-
ularly important, as a clue to deposition and to the trace fossil's ethological
function. Passive fill is defined as fill resulting from physical sedimentation
without the active involvement of the tracemaker; it occurs in abandoned bur-
rows and in burrows that are filled too rapidly for the maker to resist the process.
Accordingly, passive fill is generally laminated more or less horizontally.
Active fill is defined as fill made by the tracemaker during its lifetime. This fill
is more usually obliquely or vertically laminated than horizontally disposed,
may show signs of manipulation or pressure (scratches, tension fractures, lam-
inae of alternating lithology), and may include fecal pellets. Actively filled bur-
rows include burrows that were never open, that is, burrows made by animals
that moved within the substrate while feeding on sediment or on other creatures.
Recognition of scoured hypichnia is also necessary, especially in the study
of storm beds and turbidites. The original work by
Seilacher (1959)
is still well
worth consulting, with its discussion of
pre-depositional
trace fossils made
before a turbidity current (including scoured hypichnia) and
post-depositional
trace fossils made after it (
Uchman and Wetzel, 2012
). Many of the most del-
icate forms, originally excavated in mud, would not be preserved, had they not
been partially scoured by currents and then filled with a more resistant casting
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