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scoured and cast with sediment. For such burrows,
Ksi˛˙kiewicz (1954)
intro-
duced the term “pre-depositional”, because they were produced prior to the
deposition of a turbidite. The trace fossils within previously deposited beds
are named “post-depositional” (see also
Leszczy´ski, 1993a; Seilacher,
1962
). As a rule, the post-depositional suite consists of deeply penetrating trace
fossils, whereas the pre-depositional suite includes highly organized, often del-
icate burrows for which
Fuchs (1895)
coined the term “graphoglyptids”. The
pre-depositional trace fossils are normally produced by shallow burrowing
organisms which are mostly mud dwellers (
Kern, 1980
).
In most cases, the producers of deep-sea trace fossils are unknown, and
commonly they are referred to as “worms” of unknown taxonomic affinity.
However, some burrows are formed by crustaceans (e.g.,
Ophiomorpha
,
Thalassinoides
), bivalves (e.g.,
Protovirgularia
), or echinoids (
Scolicia
), based
on the recognition of characteristic features.
The ethological interpretation of trace fossils is based on the analysis of their
functional morphology. The basic ethological categories were introduced by
Seilacher (1953)
and new ones were subsequently added (see
Rindsberg, 2012
,
for a review). In the deep sea, the most common categories are the following:
Pascichnia: mostly horizontal burrows produced by vagile deposit-feeding
organisms (e.g.,
Scolicia
,
Protovirgularia
).
l
Fodinichnia:
traces produced during localized deposit-feeding (e.g.,
l
Zoophycos
).
Agrichnia: delicate, mostly shallow, regularly patterned burrow systems
showing a range of morphologically varying meanders (e.g.,
Helmintho-
rhaphe
), spirals (
Spirorhaphe
), rosettes (
Lorenzinia
), or nets (
Paleodictyon
),
produced for the trapping or farming of microbes or other very small organ-
isms; most of the trace fossils within this category are termed “graphoglyp-
tids” (
Fuchs, 1895; Miller, 1991b; Seilacher, 1977a; Uchman, 2003
).
l
Chemichnia: structures produced by organisms feeding on chemosymbio-
tic microbes; the organisms maintain a connection to oxygenated water but
penetrate into anoxic sediments rich in sulfides or ammonium that are
required for microbe-feeding (e.g.,
Chondrites
,
Trichichnus
).
l
Domichnia: open burrows used as dwelling structures (e.g.,
Ophiomorpha
rudis
); transitional forms to fodinichnia or even to agrichnia are common
(the case of
O. rudis
; see
Cummings and Hodgson, 2011a; Uchman, 2009
).
l
Repichnia:
structures
recording the movement of organisms
(e.g.,
l
Helminthopsis
).
Some of the deep-marine trace fossils display a very complex morphology,
suggesting that they may have been produced by more than one ethological
activity, for instance,
Hillichnus
, which is interpreted as a bivalve locomotion
and feeding trace (
Bromley et al., 2003
). A complex morphology is ascribed to
either the living strategy or the various behavioral activities of the tracemaker
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