Fluvial Environments - Trace Fossils as Indicators of Sedimentary Environments - page 324

each category is defined on the basis of the morphology of the trace fossil, some
interpretative names of common use in the literature are adopted (e.g., “arthro-
pod trackway”, “bird track”, “sauropod track”).
This simple classification scheme is not intended to replace the existing
taxonomic approach for invertebrate and vertebrate trace fossils. Instead, by
reducing the number of categories, it may facilitate recognition of recurrent
associations of trace fossils that must be contrasted with definite ichnotaxo-
nomic assignments. In addition, biogenic structures that cannot be or were
not identified ichnotaxonomically in the literature can be compared with a
trace-fossil category. However, unequivocal comparison of a trace-fossil
assemblage with an ichnofacies is possible only through ichnotaxonomic
assignment of the component trace fossils.
About 250 case studies describing fluvial trace-fossil assemblages in a defi-
nite facies context and with a clear ichnotaxonomical assignment were analyzed
for this chapter. A detail of the included case studies can be found as Supple-
mentary Material in http://booksite.elsevier.com/9780444538130 . The data-
base is biased toward the description of invertebrate trace-fossil assemblages
(52%), a lower number of studies describe vertebrate and invertebrate trace fos-
sils in conjunction (33%), and the less common studies are those that describe
vertebrate trace fossils in a definite facies context (15%). There are many papers
that are concerned with the description of tetrapod tracks and trackways that are
not accompanied by a description of the sedimentary facies, and are thus
excluded from this analysis. Only trace-fossil assemblages that were recovered
from inland fluvial facies are considered, omitting those that appear in deltaic,
estuarine, and other coastal settings. In the analysis of each case study, we dis-
tinguished the trace fossils found in channel belts and floodplain facies.
Channel-belt deposits belong to the zone of influence of free lateral migration
of a river ( Bridge and Leeder, 1979 ) and include channel-bar and channel-fill
deposits. The term “channel” sensu lato is also used to refer to “channel belts”,
which is the common usage of the term in the sedimentological literature.
The different trace-fossil assemblages from fluvial sediments were assigned
to channel-belt, floodbasin-pond, crevasse-splay, and pedogenized floodplain
(paleosol) deposits according to the interpretation of the authors of each case
study. Trace-fossil assemblages included under pedogenized floodplain are
those that are hosted in rocks that exhibit evidence of pedogenic processes, irre-
spective of the subaqueous origin of the sediments where the paleosol devel-
oped (e.g., crevasse-splay levee, channel).
3. ICHNOFACIES
The recognition of archetypal, recurrent, or Seilacherian ichnofacies in the conti-
nental realmhas been the subject of substantial debate. Invertebrate archetypal ich-
nofacies for continental deposits have received general acceptance in the scientific
community, in spite of having been proposed only since the 1990s ( Buatois and