Environmental Engineering Reference
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perceived. Overall, there is a similar number of trace-fossil types that can
appear in floodplain facies as in channel facies ( Fig. 8 A). When considering
individual trace-fossil assemblages, it is noteworthy that the majority come
from floodplain deposits (175 trace-fossil assemblages against 82 from chan-
nels), probably reflecting contrasting preservational conditions. For example,
Melchor et al. (2010) found eight trace-fossil assemblages in channel-belt
deposits and 16 in floodplain deposits from the more than 5-km-thick domi-
nantly fluvial succession of the Neogene Vinchina Formation of north-western
Argentina. The bulk of channel deposits is typically devoid of trace fossils, and
most of them are concentrated on particular surfaces and stratigraphic intervals.
In fluvial channels, the more common trace-fossil types are meniscate burrows
and simple vertical burrows, followed by arthropod trackways, J-, Y-, or
U-shaped vertical burrows, simple horizontal burrows, trough-like reliefs,
and simple horizontal trails with a subordinate participation of a variety of ver-
tebrate trace fossils. Vertebrate traces are mostly bird-like bipedal trackways
and trackways of tri-tetradactyl bipeds with thick digits, and several quadrupe-
dal trackways (the more common are Q 4/5, Q 5/5 sl, Q 5/5 st, chirotheriid
tracks; Fig. 8 A). In spite of the relatively large variety of trace-fossil types that
may appear in a fluvial channel, the average ichnodiversity of individual assem-
blages from channel deposits is fairly similar to that found in floodplain deposits
(four versus five trace-fossil morphologies, respectively). About one-third of
the trace-fossil assemblages from channel-belt deposits are composed of one
or two trace-fossil morphologies. Some of these cases contain either only dis-
crete meniscate burrows (e.g., Graham and Pollard, 1982; Hubert and Dutcher,
2010; Morrissey and Braddy, 2004; Pollard, 1976; Squires and Advocate, 1984 )
or a highly bioturbated ichnofabric composed of meniscate burrows ( Buatois
et al., 2007 ); other cases are represented by simple horizontal and/or vertical
burrows ( Gibert and S´ez, 2009; Kim et al., 2002; Sarkar and Chaudhuri,
1992 ) or trackways of bipedal or quadrupedal animals (e.g., Chiappe et al.,
2004; Difley and Ekdale, 2002; Platt and Meyer, 1991 ). A particular case of
a low-diversity assemblage from channel facies was described by Cohen
(1982) from the Pleistocene of Kenya, where vertical and oblique rhizoliths
dominate in multistory ephemeral channels.
Trace-fossil assemblages that display a high ichnodiversity (up to 11 trace-
fossil morphologies) in fluvial channel belts are not unusual. Most of them have
only few, simple invertebrate traces (simple horizontal trails, meniscate bur-
rows, arthropod trackways) and a more diverse group of tetrapod tracks.
Between them, we can distinguish a conspicuous group of Late Paleozoic ich-
nofaunas that exhibits a dominance of Q 4/5, Q 5/5 sl, and Q 5/5 st (e.g., Mack
et al., 2003; Van Allen et al., 2005 ). Additional case studies are known from the
Lower Jurassic of Lesotho ( Smith et al., 2009 ) and from the Miocene of Argen-
tina ( Krapovickas et al., 2009 ). The South African example was recorded from
outstanding exposures of low-angle accretion surfaces on pointbar deposits
from a meandering river system. Although a revision of the tetrapod ichnotaxa
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