Fluvial Environments - Trace Fossils as Indicators of Sedimentary Environments - page 340

which occur in Permian-Triassic fluvial redbeds, although a more restricted
facies discrimination is not possible at present. Large herbivore (probably
produced by dicynodonts) coprolites from swampy environments are the typical
components of the Dicynodontocopros Ichnofacies ( Hunt et al., 2007 ).

3.10 Potential Ichnofacies from Paleosols
Some trace-fossil assemblages ( n

40) recorded essentially in floodplain sedi-
ments with low to moderate pedogenesis are dominated by rhizoliths or other
root structures (including networks of small roots, medium-sized taproots, and
tree-sized taproots; see Fig. 4 D and E), vertical J, and Y-shaped burrows
( Fig. 4 F), large vertebrate burrows ( Fig. 4 C), meniscate burrows, and burrows
with pelletal fill. These components are shared with the Coprinisphaera and
Celliforma ichnofacies but insect trace fossils are absent or rare in these assem-
blages. The mentioned trace-fossil assemblages cannot be included in any of the
recognized ichnofacies, and it is not clear if they meet some criteria for the
establishment of a new ichnofacies (temporal and geographic recurrence and
definite environmental meaning). Instead, there seems to be at least three dis-
tinct groups of assemblages that are distinguished by the dominance of large
vertebrate burrows and trace fossils attributed to crayfishes and root structures.
The first group is typified by the occurrence of large vertebrate burrows,mostly
exhibiting a helical pattern with a terminal chamber ( Daimonelix ) or a low-angle
ramp tunnelwith a rounded end (thatmayormaynot beenlarged).Associated trace
fossils are rhizoliths, meniscate burrows, and rare insect trace fossils (ant nests and
possible dung beetle burrows). These examples commonly appear in well-drained
soils, with carbonate nodules or nodular horizons, developed in an arid or semiarid
climate (e.g., Gobetz and Martin, 2006; Groenewald et al., 2001; Martin and
Bennett, 1977; Sidor et al., 2008; Smith, 1987; Smith et al., 2010 ).
The second group is characterized by ichnogenera assigned to crayfishes
( Loloichnus , Camborygma , Dagnichnus , Katbergia , and two ichnospecies of
Cellicallichnus ) associated with rhizoliths and meniscate burrows ( Taenidium ,
Beaconites ). Some of the case studies come from paleosols that exhibit
evidence for a fluctuating water table and were developed in a warm climate
( Bedatou et al., 2008; Genise et al., 2008; Hasiotis and Honey, 2000 ).
The third group is typified by trace-fossil assemblages almost exclusively
composed of root structures, including rhizoliths and stump casts. A compre-
hensive classification for rhizolith types is available ( Klappa, 1980 ), but a com-
mon and uniform descriptive terminology has not been adopted. Rhizoliths have
not received an ichnotaxonomic treatment to date, in part because plant trace
fossils are not recognized in the International Code of Botanical Nomenclature
( Bertling et al., 2006 ). Bockelie (1994) proposed a morphological classification
of rhizoliths in core, and he was able to recognize “root facies” in Jurassic
non-marine and marginal-marine successions. The idea of defining a rhizolith
ichnofacies is tempting because there are trace-fossil assemblages dominated

¼