Fluvial Environments - Trace Fossils as Indicators of Sedimentary Environments - page 355

FIGURE 11 Histogram showing the participation of trace-fossil types in several floodplain sub-
environments (pond, crevasse splay, and pedogenized floodplain). References as for Fig. 8 .
Some examples of trace-fossil assemblage representatives of different ichnofa-
cies that belong to the pedogenized floodplain setting are from the Eocene of Uru-
guay ( Genise, 2004 ), the Late Oligocene of United States ( Retallack et al., 2000 ),
the Oligocene-Miocene of Egypt ( Bown, 1982; Genise and Bown, 1994 ), and the
Oligocene of Argentina ( Bellosi et al., 2010 ).
Several trace-fossil morphologies that are typical of the Mermia Ichnofacies
occur preferentially in floodbasin-pond assemblages, including simple horizon-
tal trails (e.g., Archaeonassa , Helminthoidichnites , Helminthopsis , Cochlich-
nus ), complex sinusoidal trails (e.g., Undichna ), and tetrapod swim traces
(e.g., Characichnos ). Bird tracks (e.g., Gruipeda , Aquatilavipes , Ignotormis ,
Barrosopus ) and arthropod-produced trace fossils, mainly trackways (e.g.,
Diplichnites , Umfolozia , Protichnites ), trough-like reliefs (e.g., Rusophycus ,
Selenichnites , Gluckstadtella ), and bilobed burrows/trails ( Cruziana ), also
occur preferentially in pond facies. Most tetrapod-track types seem to be
equally represented in floodbasin-pond and crevasse-splay facies, but they
are very rare in paleosols. The previously mentioned track types include bipedal
tri- or tetradactyl trackways with thick digits ( Grallator , Anchisauripus ),
bipedal tridactyl tracks with stout digits (“iguanodontid tracks”), Q 4/5 ( Batrach-
ichnus ), Q 5/5 sl ( Rhynchosauroides , Dromopus , Gilmoreichnus ), Q 5/5 st
( Ichniotherium , Amphisauropus ), quadrupedal bilobed tracks ( Entelodontipus ,
“bovid tracks”), sauropod tracks ( Brontopodus ), and chirotheriid tracks
( Chirotherium , Brachychirotherium , Tetrasauropus ). Some selected examples
of typical floodbasin-pond assemblages are from (1) the Early Devonian Peel
Sandstone Group (Isle of Man), dominated by arthropod trackways ( Crowley
et al., 2009 ); (2) the Late Carboniferous Tupe Formation (Argentina), essentially
composed of horizontal burrows and simple trails ( Buatois and M ´ ngano, 2002 );
and (3) the Late Cretaceous Anacleto Formation (Argentina), characterized by
three ichnotaxa of bird footprints associated with meniscate burrows and simple
trails and burrows.
Except for the differences mentioned above, trace-fossil assemblages from
crevasse-splay deposits appear to lack distinctive features. The crevasse-splay