Fluvial Environments - Trace Fossils as Indicators of Sedimentary Environments - page 336

FIGURE 5 Examples of trace fossils from the Mermia Ichnofacies (A and B) and Skolithos
Ichnofacies (C and D). (A) Archaeonassa (simple horizontal trail) on top of a rippled-bedding plane.
(B) Helminthoidichnites (simple horizontal trail) preserved in negative epirelief. (C) and (D) Several
Skolithos specimens (simple vertical burrow) in cross section (some of the burrows are indicated by
arrows). Photographs are from the Oligocene Vinchina Formation in La Rioja province, Argentina
(A); from the Permian Carapacha Formation in La Pampa province, Argentina (B); from the Middle
Triassic Tarjados Formation in La Rioja province, Argentina (C); and from the Early Jurassic Santo
Domingo Formation in La Rioja province, Argentina (D).

floodbasin-pond facies. These assemblages are typically subaqueous and reflect
simple feeding or grazing strategies in temporary water bodies.

3.6 Ichnofacies

The Skolithos Ichnofacies (originally defined in the marine realm) has been
tentatively recognized in fluvial channel-belt deposits and high-energy lacus-
trine settings ( Buatois and M ´ ngano, 1998, 2004, 2007; Melchor et al., 2003 ).
These ichnofaunas are commonly monospecific, dominated by simple vertical
burrows and may result in ichnofabrics with a high degree of bioturbation
(piperock). This ichnofacies is recognized by the dominance of simple vertical
burrows ( Fig. 5 C and D) and Y, or U-shaped vertical burrows, although
bilobed burrows/trails, horizontal burrows, simple horizontal trails, and menis-
cate burrows may be present ( Fig. 1 F). These assemblages were interpreted as

Skolithos