Deltas - Trace Fossils as Indicators of Sedimentary Environments - page 506

heterolithic sandstones with moderate intensity and diversity. The delta front is
characterized by moderate- to high-diversity trace-fossil assemblages with a
strongly heterolithic nature. The prodeltaic facies is similar to the facies of other
end-member deltaic types of fluvial- and wave-dominated deltas but is character-
ized by variable intensities and high-diversity trace-fossil assemblages. Euryha-
line tracemakers of Planolites , Teichichnus , Phycosiphon , Rosellia , Asterosoma ,
Chondrites , Taenidium , Ophiomorpha , Palaeophycus , Nereites , Scolicia , and
Diplocraterion characterize the delta and prodeltaic facies of tide-dominated
ancient deltas ( Carmona et al., 2009; Ichaso and Dalrymple, 2009; McIlroy,
2004b; McIlroy et al., 2005; Rebata-H et al., 2006; Willis and Gabel, 2001 ).

5.3 Wave-Dominated Deltaic Ichnology
High diversity of trace-fossil assemblages and moderate to intense bioturbation
intensities (BI 3-5; see Supplementary Table 1: http://booksite.elsevier.com/

9780444538130 and Fig. 3 C) characterize the delta front and prodelta of wave-
dominated ancient deltaic successions. Ancient wave-dominated river deltas
developed shoreface facies and may be difficult to distinguish from non-deltaic
shorelines unless the large-scale spatial context is well delineated by seismic data,
good outcrop exposures or closely spaced, reliably correlated core, or well-log
data ( Hampson and Howell, 2005 ). In the wave-dominated prodeltaic facies,
the BI and ichnodiversity are the highest of all deltaic types as a function of
extremely well mixed and highly oxygenated waters that have a full marine
signature, creating optimal conditions for colonization of the ancient sea floor.
Trace-fossil assemblages in the lower delta plain to delta front result from eury-
haline tracemakers of Planolites , Ophiomorpha , Teichichnus , Skolithos , Phycosi-
phon , Helminthopsis , Thalassinoides , Cylindrichnus , Arenicolites , Rosellia ,
Asterosoma , Chondrites , Rhizocorallium , Palaeophycus , Diplocraterion ,and
Macaronichnus ( Buatois et al., 2008; Charvin et al., 2010; Gingras et al., 1998;
Reid and Pemberton, 2007 ). In the prodelta, marine tracemakers such as those
of Zoophycos and Scolicia are found. In wave-dominated deltas, the lower delta
plain and proximal delta front to prodelta may be indistinguishable from non-
deltaic successions (e.g., shorefaces) unless a fluvial point source can be recog-
nized and the spatial context is constrained by seismic or continuous outcrop
exposures.

¼

6. CONCLUSIONS
The dominant physico-chemical controls in ancient river deltas are the sedimen-
tation rate and the salinity; these parameters control the spatial distribution of
trace fossils. Bioturbated fluvial-dominated and tidal-dominated ancient deltaic
successions contain mostly of trace fossils made by euryhaline organisms, while
wave-dominated deltaic successions contain a mix of both euryhaline and
stenohaline organisms. Deltaic successions are typically stressed or mixed