Deltas - Trace Fossils as Indicators of Sedimentary Environments - page 493

wave-dominated deltas into symmetric, asymmetric, and deflected morpholo-
gies ( Bhattacharya and Giosan, 2003 ). Deltas have also been described in
terms of river mouth process and dispersal into (1) hypopycnal (buoyancy- and
friction-dominated deltas), (2) hyperpycnal (inertia-dominated deltas), and (3)
homopycnal (friction-dominated deltas) (see Bhattacharya, 2006; Wright, 1977 ),
which affects the mouth-bar development ( Postma, 1990 ).
The ichnology of the three endmembers of the deltaic classification of Galloway
(1975) is discussed herein (Supplementary Table 1: http://booksite.elsevier.com/
9780444538130 and Fig. 1 ). Most deltas encompass a combination of pro-
cesses ( Galloway, 1975 ; Supplementary Table 1: http://booksite.elsevier.com/
9780444538130 ) . Detailed sedimentological descriptions and facies analysis of
fluvial-dominated, wave-dominated, and tide-dominated ancient deltaic succes-
sions are not covered in this chapter, as several excellent reviews exist in the current
literature (see Bhattacharya, 2010;Dalrymple, 2010; Reading andCollinson, 1996 ).
2.1 Bioturbation Intensity and Ichnodiversity
The intensity of bioturbation (BI) and ichnological diversity in ancient deltaic
settings are useful first-order tools in recognition of deltaic facies, facies associ-
ation, and the dominant sedimentary processes. BI is ameasure of the destruction
FIGURE 1 Tripartite classification of ancient deltas based on the dominant processes of fluvial,
tidal, and wave energy (based on Galloway, 1975 ). Mixed-influence deltas lie in the central area of
the triangle. Twenty-two examples from refereed publications on fine-grained ancient deltas are
used (see Supplementary Table 1: http://booksite.elsevier.com/9780444538130 ) .