Deltas - Trace Fossils as Indicators of Sedimentary Environments - page 492

shallowing-upward progradational packages of siliciclastic rocks. Deltaic succes-
sions are abundant and widely distributed throughout geological time (see Supple-
mentary Table 1: http://booksite.elsevier.com/9780444538130 ) .
Deltaic research, from a geological perspective, began in the late 1880s and
focused on the facies architecture, sedimentary processes, and stratigraphic evo-
lution of deltaic sedimentary successions ( Barrell, 1912; Gilbert, 1885 ; see histor-
ical review in Le Blanc, 1975 ).Microfossils andmacrofossils are routinely used as
proxies for deltaic paleoenvironmental reconstruction, including their use in
defining the extent of marine influence and brackish to freshwater fluvial condi-
tions (e.g., Beerbower, 1961; Coleman and Wright, 1975; Galloway, 1975; Horo-
witz, 1966; Murphy and Schlanger, 1962 ). Ichnology was not an integral part of
deltaic studies until the 1960s, this coinciding with the promotion of ichnological
research (see Baucon et al., 2012 ). The integration of ichnology into facies anal-
ysis has been used to help understand bothmodern and ancient deltas since the late
1960s ( Allen, 1970; Fisher andMcGowen, 1969; Oomkens, 1970 ). Several recent
studies of ancient deltas have used ichnology as a tool to classify and define sub-
environments and facies within deltaic systems (see Supplementary Table 1:
http://booksite.elsevier.com/9780444538130 ), although further

research is

required to fully understand these dynamic environments.
The sedimentology of deltaic environments is comparatively well understood,
and a significant amount of published literature is available (reviews in Bhatta-
charya, 2006, 2010; Reading and Collinson, 1996 ). The wealth of studies of mod-
ern deltaic systems such as the Mississippi River Delta (review in Roberts, 1997 )
stems from their importance as sites of agriculture and trade. In addition, ancient
deltas host significant hydrocarbon reserves ( Whateley and Pickering, 1989 ).
Ichnology can, with care, be used to help determine delta type, define subenviron-
ments, and characterizedepositional facies, when combinedwith sedimentological
datasets (e.g., MacEachern et al., 2005; McIlroy, 2004b; Pemberton et al., 2001 ).
This chapter focuses on the subaqueous marine component of the deltaic system
and aims to clarify the application of ichnology in ancient deltas and discuss its
use as a tool for study of deltaic paleoenvironments and facies analysis.

2. CLASSIFICATION OF DELTAIC SYSTEMS
Modern deltas can be classified in terms of (1) the dominant process (fluvial,
tidal, or wave energy; see Galloway, 1975 ); (2) grain size (see Orton and
Reading, 1993 ); (3) delta morphology ( Weise, 1980 ); (4) type of feeder; (5)
water depth; and (6) mouth-bar type (see Postma, 1990 ). Characterization of
ancient deltas is somewhat more challenging, as the deltaic coastline morpho-
logy (e.g., elongate, lobate) can usually only be studied in 3D seismic. Outcrop
and 2D seismic datasets cannot fully characterize the geomorphology of a delta
unless the limit of progradation of a deltaic package can be mapped. Deltaic
sediments have significant potential to be reworked by subsequent deltaic pro-
cesses (e.g., ravinement during abandonment or through erosion by subsequent
distributary channels; see McIlroy et al., 2005 ). Recent classifications subdivide