Environmental Engineering Reference
In-Depth Information
the polychaete
Arenicolamarina
and the bivalve
Mya arenaria
typically produce
significant bioturbation (
Reineck and Singh, 1980; Sch¨fer, 1972
).
On low-energy sand flats, relatively quiet conditions, coupled with very
short periods of subaerial exposure, allow the development of a diverse resident
fauna. These tidal flats are typically dominated by high-diversity assemblages
of horizontal burrows and trails of deposit and detritus feeders, as well as pred-
ators, namely,
Cruziana
,
Rusophycus
,
Asteriacites
,
Pentichnus
,
Psammichnites
,
Curvolithus
,
Nereites
,
Lockeia
,
Protovirgularia
,
Palaeophycus
, and
Planolites
(
Fig. 7
A-D). This assemblage illustrates the
Cruziana
Ichnofacies (
M
´
ngano
and Buatois, 2004b; M
´
ngano et al., 2002a
).
2.5 Tidal Channels and Creeks
Tidal-flat deposits are commonly dissected by a network of meandering tidal
channels and creeks (also known as gullies) that migrate across the intertidal
zone, producing lateral accretion in point bars and resulting in inclined hetero-
lithic stratification (
Fig. 2
;
Thomas et al., 1987
). In the muddy upper intertidal
zone, channels are small to medium size, but in the lower sandy areas, they
tend to coalesce to form wider and deeper channels (
Dalrymple, 2010
). The
FIGURE 7
Sand flat containing the
Cruziana
Ichnofacies. Traces are preserved at the soles of
sandstone beds. Late Carboniferous Stull Shale, Kanwaka Formation, Waverly fossil site, Kansas,
USA. (A)
Nereites imbricata
. (B)
Asteriacites lumbricalis
(
As
). (C) Intergradation between
Lockeia
ornata
(
Lo
) and
Protovirgularia rugosa
(
Pr
). (D)
Psammichnites implexus
.
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