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replaced by the resident community during extended periods of fair-weather
and the resultant burrows are commonly overprinted. Tempestites may also
contain fugichnia (escape traces), recording the disturbance of stratification
by animals buried by the rapidly deposited sediment, as they attempted to reach
the new sediment/water interface ( Fig. 5D ). The distribution of trace fossils
records the typical character of ecological stresses imparted by episodic depo-
sitional events (cf. Bann et al., 2008; MacEachern and Bann, 2008; MacEachern,
et al., 2007; Pemberton and MacEachern, 1997; Pemberton et al., 1992b ). Trace
fossils such as Helminthopsis , Phycosiphon , Planolites , and Teichichnus record
the reestablishment of grazing and deposit-feeding infauna following the event
and typically occur near the tops of sandstone beds or within the mudstones cap-
ping them. The low abundance of suspension-feeding traces suggests that most
sandstone beds were quickly buried by silt and mud following the depositional
event, precluding colonization by organisms that favor sandy substrates.
2.2 Lower-Middle Shoreface Complex
2.2.1 Lower Shoreface
The lower shoreface begins at the lower limit of the fair-weather (effective) wave
base, where offshore processes continue to dominate deposition ( Reinson, 1984 ).
Waves constitute the dominant physical process controlling deposition in the
interval, and most physical sedimentary structures reflect storm deposition,
such as hummocky cross-stratification (HCS; cf. Dott and Bourgeois, 1982;
Duke, 1985 ), rare swaley cross-stratification (SCS; cf. Leckie and Walker,
1982 ), and quasi-planar lamination (QPL; cf. Arnott, 1993 ). Intervals without
significant erosional amalgamation may show waning-stage oscillation or
combined-flow ripple-lamination capping HCS and QPL. SCS characterizes
strongly erosionally amalgamated bed sets. Fair-weather-generated oscillation
ripples may be present but are relatively uncommon because of bioturbation.
The intensity of burrowing within lower shoreface deposits is highly variable,
depending upon the degree of storm influence ( Fig. 6 ). High-intensity and
high-frequency storm events favor minimal preservation of burrowing,
whereas low-intensity and infrequent storms permit thorough homogenization
of the tempestites and accumulation of thick fair-weather intervals (e.g.,
Fig. 6D ).
The trace-fossil suites represent a proximal expression of the Cruziana
Ichnofacies (cf. MacEachern and Bann, 2008 ; Fig. 3 ). Deposit-feeding and
mobile carnivore traces of the Cruziana Ichnofacies include such traces as
robust Rosselia , Asterosoma , Teichichnus , Cylindrichnus , Schaubcylindrich-
nus , Planolites , Thalassinoides , Ancorichnus , Phoebichnus , Siphonichnus ,
Macaronichnus, Chondrites , and Rhizocorallium ( Fig. 6 ). Rarer grazing/forag-
ing traces, largely confined to muddier zones, are also locally present and
include Phycosiphon and very rare Zoophycos , Scolicia , and Aulichnites .
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