Slopes - Trace Fossils as Indicators of Sedimentary Environments - page 595

muddy cohesive substrates ( Frey and Seilacher, 1980; Seilacher, 1978 ). There-
fore, it is not surprising that ancient deposits associated with the ichnofacies
include those attributed to shelf and muddy slope settings, where the accumu-
lation of abundant organic matter from suspension are characteristic (e.g., Oli-
vero and Gaillard, 1996; Wetzel, 1984 ). However, as the supply of oxygen and
food to the substrate increase, departures from this archetypal expression are to
be expected. The resulting high diversity and high abundance suites may indi-
cate parts of the slope swept by various oceanic currents (e.g., contour currents
and density currents).
3.2 Skolithos Ichnofacies
Conduits for currents and sediment transport across continental slopes are asso-
ciated with deposits typified by trace-fossil suites notably distinct from those of
the background slope. Trace fossils more commonly attributed to high-energy,
shallow-marine settings comprise important constituents of suites, manifested
by localized to semi-regional occurrences of the Skolithos and Glossifungites
ichnofacies (e.g., Hubbard and Shultz, 2008; Kane et al., 2007; Shultz and Hub-
bard, 2005 ).
Sandy, shifting (non-cohesive) substrates associated with persistently high
energy, impacted by frequent and abrupt shifts in sedimentation and erosion,
aremore typical of nearshore sedimentary environments. However, a comparable
set of physical conditions can also be achieved in some slope regimes, particularly
submarine canyons, gullies, and other deep-marine channels (cf. Crimes, 1970;
Frey, 1971; Frey and Howard, 1970; Frey et al., 1990; Hayward, 1976; Ineson,
1987 ). Food and oxygenated waters are transported throughout bathyal depths,
particularly in areas where canyon heads are located adjacent to fluvio-deltaic
point sources (e.g., Cartes et al., 2010;Morse andBeazley, 2008 ). Submarine can-
yon, intraslope minibasin, and lower-slope channel deposits have been shown to
locally exhibit typically impoverished ichnological suites commonly assigned to
the Skolithos Ichnofacies, which include Skolithos , Arenicolites , Ophiomorpha
nodosa , O. rudis , Diplocraterion , Cylindrichnus ,and Rosselia (e.g., Crimes,
1970, 1977; Crimes et al., 1981; Cummings and Hodgson, 2011; Heard and
Pickering, 2008; Kane et al., 2007; Kern and Warme, 1974; Shultz and Hubbard,
2005 ).
3.3 Glossifungites Ichnofacies
Passively filled burrows excavated into firm, erosionally exhumed substrates
are common on slopes, particularly in areas dominated by recurring, high-
energy currents (e.g., Anderson et al., 2006; Callow et al., 2012a; Di Celma
et al., 2010; Eyles et al., 1992; Hayward, 1976; Hubbard and Shultz, 2008;
MacEachern et al., 2007b; Pemberton and MacEachern, 2005; Savrda et al.,
2001 ). Such firmground suites are attributable to the Glossifungites Ichnofacies.