Slopes - Trace Fossils as Indicators of Sedimentary Environments - page 591

complexity of slope deposits, inspiring their recognition in both the subsurface
and outcrops. Many of these intervals may otherwise have been misclassified as
basin-floor fan or shelf deposits (cf. Gjelberg et al., 2001; Shultz and Hubbard,
2005; Sømme et al., 2009 ).
Despite the challenges associated with slope-deposit recognition, a number of
studies have provided tremendous insight into ichnological trends on high-relief
slope-to-basin-floor transects in ancient basins (e.g., Crimes, 1977; Heard and
Pickering, 2008; Savrda et al., 2001 ).Many studies of shelf strata, aswell as others
focused on abyssal fan deposits, have incorporated analyses of slope units (e.g.,
Eyles et al., 1992; Uchman, 2009 ). Furthermore, some studies have focused on
ichnological components frombathyal deposits (e.g., Bromley et al., 2003; Miller
and Vokes, 1998; Savrda, 2012 ). In general, suites from these higher-relief slope
regimes vary markedly in diversity at any one locality. Ambient suites yield rea-
sonably diverse associations that fall into either distal expression of the Cruziana
Ichnofacies or to high-diversity expressions of the Zoophycos Ichnofacies. These
are commonly interstratified with low-diversity opportunistic suites associated
either with turbiditic sands, turbiditic muds, or contourite-(oceanic-current)-
generated muddy heterolithic facies. Although pelagic to hemipelagic deposition
is not uncommon in slope regimes, ichnological associations lack the graphoglyp-
tid suites diagnostic of the Nereites Ichnofacies. Graphoglyptid-bearing suites are
generally regarded to represent the stable environmental conditions associated
with the abyssal plain and probably represent compelling evidence of basin-floor
positions (cf. Uchman and Wetzel, 2011, 2012 ). Trace fossils typical of facies
deposited on the slope are numerous and include such elements as Arenicolites ,
Asterosoma , Chondrites , Cosmorhaphe , Cylindrichnus , Gyrochorte , Diplocra-
terion , Helminthopsis , Neonereites , Nereites , Ophiomorpha , Palaeophycus , Phy-
codes , Phycosiphon , Planolites , Rhizocorallium , Rosselia , Scolicia , Skolithos ,
Spirophyton , Teichichnus , Thalassinoides , and Zoophycos ( Fig. 2 ).
3.1 Zoophycos Ichnofacies
The Zoophycos Ichnofacies is typically considered intermediate between ichno-
facies typical of inner shelf or offshore deposits (i.e., the Cruziana Ichnofacies)
and abyssal deposits (i.e., the Nereites Ichnofacies). Correspondingly, deposits
of the bathyal zone are most commonly ascribed to the Zoophycos Ichnofacies
(cf. MacEachern et al., 2007a, 2010; Seilacher, 1967 ). Low-energy shelves, par-
ticularly those that are mud-prone, however, are also typified by the Zoophycos
Ichnofacies (cf. Pemberton et al., 2012 ; MacEachern et al., 2012 ). Shelfal
expressions of the Zoophycos Ichnofacies, however, tend to comprise
low-diversity suites of grazing and deposit-feeding structures, dominated by
low-energy and/or facies-crossing components common to both the Cruziana
Ichnofacies and the Zoophycos Ichnofacies (e.g., Zoophycos , Helminthorhaphe ,
Phycosiphon , Cosmorhaphe , Chondrites , Planolites , and Thalassinoides ).