Slopes - Trace Fossils as Indicators of Sedimentary Environments - page 590

Faunal densities and diversities on slopes are significantly influenced by
their proximity to sediment point sources on the adjacent shelf and shoreline,
as well as by the presence of sediment/current conduits, such as submarine can-
yons ( Cartes et al., 2010; Griggs et al., 1969; Morse and Beazley, 2008; Rowe,
1971; Vetter and Dayton, 1998 ). Factors that influence faunal distribution
trends include strong currents, varied oxygenation of bottom and interstitial
waters, focused sedimentation and erosion, and elevated organic enrichment
(e.g., via primary production at the water surface and transported terrestrial
detritus; Cartes et al., 2010; Gerino et al., 1999; Josselyn et al., 1983; Morse
and Beazley, 2008; Rowe, 1971; Vetter and Dayton, 1998; Vetter et al.,
2010; Wetzel, 2008 ).
Parameters controlling the distribution, diversity, and abundance of benthic
organisms on the slope are numerous, as is typical of any depositional setting.
Consequently, no single physico-chemical factor can be used to explain the
diversity and abundance trends observed in the bathyal realm ( Levin and
Gage, 1998 ). Physical and chemical factors such as current energy, sedimenta-
tion rate, mass-wasting, pressure, light, substrate particle size, substrate consis-
tency, oxygenation, food availability, temperature, and turbidity, as well as
biological controls such as productivity, predation, and competitive displace-
ment, can vary with depth and influence feeding behaviors ( Carney, 2005; Flach
and Thomsen, 1998; Gage and Tyler, 1991; Levin and Gage, 1998; Morse and
Beazley, 2008; Puig et al., 2001; Rogers, 2000; Savrda et al., 1984; Stuart et al.,
2003; Young and Richardson, 1998 ). In the vicinity of submarine canyons or
gullies, increased food resources, oxygenation, and sedimentation rates com-
monly lead to conditions on the slope akin to those of shelf or coastal settings
( Blake and Hilbig, 1994; Rhoads and Hecker, 1994 ). Thus, many slopes on the
margins of continents or peripheral seas like the Mediterranean are character-
ized by species normally associated with shelf environments (e.g., Rhoads and
Hecker, 1994; Stora et al., 1999; Wetzel, 2008 ). The resulting variability in
organism distribution trends observed on basin-margin slopes indicates that
species diversity and abundance develop in response to local conditions and that
a fundamental response to water depth does not exist ( Gage et al., 2000; Heezen
and Hollister, 1971 ).
3. ICHNOFACIES IN BATHYAL SETTINGS
The ichnological characterization of ancient slope deposits constitutes a highly
underdeveloped research topic. Likewise, even the basic sedimentological
criteria defining slope deposits are vague compared to the adjacent shelf and
basin-floor counterparts, often requiring expansive outcrops in order to recog-
nize the large-scale features that might typically be regarded as diagnostic, such
as mass-transport complexes (e.g., Armitage et al., 2009 ). Over the past two
decades, high-resolution bathymetric images and 3D seismic surveys have
enlightened sedimentologists and stratigraphers as to the characteristics and