Environmental Engineering Reference
In-Depth Information
employ opportunistic feeding strategies. Ichnogenera typical of suites attributed
to the
Nereites
Ichnofacies generally reflect organism behaviors that attempt to
optimize sea-floor coverage in response to resource deficiency.
Since the pioneering work of
Seilacher (1967)
, sedimentologists have
attempted to use trace fossils and trace-fossil suites as a proxy for interpreting
paleo-water depths. Physical and chemical parameters do not change consis-
tently with water depth from basin to basin, nor even along an individual
basin's margin. Factors, such as basin circulation, water stratification, shelf
width, and the details of sediment supply to the basin (e.g., point source
versus
line source), impart significant influences on infaunal distributions of modern
slopes, and without doubt, in ancient slope deposits as well. The consideration
of trace-fossil suites that can be assigned to a series of ichnofacies, including
the
Zoophycos
,
Cruziana
,
Skolithos
,
Glossifungites
,and
Nereites
ichnofacies,
is a reflection of the varied conditions that influence organisms across
the slope.
Abandoning attempts to tie trace-fossil suites to paleobathymetry (cf.
Frey
et al., 1990
), high-resolution ichnological analyses have more potential for
developing means to differentiate subtle facies changes in ancient slope
deposits. Such an approach is common in the analysis of marginal- and
shallow-marine deposits (e.g.,
Bann et al., 2004; Frey and Pemberton, 1987;
MacEachern et al., 2005
). In one such example of this type of investigation
in bathyal strata,
Cummings and Hodgson (2011)
document systematic changes
in trace-fossil assemblages across levees relative to their proximity to a channel
margin (e.g., increases in graphoglyptids distally). Overall, linking subtle facies
and trace-fossil shifts across the deposits of slope subenvironments has been
rather poorly assessed until recently (e.g.,
Callow et al., 2012a,b; Greene
et al., 2012; Phillips et al., 2011
). Future ichnological work, linked closely with
the stratigraphic architecture of slope deposits, will undoubtedly uncover
insights into a range of paleoenvironmental conditions and establish the utility
of deep-water ichnology in high-resolution slope-facies modeling.
ACKNOWLEDGMENTS
S. M. H. graciously acknowledges the support of Chevron Energy Technology Company,
ConocoPhillips Company, Marathon Oil Corporation, Talisman Energy Inc., Roh¨ l-
Aufsuchungs AG, and the Natural Sciences and Engineering Research Council of Canada
(NSERC) for research on slope deposits. J. A. MacEachern acknowledges funding via NSERC
Discovery Grant 184293. Reviews by Drs. Ian Kane, Dirk Knaust, and Richard Bromley
improved the clarity of the chapter and are greatly appreciated.
REFERENCES
Search WWH ::
Custom Search