Deep-Sea Fans - Trace Fossils as Indicators of Sedimentary Environments - page 630

shallow foreland basins and turbidite-dominated, so-called flysch deposits in
deep-marine basins (i.e., trenches) in the front of orogens. Initially, the resolu-
tion of this model was lowwithin deep-marine turbidites, being grouped into the
Nereites Ichnofacies, which is characterized by graphoglyptids and meandering
trace fossils ( Seilacher, 1967 ). Muddy deposits below the upper offshore zone
are ascribed to the Zoophycos Ichnofacies, which is characterized by the
ichnogenera Zoophycos , Phycosiphon , and Chondrites . Traditionally,
this ichnofacies is related to slope deposits ( Seilacher, 1967 ). Principal ecologi-
cal factors, such as organic-matter input, sedimentation rate, grain size,
oxygenation, etc., vary significantly in the deep sea, and consequently deep-
sea ichnofacies cannot be ascribe to a specific water depth with any precision
( Wetzel, 1983 ).
The ichnofacies are considered to some extent as taphofacies, and thus as
dependent on the level of preservation of the trace fossils (e.g., Bromley and
Asgaard, 1991 ). For instance, graphoglyptids characterizing the Nereites Ichno-
facies require subtle scouring and casting in order to be preserved. Photographs
of the modern deep-sea floor, however, document graphoglyptid lebensspuren
(e.g., Gaillard, 1991 ), also in places where their preservation seems almost
impossible due to the absence of such processes ( Ekdale, 1985; Miller,
1991b ). This is probably true for many fossil pelagites not preserving grapho-
glyptids but trace fossils typical of the Zoophycos Ichnofacies (e.g., Wetzel,
2010 ).
With time, the Nereites Ichnofacies has been subdivided into the Ophiomor-
pha rudis subichnofacies for thick-bedded sandstones in channels and proximal
lobes in turbidite successions ( Heard and Pickering, 2008; Knaust, 2009;
Phillips et al., 2011; Uchman, 2001, 2009 ); the Paleodictyon subichnofacies
for more sandy, medium-to-thin bedded “normal” flysch; and the Nereites
subichnofacies for mud-rich distal flysch ( Seilacher, 1974 ). Roughly, the
Ophiomorpha rudis - Paleodictyon - Nereites subichnofacies may express a
bathymetric trend from inner to outer fan ( Uchman, 2007a ) and a non-
bathymetric trend from channel axis, levee to overbank or inter-channel areas
( Monaco et al., 2010, Olivero et al., 2010; Uchman, 2009 ). In addition, within
sandy flysch deposits, graphoglyptids are frequent (e.g., Paleodictyon , Desmo-
grapton ) and muddy deposits contain relatively more meandering forms.
Monaco et al. (2010) noted a higher abundance and diversity of graphoglyptids
in detached lobes than in attached lobes, and a reduced ichnodiversity in chan-
nelized areas. However, the diversity and composition of the trace-fossil asso-
ciations are affected by the lithological variability and other ecological
( Uchman, 2001 ) and evolutionary factors ( Uchman, 2004a ).
The Nereites Ichnofacies occurs over a wide bathymetric range. To give an
example, the Paleodictyon subichnofacies occurs in an Eocene turbidite succes-
sion a few tens of meters below tempestites in the Sinop Basin, Turkey
( Uchman et al., 2004 ). This subichnofacies occurs even in tempestite-bearing,
deep intra-shelf troughs reported from the Late Cretaceous shelf of Tanzania