Deep-Sea Fans - Trace Fossils as Indicators of Sedimentary Environments - page 631

( Ernst and Zander, 1993 ). However, it is questionable whether these cases
should be regarded as some odd exceptions or as an indication for a habitat with
such conditions. The trace-fossil assemblage of the Early Cretaceous Kamchia
Formation, Bulgaria, contains a mixture of forms typical of both the Nereites
Ichnofacies ( Squamodictyon ) and the Cruziana Ichnofacies ( Curvolithus ,
Gyrochorte ). Probably, the sediments of the Kamchia Formation were deposi-
ted in an offshore to deeper setting with storm sand layers and marly back-
ground sedimentation. It is possible that storm-induced currents transported
producers of such traces from the shelf into the deeper sea ( Uchman and
Tchoumatchenco, 2003 ; cf. Savrda et al., 2010 ).
In general, the co-occurrence of deep-sea and shelf trace fossils can be
caused by the transport of tracemakers by storm-induced or other downslope
currents from shallower to deeper areas. This reasoning has been used to explain
the occurrence of typical “shallow-marine” trace fossils, mostly Ophiomorpha
and Thalassinoides , in deep-sea sediments ( Crimes, 1977; F ¨ llmi and Grimm,
1990; Wetzel, 1984, 2008 ). However, most of the producers of so-called
shallow-water trace fossils, such as Ophiomorpha , appear to be well adapted
to the deep-sea environment, living there for a long time in deep tiers. Size
analysis of Ophiomorpha suggests that the tracemakers cover the whole age
spectrum in the deep sea ( Uchman, 1995a ). Ichnotaxonomic analysis shows
distinct differences of the ichnospecies level, for example, between the deep
“shallow-water” forms and true shelf trace-fossils ( Uchman, 1995a, 2009 ).
Thus, most of the deep “shallow-water” forms can be ascribed probably to
permanent deep-sea residents.
In addition to using ichnofacies, distinguishing trace-fossil assemblages or
ichnocoenoses based on certain facies settings or even sedimentary features
of individual beds is also useful. For instance, Crimes and Crossley (1991) noted
for the Aberystwyth Grits Formation (Silurian) in Wales that Paleodictyon
occurs in intervals in which shale is thicker than sandstone, whereas meandering
traces (their Helminthoida crassa ) occur in opposite situations. Crimes (1973)
showed that the trace fossils content varies from lithofacies to lithofacies and
he found that rosette traces are more abundant in proximal turbidites in the
Paleogene in Zumaia (N Spain), while spiral and patterned forms as well as
winding and meandering forms are more abundant in the distal facies. Such a
distribution was challenged by Uchman (2001) for the Hecho Group (Eocene)
in N Spain and by Cummings and Hodgson (2011b) , partly for the same area.
According to Crimes (1973) , the distribution of trace fossils is only partly con-
trolled by preservational factors. While studying the Gurnigel and Schlieren
flysch units (Paleocene-Eocene) in Switzerland, Crimes et al. (1981) demon-
strated that the channelized inner fan facies contain the so-called shallow-
marine ichnotaxa ( Arenicolites , Skolithos ), but meandering (except for Hel-
minthopsis ) and network forms are absent. The inter-channel facies contain
the radiating, meandering, spiral, and network forms. In the depositional lobes
and lobe fringes, trace fossils are more abundant, with a maximum in the